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Sample records for c-mod motional stark

  1. Robotic calibration of the motional Stark effect diagnostic on Alcator C-Mod

    SciTech Connect

    Mumgaard, Robert T.; Scott, Steven D.; Ko, Jinseok

    2014-05-15

    The capability to calibrate diagnostics, such as the Motional Stark Effect (MSE) diagnostic, without using plasma or beam-into-gas discharges will become increasingly important on next step fusion facilities due to machine availability and operational constraints. A robotic calibration system consisting of a motorized three-axis positioning system and a polarization light source capable of generating arbitrary polarization states with a linear polarization angle accuracy of <0.05° has been constructed and has been used to calibrate the MSE diagnostic deployed on Alcator C-Mod. The polarization response of the complex diagnostic is shown to be fully captured using a Fourier expansion of the detector signals in terms of even harmonics of the input polarization angle. The system's high precision robotic control of position and orientation allow it to be used also to calibrate the geometry of the instrument's view. Combined with careful measurements of the narrow bandpass spectral filters, this system fully calibrates the diagnostic without any plasma discharges. The system's high repeatability, flexibility, and speed has been exploited to quantify several systematics in the MSE diagnostic response, providing a more complete understanding of the diagnostic performance.

  2. Optical and Mechanical Design of C-Mod Motional Stark Effect Diagnostic

    SciTech Connect

    D.I. Simon; E. Marmar; N.L. Bretz; R. Bravenec; R.F. Parsells

    1999-11-01

    A Motional Stark Effect (MSE) instrument is being installed on the Alcator C-Mod tokamak at MIT. This MSE diagnostic will provide measurements of the spatial profile of the internal poloidal magnetic field. The MSE has its primary collection optics inside the vacuum vessel. The light collected by the internal optics passes through a vacuum window and is relayed to a fiber optic array. The MSE optics are shared by a Beam Emission Spectroscopy (BES) diagnostic which measures electron density fluctuations and their spatial correlations. This optical system requires high throughput and spatial resolution of less than 1 cm at the focal plane in the plasma. The design requirements for the internal optics also include the effects associated with plasma impingement, plasma disruptions, and thermal excursions. The parameters that affect polarization measurement include the location and orientation of optical elements, the choice of substrates and optical materials. These unique design requirements led to a number of interesting optical and mechanical design features which are presented here.

  3. Experimental Measurements of the Lower Hybrid Electric Field on Alcator C-Mod by Stark Effect Spectroscopy

    NASA Astrophysics Data System (ADS)

    Hillis, D. L.; Mumgaard, R.; Lau, C.; Wallace, G.; Shiraiwa, S.

    2016-10-01

    A new diagnostic was installed on Alcator C-Mod capable of determining both the magnitude and direction of the lower hybrid wave electric field, ELH . The diagnostic, named SELHF (Stark Effect Lower Hybrid Field), simultaneously measures the two orthogonal polarization states of the Dβ spectra by passive optical emission spectroscopy. The ELH vector is then determined by systematically fitting the spectrum to the EZSSS (Explicit Zeeman-Stark Spectra Simulator) code which incorporates a fully quantum mechanical model comprising of the appropriate dynamic electric field and magnetic field operators. The SELHF diagnostic has 27 unique views of the LH launcher and surrounding space, each integrating over a 3 cm in diameter sightline, which is comparable to the waveguide dimension. Two sightlines are simultaneously viewed, yielding four spectra per discharge. In this presentation the diagnostic setup will be given. The methodology behind the spectral modeling and the results of the associated error analysis, yielding the accuracy of the ELH vector information, will be presented. The initial experimental results compared against a 2D cold-plasma model in COMSOL will be discussed. Work supported by DoE Contract No. DE-FC02-99ER54512 on Alcator C-Mod, a Department of Energy Office of Science user facility.

  4. The MAST motional Stark effect diagnostic

    SciTech Connect

    Conway, N. J.; De Bock, M. F. M.; Michael, C. A.; Walsh, M. J.; Carolan, P. G.; Hawkes, N. C.; Shibaev, S.; Wearing, G.; McCone, J. F. G.

    2010-10-15

    A motional Stark effect (MSE) diagnostic is now installed and operating routinely on the MAST spherical tokamak, with 35 radial channels, spatial resolution of {approx}2.5 cm, and time resolution of {approx}1 ms at angular noise levels of {approx}0.5 deg. Conventional (albeit very narrow) interference filters isolate {pi} or {sigma} polarized emission. Avalanche photodiode detectors with digital phase-sensitive detection measure the harmonics of a pair of photoelastic modulators operating at 20 and 23 kHz, and thus the polarization state. The {pi} component is observed to be significantly stronger than {sigma}, in reasonably good agreement with atomic physics calculations, and as a result, almost all channels are now operated on {pi}. Trials with a wide filter that admits the entire Stark pattern (relying on the net polarization of the emission) have demonstrated performance almost as good as the conventional channels. MSE-constrained equilibrium reconstructions can readily be produced between pulses.

  5. The MAST motional Stark effect diagnostic.

    PubMed

    Conway, N J; De Bock, M F M; Michael, C A; Walsh, M J; Carolan, P G; Hawkes, N C; Rachlew, E; McCone, J F G; Shibaev, S; Wearing, G

    2010-10-01

    A motional Stark effect (MSE) diagnostic is now installed and operating routinely on the MAST spherical tokamak, with 35 radial channels, spatial resolution of ∼2.5 cm, and time resolution of ∼1 ms at angular noise levels of ∼0.5°. Conventional (albeit very narrow) interference filters isolate π or σ polarized emission. Avalanche photodiode detectors with digital phase-sensitive detection measure the harmonics of a pair of photoelastic modulators operating at 20 and 23 kHz, and thus the polarization state. The π component is observed to be significantly stronger than σ, in reasonably good agreement with atomic physics calculations, and as a result, almost all channels are now operated on π. Trials with a wide filter that admits the entire Stark pattern (relying on the net polarization of the emission) have demonstrated performance almost as good as the conventional channels. MSE-constrained equilibrium reconstructions can readily be produced between pulses.

  6. Atomic Models for Motional Stark Effects Diagnostics

    SciTech Connect

    Gu, M F; Holcomb, C; Jayakuma, J; Allen, S; Pablant, N A; Burrell, K

    2007-07-26

    We present detailed atomic physics models for motional Stark effects (MSE) diagnostic on magnetic fusion devices. Excitation and ionization cross sections of the hydrogen or deuterium beam traveling in a magnetic field in collisions with electrons, ions, and neutral gas are calculated in the first Born approximation. The density matrices and polarization states of individual Stark-Zeeman components of the Balmer {alpha} line are obtained for both beam into plasma and beam into gas models. A detailed comparison of the model calculations and the MSE polarimetry and spectral intensity measurements obtained at the DIII-D tokamak is carried out. Although our beam into gas models provide a qualitative explanation for the larger {pi}/{sigma} intensity ratios and represent significant improvements over the statistical population models, empirical adjustment factors ranging from 1.0-2.0 must still be applied to individual line intensities to bring the calculations into full agreement with the observations. Nevertheless, we demonstrate that beam into gas measurements can be used successfully as calibration procedures for measuring the magnetic pitch angle through {pi}/{sigma} intensity ratios. The analyses of the filter-scan polarization spectra from the DIII-D MSE polarimetry system indicate unknown channel and time dependent light contaminations in the beam into gas measurements. Such contaminations may be the main reason for the failure of beam into gas calibration on MSE polarimetry systems.

  7. Motional Stark effect diagnostics for KSTAR

    NASA Astrophysics Data System (ADS)

    Chung, J.; Ko, J.; Howard, J.; Michael, C.; von Nessi, G.; Thorman, A.; De Bock, M. F. M.

    2014-10-01

    The motional Stark effect (MSE) diagnostic is used to measure the radial magnetic pitch-angle profile in neutral-beam-heated plasmas. The diagnostic relies upon the measurement of the polarization direction of Stark-split D-alpha emission from injected fast neutral atoms in a magnetic field. Measurements of the magnetic pitch angle are used with magnetic equilibrium reconstruction codes such as EFIT to calculate the safety factor in shaped plasmas. The MSE diagnostic is important for determining the shape of the q profile to optimize confinement and stability, and it has become a key element in high-performance tokamaks. For the purpose of achieving the high-performance operating region in the Korea Superconducting Tokamak Advanced Research KSTAR device, two types of methods are being studied. In KSTAR, a multichord PEM (photo-elastic modulator)-based MSE system is being developed, and an imaging MSE polarimetry system using the coherence imaging technique has been showing promising initial results during the last two KSTAR experimental campaigns in 2012 and 2013, respectively. In this paper, we describe the progress of the KSTAR MSE diagnostics.

  8. Preparations for the motional Stark effect diagnostic on EAST

    SciTech Connect

    Fu, J.; Li, Y. Y.; Lyu, B. Sheng, P.; Wan, B. N.; Zhang, Y.; Yin, X. H.; Yu, Y.; Ye, M. Y.; Shi, Y. J.

    2014-11-15

    Measurement and control of the current profile is essential for high performance and steady state operation of Experimental Advanced Superconducting Tokamak (EAST). For this purpose, a conventional Motional Stark Effect (MSE) diagnostics utilizing photoelastic modulators is proposed and investigated. The pilot experiment includes one channel to verify the feasibility of MSE, whose sightline intersects with Neutral Beam Injection at major radius of R = 2.12 m. A beam splitter is adopted for simultaneous measurements of Stark multiplets and their polarization directions. A simplified simulation code was also developed to explore the Stark splitting spectra. Finally, the filter is optimized based on the viewing geometry and neutral beam parameters.

  9. Imaging motional Stark effect measurements at ASDEX Upgrade

    SciTech Connect

    Ford, O. P.; Burckhart, A.; McDermott, R.; Pütterich, T.; Wolf, R. C.

    2016-11-15

    This paper presents an overview of results from the Imaging Motional Stark Effect (IMSE) diagnostic obtained during its first measurement campaign at ASDEX Upgrade since installation as a permanent diagnostic. A brief overview of the IMSE technique is given, followed by measurements of a standard H-mode discharge, which are compared to equilibrium reconstructions showing good agreement where expected. The development of special discharges for the calibration of pitch angle is reported and safety factor profile changes during sawteeth crashes are shown, which can be resolved to a few percent due to the high sensitivity at good time resolution of the new IMSE system.

  10. Pedestal magnetic field measurements using a motional Stark effect polarimeter.

    PubMed

    Lanctot, M J; Holcomb, C T; Allen, S L; Fenstermacher, M E; Luce, T C

    2012-10-01

    Temperature-controlled, 0.15 nm interference filters were installed on an edge-viewing system of the motional Stark effect (MSE) polarimeter on the DIII-D tokamak. The upgraded system provides a factor of two reduction in the bandpass compared to the previous design, and linear control of the bandpass, which is unaltered by wavelength tuning. With the new system, there is a reduced dependence of the inferred polarization angle on the filter wavelength calibration. Recent measurements from the calibrated edge-viewing system show increased agreement with other MSE arrays.

  11. Design of the Tore Supra motional Stark effect diagnostic

    NASA Astrophysics Data System (ADS)

    Lotte, Ph.; Echard, B.; Hess, W.; Migozzi, J. B.

    2006-10-01

    This article describes the overall design of the motional Stark effect diagnostic on Tore Supra (not water cooled in its first version) and the results obtained. The diagnostic is composed of nine viewing lines measuring the plasma every 8cm with a spatial resolution varying from 3to6cm. A tube placed inside the port adjacent to the neutral beam contains a stainless-steel mirror and SFL6 optic lenses that carry the image of the neutral beam towards the optical fibers. On Tore Supra the diagnostics having components inside the machine have to face thermal load difficulties linked with the long shots, and this will be the case for ITER diagnostics. This is why for safety reasons the insulating window is placed at the rear side of the tube, and consequently the optics is under the machine vacuum. For motional Stark effect, before reaching the thermal limits on the components, a first limitation comes from the polarization modifications induced by the temperature gradients on the lenses (birefringence effect). This limitation is estimated in terms of plasma duration. The associated diagnostic neutral beam (60keV, 400kW, 5s) works in hydrogen for a higher velocity and a better plasma penetration. As a consequence the beam spectrum exhibits a large Doppler shift and a clear separation of the Stark components. The detection uses the classical elements of the polarimetry method, wide aperture photoelastic modulators, linear polarizer, narrow interference filters, and photomultipliers. The signal is processed digitally (250kHz) for the extraction of the Fourier components that allow the calculation of the magnetic field pitch angles. The first measurements obtained during Ohmic shots for various plasma currents are in good agreement with the current diffusion calculations done with the CRONOS code.

  12. Instrumentation for a multichord motional Stark effect diagnostic in KSTAR.

    PubMed

    Chung, J; Ko, J; De Bock, M F M; Jaspers, R J E

    2014-11-01

    The motional Stark effect (MSE) diagnostic is used to measure the radial magnetic pitch angle profile in neutral beam heated plasmas. This information is used to calculate the safety factor, q, with magnetic equilibrium reconstruction codes such as EFIT. The MSE diagnostic is important during active shaping of the q profile to optimize confinement and stability, and it has become a key diagnostic in high performance tokamaks. A multichord photo-elastic modulator (PEM) based MSE system is being developed for a real-time plasma current profile control in Korea Superconducting Tokamak Advanced Research (KSTAR). The PEM-based approach is a standard method that measures the polarization direction of a single Stark line with narrow tunable bandpass filters. A tangential view of the heating beam provides good spatial resolution of 1-3 cm, which provides an opportunity to install 25 spatial channels spanning the major radius from 1.74 m to 2.84 m. Application of real-time control is a long-term technical goal after commissioning the diagnostic in KSTAR, which is expected in 2015. In this paper, we describe the design of this newly-constructed multichord MSE diagnostic in KSTAR.

  13. Instrumentation for a multichord motional Stark effect diagnostic in KSTAR

    NASA Astrophysics Data System (ADS)

    Chung, J.; Ko, J.; De Bock, M. F. M.; Jaspers, R. J. E.

    2014-11-01

    The motional Stark effect (MSE) diagnostic is used to measure the radial magnetic pitch angle profile in neutral beam heated plasmas. This information is used to calculate the safety factor, q, with magnetic equilibrium reconstruction codes such as EFIT. The MSE diagnostic is important during active shaping of the q profile to optimize confinement and stability, and it has become a key diagnostic in high performance tokamaks. A multichord photo-elastic modulator (PEM) based MSE system is being developed for a real-time plasma current profile control in Korea Superconducting Tokamak Advanced Research (KSTAR). The PEM-based approach is a standard method that measures the polarization direction of a single Stark line with narrow tunable bandpass filters. A tangential view of the heating beam provides good spatial resolution of 1-3 cm, which provides an opportunity to install 25 spatial channels spanning the major radius from 1.74 m to 2.84 m. Application of real-time control is a long-term technical goal after commissioning the diagnostic in KSTAR, which is expected in 2015. In this paper, we describe the design of this newly-constructed multichord MSE diagnostic in KSTAR.

  14. Instrumentation for a multichord motional Stark effect diagnostic in KSTAR

    SciTech Connect

    Chung, J. Ko, J.; De Bock, M. F. M.; Jaspers, R. J. E.

    2014-11-15

    The motional Stark effect (MSE) diagnostic is used to measure the radial magnetic pitch angle profile in neutral beam heated plasmas. This information is used to calculate the safety factor, q, with magnetic equilibrium reconstruction codes such as EFIT. The MSE diagnostic is important during active shaping of the q profile to optimize confinement and stability, and it has become a key diagnostic in high performance tokamaks. A multichord photo-elastic modulator (PEM) based MSE system is being developed for a real-time plasma current profile control in Korea Superconducting Tokamak Advanced Research (KSTAR). The PEM-based approach is a standard method that measures the polarization direction of a single Stark line with narrow tunable bandpass filters. A tangential view of the heating beam provides good spatial resolution of 1–3 cm, which provides an opportunity to install 25 spatial channels spanning the major radius from 1.74 m to 2.84 m. Application of real-time control is a long-term technical goal after commissioning the diagnostic in KSTAR, which is expected in 2015. In this paper, we describe the design of this newly-constructed multichord MSE diagnostic in KSTAR.

  15. Spectrally resolved motional Stark effect measurements on ASDEX Upgrade

    SciTech Connect

    Reimer, R.; Dinklage, A.; Wolf, R.; Fischer, R.; Hobirk, J.; Löbhard, T.; Mlynek, A.; Reich, M.; Sawyer, L.; Collaboration: ASDEX Upgrade

    2013-11-15

    A spectrally resolved Motional Stark Effect (MSE) diagnostic has been installed at ASDEX Upgrade. The MSE data have been fitted by a forward model providing access to information about the magnetic field in the plasma interior [R. Reimer, A. Dinklage, J. Geiger et al., Contrib. Plasma Phys. 50, 731–735 (2010)]. The forward model for the beam emission spectra comprises also the fast ion D{sub α} signal [W. W. Heidbrink and G. J. Sadler, Nucl. Fusion 34, 535–615 (1994)] and the smearing on the CCD-chip. The calculated magnetic field data as well as the revealed (dia)magnetic effects are consistent with the results from equilibrium reconstruction solver. Measurements of the direction of the magnetic field are affected by unknown and varying polarization effects in the observation.

  16. Available information in 2D motional Stark effect imaging.

    PubMed

    Creese, Mathew; Howard, John

    2010-10-01

    Recent advances in imaging techniques have allowed the extension of the standard polarimetric 1D motional Stark effect (MSE) diagnostic to 2D imaging of the internal magnetic field of fusion devices [J. Howard, Plasma Phys. Controlled Fusion 50, 125003 (2008)]. This development is met with the challenge of identifying and extracting the new information, which can then be used to increase the accuracy of plasma equilibrium and current density profile determinations. This paper develops a 2D analysis of the projected MSE polarization orientation and Doppler phase shift. It is found that, for a standard viewing position, the 2D MSE imaging system captures sufficient information to allow imaging of the internal vertical magnetic field component B(Z)(r,z) in a tokamak.

  17. Improved spectral analysis for the motional Stark effect diagnostic

    SciTech Connect

    Ko, J.; Klabacha, J.

    2012-10-15

    The magnetic pitch angle and the magnitude from reversed field pinch plasmas in the Madison symmetric torus (MST) have been routinely obtained from fully resolved motional Stark effect (MSE) spectrum analyses. Recently, the spectrum fit procedure has been improved by initializing and constraining the fit parameters based on the MSE model in the atomic data and analysis structure. A collisional-radiative model with level populations nlm-resolved up to n= 4 and a simple Born approximation for ion-impact cross sections is used for this analysis. Measurement uncertainty is quantified by making MSE measurements with multiple views of a single spatial location, ranging 5%-15% for typical MST operation conditions. A multi-view fit improves the goodness of fit of MSE spectral features and background.

  18. The motional Stark effect with laser-induced fluorescence diagnostic

    NASA Astrophysics Data System (ADS)

    Foley, Elizabeth; Levinton, Fred

    2007-11-01

    Traditional motional Stark effect (MSE) diagnostics exploit the polarization properties of light generated from a neutral hydrogenic beam via collisionally-induced fluorescence (CIF). MSE uses this information to determine a spatially resolved profile of the magnetic field pitch angle in a magnetized plasma. The use of laser-induced fluorescence with MSE on a dedicated diagnostic neutral beam enables an MSE pitch angle measurement at fields as low as 0.001 T, which cannot be achieved by CIF systems. The LIF system also affords the option of very precisely measuring the magnetic field magnitude as well as direction. The MSE-LIF diagnostic is under development in our laboratory, where we have a diagnostic neutral beam system, a dye laser, and a helicon plasma source. This poster will present the latest results relating to MSE-LIF measurements in plasma, as well as an analysis of the relative utility of magnetic field magnitude vs pitch angle measurements for equilibrium reconstruction.

  19. Instrumentation for the joint European torus motional Stark effect diagnostic

    SciTech Connect

    Stratton, B.C.; Long, D.; Palladino, R.; Hawkes, N.C.

    1999-01-01

    A motional Stark effect magnetic field pitch angle diagnostic has been implemented on the joint European torus (JET) tokamak. The instrumentation designed following the study by Hawkes {ital et al.} (these proceedings) is described. D{sub {alpha}} emission from the Octant 4 neutral beams is collected by optics which transport the plasma image outside the vacuum vessel and through a pair of photoelastic modulators (PEMs) and a linear polarizer. The light is fiber-optically coupled to interference filter spectrometers, which incorporate a remotely controlled filter tilting mechanism. This allows the center wavelength of the filter bandpass to be tuned over a range sufficient for observation of the {sigma} and {pi} lines of the Stark spectrum emitted by the full- and half-energy components of the beam, providing flexibility to make measurements with a variety of beam configurations. The detectors are low-noise avalanche photodiode modules. Fast digital signal processing techniques are used to extract the Fourier components of the signal at the PEM first and second harmonic frequencies. Analysis of these signals will yield the magnetic field pitch angle, which will be used as a constraint on EFIT equilibrium reconstruction modeling to obtain the q(r) profile. The system has 25 spatial channels covering the outer-half of a JET plasma with spatial resolution of 0.03{endash}0.07 m per channel with {approximately}0.05 m channel-to-channel separation. Time resolution is expected to be 1{endash}10 ms. {copyright} {ital 1999 American Institute of Physics.}

  20. Measurements of the internal magnetic field using the B-Stark motional Stark effect diagnostic on DIII-D (inivited).

    PubMed

    Pablant, N A; Burrell, K H; Groebner, R J; Holcomb, C T; Kaplan, D H

    2010-10-01

    Results are presented from the B-Stark diagnostic installed on the DIII-D tokamak. This diagnostic provides measurements of the magnitude and direction of the internal magnetic field. The B-Stark system is a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of the Stark split D(α) emission from injected neutral beams. This technique may have advantages over MSE polarimetry based diagnostics in future devices, such as the ITER. The B-Stark diagnostic technique and calibration procedures are discussed. The system is shown to provide accurate measurements of B(θ)/B(T) and ∣B∣ over a range of plasma conditions. Measurements have been made with toroidal fields in the range of 1.2-2.1 T, plasma currents in the range 0.5-2.0 MA, densities between 1.7 and 9.0×10(19) m(-3), and neutral beam voltages between 50 and 81 keV. The viewing direction and polarization dependent transmission properties of the collection optics are found using an in situ beam into gas calibration. These results are compared to values found from plasma equilibrium reconstructions and the MSE polarimetry system on DIII-D.

  1. Phonon assisted carrier motion on the Wannier-Stark ladder

    NASA Astrophysics Data System (ADS)

    Cheung, Alfred; Berciu, Mona

    2014-03-01

    It is well known that at zero temperature and in the absence of electron-phonon coupling, the presence of an electric field leads to localization of carriers residing in a single band of finite bandwidth. In this talk, we will present an implementation of the self-consistent Born approximation (SCBA) to study the effect of weak electron-phonon coupling on the motion of a carrier in a biased system. At moderate and strong electron-phonon coupling, we supplement the SCBA, describing the string of phonons left behind by the carrier, with the momentum average approximation to describe the phonon cloud that accompanies the resulting polaron. We find that coupling to the lattice delocalizes the carrier, as expected, although long-lived resonances resulting from the Wannier-Stark states of the polaron may appear in certain regions of the parameter space. We end with a discussion of how our method can be improved to model disorder, other types of electron-phonon coupling, and electron-hole pair dissociation in a biased system.

  2. The prototype imaging motional Stark effect diagnostic for ASDEX upgrade.

    PubMed

    Ford, O P; Howard, J; Wolf, R C

    2015-09-01

    This paper presents the development and testing of the prototype Imaging Motional Stark-Effect (IMSE) diagnostic, designed for ASDEX upgrade. A detailed description of the core hardware, theory of operation, and application to complex MSE spectra are presented and analytical evaluation methods suitable for the required accuracy are developed. The diagnostic is tested with a MSE-like polarised spectrum to assess the accuracy of different modulation modes suggested in previous works. Each is found to have small systematic errors due to non-ideal effects of the components, which must be carefully examined. In particular, the effect of intrinsic contrast that results from imperfect parallelism of the birefringent plates is found to have a strong effect. Methods to mitigate and correct for this are discussed. With the necessary corrections and calibrations, the accuracy of polarisation orientation is shown to be within ±0.2°. The effect of finite ellipticity is examined and the possibility to measure this to an accuracy of ±2.0° is demonstrated. The system is shown to be insensitive to broadband polarised background light, temperature variations, and critically to variations in the details of the MSE spectrum.

  3. The Motional Stark Effect (MSE) Diagnostic on NSTX

    NASA Astrophysics Data System (ADS)

    Yuh, Howard

    2005-10-01

    The adoption of the motional Stark effect (MSE) polarimetry diagnostic is due to its very good temporal and spatial resolution of the q- profile, combined with its exceedingly good accuracy. This has resulted in many important scientific contributions towards our understanding of stability and transport. This work describes the implementation of the MSE-CIF diagnostic on NSTX. Due to the low magnetic field on NSTX the implementation of the MSE diagnostic requires a different approach for the viewing optics and spectral filter. The diagnostic views a heating beam with 8 inch collection optics, imaged onto a fiber array. The optical system is configured to maximize the polarization fraction by reducing the Doppler broadening from the heating beam. This is done with a vertical aperture in front of the collection optics to reduce geometric Doppler broadening. In addition, a wide field Lyot spectral filter with high throughput and high resolution has been developed to achieve the necessary signal-to-noise. Results with the MSE-CIF diagnostic have been obtained at magnetic fields >=0.3 Tesla with eight channels providing coverage from the magnetic axis to near the outboard edge. The number of spatial channels can be increased to 19 in the future. Results of various plasmas regimes including L-mode, H-mode, and reversed shear will be presented.

  4. Initial Results from the Motional Stark Effect Diagnostic on NSTX

    NASA Astrophysics Data System (ADS)

    Levinton, Fred

    2004-11-01

    The adoption of the motional Stark effect (MSE) polarimetry diagnostic is due to its very good temporal and spatial resolution of the q-profile, combined with its exceedingly good accuracy. This has resulted in many important scientific contributions towards our understanding of stability and transport. Despite the success of MSE on mid to large size devices, with magnetic fields above 1 Tesla, it has not been implemented on low field or small experiments. This is due to the large expense of a neutral beam and/or the inability of the technique to work at magnetic fields below 0.75 Tesla. Two approaches are being developed to remedy this; (1)MSE-LIF using laser-induced fluorescence (LIF), with a small diagnostic neutral beam, and (2)MSE-CIF using collsionally induced fluorescence (CIF) to allow the MSE technique to function at significantly lower magnetic fields than previously demonstrated. This work describes the implementation of the MSE-CIF diagnostic on NSTX which views the heating beam with 8 inch collection optics, imaged onto a fiber array. The optical system is configured to maximize the polarization fraction by reducing the Doppler broadening from the heating beam. In addition, a wide field Lyot filter spectral filter with high throughput and high resolution has been developed to achieve the necessary signal-to-noise. Initial results with the MSE-CIF diagnostic has been obtained at magnetic fields ≥0.3 Tesla with four channels near the magnetic axis to determine q(0). The number of spatial channels will be increased to 19 with coverage from the geometric center to the outboard plasma edge.

  5. Asymmetries in the motional Stark effect emission on the DIII-D tokamak

    NASA Astrophysics Data System (ADS)

    Victor, B. S.; Holcomb, C. T.; Allen, S. L.; Meyer, W. H.; Makowski, M. A.; Thorman, A.

    2016-11-01

    Spectrometer measurements and filter upgrades to a motional Stark effect polarimeter measuring the outer half-radius of the DIII-D tokamak helped to identify asymmetries in the polarization angle of Stark-split emission. The measured polarization angle of the π components differs and is not orthogonal to the σ component. These differences persist over a range of densities and with low levels of background light. It is suggested that the difference in the polarization angle between components is from a change in the ellipticity of the emitted light across the Stark components coupled with imperfect polarization preservation from an in-vessel mirror.

  6. Asymmetries in the motional Stark effect emission on the DIII-D tokamak.

    PubMed

    Victor, B S; Holcomb, C T; Allen, S L; Meyer, W H; Makowski, M A; Thorman, A

    2016-11-01

    Spectrometer measurements and filter upgrades to a motional Stark effect polarimeter measuring the outer half-radius of the DIII-D tokamak helped to identify asymmetries in the polarization angle of Stark-split emission. The measured polarization angle of the π components differs and is not orthogonal to the σ component. These differences persist over a range of densities and with low levels of background light. It is suggested that the difference in the polarization angle between components is from a change in the ellipticity of the emitted light across the Stark components coupled with imperfect polarization preservation from an in-vessel mirror.

  7. Development of the B-Stark motional Stark effect diagnostic for measurements of the internal magnetic field in the DIII-D tokamak

    NASA Astrophysics Data System (ADS)

    Pablant, Novimir Antoniuk

    A new diagnostic, B⃗ -Stark, has been developed at the DIII-D tokamak for measurements of the magnitude and direction of the internal magnetic field. The B⃗ -Stark system is a version of a motional Stark effect (MSE) diagnostic based on the Stark split Dalpha emission from injected neutral beams. This diagnostic uses the spacing of the Stark lines to measure the magnitude of the magnetic field, and the intensities of the pi3 and sigma1 lines to measure the magnetic pitch angle. These lines originate from the same upper level, and are therefore not dependent on the n = 3 level populations. The measurement of the magnetic pitch angle requires a specific viewing geometry with respect to the neutral beams, which is provided by the B⃗ -Stark diagnostic installation. The B⃗ -Stark technique may have advantages over motional Stark effect polarimetry (MSE polarimetry) diagnostics in future devices with high densities and temperatures, such as ITER. Under these conditions coatings on the plasma facing mirrors are expected, which can cause changes in the polarization state of the reflected light. The B⃗ -Stark technique is insensitive to the polarization direction, and can calibrate for polarization dependent transmission by using an in-situ beam-into-gas calibration. This dissertation describes the development and characterization of the B⃗ -Stark diagnostic. The hardware design and spectral fitting techniques are discussed in detail. Calibration procedures are described including the in-situ determination of the beam emission line profiles, viewing geometry and properties of the collection optics. The performance of the system is evaluated over the range of plasma conditions accessible at DIII-D. Measurements of the magnetic field have been made with toroidal fields in the range 1.2--2.1T, plasma currents in the range 0.5--2.0MA, densities between 1.7--9.0 x 1019m -3, and neutral beam voltages between 50--81keV. These results are compared to values found from

  8. A high spatial resolution Stokes polarimeter for motional Stark effect imaging

    SciTech Connect

    Thorman, Alex; Michael, Clive; Howard, John

    2013-06-15

    We describe an enhanced temporally switched interfero-polarimeter that has been successfully deployed for high spatial resolution motional Stark effect imaging on the KSTAR superconducting tokamak. The system utilizes dual switching ferroelectric liquid crystal waveplates to image the full Stokes vector of elliptically polarized and Doppler-shifted Stark-Zeeman Balmer-alpha emission from high energy neutral beams injected into the magnetized plasma. We describe the optical system and compare its performance against a Mueller matrix model that takes account of non-ideal performance of the switching ferro-electric liquid crystal waveplates and other polarizing components.

  9. Spectral measurement of B via Motional Stark Effect in the MST RFP

    NASA Astrophysics Data System (ADS)

    den Hartog, D. J.; Craig, D.; Fiksel, G.

    2000-10-01

    Using a 30 keV, 4 A diagnostic neutral H beam, we have made an initial measurement of the separation of the pi manifolds of the H-alpha Motional Stark Effect (MSE) spectrum in the MST Reversed-Field Pinch. The wavelength separation of approximately 0.2 nm is as expected for the B of about 0.5 T in the core of MST. The DINA beam is nearly monoenergetic and has low divergence, thus the Doppler-shifted Stark manifold is clearly separated from the background H-alpha, and beam-induced smearing of the Stark components is minimized. Since the magnitude of B in the core of MST provides an important contraint for equilibrium modeling, three refinements are planned to increase measurement accuracy. First, we will accurately model the expected H-alpha MSE spectrum for low magnetic fields, assuming statistical weighting of the Stark components. Second, using an existing fast spectrometer, we will attempt time-resolved simultaneous measurement of the smeared pi and sigma manifolds. Third, we will implement a new CCD spectrometer and viewing geometry to attempt direct time integrated measurement of the individual components of the Stark manifold.

  10. Initial operation of a newly developed multichord motional Stark effect diagnostic in KSTAR

    SciTech Connect

    Chung, J. Ko, J.; Wi, H.; Messmer, M.; Schenkelaars, S.; Scheffer, M.; Jaspers, R. J. E.

    2016-11-15

    A photo-elastic modulator based 25-chord motional Stark effect (MSE) diagnostic has been successfully developed and commissioned in Korea Superconducting Tokamak Advanced Research. The diagnostic measures the radial magnetic pitch angle profile of the Stark splitting of a D-alpha line at 656.1 nm by the electric field associated with the neutral deuterium heating beam. A tangential view of the neutral beam provides a good spatial resolution of 1–3 cm for covering the major radius from 1.74 m to 2.28 m, and the time resolution is achieved at 10 ms. An in-vessel calibration before the vacuum closing as well as an in situ calibration during the tokamak operation was performed by means of specially designed polarized lighting sources. In this work, we present the final design of the installed MSE diagnostic and the first results of the commissioning.

  11. Initial operation of a newly developed multichord motional Stark effect diagnostic in KSTAR

    NASA Astrophysics Data System (ADS)

    Chung, J.; Ko, J.; Wi, H.; Messmer, M.; Schenkelaars, S.; Scheffer, M.; Jaspers, R. J. E.

    2016-11-01

    A photo-elastic modulator based 25-chord motional Stark effect (MSE) diagnostic has been successfully developed and commissioned in Korea Superconducting Tokamak Advanced Research. The diagnostic measures the radial magnetic pitch angle profile of the Stark splitting of a D-alpha line at 656.1 nm by the electric field associated with the neutral deuterium heating beam. A tangential view of the neutral beam provides a good spatial resolution of 1-3 cm for covering the major radius from 1.74 m to 2.28 m, and the time resolution is achieved at 10 ms. An in-vessel calibration before the vacuum closing as well as an in situ calibration during the tokamak operation was performed by means of specially designed polarized lighting sources. In this work, we present the final design of the installed MSE diagnostic and the first results of the commissioning.

  12. Development of signal analysis method for the motional Stark effect diagnostic on EAST

    NASA Astrophysics Data System (ADS)

    Fu, Jia; Lyu, Bo; Liu, Haiqing; Li, Yingying; Liu, Dongmei; Wei, Yongqing; Fan, Chao; Shi, Yuejiang; Wu, Zhenwei; Wan, Baonian

    2017-10-01

    A pilot single-channel Motional Stark Effect (MSE) diagnostic has been developed on EAST since 2015. The dual photo-elastic modulators (PEM) were employed to encode the polarization angle into a time-varying signal. The pitch angle was related to the ratio of modulation amplitude at the second harmonic frequency. A digital harmonic analyzer (DHA) technique was developed for extracting the second harmonic amplitude. The results were validated with a hardware phase lock-in amplifier, and is also consistent with the software dual phase-locking algorithm.

  13. Linewidth-modulated motional Stark effect measurements of internal field structure in low-field configurations

    SciTech Connect

    Reinecke, E. A.; Fonck, R. J.; Thorson, T. A.

    2001-01-01

    Motional Stark effect measurements of internal field structure in low-field magnetic confinement configurations are considered for both magnitude and direction of the local magnetic field. The amplitude and phase delay of an oscillating spectral linewidth driven by a rotating polarizer provides a means of determining the magnitude and direction of the total field simultaneously while avoiding difficulties of neutral beam energy drift. Photon-noise limit estimates for a diagnostic beam on the low-field PEGASUS toroidal experiment indicate sensitivities of roughly 20 G and 0.2{sup o} for the magnitude and direction angle. These values are sufficient to provide significant constraints on magnetic equilibrium reconstructions.

  14. Motional Stark Effect Measurements of q-Profiles in JET Optimised Shear Plasmas

    NASA Astrophysics Data System (ADS)

    Stratton, B. C.; Hawkes, N. C.; Challis, C. D.; Drozdov, V.; Lomas, P.; Joffrin, E.; Litaudon, X.; Lotte, P.; Mazon, D.; Deangelis, R.; Rachlew, E.; Reyes-Cortes, S.

    2000-10-01

    A Motional Stark Effect (MSE) diagnostic is used to measure the magnetic field pitch angle in JET discharges. The q-profile is deduced from EFIT magnetic equilibrium reconstructions constrained by MSE data. Measurements have concentrated primarily on the Optimised Shear (OS) regime in which the details of the q-profile play an important role in the formation of internal transport barriers, leading to improved confinement. q-profiles in the target and high-power phases of OS plasmas with various heating scenarios (NBI + ICRF, NBI only, and NBI + LHCD) and pre-heat timings are presented and are correlated with ITB formation in the high-power phase.

  15. Highlights of Recent Alcator C-Mod Research

    NASA Astrophysics Data System (ADS)

    Marmar, Earl

    2012-10-01

    Alcator C-Mod focuses on broad scientific issues with particular emphasis on ITER needs and requests. First results from a high power, magnetic field-aligned ICRF antenna show significant reduction of high Z impurity contamination under various plasma conditions Detailed comparisons of core and edge fluctuations in L-mode and I-mode reveal that core turbulence is reduced in I-mode before the reduction of edge turbulence and the onset of the WCM, in stark contrast to the usual turbulence changes observed in H-mode on other tokamaks. The connection among rotation reversals, non-local heat transport, energy confinement saturation (the transition between the linear Ohmic confinement, and saturated Ohmic confinement, regimes) and changes in underlying turbulence has been demonstrated. Joint pedestal studies among C-Mod, DIII-D and NSTX reveal common features, including an upper limit on pedestal pressure in ELMy H-mode determined by peeling-ballooning modes (PBMs), and pedestal width scaling approximately as βpol^1/2. A novel stochastic model for intermittent SOL plasma fluctuations has been constructed, is in excellent agreement with experiment, and reveals important details on the underlying physics. Design of the first actively heated tokamak tungsten divertor is described.

  16. The motional Stark effect polarimeter in the HL-2A tokamak.

    PubMed

    Yu, D L; Wei, Y L; Xia, F; Cao, J Y; Chen, C Y; Liu, L; Chen, W J; Ji, X Q; Liu, Y; Yan, L W; Yang, Q W; Duan, X R

    2014-05-01

    A 7-channel motional Stark effect polarimeter based on four polarizers and a spectrometer has been developed in the HL-2A tokamak, which is the first time successful utilizing this kind of polarimeter on a tokamak. The accuracy of the angle can reach ±0.25° in the calibration experiments. Pilot experiments of measuring the magnetic pitch angle have been successfully carried out in the weak motional Stark effect plasma discharge with toroidal magnetic field of ~1.3 T and beam energy of ~25 keV/amu. The pitch angles of magnetic field are obtained for 7 spatial points covering 24 cm along major radius with time resolution of 40 ms; the profiles of safety factor are obtained by combining with the Equilibrium and Reconstruction Fitting Code. The core value of safety factor (q) is less than 1 during the sawtooth oscillation and the position of q = 1 surface is well consistent with the results measured by soft X-ray array.

  17. The motional Stark effect polarimeter in the HL-2A tokamak

    SciTech Connect

    Yu, D. L. Wei, Y. L.; Xia, F.; Cao, J. Y.; Chen, C. Y.; Liu, L.; Chen, W. J.; Ji, X. Q.; Liu, Y.; Yan, L. W.; Yang, Q. W.; Duan, X. R.

    2014-05-15

    A 7-channel motional Stark effect polarimeter based on four polarizers and a spectrometer has been developed in the HL-2A tokamak, which is the first time successful utilizing this kind of polarimeter on a tokamak. The accuracy of the angle can reach ±0.25° in the calibration experiments. Pilot experiments of measuring the magnetic pitch angle have been successfully carried out in the weak motional Stark effect plasma discharge with toroidal magnetic field of ∼1.3 T and beam energy of ∼25 keV/amu. The pitch angles of magnetic field are obtained for 7 spatial points covering 24 cm along major radius with time resolution of 40 ms; the profiles of safety factor are obtained by combining with the Equilibrium and Reconstruction Fitting Code. The core value of safety factor (q) is less than 1 during the sawtooth oscillation and the position of q = 1 surface is well consistent with the results measured by soft X-ray array.

  18. Calibration and operational experience with the JET motional Stark effect diagnostic

    NASA Astrophysics Data System (ADS)

    Hawkes, N. C.; Brix, M.

    2006-10-01

    Motional Stark effect measurements of the magnetic field pitch angle on JET present several difficulties most serious of which is that the injection systems consist of more than one source, each with a different motional stark effect (MSE) angle. Attempts to describe the net polarization angle, within the EFIT equilibrium code, using the weighted sum of Stokes vectors, have proved inaccurate. Instead we rely on spectrally isolating the emission of a single source. Beam power modulation is helpful in differentiating background polarized light, but this technique fails in the presence of strong edge localized mode (ELMs). Calibration is difficult because of the presence of a mirror in the optical system. The mirror introduces a large optical phase shift which means that the polarimeter has to resolve circular as well as linear polarized components. Basic calibration is carried out off the tokamak using a motorized rotary encoder stage and a six-parameter physical model of the optical and electronic systems. This is readjusted using plasma emission, for mirror operation at 300 °C. Some of the operating experience obtained with the JET MSE diagnostic will be relevant to ITER, although the lack of independent power or voltage control of the ITER injectors is seen as the chief challenge facing the ITER MSE design.

  19. Calibration and operational experience with the JET motional Stark effect diagnostic

    SciTech Connect

    Hawkes, N. C.; Brix, M.

    2006-10-15

    Motional Stark effect measurements of the magnetic field pitch angle on JET present several difficulties most serious of which is that the injection systems consist of more than one source, each with a different motional stark effect (MSE) angle. Attempts to describe the net polarization angle, within the EFIT equilibrium code, using the weighted sum of Stokes vectors, have proved inaccurate. Instead we rely on spectrally isolating the emission of a single source. Beam power modulation is helpful in differentiating background polarized light, but this technique fails in the presence of strong edge localized mode (ELMs). Calibration is difficult because of the presence of a mirror in the optical system. The mirror introduces a large optical phase shift which means that the polarimeter has to resolve circular as well as linear polarized components. Basic calibration is carried out off the tokamak using a motorized rotary encoder stage and a six-parameter physical model of the optical and electronic systems. This is readjusted using plasma emission, for mirror operation at 300 deg. C. Some of the operating experience obtained with the JET MSE diagnostic will be relevant to ITER, although the lack of independent power or voltage control of the ITER injectors is seen as the chief challenge facing the ITER MSE design.

  20. The Alcator C-Mod FIR Polarimeter

    NASA Astrophysics Data System (ADS)

    Xu, P.; Irby, J. H.; Bosco, J.; Kanojia, A.; Leccacorvi, R.; Marmar, E. S.; Michael, P.; Murray, R.; Rokhman, Y.; Vieira, R.; Brower, D. L.; Ding, W. X.; Mansfield, D. K.

    2009-11-01

    A multi-chord FIR polarimetry diagnostic is being developed for the Alcator C-Mod Tokamak to be used to determine the q-profile and to study density and magnetic field fluctuations. This poloidally viewing system using retro-reflectors on the inner wall will have geometry and fields similar to those planned for ITER. The full optical layout will be discussed, as well as simulations of the expected Faraday and Cotton-Mouton signal levels. Bench test results from a single chord system including all optical components will be presented, and preliminary experimental results from C-Mod will be compared with simulated Faraday rotation angle calculated using Thomson Scattering density profiles and EFIT reconstructions of actual C-Mod plasmas.

  1. Measurements of the Internal Magnetic Field on DIII-D Using Intensity and Spacing of the Motional Stark Multiplet

    NASA Astrophysics Data System (ADS)

    Pablant, N. A.; Burrell, K. H.; Gu, M. F.; Holcomb, C. T.

    2008-11-01

    We describe a version of a motional Stark effect diagnostic based on the relative line intensities and spacing of Stark split Dα emission from the neutral beams. Using this technique both the magnitude and direction of the internal magnetic field can be measured, in contrast to motional Stark effect (MSE) polarimetry, which can only measure the direction. This system, named B-Stark, has been recently installed on the DIII-D tokamak. To find the magnetic pitch angle, we use the ratio of the intensities of the π3 and σ1 lines. These lines originate from the same upper level, and so are not dependent on the population levels. The magnitude of the internal B-field is determined from the wavelength separation of the various Stark components. We fit the spectra using a simple Stark model in which the upper level populations of the Dα transition are treated as free variables. The magnitude and direction of the magnetic field obtained using this diagnostic technique compare well with measurements from MSE polarimetry and EFIT.

  2. Measurement of the plasma radial electric field by the motional Stark effect diagnostic on JET plasmas

    NASA Astrophysics Data System (ADS)

    Reyes Cortes, S.; Hawkes, N. C.; Lotte, P.; Fenzi, C.; Stratton, B. C.; Hobirk, J.; De Angelis, R.; Orsitto, F.; Varandas, C. A. F.

    2003-03-01

    The radial electric field gradient or the E×B flow shear has been pointed out as the underlying mechanism for turbulence suppression, responsible for an internal transport barrier formation in advanced tokamak scenarios. A comprehensive study on these subjects requires a direct measurement of the plasma radial electric field Er. The poloidal component of the magnetic field is assessed by the motional Stark effect (MSE) polarimeter, which is currently a standard diagnostic in fusion devices, allowing a local and nonperturbative measurement of the magnetic pitch angle. A precise measure to the state of polarization of the Stark components gives the information on the direction of the magnetic field. Due to the particular orientation of the Lorentz component, that is nearly perpendicular to Er, the MSE diagnostic is very sensitive to the plasma intrinsic radial electric field. This article describes a technique to measure Er involving the change of the polarization angle of the MSE emission, by using two beam injectors at different energies, firing sequentially. Experimental results for the low Er case, i.e., with very little plasma rotation, showing the ability of the MSE to perform this measurement, will be presented. This is the first time that evidence of a direct measurement of the plasma Er is reported from the Joint European Torus.

  3. Status of motional Stark effect and Zeeman effect diagnostics for KSTAR

    NASA Astrophysics Data System (ADS)

    Ko, Jinseok; Chung, Jinil; de Bock, Maarten; KSTAR Team

    2014-10-01

    The motional Stark effect (MSE) diagnostic system is under development aiming at commissioning in 2015. The design and fabrication of the polarization preserving front optics has been complete, including the multi-layer dielectric coated mirror and beam splitter, the latter being required to split the incident light into that above 600 nm for MSE and that below 600 nm for the Charge Exchange Spectroscopy (CES) that shares the front optics with MSE. The bandpass filters with a sharp transmission function and a minimum distortion against tilting have been procured. Both the analog lock-in and the post-processing numerical Fourier transform will be exploited. The Li-beam based Zeeman effect (ZE) diagnostic system is under conceptual design. Its details on the design are introduced in this work including the radial resolution and sensitivity to the change of the magnetic field pitch near the pedestal region. Work supported by the Ministry of Science, ICT and Future Planning, Korea.

  4. The multi-spectral line-polarization MSE system on Alcator C-Mod

    DOE PAGES

    Mumgaard, R. T.; Scott, S. D.; Khoury, M.

    2016-08-17

    A multi-spectral line-polarization motional Stark effect (MSE-MSLP) diagnostic has been developed for the Alcator C-Mod tokamak wherein the Stokes vector is measured in multiple wavelength bands simultaneously on the same sightline to enable better polarized background subtraction. A ten-sightline, four wavelength MSE-MSLP detector system was designed, constructed, and qualified. This system consists of a high-throughput polychromator for each sightline designed to provide large étendue and precise spectral filtering in a cost-effective manner. Each polychromator utilizes four narrow bandpass interference filters and four custom large diameter avalanche photodiode detectors. Two filters collect light to the red and blue of the MSEmore » emission spectrum while the remaining two filters collect the beam pi and sigma emission generated at the same viewing volume. The filter wavelengths are temperature tuned using custom ovens in an automated manner. Furthermore, all system functions are remote controllable and the system can be easily retrofitted to existing single-wavelength line-polarization MSE systems.« less

  5. The multi-spectral line-polarization MSE system on Alcator C-Mod

    SciTech Connect

    Mumgaard, R. T.; Scott, S. D.; Khoury, M.

    2016-08-17

    A multi-spectral line-polarization motional Stark effect (MSE-MSLP) diagnostic has been developed for the Alcator C-Mod tokamak wherein the Stokes vector is measured in multiple wavelength bands simultaneously on the same sightline to enable better polarized background subtraction. A ten-sightline, four wavelength MSE-MSLP detector system was designed, constructed, and qualified. This system consists of a high-throughput polychromator for each sightline designed to provide large étendue and precise spectral filtering in a cost-effective manner. Each polychromator utilizes four narrow bandpass interference filters and four custom large diameter avalanche photodiode detectors. Two filters collect light to the red and blue of the MSE emission spectrum while the remaining two filters collect the beam pi and sigma emission generated at the same viewing volume. The filter wavelengths are temperature tuned using custom ovens in an automated manner. Furthermore, all system functions are remote controllable and the system can be easily retrofitted to existing single-wavelength line-polarization MSE systems.

  6. The multi-spectral line-polarization MSE system on Alcator C-Mod

    SciTech Connect

    Mumgaard, R. T. Khoury, M.; Scott, S. D.

    2016-11-15

    A multi-spectral line-polarization motional Stark effect (MSE-MSLP) diagnostic has been developed for the Alcator C-Mod tokamak wherein the Stokes vector is measured in multiple wavelength bands simultaneously on the same sightline to enable better polarized background subtraction. A ten-sightline, four wavelength MSE-MSLP detector system was designed, constructed, and qualified. This system consists of a high-throughput polychromator for each sightline designed to provide large étendue and precise spectral filtering in a cost-effective manner. Each polychromator utilizes four narrow bandpass interference filters and four custom large diameter avalanche photodiode detectors. Two filters collect light to the red and blue of the MSE emission spectrum while the remaining two filters collect the beam pi and sigma emission generated at the same viewing volume. The filter wavelengths are temperature tuned using custom ovens in an automated manner. All system functions are remote controllable and the system can be easily retrofitted to existing single-wavelength line-polarization MSE systems.

  7. Lower hybrid current drive experiments on Alcator C-Mod: Comparison with theory and simulationa)

    NASA Astrophysics Data System (ADS)

    Bonoli, P. T.; Ko, J.; Parker, R.; Schmidt, A. E.; Wallace, G.; Wright, J. C.; Fiore, C. L.; Hubbard, A. E.; Irby, J.; Marmar, E.; Porkolab, M.; Terry, D.; Wolfe, S. M.; Wukitch, S. J.; Alcator C-Mod Team; Wilson, J. R.; Scott, S.; Valeo, E.; Phillips, C. K.; Harvey, R. W.

    2008-05-01

    Lower hybrid (LH) current drive experiments have been carried out on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] using a radio-frequency system at 4.6GHz. Up to 900kW of LH power has been coupled and driven LH currents have been inferred from magnetic measurements by extrapolating to zero loop voltage, yielding an efficiency of neILHR0/PLH≈2.5±0.2×1019(A/W/m2). We have simulated the LH current drive in these discharges using the combined ray tracing/three-dimensional (r,v⊥,v∥) Fokker-Planck code GENRAY-CQL3D (R. W. Harvey and M. McCoy, in Proceedings of the IAEA Technical Committee Meeting on Simulation and Modeling of Thermonuclear Plasmas, Montreal, Canada, 1992) and found similar current drive efficiencies. The simulated profiles of current density from CQL3D, including both ohmic plus LH drive have been found to be in good agreement with the measured current density from a motional Stark effect diagnostic. Measurements of nonthermal x-ray emission confirm the presence of a significant fast electron population and the three-dimensional (r,v⊥,v∥) electron distribution function from CQL3D has been used in a synthetic diagnostic code to simulate the measured hard x-ray data.

  8. The multi-spectral line-polarization MSE system on Alcator C-Mod

    SciTech Connect

    Mumgaard, R. T.; Scott, S. D.; Khoury, M.

    2016-08-17

    A multi-spectral line-polarization motional Stark effect (MSE-MSLP) diagnostic has been developed for the Alcator C-Mod tokamak wherein the Stokes vector is measured in multiple wavelength bands simultaneously on the same sightline to enable better polarized background subtraction. A ten-sightline, four wavelength MSE-MSLP detector system was designed, constructed, and qualified. This system consists of a high-throughput polychromator for each sightline designed to provide large étendue and precise spectral filtering in a cost-effective manner. Each polychromator utilizes four narrow bandpass interference filters and four custom large diameter avalanche photodiode detectors. Two filters collect light to the red and blue of the MSE emission spectrum while the remaining two filters collect the beam pi and sigma emission generated at the same viewing volume. The filter wavelengths are temperature tuned using custom ovens in an automated manner. Furthermore, all system functions are remote controllable and the system can be easily retrofitted to existing single-wavelength line-polarization MSE systems.

  9. The multi-spectral line-polarization MSE system on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Mumgaard, R. T.; Scott, S. D.; Khoury, M.

    2016-11-01

    A multi-spectral line-polarization motional Stark effect (MSE-MSLP) diagnostic has been developed for the Alcator C-Mod tokamak wherein the Stokes vector is measured in multiple wavelength bands simultaneously on the same sightline to enable better polarized background subtraction. A ten-sightline, four wavelength MSE-MSLP detector system was designed, constructed, and qualified. This system consists of a high-throughput polychromator for each sightline designed to provide large étendue and precise spectral filtering in a cost-effective manner. Each polychromator utilizes four narrow bandpass interference filters and four custom large diameter avalanche photodiode detectors. Two filters collect light to the red and blue of the MSE emission spectrum while the remaining two filters collect the beam pi and sigma emission generated at the same viewing volume. The filter wavelengths are temperature tuned using custom ovens in an automated manner. All system functions are remote controllable and the system can be easily retrofitted to existing single-wavelength line-polarization MSE systems.

  10. Motional Stark Effect Diagnostic Expansion for the DIII-D Tokamak

    SciTech Connect

    Holcomb, C. T.; Allen, S.; Ellis, R. F.; Geer, R.; Jayakumar, R. J.; Morris, K.; Makowski, M. A.; Moller, J. M.; Seppala, L.

    2005-08-01

    A repositioning of a heating neutral beam on the DIII-D tokamak provides an opportunity to expand and improve the Motional Stark Effect diagnostic (MSE) used to constrain the current profile. Dα emission from the neutral beam is split into components parallel (π) and perpendicular (σ) to the total electric field ETotal = vxB + Eplasma. The MSE diagnostic measures the polarization of the σ component to determine the local magnetic field pitch angle Bz/Bφ and the local radial plasma electric field ER. This is typically done using the EFIT current profile reconstruction code. Two independent measurements of the pitch angle γ at each radius are required to differentiate the contributions from the Stark and plasma electric fields. Presently, three MSE diagnostics provide multiple views of a single neutral beam. Our ability to accurately differentiate Bz and ER is limited because these views do not overlap with sufficient radial resolution in some locations, and this limits the accuracy of the current profile reconstructions. The beam rearrangement allows us to build a fourth MSE view of a second beam injected counter to the plasma current. The combination of the new view with the old will improve radial resolution about a factor of 3, reduce ER uncertainty by a factor of 2 in the core and 5-6 in the edge, and reduce Bz uncertainty by 20-30%. The design of the new system is presented in this paper, focusing on the mechanical and optical details at the tokamak port on which it will be installed.

  11. Polarimetry of motional Stark effect and determination of current profiles in DIII-D

    SciTech Connect

    Wroblewski, D. ); Lao, L.L. )

    1992-05-01

    The motional electric field E = v {times} B, where v is the velocity and B is the tokamak magnetic field, produces a strong Stark effect in spectral lines emitted by hydrogenic neutral beams. The tilt angle of the magnetic field line, a quantity related directly to the distribution of the plasma toroidal current, is deduced from a measurement of the direction of polarization of the Stark components. In the DIII-D tokamak, the Balmer-{alpha} line of deuterium emitted by one of the high-power heating beams is analyzed. A multichord polarimeter measures the magnetic field pitch angle at eight spatial locations covering {approximately}0.6 of the nominal plasma diameter at the midplane outboard side. The diagnostic offers 2 to 8 cm resolution in the major radius and 1 ms integration time. The accuracy of the measurement of the polarization direction necessary for an adequate reconstruction of the current profiles is obtained with the use of active polarizing elements which produce high frequency intensity modulation with an amplitude related to the direction of linear polarization of the plasma radiation. The current profiles in highly shaped (non-circular) plasmas cannot be determined solely from the tilt angle measurements because they do not provide any information about the shape of magnetic surfaces. Thus, the polarization measurement are used in conjunction with a large set of external magnetic measurements (magnetic field and flux probes, diamagnetic loops, and Rogowski coils) by the magnetic field equilibrium code EFIT, and provide a constraint on the possible solutions for the current profile.

  12. Polarimetry of motional Stark effect and determination of current profiles in DIII-D (invited)

    SciTech Connect

    Wroblewski, D. ); Lao, L.L. )

    1992-10-01

    The motional electric field {ital E}={ital v}{times}{ital B}, where {ital v} is the velocity and {ital B} is the tokamak magnetic field, produces a strong Stark effect in spectral lines emitted by hydrogenic neutral beams. The tilt angle of the magnetic field line, a quantity related directly to the distribution of the plasma toroidal current, is deduced from a measurement of the direction of polarization of the Stark components. In the DIII-D tokamak, the Balmer-{alpha} line of deuterium emitted by one of the high-power heating beams is analyzed. A multichord polarimeter measures the magnetic field pitch angle at eight spatial locations covering {similar to}0.6 of the nominal plasma diameter at the midplane outboard side. The diagnostic offers 2--8-cm resolution in the major radius and 1-ms integration time. The accuracy of the measurement of the polarization direction necessary for an adequate reconstruction of the current profiles is obtained with the use of active polarizing elements which produce high-frequency intensity modulation with an amplitude related to the direction of linear polarization of the plasma radiation. The current profiles in highly shaped (noncircular) plasmas cannot be determined solely from the tilt angle measurements because they do not provide any information about the shape of magnetic surfaces. Thus, the polarization measurements are used in conjunction with a large set of external magnetic measurements (magnetic field and flux probes, diamagnetic loops, and Rogowski coils) by the magnetic field equilibrium code EFIT, and provide a constraint on the possible solutions for the current profile.

  13. Density fluctuation measurement using motional Stark effect optics in JT-60U

    SciTech Connect

    Suzuki, T.; Fujita, T.; Oyama, N.; Isayama, A.; Matsunaga, G.; Oikawa, T.; Asakura, N.; Takechi, M.

    2006-10-15

    The multichannel motional Stark effect (MSE) diagnostic system in JT-60U has been upgraded to measure density fluctuation profile. A 16-channel fast-sampling digitizer has been added in order to measure photomultiplier-tube signals at measurement frequency of 0.5-1 MHz. The new system works as a MSE and beam emission spectroscopy diagnostic. Spatially resolved electron density fluctuation profile measurement in various operation regimes is presented. In the core plasma, density fluctuation induced by rotation of tearing mode islands was observed. Temporal evolution of the fluctuation frequency agrees with that measured by Mirnov coils (poloidal and toroidal mode numbers: 2 and 1, respectively). The phases of the fluctuations on either side of the q=2 surface are inverted, which is consistent with electron cyclotron emission. These measurements show that the density fluctuation is caused by a rotating magnetic island structure induced by the tearing mode. In the scrape-off layer of a H-mode plasma with edge-localized-mode (ELM), i. e., ELMy H-mode outward propagation of strong intermittent emission corresponding to ELM crash was also observed. The propagation velocity is 0.69-2.2 km/s along the MSE measurement points, the time lag and distance between adjacent channels being 67{+-}35 {mu}s and 70 mm, respectively.

  14. Magnetic fluctuation profile measurement using optics of motional Stark effect diagnostics in JT-60U

    SciTech Connect

    Suzuki, T.; Isayama, A.; Matsunaga, G.; Oyama, N.; Fujita, T.; Oikawa, T.

    2008-10-15

    Motional Stark effect (MSE) diagnostics in JT-60U works as polarimeter to measure the pitch angle of magnetic field as well as beam-emission-spectroscopy (BES) monochromator simultaneously at 30 spatial channels. Fluctuation in the BES signal using MSE optics (MSE/BES) contains fluctuations in not only the density but also the pitch angle (or the magnetic field). Correlation analysis of the magnetic fluctuation between two spatial channels is applied to high-beta plasma with a magnetohydrodynamic activity at frequency of about 0.9 kHz. It has been found that the magnetic fluctuation measured by the MSE/BES is spatially localized near the magnetic flux surface having safety factor and that the phase of the fluctuation is inverted at about the surface, suggesting magnetic island structure by tearing mode. The phase of the magnetic fluctuation measured by the MSE/BES at outside of the q=2 surface is consistent with that by the pickup coil placed outside the plasma.

  15. Magnetohydrodynamic interference with the edge pedestal motional Stark effect diagnostic on DIII-D

    SciTech Connect

    King, J. D.; Makowski, M. A.; Holcomb, C. T.; Allen, S. L.; Hill, D. N.; Meyer, W. H.; Geer, R.; La Haye, R. J.; Petty, C. C.; Van Zeeland, M. A.; Turco, F.; Rhodes, T. L.; Morse, E. C.

    2011-03-15

    Accurate measurement of internal magnetic field direction using motional Stark effect (MSE) polarimetry in the edge pedestal is desired for nearly all tokamak scenario work. A newly installed 500 kHz 32-channel digitizer on the MSE diagnostic of DIII-D allows full spectral information of the polarimeter signal to be recovered for the first time. Fourier analysis of this data has revealed magnetohydrodynamic (MHD) fluctuations in the plasma edge pedestal at {rho}{>=} 0.92. By correlating edge localized mode fluctuations seen on lock-in amplifier outputs with MSE spectrograms, it has been shown that edge pedestal tearing mode fluctuations cause interference with MSE second harmonic instrument frequencies. This interference results in unrecoverable errors in the real-time polarization angle measurement that are more than an order of magnitude larger than typical polarimeter uncertainties. These errors can cause as much as a 38% difference in local q. By using a redundant measure of the linear polarization found at the fourth harmonic photo-elastic modulator (PEM) frequency, MHD interference can be avoided. However, because of poorer signal-to-noise the fourth harmonic signal computed polarization angle shows no improvement over the MHD polluted second harmonics. MHD interference could be avoided in future edge pedestal tokamak polarimeters by utilizing PEMs with higher fundamental frequencies and a greater separation between their frequencies.

  16. Note: Spectral motional Stark effect diagnostic for measurement of magnetic fields below 0.3 T

    SciTech Connect

    Lizunov, A.; Donin, A.; Savkin, V.

    2013-08-15

    The paper reports on development of the spectral motional Stark effect (MSE) diagnostic in the midplane of the gas dynamic trap (GDT) linear system for magnetic confinement of anisotropic hot-ion plasma. The axially symmetric GDT vacuum magnetic field has a minimum value in the midplane, which varies from 0.2 to 0.35 T in different regimes of operation. Buildup of 15 keV ion population generates a diamagnetic reduction of magnetic field in the plasma core of up to 30% in the maximum density region, as measured by the existing eight-line MSE diagnostic. Commissioning of the midplane MSE provided first direct measurements of diamagnetic modifications in the minimum magnetic field GDT section, a necessary complement to the understanding of equilibrium and self-organization of high-β plasmas in GDT. Making use of the stable short-pulse diagnostic beam and calibration of the apparent spectral width of beam emission lines allow for the measurement of the plasma magnetic field of 0.29 ± 0.007 T with the integration time of 200 μs.

  17. A digital lock-in upgrade of the motional Stark effect diagnostic on DIII-D.

    PubMed

    King, J D; Makowski, M A; Holcomb, C T; Allen, S L; Geer, R; Meyer, W H; Hill, D N; Pham, D; Morse, E C

    2010-10-01

    The use of lock-in amplifiers for phase sensitive detection of motional Stark effect (MSE) diagnostic signals is of critical importance to real-time internal current profile measurements in tokamak plasmas. A digital lock-in (DLI) upgrade utilizing field programable gate array firmware has been installed on the MSE system of the DIII-D tokamak for the eventual replacement of largely obsolete analog units. While the new digital system has shown a small reduction in electronic noise over the analog, the main advantages are reduced cost, hardware simplicity, compact size, and phase tracking during plasma operations. DLI recovery of MSE polarization angles was accomplished through use of reference processing to produce only photoelastic modulator (PEM) second harmonic frequencies and electronic signal processing to maximize the fidelity of the recovered signal. A simplified discrete analytical solution was found that accurately describes the new DLI hardware. The DLI algorithm was found to cause a prohibitively large oscillating artifact atop the demodulated signal. The artifact was caused by the accumulator interval not containing an exact integer number of PEM multiplier periods. Successful MSE measurements require the minimization of this oscillating artifact amplitude. The analytical solution was used to select an appropriate accumulator interval that both reduces the artifact and maintains the greatest temporal resolution possible. Sample EFIT equilibria reconstructions and corresponding safety factor profiles showed very close agreement between the analog and digital lock-ins.

  18. A digital lock-in upgrade of the motional Stark effect diagnostic on DIII-Da)

    NASA Astrophysics Data System (ADS)

    King, J. D.; Makowski, M. A.; Holcomb, C. T.; Allen, S. L.; Geer, R.; Meyer, W. H.; Hill, D. N.; Pham, D.; Morse, E. C.

    2010-10-01

    The use of lock-in amplifiers for phase sensitive detection of motional Stark effect (MSE) diagnostic signals is of critical importance to real-time internal current profile measurements in tokamak plasmas. A digital lock-in (DLI) upgrade utilizing field programable gate array firmware has been installed on the MSE system of the DIII-D tokamak for the eventual replacement of largely obsolete analog units. While the new digital system has shown a small reduction in electronic noise over the analog, the main advantages are reduced cost, hardware simplicity, compact size, and phase tracking during plasma operations. DLI recovery of MSE polarization angles was accomplished through use of reference processing to produce only photoelastic modulator (PEM) second harmonic frequencies and electronic signal processing to maximize the fidelity of the recovered signal. A simplified discrete analytical solution was found that accurately describes the new DLI hardware. The DLI algorithm was found to cause a prohibitively large oscillating artifact atop the demodulated signal. The artifact was caused by the accumulator interval not containing an exact integer number of PEM multiplier periods. Successful MSE measurements require the minimization of this oscillating artifact amplitude. The analytical solution was used to select an appropriate accumulator interval that both reduces the artifact and maintains the greatest temporal resolution possible. Sample EFIT equilibria reconstructions and corresponding safety factor profiles showed very close agreement between the analog and digital lock-ins.

  19. Development of the Motional Stark Effect with Laser-Induced Fluorescence (MSE-LIF) Diagnostic

    NASA Astrophysics Data System (ADS)

    Foley, Elizabeth L.

    2005-10-01

    The motional Stark effect with laser-induced fluorescence (MSE- LIF) diagnostic is under development to extend the MSE magnetic pitch angle diagnostic to lower fields ( < 0.5 T) and enable measurement of magnetic field magnitude as well as direction. The technique involves injecting a low energy-spread neutral hydrogen beam (30 kV, 30 mA) into plasma, and using a collinear laser to excite transitions from the n=2 to n=3 atomic states in the beam atoms. The subsequent fluorescence from the same transition (Balmer-alpha, near 650 nm for the Doppler-shifted beam) is observed, and its splitting and polarization due to the E = v X B electric field in the beam frame is used to determine the background magnetic field magnitude and direction. This poster will present recent results from MSE-LIF development, including magnetic field measurements at very low field (< 0.01 T) in neutral gas based on an enhanced LIF phenomenon, a comprehensive collisional-radiative model which determines the population fractions in the n=1, 2 and 3 states of the beam as the states mix in applied magnetic and electric fields, as well as upgrades to the experimental apparatus that will enable measurements in intermediate fields (0.01 - 0.2 T) in plasma.

  20. Overview of Alcator C-Mod Research

    NASA Astrophysics Data System (ADS)

    Marmar, Earl; Alcator C-Mod Team

    2016-10-01

    C-Mod is the only divertor tokamak in the world capable of operating at B fields up to 8 T, equaling and exceeding that planned for ITER. C-Mod is compact, accessing regimes of extreme edge power density (q|| 1 GW/m2) . surpassing the design for ITER, and approaching the levels envisioned in power plants. C-Mod results are particularly important for providing the physics basis of the high-field, compact tokamak approach. Results of experiments and related modeling span the topics of core transport and turbulence, RF heating and current drive, pedestal physics, scrape-off layer, divertor and plasma-wall interactions. ICRF has been successfully applied to control and reverse accumulation of high Z impurities in the core plasma. For the first time ever, feedback of low Z seeding for divertor power dissipation has been tied directly to real-time plasma power fluxes measured on the high-Z metal PFCs in the divertor, and used to mitigate those fluxes with no degradation of the pedestal pressure or core confinement. The naturally ELM-less I-mode and EDA-H-mode regimes have been extended BT = 8T. I-mode threshold scalings show a weak dependence on B, yielding a significantly broader window for I-mode operation at high field. Quiescence of the high-field side scrape-off layer makes this a potentially attractive location for placement of RF actuators to ameliorate plasma interactions with launchers; the wave physics for penetration and damping, for both ICRF and LHRF appears very favorable for high-field side launch. Supported by USDoE Award DE-FC02-99ER54512.

  1. Measurements of the internal magnetic field on DIII-D using intensity and spacing of the motional Stark multipleta)

    NASA Astrophysics Data System (ADS)

    Pablant, N. A.; Burrell, K. H.; Groebner, R. J.; Kaplan, D. H.; Holcomb, C. T.

    2008-10-01

    We describe a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of Stark split Dα emission from the neutral beams. This system, named B-Stark, has been recently installed on the DIII-D tokamak. To find the magnetic pitch angle, we use the ratio of the intensities of the π3 and σ1 lines. These lines originate from the same upper level and so are not dependent on the level populations. In future devices, such as ITER, this technique may have advantages over diagnostics based on MSE polarimetry. We have done an optimization of the viewing direction for the available ports on DIII-D to choose the installation location. With this placement, we have a near optimal viewing angle of 59.6° from the vertical direction. All hardware has been installed for one chord, and we have been routinely taking data since January 2007. We fit the spectra using a simple Stark model in which the upper level populations of the Dα transition are treated as free variables. The magnitude and direction of the magnetic field obtained using this diagnostic technique compare well with measurements from MSE polarimetry and EFIT.

  2. Measurements of the internal magnetic field on DIII-D using intensity and spacing of the motional Stark multiplet.

    PubMed

    Pablant, N A; Burrell, K H; Groebner, R J; Kaplan, D H; Holcomb, C T

    2008-10-01

    We describe a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of Stark split D(alpha) emission from the neutral beams. This system, named B-Stark, has been recently installed on the DIII-D tokamak. To find the magnetic pitch angle, we use the ratio of the intensities of the pi(3) and sigma(1) lines. These lines originate from the same upper level and so are not dependent on the level populations. In future devices, such as ITER, this technique may have advantages over diagnostics based on MSE polarimetry. We have done an optimization of the viewing direction for the available ports on DIII-D to choose the installation location. With this placement, we have a near optimal viewing angle of 59.6 degrees from the vertical direction. All hardware has been installed for one chord, and we have been routinely taking data since January 2007. We fit the spectra using a simple Stark model in which the upper level populations of the D(alpha) transition are treated as free variables. The magnitude and direction of the magnetic field obtained using this diagnostic technique compare well with measurements from MSE polarimetry and EFIT.

  3. Measurements of the internal magnetic field on DIII-D using intensity and spacing of the motional Stark multiplet

    SciTech Connect

    Pablant, N. A.; Burrell, K. H.; Groebner, R. J.; Kaplan, D. H.; Holcomb, C. T.

    2008-10-15

    We describe a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of Stark split D{sub {alpha}} emission from the neutral beams. This system, named B-Stark, has been recently installed on the DIII-D tokamak. To find the magnetic pitch angle, we use the ratio of the intensities of the {pi}{sub 3} and {sigma}{sub 1} lines. These lines originate from the same upper level and so are not dependent on the level populations. In future devices, such as ITER, this technique may have advantages over diagnostics based on MSE polarimetry. We have done an optimization of the viewing direction for the available ports on DIII-D to choose the installation location. With this placement, we have a near optimal viewing angle of 59.6 deg. from the vertical direction. All hardware has been installed for one chord, and we have been routinely taking data since January 2007. We fit the spectra using a simple Stark model in which the upper level populations of the D{sub {alpha}} transition are treated as free variables. The magnitude and direction of the magnetic field obtained using this diagnostic technique compare well with measurements from MSE polarimetry and EFIT.

  4. A photoelastic-modulator-based motional Stark effect polarimeter for ITER that is insensitive to polarized broadband background reflections.

    PubMed

    Thorman, A; Michael, C; De Bock, M; Howard, J

    2016-07-01

    A motional Stark effect polarimeter insensitive to polarized broadband light is proposed. Partially polarized background light is anticipated to be a significant source of systematic error for the ITER polarimeter. The proposed polarimeter is based on the standard dual photoelastic modulator approach, but with the introduction of a birefringent delay plate, it generates a sinusoidal spectral filter instead of the usual narrowband filter. The period of the filter is chosen to match the spacing of the orthogonally polarized Stark effect components, thereby increasing the effective signal level, but resulting in the destructive interference of the broadband polarized light. The theoretical response of the system to an ITER like spectrum is calculated and the broadband polarization tolerance is verified experimentally.

  5. A photoelastic-modulator-based motional Stark effect polarimeter for ITER that is insensitive to polarized broadband background reflections

    NASA Astrophysics Data System (ADS)

    Thorman, A.; Michael, C.; De Bock, M.; Howard, J.

    2016-07-01

    A motional Stark effect polarimeter insensitive to polarized broadband light is proposed. Partially polarized background light is anticipated to be a significant source of systematic error for the ITER polarimeter. The proposed polarimeter is based on the standard dual photoelastic modulator approach, but with the introduction of a birefringent delay plate, it generates a sinusoidal spectral filter instead of the usual narrowband filter. The period of the filter is chosen to match the spacing of the orthogonally polarized Stark effect components, thereby increasing the effective signal level, but resulting in the destructive interference of the broadband polarized light. The theoretical response of the system to an ITER like spectrum is calculated and the broadband polarization tolerance is verified experimentally.

  6. Magnetic field amplitude and pitch angle measurements using Spectral MSE on EAST and Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Liao, Ken; Rowan, William; Fu, Jia; Lyu, Bo; Li, Ying-Ying; Marchuk, Oleksandr; Ralchenko, Yuri

    2016-10-01

    Magnetic field amplitude and pitch angle measurements follow from the analysis of the Motional Stark Effect spectrum emitted by high energy neutral beam emission in tokamaks. Here we focus on deriving these quantities on EAST and Alcator C-Mod. These measurements provide a cross check for the polarimetry MSE diagnostics, and also act as a proof of principle for a spectral MSE diagnostic, which could potentially provide real-time measurements of the magnetic field and be used to increase the accuracy of equilibrium reconstruction. Measurement uncertainty is evaluated using the NBASS synthetic diagnostic. The same code allows design of measurements with improved accuracy such as spectral measurements techniques which take advantage of polarization. Accurate fitting of the MSE spectrum requires taking into account non-statistical beam excited state populations. The spectral MSE analysis techniques have applications to measurement of the beam density, which allows for improved analysis of the charge exchange recombination spectroscopy diagnostic. Resolution of beam components improves with increased beam energy and magnetic field, so these techniques have high applicability to future fusion devices. Supported by USDoE Award DE-FG03- 96ER-54373.

  7. Overview of Alcator C-Mod Research

    NASA Astrophysics Data System (ADS)

    White, Anne

    2015-11-01

    Research on C-Mod supports next-step-devices: RF heating, current and flow drive, divertor/PMI physics, non-ELMing regimes with enhanced confinement, and disruption mitigation/runaway dynamics. Disruption mitigation experiments in MHD-unstable plasmas show MGI works equally well with and without locked modes. The L-I-mode threshold is found to be independent of magnetic field, opening an expanded operating range at high field. The toroidal and radial structure of power deposition of RF waves into the edge plasma has been systematically quantified, through the use of a unique set of fast time resolution edge diagnostics. Progress in understanding multi-channel core transport has been significant. Full-physics, ITG/TEM/ETG gyrokinetic simulations show that nonlinear cross-scale coupling enhances both ion and electron heat flux to match experiments, explaining the origin of electron heat flux and stiffness. Dynamic, passive measurements of the core rotation velocity profiles with X-ray imaging crystal spectroscopy show the direction of intrinsic rotation reversals depends on central safety factor, not on the magnetic shear. Design studies for ADX and SPARC are establishing the engineering, economics and physics for a fusion energy development path leveraging new superconducting magnet technologies. This work is supported by the US DOE under DE- FC02-99ER54512-CMOD.

  8. An Overview Of The Motional Stark Effect Diagnostic On DIII-D And Design Work For An ITER MSE

    SciTech Connect

    Holcomb, C T; Allen, S L; Makowski, M A; Jayakumar, R J; Gu, M F; Lerner, S; Morris, K L; Latkowski, J; Moller, J M; Meyer, W; Ellis, R; Geer, R; Behne, D; Chipman, R; Smith, P; McClain, S

    2007-09-20

    The advanced tokamak research program at DIII-D relies critically on the measurement of the current density profile. This was made possible by the development of a Motional Stark Effect (MSE) polarimeter that was first installed in 1992. Three major upgrades have since occurred, and improvements in our understanding of critical performance issues and calibration techniques are ongoing. In parallel with these improvements, we have drawn on our DIII-D experience to begin studies and design work for MSE on burning plasmas and ITER. This paper first reviews how Motional Stark Effect polarimetry (MSE) is used to determine the tokamak current profile. It uses the DIII-D MSE system as an example, and shows results from the latest upgrade that incorporates an array of channels from a new counter-Ip injected neutral beam. The various calibration techniques presently used are reviewed. High-leverage or unresolved issues affecting MSE performance and reliability in ITER are discussed. Next, we show a four-mirror collection optics design for the two ITER MSE views. Finally, we discuss measurements of the polarization properties of a few candidate mirrors for the ITER MSE.

  9. Direct measurements of safety factor profiles with motional Stark effect for KSTAR tokamak discharges with internal transport barriers

    NASA Astrophysics Data System (ADS)

    Ko, J.; Chung, J.

    2017-06-01

    The safety factor profile evolutions have been measured from the plasma discharges with the external current drive mechanism such as the multi-ion-source neutral beam injection for the Korea Superconducting Tokamak Advanced Research (KSTAR) for the first time. This measurement has been possible by the newly installed motional Stark effect (MSE) diagnostic system that utilizes the polarized Balmer-alpha emission from the energetic neutral deuterium atoms induced by the Stark effect under the Lorentz electric field. The 25-channel KSTAR MSE diagnostic is based on the conventional photoelastic modulator approach with the spatial and temporal resolutions less than 2 cm (for the most of the channels except 2 to 3 channels inside the magnetic axis) and about 10 ms, respectively. The strong Faraday rotation imposed on the optical elements in the diagnostic system is calibrated out from a separate and well-designed polarization measurement procedure using an in-vessel reference polarizer during the toroidal-field ramp-up phase before the plasma experiment starts. The combination of the non-inductive current drive during the ramp-up and shape control enables the formation of the internal transport barrier where the pitch angle profiles indicate flat or slightly hollow profiles in the safety factor.

  10. Overview of equilibrium reconstruction on DIII-D using new measurements from an expanded motional Stark effect diagnostic.

    PubMed

    Holcomb, C T; Makowski, M A; Allen, S L; Meyer, W H; Van Zeeland, M A

    2008-10-01

    Motional Stark effect (MSE) measurements constrain equilibrium reconstruction of DIII-D tokamak plasmas using the equilibrium code EFIT. In 2007, two new MSE arrays were brought online, bringing the system to three core arrays, two edge arrays, and 64 total channels. We present the first EFIT reconstructions using this expanded system. Safety factor and E(R) profiles produced by fitting to data from the two new arrays and one of the other three agree well with independent measurements. Comparison of the data from the three arrays that view the core shows that one of the older arrays is inconsistent with the other two unless the measured calibration factors for this array are adjusted. The required adjustments depend on the toroidal field and plasma current direction, and on still other uncertain factors that change as the plasma evolves. We discuss possible sources of calibration error for this array.

  11. Overview of equilibrium reconstruction on DIII-D using new measurements from an expanded motional Stark effect diagnostica)

    NASA Astrophysics Data System (ADS)

    Holcomb, C. T.; Makowski, M. A.; Allen, S. L.; Meyer, W. H.; Van Zeeland, M. A.

    2008-10-01

    Motional Stark effect (MSE) measurements constrain equilibrium reconstruction of DIII-D tokamak plasmas using the equilibrium code EFIT. In 2007, two new MSE arrays were brought online, bringing the system to three core arrays, two edge arrays, and 64 total channels. We present the first EFIT reconstructions using this expanded system. Safety factor and ER profiles produced by fitting to data from the two new arrays and one of the other three agree well with independent measurements. Comparison of the data from the three arrays that view the core shows that one of the older arrays is inconsistent with the other two unless the measured calibration factors for this array are adjusted. The required adjustments depend on the toroidal field and plasma current direction, and on still other uncertain factors that change as the plasma evolves. We discuss possible sources of calibration error for this array.

  12. Overview of equilibrium reconstruction on DIII-D using new measurements from an expanded motional Stark effect diagnostic

    SciTech Connect

    Holcomb, C. T.; Makowski, M. A.; Allen, S. L.; Meyer, W. H.; Van Zeeland, M. A.

    2008-10-15

    Motional Stark effect (MSE) measurements constrain equilibrium reconstruction of DIII-D tokamak plasmas using the equilibrium code EFIT. In 2007, two new MSE arrays were brought online, bringing the system to three core arrays, two edge arrays, and 64 total channels. We present the first EFIT reconstructions using this expanded system. Safety factor and E{sub R} profiles produced by fitting to data from the two new arrays and one of the other three agree well with independent measurements. Comparison of the data from the three arrays that view the core shows that one of the older arrays is inconsistent with the other two unless the measured calibration factors for this array are adjusted. The required adjustments depend on the toroidal field and plasma current direction, and on still other uncertain factors that change as the plasma evolves. We discuss possible sources of calibration error for this array.

  13. Overview of equilibrium reconstruction on DIII-D using new measurements from an expanded motional Stark effect diagnostic

    SciTech Connect

    Holcomb, C; Makowski, M; Allen, S; Meyer, W; Van Zeeland, M

    2008-05-02

    Motional Stark effect (MSE) measurements constrain equilibrium reconstruction of DIII-D tokamak plasmas using the equilibrium code EFIT. In 2007, two new MSE arrays were brought online, bringing the system to three core arrays, two edge arrays, and 64 total channels. We present the first EFIT reconstructions using this expanded system. Safety factor and E{sub R} profiles produced by fitting to data from the two new arrays and one of the other three agree well with independent measurements. Comparison of the data from the three arrays that view the core shows that one of the older arrays is inconsistent with the other two unless the measured calibration factors for this array are adjusted. The required adjustments depend on toroidal field and plasma current direction, and on still other uncertain factors that change as the plasma evolves. We discuss possible sources of calibration error for this array.

  14. Real-time Magnetic Field Pitch Angle Estimation With a Motional Stark Effect Diagnostic Using Kalman Filtering

    SciTech Connect

    Coelho, R.; Alves, D.

    2008-03-12

    The real-time amplitude estimation of selective harmonics from an Avalanche Photo Diode (APD) signal of a Motion Stark Effect diagnostic is addressed using a Kalman filter. The proposed technique is shown to be much more robust and provide less noisy estimates than a lock-in amplifier scheme. In addition, the negative impact of Edge Localised Modes (ELMs) is minimized, reducing significantly the biasing in the amplitude estimation and ultimately allowing for the pitch angle estimation in the vicinity of the ELM. The inherent biasing in the amplitude estimation due to the 50Hz modulation in the NBI power grid is also easily circumvented with such a technique, rendering dispensable any further filtering of the data.

  15. Upgrades to the C-Mod FIR Polarimeter

    NASA Astrophysics Data System (ADS)

    Abraham, Sameer; Irby, Jim; Watterson, Reich; Vieira, Rui; Leccacorvi, Rick; Parkin, William; Murray, Rick; Marmar, Earl

    2016-10-01

    The 3-Chord FIR Polarimeter presently deployed on C-Mod is capable of responding to both fast changes in the plasma equilibrium and high frequency fluctuations. Two FIR lasers locked together with a slight frequency offset provide a signal IF at 4 MHz, which allows for the fast response of the system. Recently implemented upgrades including relocation of the laser table from the C-Mod experimental cell to a more shielded location, the design and installation of a humidity controlled beam-line to convey the FIR beams across the cell, and improved collimation optics will be discussed. Results from initial testing of the system during C-Mod operation, as well as fluctuation data from the most recent and previous campaigns will be presented and compared. Supported by USDoE Award DE-FC02-99ER54512.

  16. Divertor bypass in the Alcator C-Mod tokamak

    SciTech Connect

    Pitcher, C. S.; LaBombard, B.; Danforth, R.; Pina, W.; Silveira, M.; Parkin, B.

    2001-01-01

    The Alcator C-Mod divertor bypass has for the first time allowed in situ variations to the mechanical baffle design in a tokamak. The design utilizes small coils which interact with the ambient magnetic field inside the vessel to provide the torque required to control small flaps of a Venetian blind geometry. Plasma physics experiments with the bypass have revealed the importance of the divertor baffling to maintain high divertor gas pressures. These experiments have also indicated that the divertor baffling has only a limited effect on the main chamber pressure in C-Mod.

  17. Upgrade Plans for the C-Mod FIR Polarimeter

    NASA Astrophysics Data System (ADS)

    Watterson, R.; Garnier, D.; Irby, J.; Brower, D. L.; Xu, P.; Bergerson, W. F.; Ding, W. X.; Guttenfelder, W.; Marmar, E. S.

    2014-10-01

    The 3-chord FIR polarimeter presently deployed on C-Mod is capable of responding to both fast changes in the plasma equilibrium and high frequency fluctuations. It operates under ITER-like plasma conditions and magnetic fields, and uses an optical layout similar to that proposed for ITER. The details of this system and some results from the C-Mod 2012 campaign will be presented, along with the design of the upgrade that is now being implemented. The new system will provide horizontal chords near the mid-plane and low loss etalon windows to improve both the signal level and our ability to study magnetic fluctuations. The laser table has been relocated from the C-Mod cell to a shielded and climate controlled location, and improvements have been made to its acoustic isolation. New collimation optics, and a beam-line needed to convey the FIR beams into the tokamak port have been designed. Improvements to the detector electronics will also be discussed, as will initial testing of the laser system and reference detectors during C-Mod operation. Supported by USDoE Award DE-FC02-99ER54512.

  18. Influence of non-local thermodynamic equilibrium and Zeeman effects on magnetic equilibrium reconstruction using spectral motional Stark effect diagnostic.

    PubMed

    Reimer, R; Marchuk, O; Geiger, B; Mc Carthy, P J; Dunne, M; Hobirk, J; Wolf, R

    2017-08-01

    The Motional Stark Effect (MSE) diagnostic is a well established technique to infer the local internal magnetic field in fusion plasmas. In this paper, the existing forward model which describes the MSE data is extended by the Zeeman effect, fine-structure, and relativistic corrections in the interpretation of the MSE spectra for different experimental conditions at the tokamak ASDEX Upgrade. The contribution of the non-Local Thermodynamic Equilibrium (non-LTE) populations among the magnetic sub-levels and the Zeeman effect on the derived plasma parameters is different. The obtained pitch angle is changed by 3°…4° and by 0.5°…1° including the non-LTE and the Zeeman effects into the standard statistical MSE model. The total correction is about 4°. Moreover, the variation of the magnetic field strength is significantly changed by 2.2% due to the Zeeman effect only. While the data on the derived pitch angle still could not be tested against the other diagnostics, the results from an equilibrium reconstruction solver confirm the obtained values for magnetic field strength.

  19. Influence of non-local thermodynamic equilibrium and Zeeman effects on magnetic equilibrium reconstruction using spectral motional Stark effect diagnostic

    NASA Astrophysics Data System (ADS)

    Reimer, R.; Marchuk, O.; Geiger, B.; Mc Carthy, P. J.; Dunne, M.; Hobirk, J.; Wolf, R.; ASDEX Upgrade Team

    2017-08-01

    The Motional Stark Effect (MSE) diagnostic is a well established technique to infer the local internal magnetic field in fusion plasmas. In this paper, the existing forward model which describes the MSE data is extended by the Zeeman effect, fine-structure, and relativistic corrections in the interpretation of the MSE spectra for different experimental conditions at the tokamak ASDEX Upgrade. The contribution of the non-Local Thermodynamic Equilibrium (non-LTE) populations among the magnetic sub-levels and the Zeeman effect on the derived plasma parameters is different. The obtained pitch angle is changed by 3 ° … 4 ° and by 0 . 5 ° … 1 ° including the non-LTE and the Zeeman effects into the standard statistical MSE model. The total correction is about 4°. Moreover, the variation of the magnetic field strength is significantly changed by 2.2% due to the Zeeman effect only. While the data on the derived pitch angle still could not be tested against the other diagnostics, the results from an equilibrium reconstruction solver confirm the obtained values for magnetic field strength.

  20. Method for correction of measured polarization angles from motional Stark effect spectroscopy for the effects of electric fields

    NASA Astrophysics Data System (ADS)

    Luce, T. C.; Petty, C. C.; Meyer, W. H.; Holcomb, C. T.; Burrell, K. H.; Bergsten, L. J.

    2016-12-01

    An approximate method to correct the motional Stark effect (MSE) spectroscopy for the effects of intrinsic plasma electric fields has been developed. The motivation for using an approximate method is to incorporate electric field effects for between-pulse or real-time analysis of the current density or safety factor profile. The toroidal velocity term in the momentum balance equation is normally the dominant contribution to the electric field orthogonal to the flux surface over most of the plasma. When this approximation is valid, the correction to the MSE data can be included in a form like that used when electric field effects are neglected. This allows measurements of the toroidal velocity to be integrated into the interpretation of the MSE polarization angles without changing how the data is treated in existing codes. In some cases, such as the DIII-D system, the correction is especially simple, due to the details of the neutral beam and MSE viewing geometry. The correction method is compared using DIII-D data in a variety of plasma conditions to analysis that assumes no radial electric field is present and to analysis that uses the standard correction method, which involves significant human intervention for profile fitting. The comparison shows that the new correction method is close to the standard one, and in all cases appears to offer a better result than use of the uncorrected data. The method has been integrated into the standard DIII-D equilibrium reconstruction code in use for analysis between plasma pulses and is sufficiently fast that it will be implemented in real-time equilibrium analysis for control applications.

  1. Method for correction of measured polarization angles from motional Stark effect spectroscopy for the effects of electric fields

    DOE PAGES

    Luce, T. C.; Petty, C. C.; Meyer, W. H.; ...

    2016-11-02

    An approximate method to correct the motional Stark effect (MSE) spectroscopy for the effects of intrinsic plasma electric fields has been developed. The motivation for using an approximate method is to incorporate electric field effects for between-pulse or real-time analysis of the current density or safety factor profile. The toroidal velocity term in the momentum balance equation is normally the dominant contribution to the electric field orthogonal to the flux surface over most of the plasma. When this approximation is valid, the correction to the MSE data can be included in a form like that used when electric field effectsmore » are neglected. This allows measurements of the toroidal velocity to be integrated into the interpretation of the MSE polarization angles without changing how the data is treated in existing codes. In some cases, such as the DIII-D system, the correction is especially simple, due to the details of the neutral beam and MSE viewing geometry. The correction method is compared using DIII-D data in a variety of plasma conditions to analysis that assumes no radial electric field is present and to analysis that uses the standard correction method, which involves significant human intervention for profile fitting. The comparison shows that the new correction method is close to the standard one, and in all cases appears to offer a better result than use of the uncorrected data. Lastly, the method has been integrated into the standard DIII-D equilibrium reconstruction code in use for analysis between plasma pulses and is sufficiently fast that it will be implemented in real-time equilibrium analysis for control applications.« less

  2. Method for correction of measured polarization angles from motional Stark effect spectroscopy for the effects of electric fields

    SciTech Connect

    Luce, T. C.; Petty, C. C.; Meyer, W. H.; Holcomb, C. T.; Burrell, K. H.; Bergsten, L. J.

    2016-11-02

    An approximate method to correct the motional Stark effect (MSE) spectroscopy for the effects of intrinsic plasma electric fields has been developed. The motivation for using an approximate method is to incorporate electric field effects for between-pulse or real-time analysis of the current density or safety factor profile. The toroidal velocity term in the momentum balance equation is normally the dominant contribution to the electric field orthogonal to the flux surface over most of the plasma. When this approximation is valid, the correction to the MSE data can be included in a form like that used when electric field effects are neglected. This allows measurements of the toroidal velocity to be integrated into the interpretation of the MSE polarization angles without changing how the data is treated in existing codes. In some cases, such as the DIII-D system, the correction is especially simple, due to the details of the neutral beam and MSE viewing geometry. The correction method is compared using DIII-D data in a variety of plasma conditions to analysis that assumes no radial electric field is present and to analysis that uses the standard correction method, which involves significant human intervention for profile fitting. The comparison shows that the new correction method is close to the standard one, and in all cases appears to offer a better result than use of the uncorrected data. Lastly, the method has been integrated into the standard DIII-D equilibrium reconstruction code in use for analysis between plasma pulses and is sufficiently fast that it will be implemented in real-time equilibrium analysis for control applications.

  3. Divertor IR thermography on Alcator C-Mod

    SciTech Connect

    Terry, J. L.; LaBombard, B.; Brunner, D.; Payne, J.; Wurden, G. A.

    2010-10-15

    Alcator C-Mod is a particularly challenging environment for thermography. It presents issues that will similarly face ITER, including low-emissivity metal targets, low-Z surface films, and closed divertor geometry. In order to make measurements of the incident divertor heat flux using IR thermography, the C-Mod divertor has been modified and instrumented. A 6 deg. toroidal sector has been given a 2 deg. toroidal ramp in order to eliminate magnetic field-line shadowing by imperfectly aligned divertor tiles. This sector is viewed from above by a toroidally displaced IR camera and is instrumented with thermocouples and calorimeters. The camera provides time histories of surface temperatures that are used to compute incident heat-flux profiles. The camera sensitivity is calibrated in situ using the embedded thermocouples, thus correcting for changes and nonuniformities in surface emissivity due to surface coatings.

  4. Divertor IR thermography on Alcator C-Mod.

    PubMed

    Terry, J L; LaBombard, B; Brunner, D; Payne, J; Wurden, G A

    2010-10-01

    Alcator C-Mod is a particularly challenging environment for thermography. It presents issues that will similarly face ITER, including low-emissivity metal targets, low-Z surface films, and closed divertor geometry. In order to make measurements of the incident divertor heat flux using IR thermography, the C-Mod divertor has been modified and instrumented. A 6° toroidal sector has been given a 2° toroidal ramp in order to eliminate magnetic field-line shadowing by imperfectly aligned divertor tiles. This sector is viewed from above by a toroidally displaced IR camera and is instrumented with thermocouples and calorimeters. The camera provides time histories of surface temperatures that are used to compute incident heat-flux profiles. The camera sensitivity is calibrated in situ using the embedded thermocouples, thus correcting for changes and nonuniformities in surface emissivity due to surface coatings.

  5. Progress on the C-Mod FIR Polarimeter System

    NASA Astrophysics Data System (ADS)

    Xu, P.; Irby, J. H.; Bergerson, W. F.; Brower, D. L.; Ding, W. X.; Shiraiwa, S.; Wolfe, S.

    2010-11-01

    A poloidally viewing FIR polarimetry diagnostic is being developed for the Alcator C-Mod Tokamak. The primary diagnostic components are a two-wave FIR laser at 117.73 microns and newly developed detectors whose performance characteristics will be described. Faraday rotation will be used both to refine the q-profile measurement by adding constraints to EFIT , and to study density and magnetic field fluctuations. A three-chord system has been installed, one chord of which is being tested during the FY10 C-Mod campaign. The FIR laser source is affected by both stray magnetic fields and mechanical vibrations present in the experimental cell thereby impacting the measurement. Methods developed to mitigate and correct for these effects will be discussed. Initial Faraday data will be compared with expectations from numerical simulation.

  6. Benchmarking Nonlinear Turbulence Simulations on Alcator C-Mod

    SciTech Connect

    M.H. Redi; C.L. Fiore; W. Dorland; M.J. Greenwald; G.W. Hammett; K. Hill; D. McCune; D.R. Mikkelsen; G. Rewoldt; J.E. Rice

    2004-06-22

    Linear simulations of plasma microturbulence are used with recent radial profiles of toroidal velocity from similar plasmas to consider nonlinear microturbulence simulations and observed transport analysis on Alcator C-Mod. We focus on internal transport barrier (ITB) formation in fully equilibrated H-mode plasmas with nearly flat velocity profiles. Velocity profile data, transport analysis and linear growth rates are combined to integrate data and simulation, and explore the effects of toroidal velocity on benchmarking simulations. Areas of interest for future nonlinear simulations are identified. A good gyrokinetic benchmark is found in the plasma core, without extensive nonlinear simulations. RF-heated C-Mod H-mode experiments, which exhibit an ITB, have been studied with the massively parallel code GS2 towards validation of gyrokinetic microturbulence models. New, linear, gyrokinetic calculations are reported and discussed in connection with transport analysis near the ITB trigger time of shot No.1001220016.

  7. C-Mod Collaboration Informal Technical Progress Report

    SciTech Connect

    Kenneth W. Gentle

    2007-12-31

    The aims of the collaboration have not changed. A specific list of tasks was agreed upon during the Fall of 2006 in preparation for the 2007 C-Mod campaign by Earl Marmar, Head of the Alcator Project, Kenneth Gentle, Principal Investigator, and William Rowan, Collaboration Coordinator with the facilitation of Adam Rosenberg (DOE grant monitor for the collaboration). The activities follow the list of tasks and are discussed in this progress report.

  8. Turbulent impurity transport modeling for Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Fu, X. R.; Horton, W.; Bespamyatnov, I. O.; Rowan, W. L.; Benkadda, S.; Fiore, C. L.; Futatani, S.; Liao, K. T.; Liao

    2013-10-01

    Turbulent particle transport is investigated with a quasilinear theory that is motivated by the boron impurity transport experiments in the Alcator C-Mod. Eigenvalue problems for sets of reduced fluid equations for multi-component plasmas are solved for the self-consistent fluctuating field vectors composed of the electric potential φ, the main ion density δni , the impurity density δnz and the ion temperature fluctuation δTi . For Alcator C-Mod parameters, we investigate two drift wave models: (1) the density-gradient-driven impurity drift wave and (2) the ion-temperature-gradient-driven ion temperature gradient (ITG) mode. Analytic and numerical results for particle transport coefficients are derived and compared with the transport data and the neoclassical theory. We explore the ability of the model to explain impurity density profiles in three confinement regimes: H-mode, I-mode and internal transport barrier (ITB) regime in C-Mod. Related experiments reported on the Large Helical Device are briefly discussed.

  9. Edge Zonal Flows and Blob Propagation in Alcator C-Mod

    SciTech Connect

    Zweben, S; Agostini, M; Davis, B; Grulke, O; Hager, R; Hughes, J; LaBombard, B; D'Ippolito, D A; Myra, J R; Russell, D A

    2011-07-25

    Here we describe recent measurements of the 2-D motion of turbulence in the edge and scrape-off layer (SOL) of the Alcator C-Mod tokamak. This data was taken using the outer midplane gas puff imaging (GPI) camera, which views a 6 cm radial by 6 cm poloidal region near the separatrix just below the outer midplane [1]. The data were taken in Ohmic or RF heated L-mode plasmas at 400,000 frames/sec for {approx}50 msec/shot using a Phantom 710 camera in a 64 x 64 pixel format. The resulting 2-D vs. time movies [2] can resolve the structure and motion of the turbulence on a spatial scale covering 0.3-6 cm. The images were analyzed using either a 2-D cross-correlation code (Sec. 2) or a 2-D blob tracking code (Sec. 3).

  10. Edge Turbulence Imaging on NSTX and Alcator C-Mod

    SciTech Connect

    S.J. Zweben; R.A. Maqueda; J.L. Terry; B. Bai; C.J. Boswell; C.E. Bush; D. D'Ippolito; E.D. Fredrickson; M. Greenwald; K. Hallatschek; S. Kaye; B. LaBombard; R. Maingi; J. Myra; W.M. Nevins; B.N. Rogers; D.P. Stotler; J. Wilgen; and X.Q. Xu

    2002-07-10

    Edge turbulence images have been made using an ultra-high speed CCD camera on both NSTX and Alcator C-Mod. In both cases, the D-alpha or HeI (587.6 nm) line emission from localized deuterium or helium gas puffs was viewed along a local magnetic field line near the outer midplane. Fluctuations in this line emission reflect fluctuations in electron density and/or electron temperature through the atomic excitation rates, which can be modeled using the DEGAS-2 code. The 2-D structure of the measured turbulence can be compared with theoretical simulations based on 3-D fluid models.

  11. Real-time data processing and magnetic field pitch angle estimation of the JET motional Stark effect diagnostic based on Kalman filtering

    SciTech Connect

    Coelho, R.; Alves, D. [Instituto de Plasmas e Fusao Nuclear, Associacao Euratom Hawkes, N.; Brix, M. [Euratom Collaboration: JET EFDA Contributors

    2009-06-15

    A novel technique for the real-time measurement of the magnetic field pitch angle in JET discharges using the motional Stark effect diagnostic is presented. Kalman filtering techniques are adopted to estimate the amplitude of the avalanche photodiode signals' harmonics that are relevant for the pitch angle calculation. The proposed technique {l_brace}for extended technical details of the generic algorithm see [R. Coelho and D. Alves, IEEE Trans. Plasma Sci. 37, 164 (2009)]{r_brace} is shown to be much more robust and provides less noisy estimates than an equivalent lock-in amplifier scheme, in particular when dealing with edge localized modes.

  12. Real-time data processing and magnetic field pitch angle estimation of the JET motional Stark effect diagnostic based on Kalman filtering.

    PubMed

    Coelho, R; Alves, D; Hawkes, N; Brix, M

    2009-06-01

    A novel technique for the real-time measurement of the magnetic field pitch angle in JET discharges using the motional Stark effect diagnostic is presented. Kalman filtering techniques are adopted to estimate the amplitude of the avalanche photodiode signals' harmonics that are relevant for the pitch angle calculation. The proposed technique {for extended technical details of the generic algorithm see [R. Coelho and D. Alves, IEEE Trans. Plasma Sci. 37, 164 (2009)]} is shown to be much more robust and provides less noisy estimates than an equivalent lock-in amplifier scheme, in particular when dealing with edge localized modes.

  13. Correlation ECE diagnostic in Alcator C-Mod

    DOE PAGES

    Sung, C.; White, A. E.; Howard, N. T.; ...

    2015-03-12

    Correlation ECE (CECE) is a diagnostic technique that allows measurement of small amplitude electron temperature, Te, fluctuations through standard cross-correlation analysis methods. In Alcator C-Mod, a new CECE diagnostic has been installed[Sung RSI 2012], and interesting phenomena have been observed in various plasma conditions. We find that local Te fluctuations near the edge (ρ ~ 0:8) decrease across the linearto- saturated ohmic confinement transition, with fluctuations decreasing with increasing plasma density[Sung NF 2013], which occurs simultaneously with rotation reversals[Rice NF 2011]. Te fluctuations are also reduced across core rotation reversals with an increase of plasma density in RF heated L-modemore » plasmas, which implies that the same physics related to the reduction of Te fluctuations may be applied to both ohmic and RF heated L-mode plasmas. In I-mode plasmas, we observe the reduction of core Te fluctuations, which indicates changes of turbulence occur not only in the pedestal region but also in the core across the L/I transition[White NF 2014]. The present CECE diagnostic system in C-Mod and these experimental results are described in this paper.« less

  14. C-Mod MHD stability analysis with LHCD

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Fatima; Bhattacharjee, A.; Delgado, L.; Scott, S.; Wilson, J. R.; Wallace, G. M.; Shiraiwa, S.; Mumgaard, R. T.

    2016-10-01

    In lower hybrid current drive (LHCD) experiments on the Alcator C-Mod, sawtooth activity could be suppressed as the safety factor q on axis is raised above unity. However, in some of these experiments, after applying LHCD, the onset of MHD mode activity caused the current drive efficiency to significantly drop. Here, we study the stability of these experiments by performing MHD simulations using the NIMROD code starting with experimental EFIT equilibria. First, consistent with the LHCD experiment with no signature of MHD activity, MHD mode activity was also absent in the simulations. Second, for experiments with MHD mode activity, we find that a core n=1 reconnecting mode with dominate poloidal modes of m=2,3 is unstable. This mode is a resistive current-driven mode as its growth rate scales with a negative power of the Lundquist number in the simulations. In addition, with further enhanced reversed-shear q profile in the simulations, a core double tearing mode is found to be unstable. This work is supported by U.S. DOE cooperative agreement DE-FC02-99ER54512 using the Alcator C-Mod tokamak, a DOE Office of Science user facility.

  15. Correlation ECE diagnostic in Alcator C-Mod

    SciTech Connect

    Sung, C.; White, A. E.; Howard, N. T.; Mikkelsen, D.; Irby, J.; Leccacorvi, R.; Vieira, R.; Oi, C.; Rice, J.; Reinke, M.; Gao, C.; Ennever, P.; Porkolab, M.; Churchill, R.; Theiler, C.; Walk, J.; Hughes, J.; Hubbard, A.; Greenwald, M.

    2015-03-12

    Correlation ECE (CECE) is a diagnostic technique that allows measurement of small amplitude electron temperature, Te, fluctuations through standard cross-correlation analysis methods. In Alcator C-Mod, a new CECE diagnostic has been installed[Sung RSI 2012], and interesting phenomena have been observed in various plasma conditions. We find that local Te fluctuations near the edge (ρ ~ 0:8) decrease across the linearto- saturated ohmic confinement transition, with fluctuations decreasing with increasing plasma density[Sung NF 2013], which occurs simultaneously with rotation reversals[Rice NF 2011]. Te fluctuations are also reduced across core rotation reversals with an increase of plasma density in RF heated L-mode plasmas, which implies that the same physics related to the reduction of Te fluctuations may be applied to both ohmic and RF heated L-mode plasmas. In I-mode plasmas, we observe the reduction of core Te fluctuations, which indicates changes of turbulence occur not only in the pedestal region but also in the core across the L/I transition[White NF 2014]. The present CECE diagnostic system in C-Mod and these experimental results are described in this paper.

  16. Investigation of ELMs on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Terry, J. L.

    2005-10-01

    C-Mod typically operates in regimes without large ELMs. Recently, discrete ELMs have been routinely produced by making plasmas with large lower triangularity (i.e. >0.75), compared to the more typical C-Mod values <0.6. The ELM character was substantially modified as the triangularity was reduced, changing from discrete ELMs of ˜60 μsec duration, to H-to-L mode back transitions, lasting ˜4msec. The discrete ELMs are most apparent when the density is just above the low-density H-mode threshold, ne˜8x10^19m-3. Pedestal Te up to 1 keV was measured early in the H-mode phase. The spatial structure and propagation of the discrete ELMs are studied using fast-framing (˜250 kHz) cameras and other high resolution optical diagnostics. The magnetics and the optical diagnostics show a rapidly-growing precursor oscillation (100-200 kHz just prior to the ELM crash) that is localized radially to around the top of the pedestal. Outside the LCFS the enhanced emission from the ELM propagates radially outward with a complicated spatial structure, similar in many respects to `blobs.'

  17. Correlation ECE diagnostic in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Sung, C.; White, A. E.; Howard, N. T.; Mikkelsen, D.; Irby, J.; Leccacorvi, R.; Vieira, R.; Oi, C.; Rice, J.; Reinke, M.; Gao, C.; Ennever, P.; Porkolab, M.; Churchill, R.; Theiler, C.; Walk, J.; Hughes, J.; Hubbard, A.; Greenwald, M.

    2015-03-01

    Correlation ECE (CECE) is a diagnostic technique that allows measurement of small amplitude electron temperature, Te, fluctuations through standard cross-correlation analysis methods. In Alcator C-Mod, a new CECE diagnostic has been installed[Sung RSI 2012], and interesting phenomena have been observed in various plasma conditions. We find that local Te fluctuations near the edge (ρ ~ 0:8) decrease across the linearto- saturated ohmic confinement transition, with fluctuations decreasing with increasing plasma density[Sung NF 2013], which occurs simultaneously with rotation reversals[Rice NF 2011]. Te fluctuations are also reduced across core rotation reversals with an increase of plasma density in RF heated L-mode plasmas, which implies that the same physics related to the reduction of Te fluctuations may be applied to both ohmic and RF heated L-mode plasmas. In I-mode plasmas, we observe the reduction of core Te fluctuations, which indicates changes of turbulence occur not only in the pedestal region but also in the core across the L/I transition[White NF 2014]. The present CECE diagnostic system in C-Mod and these experimental results are described in this paper.

  18. Energetic Ion Losses in the Alcator C-Mod Tokamak

    NASA Astrophysics Data System (ADS)

    Pace, D. C.; Granetz, R. S.; Bader, A.; Parker, R. R.; Vieira, R.; Wukitch, S. J.; Darrow, D. S.; Zweben, S. J.

    2011-10-01

    A scintillator-based fast ion loss detector (FILD) is presently being commissioned on the Alcator C-Mod tokamak to resolve the energy and pitch angle of energetic ions that are lost from the plasma due to interactions with MHD modes, edge localized modes, and ion cyclotron resonance heating (ICRH) injection. Energetic ion populations are generated by applying ICRH in the minority heating regime, producing tail energies up to 2 MeV and driving a variety of Alfvén eigenmodes. The 2 MHz sampling rate of the detector allows for the identification of convective losses across the range of encountered Alfvénic frequencies. A comprehensive design study optimized the FILD to overlap its observed ion phase space with that of the compact neutral particle analyzer array that measures radial energy and density profiles of confined ICRH tail ions. Initial results from this diagnostic system will be presented in the context of the extensive C-Mod ICRH experiment and simulation/modeling effort. Work supported by US DOE through an appointment in the Fusion Energy Postdoctoral Research Program and under DE-FC02-99ER54512.

  19. Implementation of LHCD Experiments on Alcator C-Mod

    SciTech Connect

    Parker, R.; Basse, N.; Beck, W.; Childs, R.; Grimes, M.; Gwinn, D.; Irby, J.; Koert, P.; Labombard, B.; Liptac, J.; Marmar, E.; Terry, D.; Terry, J.; Vieira, R.; Wallace, G.; Wilson, J.R.; Zaks, J.; Bernabei, S.; Ellis, R.; Fredd, E.

    2005-09-26

    An antenna-transmitter system for driving current in the LHRF has been installed in Alcator C-Mod. The antenna is a grill consisting of 4 poloidal rows of waveguides, each with 24 guides in the toroidal direction. Power is supplied by 12 klystrons capable of 250 kW operation at a frequency of 4.6 GHz. Thus the total source power is 3 MW, with about 1.5 MW available to be coupled to the plasma. Power supply and heat throughput limits in C-Mod limit the pulse length to 5 s, which however represents several current redistribution times. With 90 deg. phasing, the n parallel spectrum is sharply peaked at 2.3 and the range 1.5 < n parallel < 3.5 can be accessed dynamically by varying the phase of the klystrons. The system is in the commissioning phase with klystron power limited to {approx}20 kW and pulse length to 10 ms. Early results from plasma operation are discussed.

  20. Testing Gyrokinetics on C-Mod and NSTX

    SciTech Connect

    M.H. Redi; W. Dorland; C.L. Fiore; D. Stutman; J.A. Baumgaertel; B. Davis; S.M. Kaye; D.C. McCune; J. Menard; G. Rewoldt

    2005-06-20

    Quantitative benchmarks of computational physics codes against experiment are essential for the credible application of such codes. Fluctuation measurements can provide necessary critical tests of nonlinear gyrokinetic simulations, but such require extraordinary computational resources. Linear micro-stability calculations with the GS2 [1] gyrokinetic code have been carried out for tokamak and ST experiments which exhibit internal transport barriers (ITB) and good plasma confinement. Qualitative correlation is found for improved confinement before and during ITB plasmas on Alcator C-Mod [2] and NSTX [3], with weaker long wavelength micro-instabilities in the plasma core regions. Mixing length transport models are discussed. The NSTX L-mode is found to be near marginal stability for kinetic ballooning modes. Fully electromagnetic, linear, gyrokinetic calculations of the Alcator C-Mod ITB during off-axis rf heating, following four plasma species and including the complete electron response show ITG/TEM microturbulence is suppressed in the plasma core and in the barrier region before barrier formation, without recourse to the usual requirements of velocity shear or reversed magnetic shear [4-5]. No strongly growing long or short wavelength drift modes are found in the plasma core but strong ITG/TEM and ETG drift wave turbulence is found outside the barrier region. Linear microstability analysis is qualitatively consistent with the experimental transport analysis, showing low transport inside and high transport outside the ITB region before barrier formation, without consideration of ExB shear stabilization.

  1. Volume Recombination in Alcator C-Mod Divertor Plasmas

    NASA Astrophysics Data System (ADS)

    Terry, J. L.

    1997-11-01

    Volume recombination has been predicted(See, for example, A. Loarte, Proc. 12th PSI Conf, J. Nucl. Mater (1996) I9, in press.) to be a significant sink for plasma ions under the detached divertor conditions achieved on many tokamaks. This volume recombination sink was observed initially in Alcator C-Mod and shown to be a major fraction of the ion loss. Signatures of recombination have now been observed on DIII-D(R.C. Isler, et al., paper submitted for publication), Asdex-UG (B. Napiontek, et al. 24th EPS Conf., Berchtesgaden, Germany, 1997, P4.007, in press.), and JET(R.D. Monk, et al. 24th EPS Conf., Berchtesgaden, Germany, 1997, P1.030, in press.). It is important primarily because the recombined atoms are not accelerated through the sheath - thus reducing divertor plate sputtering, and because most of the potential energy of recombination (13.6 eV) is released as radiation before the ion strikes the plate. The Alcator C-Mod measurements show that the recombination occurs in low Te ( ~1 eV), high ne ( ~1× 10^21 m-3) regions, and is significantly larger in detached regions. At the inboard, detached divertor plate the measured volume recombination rate is typically greater than the rate of ion collection at that plate and is about an order of magnitude higher than on the attached, outer plate. These spatially resolved measurements also show that the recombination rate is peaked near the strike point and imply that the recombination is occurring close to the plate surface. The C-Mod observations about the magnitude and spatial distribution of the recombination are consistent with the modelling of similar discharges(F. Wising et al., Contrib. Plasma Phys. 36, p 136 (1996).). The experimental evidence for recombination is found in the deuterium emission spectra from the divertor, in particular in the Balmer- and/or Lyman-series. The spectra show that the dominant recombination mechanism is 3-body recombination into excited states of deuterium and that the populations

  2. Recent Results from the C-Mod Polarimeter

    NASA Astrophysics Data System (ADS)

    Xu, P.; Irby, J. H.; Bergerson, W. F.; Brower, D. L.; Ding, W. X.; Marmar, E. S.; Delgado-Aparicio, L.; Ernst, D.; Hughes, J. W.; Mumgaard, R.; Parker, R.; Scott, S.; Shiraiwa, S.; Wallace, G. M.; White, A. E.; Wolfe, S. M.

    2013-10-01

    The C-Mod 3 chord FIR polarimeter, with a 2 MHz bandwidth, is capable of responding to both fast changes in the plasma equilibrium and high frequency fluctuations. It operates under ITER-like plasma conditions and magnetic fields, and uses an optical layout and FIR sources very similar to those proposed for the ITER polarimeter. Results from the polarimeter as a function of plasma density and current will be discussed, as well as the effects of lower hybrid power levels, phasing and plasma density on the current drive efficiency. The possible identification of some broadband fluctuations as primarily magnetic in nature, and gyrokinetic simulation results from the modeling of these fluctuations will also be presented. Estimates of the localization of this mode will be described. The polarimeter response to low frequency MHD modes will be compared with results from the Fast Two-Color-Interferometer. USDoE contract DE-FC02-99ER54512.

  3. Edge Minority Heating Experiment in Alcator C-Mod

    SciTech Connect

    S.J. Zweben; J.L. Terry; P. Bonoli; R. Budny; C.S. Chang; C. Fiore; G. Schilling; S. Wukitch; J. Hughes; Y. Lin; R. Perkins; M. Porkolab; the Alcator C-Mod Team

    2005-03-25

    An attempt was made to control global plasma confinement in the Alcator C-Mod tokamak by applying ion cyclotron resonance heating (ICRH) power to the plasma edge in order to deliberately create a minority ion tail loss. In theory, an edge fast ion loss could modify the edge electric field and so stabilize the edge turbulence, which might then reduce the H-mode power threshold or improve the H-mode barrier. However, the experimental result was that edge minority heating resulted in no improvement in the edge plasma parameters or global stored energy, at least at power levels of radio-frequency power is less than or equal to 5.5 MW. A preliminary analysis of these results is presented and some ideas for improvement are discussed.

  4. Progress in characterizing pedestal stability on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Hughes, J. W.; Churchill, R. M.; Cziegler, I.; Davis, E. M.; Dominguez, A.; Ennever, P.; Ernst, D.; Hubbard, A. E.; Lipschultz, B.; Ma, Y.; Walk, J. R.; Wolfe, S. M.; Snyder, P. B.; Osborne, T.; Xu, X.; Sugiyama, L.

    2011-10-01

    Experimental studies on Alcator C-Mod explore pedestal structure and edge relaxation mechanisms primarily in three high confinement regimes: ELMy H-mode, EDA H-mode and I-mode. Extensive scans of BT, IP, ne, Pnet and shaping parameters have been carried out in these regimes, allowing the characterization of the operating space for ELMs as well as benign pedestal relaxation mechanisms (e.g. quasi- and weakly coherent modes). Well resolved edge profiles and accurate equilibrium reconstructions are produced from typical discharges, enabling evaluation of edge stability using various computational tools, such as ELITE, BOUT++, M3D and GS2. Relationships among dominant edge instabilities, radial transport and pedestal structure will be discussed. Supported by US DoE Award DE-FC02-99-ER54512.

  5. Stationary density profiles in the Alcator C-mod tokamak

    NASA Astrophysics Data System (ADS)

    Kesner, J.; Ernst, D.; Hughes, J.; Mumgaard, R.; Scott, S.; Shiraiwa, S.; Whyte, D.

    2012-12-01

    In the absence of an internal particle source, plasma turbulence will impose an intrinsic relationship between an inwards pinch and an outwards diffusion resulting in a stationary density profile. The Alcator C-mod tokamak utilizes RF heating and current drive so that fueling only occurs in the vicinity of the separatrix. Discharges that transition from L-mode to I-mode are seen to maintain a self-similar stationary density profile as measured by Thomson scattering. For discharges with negative magnetic shear, an observed rise of the safety factor in the vicinity of the magnetic axis appears to be accompanied by a decrease of electron density, qualitatively consistent with the theoretical expectations.

  6. Stationary Density Profiles in Alcator C-mod

    NASA Astrophysics Data System (ADS)

    Kesner, J.; Ernst, D.; Hughes, J. W.; Mumgaard, R.; Shiraiwa, S.; Whyte, D. G.

    2012-10-01

    In the absence of an internal particle source, plasma turbulence will impose an intrinsic relationship between an inwards pinch and an outwards diffusion resulting in a stationary density profile as determined by the turbulent equipartition (TEP) theory. The Alcator C-mod tokamak utilizes RF heating and current drive so that fueling only occurs in the vicinity of the separatrix. Density is determined from Thomson scattering. Discharges that transition from L-mode to I-mode are seen to maintain a stationary profile. For reversed shear discharges maintained by non-inductive current drive (Vloop 0) a drop of density in the vicinity of the axis is consistent with an observed rise in q, although error in the measurement precludes making this observation definitive.

  7. Extension of Alcator C-mod's ICRF Experimental Capability

    SciTech Connect

    Schilling, G.; Hosea, J.C.; Wilson, J.R.; Bonoli, P.T.; Lee, W.D.

    1999-06-01

    A new 4-strap single-ended ICRF antenna has been added to the Alcator C-Mod tokamak. PPPL designed, fabricated, and tested the antenna up to 45 kV on an rf test stand. It is capable of symmetric phasing for ICRF heating studies, and asymmetric phasing with an improved directed wave spectrum for current drive. Two new 2 MW transmitters, tunable from 40-80 MHz, allow operation in plasma at 43, 60, and 78 MHz to match a variety of toroidal fields and plasma conditions. This addition increases the total available ICRF power to 4 MW at 80 MHz plus 4 MW at 40-80 MHz. Plasma heating and current drive experiments at the extended power levels and new frequencies are planned, and initial system performance will be discussed.

  8. Development of the Alcator C-Mod FIR Polarimeter

    NASA Astrophysics Data System (ADS)

    Xu, P.; Irby, J. H.; Bosco, J.; Kanojia, A.; Leccacorvi, R.; Marmar, E. S.; Michael, P.; Murray, R.; Vieira, R.; Wolfe, S.; Brower, D. L.; Ding, W. X.; Mansfield, D. K.

    2008-11-01

    A multi-chord FIR polarimetry diagnostic is being developed for the Alcator C-Mod Tokamak to be used to determine the q-profile and to study density and magnetic field fluctuations. This poloidally viewing system using retro-reflectors on the inner wall will have geometry and fields similar to those planned for ITER. The optical layout will be discussed, as well as simulations of the expected Faraday and Cotton-Mouton signal levels, and the plans to integrate these data into EFIT. Details of the hardware being developed and procured including the FIR laser system, the laser power and frequency control system, optical components, detectors, beam position feedback system, and inner wall retro-reflectors and shutter will be presented.

  9. Neutral particle dynamics in the Alcator C-Mod tokamak

    SciTech Connect

    Niemczewski, Artur P.

    1995-08-01

    This thesis presents an experimental study of neutral particle dynamics in the Alcator C-Mod tokamak. The primary diagnostic used is a set of six neutral pressure gauges, including special-purpose gauges built for in situ tokamak operation. While a low main chamber neutral pressure coincides with high plasma confinement regimes, high divertor pressure is required for heat and particle flux dispersion in future devices such as ITER. Thus we examine conditions that optimize divertor compression, defined here as a divertor-to-midplane pressure ratio. We find both pressures depend primarily on the edge plasma regimes defined by the scrape-off-layer heat transport. While the maximum divertor pressure is achieved at high core plasma densities corresponding to the detached divertor state, the maximum compression is achieved in the high-recycling regime. Variations in the divertor geometry have a weaker effect on the neutral pressures. For otherwise similar plasmas the divertor pressure and compression are maximum when the strike point is at the bottom of the vertical target plate. We introduce a simple flux balance model, which allows us to explain the divertor neutral pressure across a wide range of plasma densities. In particular, high pressure sustained in the detached divertor (despite a considerable drop in the recycling source) can be explained by scattering of neutrals off the cold plasma plugging the divertor throat. Because neutrals are confined in the divertor through scattering and ionization processes (provided the mean-free-paths are much shorter than a typical escape distance) tight mechanical baffling is unnecessary. The analysis suggests that two simple structural modifications may increase the divertor compression in Alcator C-Mod by a factor of about 5. Widening the divertor throat would increase the divertor recycling source, while closing leaks in the divertor structure would eliminate a significant neutral loss mechanism.

  10. Overview of Recent Alcator C-Mod Results

    NASA Astrophysics Data System (ADS)

    Marmar, Earl; Alcator C-Mod Team

    2014-10-01

    Alcator C-Mod research currently emphasizes RF heating, current and flow drive, divertor/PMI issues, non-ELMing pedestal regimes with enhanced confinement, and disruption mitigation/runaway dynamics. Stability analysis of I-mode pedestals shows pressures well below the peeling-ballooning limit, as well as expected kinetic ballooning mode thresholds, consistent with the lack of ELMs. Results with the magnetic field aligned ICRF antenna show reductions in high-Z metallic impurities. Implementation of novel ``mirror-probe'' electronics has enabled simultaneous measurements of Te, ne and φ with 1 μs time response using a single probe tip, revealing important properties of the Quasi-Coherent-Mode (QCM) which regulates edge particle transport in EDA H-mode. An Accelerator-based In-situ Material Surveillance diagnostic has been deployed, providing the first between-shot measurements of surface evolution of the all-metal wall. We have observed suppression of boundary turbulence and τE improvement using LHRF into high-density H-modes, with H-factor increases up to 30%. Upgrades which are ready for construction and near term installation on C-Mod include: an off-midplane LH launcher to test theories of improved current drive at high density and an actively heated (900 K) tungsten DEMO-like outer divertor. We are proposing a new facility, ADX, based on Alcator technology, to access advanced magnetic topologies to solve the divertor PMI problem, combined with high-field launch LHCD and ICRF to extend the tokamak to steady-state with reactor relevant tools. Supported by USDOE.

  11. FIR polarimetry diagnostic for the C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Irby, J. H.; Bergerson, W. F.; Brower, D. L.; Ding, W. X.; Marmar, E. S.; Xu, P.

    2012-02-01

    A three-chord polarimeter on Alcator C-Mod will make measurements of the poloidal magnetic field and plasma fluctuations. The beams from two frequency-offset, 200 mW, FIR lasers operating at 117.73 μm are combined to produce collinear, counter-rotating, circularly polarized beams. The beams are divided into three chords which are directed into the plasma at one toroidal location. Corner cube retro-reflectors mounted on the inside wall return the beam for a double pass. The mixing product of the two beams is detected both before (reference) and after (signal) the plasma using polarization sensitive detectors that produce a beat signal at ~ 4 MHz. During the plasma discharge, the phase delay of the signal mixer, which depends on the Faraday effect, is evaluated with respect to the reference and produces line-integrated information on the poloidal magnetic field. Measurements on C-Mod require the phase error to be at the 0.1 degree level, and great care in the design of optical mounts, polarizers, beam-splitters, focusing optics, and acoustic and magnetic shielding was required. Development of new planar diode Schottky detectors was necessary to provide high sensitivity for a diagnostic that will eventually have at least six chords. Absorption of the FIR laser light by water vapor requires that the entire beam path be purged with dry air. Six retro-reflectors on the inner wall arranged in an ITER-like configuration provide poloidally viewing chords from near the mid-plane to well into the plasma scrape off layer. A pneumatically controlled shutter protects the in-vessel optics during boronizations and during limited discharges that might accelerate damage to the retro-reflector surfaces. Tests indicate there is no measurable signal contamination from the toroidal magnetic field due to the Cotton-Mouton effect. Polarization sensitivity of the wire mesh beamsplitters necessitated system calibration. Good agreement to EFIT reconstructions has been observed along with

  12. Overview of Recent Alcator C-Mod Highlights

    NASA Astrophysics Data System (ADS)

    Marmar, Earl; C-Mod Team

    2013-10-01

    Analysis and modeling of recent C-Mod experiments has yielded significant results across multiple research topics. I-mode provides routine access to high confinement plasma (H98 up to 1.2) in quasi-steady state, without large ELMs; pedestal pressure and impurity transport are regulated by short-wavelength EM waves, and core turbulence is reduced. Multi-channel transport is being investigated in Ohmic and RF-heated plasmas, using advanced diagnostics to validate non-linear gyrokinetic simulations. Results from the new field-aligned ICRF antenna, including significantly reduced high-Z metal impurity contamination, and greatly improved load-tolerance, are being understood through antenna-plasma modeling. Reduced LHCD efficiency at high density correlates with parametric decay and enhanced edge absorption. Strong flow drive and edge turbulence suppression are seen from LHRF, providing new approaches for plasma control. Plasma density profiles directly in front of the LH coupler show non-linear modifications, with important consequences for wave coupling. Disruption-mitigation experiments using massive gas injection at multiple toroidal locations show unexpected results, with potentially significant implications for ITER. First results from a novel accelerator-based PMI diagnostic are presented. What would be the world's first actively-heated high-temperature advanced tungsten divertor is designed and ready for construction. Conceptual designs are being developed for an ultra-advanced divertor facility, Alcator DX, to attack key FNSF and DEMO heat-flux challenges integrated with a high-performance core. Supported by USDOE.

  13. H-modes on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Snipes, J. A.; Hubbard, A. E.; Garnier, D. T.; Golovato, S. N.; Granetz, R. S.; Greenwald, M.; Hutchinson, I. H.; Irby, J.; La Bombard, B.; Marmar, E. S.; Niemczewski, A.; O'Shea, P. J.; Porkolab, M.; Stek, P.; Takase, Y.; Terry, J. L.; Watterson, R.; Wolfe, S. M.

    1996-08-01

    H-modes exhibiting improved confinement above the L-mode are achieved in Alcator C-Mod with ICRF and with ohmic heating alone without boronization. Both ELM-free and ELMy H-modes are obtained with total input power from 0.75 to 4.2 MW over a range of densities (0.8 to 0741-3335/38/8/005/img1) and toroidal fields (3 to 8 T). Type III ELMs are often observed to have coherent, high m and n precursor oscillations with frequencies of 100 - 160 kHz. The threshold power required to achieve the H-mode increases with density and toroidal field, in rough agreement with scalings derived from other tokamaks. The power densities and density times toroidal field products are an order of magnitude larger than in other tokamaks, in the range of values expected for ITER. The L - H and H - L transitions occur at approximately the same edge electron temperature. A low density limit to the H-mode is found at about 0741-3335/38/8/005/img2. A high midplane neutral pressure limit of about 0.6 mTorr is also observed.

  14. Transport of light, trace impurities in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Rowan, W. L.; Bespamyatnov, I. O.; Liao, K. T.; Horton, W.; Fu, X. R.; Hughes, J. W.

    2012-10-01

    Light impurity profiles for boron were measured in ITB, H-mode, L-mode, and I-mode discharges in Alcator C-Mod. Within this wide range of modes, the profiles varied from peaked to hollow to flat. Specifically, hollow profiles are often observed in H-mode, while ITBs produce strong peaking, and L-mode produces moderate peaking. I-mode discharges are characterized by flat impurity profiles. For the study reported here, the profiles were measured with charge exchange recombination spectroscopy. The dependences of Rv/D were sought on dimensionless quantities including ion density scale length, effective charge, collisionality, and temperature scale length. We find that neoclassical transport consistently underestimates the measured transport. The excess measured transport is assumed to be turbulent. The strongest dependence of Rv/D is with temperature scale length. In addition, the measured transport was compared with the prediction of an analytical theory of drift wave turbulence that identifies transport implications for drift waves driven by ion and impurity density gradients.

  15. Highlights of the Alcator C-Mod Research Campaign

    NASA Astrophysics Data System (ADS)

    Greenwald, Martin; Alcator Team

    2011-10-01

    Alcator C-Mod has completed an experimental campaign focusing on broad scientific issues with particular emphasis on ITER needs and requests. Experiments with no NBI torque have investigated spontaneous flow reversal, creation of transport barriers aided by the shear of intrinsic rotation and a variety of RF flow drive schemes. Studies of I-mode have found conditions where a wide operating regime opens up, allowing easy access to long-lived, high-performance discharges with L-mode like particle confinement. We are validating the EPED and BOUT++ models for pedestal height/width and ELM onset using extended parameter scans in ELMy H-mode. The challenge of high-Z impurity generation with ICRF is being addressed first by deployment of a novel antenna whose current straps and antenna box are perpendicular to the total magnetic field -second by studies of the modification of edge impurity transport, where fine-scale Er structures in the SOL in the presence of ICRF heating have been found. LH current drive has produced non-inductive reversed shear regimes at n ~ 5x1019 which exhibit electron temperature ITBs. The first observations have been made of in-tokamak production of divertor tungsten nano-structures (fuzz), which had previously been seen only in linear laboratory experiments. Supported by DoE DE-FC02-99ER54512.

  16. Digital Plasma Control System for Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Ferrara, M.; Wolfe, S.; Stillerman, J.; Fredian, T.; Hutchinson, I.

    2004-11-01

    A digital plasma control system (DPCS) has been designed to replace the present C-Mod system, which is based on hybrid analog-digital computer. The initial implementation of DPCS comprises two 64 channel, 16 bit, low-latency cPCI digitizers, each with 16 analog outputs, controlled by a rack-mounted single-processor Linux server, which also serves as the compute engine. A prototype system employing three older 32 channel digitizers was tested during the 2003-04 campaign. The hybrid's linear PID feedback system was emulated by IDL code executing a synchronous loop, using the same target waveforms and control parameters. Reliable real-time operation was accomplished under a standard Linux OS (RH9) by locking memory and disabling interrupts during the plasma pulse. The DPCS-computed outputs agreed to within a few percent with those produced by the hybrid system, except for discrepancies due to offsets and non-ideal behavior of the hybrid circuitry. The system operated reliably, with no sample loss, at more than twice the 10kHz design specification, providing extra time for implementing more advanced control algorithms. The code is fault-tolerant and produces consistent output waveforms even with 10% sample loss.

  17. Helium Diagnostic for Alcator C-Mod Edge Studies

    NASA Astrophysics Data System (ADS)

    Pappas, D. A.; Labombard, B.; Lipschultz, B.; Pitcher, C. S.; Brix, M.; Schweer, B.

    1997-11-01

    We are developing a diagnostic based on the thermal helium beam technique pioneered on TEXTOR [1,2], which is intended to continuously measure electron temperature and density profiles in the edge plasma at the midplane with high radial and temporal resolution (Δr=1 mm, Δt=1 ms). As a He neutral source, we are presently using a simple gas capillary embedded in one of the C-Mod limiters at the midplane, typically 10 to 15 mm away from the location of the plasma separatrix. Four fibers from a tangentially viewing telescope, which are fed to a visible spectrometer, are used to monitor the HeI lines of interest. We are looking at both the red (667.8 nm, 706.5 nm, 728.1 nm) and the green (471.3 nm, 501.5 nm, 504.7 nm) lines [2], whose intensity ratios can be used to obtain electron temperature and density. The experiments are performed under a variety of plasma conditions and the results are compared to those obtained with a scanning probe. [1] B. Schweer, et al., J. Nucl. Mat. 196-198, 174 (1992). [2] M. Brix and B. Schweer, 24^th EPS Conference, Berchtesgaden, Germany, June 1997. * Work Supported by D.o.E. Contract DE-AC02-78ET51013

  18. Stimulation of MHD Modes in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Golfinopoulos, T.; Granetz, R.; Labombard, B.; Lin, Y.; Parker, R. R.; Sears, J.; Wukitch, S. J.

    2010-11-01

    Active MHD (AMHD) spectroscopy involves stimulating MHD modes by external means to study the modes or diagnose the plasma. In many AMHD experiments, drive frequency is swept across a 100-200 kHz range in which modes are expected; this allows for robust techniques to detect resonant poles in the presence of direct pickup from the driver. However, there is flexibility in the drive mechanism. At Alcator, we have employed a parametric excitation method, amplitude-modulating the ICRF wave (80 MHz) with envelope signals in the AE frequency range (100's kHz). This builds off the ICRF beat technique used in JET in 1996 and ASDEX Upgrade in 2006, but is unique in its use of a single antenna, improving coherence. An advantage of this approach is its ability to couple to the plasma core. It also has high input power, though efficiency is limited by the Manley-Rowe relations. In initial experiments, we excited weak, stable modes in the toroidal Alfvén eigenmode band gap. We plan to explore this and other methods for coupling to various MHD-like modes, especially C-Mod's Quasi Coherent mode.

  19. ICRF heating scenarios in Alcator C-MOD

    NASA Astrophysics Data System (ADS)

    Takase, Y.; Bonoli, P. T.; Golovato, S. N.; Porkolab, M.

    1994-10-01

    Alcator C-MOD tokamak (R=0.67 m, α=0/21 m, κ `1.8, B≤9 T, I≤3 MA) will start operating in April 1993. Initially 2 MW of rf power at 80 MHz will be available, which will be upgraded to 4 MW by early 1994. Additional 2-4 MW of 40-80 MHz tunable power may be installed in 1996 in collaboration with PPPL. With the 80 MHz transmitters, He3 minority heating at B=7.9 T and H minority heating at 5.3 T are the main heating scenarios, with possibilites of He3 and H second harmonic minority heating (at 3.9 T and 2.6 T, respectively) and direct electron heating by ELD/TTMP. The tunable transmitter will enable fundamental He3 and H minority heating at lower fields, and Alfvén wave heating below the ion cyclotron frequency at fields above 4 T in H plasmas. Advanced tokamak scenarios with high bootstrap current fraction and high normalized beta can also be studied in combination with pellet fueling and 4.6 GHz LHCD under TPX-like conditions (B˜4 T, n¯e≲1×1020 m-3) for pulse lengths exceeding the L/R time.

  20. ICRF heating scenarios in Alcator C-MOD

    SciTech Connect

    Takase, Y.; Bonoli, P.T.; Golovato, S.N.; Porkolab, M. )

    1994-10-15

    Alcator C-MOD tokamak ([ital R]=0.67 m, [alpha]=0/21 m, [kappa cur]1.8, [ital B][le]9 T, [ital I][le]3 MA) will start operating in April 1993. Initially 2 MW of rf power at 80 MHz will be available, which will be upgraded to 4 MW by early 1994. Additional 2--4 MW of 40--80 MHz tunable power may be installed in 1996 in collaboration with PPPL. With the 80 MHz transmitters, He[sup 3] minority heating at [ital B]=7.9 T and H minority heating at 5.3 T are the main heating scenarios, with possibilites of He[sup 3] and H second harmonic minority heating (at 3.9 T and 2.6 T, respectively) and direct electron heating by ELD/TTMP. The tunable transmitter will enable fundamental He[sup 3] and H minority heating at lower fields, and Alfven wave heating below the ion cyclotron frequency at fields above 4 T in H plasmas. Advanced tokamak scenarios with high bootstrap current fraction and high normalized beta can also be studied in combination with pellet fueling and 4.6 GHz LHCD under TPX-like conditions ([ital B][similar to]4 T, [ital [bar n

  1. Alcator C-Mod ICRF antenna and matching circuit

    SciTech Connect

    Golovato, S.N.; Porkolab, M.; Takase, Y.; Holcomb, H.L. )

    1989-07-01

    Alcator C-mod will be a compact, high field, high density, divertor tokamak. Two FMIT transmitters will supply 4 MW of power in 1 sec pulses at 80 MHz for ICRF heating. Fast wave minority heating experiments are planned in D({sup 3}He) at 8 T and D(H) at 5.5 T. The first antenna will have a single current strap inside a box structure, which will be movable radially. The antenna will be inserted through a side port, making the rf power density on the antenna surface {similar to}2 kW/cm{sup 2} at 2 MW. the antenna will be center-trapped for mechanical strength and have a double layer Faraday screen tilted along the field lines. The antenna geometry was chosen to maximize power coupling assuming voltage-limited operation. A wide antenna with slotted box sides appears the best design, and 10 {Omega} of loading is required to couple 2 MW of power at a voltage limit of 40 kV. Matching is achieved by choice of the drive point to a resonant circuit formed by the antenna and a loop of transmission line outside of the vacuum and by tuning elements in the transmission line to the transmitter.

  2. Alcator C-Mod ICRF antenna and matching circuit

    SciTech Connect

    Golovato, S.N.; Porkolab, M.; Takase, Y.; Holcomb, H.L.

    1989-06-01

    Alcator C-Mod will be a compact, high field, high density, divertor tokamak. Two FMIT transmitters will supply 4 MW of power in 1 sec pulses at 80 MHz for ICRF heating. Fast wave minority heating experiments are planned in D(/sup 3/He) at 8 T and D(H) at 5.5 T. The first antenna will have a single current strap inside a box structure, which will be movable radially. The antenna will be inserted through a side port, making the rf power density on the antenna surface /approximately/2 kW/cm/sup 2/ at 2 MW. The antenna will be center-tapped for mechanical strength and have a double layer Faraday screen tilted along the field lines. The antenna geometry was chosen to maximize power coupling assuming voltage-limited operation. A wide antenna with slotted box sides appears the best design, and 10 /Omega/ of loading is required to couple 2 MW of power at a voltage limit of 40 kV. Matching is achieved by choice of the drive point to a resonant circuit formed by the antenna and a loop of transmission line outside of the vacuum and by tuning elements in the transmission line to the transmitter. 6 refs., 4 figs.

  3. Identification of Mercier instabilities in Alcator C-Mod tokamak

    SciTech Connect

    In, Y.; Ramos, J. J.; Hastie, R. J.; Catto, P. J.; Hubbard, A. E.; Hutchinson, I. H.; Marmar, E.; Porkolab, M.; Snipes, J.; Wolfe, S.

    2000-12-01

    During current ramp-up discharges, highly localized magnetohydrodynamic (MHD) fluctuations were observed on the electron cyclotron emission diagnostics of Alcator C-Mod tokamak [I. H. Hutchinson , Phys. Plasmas 1, 1511 (1994)]. The electron temperature profile was hollow, while the density profile was weakly decreasing. Assuming that the equilibration time was short enough to quickly thermalize ions the pressure profile was also found to be hollow. Using this pressure profile as an additional constraint to the EFIT program, an equilibrium with reversed shear was constructed having a q(0)>>1. The localized MHD activity was observed near the inner q=5 rational surface in this reconstructed equilibrium, where the Mercier criterion for ideal MHD stability was violated because of the reversed pressure gradient (dp/dr>0), q>1 and moderate shear. When kinetic effects were added, the ideal Mercier mode was finite ion Larmor radius stabilized. However, ion Landau damping was found to be strong enough to drive a kinetic Mercier instability.

  4. Charged fusion product diagnostics in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Boivin, R. L.; Kurz, C.; Lo, D. H.; Fiore, C. L.; Granetz, R.; Petrasso, R. D.

    1992-10-01

    With a plasma current of up to 3 MA, toroidal field of up to 9 T, the confinement of the charged fusion products (CFPs) in Alcator C-Mod is expected to be excellent. For example, at maximum current and field, classical losses of the 0.8 MeV 3He, 1 MeV triton, 3 MeV proton, 3.5 and 3.7 MeV alphas are expected to be less than 5%. For the study of the global confinement of CFPs, we plan to measure the burnup of the 1 MeV triton (from the D-D reaction) using a proton recoil detector (NE-213) for the detection of the 14 MeV neutron resulting from the secondary fusion reaction (D-T). On the other hand, loss measurements of CFPs will be made inside the first wall with two detectors (one at the bottom, one at the midplane) using silicon based detectors. The midplane detector will be used to diagnose D-3He plasmas by looking at the unconfined 14.7 MeV proton. In addition to the derivation of fusion yield, energy distribution of the escaping protons will provide information about the ion velocity distribution of the reactants. The bottom detector is time, pitch angle and energy resolved, and thus will be used to study loss mechanisms such as first orbit, toroidal field ripple and magnetohydrodynamics-induced diffusion.

  5. Escaping charged fusion product spectrometer on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Lo, Daniel H.; Boivin, Réjean L.; Petrasso, Richard D.

    1995-01-01

    A spectrometer for studying escaping charged fusion products has been designed, built, and installed on the Alcator C-Mod tokamak. The ultimate goal of deploying this diagnostic is to evaluate the effectiveness of 3He minority heating through the broadened spectrum of unconfined 14.7 MeV protons from D-3He reactions. Other physics issues that will be addressed with this diagnostic include: first-orbit losses, central ion temperature, 3He burnup, etc. The spectrometer is located 25.8 cm below the midplane and at least 5 cm behind the shadow of the rf limiter. The diagnostic is equipped with a 300 μm thick ion-implanted-silicon detector that is bakeable up to 200 °C. Eighteen apertures of various dimensions and viewing angles, with aluminum foils of various thicknesses, allow for a choice of different charged fusion products and a control of the signal level. In-vessel calibration is provided by two weak radioactive sources of α particles.

  6. Initial Active MHD Spectroscopy Experiments on Alcator C-MOD

    NASA Astrophysics Data System (ADS)

    Schmittdiel, D. A.; Snipes, J. A.; Granetz, R. S.; Parker, R. R.; Wolfe, S. M.; Fasoli, A.

    2002-11-01

    The Active MHD Spectroscopy system is a new diagnostic on C-MOD that will be used to study low frequency MHD modes and TAE's present at high B_tor, n_e, and Te ˜= T_i. The present system consists of two antennas, power amplifiers, and an impedance matching network. Each antenna is 15 × 25 cm with five turns, an inductance of ˜10 μH, and is covered by boron nitride tiles. The two antennas are placed at the same toroidal location, symmetrically above and below the midplane. Each antenna is driven by a ˜1 kW power amplifier in the range of 1 kHz - 1 MHz with an expected antenna current ˜10 A, which will produce a vacuum field of ˜0.5 G at the q = 1.5 surface. This diagnostic is designed to excite high n ( ˜20) stable TAE's and initial results regarding their frequency, mode structure, and damping rate will be presented. Evolution of these modes could also provide information on the q profile to compare with MSE measurements, which will be important for planned lower hybrid current drive operation in 2003.

  7. Lower Hybrid Current Drive Experiments in Alcator C-Mod

    SciTech Connect

    J.R. Wilson, S. Bernabei, P. Bonoli, A. Hubbard, R. Parker, A. Schmidt, G. Wallace, J. Wright, and the Alcator C-Mod Team

    2007-10-09

    A Lower Hybrid Current Drive (LHCD) system has been installed on the Alcator C-MOD tokamak at MIT. Twelve klystrons at 4.6 GHz feed a 4x22 waveguide array. This system was designed for maximum flexibility in the launched parallel wave-number spectrum. This flexibility allows tailoring of the lower hybrid deposition under a variety of plasma conditions. Power levels up to 900 kW have been injected into the tokomak. The parallel wave number has been varied over a wide range, n|| ~ 1.6–4. Driven currents have been inferred from magnetic measurements by extrapolating to zero loop voltage and by direct comparison to Fisch-Karney theory, yielding an efficiency of n20IR/P ~ 0.3. Modeling using the CQL3D code supports these efficiencies. Sawtooth oscillations vanish, accompanied with peaking of the electron temperature (Te0 rises from 2.8 to 3.8 keV). Central q is inferred to rise above unity from the collapse of the sawtooth inversion radius, indicating off-axis cd as expected. Measurements of non-thermal x-ray and electron cyclotron emission confirm the presence of a significant fast electron population that varies with phase and plasma density. The x-ray emission is observed to be radialy broader than that predicted by simple ray tracing codes. Possible explanations for this broader emission include fast electron diffusion or broader deposition than simple ray tracing predictions (perhaps due to diffractive effects).

  8. Lower Hybrid Wave Induced Rotation on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Parker, Ron; Podpaly, Yuri; Rice, John; Schmidt, Andrea

    2009-11-01

    Injection of RF power in the vicinity of the lower hybrid frequency has been observed to cause strong counter current rotation in Alcator C-Mod plasmas [1,2]. The spin-up rate is consistent with the rate at which momentum is injected by the LH waves, and also the rate at which fast electron momentum is transferred to the ions. A momentum diffusivity of ˜ 0.1 m^2/s is sufficient to account for the observed steady-state rotation. This value is also comparable with that derived from an analysis of rotation induced by RF mode conversion [3]. Radial force balance requires a radial electric field, suggesting a buildup of negative charge in the plasma core. This may be the result of an inward pinch of the LH produced fast electrons, as would be expected for resonant trapped particles. Analysis of the fast-electron-produced bremsstrahlung during LH power modulation experiments yields an inward pinch velocity of ˜ 1 m/s, consistent with the estimated trapped particle pinch velocity. [4pt] [1] A. Ince-Cushman, et.al., Phys. Rev. Lett., 102, 035002 (2009)[0pt] [2] J. E. Rice, et. al., Nucl. Fusion 49, 025004 (2009)[0pt] [3] Y. Lin, et.al., this meeting

  9. Integrated modeling of LHCD experiment on Alcator C-Mod

    SciTech Connect

    Shiraiwa, S.; Bonoli, P.; Parker, R.; Wallace, G.

    2014-02-12

    Recent progress in integrating the latest LHCD model based on ray-tracing into the Integrated Plasma Simulator (IPS) is reported. IPS, a python based framework for time dependent tokamak simulation, was expanded recently to incorporate LHCD simulation using GENRAY/CQL3D (ray-tracing/3D Fokker-Planck package). Using GENRAY/CQL3D in the IPS framework, it becomes possible to include parasitic LHCD power loss near the plasma edge, which was found to be important in experiments particularly at high density as expected on reactors. Moreover, it allows for evolving the velocity distribution function in 4 D (ν{sub ∥}, ν⊥, r/a, t) space self-consistently. In order to validate the code, IPS is applied to LHCD experiments on Alctor C-Mod. In this paper, a LHCD experiment performed at the density of n{sub e}∼0.5×10{sup 20}m{sup −3} where good LHCD efficiency and the development of internal transport barrier (ITB) was reported, is modelled in a predictive mode and the result is compared with experiment.

  10. Measurement of particle transport coefficients on Alcator C-Mod

    SciTech Connect

    Luke, T.C.T.

    1994-10-01

    The goal of this thesis was to study the behavior of the plasma transport during the divertor detachment in order to explain the central electron density rise. The measurement of particle transport coefficients requires sophisticated diagnostic tools. A two color interferometer system was developed and installed on Alcator C-Mod to measure the electron density with high spatial ({approx} 2 cm) and high temporal ({le} 1.0 ms) resolution. The system consists of 10 CO{sub 2} (10.6 {mu}m) and 4 HeNe (.6328 {mu}m) chords that are used to measure the line integrated density to within 0.08 CO{sub 2} degrees or 2.3 {times} 10{sup 16}m{sup {minus}2} theoretically. Using the two color interferometer, a series of gas puffing experiments were conducted. The density was varied above and below the threshold density for detachment at a constant magnetic field and plasma current. Using a gas modulation technique, the particle diffusion, D, and the convective velocity, V, were determined. Profiles were inverted using a SVD inversion and the transport coefficients were extracted with a time regression analysis and a transport simulation analysis. Results from each analysis were in good agreement. Measured profiles of the coefficients increased with the radius and the values were consistent with measurements from other experiments. The values exceeded neoclassical predictions by a factor of 10. The profiles also exhibited an inverse dependence with plasma density. The scaling of both attached and detached plasmas agreed well with this inverse scaling. This result and the lack of change in the energy and impurity transport indicate that there was no change in the underlying transport processes after detachment.

  11. Overview of recent Alcator C-Mod research

    NASA Astrophysics Data System (ADS)

    Marmar, E. S.; Bai, B.; Boivin, R. L.; Bonoli, P. T.; Boswell, C.; Bravenec, R.; Carreras, B.; Ernst, D.; Fiore, C.; Gangadhara, S.; Gentle, K.; Goetz, J.; Granetz, R.; Greenwald, M.; Hallatschek, K.; Hastie, J.; Hosea, J.; Hubbard, A.; Hughes, J. W.; Hutchinson, I.; In, Y.; Irby, J.; Jennings, T.; Kopon, D.; Kramer, G.; La Bombard, B.; Lee, W. D.; Lin, Y.; Lipschultz, B.; Liptac, J.; Lynn, A.; Marr, K.; Maqueda, R.; Melby, E.; Mikkelsen, D.; Mossessian, D.; Nazikian, R.; Nevins, W. M.; Parker, R.; Pedersen, T. S.; Phillips, C. K.; Phillips, P.; Pitcher, C. S.; Porkolab, M.; Ramos, J.; Redi, M.; Rice, J.; Rogers, B. N.; Rowan, W. L.; Sampsell, M.; Schilling, G.; Scott, S.; Snipes, J.; Snyder, P.; Stotler, D.; Taylor, G.; Terry, J. L.; Wilson, H.; Wilson, J. R.; Wolfe, S. M.; Wukitch, S.; Xu, X. Q.; Youngblood, B.; Yuh, H.; Zhurovich, K.; Zweben, S.

    2003-12-01

    Research on the Alcator C-Mod tokamak [1] is focused on high particle- and power-density plasma regimes to understand particle and energy transport in the core, the dynamics of the H-mode pedestal, and scrape-off layer and divertor physics. The auxiliary heating is provided exclusively by RF waves, and both the physics and technology of RF heating and current drive are studied. The momentum which is manifested in strong toroidal rotation, in the absence of direct momentum input, has been shown to be transported in from the edge of the plasma following the L-H transition, with timescale comparable to that for energy transport. In discharges which develop internal transport barriers, the rotation slows first inside the barrier region, and then subsequently outside of the barrier foot. Heat pulse propagation studies using sawteeth indicate a very narrow region of strongly reduced energy transport, located near r/a = 0.5. Addition of on-axis ICRF heating arrests the buildup of density and impurities, leading to quasi-steady conditions. The quasi-coherent mode associated with enhanced D-Alpha (EDA) H-mode appears to be due to a resistive ballooning instability. As the pedestal pressure gradient and temperature are increased in EDA H-mode, small ELMs appear; detailed modelling indicates that these are due to intermediate n peeling-ballooning modes. Phase contrast imaging has been used to directly detect density fluctuations driven by ICRF waves in the core of the plasma, and mode conversion to an intermediate wavelength ion cyclotron wave has been observed for the first time. The bursty turbulent density fluctuations, observed to drive rapid cross-field particle transport in the edge plasma, appear to play a key role in the dynamics of the density limit. Preparations for quasi-steady-state advanced tokamak studies with lower hybrid current drive are well underway, and time dependent modelling indicates that regimes with high bootstrap fraction can be produced.

  12. Investigation of Edge Localized Modes in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Terry, J. L.

    2006-10-01

    Characteristics of discrete ELMs produced in Alcator C-Mod discharges of low edge collisionality and high triangularity are examined. These discharges have high values for central Te and ne (reaching 4.5 keV and 2x10^20 m-3 respectively) and good confinement, consistent with ITER98y2 ELMy H-mode scaling. Pedestal temperature heights reach 0.9 keV at densities above 1x10^20 m-3. Studies of the stability of the pedestal profiles to peeling/ballooning modes will be presented. The energy lost per ELM from the H-mode pedestal is ˜10-20% of the pedestal energy. These ELMs exhibit relatively long-lived precursor oscillations, often with two modes of intermediate (n˜10) toroidal mode number present. At the ELM ``crash'' a high frequency (˜0.5 MHz), short-lived magnetic oscillation is initiated, and multiple plasma filament structures are expelled into the Scrape-Off-Layer. The initial ELM filaments, ``primaries'', are large perturbations to the SOL. The perturbation increases the local Dα emission by factors ranging from 1.5 (just outside the LCFS) to ˜100. In the outboard midplane region the primary filaments have radial extents of 0.5-1 cm and typical radial propagation velocities of 1-2 km/s. The poloidal extent of the filaments is greater than the 4.5 cm diagnostic field-of-view. The initial filaments are followed (at intervals of ˜100μs) by multiple, less perturbing ``secondary'' filaments. The radial dynamics of the ELM are also studied at the inboard midplane. The perturbation on the inboard edge appears to be a rapid profile relaxation and recovery. The onset of the inboard profile relaxation is sometimes observed to occur before filaments are seen on the outboard side.

  13. Overview of the Alcator C-MOD Research Program

    SciTech Connect

    S. Scott, A. Bader, M. Bakhtiari, N. Basse, W. Beck, T. Biewer, S. Bernabei, P. Bonoli, et al.

    2007-11-13

    Recent research on the high-field, high-density diverted Alcator C-MOD tokamak has focussed on the plasma physics and plasma engineering required for ITER and for attractive fusion reactors. Experimental campaigns over the past two years have focused on understanding the physical mechanisms that affect the plasma performance realized with all-molybdenum walls versus walls with low-Z coatings. RF sheath rectification along flux tubes that intersect the RF antenna is found to be a major cause of localized boron erosion and impurity generation. Initial lower-hybrid current drive (LHCD) experiments (PLH < 900 kW) have demonstrated fully noninductive current drive at Ιρ ~ 1.0 MA with good efficiency, Ιdrive = 0.4PLH/neoR (MA,MW,1020m-3,m). Disruption mitigation via massive gas-jet impurity puffing has proven successful at high plasma pressure, indicating this technique has promise for implementation on ITER. Pressure gradients in the near SOL of Ohmic L-mode plasmas are observed to scale consistently as Ι 2(over)ρ, and show a significant dependence on X-point topology. Modeling of H-mode edge fueling indicates high self-screening to neutrals in the pedestal and scrape-off layer (SOL), and reproduces experimental density pedestal response to changes in neutral source. Detailed measurements of the temperature and density profiles in the near sol and fast framing movies of the turbulent structures provide improved understanding of the mechanisms that control transport in the edge region.

  14. Scaling of Global LHCD Efficiency in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Scott, S.; Bonoli, P.; Mumgaard, R.; Shiraiwa, S.; Wallace, G.; Whyte, D.

    2014-10-01

    A database of global current-drive efficiency by Lower Hybrid waves has been assembled covering nine years of C-Mod operation. Plasma conditions were averaged over 50-ms time slices during equilibrated current-profile time periods, excluding transient events such as Prad spikes. The database comprises 1800 time slices spanning: PLH < 1 . 1 MW, n|| = 1.5-2.3, Ip = 0.3-1.0 MA, nebar = 0.35-1.5 e20. Nine percent of the data points are approximately non-inductive (ΔV/V >0.9), while 17 percent experience low m,n MHD that degrades the LHCD efficiency. During LHCD, a simple Spitzer model is used to estimate the residual inductively-driven current which scales the pre-LH current by the ratio of the loop voltage to the pre-LH loop voltage, correcting also for the change in conductivity. The current-drive efficiency is defined as η = nebar R ILHCD /PLH [1020 MA/m2 MW], where ILHCD is the current driven by LH waves and PLH is the forward-directed LH power. In approximately non-inductive, MHD-free plasmas, the global current drive efficiency shows a striking positive correlation with plasma current, η = 0.065 + 0.40 x Ip [MA], reaching a value of η = 0.47 at Ip =1.02 MA. A positive but weaker correlation between η and Teo does not explain the η dependence on Ip. Preliminary GENRAY/CQL3D simulations at Ip =1.0 MA predict 900 kA of driven current versus 1000 kA observed. Comparisons of η to numerical simulations over a wide parameter range will be discussed. Work supported by DoE Awards DE-FC02-99ER54512 and DE-AC02-09CH11466.

  15. Double Transport Barrier Experiments on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Wukitch, S. J.

    2001-10-01

    Double transport barrier modes (core and edge barrier) have been observed with intense, off-axis ICRF heating in Alcator C-Mod. An internal transport barrier (ITB) is routinely produced in enhanced D_α H-mode, 4.5 T, sawtoothing discharges with the minority resonance layer r/a ~ -0.5 to the high field side of the magnetic axis during current flat top. The measured density and calculated \\chi_eff (from TRANSP) profiles suggest the central particle and thermal barriers are formed less than one energy confinement time after the H-mode develops. The density, radiation and \\chi_eff profiles indicate that the foot of the barrier is r/a ~ 0.5. Furthermore, the thermal and particle confinement are improved across the entire region inside the barrier. Interestingly, the central toroidal rotation reverses from co-current direction, typical of H-mode plasmas, to the counter-current direction as the density profile becomes more peaked. Typically, increased core impurity radiation, presumably due to improved particle confinement, leads to a barrier collapse after ~ 10 energy confinement times. A BT scan showed that the double barrier mode was accessed for B_T=4.1-4.5 T with the foot of the ITB remaining at r/a ~ 0.5. Importantly, experiments with additional central ICRF heating maintained the double barrier mode for as long as the ICRF was applied ( ~ 6 confinement times). With the application of central heating, the central rotation reversed back to the co-current direction. In addition, the density peaking and impurity accumulation were arrested with the application of the central heating. Thus, the additional central heating appears to provide a means for controlling this mode.

  16. The LHCD Launcher for Alcator C-Mod - Design, Construction, Calibration and Testing

    SciTech Connect

    J. Hosea; D. Beals; W. Beck; S. Bernabei; W. Burke; R. Childs; R. Ellis; E. Fredd; N. Greenough; M. Grimes; D. Gwinn; J. Irby; S. Jurczynski; P. Koert; C.C. Kung; G.D. Loesser; E. Marmar; R. Parker; J. Rushinski; G. Schilling; D. Terry; R. Vieira; J.R. Wilson; J. Zaks

    2005-06-27

    MIT and PPPL have joined together to fabricate a high-power lower hybrid current drive (LHCD) system for supporting steady-state AT regime research on Alcator C-Mod. The goal of the first step of this project is to provide 1.5 MW of 4.6 GHz rf [radio frequency] power to the plasma with a compact launcher which has excellent spectral selectivity and fits into a single C-Mod port. Some of the important design, construction, calibration and testing considerations for the launcher leading up to its installation on C-Mod are presented here.

  17. Overview of the Alcator C-MOD research programme

    NASA Astrophysics Data System (ADS)

    Scott, S.; Bader, A.; Bakhtiari, M.; Basse, N.; Beck, W.; Biewer, T.; Bernabei, S.; Bonoli, P.; Bose, B.; Bravenec, R.; Bespamyatnov, I.; Childs, R.; Cziegler, I.; Doerner, R.; Edlund, E.; Ernst, D.; Fasoli, A.; Ferrara, M.; Fiore, C.; Fredian, T.; Graf, A.; Graves, T.; Granetz, R.; Greenough, N.; Greenwald, M.; Grimes, M.; Grulke, O.; Gwinn, D.; Harvey, R.; Harrison, S.; Hender, T. C.; Hosea, J.; Howell, D. F.; Hubbard, A. E.; Hughes, J. W.; Hutchinson, I.; Ince-Cushman, A.; Irby, J.; Jernigan, T.; Johnson, D.; Ko, J.; Koert, P.; La Bombard, B.; Kanojia, A.; Lin, L.; Lin, Y.; Lipschultz, B.; Liptac, J.; Lynn, A.; MacGibbon, P.; Marmar, E.; Marr, K.; May, M.; Mikkelsen, D. R.; McDermott, R.; Parisot, A.; Parker, R.; Phillips, C. K.; Phillips, P.; Porkolab, M.; Reinke, M.; Rice, J.; Rowan, W.; Sampsell, M.; Schilling, G.; Schmidt, A.; Smick, N.; Smirnov, A.; Snipes, J.; Stotler, D.; Stillerman, J.; Tang, V.; Terry, D.; Terry, J.; Ulrickson, M.; Vieira, R.; Wallace, G.; Whyte, D.; Wilson, J. R.; Wright, G.; Wright, J.; Wolfe, S.; Wukitch, S.; Wurden, G.; Yuh, H.; Zhurovich, K.; Zaks, J.; Zweben, S.

    2007-10-01

    Alcator C-MOD has compared plasma performance with plasma-facing components (PFCs) coated with boron to all-metal PFCs to assess projections of energy confinement from current experiments to next-generation burning tokamak plasmas. Low-Z coatings reduce metallic impurity influx and diminish radiative losses leading to higher H-mode pedestal pressure that improves global energy confinement through profile stiffness. RF sheath rectification along flux tubes that intersect the RF antenna is found to be a major cause of localized boron erosion and impurity generation. Initial lower hybrid current drive (LHCD) experiments (PLH < 900 kW) in preparation for future advanced-tokamak studies have demonstrated fully non-inductive current drive at Ip ~ 1.0 MA with good efficiency, Idrive = 0.4 PLH/neoR (MA, MW, 1020 m-3,m). The potential to mitigate disruptions in ITER through massive gas-jet impurity puffing has been extended to significantly higher plasma pressures and shorter disruption times. The fraction of total plasma energy radiated increases with the Z of the impurity gas, reaching 90% for krypton. A positive major-radius scaling of the error field threshold for locked modes (Bth/B ~ R0.68±0.19) is inferred from its measured variation with BT that implies a favourable threshold value for ITER. A phase contrast imaging diagnostic has been used to study the structure of Alfvén cascades and turbulent density fluctuations in plasmas with an internal transport barrier. Understanding the mechanisms responsible for regulating the H-mode pedestal height is also crucial for projecting performance in ITER. Modelling of H-mode edge fuelling indicates high self-screening to neutrals in the pedestal and scrape-off layer (SOL), and reproduces experimental density pedestal response to changes in neutral source, including a weak variation of pedestal height and constant width. Pressure gradients in the near SOL of Ohmic L-mode plasmas are observed to scale consistently as I_p^2

  18. Twenty Years of Research on the Alcator C-Mod Tokamak

    NASA Astrophysics Data System (ADS)

    Greenwald, Martin

    2013-10-01

    Alcator C-Mod is a compact, high-field tokamak, whose unique design and operating parameters have produced a wealth of new and important results since its start in 1993, contributing data that extended tests of critical physical models into new parameter ranges and into new regimes. Using only RF for heating and current drive with innovative launching structures, C-Mod operates routinely at very high power densities. Research highlights include direct experimental observation of ICRF mode-conversion, ICRF flow drive, demonstration of Lower-Hybrid current drive at ITER-like densities and fields and, using a set of powerful new diagnostics, extensive validation of advanced RF codes. C-Mod spearheaded the development of the vertical-target divertor and has always operated with high-Z metal plasma facing components--an approach adopted for ITER. C-Mod has made ground-breaking discoveries in divertor physics and plasma-material interactions at reactor-like power and particle fluxes and elucidated the critical role of cross-field transport in divertor operation, edge flows and the tokamak density limit. C-Mod developed the I-mode and EDA H-mode regimes which have high performance without large ELMs and with pedestal transport self-regulated by short-wavelength electromagnetic waves. C-Mod has carried out pioneering studies of intrinsic rotation and found that self-generated flow shear can be strong enough to significantly modify transport. C-Mod made the first quantitative link between pedestal temperature and H-mode performance, showing that the observed self-similar temperature profiles were consistent with critical-gradient-length theories and followed up with quantitative tests of nonlinear gyrokinetic models. Disruption studies on C-Mod provided the first observation of non-axisymmetric halo currents and non-axisymmetric radiation in mitigated disruptions. Work supported by U.S. DoE

  19. Design, Engineering, and Testing for the Alcator C-Mod Outer Divertor Upgrade

    NASA Astrophysics Data System (ADS)

    Harrison, S.; Vieira, R.; Lipschultz, B.; Ellis, R.; Karnes, D.; Doody, J.; Zhou, L.; Titus, P.; Zhang, H.; Beck, W.; Granetz, R.

    2012-10-01

    Alcator C-mod's major outer divertor upgrade will enable significant advances in our understanding of reactor relevant physics and operations. Two primary features of the new outer divertor are its toroidally continuous design (electrical and mechanical), and ability to be operated up to or independently heated to 600 C. Full control of the divertor PFC temperature from ambient vessel temperature to 600 C, will enable new and important tokamak research into the temperature dependence of fuel retention, PFC deposition and erosion, and divertor recycling. Significant design, analysis, and testing is underway to complete this important and challenging upgrade, which will provide valuable information for ITER and future reactors. Among other aspects of the innovative approach, the divertor plate supports, halo current shunts, and thermal shield assemblies will be discussed. The divertor supports enable pure radial motion of the divertor ring as it expands thermally and robustness to massive disruption induced electro-mechanical loads. Halo current shunts conduct 400kA in an 8T magnetic field and allow for divertor displacement relative to the vessel. Thermal shielding significantly reduces radiation and conduction to surrounding vessel structures.

  20. Measurement of Type-I ELM Pulse Propagation in Scrape-Off Layer Using Optical System of Motional Stark Effect Diagnostics in JT-60U

    NASA Astrophysics Data System (ADS)

    Suzuki, Takahiro; Oyama, Naoyuki; Asakura, Nobuyuki

    2009-11-01

    Propagation of plasma ejected by type-I ELM has been measured in scrape-off layer (SOL), using optical system of motional Stark effect (MSE) diagnostics in JT-60U as beam emission spectroscopy (BES) diagnostics. This MSE/BES system measures Dalpha emission from heating neutral beam excited by collisions with the ejected plasma, as well as background light (e.g. bremsstrahlung). In order to separate the beam emission and the background light, a two-wavelength detector is introduced into the MSE/BES system The detector observes simultaneously at the same spatial point in two distinct wavelengths using two photomultiplier tubes through two interference filters. One of the filters is adjusted to the central wavelength of the beam emission and the other is outside the beam emission spectrum Subtracting the background light, temporal change in the net beam emission in SOL has been evaluated Comparing conditionally-averaged beam emission with respect to 594 ELMs at 5 spatial channels (0.02-0.3 m outside the main plasma near equatorial plane), radial velocity of the ELM pulse propagation in SOL is about 0.8-1.8 km/s. Work supported by Grand-in-Aid for Young Scientists (B) No. 20760586

  1. 20 years of research on the Alcator C-Mod tokamak

    SciTech Connect

    Greenwald, M.; Baek, S.; Barnard, H.; Beck, W.; Bonoli, P.; Brunner, D.; Burke, W.; Ennever, P.; Ernst, D.; Faust, I.; Fiore, C.; Fredian, T.; Gao, C.; Golfinopoulos, T.; Granetz, R.; Hartwig, Z.; Hubbard, A.; Hughes, J.; Hutchinson, I.; Irby, J.; and others

    2014-11-15

    The object of this review is to summarize the achievements of research on the Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 (1994) and Marmar, Fusion Sci. Technol. 51, 261 (2007)] and to place that research in the context of the quest for practical fusion energy. C-Mod is a compact, high-field tokamak, whose unique design and operating parameters have produced a wealth of new and important results since it began operation in 1993, contributing data that extends tests of critical physical models into new parameter ranges and into new regimes. Using only high-power radio frequency (RF) waves for heating and current drive with innovative launching structures, C-Mod operates routinely at reactor level power densities and achieves plasma pressures higher than any other toroidal confinement device. C-Mod spearheaded the development of the vertical-target divertor and has always operated with high-Z metal plasma facing components—approaches subsequently adopted for ITER. C-Mod has made ground-breaking discoveries in divertor physics and plasma-material interactions at reactor-like power and particle fluxes and elucidated the critical role of cross-field transport in divertor operation, edge flows and the tokamak density limit. C-Mod developed the I-mode and the Enhanced Dα H-mode regimes, which have high performance without large edge localized modes and with pedestal transport self-regulated by short-wavelength electromagnetic waves. C-Mod has carried out pioneering studies of intrinsic rotation and demonstrated that self-generated flow shear can be strong enough in some cases to significantly modify transport. C-Mod made the first quantitative link between the pedestal temperature and the H-mode's performance, showing that the observed self-similar temperature profiles were consistent with critical-gradient-length theories and followed up with quantitative tests of nonlinear gyrokinetic models. RF research highlights include direct experimental

  2. 20 years of research on the Alcator C-Mod tokamaka)

    NASA Astrophysics Data System (ADS)

    Greenwald, M.; Bader, A.; Baek, S.; Bakhtiari, M.; Barnard, H.; Beck, W.; Bergerson, W.; Bespamyatnov, I.; Bonoli, P.; Brower, D.; Brunner, D.; Burke, W.; Candy, J.; Churchill, M.; Cziegler, I.; Diallo, A.; Dominguez, A.; Duval, B.; Edlund, E.; Ennever, P.; Ernst, D.; Faust, I.; Fiore, C.; Fredian, T.; Garcia, O.; Gao, C.; Goetz, J.; Golfinopoulos, T.; Granetz, R.; Grulke, O.; Hartwig, Z.; Horne, S.; Howard, N.; Hubbard, A.; Hughes, J.; Hutchinson, I.; Irby, J.; Izzo, V.; Kessel, C.; LaBombard, B.; Lau, C.; Li, C.; Lin, Y.; Lipschultz, B.; Loarte, A.; Marmar, E.; Mazurenko, A.; McCracken, G.; McDermott, R.; Meneghini, O.; Mikkelsen, D.; Mossessian, D.; Mumgaard, R.; Myra, J.; Nelson-Melby, E.; Ochoukov, R.; Olynyk, G.; Parker, R.; Pitcher, S.; Podpaly, Y.; Porkolab, M.; Reinke, M.; Rice, J.; Rowan, W.; Schmidt, A.; Scott, S.; Shiraiwa, S.; Sierchio, J.; Smick, N.; Snipes, J. A.; Snyder, P.; Sorbom, B.; Stillerman, J.; Sung, C.; Takase, Y.; Tang, V.; Terry, J.; Terry, D.; Theiler, C.; Tronchin-James, A.; Tsujii, N.; Vieira, R.; Walk, J.; Wallace, G.; White, A.; Whyte, D.; Wilson, J.; Wolfe, S.; Wright, G.; Wright, J.; Wukitch, S.; Zweben, S.

    2014-11-01

    The object of this review is to summarize the achievements of research on the Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 (1994) and Marmar, Fusion Sci. Technol. 51, 261 (2007)] and to place that research in the context of the quest for practical fusion energy. C-Mod is a compact, high-field tokamak, whose unique design and operating parameters have produced a wealth of new and important results since it began operation in 1993, contributing data that extends tests of critical physical models into new parameter ranges and into new regimes. Using only high-power radio frequency (RF) waves for heating and current drive with innovative launching structures, C-Mod operates routinely at reactor level power densities and achieves plasma pressures higher than any other toroidal confinement device. C-Mod spearheaded the development of the vertical-target divertor and has always operated with high-Z metal plasma facing components—approaches subsequently adopted for ITER. C-Mod has made ground-breaking discoveries in divertor physics and plasma-material interactions at reactor-like power and particle fluxes and elucidated the critical role of cross-field transport in divertor operation, edge flows and the tokamak density limit. C-Mod developed the I-mode and the Enhanced Dα H-mode regimes, which have high performance without large edge localized modes and with pedestal transport self-regulated by short-wavelength electromagnetic waves. C-Mod has carried out pioneering studies of intrinsic rotation and demonstrated that self-generated flow shear can be strong enough in some cases to significantly modify transport. C-Mod made the first quantitative link between the pedestal temperature and the H-mode's performance, showing that the observed self-similar temperature profiles were consistent with critical-gradient-length theories and followed up with quantitative tests of nonlinear gyrokinetic models. RF research highlights include direct experimental

  3. Measurement of type-I edge localized mode pulse propagation in scrape-off layer using optical system of motional Stark effect diagnostics in JT-60U

    NASA Astrophysics Data System (ADS)

    Suzuki, T.; Oyama, N.; Asakura, N.

    2010-04-01

    Propagation of plasma ejected by type-I edge localized mode (ELM) has been measured in scrape-off layer (SOL) of the JT-60U tokamak, using optical system of motional Stark effect (MSE) diagnostics as beam emission spectroscopy (BES) diagnostics through a new technique developed. This MSE/BES system measures Dα emission from heating neutral beam excited by collisions with the ejected plasma, as well as background light (e.g., bremsstrahlung). While spatio-temporal change in the beam emission gives information on propagation of the ejected plasma, the background light that is observed simultaneously in all spatial channels veils the information. In order to separate the beam emission and the background light, a two-wavelength detector is newly introduced into the MSE/BES system. The detector observes simultaneously at the same spatial point in two distinct wavelengths using two photomultiplier tubes through two interference filters. One of the filters is adjusted to the central wavelength of the beam emission for the MSE diagnostics, and the other is outside the beam emission spectrum. Eliminating the background light, temporal change in the net beam emission in the SOL has been evaluated. Comparing conditionally averaged beam emission with respect to 594 ELMs in a discharge at five spatial channels (0.02-0.3 m outside the main plasma near equatorial plane), radial velocity of the ELM pulse propagation in SOL is evaluated to be 0.8-1.8 km/s (˜1.4 km/s for least-mean-squared fitting).

  4. Real-time sensing and gas jet mitigation of VDEs on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Granetz, R. S.; Wolfe, S. M.; Izzo, V. A.; Reinke, M. L.; Terry, J. L.; Hughes, J. W.; Zhurovich, K.; Whyte, D. G.; Bakhtiari, M.; Wurden, G.

    2006-10-01

    Experiments have been carried out in Alcator C-Mod to test the effectiveness of gas jet disruption mitigation of VDEs with real-time detection and triggering by the C-Mod digital plasma control system (DPCS). The DPCS continuously computes the error in the plasma vertical position from the magnetics diagnostics. When this error exceeds an adjustable preset value, the DPCS triggers the gas jet valve (with a negligible latency time). The high-pressure gas (argon) only takes a few milliseconds to enter the vacuum chamber and begin affecting the plasma, but this is comparable to the VDE timescale on C-Mod. Nevertheless, gas jet injection reduced the halo current, increased the radiated power fraction, and reduced the heating of the divertor compared to unmitigated disruptions, but not quite as well as in earlier mitigation experiments with vertically stable plasmas. Presumably a faster overall response time would be beneficial, and several ways to achieve this will also be discussed.

  5. Anomalous transport in the H-mode pedestal of Alcator C-Mod discharges

    NASA Astrophysics Data System (ADS)

    Pankin, A. Y.; Hughes, J. W.; Greenwald, M. J.; Kritz, A. H.; Rafiq, T.

    2017-02-01

    Anomalous transport in the H-mode pedestal region of five Alcator C-Mod discharges, representing a collisionality scan is analyzed. The understanding of anomalous transport in the pedestal region is important for the development of a comprehensive model for the H-mode pedestal slope. In this research, a possible role of the drift resistive inertial ballooning modes (Rafiq et al 2010 Phys. Plasmas 17 082511) in the edge of Alcator C-Mod discharges is analyzed. The stability analysis, carried out using the TRANSP code, indicates that the DRIBM modes are strongly unstable in Alcator C-Mod discharges with large electron collisionality. An improved interpretive analysis of H-mode pedestal experimental data is carried out utilizing the additive flux minimization technique (Pankin et al 2013 Phys. Plasmas 20 102501) together with the guiding-center neoclassical kinetic XGC0 code. The neoclassical and neutral physics are simulated in the XGC0 code and the anomalous fluxes are computed using the additive flux minimization technique. The anomalous fluxes are reconstructed and compared with each other for the collisionality scan Alcator C-Mod discharges. It is found that the electron thermal anomalous diffusivities at the pedestal top increase with the electron collisionality. This dependence can also point to the drift resistive inertial ballooning modes as the modes that drive the anomalous transport in the plasma edge of highly collisional discharges.

  6. Transverse stability in a Stark decelerator

    SciTech Connect

    Meerakker, Sebastiaan Y. T. van de; Bethlem, Hendrick L.; Vanhaecke, Nicolas; Meijer, Gerard

    2006-02-15

    The concept of phase stability in a Stark decelerator ensures that polar molecules can be accelerated, guided, or decelerated without loss; molecules within a certain position and velocity interval are kept together throughout the deceleration process. In this paper the influence of the transverse motion on phase stability in a Stark decelerator is investigated. For typical deceleration experiments--i.e., for high values of the phase angle {phi}{sub 0}--the transverse motion considerably enhances the region in phase space for which phase stable deceleration occurs. For low values of {phi}{sub 0}, however, the transverse motion reduces the acceptance of a Stark decelerator and unstable regions in phase space appear. These effects are quantitatively explained in terms of a coupling between the longitudinal and transverse motion. The predicted longitudinal acceptance of a Stark decelerator is verified by measurements on a beam of OH (X {sup 2}{pi}{sub 3/2},J=3/2) radicals passing through a Stark decelerator.

  7. Analysis of Runaway Electron Synchrotron Radiation in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Tinguely, R. A.; Granetz, R. S.

    2015-11-01

    In Alcator C-Mod, runaway electron (RE) beams can reach energies of ~30 MeV or higher, emitting synchrotron radiation in the visible wavelength range. Two spectrometers, with spectral ranges of 350-1020 nm and resolutions of ~4 nm, have been installed and absolutely calibrated on C-Mod to observe this emission. Recent theoretical work predicts that the RE distribution tends toward a mono-energetic bump as the synchrotron radiation and collisional friction balance the electric force. Our analysis of RE synchrotron spectra shows that it is possible to distinguish the emission of a mono-energetic and mono-pitch beam from that of a distribution of energies and pitch angles (as calculated in). Preliminary results indicate that the mono-energetic bump is formed as predicted, instead of a broader distribution. Supported by US DoE award DE-FC02-99ER54512.

  8. Analysis of Runaway Electron Synchrotron Emission in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Tinguely, A.; Granetz, R.; Stahl, A.

    2016-10-01

    Alcator C-Mod's high magnetic field allows relativistic ``runaway'' electron (RE) synchrotron radiation (SR) to be observed in the visible wavelength range. Our aim is to determine the evolution of the RE energy distribution function, current, and density from measured SR spectra, providing insight into basic plasma physics as well as mitigation for fusion devices. Recent theoretical studies predict that the SR reaction force and collisional friction will balance the electric force, forming a ``bump'' on the tail of the energy distribution. However, both mono-energetic and monotonically-decreasing distributions fit the experimental data equally well. The COllisonal Distribution of Electrons code is applied to C-Mod RE discharges and compared to experiment. In addition, a scan in magnetic field from 2.7 - 8 T explores the importance of SR as a power loss mechanism and limit on the maximum RE energy. Supported by USDoE Award DE-FC02-99ER54512.

  9. Collisionality Dependence of Multi-species Density Peaking in Turbulence Simulations of C-Mod Plasmas

    NASA Astrophysics Data System (ADS)

    Mikkelsen, D. R.; Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Greenwald, M.; Howard, N.; Podpaly, Y.; Reinke, M.; Rice, J. E.; Hughes, J. W.; Ma, Y.; Candy, J.; Waltz, R. E.

    2012-10-01

    In nonlinear GYRO simulations of C-Mod plasmas, a turbulently driven pinch produces modest density peaking of all species. The ratio of density at r/a=0.44 and 0.74 is 1.2 for the majority and minority D & H (and electrons), and increases with impurity Z: 1.1 for helium, 1.15 for boron, 1.29 for neon, 1.36 for argon, 1.47 for molybdenum. Density peaking is only weakly affected when the ion temperature profile is varied to align the predicted heat flux to the experimental transport analysis. New simulations will extend the collisionality to the lower part of the experimentally accessible range in C-Mod to study the collisionality dependence of density peaking, and to establish whether much stronger peaking is predicted for lower collisionalities. Simulations based on measured I-mode ion and electron temperature profiles will also be presented.

  10. Observation of Co and Counter Rotation Produced by Lower Hybrid Waves in Alcator C-Mod

    SciTech Connect

    Parker, R. R.; Podpaly, Y.; Lee, J.; Reinke, M. L.; Rice, J. E.; Bonoli, P. T.; Meneghini, O.; Shiraiwa, S.; Wallace, G. M.; Wilson, J. R.

    2011-12-23

    Lower hybrid waves launched uni-directionally into tokamak plasmas impart momentum to the electrons. This momentum can be transferred to the ions, leading to substantial counter current rotation. Observations of LH-induced counter rotation have been previously reported [1], and the initial rate of increase has been found to be consistent with the calculated rate of wave momentum injection [2]. However, in recent experiments in Alcator C-Mod it has been found that application of LH waves to relatively low current (I{sub p}{approx}0.4-0.6 MA) plasmas can result in a co-current change of rotation, which implies a different mechanism than that described above. This appears to be linked to the so-called intrinsic rotation commonly observed in Alcator C-Mod and other tokamaks [3]. In addition to the change in direction at low current, some dependence on the magnetic configuration (USL vs. LSN) has been observed.

  11. Alcator C-Mod: research in support of ITER and steps beyond

    NASA Astrophysics Data System (ADS)

    Marmar, E. S.; Baek, S. G.; Barnard, H.; Bonoli, P.; Brunner, D.; Candy, J.; Canik, J.; Churchill, R. M.; Cziegler, I.; Dekow, G.; Delgado-Aparicio, L.; Diallo, A.; Edlund, E.; Ennever, P.; Faust, I.; Fiore, C.; Gao, Chi; Golfinopoulos, T.; Greenwald, M.; Hartwig, Z. S.; Holland, C.; Hubbard, A. E.; Hughes, J. W.; Hutchinson, I. H.; Irby, J.; LaBombard, B.; Lin, Yijun; Lipschultz, B.; Loarte, A.; Mumgaard, R.; Parker, R. R.; Porkolab, M.; Reinke, M. L.; Rice, J. E.; Scott, S.; Shiraiwa, S.; Snyder, P.; Sorbom, B.; Terry, D.; Terry, J. L.; Theiler, C.; Vieira, R.; Walk, J. R.; Wallace, G. M.; White, A.; Whyte, D.; Wolfe, S. M.; Wright, G. M.; Wright, J.; Wukitch, S. J.; Xu, P.

    2015-10-01

    This paper presents an overview of recent highlights from research on Alcator C-Mod. Significant progress has been made across all research areas over the last two years, with particular emphasis on divertor physics and power handling, plasma-material interaction studies, edge localized mode-suppressed pedestal dynamics, core transport and turbulence, and RF heating and current drive utilizing ion cyclotron and lower hybrid tools. Specific results of particular relevance to ITER include: inner wall SOL transport studies that have led, together with results from other experiments, to the change of the detailed shape of the inner wall in ITER; runaway electron studies showing that the critical electric field required for runaway generation is much higher than predicted from collisional theory; core tungsten impurity transport studies reveal that tungsten accumulation is naturally avoided in typical C-Mod conditions.

  12. Evidence for Chaotic Edge Turbulence in the Alcator C-Mod Tokamak

    NASA Astrophysics Data System (ADS)

    Zhu, Ziyan; White, Anne; Carter, Troy; Terry, Jim; Baek, Seung Gyou

    2016-10-01

    Turbulence greatly reduces the confinement time of magnetic-confined plasmas; understanding the nature of this turbulence and the associated transport is therefore of great importance. This research seeks to establish whether turbulent fluctuations in Alcator C-Mod are chaotic or stochastic. This has an important impact on transport caused by turbulence in C-Mod: stochastic fluctuations sample all of phase space and can lead to diffusive transport, whereas chaotic fluctuations live in a restricted phase space (e.g. on attractors) and a diffusive description may not be valid. By analyzing the time series from an O-Mode reflectometer, turbulent edge density fluctuations in Ohmic plasmas and L-mode plasmas in the Alcator C-Mod tokamak are shown to be chaotic. Supporting evidence for chaos in the edge region includes: the observation of an exponential power spectra (which is associated with Lorentzian-shaped pulses in the time series) and the location of the signal in the Complexity-Entropy plane (C-H plane) and its corresponding Brandt-Pompe (BP) probability distribution. These analysis techniques will be briefly introduced along with a discussion of the analysis results. Different diagnostic techniques, such as Gas Puff Imaging (GPI), could be used to confirm the results. Work supported by the U.S. Department of Energy Office of Science under Agreement DE-FC02-99ER54512 and DE-FC02-07ER54918:011.

  13. Long Term Retention of Deuterium and Tritium in Alcator C-Mod

    SciTech Connect

    FIORE,C.; LABOMBARD,B.; LIPSCHULTZ,B.; PITCHER,C.S.; SKINNER,C.H.; WAMPLER,WILLIAM R.

    1999-11-03

    We estimate the total in-vessel deuterium retention in Alcator C-Mod from a run campaign of about 1090 plasmas. The estimate is based on measurements of deuterium retained on 22 molybdenum tiles from the inner wall and divertor. The areal density of deuterium on the tiles was measured by nuclear reaction analysis. From these data, the in-vessel deuterium inventory is estimated to be about 0.1 gram, assuming the deuterium coverage is toroidally symmetric. Most of the retained deuterium is on the walls of the main plasma chamber, only about 2.5% of the deuterium is in the divertor. The D coverage is consistent with a layer saturated by implantation with ions and charge-exchange neutrals from the plasma. This contrasts with tokamaks with carbon plasma-facing components (PFC's) where long-term retention of tritium and deuterium is large and mainly in the divertor due to codeposition with carbon eroded by the plasma. The low deuterium retention in the C-Mod divertor is mainly due to the absence of carbon PFC's in C-Mod and the low erosion rate of Mo.

  14. Experiments and Simulations of ITER-like Plasmas in Alcator C-Mod

    SciTech Connect

    .R. Wilson, C.E. Kessel, S. Wolfe, I.H. Hutchinson, P. Bonoli, C. Fiore, A.E. Hubbard, J. Hughes, Y. Lin, Y. Ma, D. Mikkelsen, M. Reinke, S. Scott, A.C.C. Sips, S. Wukitch and the C-Mod Team

    2010-09-24

    Alcator C-Mod is performing ITER-like experiments to benchmark and verify projections to 15 MA ELMy H-mode Inductive ITER discharges. The main focus has been on the transient ramp phases. The plasma current in C-Mod is 1.3 MA and toroidal field is 5.4 T. Both Ohmic and ion cyclotron (ICRF) heated discharges are examined. Plasma current rampup experiments have demonstrated that (ICRF and LH) heating in the rise phase can save voltseconds (V-s), as was predicted for ITER by simulations, but showed that the ICRF had no effect on the current profile versus Ohmic discharges. Rampdown experiments show an overcurrent in the Ohmic coil (OH) at the H to L transition, which can be mitigated by remaining in H-mode into the rampdown. Experiments have shown that when the EDA H-mode is preserved well into the rampdown phase, the density and temperature pedestal heights decrease during the plasma current rampdown. Simulations of the full C-Mod discharges have been done with the Tokamak Simulation Code (TSC) and the Coppi-Tang energy transport model is used with modified settings to provide the best fit to the experimental electron temperature profile. Other transport models have been examined also. __________________________________________________

  15. Multi-channel transport experiments at Alcator C-Mod and comparison with gyrokinetic simulationsa)

    NASA Astrophysics Data System (ADS)

    White, A. E.; Howard, N. T.; Greenwald, M.; Reinke, M. L.; Sung, C.; Baek, S.; Barnes, M.; Candy, J.; Dominguez, A.; Ernst, D.; Gao, C.; Hubbard, A. E.; Hughes, J. W.; Lin, Y.; Mikkelsen, D.; Parra, F.; Porkolab, M.; Rice, J. E.; Walk, J.; Wukitch, S. J.; Team, Alcator C-Mod

    2013-05-01

    Multi-channel transport experiments have been conducted in auxiliary heated (Ion Cyclotron Range of Frequencies) L-mode plasmas at Alcator C-Mod [Marmar and Alcator C-Mod Group, Fusion Sci. Technol. 51(3), 3261 (2007)]. These plasmas provide good diagnostic coverage for measurements of kinetic profiles, impurity transport, and turbulence (electron temperature and density fluctuations). In the experiments, a steady sawtoothing L-mode plasma with 1.2 MW of on-axis RF heating is established and density is scanned by 20%. Measured rotation profiles change from peaked to hollow in shape as density is increased, but electron density and impurity profiles remain peaked. Ion or electron heat fluxes from the two plasmas are the same. The experimental results are compared directly to nonlinear gyrokinetic theory using synthetic diagnostics and the code GYRO [Candy and Waltz, J. Comput. Phys. 186, 545 (2003)]. We find good agreement with experimental ion heat flux, impurity particle transport, and trends in the fluctuation level ratio (T˜e/Te)/(n ˜e/ne), but underprediction of electron heat flux. We find that changes in momentum transport (rotation profiles changing from peaked to hollow) do not correlate with changes in particle transport, and also do not correlate with changes in linear mode dominance, e.g., Ion Temperature Gradient versus Trapped Electron Mode. The new C-Mod results suggest that the drives for momentum transport differ from drives for heat and particle transport. The experimental results are inconsistent with present quasilinear models, and the strong sensitivity of core rotation to density remains unexplained.

  16. Perturbative thermal diffusivity from partial sawtooth crashes in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Creely, A. J.; White, A. E.; Edlund, E. M.; Howard, N. T.; Hubbard, A. E.

    2016-03-01

    Perturbative thermal diffusivity has been measured on Alcator C-Mod via the use of the extended-time-to-peak method on heat pulses generated by partial sawtooth crashes. Perturbative thermal diffusivity governs the propagation of heat pulses through a plasma. It differs from power balance thermal diffusivity, which governs steady state thermal transport. Heat pulses generated by sawtooth crashes have been used extensively in the past to study heat pulse thermal diffusivity (Lopes Cardozo 1995 Plasma Phys. Control. Fusion 37 799), but the details of the sawtooth event typically lead to non-diffusive ‘ballistic’ transport, making them an unreliable measure of perturbative diffusivity on many tokamaks (Fredrickson et al 2000 Phys. Plasmas 7 5051). Partial sawteeth are common on numerous tokamaks, and generate a heat pulse without the ‘ballistic’ transport that often accompanies full sawteeth (Fredrickson et al 2000 Phys. Plasmas 7 5051). This is the first application of the extended-time-to-peak method of diffusivity calculation (Tubbing et al 1987 Nucl. Fusion 27 1843) to partial sawtooth crashes. This analysis was applied to over 50 C-Mod shots containing both L- and I-Mode. Results indicate correlations between perturbative diffusivity and confinement regime (L- versus I-mode), as well as correlations with local temperature, density, the associated gradients, and gradient scale lengths (a/L Te and a/L n ). In addition, diffusivities calculated from partial sawteeth are compared to perturbative diffusivities calculated with the nonlinear gyrokinetic code GYRO. We find that standard ion-scale simulations (ITG/TEM turbulence) under-predict the perturbative thermal diffusivity, but new multi-scale (ITG/TEM coupled with ETG) simulations can match the experimental perturbative diffusivity within error bars for an Alcator C-Mod L-mode plasma. Perturbative diffusivities extracted from heat pulses due to partial sawteeth provide a new constraint that can be used to

  17. Advances in lower hybrid current drive technology on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Wallace, G. M.; Shiraiwa, S.; Hillairet, J.; Preynas, M.; Beck, W.; Casey, J. A.; Doody, J.; Faust, I. C.; Fitzgerald, E.; Johnson, D. K.; Kanojia, A. D.; Koert, P.; Lau, C.; Lin, Y.; Leccacorvi, R.; MacGibbon, P.; Meneghini, O.; Murray, R.; Parker, R. R.; Terry, D. R.; Vieira, R.; Wilson, J. R.; Wukitch, S.; Zhou, L.

    2013-07-01

    Lower hybrid current drive (LHCD) is an attractive option for non-inductive tokamak operation due to its high current drive efficiency and ability to drive current off axis. The parameters of the Alcator C-Mod LHCD system (f0 = 4.6 GHz, Bφ ≃ 5.5 T, \\bar{n}_\\rme \\simeq 10^{20}\\,m^{-3} ) are similar to the proposed LHCD system on ITER. This paper will describe improvements in LHCD technology on C-Mod designed to increase single-pass absorption at high \\bar{n}_\\rme , extend pulse length (to >3 s), and increase power delivered to the plasma (to ∼2 MW). Modelling of lower hybrid (LH) wave propagation indicates that the observed loss of LHCD efficiency at higher \\bar{n}_\\rme can be mitigated by enhancing the single pass power absorption through use of an off mid-plane launcher. The four rows of the launcher are located above the mid-plane (with Ip and Bφ both clockwise viewing from the top down) in order to exploit the poloidal upshift of n‖ as rays propagate from the antenna into the plasma. The transmitter protection system (TPS) was redesigned to model the coolant temperature in real time and shut off the klystron beam voltage if the coolant is close to boiling. The TPS upgrade has been installed and operated on C-Mod for pulses up to 4.5 s into dummy loads and 1.0 s into the plasma. A new movable local LH launcher protection limiter was designed to reduce reflection coefficients across a wide range of launcher positions. Finally, a high power waveguide double-stub tuner is under development to provide feedback controlled load matching to reduce power reflected from the antenna under poor coupling conditions.

  18. Multi-channel transport experiments at Alcator C-Mod and comparison with gyrokinetic simulations

    SciTech Connect

    White, A. E.; Howard, N. T.; Greenwald, M.; Reinke, M. L.; Sung, C.; Baek, S.; Barnes, M.; Dominguez, A.; Ernst, D.; Gao, C.; Hubbard, A. E.; Hughes, J. W.; Lin, Y.; Parra, F.; Porkolab, M.; Rice, J. E.; Walk, J.; Wukitch, S. J.; Team, Alcator C-Mod; Candy, J.; and others

    2013-05-15

    Multi-channel transport experiments have been conducted in auxiliary heated (Ion Cyclotron Range of Frequencies) L-mode plasmas at Alcator C-Mod [Marmar and Alcator C-Mod Group, Fusion Sci. Technol. 51(3), 3261 (2007)]. These plasmas provide good diagnostic coverage for measurements of kinetic profiles, impurity transport, and turbulence (electron temperature and density fluctuations). In the experiments, a steady sawtoothing L-mode plasma with 1.2 MW of on-axis RF heating is established and density is scanned by 20%. Measured rotation profiles change from peaked to hollow in shape as density is increased, but electron density and impurity profiles remain peaked. Ion or electron heat fluxes from the two plasmas are the same. The experimental results are compared directly to nonlinear gyrokinetic theory using synthetic diagnostics and the code GYRO [Candy and Waltz, J. Comput. Phys. 186, 545 (2003)]. We find good agreement with experimental ion heat flux, impurity particle transport, and trends in the fluctuation level ratio (T(tilde sign){sub e}/T{sub e})/(ñ{sub e}/n{sub e}), but underprediction of electron heat flux. We find that changes in momentum transport (rotation profiles changing from peaked to hollow) do not correlate with changes in particle transport, and also do not correlate with changes in linear mode dominance, e.g., Ion Temperature Gradient versus Trapped Electron Mode. The new C-Mod results suggest that the drives for momentum transport differ from drives for heat and particle transport. The experimental results are inconsistent with present quasilinear models, and the strong sensitivity of core rotation to density remains unexplained.

  19. Two-dimensional full-wave simulation of microwave reflectometry on Alcator C-Mod

    SciTech Connect

    Lin, Y.; Irby, J. H.; Nazikian, R.; Marmar, E. S.; Mazurenko, A.

    2001-01-01

    A new two-dimensional full-wave code has been developed to simulate ordinary (O) mode reflectometry signals caused by plasma density fluctuations. The code uses the finite-difference time-domain method with a perfectly matched layer absorption boundary to solve Maxwell's equations. Huygens wave sources are incorporated to generate Gaussian beams. The code has been used to simulate the reflectometer measurement of the quasicoherent mode (60--250 kHz) associated with enhanced D{sub {alpha}} (EDA) H modes in the Alcator C-Mod tokamak. It is found that an analysis of the realistic experimental layout is essential for the quantitative interpretation of the mode amplitude.

  20. Edge temperature gradient as intrinsic rotation drive in Alcator C-Mod tokamak plasmas.

    PubMed

    Rice, J E; Hughes, J W; Diamond, P H; Kosuga, Y; Podpaly, Y A; Reinke, M L; Greenwald, M J; Gürcan, Ö D; Hahm, T S; Hubbard, A E; Marmar, E S; McDevitt, C J; Whyte, D G

    2011-05-27

    Intrinsic rotation has been observed in I-mode plasmas from the C-Mod tokamak, and is found to be similar to that in H mode, both in its edge origin and in the scaling with global pressure. Since both plasmas have similar edge ∇T, but completely different edge ∇n, it may be concluded that the drive of the intrinsic rotation is the edge ∇T rather than ∇P. Evidence suggests that the connection between gradients and rotation is the residual stress, and a scaling for the rotation from conversion of free energy to macroscopic flow is calculated.

  1. Simulated plasma facing component measurements for an in situ surface diagnostic on Alcator C-Mod

    SciTech Connect

    Hartwig, Z. S.; Whyte, D. G.

    2010-10-15

    The ideal in situ plasma facing component (PFC) diagnostic for magnetic fusion devices would perform surface element and isotope composition measurements on a shot-to-shot ({approx}10 min) time scale with {approx}1 {mu}m depth and {approx}1 cm spatial resolution over large areas of PFCs. To this end, the experimental adaptation of the customary laboratory surface diagnostic - nuclear scattering of MeV ions - to the Alcator C-Mod tokamak is being guided by ACRONYM, a Geant4 synthetic diagnostic. The diagnostic technique and ACRONYM are described, and synthetic measurements of film thickness for boron-coated PFCs are presented.

  2. Quasi-coherent fluctuations limiting the pedestal growth on Alcator C-Mod: Experiment and modelling

    SciTech Connect

    Diallo, A.; Hughes, J. W.; Baek, S. -G.; LaBombard, Brian; Terry, J.; Cziegler, I.; Hubbard, A.; Davis, E.; Walk, J.; Delgado-Aparicio, L.; Reinke, M. L.; Theiler, C.; Churchhill, R. M.; Edlund, E. M.; Canik, John; Snyder, P.; Greenwald, M.; White, A.

    2015-04-09

    Performance predictions for future fusion devices rely on an accurate model of the pedestal structure. The candidate for predictive pedestal structure is EPED, and it is imperative to test the underlying hypotheses to further gain confidence for ITER projections. Here, we present experimental work testing one of the EPED hypotheses, namely the existence of a soft limit set by microinstabilities such as the kinetic ballooning mode. Furthermore, this work extends recent work on Alactor C-Mod (Diallo et al 2014 Phys. Rev. Lett. 112 115001), to include detailed measurements of the edge fluctuations and comparisons of edge simulation codes and experimental observations.

  3. Novel energy resolving x-ray pinhole camera on Alcator C-Mod

    SciTech Connect

    Pablant, N. A.; Delgado-Aparicio, L.; Bitter, M.; Ellis, R.; Hill, K. W.; Brandstetter, S.; Eikenberry, E.; Hofer, P.; Schneebeli, M.

    2012-10-15

    A new energy resolving x-ray pinhole camera has been recently installed on Alcator C-Mod. This diagnostic is capable of 1D or 2D imaging with a spatial resolution of Almost-Equal-To 1 cm, an energy resolution of Almost-Equal-To 1 keV in the range of 3.5-15 keV and a maximum time resolution of 5 ms. A novel use of a Pilatus 2 hybrid-pixel x-ray detector [P. Kraft et al., J. Synchrotron Rad. 16, 368 (2009)] is employed in which the lower energy threshold of individual pixels is adjusted, allowing regions of a single detector to be sensitive to different x-ray energy ranges. Development of this new detector calibration technique was done as a collaboration between PPPL and Dectris Ltd. The calibration procedure is described, and the energy resolution of the detector is characterized. Initial data from this installation on Alcator C-Mod is presented. This diagnostic provides line-integrated measurements of impurity emission which can be used to determine impurity concentrations as well as the electron energy distribution.

  4. Fast imaging of filaments in the X-point region of Alcator C-Mod

    DOE PAGES

    Terry, J. L.; Ballinger, S.; Brunner, D.; ...

    2017-01-27

    A rich variety of field-aligned fluctuations has been revealed using fast imaging of Dα emission from Alcator C-Mod's lower X-point region. Field-aligned filamentary fluctuations are observed along the inner divertor leg, within the Private-Flux-Zone (PFZ), in the Scrape-Off Layer (SOL) outside the outer divertor leg, and, under some conditions, at or above the X-point. The locations and dynamics of the filaments in these regions are strikingly complex in C-Mod. Changes in the filaments’ generation appear to be ordered by plasma density and magnetic configuration. Filaments are not observed for plasmas with n/nGreenwald ≲ 0.12 nor are they observed in Uppermore » Single Null configurations. In a Lower Single Null with 0.12 ≲ n/nGreenwald ≲ 0.45 and Bx∇B directed down, filaments typically move up the inner divertor leg toward the X-point. Reversing the field direction results in the appearance of filaments outside of the outer divertor leg. With the divertor targets “detached”, filaments inside the LCFS are seen. Lastly, these studies were motivated by observations of filaments in the X-point and PFZ regions in MAST, and comparisons with those observations are made.« less

  5. Comparison of Small ELM Characteristics and Regimes in Alcator C-Mod, MAST, and NSTX

    SciTech Connect

    Maingi, Rajesh; Hubbard, A.E.; Meyer, H.; Kirk, A.; Maqueda, R.; Terry, J. L.

    2011-01-01

    We report on the status of a set of ITPA-coordinated experiments between the Alcator C-Mod, MAST and NSTX devices to compare the characteristics and access conditions of discharges with small edge-localized modes (ELMs). The small ELMs in C-Mod, MAST and one of the two small ELM types in NSTX exist when {beta}{sub ped}{sup pol} approached 10-15%, although the lower/upper limits of the operational windows differ. These small ELM regimes appear in diverted configurations very close to balanced double-null in each device. We classify these small ELMs as type II, based on the published characteristics from a number of previous studies. In addition, these type II ELMs in each device had multiple filaments with propagation in the co-I{sub p} or ion diamagnetic drift direction. Moreover, we conclude that these type II ELMs are distinct from the type V ELMs routinely observed in NSTX, which have one or two filaments and propagate in the electron diamagnetic drift direction.

  6. Access to and performance of I-mode plasmas on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Hubbard, A. E.; Wolfe, S. M.; Baek, S.-G.; Churchill, R. M.; Howard, N.; Hughes, J. W.; Lin, Y.; Marmar, E. S.; Reinke, M. L.; Rice, J. E.; Terry, J. L.; Theiler, C.; Walk, J. R.; White, A. E.; Whyte, D. G.; Wukitch, S. J.; Cziegler, I.

    2013-10-01

    The I-mode regime of operation features an edge thermal transport barrier, without a particle barrier. Stationary conditions are thus achieved without impurity accumulation, and usually without ELMs. In contrast to the EDA H-mode regime on Alcator C-Mod, it is readily accessed at low q95 and low collisionality, both relevant for ITER. Analysis of a dataset of 400 discharges at q95 ~ 3 shows normalized energy confinement in I-modes reaches or exceeds that in most H-modes, up to H98 = 1.2. Confinement and pedestal temperature increase with input power. In some cases I-mode is maintained up to the maximum available power (5 MW ICRF) while in others a transition to H-mode limits the performance. Understanding and extending the conditions for entering and staying in I-mode is thus critical for extrapolation of the regime. Experiments have extended the regime both to lower densities and to higher densities and powers through gas puffing into established I-modes. Results from an expanded database of C-Mod discharges will be presented, along with details of I-mode profiles and fluctuations, including GAMs and a weakly coherent mode, which are providing insights into the physics of the regime. Supported by DOE award DE-FC02-99ER54512.

  7. I-mode access and transitions in an expanded operating space on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Hubbard, A. E.; Baek, S.-G.; Churchill, R. M.; Golfinopoulos, T.; Hughes, J. W.; Lin, Y.; Marmar, E. S.; Terry, J. L.; Theiler, C.; Walk, J. R.; White, A. E.; Whyte, D. G.; Wolfe, S. M.; Wukitch, S. J.; Cziegler, I.; Edlund, E.

    2014-10-01

    New experiments in the I-mode regime on Alcator C-Mod have further expanded the wide range of conditions over which it has been studied. I-mode is attractive in that it combines the high energy confinement of H-mode, up to H98 = 1.2, with the low particle/impurity confinement of L-Mode. Accessing and maintaining the regime, without transitions to L-mode or H-mode, is key to its extrapolation. The most robust conditions on C-Mod have been in lower null plasmas with unfavorable drift and BT of 5-6 T, spanning the ITER value. In 2014, experiments at 2.8 T showed that the power range between L-I and I-H transitions was significantly lower, consistent with results on DIII-D and AUG. I-mode was also accessed in near double null. Fueling into I-modes can raise the density, up to 2×1020 m-3. The upper ne increases with input power. Local pedestal parameters and evolution of turbulence at transitions are being assessed with the aim of understanding the physical mechanisms and for extrapolation. Supported by DOE Award DE-FC02-99ER54512.

  8. A new interferometry-based electron density fluctuation diagnostic on Alcator C-Mod.

    PubMed

    Kasten, C P; Irby, J H; Murray, R; White, A E; Pace, D C

    2012-10-01

    The two-color interferometry diagnostic on the Alcator C-Mod tokamak has been upgraded to measure fluctuations in the electron density and density gradient for turbulence and transport studies. Diagnostic features and capabilities are described. In differential mode, fast phase demodulation electronics detect the relative phase change between ten adjacent, radially-separated (ΔR = 1.2 cm, adjustable), vertical-viewing chords, which allows for measurement of the line-integrated electron density gradient. The system can be configured to detect the absolute phase shift of each chord by comparison to a local oscillator, measuring the line-integrated density. Each chord is sensitive to density fluctuations with k(R) < 20.3 cm(-1) and is digitized at up to 10 MS/s, resolving aspects of ion temperature gradient-driven modes and other long-wavelength turbulence. Data from C-Mod discharges is presented, including observations of the quasi-coherent mode in enhanced D-alpha H-mode plasmas and the weakly coherent mode in I-mode.

  9. Characterization of the Pedestal in I-Mode Plasmas on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Walk, J. R.; Hughes, J. W.; Terry, J. L.; Hubbard, A. E.; Whyte, D. G.; White, A. E.; Marmar, E. S.; Rice, J. E.; Churchill, R. M.; Theiler, C.; Labombard, B.; Brunner, D.; Reinke, M. L.; Dominguez, A.; Sung, C.

    2012-10-01

    I-mode is an improved energy confinement regime on C-Mod, notably featuring an edge temperature pedestal without the accompanying density pedestal found in H-mode operation. I-mode has been shown to be capable of stationary operation, with the mode sustained for ˜10 energy confinement times, and to have a pedestal naturally lacking large ELMs. Combined with comparable performance to H-mode operation and weaker degradation with input power, this makes I-modes potentially favorable as a reactor regime. A full characterization using the suite of high-resolution edge diagnostics on C-Mod of the pedestal in reversed-field, lower-single-null I-modes (therefore with the ion ∇B drift away from the x-point) is presented here. The presented discharges primarily feature detailed scans of plasma current and ICRF heating power at several density values. The pedestal structure found in these I-modes is also contrasted with previous studies of the pedestal in EDA and ELMy H-modes, particularly potential scalings with βp,ped consistent with the KBM-limited pedestals found in these H-modes.

  10. Perturbative Thermal Transport Studies on Alcator C-Mod and ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Creely, A. J.; White, A. E.; Edlund, E. M.; Howard, N. T.; Hubbard, A. E.; Ryter, F.

    2015-11-01

    Perturbative thermal diffusivity has been measured on Alcator C-Mod and ASDEX Upgrade via the extended-time-to-peak method with heat pulses generated by partial sawtooth crashes. Heat pulses generated by sawtooth crashes have been used extensively in the past to study perturbative diffusivity, but the details of the sawtooth event lead to non-diffusive ``ballistic'' transport, invalidating their use for measuring perturbative diffusivity. Partial sawteeth generate a heat pulse without the ballistic transport of full sawteeth [Fredrickson 2000]. Partial sawtooth analysis was applied to over 50 C-Mod shots containing both L- and I-Mode, as well as ASDEX Upgrade plasmas, though partial sawteeth were less common on AUG. Results indicate correlations between perturbative diffusivity and confinement regime (L- vs. I-mode), as well as correlations with local temperature, density, the associated gradients, and gradient scale lengths (a/LTe and a/Ln). Finally, diffusivities calculated from partial sawteeth were compared to perturbative diffusivities calculated with the GYRO gyrokinetic code, leading to quantitative agreement with multi-scale GYRO simulations. This work is supported by the US DOE under grants DE-SC0006419 and DE-FC02-99ER54512-CMOD.

  11. Transport and Stability in C-Mod ITBs in Diverse Regimes

    NASA Astrophysics Data System (ADS)

    Fiore, C. L.; Ernst, D. R.; Howard, N. T.; Kasten, C. P.; Mikkelsen, D.; Reinke, M. L.; Rice, J. E.; White, A. E.; Rowan, W. L.; Bespamyatnov, I.

    2012-10-01

    Internal Transport Barriers (ITBs) in C-Mod feature highly peaked density and pressure profiles and are typically induced by the introduction of radio frequency power in the ion cyclotron range of frequencies (ICRF) with the second harmonic of the resonance for minority hydrogen ions positioned off-axis at the plasma half radius on either the low or high field side of the plasma. These ITBs are formed in the absence of particle or momentum injection, and with monotonic q profiles with qmin< 1. Thus they allow exploration of ITB dynamics in a reactor relevant regime. Recently, linear and non-linear gyrokinetic simulations have demonstrated that changes in the ion temperature and plasma rotation profiles, coincident with the application of off-axis ICRF heating, contribute to greater stability to ion temperature gradient driven fluctuation in the plasma. This results in reduced turbulent driven outgoing heat flux. To date, ITB formation in C-Mod has only been observed in EDA H-mode plasmas with moderate (2-3 MW) ICRF power. Experiments to explore the formation of ITBs in other operating regimes such as I-mode and also with high ICRF power are being undertaken to understand further the process of ITB formation and sustainment, especially with regard to turbulent driven transport.

  12. Edge Ion Velocity Measurements with a Novel Doppler Spectrometer at the Alcator C-Mod Tokamak

    NASA Astrophysics Data System (ADS)

    Graf, Alexander; May, Mark; Beiersdorfer, Peter; Terry, Jim

    2006-10-01

    A high throughput, f/# ˜3.1, transmission grating Doppler spectrometer for visible light (3500-6700 å) is currently measuring ion or neutral velocities and temperatures at the Alcator C-Mod tokamak. The ion velocities are measured through the Doppler shift of impurities that are present in the plasma. A line width of as small as 0.4 å(velocity sensitivity of ˜10^5 cm/s) has been measured using calibration lamps. The spectrometer is fiber optically coupled and has access to toroidal and poloidal views. A spectral survey has been done with various views of the C-Mod plasma identifying various intrinsic impurities. The first Doppler measurements of B II were recorded with ˜15 ms per frame. Additional Doppler velocity and temperature measurements in both poloidal and toroidal directions for some of the brighter impurities (e.g. He II and N III), will be given. This work is supported was performed under the auspices of the DoE by UC LLNL under contract W-7405-ENG-48 and also under DoE Coop. Agreement DE-FC02-99ER54512.

  13. Novel energy resolving x-ray pinhole camera on Alcator C-Mod.

    PubMed

    Pablant, N A; Delgado-Aparicio, L; Bitter, M; Brandstetter, S; Eikenberry, E; Ellis, R; Hill, K W; Hofer, P; Schneebeli, M

    2012-10-01

    A new energy resolving x-ray pinhole camera has been recently installed on Alcator C-Mod. This diagnostic is capable of 1D or 2D imaging with a spatial resolution of ≈1 cm, an energy resolution of ≈1 keV in the range of 3.5-15 keV and a maximum time resolution of 5 ms. A novel use of a Pilatus 2 hybrid-pixel x-ray detector [P. Kraft et al., J. Synchrotron Rad. 16, 368 (2009)] is employed in which the lower energy threshold of individual pixels is adjusted, allowing regions of a single detector to be sensitive to different x-ray energy ranges. Development of this new detector calibration technique was done as a collaboration between PPPL and Dectris Ltd. The calibration procedure is described, and the energy resolution of the detector is characterized. Initial data from this installation on Alcator C-Mod is presented. This diagnostic provides line-integrated measurements of impurity emission which can be used to determine impurity concentrations as well as the electron energy distribution.

  14. Fast Imaging of Filaments in the X-Point Region of Alcator C-MOD

    NASA Astrophysics Data System (ADS)

    Terry, J. L.; Ballinger, S.; Brunner, D.; Labombard, B.; White, A. E.; Zweben, S. J.

    2016-10-01

    A rich variety of field-aligned fluctuations has been revealed using fast imaging of Dα emission from Alcator C-Mod's lower X-point region. Field-aligned filamentary fluctuations are observed along the inner divertor leg, within the Private-Flux-Zone (PFZ), in the Scrape-Off Layer outside the outer divertor leg, and, under some conditions, at or above the X-point. The locations and dynamics of the filaments in these regions are strikingly complex in C-Mod. Changes in the filaments' generation appear to be ordered by plasma density and magnetic configuration. In a Lower Single Null with 0.12 < n /nGreenwald <0.45 and Bx ∇B directed down, filaments typically move up the inner divertor leg toward the X-point. Reversing the field direction results in the appearance of filaments outside of the outer divertor leg. With the divertor targets ``detached'', filaments inside the LCFS are seen. These studies were motivated by observations of filaments in the X-point and PFZ regions in MAST, and comparisons with those observations will be made. Supported by USDoE Awards DE-FC02-99ER54512 and DE-AC02-09CH11466.

  15. Wall scanning probe for high-field side plasma measurements on Alcator C-Mod.

    PubMed

    Smick, Noah; LaBombard, Brian

    2009-02-01

    A new, high-field side scanning probe has been added to Alcator C-Mod's complement of edge diagnostics. The wall scanning probe is designed to provide all the benefits of a linear plunge, multielectrode scanning probe while working from the confined space of the inner tokamak wall. The drive mechanism is an embedded coil which produces a torque with the ambient toroidal magnetic field when energized, thus allowing the probe to plunge to different preprogramed depths at different times during a plasma discharge. The probe tip is designed for easy replacement and is presently configured to operate as a modified, high heat-flux "Gundestrup-type" probe with four tungsten electrodes. The probe has demonstrated the ability to obtain cross-field profiles for electron temperature, density, floating potential, and plasma flow information (parallel and perpendicular to B) up to a depth of a few millimiters inside the last-closed flux surface in standard C-Mod discharges. The tungsten-tipped probe has proved very robust and shows little or no damage though it routinely handles surface heat fluxes on the order of 100 MW/m(2) at peak insertion.

  16. Particle transport and density peaking at low collisionality on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Greenwald, M.; Hughes, J. W.; Mikkelsen, D.; Terry, J.

    2007-11-01

    While H-modes tend to have very flat density profiles, modest density peaking is advantageous for fusion performance. Thus robust pinch mechanisms that could allow operation with peaked profiles, in the absence of any internal particle source, are of considerable interest. Recent experiments on C-Mod^1, at low collisionality, show just such peaking and are quantitatively consistent with earlier results from ASDEX-U^2 and JET^3. By extending the range in machine size, these data break the covariance between collisionality and n/nG, the density normalized to the density limit and strongly support the primary role of collisionality in determining the profile. The implication is that ITER will have density profiles with ne( 0 )/˜1.4-1.6. The C-Mod data also show a small but statistically significant dependence of the peaking factor on the edge safety factor, q. The effect is to increase the peaking by no more than 10% when q is raised from 3.5 to 5.Initial studies of gyrokinetic simulations for these discharges will be shown. ^1M. Greenwald, submitted to Nucl. Fusion, 2007 ^2C. Angioni, et al., PRL 90, 205003, 2003 ^3H.Weisen, Nucl. Fusion 45, L1, 2005

  17. ICRF antenna matching system with ferrite tuners for the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Binus, A.; Wukitch, S. J.; Koert, P.; Murray, R.; Pfeiffer, A.

    2015-12-01

    Real-time fast ferrite tuning (FFT) has been successfully implemented on the ICRF antennas on Alcator C-Mod. The former prototypical FFT system on the E-port 2-strap antenna has been upgraded using new ferrite tuners that have been designed specifically for the operational parameters of the Alcator C-Mod ICRF system (˜ 80 MHz). Another similar FFT system, with two ferrite tuners and one fixed-length stub, has been installed on the transmission line of the D-port 2-strap antenna. These two systems share a Linux-server-based real-time controller. These FFT systems are able to achieve and maintain the reflected power to the transmitters to less than 1% in real time during the plasma discharges under almost all plasma conditions, and help ensure reliable high power operation of the antennas. The innovative field-aligned (FA) 4-strap antenna on J-port has been found to have an interesting feature of loading insensitivity vs. plasma conditions. This feature allows us to significantly improve the matching for the FA J-port antenna by installing carefully designed stubs on the two transmission lines. The reduction of the RF voltages in the transmission lines has enabled the FA J-port antenna to deliver 3.7 MW RF power to plasmas out of the 4 MW source power in high performance I-mode plasmas.

  18. The ORNL fast wave ICRF (Ion Cyclotron Range of Frequencies) antenna for Alcator C-Mod

    SciTech Connect

    Goulding, R.H.; Hoffman, D.J.; Conner, D.L.; Hammonds, C.J.; Ping, J.L.; Riemer, B.W.; Ryan, P.M.; Taylor, D.J.; Wysor, R.B.; Yugo, J.J. )

    1989-01-01

    A fast wave ICRF antenna is being designed for Alcator C-Mod which is prototypical in many respects of the baseline launcher design for the Compact Ignition Tokamak (CIT). The C-Mod launcher has a single current strap, with a strap and cavity geometry very similar to one quadrant of the CIT launcher, which has four straps in a 2 {times} 2 configuration. The antenna fits entirely within an 8 in. wide by 25 in. long port and is radially movable over a distance of 15 cm. It will operate at a frequency of 80 MHz for pulse lengths up to 1 s, at a maximum power level of 2 MW, corresponding to a power flux of >1.5 kW/cm{sup 2}. The antenna is an end fed double loop configuration in which the current strap is grounded in the middle to provide mechanical support. The design includes a disruption support system which accommodates thermal expansion of the antenna box while supporting large disruption loads. It also includes a novel matching system consisting of an external resonant loop with two shunt capacitors serving as tuning/matching elements. 8 refs., 5 figs., 12 tabs.

  19. Observations of Intrinsic Rotation Reversal Hysteresis in Alcator C-Mod Plasmas

    NASA Astrophysics Data System (ADS)

    Cao, Norman; Rice, John; White, Anne; Baek, Seung; Chilenski, Mark; Creely, Alexander; Ennever, Paul; Hubbard, Amanda; Hughes, Jerry; Irby, Jim; Rodriguez-Fernandez, Pablo; Reinke, Matthew; Diamond, Patrick; Alcator C-Mod Team

    2016-10-01

    Intrinsic core toroidal rotation in Alcator C-Mod L-mode plasmas has been observed to spontaneously reverse direction when the normalized collisionality ν*, evaluated at the profile minimum, passes through a critical value around 0.4. In Ohmic plasmas, the low density linear Ohmic confinement regime exhibits co-current toroidal rotation, and the higher density saturated Ohmic confinement regime exhibits counter-current rotation. The reversal manifests a hysteresis loop in ν*, where the critical collisionalities for the forward and reverse transitions differ by 10-15%. There appears to be memory associated with the rotation state, since reversals which do not begin from fully saturated rotation states do not manifest this hysteresis. In addition, high-k PCI fluctuation ``wings'' (kθρs up to 1) at low density and high current appear only in the co-current rotation state, while density peaking and ``non-local'' heat transport behavior do not appear to change significantly with the rotation state. Results from fluctuation measurements and preliminary transport and stability analyses will also be presented. This work is supported by the US DOE under Grant DE-FC02-99ER54512 (C-Mod).

  20. Linear servomotor probe drive system with real-time self-adaptive position control for the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Brunner, D.; Kuang, A. Q.; LaBombard, B.; Burke, W.

    2017-07-01

    A new servomotor drive system has been developed for the horizontal reciprocating probe on the Alcator C-Mod tokamak. Real-time measurements of plasma temperature and density—through use of a mirror Langmuir probe bias system—combined with a commercial linear servomotor and controller enable self-adaptive position control. Probe surface temperature and its rate of change are computed in real time and used to control probe insertion depth. It is found that a universal trigger threshold can be defined in terms of these two parameters; if the probe is triggered to retract when crossing the trigger threshold, it will reach the same ultimate surface temperature, independent of velocity, acceleration, or scrape-off layer heat flux scale length. In addition to controlling the probe motion, the controller is used to monitor and control all aspects of the integrated probe drive system.

  1. Plasma wave simulation based on versatile FEM solver on Alcator C-mod

    SciTech Connect

    Shiraiwa, S.; Meneghini, O.; Parker, R.; Wallace, G.; Wilson, J.

    2009-11-26

    The finite element method (FEM) has the potential of simulating plasma waves seamlessly from the core to the vacuum and antenna regions. We explored the possibility of using a versatile FEM solver package, COMSOL, for lower hybrid (LH) wave simulation. Special care was paid to boundary conditions to satisfy toroidal symmetry. The non-trivial issue of introducing hot plasma effects was addressed by an iterative algorithm. These techniques are verified both analytically and numerically. In the lower hybrid (LH) grill antenna coupling problem, the FEM solver successfully reproduced the solution that was obtained analytically. Propagation of LH waves on the Alcator C and Alcator C-MOD plasmas was compared with a ray-tracing code, showing good consistency. The approach based on the FEM is computationally less intensive compared to spectral domain solvers, and more suitable for the simulation of larger device such as ITER.

  2. Design of a correlation electron cyclotron emission diagnostic for Alcator C-Mod

    SciTech Connect

    Sung, C.; White, A. E.; Irby, J. H.; Leccacorvi, R.; Vieira, R.; Oi, C. Y.; Peebles, W. A.; Nguyen, X.

    2012-10-15

    A correlation electron cyclotron emission (CECE) diagnostic has been installed in Alcator C-Mod. In order to measure electron temperature fluctuations, this diagnostic uses a spectral decorrelation technique. Constraints obtained with nonlinear gyrokinetic simulations guided the design of the optical system and receiver. The CECE diagnostic is designed to measure temperature fluctuations which have k{sub {theta}}{<=} 4.8 cm{sup -1} (k{sub {theta}}{rho}{sub s} < 0.5) using a well-focused beam pattern. Because the CECE diagnostic is a dedicated turbulence diagnostic, the optical system is also flexible, which allows for various collimating lenses and antenna to be used. The system overview and the demonstration of its operability as designed are presented in this paper.

  3. Search for gyrokinetic dependencies in helium transport at Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Liao, Kenneth; Rowan, William; Hatch, David; Bespamyatnov, Igor; Horton, Wendell

    2013-10-01

    Helium-3 and helium-4 impurity transport measurements and density profile measurements have been obtained on Alcator C-Mod in a variety of discharge conditions, using the core Charge Exchange Recombination Spectroscopy (CXRS) diagnostic. The helium concentrations range from trace (< 2 %) to large minority (~ 20 %). L-mode, H-mode, and I-mode results are included, with Ohmic heated, ICRF heated, and LH heated plasmas. Helium profiles are observed to vary with plasma current, and also change in time during ICRF shots. Linear and nonlinear gyrokinetic simulations are performed for some shots using the GENE code. Sensitivity scans are done for magnetic shear, impurity density, and other plasma parameters and transport scalings are compared with experimental results. Simulated transport flux is compared with experimentally derived D and v parameters. Supported by USDoE awards DE-FG03-96ER-54373 and DE-FC02-99ER54512.

  4. In-out impurity density asymmetry in the pedestal region of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Churchill, R. M.; Lipschultz, B.; Theiler, C.; the Alcator C-Mod Team

    2013-12-01

    Measurements are presented of the boron (B5+) density in the pedestal region at the low-field side (LFS) midplane and the high-field side (HFS) midplane of Alcator C-Mod. In H-mode plasmas, a large (≳10x) in-out asymmetry in impurity density forms, with larger densities at the HFS. In contrast, there is no impurity density asymmetry in L-mode or I-mode plasmas. A comparison of pedestal parameters in H-mode plasmas shows that the HFS impurity density pedestal width and position remain fairly fixed over a range of plasma conditions, while the LFS pedestal width widens, and the pedestal position shifts in towards the core as the plasma current is lowered, indicating a change in the underlying transport.

  5. RF current profile control studies in the alcator C-mod tokamak

    NASA Astrophysics Data System (ADS)

    Bonoli, P. T.; Porkolab, M.; Wukitch, S. J.; Bernabei, S.; Kaita, R.; Mikkelsen, D.; Phillips, C. K.; Schilling, G.

    1999-09-01

    Time dependent calculations of lower hybrid (LH) current profile control in Alcator C-Mod have been done using the TRANSP [1], FPPRF [2], and LSC [3] codes. Up to 3 MW of LH current drive power was applied in plasmas with high power ICRF minority heating (PICH=1.8-3 MW) and fast current ramp up. Using the experimentally measured temperature profiles, off-axis current generation resulted in nonmonotonic q-profiles with qmin~=1.6. Self-consistent effects of off-axis electron heating by the LH power were also included in the analysis and significant broadening of the electron temperature profile was found with qmin>~2 and a larger shear reversal radius.

  6. Rf modeling and design of a folded waveguide launcher for the Alcator C-Mod tokamak

    SciTech Connect

    Bigelow, T.S.; Fogelman, C.F.; Baity, F.W.; Carter, M.D.; Hoffman, D.J.; Ryan, P.M.; Yugo, J.J.; Golovato, S.N.; Bonoli, P.

    1993-12-01

    The folded waveguide (FWG) launcher is being investigated as an improved antenna configuration for plasma heating in the ion cyclotron range of frequencies (ICRF). A development FWG launcher was successfully tested at Oak Ridge National Laboratory (ORNL) with a low-density plasma load and found to have significantly greater power density capability than current strap-type antennas operating in similar plasmas. To further test the concept on a high density tokamak plasma, a collaboration has been set up between ORNL and Massachusetts Institute of Technology (MIT) to develop and test an 80-MHz, 2-MW FWG on the Alcator C-Mod tokamak at MIT. The radio frequency (rf) electromagnetic modeling techniques and laboratory measurements used in the design of this antenna are described in this paper. A companion paper describes the mechanical design of the FWG.

  7. Control of Internal Profiles via LHCD on Alcator C-Mod

    SciTech Connect

    Wilson, J. R.; Kessel, C.; Scott, S.; Wallace, G. M.; Parker, R. R.; Bonoli, P. T.; Hubbard, A. E.; Hughes, J. W.; Ince-Cushman, A.; Ko, J. S.; Meneghini, O.; Porkolab, M.; Reinke, M.; Rice, J. E.; Schmidt, A. E.; Shiraiwa, S.; Wright, J. C.

    2009-11-26

    LHCD on Alcator C-Mod is being used in plasmas with parameters similar to those expected on ITER for the purpose of tailoring the plasma current profile. LHCD experiments have also produced intriguing results related to momentum transport and edge pedestal physics that affect the toroidal rotation profile and the temperature and density profiles. Quantitative comparisons between local measurements and theory/simulation have been performed, confirming the off-axis localization of the current drive, as well as its magnitude and location dependence on the launched n{sub parallel} spectrum and electron temperature. Applying LHCD during the current ramp saves volt-seconds and delays the peaking of the current profile. Counter current toroidal rotation during LHCD has been observed in both L and H-mode plasmas. In H-mode plasmas the edge pedestal collisionality is reduced while the overall pressure in the pedestal increases slightly.

  8. Modification of Current Profile, Toroidal Rotation and Pedestal by Lower Hybrid Waves in Alcator C-Mod

    SciTech Connect

    Parker, R.; Bonoli, P. T.; Meneghini, O.; Porkolab, M.; Schmidt, A. E.; Shiraiwa, S.; Wallace, G.; Hubbard, A. E.; Hughes, J. W.; Ko, J.-S.; McDermott, R. M.; Reinke, M. L.; Rice, J. E.; Wilson, J. R.; Scott, S.

    2009-11-26

    Recent results from the lower hybrid current drive experiments on Alcator C-Mod are presented. These include i) MSE measurements of broadened LHCD current profiles; ii) development of counter rotation comparable to the rate of injected wave momentum; iii) modification of pedestals and rotation in H-mode; and iv) development of a new FEM-based code that models LH wave propagation from the RF source to absorption in the plasma. An improved antenna concept that will be used in the upcoming C-Mod campaigns is also briefly described.

  9. Multispecies density peaking in gyrokinetic turbulence simulations of low collisionality Alcator C-Mod plasmas

    SciTech Connect

    Mikkelsen, D. R. Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Greenwald, M.; Howard, N. T.; Hughes, J. W.; Rice, J. E.; Reinke, M. L.; Podpaly, Y.; Ma, Y.; Candy, J.; Waltz, R. E.

    2015-06-15

    Peaked density profiles in low-collisionality AUG and JET H-mode plasmas are probably caused by a turbulently driven particle pinch, and Alcator C-Mod experiments confirmed that collisionality is a critical parameter. Density peaking in reactors could produce a number of important effects, some beneficial, such as enhanced fusion power and transport of fuel ions from the edge to the core, while others are undesirable, such as lower beta limits, reduced radiation from the plasma edge, and consequently higher divertor heat loads. Fundamental understanding of the pinch will enable planning to optimize these impacts. We show that density peaking is predicted by nonlinear gyrokinetic turbulence simulations based on measured profile data from low collisionality H-mode plasma in Alcator C-Mod. Multiple ion species are included to determine whether hydrogenic density peaking has an isotope dependence or is influenced by typical levels of low-Z impurities, and whether impurity density peaking depends on the species. We find that the deuterium density profile is slightly more peaked than that of hydrogen, and that experimentally relevant levels of boron have no appreciable effect on hydrogenic density peaking. The ratio of density at r/a = 0.44 to that at r/a = 0.74 is 1.2 for the majority D and minority H ions (and for electrons), and increases with impurity Z: 1.1 for helium, 1.15 for boron, 1.3 for neon, 1.4 for argon, and 1.5 for molybdenum. The ion temperature profile is varied to match better the predicted heat flux with the experimental transport analysis, but the resulting factor of two change in heat transport has only a weak effect on the predicted density peaking.

  10. Multi-scale gyrokinetic simulation of Alcator C-Mod tokamak discharges

    NASA Astrophysics Data System (ADS)

    Howard, N. T.; White, A. E.; Greenwald, M.; Holland, C.; Candy, J.

    2014-03-01

    Alcator C-Mod tokamak discharges have been studied with nonlinear gyrokinetic simulation simultaneously spanning both ion and electron spatiotemporal scales. These multi-scale simulations utilized the gyrokinetic model implemented by GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] and the approximation of reduced electron mass (μ = (mD/me).5 = 20.0) to qualitatively study a pair of Alcator C-Mod discharges: a low-power discharge, previously demonstrated (using realistic mass, ion-scale simulation) to display an under-prediction of the electron heat flux and a high-power discharge displaying agreement with both ion and electron heat flux channels [N. T. Howard et al., Nucl. Fusion 53, 123011 (2013)]. These multi-scale simulations demonstrate the importance of electron-scale turbulence in the core of conventional tokamak discharges and suggest it is a viable candidate for explaining the observed under-prediction of electron heat flux. In this paper, we investigate the coupling of turbulence at the ion (kθρs˜O(1.0)) and electron (kθρe˜O(1.0)) scales for experimental plasma conditions both exhibiting strong (high-power) and marginally stable (low-power) low-k (kθρs < 1.0) turbulence. It is found that reduced mass simulation of the plasma exhibiting marginally stable low-k turbulence fails to provide even qualitative insight into the turbulence present in the realistic plasma conditions. In contrast, multi-scale simulation of the plasma condition exhibiting strong turbulence provides valuable insight into the coupling of the ion and electron scales.

  11. Multi-scale gyrokinetic simulation of Alcator C-Mod tokamak discharges

    SciTech Connect

    Howard, N. T. White, A. E.; Greenwald, M.; Holland, C.; Candy, J.

    2014-03-15

    Alcator C-Mod tokamak discharges have been studied with nonlinear gyrokinetic simulation simultaneously spanning both ion and electron spatiotemporal scales. These multi-scale simulations utilized the gyrokinetic model implemented by GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] and the approximation of reduced electron mass (μ = (m{sub D}/m{sub e}){sup .5} = 20.0) to qualitatively study a pair of Alcator C-Mod discharges: a low-power discharge, previously demonstrated (using realistic mass, ion-scale simulation) to display an under-prediction of the electron heat flux and a high-power discharge displaying agreement with both ion and electron heat flux channels [N. T. Howard et al., Nucl. Fusion 53, 123011 (2013)]. These multi-scale simulations demonstrate the importance of electron-scale turbulence in the core of conventional tokamak discharges and suggest it is a viable candidate for explaining the observed under-prediction of electron heat flux. In this paper, we investigate the coupling of turbulence at the ion (k{sub θ}ρ{sub s}∼O(1.0)) and electron (k{sub θ}ρ{sub e}∼O(1.0)) scales for experimental plasma conditions both exhibiting strong (high-power) and marginally stable (low-power) low-k (k{sub θ}ρ{sub s} < 1.0) turbulence. It is found that reduced mass simulation of the plasma exhibiting marginally stable low-k turbulence fails to provide even qualitative insight into the turbulence present in the realistic plasma conditions. In contrast, multi-scale simulation of the plasma condition exhibiting strong turbulence provides valuable insight into the coupling of the ion and electron scales.

  12. Plasma wave simulation based on a versatile FEM solver on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Shiraiwa, Syun'ichi

    2009-11-01

    A new efficient full wave simulation code of the lower hybrid (LH) wave was developed using the finite element method (FEM). A dielectric tensor consisting of the cold plasma contribution and the electron Landau damping (ELD) was used. The non-trivial problem of introducing non-local hot plasma effects into an FEM solver was addressed by iteratively solving the coupled problem of the Maxwell's equations with the convolution integral. With this approach, the EM problem is numerically sparse, and the computational requirements are reduced significantly compared to spectral domain solvers [1]. The simulation of an Alcator C-Mod scale plasma has been done on a desktop computer, suggesting the possibility of an ITER scale plasma simulation. The algorithm was implemented using a general purpose FEM software, COMSOL Multiphysics, and the simulation results of a Maxwellian tokamak plasma showed good agreement with ray tracing calculations in the strong single pass absorption regime. Integration of a Fokker-Planck calculation for a more realistic non-Maxwellian plasma is underway and initial results show reasonable shift of the power absorption towards the plasma edge [2]. Importantly, the FEM approach allows seamless handling of the core, SOL, and antenna regions. This flexibility has been exploited to address issues of antenna-plasma coupling in the LH and ICRF frequency ranges. Techniques to use the FEM package for this purpose were validated by solving the LH grill antenna coupling problem whose analytic solution is known. The code has been applied to a new Alcator C-Mod ICRF antenna to assess the antenna near field pattern [3]. [4pt] [1] J. C. Wright, et. al., Comput. Phys. 4, 545 (2008) [0pt] [2] O. Meneghini, et. al., this conference [0pt] [3] M. Garrett, et. al., this conference

  13. Marginal Stability Studies of Microturbulence Near ITB Onset on Alcator C-Mod

    SciTech Connect

    Baumgaertel, J.; Redi, M.H.; Budny, R.V.; McCune, D.C.; Dorland, W.; Fiore, C.L.

    2005-01-01

    Insight into microturbulence and transport in tokamak plasmas is being sought using linear simulations of drift waves near the onset time of an internal transport barrier (ITB) on Alcator C-Mod. Microturbulence is likely generated by instabilities of drift waves and causes transport of heat and particles. This transport is studied because the containment of heat and particles is important for the achievement of practical nuclear fusion. We investigate nearness to marginal stability of ion temperature gradient (ITG) modes for conditions in the ITB region at the trigger time for ITB formation. Data from C-Mod, analyzed by TRANSP (a time dependent transport analysis code), is read by the code TRXPL and made into input files for the parallel gyrokinetic model code GS2. Temperature and density gradients in these input files are modified to produce new input files. Results from these simulations show a weak ITG instability in the barrier region at the time of onset, above marginal stability; the normalized critical temperature gradient is 80% of the experimental temperature gradient. The growth rate increases linearly above the critical value, with the spectrum of ITG modes remaining parabolic up to a multiplicative factor of 2. The effect of varying density gradients is found to be much weaker and causes the fastest growing drift mode to change from ITG to trapped electron mode character. Simulations were carried out on the NERSC IBM 6000 SP using 4 nodes, 16 processors per node. Predictive simulations were examined for converged instability after 10,000-50,000 timesteps in each case. Each simulation took approximately 30 minutes to complete on the IBM SP.

  14. Marginal Stability of Microturbulence near ITB Onset on Alcator C-Mod

    SciTech Connect

    J.A. Baumgaertel; M.H. Redi; R.V. Budny; D.C. McCune; W. Dorland; C.L. Fiore

    2004-08-23

    Insight into microturbulence and transport in tokamak plasmas is being sought using linear simulations of drift waves near the onset time of an internal transport barrier (ITB) on Alcator C-Mod. Microturbulence is likely generated by instabilities of drift waves and causes transport of heat and particles. This transport is studied because the containment of heat and particles is important for the achievement of practical nuclear fusion. We investigate nearness to marginal stability of ion-temperature-gradient (ITG) modes for conditions in the ITB region at the trigger time for ITB formation. Data from C-Mod, analyzed by TRANSP (a time-dependent transport analysis code), is read by the code TRXPL and made into input files for the parallel gyrokinetic model code GS2. Temperature and density gradients in these input files are modified to produce new input files. Results from these simulations show a weak ITG instability in the barrier region at the time of onset, above marginal stability; the normalized critical temperature gradient is 80% of the experimental temperature gradient. The growth rate increases linearly above the critical value, with the spectrum of ITG modes remaining parabolic up to a multiplicative factor of 2. The effect of varying density gradients is found to be much weaker and causes the fastest growing drift mode to change from ITG to trapped-electron mode character. Simulations were carried out on the NERSC [National Energy Research Supercomputer Center] IBM 6000 SP using 4 nodes, 16 processors per node. Predictive simulations were examined for converged instability after 10,000-50,000 time-steps in each case. Each simulation took approximately 30 minutes to complete on the IBM SP.

  15. ICRF-enhanced plasma potentials in the SOL of Alcator C-Mod

    SciTech Connect

    Ochoukov, R.; Whyte, D. G.; Brunner, D.; LaBombard, B.; Lipschultz, B.; Terry, J. L.; Wukitch, S. J.; D'Ippolito, D. A.; Myra, J. R.

    2014-02-12

    We performed an extensive survey of the plasma potential in the scrape-off layer (SOL) of Ion Cyclotron Range-of Frequencies (ICRF)-heated discharges on Alcator C-Mod. Our results show that plasma potentials are enhanced in the presence of ICRF power and plasma potential values of >100 V are often observed. Such potentials are high enough to induce sputtering of high-Z molybdenum (Mo) plasma facing components by deuterium ions on C-Mod. For comparison, the plasma potential in Ohmic discharges is typically less than 10 V, well below the threshold needed to induce Mo sputtering by deuterium ions. ICRF-enhanced plasma potentials are observed in the SOL regions that both magnetically map and do not map to active ICRF antennas. Regions that magnetically map to active ICRF antennas are accessible to slow waves directly launched by the antennas and these regions experience plasma potential enhancement that is partially consistent with the slow wave rectification mechanism. One of the most defining features of the slow wave rectification is a threshold appearance of significant plasma potentials (>100 V) when the dimensionless rectification parameter Λ{sub −o} is above unity and this trend is observed experimentally. We also observe ICRF-enhanced plasma potentials >100 V in regions that do not magnetically map to the active antennas and, hence, are not accessible for slow waves launched directly by the active antennas. However, unabsorbed fast waves can reach these regions. The general trend that we observe in these 'un-mapped' regions is that the plasma potential scales with the strength of the local RF wave fields with the fast wave polarization and the highest plasma potentials are observed in discharges with the highest levels of unabsorbed ICRF power. Similarly, we find that core Mo levels scale with the level of unabsorbed ICRF power suggesting a link between plasma potentials in the SOL and the strength of the impurity source.

  16. Lower Hybrid Heating and Current Drive on the Alcator C-Mod Tokamak

    SciTech Connect

    R. Wilson, R. Parker, M. Bitter, P.T. Bonoli, C. Fiore, R.W. Harvey, K. Hill, A.E. Hubbard, J.W. Hughes, A. Ince-Cushman, C. Kessel, J.S. Ko, O. Meneghini, C.K. Phillips, M. Porkolab, J. Rice, A.E. Schmidt, S. Scott,S. Shiraiwa, E. Valeo, G.Wallace, J.C. Wright and the Alcator C-Mod Team

    2009-11-20

    On the Alcator C-Mod tokamak, lower hybrid current drive (LHCD) is being used to modify the current profile with the aim of obtaining advanced tokamak (AT) performance in plasmas with parameters similar to those that would be required on ITER. To date, power levels in excess of 1 MW at a frequency of 4.6 GHz have been coupled into a variety of plasmas. Experiments have established that LHCD on C-Mod behaves globally as predicted by theory. Bulk current drive efficiencies, n20IlhR/Plh ~ 0.25, inferred from magnetics and MSE are in line with theory. Quantitative comparisons between local measurements, MSE, ECE and hard x-ray bremsstrahlung, and theory/simulation using the GENRAY, TORIC-LH CQL3D and TSC-LSC codes have been performed. These comparisons have demonstrated the off-axis localization of the current drive, its magnitude and location dependence on the launched n|| spectrum, and the use of LHCD during the current ramp to save volt-seconds and delay the peaking of the current profile. Broadening of the x-ray emission profile during ICRF heating indicates that the current drive location can be controlled by the electron temperature, as expected. In addition, an alteration in the plasma toroidal rotation profile during LHCD has been observed with a significant rotation in the counter current direction. Notably, the rotation is accompanied by peaking of the density and temperature profiles on a current diffusion time scale inside of the half radius where the LH absorption is taking place.

  17. Fluctuating zonal flows in the I-mode regime in Alcator C-Mod

    SciTech Connect

    Cziegler, I.; Diamond, P. H.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M.; Churchill, R. M.; Hubbard, A. E.; Lipschultz, B.; Sierchio, J. M.; Terry, J. L.; Theiler, C.

    2013-05-15

    Velocity fields and density fluctuations of edge turbulence are studied in I-mode [F. Ryter et al., Plasma Phys. Controlled Fusion 40, 725 (1998)] plasmas of the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] tokamak, which are characterized by a strong thermal transport barrier in the edge while providing little or no barrier to the transport of both bulk and impurity particles. Although previous work showed no clear geodesic-acoustic modes (GAM) on C-Mod, using a newly implemented, gas-puff-imaging based time-delay-estimate velocity inference algorithm, GAM are now shown to be ubiquitous in all I-mode discharges examined to date, with the time histories of the GAM and the I-mode specific [D. Whyte et al., Nucl. Fusion 50, 105005 (2010)] Weakly Coherent Mode (WCM, f = 100–300 kHz, Δf/f≈0.5, and k{sub θ}≈1.3 cm{sup −1}) closely following each other through the entire duration of the regime. Thus, the I-mode presents an example of a plasma state in which zero frequency zonal flows and GAM continuously coexist. Using two-field (density-velocity and radial-poloidal velocity) bispectral methods, the GAM are shown to be coupled to the WCM and to be responsible for its broad frequency structure. The effective nonlinear growth rate of the GAM is estimated, and its comparison to the collisional damping rate seems to suggest a new view on I-mode threshold physics.

  18. The Submillimeter Wave Electron Cyclotron Emission Diagnostic for the Alcator C-Mod Tokamak.

    NASA Astrophysics Data System (ADS)

    Hsu, Thomas C.

    This thesis describes the engineering design, construction, and operation of a high spatial resolution submillimeter wave diagnostic for electron temperature measurements on Alcator C-Mod. Alcator C-Mod is a high performance compact tokamak capable of producing diverted, shaped plasmas with a major radius of 0.67 meters, minor radius of 0.21 centimeters, plasma current of 3 MA. The maximum toroidal field is 9 Tesla on the magnetic axis. The ECE diagnostic includes three primary components: a 10.8 meter quasioptical transmission line, a rapid scanning Michelson interferometer, and a vacuum compatible calibration source. Due to the compact size and high field of the tokamak the ECE system was designed to have a spectral range from 100 to 1000 GHz with frequency resolution of 5 GHz and spatial resolution of one centimeter. The beamline uses all reflecting optical elements including two off-axis parabolic mirrors with diameters of 20 cm. and focal lengths of 2.7 meters. Techniques are presented for grinding and finishing the mirrors to sufficient surface quality to permit optical alignment of the system. Measurements of the surface figure confirm the design goal of 1/4 wavelength accuracy at 1000 GHz. Extensive broadband tests of the spatial resolution of the ECE system are compared to a fundamental mode Gaussian beam model, a three dimensional vector diffraction model, and a geometric optics model. The Michelson interferometer is a rapid scanning polarization instrument which has an apodized frequency resolution of 5 GHz and a minimum scan period of 7.5 milliseconds. The novel features of this instrument include the use of precision linear bearings to stabilize the moving mirror and active counterbalancing to reduce vibration. Beam collimation within the instrument is done with off-axis parabolic mirrors. The Michelson also includes a 2-50 mm variable aperture and two signal attenuators constructed from crossed wire grid polarizers. To make full use of the advantages

  19. Fluctuating Zonal Flows in I-mode in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Cziegler, Istvan

    2012-10-01

    Velocity fields and density fluctuations of edge turbulence have been studied in I-mode [1] plasmas of Alcator C-Mod, which are characterized by a strong thermal transport barrier in the edge while providing little or no barrier to the transport of both bulk and impurity particles. This allows access to steady state, high performance discharges without explosive edge relaxations or impurity accumulation. The key feature in the I-mode edge seems to be a weakly coherent mode (WCM) at 100-300 kHz, with δf 150 kHz and a poloidal wavenumber k 1.5,-1. Although previous work showed no clear geodesic-acoustic modes (GAM) on C-Mod, using a newly implemented, gas-puff-imaging (GPI) based time-delay-estimate (TDE) velocity inference algorithm, GAM are now shown to be ubiquitous in all I-mode discharges, with the time histories of the GAM and the WCM closely following each other through the entire duration of the regime. The central frequency of the WCM is shown to scale with HITER,98, which itself scales with the depth of the radial electric field well in the edge [2]. Thus, the I-mode presents an example of a plasma state in which quasi-static zonal flows (ZF) and GAM continuously coexist. Using both single- (density) and two-field (density-velocity) bispectral methods, the GAM are shown to be coupled to the WCM and to be responsible for its broad frequency structure. Since the WCM activity is strongly correlated to the I-mode behavior [3], and due to the known dependence of the GAM damping on collisionality [4], the decrease in GAM amplitude, and with it WCM activity, at higher densities offers an explanation for the density limit for I-mode access [3].[4pt] [1] F. Ryter et al, Plasma Phys. Control. Fusion 40 725 (1998)[0pt] [2] R. McDermott et al, Phys. Plasmas 16 056103 (2009)[0pt] [3] D. Whyte et al, Nucl. Fus. 50 105005 (2010)[0pt] [4] S. Novakovskii et al, Phys. Plasmas 4 4272 (1997)

  20. Electron heating via mode converted ion Bernstein waves in the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Bonoli, P. T.

    1996-11-01

    Highly localized electron heating (FWHM <~ 0.2 a) via mode converted ion Bernstein waves (IBW) has been demonstrated in the Alcator C-Mod tokamak. These experiments were carried out using 80 MHz fast wave ICRF power at P_rf <~ 2.4 MW. Electron heating at or near the plasma center (r/a <~ 0.3) has been observed in H-(^3He) plasmas at B0 = (6.4 - 7.3)T. In this case the ion-ion hybrid layer is near the plasma center and the fundamental H and ^3He cyclotron resonances are located respectively on the low and high field sides of the tokamak. Off-axis heating (r/a >≈ 0.5) has also been observed in D-(^3He) plasmas at 7.9 T. In this case the ^3He cyclotron resonance is on-axis and the fundamental D resonance and mode conversion layer are on the high field side of the tokamak. The concentration of ^3He in these experiments was in the range n_^3He / ne ~= (0.2 - 0.3) and the location of the mode conversion layer was controlled by changing the ^3He concentration or the toroidal magnetic field. The rf heating profiles were deduced using an rf power modulation technique in which the local electron heating rate was obtained from a ``break in slope'' analysis of the measured electron temperature versus time. Detailed comparisons with 1-D and toroidal full-wave ICRF models (FELICE and FISIC codes) have been carried out. The 1-D predictions for the fractional electron power absorption and damping location are found to be in qualitative agreement with the experiment. However discrepancies have been found between the full-wave toroidal code predictions and experiment. This disagreement is thought to be due to a lack of radial and poloidal resolution in the solution of the mode converted ion Bernstein wave in toroidal geometry and will be discussed. A fast wave current drive package has been modified to study the current generated via the mode converted IBW. Based on these numerical results and the experimental results for power absorption, off-axis current of up to 200 kA is

  1. The development of an Omegratron plasma ion mass spectrometer for Alcator C-Mod

    SciTech Connect

    Thomas, E.E. Jr.

    1993-05-01

    A new diagnostic device, the Omegatron Probe, has been developed to investigate relative impurity levels and impurity charge state distribution in the Alcator C-Mod Tokamak edge plasma. The Omegatron probe consists of two principal components, a ``front-end`` of independently biased grids, arranged in a gridded energy analyzer fashion and a large collection cavity. Particles enter the probe in a thin ``ribbon`` through a knife-edge slit. The grids provide a means to measure and control the parallel energy distribution of the ions. In the collection cavity, an oscillating electric field is applied perpendicularly to the ambient magnetic field. Ions whose cyclotron frequencies are resonant with this electric field oscillation will gain perpendicular energy and be collected. In this way, the probe can be operated in two modes: first, by fixing the potentials on the grids and sweeping frequencies to obtain a `` Z/m spectrum`` of ion species and second, by fixing the frequency and sweeping the grid potentials to obtain the distribution function of an individual impurity species. The Omegatron probe performed successfully in tests on a Hollow Cathode Discharge (HCD) linear plasma column. It obtained measurements of T{sub e} {approx} 5 eV, T{sub i} (H{sup +}) {approx} 2.0 {plus_minus} 0.2 eV, n{sub 0} {approx} 9 {times} 10{sup 15} m{sup {minus}3}, RMS potential fluctuation levels of {approximately} 0.5 {plus_minus} 0.05 {plus_minus} T{sub e}, and obtained ``Z/m`` spectra for the plasma ions (H{sup +}, H{sub 2}{sup +}, He{sup +}). Additional experiments confirmed the theoretical scalings of the f/{delta}f resolution with the applied electric field and magnetic field strengths. The instrument yielded an absolute level of resolution, f/{delta}f, of approximately 2.5 to 3 times the theoretical values. Finally, the results from the HCD are used to project operation on Alcator C-Mod.

  2. Lower Hybrid wave edge power loss quantification on the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Faust, I. C.

    2015-11-01

    For the first time, the power deposition of Lower Hybrid RF waves into the edge plasma of a diverted tokamak has been systematically quantified. Edge deposition represents a parasitic loss of power that can greatly impact the use and efficiency of Lower Hybrid Current Drive (LHCD) at reactor-relevant densities. Through the use of a unique set of fast time resolution edge diagnostics, including innovative fast-thermocouples, an extensive set of Langmuir probes, and a Lyα ionization camera, the toroidal, poloidal and radial structure of the power deposition has been simultaneously determined. Power modulation was used to directly isolate the RF effects due to the prompt (t <τE) response of the scrape-off-layer (SOL) plasma to LHRF power. LHRF power was found to absorb more strongly in the edge at higher densities. It is found that a majority of this edge-deposited power is promptly conducted to the divertor. This correlates with the loss of current drive efficiency at high density previously observed on Alcator C-Mod, and displaying characteristics that contrast with the local RF edge absorption seen on other tokamaks. Measurements of ionization in the active divertor show dramatic changes due to LHRF power, implying that divertor region can be key for the LHRF edge power deposition physics. These observations support the existence a loss mechanism near the edge for LHRF at high density (ne > 1 . 0 .1020 [m-3]). Results will be shown addressing the distribution of power within the SOL, including the toroidal symmetry and radial distribution. These characteristics are important for deducing the cause of the reduced LHCD efficiency at high density and motivates the tailoring of wave propagation to minimize SOL interaction, for example, through the use of high-field-side launch. This work was performed on the Alcator C-Mod tokamak, a DoE Office of Science user facility, and is supported by USDoE award DE-FC02-99ER54512.

  3. Impurity transport studies on Alcator C-Mod tokamak using Charge Exchange Recombination Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bespamyatnov, Igor Olegovich

    A Charge-Exchange Recombination Spectroscopy (CXRS) diagnostic has been installed on Alcator C-Mod to study the transport of light impurities in plasma. The system provides spatially (1 cm) and temporally (12.5 msec) resolved measurements of the impurity density, temperature and flow velocities of the particular impurity. Two optical arrays: poloidal (19 channels) and toroidal (10 channels), collect the light emitted from excited impurity ion populated by charge exchange process from the Diagnostic Neutral Beam (DNB) particle. The attention of this dissertation is focused on the B4+ (n = 7 → 6) spectral line emitted by B4+ ion formed in the following charge exchange reaction (H0 + B5+ → H+ + B4+*). A complex spectral model was developed to simulate emission. The high magnetic fields of C-Mod result in broad Zeeman patterns which must be taken into account for the interpretation of the line shift and broadening in terms of impurity ion velocity and temperature. After the spectral line fitting and careful identification of the charge exchange component, the calculated Doppler broadening and shifts of the spectral line profile yield information on the ion temperature and rotation. Together with the calculation of the beam density, the absolute calibration of the CXRS optical system provides us with B5+ density measurement capabilities. One of the main objectives of this work was to use the acquired impurity density, temperature and flow velocity profiles to investigate plasma transport behavior and infer the radial electric field ER from plasma force balance equation. The focus here was placed on the region of the Internal Transport Barrier (ITB) formation 0.35 < rho < 0.8. Radial electric field ER is readily calculated in the region of the ITB foot using measured B5+ profiles. ExB velocity shearing turbulence stabilization are believed to play an important role in the physics of the ITB formation. The computed ER profiles demonstrated the large difference between

  4. Upgrade to the Gas Puff Imaging Diagnostic that Views Alcator C-Mod's Inboard Edge

    NASA Astrophysics Data System (ADS)

    Sierchio, J. M.; Terry, J. L.

    2012-10-01

    We describe an upgrade of Alcator C-Mod's Gas Puff Imaging system which views the inboard plasma edge and SOL along lines-of-sight that are approximately parallel to the local magnetic field. The views are arranged in a 2D (R,Z) array with ˜2.8 cm radial coverage and ˜2.4 cm poloidal coverage. 23 of 54 available views were coupled via fibers to individual interference filters and PIN photodiode detectors. We are in the process of upgrading the system in order to increase the sensitivity of the system by replacing the PIN photodiodes with a 4x8 array of Avalanche Photo-Diodes (APD). Light from 30 views is coupled to the single-chip APD array through a single interference filter. We expect an improvement in signal-to-noise ratio of more than 10x. The frequency response of the system will increase from ˜400 kHz to 1MHz. The dynamic range of the new system is manipulated by changing the high-voltages on the APDs. Test results of the detectors' channel-to-channel cross-talk, frequency response, and gain curves will be presented, along with schematics of the experimental setup. The upgraded system allows for more study of inboard edge fluctuations, including whether the quasi-coherent fluctuations observed in the outboard edge also exist inboard.

  5. Multi-chord Faraday-Effect measurements of fluctuations in C-Mod

    NASA Astrophysics Data System (ADS)

    Bergerson, William; Xu, P.; Brower, D. L.; Ding, W. X.; Irby, J. H.

    2012-10-01

    Three chords measuring the Faraday effect are operated routinely across all machine conditions in C-mod and allow for internal measurements of the equilibrium poloidal magnetic field. Absolute error attributed to stray magnetic field effects is below 0.5 degree and noise related to contamination from the lower hybrid and ion cyclotron radio frequency systems are not observed. Tests indicate there is no measurable signal contamination from the toroidal magnetic field due to the Cotton-Mouton effect or misalignment. Polarization sensitivity of the wire mesh beamsplitters requires system calibration which is achieved using a rotating half-wave plate. Individual channels can be modified to measure the Cotton-Mouton effect directly and yield a line integrated density measurement without ``fringe skips.'' Fluctuations on the Faraday signal associated with sawteeth, tearing modes, the quasi-coherent mode, broadband turbulence, and fast particle driven modes are observed at frequencies up to 1 MHz. Efforts are underway to differentiate between density and magnetic fluctuations in the polarimetry measurement via cross correlation techniques and combined density measurements. This work supported by DOE contract DE-FG02-01ER54615 and DE-FC02-99ER54512-CMOD.

  6. Investigating electromagnetic effects on core transport in Alcator C-Mod H-mode discharges

    NASA Astrophysics Data System (ADS)

    Guttenfelder, W.; Howard, N. T.; Irby, J.; Poli, F. M.; White, A. E.; Bergerson, W. F.; Brower, D. L.; Ding, W. X.; Kessel, C. E.; Sung, C.; Wolfe, S. M.; Xu, P.

    2014-10-01

    Understanding the importance of electromagnetic effects on core turbulence and transport is being pursued at Alcator C-Mod, especially for higher performance H-mode plasmas at increasing beta. Previously reported measurements from a line-integrated polarimeter diagnostic reveal broadband, high frequency fluctuations. The presence of these features, absent in core and edge density fluctuation measurements from phase contrast imaging, suggest they may be related to fluctuations in the magnetic field. Such features were observed in a number of H-mode plasmas over a range of normalized beta (βN ~ 1-2) and Greenwald fraction (fGW ~ 0.45-0.85). To investigate the possible influence of electromagnetic effects on core transport and turbulence, gyrokinetic simulations are used to predict microinstability of these discharges, the corresponding relative amplitude of the magnetic fluctuations in comparison to density fluctuations, and the sensitivity of these predictions to variations in beta. Results of both linear and nonlinear simulations and their comparison with transport and turbulence measurements will be presented. This work is supported by US DOE Contracts DE-AC02-09CH11466 and DE-FC02-99ER54512.

  7. Motivation and goals of the new heated outer divertor for Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Lipschultz, B.; Doody, J.; Ellis, R.; Granetz, R.; Harrison, S.; Labombard, B.; Vieira, R.; Zhang, H.; Zhou, L.

    2012-10-01

    A precision-aligned, high-temperature outer divertor is being developed for Alcator C-Mod to enhance heatflux handling and to advance our knowledge and experience with high-Z Plasma Facing Components (PFCs) in a reactor-level power density environment. Several departures from the design of the current divertor will be implemented: Instead of 10 toroidal divertor segments that expand toroidally as they heat up, the divertor plate will be toroidally continuous, with no openings or leading edges in the high-heat flux region. It will expand in the radial direction when heated while maintaining good alignment with shallow field line angles (˜ 2 degrees), a requirement for future divertors. Those characteristics will reduce both impurity sources and disruption forces. A second design goal is to be able to control the divertor temperature up to 600^oC by installing heaters in the structure. Given the Arrhenius relation between hydrogen diffusivity and temperature in tungsten (and molybdenum) this will open up a new area of study for tokamaks - exploration of the effect of PFC temperature on fuel retention. Temperature control may also open up a new area of study into the effect of changes in divertor recycling on fueling and core confinement.

  8. Upgrades to the 4-strap ICRF Antenna in Alcator C-Mod

    SciTech Connect

    G. Schilling; J.C. Hosea; J.R. Wilson; W. Beck; R.L. Boivin; P.T. Bonoli; D. Gwinn; W.E. Lee; E. Nelson-Melby; M. Porkolab; R. Vieira; S.J. Wukitch; and J.A. Goetz

    2001-06-12

    A 4-strap ICRF antenna suitable for plasma heating and current drive has been designed and fabricated for the Alcator C-Mod tokamak. Initial operation in plasma was limited by high metallic impurity injection resulting from front surface arcing between protection tiles and from current straps to Faraday shields. Antenna modifications were made in February 2000, resulting in impurity reduction, but low-heating efficiency was observed when the antenna was operated in its 4-strap rather than a 2-strap configuration. Further modifications were made in July 2000, with the installation of BN plasma-facing tiles and radio- frequency bypassing of the antenna backplane edges and ends to reduce potential leakage coupling to plasma surface modes. Good heating efficiency was now observed in both heating configurations, but coupled power was limited to 2.5 MW in H-mode, 3 MW in L-mode, by plasma-wall interactions. Additional modifications were started in February 2001 and will be completed by this meeting. All the above upgrades and their effect on antenna performance will be presented.

  9. Statistics of fluctuation induced transport in the scrape-off layer of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Kube, Ralph; Garcia, Odd Erik; Theodorsen, Audun; Labombard, Brian; Terry, James

    2016-10-01

    The fluctuation induced transport in the scrape-off layer of Alcator C-Mod is investigated in an ohmically heated lower single-null discharge using Mirror Langmuir Probes. The probes are connected to a horizontal scanning probe which dwells at the outboard mid plane limiter radius and to electrodes in the outer divertor baffle. At the limiter radius the electron density, electron temperature and plasma potential are correlated with linear correlation coefficients r of approximately r=0.8. The bursts show a steep rise and a decay on a time scales of approximately 5 and 10 microseconds respectively. Amplitudes of bursts in the density, temperature, and plasma potential time series are correlated with r approximately 0.7-0.8. Conditionally averaged bursts in the radial particle and heat flux time series are less coherent and less reproducible, their amplitudes are correlated to the amplitude of bursts in the density time series with r=0.4. Statistics of the fluctuating plasma parameters at the outer divertor baffle are qualitatively similar to those at outboard midplane. Histograms, as well as statistics for level crossings and excess times spent above a given threshold for the time series compare favorably to a stochastic model for time series of scrape-off layer plasmas.

  10. Gyrokinetic simulation of I-mode C-Mod pedestal using GENE

    NASA Astrophysics Data System (ADS)

    Liu, Xing; David, H.; Kotschenreuther, M.; Mahajan, S.; Huges, J.; Hubbard, A.; Valanju, P.

    2016-10-01

    Naturally stable to ELMs, and with widths larger than EPED predictions, the I-modes are an excellent laboratory for investigating the role of drift microinstabilities in pedestal formation since I-mode pedestal are not ``limited'' by MHD instabilities-Peeling Ballooning or the Kinetic Ballooning. Because the Weakly Coherent Mode (WCM) is shown to be correlated, primarily, to particle transport, the pedestal heat transport, in some sense, must be controlled by drift-type modes. We present here a study based on gyrokinetic simulations (using GENE) to model heat transport in the I-mode pedestals in C-Mod. Nonlinear ETG simulations, found to be streamer-dominated, can match experimental heat flux with profile adjustment well within experimental error bars. The ETG simulations reveal very notable fine-scale structure (in the parallel direction) of the eigenfunctions in both linear and nonlinear simulations. Simulations, varying impurity level (Zeff) and temperature and density profiles (within experimental error bars), are used to probe the sensitivity of ETG heat transport to the most important input parameters. Efforts to identify an instability corresponding to the WCM will also be discussed. Work supported by USDOE Grant DE-FG02-04ER54742.

  11. Integrated numerical design of an innovative Lower Hybrid launcher for Alcator C-Mod

    SciTech Connect

    Meneghini, O.; Shiraiwa, S.; Beck, W.; Irby, J.; Koert, P.; Parker, R. R.; Viera, R.; Wukitch, S.; Wilson, J.

    2009-11-26

    The new Alcator C-Mod LHCD system (LH2) is based on the concept of a four way splitter [1] which evenly splits the RF power among the four waveguides that compose one of the 16 columns of the LH grill. In this work several simulation tools have been used to study the LH2 coupling performance and the launched spectra when facing a plasma, numerically verifying the effectiveness of the four way splitter concept and further improving its design. The TOPLHA code has been used for modeling reflections at the antenna/plasma interface. TOPLHA results have been then coupled to the commercial code CST Microwave Studio to efficiently optimize the four way splitter geometry for several plasma scenarios. Subsequently, the COMSOL Multiphysics code has been used to self consistently take into account the electromagnetic-thermal-structural interactions. This comprehensive and predictive analysis has proven to be very valuable for understanding the behavior of the system when facing the plasma and has profoundly influenced several design choices of the LH2. According to the simulations, the final design ensures even poloidal power splitting for a wide range of plasma parameters, which ultimately results in an improvement of the wave coupling and an increased maximum operating power.

  12. Investigation of the transport shortfall in Alcator C-Mod L-mode plasmas

    NASA Astrophysics Data System (ADS)

    Howard, N. T.; White, A. E.; Greenwald, M.; Reinke, M. L.; Walk, J.; Holland, C.; Candy, J.; Görler, T.

    2013-03-01

    A so-called "transport shortfall," where ion and electron heat fluxes and turbulence are underpredicted by gyrokinetic codes, has been robustly identified in DIII-D L-mode plasmas for ρ >0.55 [T. L. Rhodes et al., Nucl. Fusion 51(6), 063022 (2011); and C. Holland et al., Phys. Plasmas 16(5), 052301 (2009)]. To probe the existence of a transport shortfall across different tokamaks, a dedicated scan of auxiliary heated L-mode discharges in Alcator C-Mod are studied in detail with nonlinear gyrokinetic simulations for the first time. Two discharges, only differing by the amount of auxiliary heating are investigated using both linear and nonlinear simulation of the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)]. Nonlinear gyrokinetic simulation of the low and high input power discharges reveals a discrepancy between simulation and experiment in only the electron heat flux channel of the low input power discharge. However, both discharges demonstrate excellent agreement in the ion heat flux channel, and the high input power discharge demonstrates simultaneous agreement with experiment in both the electron and ion heat flux channels. A summary of linear and nonlinear gyrokinetic results and a discussion of possible explanations for the agreement/disagreement in each heat flux channel is presented.

  13. Investigation of the transport shortfall in Alcator C-Mod L-mode plasmas

    SciTech Connect

    Howard, N. T.; White, A. E.; Greenwald, M.; Reinke, M. L.; Walk, J.; Holland, C.; Candy, J.; Goerler, T.

    2013-03-15

    A so-called 'transport shortfall,' where ion and electron heat fluxes and turbulence are underpredicted by gyrokinetic codes, has been robustly identified in DIII-D L-mode plasmas for {rho}>0.55[T. L. Rhodes et al., Nucl. Fusion 51(6), 063022 (2011); and C. Holland et al., Phys. Plasmas 16(5), 052301 (2009)]. To probe the existence of a transport shortfall across different tokamaks, a dedicated scan of auxiliary heated L-mode discharges in Alcator C-Mod are studied in detail with nonlinear gyrokinetic simulations for the first time. Two discharges, only differing by the amount of auxiliary heating are investigated using both linear and nonlinear simulation of the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)]. Nonlinear gyrokinetic simulation of the low and high input power discharges reveals a discrepancy between simulation and experiment in only the electron heat flux channel of the low input power discharge. However, both discharges demonstrate excellent agreement in the ion heat flux channel, and the high input power discharge demonstrates simultaneous agreement with experiment in both the electron and ion heat flux channels. A summary of linear and nonlinear gyrokinetic results and a discussion of possible explanations for the agreement/disagreement in each heat flux channel is presented.

  14. First Measurements of Edge Transport Driven by the Shoelace Antenna on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Golfinopoulos, T.; Labombard, B.; Parker, R. R.; Burke, W. M.; Hughes, J. W.; Brunner, D. F.; Davis, E. M.; Ennever, P. C.; Granetz, R. S.; Greenwald, M. J.; Irby, J. H.; Leccacorvi, R.; Marmar, E. S.; Parkin, W. C.; Porkolab, M.; Terry, J. L.; Vieira, R. F.; Wolfe, S. M.; Wukitch, S. J.; Alcator C-Mod Team

    2015-11-01

    The Shoelace antenna is a unique device designed to couple to the Quasi-Coherent Mode (QCM, k⊥ ~ 1 . 5 cm-1, 50 < f < 200 kHz) and Weakly-Coherent Mode (WCM, k⊥ ~ 1 . 5 cm-1, 200 < f < 500 kHz), continuous edge fluctuations that sustain high-performance confinement regimes by exhausting impurities. The antenna is used to explore whether modes like the QCM and WCM may be exploited to actively regulate edge transport. In initial experiments, the antenna excited a resonance at the QCM frequency and phase velocity, but transport measurements were unavailable. A subsequent redesign of the winding pitch allows the antenna to be field-aligned while mapping magnetically to the Mirror Langmuir Probe (MLP) on the last-closed flux surface. This has enabled the first measurements of edge transport induced by the antenna-driven fluctuation, which has been further enhanced by quadrupling the antenna source power. This work was supported by U.S. Department of Energy award DE-FC02-99ER54512, using Alcator C-Mod, a DOE SC User Facility.

  15. Simulation of disruptions on C-Mod in support of the new outer divertor project

    NASA Astrophysics Data System (ADS)

    Poli, F.; Kessel, C.; Titus, P.; Zhang, H.; Doody, J.; Granetz, R.; Lipschultz, B.

    2011-10-01

    Disruptions in C-Mod lead to large forces on structures inside the vacuum vessel and can be grouped in two classes depending on whether they begin with a thermal quench (midplane disruptions) or not (VDEs). VDEs induce the largest currents in the lower divertor, which is being re-designed to be toroidally continuous and allow operation at high temperatures (< 600C). Both types of disruptions have been simulated with TSC and the vector potential has been integrated in the ANSYS code (ANSYS® Multiphysics, Release 12.1) to calculate magnetic fields, induced currents in the structures of interest and forces. These forces are then used to calculate stress and deformation in the part. The TSC simulations are adjusted (thermal quench time, halo temperature and width, etc) to match the plasma characteristics as close as possible to experiments. The results of these simulations will be shown and the dependence of disruption time scales and characteristics on these plasma parameters and the new outer divertor structures will be discussed. This work is supported by the US Department of Energy under DE-AC02-CH0911466 and DE-FC02-99ER54512.

  16. The dynamics and structure of edge-localized-modes in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Terry, J. L.; Cziegler, I.; Hubbard, A. E.; Snipes, J. A.; Hughes, J. W.; Greenwald, M. J.; LaBombard, B.; Lin, Y.; Phillips, P.; Wukitch, S.

    2007-06-01

    Characteristics of discrete ELMs produced in Alcator C-Mod discharges of low edge collisionality (0.2 < ν∗ < 1) and large lower triangularity (δlower ∼ 0.75) are examined. The energy lost per ELM from the H-mode pedestal is ∼10% of the pedestal energy. These ELMs exhibit relatively long-lived precursor oscillations, often with two modes of intermediate toroidal mode number present. At the ELM 'crash' multiple plasma filament structures are expelled into the scrape-off-layer. A short-lived high frequency (∼0.5 MHz) magnetic oscillation is initiated at the 'crash'. The initial ELM filaments are large perturbations to the SOL with radial extents of 0.5-1 cm and typical radial propagation velocities of 1 km/s. Velocities of up to 8 km/s have been seen. The poloidal extent of the initial filaments is >4.5 cm. The initial filaments are followed (at intervals of ∼100 μs) by multiple, less perturbing secondary filaments.

  17. Characterization of enhanced D{alpha} high-confinement modes in Alcator {ital C}-Mod

    SciTech Connect

    Greenwald, M.; Boivin, R.; Bonoli, P.; Budny, R.; Fiore, C.; Goetz, J.; Granetz, R.; Hubbard, A.; Hutchinson, I.; Irby, J.; LaBombard, B.; Lin, Y.; Lipschultz, B.; Marmar, E.; Mazurenko, A.; Mossessian, D.; Sunn Pedersen, T.; Pitcher, C.S.; Porkolab, M.; Rice, J.; Rowan, W.; Snipes, J.; Schilling, G.; Takase, Y.; Terry, J.; Wolfe, S.; Weaver, J.; Welch, B.; Wukitch, S.

    1999-05-01

    Regimes of high-confinement mode have been studied in the Alcator {ital C}-Mod tokamak [Hutchinson {ital et al.}, Phys. Plasmas {bold 1}, 1511 (1994)]. Plasmas with no edge localized modes (ELM-free) have been compared in detail to a new regime, enhanced D{alpha} (EDA). EDA discharges have only slightly lower energy confinement than comparable ELM-free ones, but show markedly reduced impurity confinement. Thus EDA discharges do not accumulate impurities and typically have a lower fraction of radiated power. The edge gradients in EDA seem to be relaxed by a continuous process rather than an intermittent one as is the case for standard ELMy discharges and thus do not present the first wall with large periodic heat loads. This process is probably related to fluctuations seen in the plasma edge. EDA plasmas are more likely at low plasma current (q{gt}3.7), for moderate plasma shaping, (triangularity {approximately}0.35{endash}0.55), and for high neutral pressures. As observed in soft x-ray emission, the pedestal width is found to scale with the same parameters that determine the EDA/ELM-free boundary. {copyright} {ital 1999 American Institute of Physics.}

  18. Understanding of Neutral Gas Transport in the Alcator C-Mod Tokamak Divertor

    SciTech Connect

    D.P. Stotler; C.S. Pitcher; C.J. Boswell; B. LaBombard; J.L. Terry; J.D. Elder; S. Lisgo

    2002-05-07

    A series of experiments on the effect of divertor baffling on the Alcator C-Mod tokamak provides stringent tests on models of neutral gas transport in and around the divertor region. One attractive feature of these experiments is that a trial description of the background plasma can be constructed from experimental measurements using a simple model, allowing the neutral gas transport to be studied with a stand-alone code. The neutral-ion and neutral-neutral elastic scattering processes recently added to the DEGAS 2 Monte Carlo neutral transport code permit the neutral gas flow rates between the divertor and main chamber to be simulated more realistically than before. Nonetheless, the simulated neutral pressures are too low and the deuterium Balmer-alpha emission profiles differ qualitatively from those measured, indicating an incomplete understanding of the physical processes involved in the experiment. Some potential explanations are examined and opportunities for future exploration a re highlighted. Improvements to atomic and surface physics data and models will play a role in the latter.

  19. Reduction of Core Turbulence in I-mode Plasmas at Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    White, A. E.; Barnes, M.; Dominguez, A.; Greenwald, M.; Howard, N. T.; Hubbard, A. E.; Hughes, J. W.; Mikkelsen, D. R.; Parra, F. I.; Reinke, M. L.; Sung, C.; Walk, J.; Whyte, D. G.

    2013-10-01

    Core turbulent fluctuations (0.40 < r/a < 0.95) are reduced in the high confinement regime, I-mode, at Alcator C-Mod. Long wavelength density fluctuation levels are observed to decrease from L-mode levels by up to 30%, while long wavelength electron temperature fluctuation levels are observed to decrease by up to 70%. This reduction in core turbulence is correlated with the increases in confinement in I-mode. During some L-I transitions, density fluctuations in the core (r/a ~ 0.5) and near the top of the Te pedestal (r/a ~ 0.95) are both reduced prior to the reduction of low-frequency edge turbulence (r/a ~ 0.99-1.0), and prior to the onset of the edge-localized weakly coherent mode (WCM) (r/a ~ 0.99-1.0). This result contrasts typical observations of confinement transitions (I-mode and H-mode) where changes in edge turbulence occur prior to changes in core turbulence. Supported by USDoE: DE-FC02-99ER54512 and DE-SC0006419.

  20. Reduction of core turbulence in I-mode plasmas in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    White, A. E.; Barnes, M.; Dominguez, A.; Greenwald, M.; Howard, N. T.; Hubbard, A. E.; Hughes, J. W.; Mikkelsen, D. R.; Parra, F. I.; Reinke, M. L.; Sung, C.; Walk, J.; Whyte, D. G.

    2014-08-01

    In this paper, we report observations of reduced core (0.40 < ρ < 0.95) fluctuations in the edge localized mode (ELM)-free high-confinement regime, I-mode, at Alcator C-Mod (Marmar et al2009 Nucl. Fusion 49 104014). Long wavelength (kθρs < 0.5) density fluctuation levels are observed to decrease from L-mode levels by up to 30% in I-mode, while long wavelength (kθρs < 0.3) electron temperature fluctuation levels are observed to decrease by up to 70% in I-mode. This reduction in core turbulence is correlated with the increases in confinement in I-mode compared to L-mode. As the pedestal temperature increases across the L-I transition, core density fluctuations (0.40 < ρ < 0.95) are reduced prior to the onset of the edge-localized (ρ ˜ 0.99-1.0) weakly coherent mode (WCM) and prior to the reduction of low-frequency (ρ ˜ 0.99-1.0) turbulence in the edge/pedestal region. This result helps add to our understanding of the dynamics of confinement transitions such as I-mode and H-mode, where changes in edge turbulence are more typically observed to occur prior to changes in core turbulence.

  1. Alcator C-Mod's Quasi-Coherent Mode Antenna: Experimental Results and Interpretation

    NASA Astrophysics Data System (ADS)

    Golfinopoulos, T.; Labombard, B.; Parker, R. R.; Burke, W.; Davis, E. M.; Granetz, R.; Greenwald, M.; Marmar, E.; Porkolab, M.; Terry, J. L.; Wolfe, S. M.; Woskov, P. P.; Xu, X.

    2012-10-01

    A new ``Shoelace'' antenna has been installed on Alcator C-Mod. Its goal is to interact with edge fluctuations, and particularly the quasi-coherent mode (QCM) associated with the steady-state EDA H-mode. With k=1.5 cm-1 and frequency range, 40

  2. A Study of Electron Modes in Off-axis Heated Alcator C-Mod Plasmas

    NASA Astrophysics Data System (ADS)

    Fiore, C. L.; Ernst, D. R.; Mikkelsen, D.; Ennever, P. C.; Howard, N. T.; Gao, C.; Reinke, M. L.; Rice, J. E.; Hughes, J. W.; Walk, J. R.

    2013-10-01

    Understanding the underlying physics and stability of the peaked density internal transport barriers (ITB) that have been observed during off-axis ICRF heating of Alcator C-Mod plasmas is the goal of recent gyro-kinetic simulations. Two scenarios are examined: an ITB plasma formed with maximal (4.5 MW) off-axis heating power; also the use of off-axis heating in an I-mode plasma as a target in the hopes of establishing an ITB. In the former, it is expected that evidence of trapped electron mode instabilities could be found if a sufficiently high electron temperature is achieved in the core. Linear simulations show unstable modes are present across the plasma core from r/a = 0.2 and greater. In the latter case, despite establishing similar conditions to those in which ITBS were formed, none developed in the I-mode plasmas. Linear gyrokinetic analyses show no unstable ion modes at r/a < 0.55 in these I-mode plasmas, with both ITG and ETG modes present beyond r/a = 0.65. The details of the experimental results will be presented. Linear and non-linear simulations of both of these cases will attempt to explore the underlying role of electron and ion gradient driven instabilities to explain the observations. This work was supported by US-DoE DE-FC02-99ER54512 and DE-AC02-09CH11466.

  3. Hard x-ray diagnostic for lower hybrid experiments on Alcator C-Mod

    SciTech Connect

    Liptac, J.; Parker, R.; Tang, V.; Peysson, Y.; Decker, J.

    2006-10-15

    Alcator C-Mod's lower hybrid current drive (LHCD) system allows the exploration of advanced tokamak (AT) regimes at densities relevant to ITER and fusion reactors. The location of the LHCD is critical to AT performance and may be inferred by measuring the nonthermal bremsstrahlung emission in the hard x-ray (HXR) region. A pinhole camera using an array of 32 CdZnTe detectors is used to image energies in the 20-200 keV range. Detectors and pulse processing electronics are integrated into a compact and modular package making extensive use of printed circuit board and surface mount technology. The system also makes use of fast digitization and software signal processing techniques. An ambient environment of neutrons, gammas, and high rf power requires careful shielding. Shielding is studied using the neutron and photon transport code MCNP. The design of the diagnostic is presented along with background measurements in lieu of LHCD fast electrons. Background measurements are then compared to advanced modeling results to predict the power threshold for meaningful HXR data for a H-mode target plasma.

  4. Integrated Plasma Simulation of Lower Hybrid Current Drive Modification of Sawtooth in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Bonoli, P. T.; Hubbard, A. E.; Schmidt, A. E.; Wright, J. C.; Kessel, C. E.; Batchelor, D. B.; Berry, L. A.; Harvey, R. W.

    2010-11-01

    Experiments were performed in Alcator C-Mod, where the onset time for sawteeth was delayed significantly (up to 0.5 s) relative to ohmically heated plasmas, through injection of off-axis LH current drive power [1]. In this poster we discuss simulations of these experiments using the Integrated Plasma Simulator (IPS) [2], through which driven current density profiles and hard x-ray spectra are computed using a ray tracing code (GENRAY) and Fokker Planck code (CQL3D) [3], that are executed repeatedly in time. The background plasma is evolved in these simulations using the TSC transport code with the Porcelli sawtooth model [4]. [4pt] [1] C. E. Kessel et al, Bull. of the Am. Phys. Soc. 53, Poster PP6.00074 (2008). [0pt] [2] D. Batchelor et al, Journal of Physics: Conf. Series 125, 012039 (2008). [0pt] [3] R. W. Harvey and M. G. McCoy, Proc. of the IAEA Tech. Comm. Mtg. on Sim. and Mod. of Therm. Plasmas, Montreal, Canada (1992). [0pt] [4] S. C. Jardin et al, Journal Comp. Phys. 66, 481 (1986).

  5. Radiation asymmetry and MHD activity in gas jet rapid shutdowns on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Olynyk, Geoffrey; Granetz, Robert; Whyte, Dennis; Alcator C-Mod Team

    2013-10-01

    Radiative rapid shutdown via massive noble gas injection (MGI) is an integral part of the ITER disruption mitigation system (DMS). However, observations have shown that the radiation during MGI rapid shutdowns may be spatially asymmetric, particularly during the initial phase when the plasma's thermal energy is converted to radiation. ITER requires the radiation peaking factor (PF) to be less than approximately 2.0 to 2.5 in this thermal quench (TQ) phase in order to prevent melting of the beryllium wall even in the case of a successful MGI rapid shutdown. We report on observations of rotating MHD modes in single- and multiple-gas-jet rapid shutdowns on Alcator C-Mod, and discuss the role of mode rotation during the TQ in setting the radiation peaking factor. The implications for the ITER DMS are discussed. This work was supported by the United States Department of Energy under Contract No. DE-FC02-99ER54512 and the Natural Sciences and Engineering Research Council of Canada PGS D program.

  6. Design and Analysis of the Alcator C-Mod Two-Strap ICRF Antenna

    NASA Astrophysics Data System (ADS)

    Takase, Y.; Golovator, S. N.; Porkolab, M.; Bajwa, K.; Becker, H.; Caldwell, D.

    1992-01-01

    ICRF fast wave heating with up to 8 MW of rf power at 80 MHz is planned on the Alcator C-MOD tokamak (R=0.665 m, a=0.21 m, κ=1.8, B≤9 T, I≤3 MA). During the initial tokamak operation, a movable single-strap antenna will be used to ensure operational flexibility. The second ICRF antenna, which is currently under construction, has two current straps which can be driven out-of-phase to improve the heating efficiency and minimize impurity generation. The current straps are mechanically isolated from the 4` feedthroughs. The Faraday shield consists of a single layer of circular cross section rods which are slanted at 10° to horizontal to approximately align with the field line over a wide range of operating conditions. The antenna box is protected by TiC coated TZM (Molybdenum alloy) tiles arranged in a ``picture-frame'' fashion. These tiles can be replaced with tiles made of a lower Z material. Because of its larger size, the two-strap antenna must be assembled inside the vacuum chamber and attached to the wall of the vacuum vessel to support against larger disruption loads. The rf thermal loads are significantly lower for the same total power (2 MW per antenna), which allows a longer pulse (10 sec) operation.

  7. Alcator C-Mod Experiments in Support of the ITER Baseline 15 MA Scenario

    SciTech Connect

    C Kessel, et al

    2013-05-07

    Experiments on Alcator C-Mod have addressed several issues for the ITER 15 MA baseline scenario from 2009-2012. Rampup studies show ICRF can save significant V-s, and that an H-mode in the ramp can be utilized to save 50% more. ICRF modifications to li(1) are minimal, although the Te profile is peaked relative to ohmic in the plasma center, and alter sawtooth onset times. Rampdown studies show H-modes can be routinely sustained, avoiding an OH coil over-current associated with the H-L transition, that fast rampdowns are preferred, the density drops with Ip, and that the H-L transition occurs at Ploss/Pthr,LH ~ 1.0-1.3 at n/nGr ~ 0.85. Flattop plasmas targeting ITER baseline parameters have been sustained for 20 τE or 8-13 τCR, but only reach H98 ~ 0.6 at n/nGr = 0.85, rising to 0.9 at n/nGr = 0.65.

  8. Upgrade of the Edge Charge Exchange Diagnostic on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    McDermott, Rachael; Lipschultz, Bruce; Marr, Kenneth

    2006-10-01

    The current edge Charge Exchange Spectroscopy system is being upgraded to include both a beam viewing and a background viewing toroidal periscope. The beam viewing periscope will be focused on the center of the DNB and will cover a 4cm radial region at the edge of the plasma starting a few centimeters in from and extending up to 1centimeter outside of the last closed flux surface. The background periscope will view the same radial region but will be displaced toroidally by 36 degrees. Each periscope has 20 chordal views with a radial resolution of 2.5-3mm. The presence of a background periscope obviates the need for a chopped DNB by providing time synchronized background B^+4 spectral data that can be subtracted directly from the active beam-derived B^+4 line-shapes. This system has been designed to work in conjunction with the current poloidal Charge Exchange periscope which has 25 fibers focused in the same region with equivalent radial resolution. The new toroidal system will enable concurrent measurements of the poloidal and toroidal velocity as well as the temperature and density of the B^+5 ions in the edge pedestal region; a measurement that currently does not exist on C-Mod. This information will then be used to calculate radial electric field profiles and study edge physics phenomena.

  9. The Effect of Sawtooth Oscillations on Fast Wave Coupling and Propagation in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Reardon, J.; Bonoli, P. T.; Porkolab, M.; Wukitch, S. J.; Brambilla, M.

    1998-11-01

    On Alcator C-Mod the antenna loading seen during fast-wave minority heating with (0, π , 0, π ) phasing often shows modulation which follows the timing of central sawteeth. Both sawteeth and inverse sawteeth have been observed on the loadings of the two antennas, sometimes simultaneously. The loading can change by as much as a factor of two in 0.1 ms. The amplitude of the RF power detected by loop probes on the high-field side of the plasma, opposite the antennas, also often shows the imprint of central sawteeth: it increases immediately at the sawtooth crash, by as much as a factor of two, then decreases more slowly during the sawtooth reheat. The amount of sawtooth modulation on the loop probe signals is sensitive to I_p. Quantitative comparison of the measured antenna loading and the probe signals with the antenna radiation resistance and the outward-radiated power calculated by FELICE is used to diagnose the coupling and propagation of the fast wave.

  10. Alcator C-Mod ICRF fast wave antenna design and analysis and expected plasma performance

    NASA Astrophysics Data System (ADS)

    Takase, Y.; Golovato, S.; Porkolab, M.; Becker, H.; Diatchenko, N.; Kochan, S.; McCoy, C.; Pierce, N.

    1989-07-01

    The design and analysis of the fast wave antenna to be used for ICRF heating experiments on the Alcator C-Mod tokamak are described. A movable single-strap low-field-side-launch loop antenna will be used during the initial operation period. Structural analysis against disruption and thermal analysis are performed. Optimized two-strap antennae with twice the surface area are planned for high-power heating experiments. Antenna-plasma coupling studies indicate a poor (<20%) single-pass ion absorption for D(3He), and a radiation resistance of ≳10Ω. Minority ions are not expected to be accelerated to very high energies under typical operating densities (Teff≲50 keV for n¯e≳3×1020m-3), and energetic ions should mainly slow down on ions. The transport of minority ions broadens the energetic minority ion and slowing down profiles and reduces Teff, but the effect is small for n¯e≳3×1020m-3.

  11. Core Impurity Transport in C-Mod L-, I- and H-mode Plasmas

    NASA Astrophysics Data System (ADS)

    Rice, J.; Reinke, M.; Gao, C.; Howard, N.; Chilenski, M.; Delgado-Aparicio, L.; Granetz, R.; Greenwald, M.; Hubbard, A.; Hughes, J.; Irby, J.; Lin, Y.; Marmar, E.; Mumgaard, R.; Scott, S.; Terry, J.; Walk, J.; White, A.; Whyte, D.; Wolfe, S.; Wukitch, S.

    2014-10-01

    Core impurity transport has been investigated for a variety of confinement regimes in C-Mod plasmas from x-ray emission following laser blow-off injection of medium and high Z materials. In Ohmic L-mode discharges, impurity transport is anomalous (Deff >> Dnc) and changes very little across the LOC/SOC boundary. In ICRF heated L-mode plasmas, the core impurity confinement time decreases with increasing ICRF input power (and subsequent increasing electron temperature) and increases with plasma current. Nearly identical impurity confinement characteristics are observed in plasmas with I-mode confinement. In EDA H-mode discharges the core impurity confinement time is much larger, but exhibits a similar scaling with plasma current, although there is a covariance with the density. There is a strong connexion between core impurity confinement time and the edge density gradient. Central impurity density profiles in these stationary regimes are often flat, in spite of large amplitude sawtooth oscillations, and there is little evidence of impurity convection inside of r/a = 0.3. Supported by USDoE Award DE-FC02-99ER54512.

  12. Core impurity transport in Alcator C-Mod L-, I- and H-mode plasmas

    NASA Astrophysics Data System (ADS)

    Rice, J. E.; Reinke, M. L.; Gao, C.; Howard, N. T.; Chilenski, M. A.; Delgado-Aparicio, L.; Granetz, R. S.; Greenwald, M. J.; Hubbard, A. E.; Hughes, J. W.; Irby, J. H.; Lin, Y.; Marmar, E. S.; Mumgaard, R. T.; Scott, S. D.; Terry, J. L.; Walk, J. R.; White, A. E.; Whyte, D. G.; Wolfe, S. M.; Wukitch, S. J.

    2015-03-01

    Core impurity transport has been investigated for a variety of confinement regimes in Alcator C-Mod plasmas from x-ray emission following injection of medium and high Z materials. In ohmic L-mode discharges, impurity transport is anomalous (Deff ≫ Dnc) and changes very little across the LOC/SOC boundary. In ion cyclotron range of frequencies (ICRF) heated L-mode plasmas, the core impurity confinement time decreases with increasing ICRF input power (and subsequent increasing electron temperature) and increases with plasma current. Nearly identical impurity confinement characteristics are observed in I-mode plasmas. In enhanced Dα H-mode discharges the core impurity confinement times are much longer. There is a strong connection between core impurity confinement time and the edge density gradient across all confinement regimes studied here. Deduced central impurity density profiles in stationary plasmas are generally flat, in spite of large amplitude sawtooth oscillations, and there is little evidence of impurity convection inside of r/a = 0.3 when averaged over sawteeth.

  13. Fast-switching Langmuir probe bias electronics for Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Lyons, L.; Labombard, B.

    2006-10-01

    In order to resolve fast-changes in edge plasma density, temperature and plasma potentials with a single Langmuir electrode, the I-V characteristic must be generated and sampled at high frequency. To this end, a custom-designed package of fast-switching electronics is being assembled for use in Alcator C-Mod, employing three principal components: (1) a master TTL ‘waveform generator’, (2) fast-switching MOSFET drive circuits (˜ 30 ns rise time), and (3) current-voltage monitor circuits. Three voltage bias states are capacitively coupled to up to 6 Langmuir probes in a sequence that samples portions of the I-V characteristic: ‘ion saturation (>= -234V), ‘electron collection’ (<= +64V), and ‘near floating’ (˜ 0V). Up to 2 amps of peak current can be supplied to each probe with waveform durations of ˜ 2 seconds. Resultant I-V characteristics are digitally sampled (<= 50MHz) by cPCI transient recorders. Three additional TTL waveforms, synchronized to the data-sampling times of the different bias states, are also supplied. These may be used to report plasma conditions in real-time using a ‘mirror Langmuir probe’ technique [1]. [1] B. LaBombard and L. Lyons, manuscript in preparation.

  14. Effect on plasma rotation of lower hybrid (LH) waves in Alcator C-Mod

    SciTech Connect

    Lee, J. P.; Barnes, M.; Parker, R. R.; Rice, J. E.; Parra, F. I.; Bonoli, P. T.; Reinke, M. L.

    2014-02-12

    The injection of LH waves for current drive into a tokamak changes the ion toroidal rotation. In Alcator C-Mod, the direction of the steady state rotation change due to LH waves depends on the plasma current and the density. The change in rotation can be estimated by balancing the external torque of lower hybrid waves with the turbulent radial transport of the momentum. For high plasma current, the turbulent pinch and diffusion of the injected counter-current momentum are sufficient to explain the rotation change. However, for low plasma current, the change in the the intrinsic momentum transport (residual stress) for a non-rotating state is required to explain the co-current rotation change. Accordingly, we investigate the intrinsic momentum transport for the non-rotating state when diamagnetic flow and ExB flow cancel each other. The change in the intrinsic momentum transport due to lower hybrid waves is significant when the plasma current is low, which may explain the rotation reversal for low plasma current. The effect of changed q (safety factor) profile by lower hybrid on the intrinsic momentum transport is estimated by gyrokinetics.

  15. Hard x-ray diagnostic for lower hybrid experiments on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Liptac, J.; Parker, R.; Tang, V.; Peysson, Y.; Decker, J.

    2006-10-01

    Alcator C-Mod's lower hybrid current drive (LHCD) system allows the exploration of advanced tokamak (AT) regimes at densities relevant to ITER and fusion reactors. The location of the LHCD is critical to AT performance and may be inferred by measuring the nonthermal bremsstrahlung emission in the hard x-ray (HXR) region. A pinhole camera using an array of 32 CdZnTe detectors is used to image energies in the 20-200keV range. Detectors and pulse processing electronics are integrated into a compact and modular package making extensive use of printed circuit board and surface mount technology. The system also makes use of fast digitization and software signal processing techniques. An ambient environment of neutrons, gammas, and high rf power requires careful shielding. Shielding is studied using the neutron and photon transport code MCNP. The design of the diagnostic is presented along with background measurements in lieu of LHCD fast electrons. Background measurements are then compared to advanced modeling results to predict the power threshold for meaningful HXR data for a H-mode target plasma.

  16. BOUT++ Simulations of Edge Turbulence in Alcator C-Mod's EDA H-Mode

    NASA Astrophysics Data System (ADS)

    Davis, E. M.; Porkolab, M.; Hughes, J. W.; Labombard, B.; Snyder, P. B.; Xu, X. Q.

    2013-10-01

    Energy confinement in tokamaks is believed to be strongly controlled by plasma transport in the pedestal. The pedestal of Alcator C-Mod's Enhanced Dα (EDA) H-mode (ν* > 1) is regulated by a quasi-coherent mode (QCM), an edge fluctuation believed to reduce particle confinement and allow steady-state H-mode operation. ELITE calculations indicate that EDA H-modes sit well below the ideal peeling-ballooning instability threshold, in contrast with ELMy H-modes. Here, we use a 3-field reduced MHD model in BOUT++ to study the effects of nonideal and nonlinear physics on EDA H-modes. In particular, incorporation of realistic pedestal resistivity is found to drive resistive ballooning modes (RBMs) and increase linear growth rates above the corresponding ideal rates. These RBMs may ultimately be responsible for constraining the EDA pedestal gradient. However, recent high-fidelity mirror Langmuir probe measurements indicate that the QCM is an electron drift-Alfvén wave - not a RBM. Inclusion of the parallel pressure gradient term in the 3-field reduced MHD Ohm's law and various higher field fluid models are implemented in an effort to capture this drift wave-like response. This work was performed under the auspices of the USDoE under awards DE-FG02-94-ER54235, DE-AC52-07NA27344, DE-AC52-07NA27344, and NNSA SSGF.

  17. BOUT++ simulations of edge turbulence in Alcator C-Mod's EDA H-mode

    NASA Astrophysics Data System (ADS)

    Davis, E. M.; Porkolab, M.; Hughes, J. W.; Labombard, B.; Snyder, P. B.; Xu, X. Q.; MIT PSFC Team; Atomics Team, General; LLNL Team

    2013-10-01

    Energy confinement in tokamaks is believed to be strongly controlled by plasma transport in the pedestal. The pedestal of Alcator C-Mod's Enhanced Dα (EDA) H-mode (ν* > 1) is regulated by a quasi-coherent mode (QCM), an edge fluctuation believed to reduce particle confinement and allow steady-state H-mode operation. ELITE calculations indicate that EDA H-modes sit well below the ideal peeling-ballooning instability threshold, in contrast with ELMy H-modes. Here, we use a 3-field reduced MHD model in BOUT++ to study the effects of nonideal and nonlinear physics on EDA H-modes. In particular, incorporation of realistic pedestal resistivity is found to drive resistive ballooning modes (RBMs) and increase linear growth rates above the corresponding ideal rates. These RBMs may ultimately be responsible for constraining the EDA pedestal gradient. However, recent high-fidelity mirror Langmuir probe measurements indicate that the QCM is an electron drift-Alfvén wave - not a RBM. Inclusion of the parallel pressure gradient term in the 3-field reduced MHD Ohm's law and various higher field fluid models are implemented in an effort to capture this drift wave-like response. This work was performed under the auspices of the USDoE under awards DE-FG02-94-ER54235, DE-AC52-07NA27344, DE-AC52-07NA27344, and NNSA SSGF.

  18. Measurement of LHCD edge power deposition through modulation techniques on Alcator C-Mod

    SciTech Connect

    Faust, I. C.; Brunner, D.; LaBombard, B.; Parker, R. R.; Baek, S. G.; Chilenksi, M. A.; Hubbard, A.; Hughes, J. W.; Terry, J. L.; Shiraiwa, S.; Walk, J. R.; Wallace, G. M.; Whyte, D. G.; Edlund, E.

    2015-12-10

    The efficiency of LHCD on Alcator C-Mod drops exponentially with line average density. At reactor relevant densities (> 1 · 1020 [m{sup −3}]) no measurable current is driven. While a number of causes have been suggested, no specific mechanism has been shown to be responsible for the loss of current drive at high density. Fast modulation of the LH power was used to isolate and quantify the LHCD deposition within the plasma. Measurements from these plasmas provide unique evidence for determining a root cause. Modulation of LH power in steady plasmas exhibited no correlated change in the core temperature. A correlated, prompt response in the edge suggests that the loss in efficiency is related to a edge absorption mechanism. This follows previous results which found the generation of n{sub ||}-independent SOL currents. Multiple Langmuir probe array measurements of the conducted heat conclude that the lost power is deposited near the last closed flux surface. The heat flux induced by LH waves onto the outer divertor is calculated. Changes in the neutral pressure, ionization and hard X-ray emission at high density highlight the importance of the active divertor in the loss of efficiency. Results of this study implicate a mechanism which may occur over multiple passes, leading to power absorption near the LCFS.

  19. Toroidally resolved radiation dynamics during a gas jet mitigated disruption on Alcator C-Mod

    SciTech Connect

    Reinke, M. L.; Whyte, D. G.; Granetz, R.; Hutchinson, I. H.

    2008-12-01

    Measurements of the radiation dynamics during an Alcator C-Mod disruption induced by a high pressure He/Ar gas jet are presented. Data are analysed from four 22-channel Absolute eXtreme UltraViolet diode arrays viewing on horizontal planes from different toroidal and vertical locations, both towards and away from the gas jet. Prior to the loss of the core plasma stored energy, strong emission is seen from a shell at the plasma edge that expands toroidally and poloidally away from the the gas jet at 650 m s-1, consistent with neutral expansion rates. Both the energy loss from this region and from the bulk plasma are shown to be of comparable magnitudes and important in dissipating the electron thermal energy outside the q = 2 surface. During the thermal quench, line-integrated brightnesses exceed 100 MW m-2. But while the brightness ratio of equivalent toroidally/vertically spaced views varies from 0.4 to 4.0, energy loss integrated over the disruption is shown to be symmetric to within 25%. Radiative energy loss local to the gas jet is shown to preheat nearby surfaces making them more susceptible to melting when the bulk of the thermal energy is lost.

  20. Zonal flow production in the L-H transition in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Cziegler, I.; Tynan, G. R.; Diamond, P. H.; Hubbard, A. E.; Hughes, J. W.; Irby, J.; Terry, J. L.

    2014-07-01

    Transitions of tokamak confinement regimes from low- to high-confinement are studied on Alcator C-Mod (Hutchinson et al 1994 Phys. Plasmas 1 1511) tokamak using gas-puff-imaging, with a focus on the interaction between the edge drift-turbulence and the local shear flow. Results show that the nonlinear turbulent kinetic energy transfer rate into the shear flow becomes comparable to the estimated value of the drift turbulence growth rate at the time the turbulent kinetic energy starts to drop, leading to a net energy transfer that is comparable to the observed turbulence losses. A corresponding growth is observed in the shear flow kinetic energy. The above behavior is demonstrated across a series of experiments. Thus both the drive of the edge zonal flow and the initial reduction of turbulence fluctuation power are shown to be consistent with a lossless kinetic energy conversion mechanism, which consequently mediates the transition into H-mode. The edge pressure gradient is then observed to build on a slower (1 ms) timescale, locking in the H-mode state. These results unambiguously establish the time sequence of the transition as: first the peaking of the normalized Reynolds power, then the collapse of the turbulence, and finally the rise of the diamagnetic electric field shear as the L-H transition occurs.

  1. Design, and initial experiment results of a novel LH launcher on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Shiraiwa, S.; Meneghini, O.; Parker, R. R.; Wallace, G.; Wilson, J.; Faust, I.; Lau, C.; Mumgaard, R.; Scott, S.; Wukitch, S.; Beck, W.; Doody, J.; Irby, J.; MacGibbon, P.; Johnson, D.; Kanojia, A.; Koert, P.; Terry, D.; Vieira, R.; Alcator C-Mod Team

    2011-10-01

    The design, construction and initial results of a new lower hybrid current drive (LHCD) launcher on Alcator C-Mod (Hutchinson et al 1994 Phys. Plasmas 1 1511) are presented. The new LHCD launcher (LH2) is based on a novel splitter concept which evenly distributes the microwave power in four ways in the poloidal direction. This design allows for simplification of the feeding structure while keeping the flexibility to vary the peak launched toroidal index of refraction, Ntoroidal, from -3.8 to 3.8. An integrated model predicts good plasma coupling over a wide range of edge densities, while poloidal variations of the edge density are found to affect the evenness of power splitting in the poloidal direction. The measured transmission loss is about 30% lower than the previous launcher, and a clean Ntoroidal spectrum has been confirmed. Power handling capability exceeding an empirical weak conditioning limit and reliable operation up to 1.1 MW net LHCD power have been achieved. A survey of antenna-plasma coupling shows the existence of a millimetric vacuum gap in front of the launcher. Fully non-inductive, reversed shear plasma operation has been demonstrated and sustained for multiple current diffusion times. The current drive efficiency, ηLH ≡ neR0Ip/PLH, of these plasmas is (0.2-0.25) × 1020 m-2A W-1, which is in agreement with the expected efficiency on the International Thermonuclear Experimental Reactor (ITER).

  2. Experimental studies of edge turbulence and confinement in Alcator C-Mod

    SciTech Connect

    Cziegler, I.; Terry, J. L.; Hughes, J. W.; LaBombard, B.

    2010-05-15

    The steep gradient edge region and scrape-off-layer (SOL) on the low-field-side of Alcator C-Mod [I. H. Hutchinson, R. Boivin, F. Bombarda et al., Phys. Plasmas 1, 1511 (1994)] tokamak plasmas are studied using gas-puff-imaging diagnostics. In L-mode plasmas, the region extending approx2 cm inside the magnetic separatrix has fluctuations showing a broad, turbulent spectrum, propagating in the electron diamagnetic drift direction, whereas features in the open field line region propagate in the ion diamagnetic drift direction. This structure is robust against toroidal field strength, poloidal null-point geometry, plasma current, and plasma density. Global parameter dependence of spectral and spatial structure of the turbulence inside the separatrix is explored and characterized, and both the intensity and spectral distributions are found to depend strongly on the plasma density normalized to the tokamak density limit. In H-mode discharges the fluctuations at and inside the magnetic separatrix show fundamentally different trends compared to L-mode, with the electron diamagnetic direction propagating turbulence greatly reduced in ELM-free [F. Wagner et al., Proceedings of the Thirteenth Conference on Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1982), Vol. I, p. 277], and completely dominated by the modelike structure of the quasicoherent mode in enhanced D-alpha regimes [A. E. Hubbard, R. L. Boivin, R. S. Granetz et al., Phys. Plasmas 8, 2033 (2001)], while the normalized SOL turbulence is largely unaffected.

  3. Analytic wave model of Stark deceleration dynamics

    SciTech Connect

    Gubbels, Koos; Meijer, Gerard; Friedrich, Bretislav

    2006-06-15

    Stark deceleration relies on time-dependent inhomogeneous electric fields which repetitively exert a decelerating force on polar molecules. Fourier analysis reveals that such fields, generated by an array of field stages, consist of a superposition of partial waves with well-defined phase velocities. Molecules whose velocities come close to the phase velocity of a given wave get a ride from that wave. For a square-wave temporal dependence of the Stark field, the phase velocities of the waves are found to be odd-fraction multiples of a fundamental phase velocity {lambda}/{tau}, with {lambda} and {tau} the spatial and temporal periods of the field. Here we study explicitly the dynamics due to any of the waves as well as due to their mutual perturbations. We first solve the equations of motion for the case of single-wave interactions and exploit their isomorphism with those for the biased pendulum. Next we analyze the perturbations of the single-wave dynamics by other waves and find that these have no net effect on the phase stability of the acceleration or deceleration process. Finally, we find that a packet of molecules can also ride a wave which results from an interference of adjacent waves. In this case, small phase stability areas form around phase velocities that are even-fraction multiples of the fundamental velocity. A detailed comparison with classical trajectory simulations and with experiment demonstrates that the analytic 'wave model' encompasses all the longitudinal physics encountered in a Stark decelerator.

  4. Measurements and Modeling of X-Ray and ECE Spectra During LHCD Experiments on Alcator C-Mod

    SciTech Connect

    Schmidt, A. E.; Bonoli, P. T.; Hubbard, A. E.; Liptac, J.; Parker, R. R.; Wallace, G. M.; Wilson, J. R.; Harvey, R. W.; Smirnov, A. P.

    2007-09-28

    Lower Hybrid Current Drive (LHCD) has been demonstrated on Alcator C-Mod. The LH-driven fast electrons can be detected through hard x-ray Bremsstrahlung emission as well as relativistically downshifted electron cyclotron emission (ECE). C-Mod has a hard x-ray camera with 32 chords, as well as several outboard midplane ECE diagnostics. CQL3D/GENRAY is a modeling package that employs a 3-D Fokker-Planck solver to compute steady-state distribution functions for a given LH N{sub parallel} spectrum and plasma. It also can perform self-consistent synthetic diagnostic calculations. LH phase and power scans have been carried out. Fast electron diffusion time can be inferred from x-ray data. Experimental measurements are compared with synthetic diagnostic modeling to see how changes in phasing and power affect current profile control and to benchmark CQL3D in ITER-relevant regimes.

  5. Tungsten impurity transport experiments in Alcator C-Mod to address high priority research and development for ITER

    SciTech Connect

    Loarte, A.; Polevoi, A. R.; Hosokawa, M.; Reinke, M. L.; Chilenski, M.; Howard, N.; Hubbard, A.; Hughes, J. W.; Rice, J. E.; Walk, J.; Köchl, F.; Pütterich, T.; Dux, R.; Zhogolev, V. E.

    2015-05-15

    Experiments in Alcator C-Mod tokamak plasmas in the Enhanced D-alpha H-mode regime with ITER-like mid-radius plasma density peaking and Ion Cyclotron Resonant heating, in which tungsten is introduced by the laser blow-off technique, have demonstrated that accumulation of tungsten in the central region of the plasma does not take place in these conditions. The measurements obtained are consistent with anomalous transport dominating tungsten transport except in the central region of the plasma where tungsten transport is neoclassical, as previously observed in other devices with dominant neutral beam injection heating, such as JET and ASDEX Upgrade. In contrast to such results, however, the measured scale lengths for plasma temperature and density in the central region of these Alcator C-Mod plasmas, with density profiles relatively flat in the core region due to the lack of core fuelling, are favourable to prevent inter and intra sawtooth tungsten accumulation in this region under dominance of neoclassical transport. Simulations of ITER H-mode plasmas, including both anomalous (modelled by the Gyro-Landau-Fluid code GLF23) and neoclassical transport for main ions and tungsten and with density profiles of similar peaking to those obtained in Alcator C-Mod show that accumulation of tungsten in the central plasma region is also unlikely to occur in stationary ITER H-mode plasmas due to the low fuelling source by the neutral beam injection (injection energy ∼ 1 MeV), which is in good agreement with findings in the Alcator C-Mod experiments.

  6. Molybdenum emission from impurity-induced m= 1 snake-modes on the Alcator C-Mod tokamak

    SciTech Connect

    Delgado-Aparicio, L.; Bitter, M.; Gates, D.; Hill, K.; Pablant, N.; Granetz, R.; Reinke, M.; Podpaly, Y.; Rice, J.; Beiersdorfer, P.; Sugiyama, L.

    2012-10-15

    A suite of novel high-resolution spectroscopic imaging diagnostics has facilitated the identification and localization of molybdenum impurities as the main species during the formation and lifetime of m= 1 impurity-induced snake-modes on Alcator C-Mod. Such measurements made it possible to infer, for the first time, the perturbed radiated power density profiles from which the impurity density can be deduced.

  7. The design and performance of a twenty barrel hydrogen pellet injector for Alcator C-Mod

    SciTech Connect

    Urbahn, John A.

    1994-05-01

    A twenty barrel hydrogen pellet injector has been designed, built and tested both in the laboratory and on the Alcator C-Mod Tokamak at MIT. The injector functions by firing pellets of frozen hydrogen or deuterium deep into the plasma discharge for the purpose of fueling the plasma, modifying the density profile and increasing the global energy confinement time. The design goals of the injector are: (1) Operational flexibility, (2) High reliability, (3) Remote operation with minimal maintenance. These requirements have lead to a single stage, pipe gun design with twenty barrels. Pellets are formed by in- situ condensation of the fuel gas, thus avoiding moving parts at cryogenic temperatures. The injector is the first to dispense with the need for cryogenic fluids and instead uses a closed cycle refrigerator to cool the thermal system components. The twenty barrels of the injector produce pellets of four different size groups and allow for a high degree of flexibility in fueling experiments. Operation of the injector is under PLC control allowing for remote operation, interlocked safety features and automated pellet manufacturing. The injector has been extrusively tested and shown to produce pellets reliably with velocities up to 1400 m/sec. During the period from September to November of 1993, the injector was successfully used to fire pellets into over fifty plasma discharges. Experimental results include data on the pellet penetration into the plasma using an advanced pellet tracking diagnostic with improved time and spatial response. Data from the tracker indicates pellet penetrations were between 30 and 86 percent of the plasma minor radius.

  8. Lithium pellet injection experiments on the Alcator C-Mod tokamak

    SciTech Connect

    Garnier, Darren Thomas

    1996-06-01

    A pellet enhanced performance mode, showing significantly reduced core transport, is regularly obtained after the injection of deeply penetrating lithium pellets into Alcator C-Mod discharges. These transient modes, which typically persist about two energy confinement times, are characterized by a steep pressure gradient (ℓp ℓ a/5) in the inner third of the plasma, indicating the presence of an internal transport barrier. Inside this barrier, particle and energy diffusivities are greatly reduced, with ion thermal diffusivity dropping to near neoclassical values. Meanwhile, the global energy confinement time shows a 30% improvement over ITER89-P L-mode scaling. The addition of ICRF auxiliary heating shortly after the pellet injection leads to high fusion reactivity with neutron rates enhanced by an order of magnitude over L-mode discharges with similar input powers. A diagnostic system for measuring equilibrium current density profiles of tokamak plasmas, employing high speed lithium pellets, is also presented. Because ions are confined to move along field lines, imaging the Li+ emission from the toroidally extended pellet ablation cloud gives the direction of the magnetic field. To convert from temporal to radial measurements, the 3-D trajectory of the pellet is determined using a stereoscopic tracking system. These measurements, along with external magnetic measurements, are used to solve the Grad-Shafranov equation for the magnetic equilibrium of the plasma. This diagnostic is used to determine the current density profile of PEP modes by injection of a second pellet during the period of good confinement. This measurement indicates that a region of reversed magnetic shear exists at the plasma core. This current density profile is consistent with TRANSP calculations for the bootstrap current created by the pressure gradient. MHD stability analysis indicates that these plasmas are near the n = ∞ and the n = 1 marginal stability limits.

  9. Particle Transport in the Scrape-Off Layer of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Labombard, Brian

    2000-10-01

    Cross-field particle transport plays a dominant role in the ‘main-chamber recycling’ regime in Alcator C-Mod, a regime where the main-chamber plasma recycles primarily on the walls rather than via the divertor volume. This observation has important implications for a reactor: A tightly baffled divertor may not offer control of main-chamber neutrals such that charge-exchange heat losses and sputtering of the main-chamber walls can be avoided. Important attributes of SOL cross-field transport physics are clearly evident: (1) cross-field particle fluxes dominate over parallel fluxes in balancing local ionization, (2) effective cross-field particle diffusivities (D_eff) increase with distance from the separatrix, (3) cross-field heat convection and charge exchange losses are larger than cross-field conduction, particularly in the far scrape-off layer, and (4) main-chamber neutral pressures depend more on cross-field transport than on divertor or main-chamber wall geometry. Taking advantage of the local ionization and cross-field flux balance in this regime, one can infer D_eff profiles directly from measurements. D_eff near the separatrix is found to increase strongly with increasing plasma collisionality. As the Greenwald density is approached (highest collisionality), D_eff near the separatrix becomes very large and plasma fluctuations exhibit a bursty behavior with longer correlation times. Heat convection and charge exchange losses correspondingly increase. This behavior suggests that the discharge density limit is governed by a critical collisionality above which cross-field heat convection and charge exchange determine the SOL electron temperature rather than electron parallel heat conduction. Beyond this collisionality ( density), no stable plasma can be maintained, even in the absence of radiation.

  10. Overview of experimental results and code validation activities at Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Greenwald, M.; Bader, A.; Baek, S.; Barnard, H.; Beck, W.; Bergerson, W.; Bespamyatnov, I.; Bitter, M.; Bonoli, P.; Brookman, M.; Brower, D.; Brunner, D.; Burke, W.; Candy, J.; Chilenski, M.; Chung, M.; Churchill, M.; Cziegler, I.; Davis, E.; Dekow, G.; Delgado-Aparicio, L.; Diallo, A.; Ding, W.; Dominguez, A.; Ellis, R.; Ennever, P.; Ernst, D.; Faust, I.; Fiore, C.; Fitzgerald, E.; Fredian, T.; Garcia, O. E.; Gao, C.; Garrett, M.; Golfinopoulos, T.; Granetz, R.; Groebner, R.; Harrison, S.; Harvey, R.; Hartwig, Z.; Hill, K.; Hillairet, J.; Howard, N.; Hubbard, A. E.; Hughes, J. W.; Hutchinson, I.; Irby, J.; James, A. N.; Kanojia, A.; Kasten, C.; Kesner, J.; Kessel, C.; Kube, R.; LaBombard, B.; Lau, C.; Lee, J.; Liao, K.; Lin, Y.; Lipschultz, B.; Ma, Y.; Marmar, E.; McGibbon, P.; Meneghini, O.; Mikkelsen, D.; Miller, D.; Mumgaard, R.; Murray, R.; Ochoukov, R.; Olynyk, G.; Pace, D.; Park, S.; Parker, R.; Podpaly, Y.; Porkolab, M.; Preynas, M.; Pusztai, I.; Reinke, M.; Rice, J.; Rowan, W.; Scott, S.; Shiraiwa, S.; Sierchio, J.; Snyder, P.; Sorbom, B.; Soukhanovskii, V.; Stillerman, J.; Sugiyama, L.; Sung, C.; Terry, D.; Terry, J.; Theiler, C.; Tsujii, N.; Vieira, R.; Walk, J.; Wallace, G.; White, A.; Whyte, D.; Wilson, J.; Wolfe, S.; Woller, K.; Wright, G.; Wright, J.; Wukitch, S.; Wurden, G.; Xu, P.; Yang, C.; Zweben, S.

    2013-10-01

    Recent research on the Alcator C-Mod tokamak has focused on a range of scientific issues with particular emphasis on ITER needs and on detailed comparisons between experimental measurements and predictive models. Research on ICRF (ion cyclotron range of frequencies) heating emphasized the origins and mitigation of metallic impurities while work on lower hybrid current drive experiments have focused on linear and nonlinear wave interactions that limit efficiency at high densities in regimes with low single pass absorption. Experiments in core turbulence and transport focused on quantitative, multi-field comparisons between nonlinear gyro-kinetics simulations and experimental measurements of profiles, fluxes and fluctuations. Experiments into self-generated rotation observed spontaneous flow reversal at a critical density identical to the transition density between linear ohmic confinement and saturated ohmic confinement regimes. H-mode studies have measured pedestal widths consistent with kinetic-ballooning-mode-like instabilities, while the pedestal heights quantitatively match the EPED code predictions. Experiments with I-mode have increased the operating window for this promising edge-localized-mode-free regime. Extrapolation of I-mode to ITER suggests that the fusion gain Q ∼ 10 could be possible in ITER. Investigations into the physics and scaling of the power exhaust channel width in attached enhanced D-alpha H-mode and L-mode plasma showed a direct connection between the midplane pressure-folding length and the outer divertor target footprint. The width was found to scale inversely with IP, while being independent of conducted power, BT or q95 and insensitive to the scrape-off layer connection length—a behaviour that suggests critical-gradient physics sets both pressure and heat-flux profiles.

  11. Radial localization of edge modes in Alcator C-Mod pedestals using optical diagnostics

    NASA Astrophysics Data System (ADS)

    Theiler, C.; Terry, J. L.; Edlund, E.; Cziegler, I.; Churchill, R. M.; Hughes, J. W.; LaBombard, B.; Golfinopoulos, T.; the Alcator C-Mod Team

    2017-02-01

    Dedicated experiments in ion cyclotron range heated enhanced D-alpha (EDA) H-mode and I-mode plasmas have been performed on Alcator C-Mod to identify the location of edge fluctuations inside the pedestal and to determine their plasma frame phase velocity. For this purpose, measurements from gas puff imaging (GPI) and gas puff charge exchange recombination spectroscopy (GP-CXRS) have been collected using the same optical views. The data suggest that the EDA H-mode-specific quasi-coherent mode (QCM) is centered near the radial electric field (E r) well minimum and propagates along the ion diamagnetic drift direction in the plasma frame. The weakly coherent mode (WCM) and the geodesic acoustic mode observed in I-mode, on the other hand, are found to be located around the outer shear layer of the E r well. This results in a weak plasma frame phase velocity mostly along the electron diamagnetic drift direction for the WCM. The findings in these EDA H-mode plasmas differ from probe measurements in ohmic EDA H-mode (LaBombard et al 2014 Phys. Plasmas 21 056108), where the QCM was identified as an electron drift-wave located several mm outside the E r well minimum in a region of positive E r. To explore if instrumental effects of the optical diagnostics could be the cause of the difference, a synthetic diagnostic for GPI is introduced. This diagnostic reproduces amplitude ratios and relative radial shifts of the mode profiles determined from poloidally and toroidally oriented optics and, if instrumental effects related to GP-CXRS are also included, indicates that the measured location of the QCM and WCM relative to the E r well reported here is only weakly affected by instrumental effects.

  12. Modeling of particle and energy transport in the edge plasma of Alcator C-Mod

    SciTech Connect

    Umansky, M.V.; Krasheninnikov, S.I.; LaBombard, B.; Lipschultz, B.; Terry, J.L.

    1999-07-01

    In the present study recycling and transport in the edge plasma of Alcator C-Mod [I. H. Hutchinson {ital et al.}, Phys. Plasmas {bold 1}, 1511 (1994)] is modeled and analyzed with the multi-fluid code UEDGE [T. D. Rognlien {ital et al.}, J. Nucl. Mater. {bold 196{endash}198}, 347 (1992)]. Matching the experimental plasma density profiles in the scrape-off layer (SOL) requires a spatially dependent effective anomalous diffusion coefficient D{sub {perpendicular}} growing rapidly towards the wall. The midplane pressure of neutral gas, P{sub mid}, is a key parameter that reflects the magnitude of anomalous transport of plasma from the core. Recycling of plasma on the main chamber wall appears to be quite significant, especially in the case of high P{sub mid}{approximately}0.3 mTorr when the main wall provides {approximately}70{percent} of recycling neutrals in the main chamber. In the upper SOL (well above the {ital x} point) draining of particles by the poloidal flow is weak and thus the particle balance is predominantly radial. For the radial heat transport it is found that energy flux carried by radial plasma convection and by charge-exchange (CX) neutrals is quite significant in SOL. In the high P{sub mid} case, heat conduction by CX neutrals along with radial heat convection by plasma carries most of the power flux ({approximately}75{percent}) across the last closed flux surface. Even in the low P{sub mid} case, heat conduction by CX neutrals dominates the radial heat flux far out in the SOL. {copyright} {ital 1999 American Institute of Physics.}

  13. Fluctuation statistics in the scrape-off layer of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Kube, R.; Theodorsen, A.; Garcia, O. E.; LaBombard, B.; Terry, J. L.

    2016-05-01

    We study long time series of the ion saturation current and floating potential, sampled by Langmuir probes dwelled in the outboard mid-plane scrape-off layer and embedded in the lower divertor baffle of Alcator C-Mod. A series of ohmically heated L-mode plasma discharges is investigated with line-averaged plasma density ranging from {{\\bar{n}}\\text{e}}/{{n}\\text{G}}=0.15 to 0.42, where n G is the Greenwald density. All ion saturation current time series that are sampled in the far scrape-off layer are characterized by large-amplitude burst events. Coefficients of skewness and excess kurtosis of the time series obey a quadratic relationship and their histograms coincide partially upon proper normalization. Histograms of the ion saturation current time series are found to agree well with a prediction of a stochastic model for the particle density fluctuations in scrape-off layer plasmas. The distribution of the waiting times between successive large-amplitude burst events and of the burst amplitudes are approximately described by exponential distributions. The average waiting time and burst amplitude are found to vary weakly with the line-averaged plasma density. Conditional averaging reveals that the radial blob velocity, estimated from floating potential measurements, increases with the normalized burst amplitude in the outboard mid-plane scrape-off layer. For low density discharges, the conditionally averaged waveform of the floating potential associated with large amplitude bursts at the divertor probes has a dipolar shape. In detached divertor conditions the average waveform is random, indicating electrical disconnection of blobs from the sheaths at the divertor targets.

  14. Lower hybrid wave edge power loss quantification on the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Faust, I. C.; Brunner, D.; LaBombard, B.; Parker, R. R.; Terry, J. L.; Whyte, D. G.; Baek, S. G.; Edlund, E.; Hubbard, A. E.; Hughes, J. W.; Kuang, A. Q.; Reinke, M. L.; Shiraiwa, S.; Wallace, G. M.; Walk, J. R.

    2016-05-01

    For the first time, the power deposition of lower hybrid RF waves into the edge plasma of a diverted tokamak has been systematically quantified. Edge deposition represents a parasitic loss of power that can greatly impact the use and efficiency of Lower Hybrid Current Drive (LHCD) at reactor-relevant densities. Through the use of a unique set of fast time resolution edge diagnostics, including innovative fast-thermocouples, an extensive set of Langmuir probes, and a Lyα ionization camera, the toroidal, poloidal, and radial structure of the power deposition has been simultaneously determined. Power modulation was used to directly isolate the RF effects due to the prompt ( t < τ E ) response of the scrape-off-layer (SOL) plasma to Lower Hybrid Radiofrequency (LHRF) power. LHRF power was found to absorb more strongly in the edge at higher densities. It is found that a majority of this edge-deposited power is promptly conducted to the divertor. This correlates with the loss of current drive efficiency at high density previously observed on Alcator C-Mod, and displaying characteristics that contrast with the local RF edge absorption seen on other tokamaks. Measurements of ionization in the active divertor show dramatic changes due to LHRF power, implying that divertor region can be a key for the LHRF edge power deposition physics. These observations support the existence of a loss mechanism near the edge for LHRF at high density ( n e > 1.0 × 10 20 (m-3)). Results will be shown addressing the distribution of power within the SOL, including the toroidal symmetry and radial distribution. These characteristics are important for deducing the cause of the reduced LHCD efficiency at high density and motivate the tailoring of wave propagation to minimize SOL interaction, for example, through the use of high-field-side launch.

  15. Characterization of impurity confinement on Alcator C-Mod using a multi-pulse laser blow-off system.

    PubMed

    Howard, N T; Greenwald, M; Rice, J E

    2011-03-01

    A new laser blow-off system for use in impurity transport studies on Alcator C-Mod was developed and installed for the 2009 run campaign. Its design included capabilities for multiple impurity injections during a single plasma pulse and remote manipulation of the ablated spot size. The system uses a 0.68 J, Nd:YAG laser operating at up to 10 Hz coupled with the fast beam steering via a 2D piezoelectric mirror mount able to move spot locations in the 100 ms between laser pulses and a remote controllable optical train that allow ablated spot sizes to vary from ∼0.5 to 7 mm. The ability to ablate a wide range in target Z along with Alcator C-Mod's extensive diagnostic capabilities (soft x-ray, vacuum ultraviolet (VUV), charge exchange spectroscopy, etc.) allows for detailed studies of the impurity transport dependencies and mechanisms. This system has demonstrated the achievement of all its design goals including the ability for non-perturbative operation allowing for insight into underlying impurity transport processes. A detailed overview of the laser blow-off system and initial results of operation are presented. This includes an investigation into the characterization of impurity confinement in the I-mode confinement regime recently investigated on C-Mod.

  16. Compact multichannel neutral particle analyzer for measurement of energetic charge-exchanged neutrals in Alcator C-Mod

    SciTech Connect

    Tang, V.; Liptac, J.; Parker, R. R.; Bonoli, P. T.; Fiore, C. L.; Granetz, R. S.; Irby, J. H.; Lin, Y.; Wukitch, S. J.; Frenje, J. A.; Leiter, R.; Mcduffee, S.; Petrasso, R. D.

    2006-08-15

    A four-channel compact neutral particle analyzer (CNPA) based on operating small Si diode detectors in pulse-height analysis (PHA) mode is used to measure energetic hydrogen minority ions with energies between {approx}50 and 350 keV stemming from ion-cyclotron range-of-frequency heated D(H) Alcator C-Mod plasmas with both active and passive charge exchange (CX). First core minority ion distribution results from Alcator C-Mod discharges and a detailed description of the diagnostic are presented. The diagnostic employs integrated electronics and fast digitization of the shaping amplifier voltage. The digitized data are stored for postshot PHA, which removes the constraints of real-time PHA and allows for improved performance via elimination of base line shift effects and potentially relieving pileup through Gaussian fitting routines. The CNPA is insensitive to the large gamma and neutron background in Alcator C-Mod discharges but is susceptible to the plasma's soft x-ray flux. The soft x-ray flux limits the CNPA energy resolution to {approx}15-20 keV. A simple model is used to interpret the active CNPA data which permits rapid estimates of the core hydrogen minority temperatures and anisotropy with a time resolution of {approx}100 ms. Hydrogenlike boron is identified as an important electron donor for the CX signal.

  17. The Motional Stark Effect Diagnostic on NSTX

    NASA Astrophysics Data System (ADS)

    Levinton, Fred; Yuh, Howard

    2007-11-01

    This work describes the implementation and recent results from the MSE-CIF diagnostic on NSTX. Due to the low magnetic field on NSTX the MSE diagnostic requires a new approach for the viewing optics and spectral filter. This has been accomplished with a novel optical design that reduces the geometric Doppler broadening, and a high throughput, high resolution spectral filter to optimize signal-to-noise. This MSE diagnostic presently has 16 of a possible 19 sightlines operating, providing measurements of the magnetic field line pitch from the plasma center to near the outboard edge of the plasma. The system operates well at low magnetic field, >=0.3 T, using collisionaly induced fluorescence (CIF) from a deuterium heating beam operating at about ˜90 keV. MSE data has been obtained in several regimes, including L-mode, H-mode, and reversed shear. The measurements reveal the development of both monotonic and reversed shear q-profiles depending on the discharge evolution. The presence of MHD is found to have a significant effect on the profile evolution and will be discussed.

  18. Lower Hybrid Current Drive Experiments on Alcator C-Mod: Comparison with Theory and Simulation

    NASA Astrophysics Data System (ADS)

    Bonoli, Paul

    2007-11-01

    Recently, lower hybrid current drive (LHCD) experiments have been carried out on Alcator C-Mod using an RF system consisting of 12 klystrons at 4.6 GHz, feeding a 4 x 22 waveguide array. Up to 900 kW of LH power has been coupled in the range1.6 <= n//<= 4), where n// is the parallel refractive index. Driven LH currents have been inferred from magnetic measurements by extrapolating to zero loop voltage, yielding an efficiency of n20ILHR/PLH 0.3 [1]. We have simulated the LH current drive in these discharges using the combined ray tracing / 3D (r, v, v//) Fokker Planck code GENRAY -- CQL3D [2] and found similar current drive efficiencies. Measurements of nonthermal x-ray emission and electron cyclotron emission (ECE) confirm the presence of a significant fast electron population that varies with waveguide phasing and plasma density. Studies are currently underway to investigate the role of fast electron diffusion and full-wave effects such as diffractional broadening in determining the spatial and velocity space structure of the nonthermal electrons. The 3D (r, v, v//) electron distribution function from CQL3D has been used in synthetic diagnostic codes to simulate the measured hard x-ray and ECE emissions. Fast electron diffusion times have been inferred from x-ray data by employing a radial diffusion operator in CQL3D and determining the fast electron diffusivities that are required to reproduce the experimentally observed profiles of hard x-ray emission. Finally, we have been performing full-wave LH field simulations using the massively parallel TORIC --LH solver [3] in order to assess spatial and spectral broadening of the incident wave front that can result from diffraction and wave focusing effects. [1] R. Parker, Bull. Am. Phys. Soc. 51, 20 (2006). [2] R.W. Harvey and M. McCoy, ``The CQL3D Fokker Planck Code,'' Proc. IAEA Tech. Comm. Meeting on Simulation and Modeling of Thermonuclear Plasmas, Montreal, Canada, 1992. [3] J. C. Wright et al., Nucl. Fusion 45

  19. Impurity Screening in Ohmic and H-Mode Plasmas in the Alcator C-Mod Tokamak^*

    NASA Astrophysics Data System (ADS)

    McCracken, G. M.

    1996-11-01

    The impurity density in the confined plasma is determined not only by the impurity production rate but also by screening, i.e. the balance between the perpendicular and parallel transport in the SOL. The relative importance of screening has been studied by injecting gaseous recycling (Ne, Ar) and non-recycling impurities (N, C) into various poloidal positions of the SOL and divertor in C-Mod. The density of the non-recycling impurities in the core is a function of the poloidal position of injection, while the screening of recycling impurities is not. In both cases screening is significantly worse ( ~3x) during divertor detachment. For a given injection rate of N2 gas into H-mode discharges, the number of impurities in the core is typically a factor of 3 greater than for ohmic discharges. Optical imaging of low charge states of the injected non-recycling impurities using a camera and spectral filters shows a directed plume, indicating flow of impurities towards the divertor target at all positions studied, even at the inboard midplane. This implies that the friction force due to plasma flow dominates the parallel ion temperature gradient force. The spatial distribution of low charge states in the divertor has been studied using a multichord visible spectrometer, and the distribution of the nitrogen radiation has been been studied using a 20 chord bolometer array. The results show that for attached discharges the nitrogen radiation is predominantly in the SOL below the X-point. The position of the radiation is not strongly dependent on the position of nitrogen injection. The screening has been compared with calculations using the DIVIMP Monte Carlo code [1] and with an analytical model of the impurity transport. Work supported by U.S. DOE Contract No. DE-AC02-78ET51013. În collaboration with B Lipschultz, B LaBombard, J A Goetz, R Granetz, D Jablonski, H Ohkawa, J Terry, MIT, S Lisgo, P C Stangeby, University of Toronto, ^1P.C. Stangeby and D. Elder, J. Nucl. Mater

  20. Kinetic modeling of divertor heat load fluxes in the Alcator C-Mod and DIII-D tokamaks

    NASA Astrophysics Data System (ADS)

    Pankin, A. Y.; Rafiq, T.; Kritz, A. H.; Park, G. Y.; Chang, C. S.; Brunner, D.; Groebner, R. J.; Hughes, J. W.; LaBombard, B.; Terry, J. L.; Ku, S.

    2015-09-01

    The guiding-center kinetic neoclassical transport code, XGC0 [Chang et al., Phys. Plasmas 11, 2649 (2004)], is used to compute the heat fluxes and the heat-load width in the outer divertor plates of Alcator C-Mod and DIII-D tokamaks. The dependence of the width of heat-load fluxes on neoclassical effects, neutral collisions, and anomalous transport is investigated using the XGC0 code. The XGC0 code includes realistic X-point geometry, a neutral source model, the effects of collisions, and a diffusion model for anomalous transport. It is observed that the width of the XGC0 neoclassical heat-load is approximately inversely proportional to the total plasma current Ip. The scaling of the width of the divertor heat-load with plasma current is examined for an Alcator C-Mod discharge and four DIII-D discharges. The scaling of the divertor heat-load width with plasma current is found to be weaker in the Alcator C-Mod discharge compared to scaling found in the DIII-D discharges. The effect of neutral collisions on the 1/Ip scaling of heat-load width is shown not to be significant. Although inclusion of poloidally uniform anomalous transport results in a deviation from the 1/Ip scaling, the inclusion of the anomalous transport that is driven by ballooning-type instabilities results in recovering the neoclassical 1/Ip scaling. The Bohm or gyro-Bohm scalings of anomalous transport do not strongly affect the dependence of the heat-load width on plasma current. The inclusion of anomalous transport, in general, results in widening the width of neoclassical divertor heat-load and enhances the neoclassical heat-load fluxes on the divertor plates. Understanding heat transport in the tokamak scrape-off layer plasmas is important for strengthening the basis for predicting divertor conditions in ITER.

  1. Pedestal structure and stability in H-mode and I-mode: a comparative study on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Hughes, J. W.; Snyder, P. B.; Walk, J. R.; Davis, E. M.; Diallo, A.; LaBombard, B.; Baek, S. G.; Churchill, R. M.; Greenwald, M.; Groebner, R. J.; Hubbard, A. E.; Lipschultz, B.; Marmar, E. S.; Osborne, T.; Reinke, M. L.; Rice, J. E.; Theiler, C.; Terry, J.; White, A. E.; Whyte, D. G.; Wolfe, S.; Xu, X. Q.

    2013-04-01

    New experimental data from the Alcator C-Mod tokamak are used to benchmark predictive modelling of the edge pedestal in various high-confinement regimes, contributing to greater confidence in projection of pedestal height and width in ITER and reactors. ELMy H-modes operate near stability limits for ideal peeling-ballooning modes, as shown by calculations with the ELITE code. Experimental pedestal width in ELMy H-mode scales as the square root of βpol at the pedestal top, i.e. the dependence expected from theory if kinetic ballooning modes (KBMs) were responsible for limiting the pedestal width. A search for KBMs in experiment has revealed a short-wavelength electromagnetic fluctuation in the pedestal that is a candidate driver for inter-edge localized mode (ELM) pedestal regulation. A predictive pedestal model (EPED) has been tested on an extended set of ELMy H-modes from C-Mod, reproducing pedestal height and width reasonably well across the data set, and extending the tested range of EPED to the highest absolute pressures available on any existing tokamak and to within a factor of three of the pedestal pressure targeted for ITER. In addition, C-Mod offers access to two regimes, enhanced D-alpha (EDA) H-mode and I-mode, that have high pedestals, but in which large ELM activity is naturally suppressed and, instead, particle and impurity transport are regulated continuously. Pedestals of EDA H-mode and I-mode discharges are found to be ideal magnetohydrodynamic (MHD) stable with ELITE, consistent with the general absence of ELM activity. Invocation of alternative physics mechanisms may be required to make EPED-like predictions of pedestals in these kinds of intrinsically ELM-suppressed regimes, which would be very beneficial to operation in burning plasma devices.

  2. Kinetic modeling of divertor heat load fluxes in the Alcator C-Mod and DIII-D tokamaks

    SciTech Connect

    Pankin, A. Y.; Rafiq, T.; Kritz, A. H.; Park, G. Y.; Chang, C. S.; Ku, S.; Brunner, D.; Hughes, J. W.; LaBombard, B.; Terry, J. L.; Groebner, R. J.

    2015-09-15

    The guiding-center kinetic neoclassical transport code, XGC0 [Chang et al., Phys. Plasmas 11, 2649 (2004)], is used to compute the heat fluxes and the heat-load width in the outer divertor plates of Alcator C-Mod and DIII-D tokamaks. The dependence of the width of heat-load fluxes on neoclassical effects, neutral collisions, and anomalous transport is investigated using the XGC0 code. The XGC0 code includes realistic X-point geometry, a neutral source model, the effects of collisions, and a diffusion model for anomalous transport. It is observed that the width of the XGC0 neoclassical heat-load is approximately inversely proportional to the total plasma current I{sub p.} The scaling of the width of the divertor heat-load with plasma current is examined for an Alcator C-Mod discharge and four DIII-D discharges. The scaling of the divertor heat-load width with plasma current is found to be weaker in the Alcator C-Mod discharge compared to scaling found in the DIII-D discharges. The effect of neutral collisions on the 1/I{sub p} scaling of heat-load width is shown not to be significant. Although inclusion of poloidally uniform anomalous transport results in a deviation from the 1/I{sub p} scaling, the inclusion of the anomalous transport that is driven by ballooning-type instabilities results in recovering the neoclassical 1/I{sub p} scaling. The Bohm or gyro-Bohm scalings of anomalous transport do not strongly affect the dependence of the heat-load width on plasma current. The inclusion of anomalous transport, in general, results in widening the width of neoclassical divertor heat-load and enhances the neoclassical heat-load fluxes on the divertor plates. Understanding heat transport in the tokamak scrape-off layer plasmas is important for strengthening the basis for predicting divertor conditions in ITER.

  3. The Instrumental Function of the new X-ray Imaging Crystal Spectrometer on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Bitter, M.; Hill, K. W.; Mikkelson, D.; Scott, S.; Ince-Cushman, A.; Reinke, M.; Rice, J. E.; Beiersdorfer, P.; Gu, M. F.

    2007-11-01

    A new high-resolution X-ray imaging crystal spectrometer was installed on Alcator C-Mod to determine the radial profiles of the ion temperature and toroidal plasma rotation velocity from the Doppler widths and Doppler shifts of spectral lines from He- and H-like argon. The instrument consists of two spherically bent crystals and high count rate, semi-conductor diode arrays, so-called PILATUS II detector modules, which are arranged in the Johann configuration. The poster will present analytical and numerical calculations of the instrumental function and the observed spectral line profiles. The results obtained from these calculations will be compared with the experimental data.

  4. Higher-order resonances in a Stark decelerator

    SciTech Connect

    Meerakker, Sebastiaan Y.T. van de; Bethlem, Hendrick L.; Vanhaecke, Nicolas; Meijer, Gerard

    2005-05-15

    The motion of polar molecules can be controlled by time-varying inhomogeneous electric fields. In a Stark decelerator, this is exploited to select a fraction of a molecular beam that is accelerated, transported, or decelerated. Phase stability ensures that the selected bunch of molecules is kept together throughout the deceleration process. In this paper an extended description of phase stability in a Stark decelerator is given, including higher-order effects. This analysis predicts a wide variety of resonances that originate from the spatial and temporal periodicity of the electric fields. These resonances are experimentally observed using a beam of OH ({sup 2}{pi}{sub 3/2},v=0,J=3/2) radicals passing through a Stark decelerator.

  5. THz stark spectroscopy (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Feurer, Thomas; Rohwer, Egmont; Akbarimoosavi, Maryam

    2016-09-01

    Stark spectroscopy has been pioneered many decades ago and is a unique tool to extract information on molecular constants such as changes of dipole moments or polarizabilities upon excitation. Here we introduce a new twist, i.e. THz Stark spectroscopy. In THz fields the electric field vector oscillates on time scales of picoseconds and thus much faster than in conventional Stark spectroscopy. It therefore may allow to distinguish between different electric field contributions by analyzing the dynamics of the THz response. We first demonstrate that conventional THz sources can be boosted by combination with field enhancement structures, reaching field strength of GV/m driving several different materials into the nonlinear response regime. Then we discuss THz fields influencing charge transfer in different molecules.

  6. Study of toroidal flow generation by ion cyclotron range of frequency minority heating in the Alcator C-Mod plasma

    NASA Astrophysics Data System (ADS)

    Murakami, S.; Itoh, K.; Zheng, L. J.; Van Dam, J. W.; Bonoli, P.; Rice, J. E.; Fiore, C. L.; Gao, C.; Fukuyama, A.

    2016-01-01

    The averaged toroidal flow of energetic minority ions during ICRF (ion cyclotron range of frequencies) heating is investigated in the Alcator C-Mod plasma by applying the GNET code, which can solve the drift kinetic equation with complicated orbits of accelerated energetic particles. It is found that a co-directional toroidal flow of the minority ions is generated in the region outside of the resonance location, and that the toroidal velocity reaches more than 40% of the central ion thermal velocity (Vtor ˜ 300 km/s with PICRF ˜ 2 MW). When we shift the resonance location to the outside of |r /a |˜0.5 , the toroidal flow immediately inside of the resonance location is reduced to 0 or changes to the opposite direction, and the toroidal velocity shear is enhanced at r/a ˜ 0.5. A radial diffusion equation for toroidal flow is solved by assuming a torque profile for the minority ion mean flow, and good agreements with experimental radial toroidal flow profiles are obtained. This suggests that the ICRF driven minority ion flow is related to the experimentally observed toroidal rotation during ICRF heating in the Alcator C-Mod plasma.

  7. Thermal Analysis to Calculate the Vessel Temperature and Stress in Alcator C-Mod Due to the Divertor Upgrade

    SciTech Connect

    Han Zhang, Peter H. Titus, Robert Ellis, Soren Harrison and Rui Vieira

    2012-08-29

    Alcator C-Mod is planning an upgrade to its outer divertor. The upgrade is intended to correct the existing outer divertor alignment with the plasma, and to operate at elevated temperatures. Higher temperature operation will allow study of edge physics behavior at reactor relevant temperatures. The outer divertor and tiles will be capable of operating at 600oC. Longer pulse length, together with the plasma and RF heat of 9MW, and the inclusion of heater elements within the outer divertor produces radiative energy which makes the sustained operation much more difficult than before. An ANSYS model based on ref. 1 was built for the global thermal analysis of C-Mod. It models the radiative surfaces inside the vessel and between the components, and also includes plasma energy deposition. Different geometries have been simulated and compared. Results show that steady state operation with the divertor at 600oC is possible with no damage to major vessel internal components. The differential temperature between inner divertor structure, or "girdle" and inner vessel wall is ~70oC. This differential temperature is limited by the capacity of the studs that hold the inner divertor backing plates to the vessel wall. At a 70oC temperature differential the stress on the studs is within allowable limits. The thermal model was then used for a stress pass to quantify vessel shell stresses where thermal gradients are significant.

  8. Access to high-confinement regimes on Alcator C-Mod and the complex influence of divertor geometry

    NASA Astrophysics Data System (ADS)

    Hughes, J. W.; Labombard, B.; Brunner, D.; Hubbard, A.; Terry, J.; Rice, J.; Walk, J.; Cziegler, I.; Edlund, E.; Theiler, C.

    2015-11-01

    Placement of X-points and strike points in a diverted tokamak can have a remarkable impact on plasma properties, including thermal and particle confinement. The distinctive divertor of Alcator C-Mod allows substantial variation of divertor leg length, field line attack angle and divertor baffling, allowing us to induce changes in both L-mode confinement and access to both H-mode and I-mode. With the ion ∇B drift directed toward the divertor, scanning the strike point can induce ~ 2 × reductions in H-mode power threshold, and can produce a window for I-mode operation with H98 > 1 . Detailed high-resolution measurements, spanning the last closed flux surface, provide profiles of key quantities (n, T, ϕ) and their gradients, which are of likely importance in determining whether a discharge evolves an edge transport barrier, or remains in an L-mode state. Advances in Langmuir probes have enabled characterization of both radial profiles and fast (< 1 MHz) fluctuations in L-mode as the L-H threshold power is approached. These data allow new tests of models for H-mode access, especially those attempting to explain the non-monotonic density dependence of the H-mode power threshold through changes in transport and/or turbulence. Supported by U.S. Department of Energy award DE-FC02-99ER54512, using Alcator C-Mod, a DOE Office of Science User Facility.

  9. Recent edge CXRS measurements in I-mode and ELMy H-mode plasmas on C-Mod

    NASA Astrophysics Data System (ADS)

    Theiler, C.; Churchill, R. M.; Hubbard, A.; Hughes, J. W.; Lipschultz, B.; Marmar, E.; Reinke, M. L.; Terry, J. L.; Walk, J. R.; Whyte, D.; Diallo, A.

    2012-10-01

    A high-resolution charge exchange recombination spectroscopy (CXRS) diagnostic is installed on Alcator C-Mod to measure edge profiles of B^5+ density, temperature, and flows and to deduce radial electric field profiles. As donor particles for CX, both hydrogen from a modulated diagnostic neutral beam and deuterium from a local gas puff are employed. While the former technique often suffers from low signal intensities near the LCFS, the latter can be complicated by contamination of the signal by molecular lines and cross-section effects. After discussing how these challenges are overcome in data analysis, we present recent measurements in regimes which have not extensively been investigated previously with edge CXRS on C-Mod. The first one is the I-mode regime, which is characterized by H-mode like energy confinement and L-mode like particle transport. Focusing on I-modes with unfavorable ion B x∇B drift, we study profile scalings with plasma parameters such as density, plasma current and heating power. The second regime is ELMy H-mode, where we explore the capabilities of the CXRS diagnostic to measure profile evolutions during and in between ELMs.

  10. Correlation Electron Temperature Fluctuation Measurements on Alcator C-Mod and ASDEX Upgrade: Cross Machine Comparisons and Transport Model Validation

    NASA Astrophysics Data System (ADS)

    White, A. E.; Creely, A. J.; Freethy, S.; Cao, N.; Conway, G. D.; Goerler, T.; Happel, T.; Howard, N. T.; Inman, C.; Rice, J. E.; Rodriguez Fernandez, P.; Sung, C.; C-Mod, Alcator; Upgrade, Asdex

    2016-10-01

    Correlation Electron Cyclotron Emission diagnostics have been developed for Alcator C-Mod and ASDEX Upgrade. Measurements of long wavelength (ktheta rhos <0.5) electron temperature fluctuations have been measured in the core plasma (0.5 C-Mod and AUG are presented. This work is supported by the US DOE under Grants DE-SC0006419 and DEFC02-99ER54512-CMOD.

  11. Validation of nonlinear gyrokinetic simulations of L- and I-mode plasmas on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Creely, A. J.; Howard, N. T.; Rodriguez-Fernandez, P.; Cao, N.; Hubbard, A. E.; Hughes, J. W.; Rice, J. E.; White, A. E.; Candy, J.; Staebler, G. M.; Conway, G. D.; Freethy, S. J.; Sung, C.

    2017-05-01

    New validation of global, nonlinear, ion-scale gyrokinetic simulations (GYRO) is carried out for L- and I-mode plasmas on Alcator C-Mod, utilizing heat fluxes, profile stiffness, and temperature fluctuations. Previous work at C-Mod found that ITG/TEM-scale GYRO simulations can match both electron and ion heat fluxes within error bars in I-mode [White PoP 2015], suggesting that multi-scale (cross-scale coupling) effects [Howard PoP 2016] may be less important in I-mode than in L-mode. New results presented here, however, show that global, nonlinear, ion-scale GYRO simulations are able to match the experimental ion heat flux, but underpredict electron heat flux (at most radii), electron temperature fluctuations, and perturbative thermal diffusivity in both L- and I-mode. Linear addition of electron heat flux from electron scale runs does not resolve this discrepancy. These results indicate that single-scale simulations do not sufficiently describe the I-mode core transport, and that multi-scale (coupled electron- and ion-scale) transport models are needed. A preliminary investigation with multi-scale TGLF, however, was unable to resolve the discrepancy between ion-scale GYRO and experimental electron heat fluxes and perturbative diffusivity, motivating further work with multi-scale GYRO simulations and a more comprehensive study with multi-scale TGLF.

  12. Access conditions, energy and particle confinement of the I-mode regime on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Hubbard, Amanda

    2015-11-01

    Experiments on C-Mod have shown an extended operating range for I-mode at higher magnetic fields, offering options for high-performance, ELM-suppressed operation in future devices. Stationary regimes without significant ELMs are a requirement for ITER and other large burning devices. The I-mode regime offers one potential solution. It features a strong Te and Ti pedestal, up to 1 keV, without a density pedestal. I-mode has been demonstrated on the C-Mod, ASDEX Upgrade and DIII-D tokamaks, over increasingly wide parameter ranges. On C-Mod, global energy confinement is comparable to H-mode, with H98 between 0.7 and 1.2. Scaling of τE with Pheat-0 . 3 is more favorable than H-mode. This lack of saturation and the natural stability to ELMs can now be understood in terms of pedestal stability, with pressure and current gradients well away from stability limits. Impurity confinement τimp is similar in level and scaling to that in L-mode, 15-30 ms for both Ca and Mo, vs 0.1-1 s in H-mode. Key questions for extrapolation to other devices are the conditions for L-I transitions and for avoiding transitions to H-mode. An important new result is that the L-I threshold is independent of field, while the upper range of power for I-mode increases with BT leading to a wider operating space; at 5 T and above, many discharges remain in stationary I-mode with the full heating power of 5 MW. Scaling thresholds with size suggests that I-mode should be obtainable on ITER. Some I-modes have been observed up to 8 T. Another key question for any regime is compatibility with boundary solutions. In usual operation with Bxgrad drift away from the X-point, heat flux is predominantly to the inner divertor leg. Impurity seeding is used to reduce the flux, taking advantage of low τimp. I-modes have now been extended to near-balanced double null. Supported by DOE Award DEFC02- 99ER54512-CMOD.

  13. In-situ erosion and deposition measurements of plasma-facing surfaces in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Barnard, Harold S.

    2014-10-01

    The Accelerator Based In-situ Materials Surveillance (AIMS) diagnostic was recently developed to demonstrate the novel application of ion beam analysis (IBA) to in-vessel studies of plasma materials interactions in Alcator C-Mod. The AIMS diagnostic injects a 900 keV deuterium ion beam into the tokamak's vacuum vessel between plasma discharges while magnetic fields are used to steer the ion beam to plasma facing component (PFC) surfaces. Spectroscopic analysis of neutrons and gamma rays from the induced nuclear reactions provides a quantitative, spatially resolved map of the PFC surface composition that includes boron (B) and deuterium (D) content. Since AIMS is sensitive to low-Z elements and C-Mod regularly boronizes PFCs, the evolution of B and D on PFCs can be used to directly study erosion, deposition, and fuel retention in response to plasma operations and wall conditioning processes. AIMS analysis of 18 lower single null I-mode discharges show a net boron deposition rate of 6 +/- 2 nm/s on the inner wall while subsequent inner wall limited discharges and a disruption did not show significant changes in B. Measurements of D content showed relative changes of >2.5 following a similar trend. This suggests high D retention rates and net B deposition rates of ~18 cm/year of plasma exposure are possible and depend strongly on the plasma conditions. Ex-situ IBA was also performed on the same PFCs after removal from C-Mod, successfully validating the AIMS technique. These IBA measurements also show that the B content on the inner wall varied toroidally and poloidally from 0 to 3000 nm, demonstrating the importance of the spatial resolution provided by AIMS and the sensitivity of PFCs to B-field alignment. AIMS upgrades are underway for operation in 2014 and we anticipate new measurements correlating the evolution of PFC surfaces to plasma configuration, RF heating, and current drive scenarios. This work is supported by U.S. DOE Grant No. DE-FG02-94ER54235 and

  14. Multi-Channel Validation of Nonlinear Gyrokinetic Simulations in Alcator C-Mod I-mode Plasmas

    NASA Astrophysics Data System (ADS)

    Creely, A. J.

    2016-10-01

    New multi-channel validation of nonlinear gyrokinetic simulations (GYRO) is carried out for I-mode plasmas on Alcator C-Mod, utilizing heat fluxes, profile stiffness, and density and temperature fluctuations. I-mode plasmas are characterized by high energy confinement, similar to H-mode, but with L-mode-like particle confinement, making them favorable for reactors due to natural absence of ELMs, but without impurity accumulation [Whyte NF 2010]. At C-Mod, I-mode plasmas have been obtained across a wide range of plasma currents (Ip = 0.55-1.2MA) and magnetic fields (Bt = 2.8-8.0T). I-mode is also actively studied at ASDEX Upgrade, DIII-D and other tokamaks [Hubbard NF 2016]. Open questions remain regarding core transport in I-mode compared to L and H-mode, making validation studies in I-mode of great interest. Previous work at C-Mod found that ITG/TEM-scale GYRO simulations can match both electron and ion heat fluxes within error bars in I-mode [White PoP 2015], suggesting that multi-scale, cross-scale coupling effects [Howard PoP 2016] may be less important in I-mode than in L-mode. Adding the constraint of experimental perturbative heat diffusivity, however, revealed that ITG/TEM scale simulations do not adequately capture the high profile stiffness in I-mode [Creely NF 2016]. These results motivated more comprehensive comparisons of gyrokinetic simulations with I-mode plasmas. This talk expands upon past I-mode GYRO validation work to simultaneously constrain nonlinear gyrokinetic simulations with experimental electron and ion heat fluxes, electron temperature fluctuations measured with Correlation ECE, density fluctuations measured with Phase Contrast Imaging and reflectometry, and the temperature profile stiffness measured using partial sawtooth heat pulses. This work is supported by the US DOE under Grants DE-SC0006419 and DEFC02-99ER54512-CMOD.

  15. Stability of Microturbulent Drift Modes during Internal Transport Barrier Formation in the Alcator C-Mod Radio Frequency Heated H-mode

    SciTech Connect

    M.H. Redi; C.L. Fiore; W. Dorland; D.R. Mikkelsen; G. Rewoldt; P.T. Bonoli; D.R. Ernst; J.E. Rice; S.J. Wukitch

    2003-11-20

    Recent H-mode experiments on Alcator C-Mod [I.H. Hutchinson, et al., Phys. Plasmas 1 (1994) 1511] which exhibit an internal transport barrier (ITB), have been examined with flux tube geometry gyrokinetic simulations, using the massively parallel code GS2 [M. Kotschenreuther, G. Rewoldt, and W.M. Tang, Comput. Phys. Commun. 88 (1995) 128]. The simulations support the picture of ion/electron temperature gradient (ITG/ETG) microturbulence driving high xi/ xe and that suppressed ITG causes reduced particle transport and improved ci on C-Mod. Nonlinear calculations for C-Mod confirm initial linear simulations, which predicted ITG stability in the barrier region just before ITB formation, without invoking E x B shear suppression of turbulence. Nonlinear fluxes are compared to experiment, which both show low heat transport in the ITB and higher transport within and outside of the barrier region.

  16. EMC3-EIRENE modelling of toroidally-localized divertor gas injection experiments on Alcator C-Mod

    SciTech Connect

    Lore, Jeremy D.; Reinke, M. L.; LaBombard, Brian; Lipschultz, B.; Churchill, R. M.; Pitts, R. A.; Feng, Y.

    2014-09-30

    Experiments on Alcator C-Mod with toroidally and poloidally localized divertor nitrogen injection have been modeled using the three-dimensional edge transport code EMC3-EIRENE to elucidate the mechanisms driving measured toroidal asymmetries. In these experiments five toroidally distributed gas injectors in the private flux region were sequentially activated in separate discharges resulting in clear evidence of toroidal asymmetries in radiated power and nitrogen line emission as well as a ~50% toroidal modulation in electron pressure at the divertor target. The pressure modulation is qualitatively reproduced by the modelling, with the simulation yielding a toroidal asymmetry in the heat flow to the outer strike point. Finally, toroidal variation in impurity line emission is qualitatively matched in the scrape-off layer above the strike point, however kinetic corrections and cross-field drifts are likely required to quantitatively reproduce impurity behavior in the private flux region and electron temperatures and densities directly in front of the target.

  17. Experimental Study of Reversed Shear Alfven Eigenmodes During The Current Ramp In The Alcator C-Mod Tokamak

    SciTech Connect

    Edlund, E. M.; Porkolab, M.; Kramer, G. J.; Lin, L.; Lin, Y.; Tsuji, N.; Wukitch, S. J.

    2010-08-27

    Experiments conducted in the Alcator C-Mod tokamak at MIT have explored the physics of reversed shear Alfven eigenmodes (RSAEs) during the current ramp. The frequency evolution of the RSAEs throughout the current ramp provides a constraint on the evolution of qmin, a result which is important in transport modeling and for comparison with other diagnostics which directly measure the magnetic field line structure. Additionally, a scaling of the RSAE minimum frequency with the sound speed is used to derive a measure of the adiabatic index, a measure of the plasma compressibility. This scaling bounds the adiabatic index at 1.40 ± 0:15 used in MHD models and supports the kinetic calculation of separate electron and ion compressibilities with an ion adiabatic index close to 7~4.

  18. Response to ""Comment on ""Magnetic topology effects on alcator c-mod scrape-off layer flow

    SciTech Connect

    Simakov, Andrei N; Catto, Peter J

    2008-01-01

    Recent interest in the experimental study of tokamak plasma flow for different magnetic field geometries calls for theoretical understanding of the effects of tokamak magnetic topology changes on the flow. The consequences of total magnetic field reversal and/or X-point reversal on divergence-free plasma flow within magnetic flux surfaces are considered and the results are applied to interpret recent Alcator C-Mod scrape-off layer flow measurements. In his comment to that work, Aydemir asserted that poloidal plasma flow reversal is not a valid response to toroidal magnetic field reversal in an up-down symmetric tokamak, and that the toroidal plasma flow must reverse instead. We show that this assertion is wrong due to his misunderstanding of the corresponding symmetry transformation.

  19. Estimation of the ion toroidal rotation source due to momentum transfer from Lower Hybrid waves in Alcator C-Mod

    SciTech Connect

    Lee, J. P.; Wright, J. C.; Bonoli, P. T.; Parker, R. R.; Catto, P. J.; Podpaly, Y. A.; Rice, J. E.; Reinke, M. L.

    2011-12-23

    Significant ion toroidal rotation (50km/s) has been measured by X-Ray spectroscopy for impurities in Alcator C-Mod during lower hybrid (LH) RF power injection. We investigate the relation between the computed toroidal momentum input from LH waves and the measured INITIAL change of ion toroidal rotation when the LH power is turned on. The relation may depend on the plasma current and magnetic configuration. Because of the fast build up time of the electron quasilinear plateau (<1 millisecond), the electron distribution function rapidly reaches steady state in which the electrons transfer momentum to the ions. The LH wave momentum input is computed from the self consistent steady state electron distribution function and a bounce-averaged quasilinear diffusion coefficient that are obtained by iterating a full wave code (TORLH) with a Fokker Plank code (CQL3D)

  20. Profiles of Helium-like Argon Spectra from Alcator C-Mod with High Spatial and Spectral Resolution

    NASA Astrophysics Data System (ADS)

    Hill, K. W.; Bitter, M.; Stratton, B.; Roquemore, L.; Mastrovito, D.; Lee, S. G.; Bak, J. G.; Nam, U. W.; Rice, J. E.; Marmar, E.; Smith, G.

    2003-10-01

    Preliminary measurements of time resolved helium-like argon spectra have been made on Alcator C-Mod with a high resolution x-ray imaging crystal spectrometer, built for use on NSTX. A spherically bent crystal and a 10 cm x 30 cm imaging detector, developed for KSTAR, allow measurement of spectra across the entire plasma profile with a spatial resolution of 1 cm. The estimated resolving power, R = E/dE, for the spectrometer is about 4000. However, in these preliminary measurements R was significantly reduced, possibly due to high count rate effects. Addition of radiation shielding to reduce the background and use of a new detector with better position resolution will enable measurement of profiles of Ti, Te, charge-state equilibrium, and poloidal/toroidal rotation. The spectrometer and initial spectra will be presented, as well as observations regarding background and shielding and system resolution and throughput.

  1. Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

    NASA Astrophysics Data System (ADS)

    Sung, C.; White, A. E.; Mikkelsen, D. R.; Greenwald, M.; Holland, C.; Howard, N. T.; Churchill, R.; Theiler, C.

    2016-04-01

    Long wavelength turbulent electron temperature fluctuations (kyρs < 0.3) are measured in the outer core region (r/a > 0.8) of Ohmic L-mode plasmas at Alcator C-Mod [E. S. Marmar et al., Nucl. Fusion 49, 104014 (2009)] with a correlation electron cyclotron emission diagnostic. The relative amplitude and frequency spectrum of the fluctuations are compared quantitatively with nonlinear gyrokinetic simulations using the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] in two different confinement regimes: linear Ohmic confinement (LOC) regime and saturated Ohmic confinement (SOC) regime. When comparing experiment with nonlinear simulations, it is found that local, electrostatic ion-scale simulations (kyρs ≲ 1.7) performed at r/a ˜ 0.85 reproduce the experimental ion heat flux levels, electron temperature fluctuation levels, and frequency spectra within experimental error bars. In contrast, the electron heat flux is robustly under-predicted and cannot be recovered by using scans of the simulation inputs within error bars or by using global simulations. If both the ion heat flux and the measured temperature fluctuations are attributed predominantly to long-wavelength turbulence, then under-prediction of electron heat flux strongly suggests that electron scale turbulence is important for transport in C-Mod Ohmic L-mode discharges. In addition, no evidence is found from linear or nonlinear simulations for a clear transition from trapped electron mode to ion temperature gradient turbulence across the LOC/SOC transition, and also there is no evidence in these Ohmic L-mode plasmas of the "Transport Shortfall" [C. Holland et al., Phys. Plasmas 16, 052301 (2009)].

  2. Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

    SciTech Connect

    Sung, C.; White, A. E.; Greenwald, M.; Howard, N. T.; Mikkelsen, D. R.; Churchill, R.; Holland, C.; Theiler, C.

    2016-04-15

    Long wavelength turbulent electron temperature fluctuations (k{sub y}ρ{sub s} < 0.3) are measured in the outer core region (r/a > 0.8) of Ohmic L-mode plasmas at Alcator C-Mod [E. S. Marmar et al., Nucl. Fusion 49, 104014 (2009)] with a correlation electron cyclotron emission diagnostic. The relative amplitude and frequency spectrum of the fluctuations are compared quantitatively with nonlinear gyrokinetic simulations using the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] in two different confinement regimes: linear Ohmic confinement (LOC) regime and saturated Ohmic confinement (SOC) regime. When comparing experiment with nonlinear simulations, it is found that local, electrostatic ion-scale simulations (k{sub y}ρ{sub s} ≲ 1.7) performed at r/a ∼ 0.85 reproduce the experimental ion heat flux levels, electron temperature fluctuation levels, and frequency spectra within experimental error bars. In contrast, the electron heat flux is robustly under-predicted and cannot be recovered by using scans of the simulation inputs within error bars or by using global simulations. If both the ion heat flux and the measured temperature fluctuations are attributed predominantly to long-wavelength turbulence, then under-prediction of electron heat flux strongly suggests that electron scale turbulence is important for transport in C-Mod Ohmic L-mode discharges. In addition, no evidence is found from linear or nonlinear simulations for a clear transition from trapped electron mode to ion temperature gradient turbulence across the LOC/SOC transition, and also there is no evidence in these Ohmic L-mode plasmas of the “Transport Shortfall” [C. Holland et al., Phys. Plasmas 16, 052301 (2009)].

  3. On the correlation between ‘non-local’ effects and intrinsic rotation reversals in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Rodriguez-Fernandez, P.; Rice, J. E.; Cao, N. M.; Creely, A. J.; Howard, N. T.; Hubbard, A. E.; Irby, J. H.; White, A. E.

    2017-07-01

    Contemporary predictive models for heat and particle transport in tokamak plasmas are based on the assumption that local fluxes can be described in terms of local plasma parameters, where electromagnetic drift-wave-type turbulence is driven by local gradients and results in cross-field transport. The question of whether or not transport could be dominated by non-local terms in certain circumstances is essential for our understanding of transport in magnetically confined plasmas, and critical for developing predictive models for future tokamaks, such as ITER. Perturbative transport experiments using cold-pulse injections at low density seem to challenge the local closure of anomalous transport: a rapid temperature increase in the core of the plasma following a sharp edge cooling is widely observed in tokamaks and helical devices. Past work in Ohmic plasmas in Alcator C-Mod and in ECH plasmas in KSTAR found that the temperature inversions disappear at higher densities, above the intrinsic toroidal rotation reversal density. These observations suggested that the so-called ‘non-local’ heat transport effects were related to the intrinsic rotation reversal, and therefore to changes in momentum transport. In this work, new experiments and analysis at Alcator C-Mod show that intrinsic rotation reversals and disappearance of temperature inversions are not concomitant in Ohmic plasmas at high plasma current and in ICRH L-modes. This new data set shows that the correlation between transient temperature inversions and intrinsic rotation reversals is not universal, suggesting that ‘non-local’ heat transport and momentum transport effects may be affected by different physical mechanisms.

  4. Initial Results from the C-Mod Divertor Thomson Scattering System

    NASA Astrophysics Data System (ADS)

    Grek, B.; Johnson, D.; Paladino, R.; Bartolick, J.; Dimock, D.; Lowrance, J.; Lipshultz, B.; Labombard, B.

    1996-11-01

    Thomson scattering system has been installed recently to diagnose the x-point and divertor plasma regions with a resolution of 2-3 mm over a 12 cm field. The light scattered from a 30 HZ Nd:YAG laser is viewed from below through a slot in the outer divertor plate with a reentrant, high throughput collection system. A compact laser dump is located inside the inner divertor plate. Laser alignment is maintained under feedback control to track vessel motion. A filter polychromator spectrally resolves the scattered light from 25 spatial positions onto four 25 element avalanche photodiode arrays. System performance is described in terms of both calibration results and initial measurements of divertor plasma parameters. Supported by U.S. DOE Contract No. DE-AC02-78ET51013, DE-AC02-76-CHO-3073 and SBIR Grant No. 20431-92-II.

  5. Poloidal variation of high-Z impurity density in Alcator C-Mod ICRF-heated plasmas

    NASA Astrophysics Data System (ADS)

    Reinke, Matthew

    2012-10-01

    The poloidal variation of molybdenum density is measured in the core of ICRF-heated Alcator C-Mod plasmas and found to exhibit strong in/out asymmetries. Existing neoclassical parallel impurity transport theory is extended to include the effects of fast-ions and is shown to agree quantitatively with C-Mod measurements. The flux-surface variation of molybdenum is well described by nz(θ)/=1+nz,c cos(θ)+nz,ssin(θ), where -0.2 < nz,c/ < 0.3 and -0.1 < nz,s/ < 0.1 are observed over a wide range of Ohmic, L/I-mode and EDA H-mode plasmas for r/a < 0.9. The in/out asymmetry, nz,c/, is determined by a combination of centrifugal force due to toroidal rotation, leading to low-field side (LFS) accumulation, and poloidal electric fields sustained by magnetic trapping of cyclotron heated minority ions, leading to high field side (HFS) accumulation. While LFS accumulation due to centrifugal effects has been seen on other tokamaks, this represents the first observation of the effect driven entirely by intrinsic rotation. Scans of the D(H) resonance layer are shown to modify the in/out asymmetry by altering the fast-ion temperature anisotropy, T-/T||, and changing the ICRF power density, PRF/ne, either by ramping down the input power or increasing the density is found to reduce HFS accumulation. Observations of up/down asymmetries nz,s/, of molybdenum density are found to disagree with existing theories in the trace limit, nzZ^2/ni 1, in the collisionless main-ion regime. The link between nz(θ) and poloidal rotation, vθ, is emphasized, as both are assumed to be determined by neoclassical parallel impurity transport, and a more rigorous test of theory which includes matching asymmetries and vθ is discussed. The use of the poloidal variation in nz as a diagnostic for Eθ and T-/T|| as well as the impact of nz,c/ on radial transport are also discussed.

  6. Parallel transport studies of high-Z impurities in the core of Alcator C-Mod plasmas

    SciTech Connect

    Reinke, M. L.; Hutchinson, I. H.; Rice, J. E.; Greenwald, M.; Howard, N. T.; Hubbard, A.; Hughes, J. W.; Terry, J. L.; Wolfe, S. M.

    2013-05-15

    Measurements of poloidal variation, ñ{sub z}/, in high-Z impurity density have been made using photodiode arrays sensitive to vacuum ultraviolet and soft x-ray emission in Alcator C-Mod plasmas. In/out asymmetries in the range of −0.2<0.3 are observed for r/a<0.8, and accumulation on both the high-field side, n{sub z,cos}<0, and low-field side, n{sub z,cos}>0, of a flux surface is found to be well described by a combination of centrifugal, poloidal electric field, and ion-impurity friction effects. Up/down asymmetries, −0.05<0.10, are observed over 0.50 corresponding to accumulation opposite the ion ∇B drift direction. Measurements of the up/down asymmetry of molybdenum are found to disagree with predictions from recent neoclassical theory in the trace limit, n{sub z}Z{sup 2}/n{sub i}≪1. Non-trace levels of impurities are expected to modify the main-ion poloidal flow and thus change friction-driven impurity density asymmetries and impurity poloidal rotation, v{sub θ,z}. Artificially modifying main-ion flow in parallel transport simulations is shown to impact both ñ{sub z}/ and v{sub θ,z}, but simultaneous agreement between measured and predicted up/down and in/out asymmetry as well as impurity poloidal rotation is not possible for these C-Mod data. This link between poloidal flow and poloidal impurity density variation outlines a more stringent test for parallel neoclassical transport theory than has previously been performed. Measurement and computational techniques specific to the study of poloidal impurity asymmetry physics are discussed as well.

  7. EMC3-EIRENE modelling of toroidally-localized divertor gas injection experiments on Alcator C-Mod

    DOE PAGES

    Lore, Jeremy D.; Reinke, M. L.; LaBombard, Brian; ...

    2014-09-30

    Experiments on Alcator C-Mod with toroidally and poloidally localized divertor nitrogen injection have been modeled using the three-dimensional edge transport code EMC3-EIRENE to elucidate the mechanisms driving measured toroidal asymmetries. In these experiments five toroidally distributed gas injectors in the private flux region were sequentially activated in separate discharges resulting in clear evidence of toroidal asymmetries in radiated power and nitrogen line emission as well as a ~50% toroidal modulation in electron pressure at the divertor target. The pressure modulation is qualitatively reproduced by the modelling, with the simulation yielding a toroidal asymmetry in the heat flow to the outermore » strike point. Finally, toroidal variation in impurity line emission is qualitatively matched in the scrape-off layer above the strike point, however kinetic corrections and cross-field drifts are likely required to quantitatively reproduce impurity behavior in the private flux region and electron temperatures and densities directly in front of the target.« less

  8. Changes in core electron temperature fluctuations across the ohmic energy confinement transition in Alcator C-Mod plasmas

    NASA Astrophysics Data System (ADS)

    Sung, C.; White, A. E.; Howard, N. T.; Oi, C. Y.; Rice, J. E.; Gao, C.; Ennever, P.; Porkolab, M.; Parra, F.; Mikkelsen, D.; Ernst, D.; Walk, J.; Hughes, J. W.; Irby, J.; Kasten, C.; Hubbard, A. E.; Greenwald, M. J.; the Alcator C-Mod Team

    2013-08-01

    The first measurements of long wavelength (kyρs < 0.3) electron temperature fluctuations in Alcator C-Mod made with a new correlation electron cyclotron emission diagnostic support a long-standing hypothesis regarding the confinement transition from linear ohmic confinement (LOC) to saturated ohmic confinement (SOC). Electron temperature fluctuations decrease significantly (∼40%) crossing from LOC to SOC, consistent with a change from trapped electron mode (TEM) turbulence domination to ion temperature gradient (ITG) turbulence as the density is increased. Linear stability analysis performed with the GYRO code (Candy and Waltz 2003 J. Comput. Phys. 186 545) shows that TEMs are dominant for long wavelength turbulence in the LOC regime and ITG modes are dominant in the SOC regime at the radial location (ρ ∼ 0.8) where the changes in electron temperature fluctuations are measured. In contrast, deeper in the core (ρ < 0.8), linear stability analysis indicates that ITG modes remain dominant across the LOC/SOC transition. This radial variation suggests that the robust global changes in confinement of energy and momentum occurring across the LOC/SOC transition are correlated to local changes in the dominant turbulent mode near the edge.

  9. Quantitative comparison of experimental impurity transport with nonlinear gyrokinetic simulation in an Alcator C-Mod L-mode plasma

    NASA Astrophysics Data System (ADS)

    Howard, N. T.; Greenwald, M.; Mikkelsen, D. R.; Reinke, M. L.; White, A. E.; Ernst, D.; Podpaly, Y.; Candy, J.

    2012-06-01

    Nonlinear gyrokinetic simulations of impurity transport are compared to experimental impurity transport for the first time. The GYRO code (Candy and Waltz 2003 J. Comput. Phys. 186 545) was used to perform global, nonlinear gyrokinetic simulations of impurity transport for a standard Alcator C-Mod, L-mode discharge. The laser blow-off technique was combined with soft x-ray measurements of a single charge state of calcium to provide time-evolving profiles of this non-intrinsic, non-recycling impurity over a radial range of 0.0 ⩽ r/a ⩽ 0.6. Experimental transport coefficient profiles and their uncertainties were extracted from the measurements using the impurity transport code STRAHL and rigorous Monte Carlo error analysis. To best assess the agreement of gyrokinetic simulations with the experimental profiles, the sensitivity of the GYRO predicted impurity transport to a wide range of turbulence-relevant plasma parameters was investigated. A direct comparison of nonlinear gyrokinetic simulation and experiment is presented with an in depth discussion of error sources and a new data analysis methodology.

  10. High-performance finite-difference time-domain simulations of C-Mod and ITER RF antennas

    NASA Astrophysics Data System (ADS)

    Jenkins, Thomas G.; Smithe, David N.

    2015-12-01

    Finite-difference time-domain methods have, in recent years, developed powerful capabilities for modeling realistic ICRF behavior in fusion plasmas [1, 2, 3, 4]. When coupled with the power of modern high-performance computing platforms, such techniques allow the behavior of antenna near and far fields, and the flow of RF power, to be studied in realistic experimental scenarios at previously inaccessible levels of resolution. In this talk, we present results and 3D animations from high-performance FDTD simulations on the Titan Cray XK7 supercomputer, modeling both Alcator C-Mod's field-aligned ICRF antenna and the ITER antenna module. Much of this work focuses on scans over edge density, and tailored edge density profiles, to study dispersion and the physics of slow wave excitation in the immediate vicinity of the antenna hardware and SOL. An understanding of the role of the lower-hybrid resonance in low-density scenarios is emerging, and possible implications of this for the NSTX launcher and power balance are also discussed. In addition, we discuss ongoing work centered on using these simulations to estimate sputtering and impurity production, as driven by the self-consistent sheath potentials at antenna surfaces.

  11. Upgraded PMI diagnostic capabilities using Accelerator-based In-situ Materials Surveillance (AIMS) on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Kesler, Leigh; Barnard, Harold; Hartwig, Zachary; Sorbom, Brandon; Lanza, Richard; Terry, David; Vieira, Rui; Whyte, Dennis

    2014-10-01

    The AIMS diagnostic was developed to rapidly and non-invasively characterize in-situ plasma material interactions (PMI) in a tokamak. Recent improvements are described which significantly expand this measurement capability on Alcator C-Mod. The detection time at each wall location is reduced from about 10 min to 30 s, via improved hardware and detection geometry. Detectors are in an augmented re-entrant tube to maximize the solid angle between detectors and diagnostic locations. Spatial range is expanded by using beam dynamics simulation to design upgraded B-field power supplies to provide maximal poloidal access, including a ~20° toroidal range in the divertor. Measurement accuracy is improved with angular and energy resolved cross section measurements obtained using a separate 0.9 MeV deuteron ion accelerator. Future improvements include the installation of recessed scintillator tiles as beam targets for calibration of the diagnostic. Additionally, implanted depth marker tiles will enable AIMS to observe the in-situ erosion and deposition of high-Z plasma-facing materials. This work is supported by U.S. DOE Grant No. DE-FG02-94ER54235 and Cooperative Agreement No. DE-FC02-99ER54512.

  12. A `shoelace' antenna system for direct excitation of C-Mod's quasi-coherent mode and boundary layer turbulence

    NASA Astrophysics Data System (ADS)

    Labombard, B.; Golfinopoulos, T.; Parker, R.; Burke, W.; Leccacorvi, R.; Vieira, R.; Zaks, J.; Granetz, R.; Greenwald, M.; Marmar, E.; Porkolab, M.; Wolfe, S.; Woskov, P.; Wuktich, S.

    2011-10-01

    Experiments indicate that short wavelength, drift-Alfvenic turbulence largely sets the transport levels in the plasma edge: pressure gradients in L and H-mode are `clamped' at canonical values of the MHD parameter (αMHD) ; broadband and coherent fluctuations have strong magnetic signatures, with k⊥ρs ~ 0.1 being prominent. A quasi-coherent mode (50 kHz < f < 150 kHz, 1 < k⊥ < 2 cm-1) drives particle transport in C-Mod's EDA H-modes, making them steady-state without ELMs. With the idea of exciting, controlling or otherwise exploiting this transport behavior, we are developing a novel, high k⊥ antenna system to drive drift-Alfvenic modes at the outer midplane with k⊥ ~ 1.5 cm-1. A `shoelace' style winding is placed in close proximity to the last-closed flux surface. In principle, this scheme inductively drives parallel current fluctuations that mimic intrinsic plasma fluctuations but at larger amplitude. Details of the antenna system design, its planned modes of operation and initial results will be presented. Supported by USDoE award DE-FC02-99ER54512.

  13. LETTER: Fast electron driven Alfvén eigenmodes in the current rise in Alcator C-MOD

    NASA Astrophysics Data System (ADS)

    Snipes, J. A.; Parker, R. R.; Phillips, P. E.; Schmidt, A.; Wallace, G.

    2008-07-01

    The injection of 0.3-1 MW of lower hybrid current drive (LHCD) from the very start of the plasma drives a suprathermal electron tail that excites a series of bursting high frequency (100-700 kHz) instabilities in the current rise in Alcator C-Mod. These high frequency bursting modes have relatively small amplitude (\\tilde {B}_\\theta \\le 5\\times 10^{-6}\\,T) measured with poloidal field pick-up coils on outboard limiters. They are observed very early in the current rise with one to three bands of frequencies. The frequency at each burst corresponds very closely to the centre of the gap frequency for toroidal Alfvén eigenmodes (TAEs), ωTAE = vA/2qR, for integer and half integer q values ranging typically from 11 down to 5.5. Measured average hard x-ray photon energies in the range 20-35 keV are in reasonable agreement with the theoretically calculated fast electron energy that matches the precession drift resonance condition for exciting Alfvén eigenmodes.

  14. Lower Hybrid Wave Induced SOL Emissivity Variation at High Density on the Alcator C-Mod Tokamak

    SciTech Connect

    Faust, I.; Terry, J. L.; Reinke, M. L.; Meneghini, O.; Shiraiwa, S.; Wallace, G. M.; Parker, R. R.; Schmidt, A. E.; Wilson, J. R.

    2011-12-23

    Lower Hybrid Current Drive (LHCD) in the Alcator C-Mod tokamak provides current profile control for the generation of Advanced Tokamak (AT) plasmas. Non-thermal electron bremsstrahlung emission decreases dramatically at n-bar{sub e}>1{center_dot}10{sup 20}[m{sup -3}] for diverted discharges, indicating low current drive efficiency. It is suggested that Scrape-Off-Layer (SOL) collisional absorption of LH waves is the cause for the absence of non-thermal electrons at high density. VUV and visible spectroscopy in the SOL provide direct information on collision excitation processes. Deuterium Balmer-, Lyman- and He-I transition emission measurements were used for initial characterization of SOL electron-neutral collisional absorption. Data from Helium and Deuterium LHCD discharges were characterized by an overall increase in the emissivity as well as an outward radial shift in the emissivity profile with increasing plasma density and applied LHCD power. High-temperature, high-field (T{sub e} = 5keV,B{sub t} = 8T) helium discharges at high density display increased non-thermal signatures as well as reduced SOL emissivity. Variations in emissivity due to LHCD were seen in SOL regions not magnetically connected to the LH Launcher, indicating global SOL effects due to LHCD.

  15. High-Performance Computational Modeling of ICRF Physics and Plasma-Surface Interactions in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Jenkins, Thomas; Smithe, David

    2016-10-01

    Inefficiencies and detrimental physical effects may arise in conjunction with ICRF heating of tokamak plasmas. Large wall potential drops, associated with sheath formation near plasma-facing antenna hardware, give rise to high-Z impurity sputtering from plasma-facing components and subsequent radiative cooling. Linear and nonlinear wave excitations in the plasma edge/SOL also dissipate injected RF power and reduce overall antenna efficiency. Recent advances in finite-difference time-domain (FDTD) modeling techniques allow the physics of localized sheath potentials, and associated sputtering events, to be modeled concurrently with the physics of antenna near- and far-field behavior and RF power flow. The new methods enable time-domain modeling of plasma-surface interactions and ICRF physics in realistic experimental configurations at unprecedented spatial resolution. We present results/animations from high-performance (10k-100k core) FDTD/PIC simulations spanning half of Alcator C-Mod at mm-scale resolution, exploring impurity production due to localized sputtering (in response to self-consistent sheath potentials at antenna surfaces) and the physics of parasitic slow wave excitation near the antenna hardware and SOL. Supported by US DoE (Award DE-SC0009501) and the ALCC program.

  16. The influence of divertor geometry on access to high confinement regimes on the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Hughes, J. W.; Labombard, B.; Hubbard, A.; Marmar, E.; Terry, J.; Rice, J.; Walk, J.; Whyte, D.; Ma, Y.; Cziegler, I.; Edlund, E.; Theiler, C.

    2014-10-01

    The placement of X-point and strike points in a diverted tokamak can have a remarkable impact on properties of the discharge, including thermal and particle confinement. The distinctive divertor of Alcator C-Mod allows us to demonstrate these effects experimentally, as we vary equilibrium shaping to obtain substantial variation of divertor leg length, field line attack angle and divertor baffling. In response to these changes, we observe differences in both L-mode confinement and access to high-confinement regimes (i.e. ELMy H-mode and I-mode). With the ion grad-B drift directed toward the divertor, scanning the strike point can induce ~2× reductions in H-mode power threshold, and can produce a window for I-mode operation with H98 > 1. Recent experiments seek to explore these effects using improved diagnostics, and to extend them to the case with ion grad-B drift directed away from the divertor. Supported by USDoE award DE-FC02-99ER54512.

  17. Heat-flux footprints for I-mode and EDA H-mode plasmas on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Terry, J. L.; LaBombard, B.; Brunner, D.; Hughes, J. W.; Reinke, M. L.; Whyte, D. G.

    2013-07-01

    IR thermography is used to measure the heat flux footprints on C-Mod's outer target in I-mode and EDA H-mode plasmas. The footprint profiles are fit to a function with a simple physical interpretation. The fit parameter that is sensitive to the power decay length into the SOL, λSOL, is ˜1-3× larger in I-modes than in H-modes at similar plasma current, which is the dominant dependence for the H-mode λSOL. In contrast, the fit parameter sensitive to transport into the private-flux-zone along the divertor leg is somewhat smaller in I-mode than in H-mode, but otherwise displays no obvious dependence on Ip, Bt, or stored energy. A third measure of the footprint width, the "integral width", is not significantly different between H- and I-modes. Also discussed are significant differences in the global power flows of the H-modes with "favorable"∇B drift direction and those of the I-modes with "unfavorable"∇B drift direction.

  18. Progress in Performance and Understanding of Steady ELM-free I-modes on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Hubbard, A. E.; Whyte, D. G.; Dominguez, A.; Greenwald, M. J.; Howard, N.; Hughes, J. W.; Labombard, B.; Lin, Y.; Lipschultz, B.; Marmar, E. S.; Reinke, M. L.; Rice, J. E.; Terry, J. L.; Walk, J.; White, A. E.; Wukitch, S. J.; Snyder, P.

    2012-10-01

    The I-mode regime of operation has been extended in recent Alcator C-Mod campaigns in duration and robustness, over a wide range of parameters. It features an edge thermal barrier, with L-mode like density profiles and particle transport [1]. I-modes are now routinely maintained in stationary conditions for over 10 τE. They are usually ELM free, a key advantage given the concern over divertor heat pulses on ITER. Instead, a continuous pedestal fluctuation, the ``weakly coherent mode,'' appears to enhance selectively particle over thermal transport. High performance I-modes are usually obtained with unfavorable ion drift direction, and extend to low q95=2.5and νped^*=1.3. τE is in the range of H-mode (H98,y2 up to 1.2), and exhibits less power degradation (W˜P^0.7). Power thresholds for I-mode are higher than typical L-H scalings, and increase with Ip as well as density. The widest power range for I-mode, nearly a factor of two above the L-I threshold, has been obtained in reversed field, lower null discharges at moderate ne. The focus of 2012 experiments is on assessing the density range and dependences, important for extrapolating to ITER, and measuring the pedestal profiles and fluctuations in greater detail.[4pt] [1] Whyte D G et al 2010 Nucl. Fusion 50 105005

  19. Characterization of SOL plasma flows and potentials in ICRF-heated plasmas in Alcator C-mod

    NASA Astrophysics Data System (ADS)

    Hong, R.; Wukitch, S. J.; Lin, Y.; Terry, J. L.; Cziegler, I.; Reinke, M. L.; Tynan, G. R.

    2017-10-01

    Gas-puff imaging techniques are employed to determine the far SOL region radial electric field and the plasma potential in ICRF heated discharges in the Alcator C-Mod tokamak. The two-dimensional velocity fields of the turbulent structures, which are advected by RF-induced {E}× {B} flows, are obtained via the time-delay estimation (TDE) techniques. Both the magnitude and radial extension of the radial electric field E r are observed to increase with the toroidal magnetic field strength B φ and the ICRF power. In particular, the RF-induced E r extends from the vicinity of the ICRF antenna to the separatrix when {B}\\varphi =7.9 {{T}} and {P}{ICRF}≳ 1 {MW}. In addition, low-Z impurity seeding near the antenna is found to substantially reduce the sheath potential associated with ICRF power. The TDE techniques have also been used to revisit and estimate ICRF-induced potentials in different antenna configurations: (1) conventional toroidally aligned (TA) antenna versus field-aligned (FA) antenna; (2) FA monopole versus FA dipole. It shows that FA and TA antennas produce similar magnitude of plasma potentials, and the FA monopole induced greater potential than the FA dipole phasing. The TDE estimations of RF-induced plasma potentials are consistent with previous results based on the poloidal phase velocity.

  20. Comparison of Scrape-off Layer Turbulence in Alcator C-Mod with Three Dimensional Gyrofluid Computations

    SciTech Connect

    Zweben, S. J.; Scott, B. D.; Terry, J. L.; LaBombard, B.; Hughes, J. W.; Stotler, D. P.

    2009-09-01

    This paper describes quantitative comparisons between turbulence measured in the scrape-off layer (SOL) of Alcator C-Mod [S. Scott, A. Bader, M. Bakhtiari et al., Nucl. Fusion 47, S598 (2007)] and three dimensional computations using electromagnetic gyrofluid equations in a two-dimensional tokamak geometry. These comparisons were made for the outer midplane SOL for a set of inner-wall limited, near-circular Ohmic plasmas. The B field and plasma density were varied to assess gyroradius and collisionality scaling. The poloidal and radial correlation lengths in the experiment and computation agreed to within a factor of 2 and did not vary significantly with either B or density. The radial and poloidal propagation speeds and the frequency spectra and poloidal k-spectra also agreed fairly well. However, the autocorrelation times and relative Da fluctuation levels were higher in the experiment by more than a factor of 2. Possible causes for these disagreements are discussed. 2009 American Institute of Physics.

  1. Reduction of ion transport and turbulence via dilution with nitrogen and neon injection in C-Mod deuterium plasmas

    NASA Astrophysics Data System (ADS)

    Porkolab, M.; Ennever, P.; Baek, S. G.; Creely, A. J.; Edlund, E. M.; Hughes, J.; Rice, J. E.; Rost, J. C.; White, A. E.; Reinke, M. L.; Staebler, G.; Candy, J.; Alcator C-Mod Team

    2016-10-01

    Recent experiments on C-Mod ohmic plasmas and gyrokinetic studies indicated that dilution of deuterium plasmas by injection of nitrogen decreased the ion diffusivity and may also alter the direction of intrinsic toroidal rotation. Simulations with TGLF and GYRO showed that dilution of deuterium ions in low density (LOC) plasmas increased the critical ion temperature gradient, while in high density (SOC) plasmas it decreased the stiffness. The density fluctuation spectrum measured in low q95 plasmas with Phase Contrast Imaging (PCI), and corroborated with spatially localized reflectometer measurements show a reduction of turbulence near r/a = 0.8 with kρs <= 1, in agreement with modeling predictions in this region where the ion turbulence is well above marginal stability. Measurements also indicate that reversal of the toroidal rotation direction near the SOC-LOC transition may depend on ion collisionality rather than that of electrons. New experiments with neon seeding, which may be more relevant to ITER than with nitrogen seeding, show similar results. The impact of dilution on Te turbulence as measured with CECE diagnostic will also be presented. Supported by US DOE Awards DE-FG02-94-ER54235 and DE-FC02-99-ER54512.

  2. 3D modeling of toroidal asymmetry due to localized divertor nitrogen puffing on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Lore, J. D.; Reinke, M. L.; Labombard, B.; Lipschultz, B.; Pitts, R.

    2013-10-01

    For inductive operation at Q =10, ITER will need to run with partially detached divertor plasmas in order to maximize target lifetime and remain below engineering heat-flux limits. The radiated power fraction will be controlled via a divertor gas injection system that consists of six valves. To investigate the effect of potential toroidal asymmetry introduced by a finite number of gas valves, or the failure of one or more valves, experiments were performed on Alcator C-Mod. Nitrogen was injected through each of five toroidally spaced divertor gas valves into Ohmic L-mode plasmas with a high recycling divertor. Clear, reproducible toroidal variation in divertor radiated power and impurity line radiation was measured. The 3D scrape-off-layer transport code EMC3-EIRENE is being used to model and interpret these experiments. Initial results indicate that trends in the radiated power and nitrogen emission asymmetry are reproduced. Both experimental and modeling results will be presented. Work supported by D.O.E. contracts DE-AC05-00OR22725 and DE-FC02-99ER54512.

  3. Measurement of electron temperature fluctuations using a tunable correlation electron cyclotron emission system on Alcator C-Mod

    SciTech Connect

    Howard, N. T.; Sung, C.; White, A. E.

    2014-11-15

    A tunable correlation electron cyclotron (CECE) system was recently installed on the Alcator C-Mod tokamak to provide local, quantitative measurement of electron temperature fluctuations in the tokamak core. This system represents a significant upgrade from the original CECE system, expanding the measurement capabilities from 4 to 8 total channels, including 2 remotely tunable YIG filters (6–18 GHz; 200 MHz bandwidth). Additional upgrades were made to the optical system to provide enhanced poloidal resolution and allow for measurement of turbulent fluctuations below k{sub θ}ρ{sub s} < 0.3. These expanded capabilities allow for single shot measurement of partial temperature fluctuation profiles in the region ρ = 0.7 − 0.9 (square root of normalized toroidal flux) in a wide variety of plasma conditions. These measurements are currently being used to provide stringent tests of the gyrokinetic model in ongoing model validation efforts. Details of the hardware upgrades, turbulent fluctuation measurements, and ongoing comparisons with simulations are presented.

  4. Stark broadening data for stellar plasma research.

    NASA Astrophysics Data System (ADS)

    Dimitrijević, M. S.

    Results of an effort to provide to astrophysicists and physicists an as much as possible complete set of Stark broadening parameters needed for stellar opacity calculations, stellar atmosphere modelling, abundance determinations and diagnostics of different plasmas in astrophysics, physics and plasma technology, are presented. Stark broadening has been considered within the semiclassical perturbation, and the modified semiempirical approaches.

  5. Microturbulent Drift Mode Stability before Internal Transport Barrier Formation in the Alcator C-Mod Radio Frequency Heated H-mode

    SciTech Connect

    M.H. Redi; W. Dorland; C.L. Fiore; P.T. Bonoli; M.J. Greenwald; J.E. Rice; J.A. Baumgaertel; T.S. Hahm; G.W. Hammett; K. Hill; D.C. McCune; D.R. Mikkelsen; G. Rewoldt

    2004-09-01

    H-mode experiments on Alcator C-Mod [I.H. Hutchinson, et al., Phys. Plasma 1 (1994) 1511] which exhibit an internal transport barrier (ITB), have been examined with gyrokinetic simulations, near the ITB onset time. Linear simulations support the picture of ion and electron temperature gradient (ITG, ETG) microturbulence driving high {chi}{sub i} and {chi}{sub e}, respectively, and that stable ITG correlates with reduced particle transport and improved ion thermal confinement on C-Mod. In the barrier region ITG is weakly unstable, with a critical temperature gradient higher than expected from standard models. Nonlinear calculations and the role of E x B shear suppression of turbulence outside the plasma core are discussed in light of recent profile measurements for the toroidal velocity. The gyrokinetic model benchmarks successfully against experiment in the plasma core.

  6. Status of diagnostic development to measure parallel wavenumber of lower hybrid waves on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Baek, S. G.; Wallace, G. M.; Shinya, T.; Shiraiwa, S.; Parker, R. R.; Takase, Y.; Brunner, D.

    2015-12-01

    Recent lower hybrid (LH) current drive experiments on Alcator C-Mod have motivated measurement of the parallel wavenumber of LH waves with an aim to understand the significance of the k|| up-shift mechanisms such as scattering by turbulence or parametric decay instabilities. To this end, a new diagnostic system is under development, consisting of two rows of three RF magnetic loop probes (one row sensitive to B||, the other row B⊥) and three Langmuir probes. These will be mounted on a radially movable probe system on the low field side of the tokamak, which is magnetically mapped to the LH launcher but toroidally separated by about 110 deg from the launcher. This location is expected to be ideal for detecting the parallel wavenumber spectrum of the pump and sideband LH waves up to n|| of 6.5. The use of the loop probes will help unambiguously resolve the polarization of these waves. These loop probes have been developed under the collaboration with the University of Tokyo, and vacuum-compatible versions have recently been fabricated and tested on the bench. To evaluate the phase of the detected waves, the signals at 4.6 GHz will be frequency down-converted to 25 MHz in an intermediate frequency stage, and directly digitized at a sampling rate of 100 MS/sec. This system will output the dominant parallel wavenumber for each frequency, selected by controlling the frequency of a local oscillator in the IF stage. In addition to these loop probes, the Langmuir probes will be used to provide the density and temperature information at the measurement location to perform instability analyses. The Langmuir probes will be also used to examine the sensitivity of the radial measurement location on the strength of the sideband LH waves. Details of this proposed diagnostic system and the latest status will be presented.

  7. Local gas injection as a scrape-off layer diagnostic on the Alcator C-Mod tokamak

    SciTech Connect

    Jablonski, David F.

    1996-05-01

    A capillary puffing array has been installed on Alcator C-Mod which allows localized introduction of gaseous species in the scrape-off layer. This system has been utilized in experiments to elucidate both global and local properties of edge transport. Deuterium fueling and recycling impurity screening are observed to be characterized by non-dimensional screening efficiencies which are independent of the location of introduction. In contrast, the behavior of non-recycling impurities is seen to be characterized by a screening time which is dependent on puff location. The work of this thesis has focused on the use of the capillary array with a camera system which can view impurity line emission plumes formed in the region of an injection location. The ionic plumes observed extend along the magnetic field line with a comet-like asymmetry, indicative of background plasma ion flow. The flow is observed to be towards the nearest strike-point, independent of x-point location, magnetic field direction, and other plasma parameters. While the axes of the plumes are generally along the field line, deviations are seen which indicate cross-field ion drifts. A quasi-two dimensional fluid model has been constructed to use the plume shapes of the first charge state impurity ions to extract information about the local background plasma, specifically the temperature, parallel flow velocity, and radial electric field. Through comparisons of model results with those of a three dimensional Monte Carlo code, and comparisons of plume extracted parameters with scanning probe measurements, the efficacy of the model is demonstrated. Plume analysis not only leads to understandings of local edge impurity transport, but also presents a novel diagnostic technique.

  8. Feedback system for divertor impurity seeding based on real-time measurements of surface heat flux in the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Brunner, D.; Burke, W.; Kuang, A. Q.; LaBombard, B.; Lipschultz, B.; Wolfe, S.

    2016-02-01

    Mitigation of the intense heat flux to the divertor is one of the outstanding problems in fusion energy. One technique that has shown promise is impurity seeding, i.e., the injection of low-Z gaseous impurities (typically N2 or Ne) to radiate and dissipate the power before it arrives to the divertor target plate. To this end, the Alcator C-Mod team has created a first-of-its-kind feedback system to control the injection of seed gas based on real-time surface heat flux measurements. Surface thermocouples provide real-time measurements of the surface temperature response to the plasma heat flux. The surface temperature measurements are inputted into an analog computer that "solves" the 1-D heat transport equation to deliver accurate, real-time signals of the surface heat flux. The surface heat flux signals are sent to the C-Mod digital plasma control system, which uses a proportional-integral-derivative (PID) algorithm to control the duty cycle demand to a pulse width modulated piezo valve, which in turn controls the injection of gas into the private flux region of the C-Mod divertor. This paper presents the design and implementation of this new feedback system as well as initial results using it to control divertor heat flux.

  9. Feedback system for divertor impurity seeding based on real-time measurements of surface heat flux in the Alcator C-Mod tokamak.

    PubMed

    Brunner, D; Burke, W; Kuang, A Q; LaBombard, B; Lipschultz, B; Wolfe, S

    2016-02-01

    Mitigation of the intense heat flux to the divertor is one of the outstanding problems in fusion energy. One technique that has shown promise is impurity seeding, i.e., the injection of low-Z gaseous impurities (typically N2 or Ne) to radiate and dissipate the power before it arrives to the divertor target plate. To this end, the Alcator C-Mod team has created a first-of-its-kind feedback system to control the injection of seed gas based on real-time surface heat flux measurements. Surface thermocouples provide real-time measurements of the surface temperature response to the plasma heat flux. The surface temperature measurements are inputted into an analog computer that "solves" the 1-D heat transport equation to deliver accurate, real-time signals of the surface heat flux. The surface heat flux signals are sent to the C-Mod digital plasma control system, which uses a proportional-integral-derivative (PID) algorithm to control the duty cycle demand to a pulse width modulated piezo valve, which in turn controls the injection of gas into the private flux region of the C-Mod divertor. This paper presents the design and implementation of this new feedback system as well as initial results using it to control divertor heat flux.

  10. Motion.

    ERIC Educational Resources Information Center

    Brand, Judith, Ed.

    2002-01-01

    This issue of Exploratorium Magazine focuses on the topic of motion. Contents include: (1) "First Word" (Zach Tobias); (2) "Cosmic Collisions" (Robert Irion); (3) "The Mobile Cell" (Karen E. Kalumuck); (4) "The Paths of Paths" (Steven Vogel); (5) "Fragments" (Pearl Tesler); (6) "Moving Pictures" (Amy Snyder); (7) "Plants on the Go" (Katharine…

  11. Motion.

    ERIC Educational Resources Information Center

    Gerhart, James B.; Nussbaum, Rudi H.

    This monograph was written for the Conference on the New Instructional Materials in Physics held at the University of Washington in summer, 1965. It is intended for use in an introductory course in college physics. It consists of an extensive qualitative discussion of motion followed by a detailed development of the quantitative methods needed to…

  12. Motion.

    ERIC Educational Resources Information Center

    Brand, Judith, Ed.

    2002-01-01

    This issue of Exploratorium Magazine focuses on the topic of motion. Contents include: (1) "First Word" (Zach Tobias); (2) "Cosmic Collisions" (Robert Irion); (3) "The Mobile Cell" (Karen E. Kalumuck); (4) "The Paths of Paths" (Steven Vogel); (5) "Fragments" (Pearl Tesler); (6) "Moving Pictures" (Amy Snyder); (7) "Plants on the Go" (Katharine…

  13. Multichannel Transport in L-mode and I-mode Plasmas at Alcator C-Mod and Comparison with Gyrokinetic Simulations

    NASA Astrophysics Data System (ADS)

    White, A. E.

    2012-10-01

    New experiments at Alcator C-Mod are challenging and expanding our understanding of electron, impurity particle, and momentum transport. Understanding these coupled transport channels is important, since alpha particles will slow down mostly on electrons in ITER intrinsically rotating, alpha-heated plasmas. Core density fluctuations are reduced in high performance (H98˜1) I-mode plasmas by up to 30% compared to L-mode. At the L-I transition, the core turbulence changes lead the edge turbulence changes. This is in contrast to observations at L-H transitions, where the edge turbulence changes lead the core turbulence changes. It is also found that L-mode and I-mode plasmas are both ITG dominant, with lower linear ITG growth rates in I-mode. TRANSP analysis indicates that core electron heat transport is reduced in I-mode compared to L-mode, with little change in ion heat transport. This indicates that significant electron heat transport is driven by ITG turbulence in L-mode. However, impurity particle transport is similar in L-mode and I-mode, suggesting that tracking changes in ITG drive alone does not describe as well the transport in this channel. Additionally, in L-mode plasmas, small < 20% changes in line averaged density lead to dramatic differences in the on-axis rotation, due to a hollowing of the radial profile at marginally lower density. This change in the shape of the rotation profile in L-mode plasmas does not appear to occur at the ITG/TEM boundary, contrary to similar phenomena seen in Ohmic plasmas. For the first time, local, long-wavelength density and electron temperature fluctuations in the core plasma (0.4 < r/a < 0.9) at C-Mod have been measured with reflectometry and correlation ECE. These new fluctuation measurements at C-Mod will allow for better testing and validation of transport models. Gyrokinetic simulations are in progress to interpret the new multichannel and multifield turbulence/transport results from C-Mod.

  14. A Spatially Resolving X-ray Crystal Spectrometer for Measurement of Ion-temperature and Rotation-velocity Profiles on the AlcatorC-Mod Tokamak

    SciTech Connect

    Hill, K. W.; Bitter, M. L.; Scott, S. D.; Ince-Cushman, A.; Reinke, M.; Rice, J. E.; Beiersdorfer, P.; Gu, M. F.; Lee, S. G.; Broennimann, C. H.; Eikenberry, E. F.

    2009-03-24

    A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra (λ/dλ > 6000) of He-like and H-like Ar Kα lines with good spatial (~1 cm) and temporal (~10 ms) resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic inversion enables inference of local line emissivity, ion temperature (Ti), and toroidal plasma rotation velocity (vφ) from the line Doppler widths and shifts. The data analysis techniqu

  15. Plasma heating and generation of energetic ions with novel three-ion ICRF scenarios on Alcator C-Mod and JET tokamak facilities

    NASA Astrophysics Data System (ADS)

    Kazakov, Yevgen

    2016-10-01

    This talk will report the first experimental results of novel three-ion ICRF scenarios (two or more majority ion species and one minority) for plasma heating and generating energetic ions in fusion facilities. The key feature of these scenarios is strong absorption of RF power possible at lower concentrations of minority ions than in two-ion plasmas. Effective plasma heating by injecting a small amount of 3He ions into H-D plasma mixtures with nH /ne 70 % has been successfully demonstrated in Alcator C-Mod and JET tokamaks. In C-Mod, efficient plasma heating was observed for 3He concentrations from 0.4-2%. During the discharges, a strong increase in Alfvén eigenmode activity was found to coincide with the addition of 3He to the H-D plasmas. Even lower 3He concentrations ( 0.2 %) were utilized in recent JET experiments. The potential of the D-(3He) -H scenario for plasma heating and generating MeV-range ions in JET plasmas was confirmed by a set of independent measurements, including stabilization of sawteeth, characteristic γ-ray emission, fast-ion loss detector. Furthermore, toroidal Alfvén eigenmodes with a range of toroidal mode numbers n were detected, which is another indication for the presence of significant population of high-energy 3He ions in a plasma. The discussed mechanism of resonant wave-particle interaction opens up various unexplored opportunities for ICRF system, including new scenarios for plasma heating. Three-ion ICRF scenarios are also relevant for the experimental programme of ITER. The possibility of using intrinsic 9Be impurities as the minority (instead of 3He) was suggested for heating bulk ions in D-T plasmas of JET and ITER, as well as heating trace amounts of 3He and 4He ions in H majority plasmas of ITER. The latest results and simulation comparisons will be presented. On behalf of Alcator C-Mod Team (MIT-PSFC, US) and JET Contributors (Culham, UK). Work supported by the US DOE (C-Mod DE-FC02-99ER54512 and SciDAC DE-FC02-01ER54648

  16. Stark echo modulation for quantum memories

    NASA Astrophysics Data System (ADS)

    Arcangeli, A.; Ferrier, A.; Goldner, Ph.

    2016-06-01

    Quantum memories for optical and microwave photons provide key functionalities in quantum processing and communications. Here we propose a protocol well adapted to solid-state ensemble-based memories coupled to cavities. It is called Stark echo modulation memory (SEMM) and allows large storage bandwidths and low noise. This is achieved in an echo-like sequence combined with phase shifts induced by small electric fields through the linear Stark effect. We investigated the protocol for rare-earth nuclear spins and found a high suppression of unwanted collective emissions that is compatible with single-photon-level operation. Broadband storage together with high fidelity for the Stark retrieval process is also demonstrated. SEMM could be used to store optical or microwave photons in ions and/or spins. This includes nitrogen-vacancy centers in diamond and rare-earth-doped crystals, which are among the most promising solid-state quantum memories.

  17. The Stark effect in linear potentials

    NASA Astrophysics Data System (ADS)

    Robinett, R. W.

    2010-01-01

    We examine the Stark effect (the second-order shifts in the energy spectrum due to an external constant force) for two one-dimensional model quantum mechanical systems described by linear potentials, the so-called quantum bouncer (defined by V(z) = Fz for z > 0 and V(z) = ∞ for z < 0) and the symmetric linear potential (given by V(z) = F|z|). We show how straightforward use of the most obvious properties of the Airy function solutions and simple Taylor expansions gives closed form results for the Stark shifts in both systems. These exact results are then compared to other approximation techniques, such as perturbation theory and WKB methods. These expressions add to the small number of closed-form descriptions available for the Stark effect in model quantum mechanical systems.

  18. Improved Spectral Fitting Models for the B-Stark Diagnostic at DIII-D

    NASA Astrophysics Data System (ADS)

    Pablant, N. A.; Grierson, B. A.; Burrell, K. H.; Groebner, R. J.; Kaplan, D. H.; Holcomb, C. T.

    2010-11-01

    Recent results are presented from the B-Stark diagnostic installed on the DIII-D tokamak. This diagnostic provides measurements of the magnitude and direction of the internal magnetic field. The B-Stark system is a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of the Stark split Dα emission from injected neutral beams. Improvements to the spectral fitting model are presented, including the addition of an analytical model for Dα emission from the fast-ion distribution. We discuss the accuracy of using in-situ beam-into-gas calibrations to find the beam emission line profiles, the viewing direction and the transmission properties of the collection optics. We also present results of efforts to improve the determination of the beam emission line profiles. Finally, the magnetic field measured with the B-Stark system is compared to values found from plasma equilibrium reconstructions (EFIT) and the MSE polarimetry system on DIII-D.

  19. Stark broadening of Kr UV spectral lines

    SciTech Connect

    Cirisan, M.; Djurovic, S.; Pelaez, R. J.; Aparicio, J. A.; Mar, S.

    2011-01-15

    This work reports new data for the Stark parameters of doubly ionized krypton spectral lines. Stark widths and shifts of Kr iii lines belonging to the UV region (245-300 nm) have been measured. A low-pressure pulsed arc, containing a mixture of 8% krypton and 92% helium, was used as a plasma source. Measured electron densities and electron temperatures were in the range (0.7-2.0)x10{sup 23} m{sup -3} and 16 000-20 000 K, respectively. Experimentally obtained data were compared to theoretical results calculated using simplified modified semiempirical formulas.

  20. Outer midplane scrape-off layer profiles and turbulence in simulations of Alcator C-Mod inner-wall limited discharges

    DOE PAGES

    Halpern, Federico D.; LaBombard, Brian; Terry, James L.; ...

    2017-06-27

    A region of steep plasma gradients, the so-called ”narrow-feature”, has been found in the near scrape-off layer (SOL) of inner-wall limited (IWL) discharges. Dedicated IWL discharges were carried out in Alcator C-Mod [E.S. Marmar et al., Nucl. Fusion 55, (2015)] to study this phenomenon, allowing detailed observations of the plasma profiles and fluctuations. Langmuir probe (LP) measurements show a clear two decay length ne and Te profile structure at the outer midplane. The Gas-Puff Imaging (GPI) diagnostic shows large turbulent fluctuations across the last closed flux-surface, hence supporting the hypothesis that turbulent phenomena play a role in setting the profilemore » steepness. We have carried out the flux-driven non-linear turbulence simulations of two C-Mod discharges which allows a three-way comparison between LP, GPI, and simulation data. Observations and simulations correlate the steep gradient region characterizing the narrow feature with sheared poloidal flows and a deviation of the plasma potential from its floating value. Furthermore, the E x B shear rate exceeds the linear ballooning growth rate, indicating that the narrow feature could result from the effects of sheared flows, although causality could not be established. The fluctuation level in the narrow feature remains of order unity across the entire SOL, indicating that the transport reduction in the near-SOL cannot result from a simple quench rule.« less

  1. Search for Correlation Between Plasma Rotation and Electron Temperature Gradient Scale Length in LOC/SOC Transition at Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Houshmandyar, Saeid; Rowan, William L.; Phillips, Perry E.; Walk, John R.; Rice, John E.

    2015-11-01

    Understanding the mechanism governing the linear ohmic confinement (LOC) and the transition to saturated ohmic confinement (SOC) has long been a focus of tokamak research. It is commonly accepted that at low density, the confinement is dominated by electron-scale turbulence while at high density, the turbulence is dominated by ion temperature gradient. At Alcator C-Mod, the core rotation reversal was shown to be consistent with this ansatz. However a recent study at AUG suggests that the intrinsic rotation behavior is rather determined by local plasma parameters regardless of the heating method or the confinement regime. Here, we follow this idea and search for dependence of intrinsic rotation on electron temperature gradient scale length, a quantity with a pivotal role in plasma transport. The high-resolution (1 μs, 7mm) electron cyclotron emission diagnostic at C-Mod (FRCECE) coupled with the BT jog technique allows direct LTe measurements. In the BT jog technique, a 1.5% change in the toroidal magnetic field shifts the viewing volume of the ECE by ~ 1 cm, and the ratio of the average of the signal to the change in the signal during its ramp-up yields LTe. Supported by USDoE awards DE-FG03-96ER-54373 and DE-FC02-99ER54512.

  2. Validation of full-wave simulations for mode conversion of waves in the ion cyclotron range of frequencies with phase contrast imaging in Alcator C-Mod

    SciTech Connect

    Tsujii, N.; Porkolab, M.; Bonoli, P. T.; Edlund, E. M.; Ennever, P. C.; Lin, Y.; Wright, J. C.; Wukitch, S. J.; Jaeger, E. F.; Green, D. L.; Harvey, R. W.

    2015-08-15

    Mode conversion of fast waves in the ion cyclotron range of frequencies (ICRF) is known to result in current drive and flow drive under optimised conditions, which may be utilized to control plasma profiles and improve fusion plasma performance. To describe these processes accurately in a realistic toroidal geometry, numerical simulations are essential. Quantitative comparison of these simulations and the actual experimental measurements is important to validate their predictions and to evaluate their limitations. The phase contrast imaging (PCI) diagnostic has been used to directly detect the ICRF waves in the Alcator C-Mod tokamak. The measurements have been compared with full-wave simulations through a synthetic diagnostic technique. Recently, the frequency response of the PCI detector array on Alcator C-Mod was recalibrated, which greatly improved the comparison between the measurements and the simulations. In this study, mode converted waves for D-{sup 3}He and D-H plasmas with various ion species compositions were re-analyzed with the new calibration. For the minority heating cases, self-consistent electric fields and a minority ion distribution function were simulated by iterating a full-wave code and a Fokker-Planck code. The simulated mode converted wave intensity was in quite reasonable agreement with the measurements close to the antenna, but discrepancies remain for comparison at larger distances.

  3. Numerical investigation of edge plasma phenomena in an enhanced D-alpha discharge at Alcator C-Mod: Parallel heat flux and quasi-coherent edge oscillations

    SciTech Connect

    Russell, D. A.; D'Ippolito, D. A.; Myra, J. R.; LaBombard, B.; Terry, J. L.; Zweben, S. J.

    2012-08-15

    Reduced-model scrape-off layer turbulence (SOLT) simulations of an enhanced D-alpha (EDA) H-mode shot observed in the Alcator C-Mod tokamak were conducted to compare with observed variations in the scrape-off-layer (SOL) width of the parallel heat flux profile. In particular, the role of the competition between sheath- and conduction-limited parallel heat fluxes in determining that width was studied for the turbulent SOL plasma that emerged from the simulations. The SOL width decreases with increasing input power and with increasing separatrix temperature in both the experiment and the simulation, consistent with the strong temperature dependence of the parallel heat flux in balance with the perpendicular transport by turbulence and blobs. The particularly strong temperature dependence observed in the case analyzed is attributed to the fact that these simulations produce SOL plasmas which are in the conduction-limited regime for the parallel heat flux. A persistent quasi-coherent (QC) mode dominates the SOLT simulations and bears considerable resemblance to the QC mode observed in C-Mod EDA operation. The SOLT QC mode consists of nonlinearly saturated wave-fronts located just inside the separatrix that are convected poloidally by the mean flow, continuously transporting particles and energy and intermittently emitting blobs into the SOL.

  4. Outer midplane scrape-off layer profiles and turbulence in simulations of Alcator C-Mod inner-wall limited discharges

    NASA Astrophysics Data System (ADS)

    Halpern, Federico D.; LaBombard, Brian; Terry, James L.; Zweben, Stewart J.

    2017-07-01

    A region of steep plasma gradients, the so-called "narrow-feature," has been found in the near scrape-off layer (SOL) of inner-wall limited (IWL) discharges. Dedicated IWL discharges were carried out in Alcator C-Mod [Marmar et al., Nucl. Fusion 55, 104020 (2015)] to study this phenomenon, allowing detailed observations of the plasma profiles and fluctuations. Langmuir probe (LP) measurements show a clear two-decay length ne and Te profile structure at the outer midplane. The Gas-Puff Imaging (GPI) diagnostic shows large turbulent fluctuations across the last closed flux-surface, hence supporting the hypothesis that turbulent phenomena play a role in setting the profile steepness. Flux-driven non-linear turbulence simulations of two C-Mod discharges have been carried out, allowing a three-way comparison between LP, GPI, and simulation data. Observations and simulations correlate the steep gradient region characterizing the narrow feature with sheared poloidal flows and a deviation of the plasma potential from its floating value. The E × B shear rate exceeds the linear ballooning growth rate, indicating that the narrow feature could result from the effects of sheared flows, although causality could not be established. The fluctuation level in the narrow feature remains of order unity across the entire SOL, indicating that the transport reduction in the near-SOL cannot result from a simple quench rule.

  5. Perturbative transport modeling and comparison to cold-pulse and heat-pulse propagation experiments in Alcator C-Mod and DIII-D

    NASA Astrophysics Data System (ADS)

    Rodriguez Fernandez, P.; White, A. E.; Cao, N. M.; Creely, A. J.; Greenwald, M. J.; Howard, N. T.; Hubbard, A. E.; Hughes, J. W.; Irby, J. H.; Petty, C. C.; Rice, J. E.; Alcator C-Mod Team

    2016-10-01

    Possible ``non-local'' transport phenomena are often observed in tokamak plasmas. Different models have been proposed to explain fast responses during perturbative transport experiments, including non-diffusive effects. Specific tools to characterize the dynamic behavior and power balance analysis using TRANSP and the quasi-linear trapped gyro-landau fluid code TGLF have been developed to analyze Alcator C-Mod experiments. Recent results from cold pulse experiments show that fast core temperature increases following edge cold-pulse injections (peak within 10ms , while τE 25ms) are not correlated with the direction of intrinsic rotation, and instead the amplitude of the core response depends on density, plasma current and RF input power. The propagation of the cold pulse can be compared with propagation of heat pulses from sawteeth, and both may be used to probe changes in temperature profile stiffness. A Laser Blow Off (LBO) system is being developed for DIII-D that will allow further validation and cross-machine comparison of cold pulse experiments. LBO at DIII-D will also allow for direct comparisons with ECH perturbative heat pulse experiments. Work supported by US DOE under Grants DE-FC02-99ER54512 (C-Mod) and DE-FC02-04ER54698 (DIII-D) and La Caixa Fellowship.

  6. Development of a reciprocating probe servomotor control system with real-time feedback on plasma position for the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Brunner, D.; Kuang, A. Q.; Labombard, B.; Burke, W.

    2015-11-01

    Reciprocating probe drives are one of the diagnostic workhorses in the boundary of magnetic confinement fusion experiments. The probe is scanned into an exponentially increasing heat flux, which demands a prompt and precise turn around to maintain probe integrity. A new linear servomotor controlled reciprocating drive utilizing a commercial linear servomotor and drive controller has been developed for the Alcator C-Mod tokamak. The quick response of the controller (able to apply an impulse of 50A in about 1ms) along with real-time plasma measurements from a Mirror Langmuir Probe (MLP) allows for real-time control of the probe trajectory based on plasma conditions at the probe tip. Since the primary concern for probe operation is overheating, an analog circuit has been created that computes the surface temperature of the probe from the MLP measurements. The probe can be programmed to scan into the plasma at various times and then turns around when the computed surface temperature reaches a set threshold, maximizing the scan depth into the plasma while avoiding excessive heating. Design, integration, and first measurements with this new system will be presented. This work was supported by U.S. Department of Energy award DE-FC02-99ER54512, using Alcator C-Mod, A DOE SC User Facility.

  7. Nominees Serve Up Stark Differences on Education

    ERIC Educational Resources Information Center

    Klein, Alyson

    2012-01-01

    During the recently concluded presidential nominating conventions, President Barack Obama and former Massachusetts Gov. Mitt Romney offered stark choices on K-12 policy while downplaying areas of agreement between their two parties--and the tensions within each party on education issues. In Charlotte, North Carolina, last week, the Democrats put a…

  8. Far-infrared polarimetry diagnostic for measurement of internal magnetic field dynamics and fluctuations in the C-MOD Tokamak (invited)a)

    NASA Astrophysics Data System (ADS)

    Bergerson, W. F.; Xu, P.; Irby, J. H.; Brower, D. L.; Ding, W. X.; Marmar, E. S.

    2012-10-01

    A laser-based (2.55 THz) mulitchord polarimeter is now operational on Alcator C-Mod and is used to make measurements of the internal magnetic field structure as well as plasma fluctuations. The polarimeter is designed to measure the Faraday effect for high-field (up to 8.3 T) and high-density (up to 5 × 1020 m-3) ITER relevant plasma conditions. Initial 3 chord tests are consistent with magnetic equilibrium reconstructions and indicate no measurable contamination from the toroidal magnetic field due to the Cotton-Mouton effect or misalignment. Time response of <1 μs enables the measurement of fast equilibrium temporal dynamics as well as high-frequency fluctuations.

  9. Identification of waves in the lower-hybrid frequency range in the scrape-off layer plasma of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Shinya, Takahiro; Gyou Baek, Seung; Wallace, Gregory M.; Shiraiwa, Syun'ichi; Takase, Yuichi; Parker, Ronald R.; Bonoli, Paul T.; Brunner, Dan; Faust, Ian; LaBombard, Brian L.; Wukitch, Steve

    2017-03-01

    Polarization resolved measurements of the parallel refractive index {{N}\\parallel}\\equiv c{{k}\\parallel}/ω of the driven RF waves in the lower hybrid (LH) range of frequencies are performed using arrays of RF magnetic probes in the scrape-off layer plasma of Alcator C-Mod. The measured {{N}\\parallel} of the RF magnetic field component parallel to the background magnetic field is about  -1.6, which corresponds to the peak of the launched LH {{N}\\parallel} spectrum. Based on the wave dispersion relationship, this wave is identified as the LH slow wave. On the other hand, the RF magnetic field component perpendicular to the magnetic field is found to have a lower {{N}\\parallel} of  -1.2, and is detected only near the last closed flux surface. This wave is identified as the LH fast wave generated by slow-fast wave mode conversion.

  10. Inference of Ion-Temperature and Rotation-Velocity Profiles from a Spatially Resolving X-Ray Crystal Spectrometer on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Hill, K. W.; Bitter, M.; Beiersdorfer, P.; Ince-Cushman, A.; Gu, Ming-Feng; Lee, S. G.; Reinke, M.; Rice, J. E.; Scott, S. D.

    2007-11-01

    A new x-ray crystal spectrometer capable of providing spatially (˜1.5 cm) and temporally (˜10 ms) resolved, high resolution spectra of He-like Ar Kα lines has been installed on Alcator C-Mod. The imaging spectrometer consists of a spherically bent crystal and three Pilatus II 2d pixel detectors. Spectra are simultaneously measured from 12 -- 45 chords covering the region r/a = 0 - 0.8 with count rates of 0.1 -- 5.0 MHz per chord, enabling measurement with good statistics. Preliminary ion-temperature (Ti) and rotation-velocity (vφ) profiles are inferred from the Doppler widths and shifts of the chordally integrated spectral lines. The data analysis techniques, Ti and vφ profile results, analysis of background resulting from fusion neutrons, and predictions of performance on ITER and other tokamaks will be presented.

  11. A spatially resolving x-ray crystal spectrometer for measurement of ion-temperature and rotation-velocity profiles on the Alcator C-Mod tokamaka)

    NASA Astrophysics Data System (ADS)

    Hill, K. W.; Bitter, M. L.; Scott, S. D.; Ince-Cushman, A.; Reinke, M.; Rice, J. E.; Beiersdorfer, P.; Gu, M.-F.; Lee, S. G.; Broennimann, Ch.; Eikenberry, E. F.

    2008-10-01

    A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra (λ /dλ>6000) of He-like and H-like Ar Kα lines with good spatial (˜1 cm) and temporal (˜10 ms) resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic inversion enables inference of local line emissivity, ion temperature (Ti), and toroidal plasma rotation velocity (vϕ) from the line Doppler widths and shifts. The data analysis techniques, Ti and vϕ profiles, analysis of fusion-neutron background, and predictions of performance on other tokamaks, including ITER, will be presented.

  12. A spatially resolving x-ray crystal spectrometer for measurement of ion-temperature and rotation-velocity profiles on the Alcator C-Mod tokamak

    SciTech Connect

    Hill, K. W.; Bitter, M. L.; Scott, S. D.; Ince-Cushman, A.; Reinke, M.; Rice, J. E.; Beiersdorfer, P.; Gu, M.-F.; Lee, S. G.; Broennimann, Ch.; Eikenberry, E. F.

    2008-10-15

    A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra ({lambda}/d{lambda}>6000) of He-like and H-like Ar K{alpha} lines with good spatial ({approx}1 cm) and temporal ({approx}10 ms) resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic inversion enables inference of local line emissivity, ion temperature (T{sub i}), and toroidal plasma rotation velocity (v{sub {phi}}) from the line Doppler widths and shifts. The data analysis techniques, T{sub i} and v{sub {phi}} profiles, analysis of fusion-neutron background, and predictions of performance on other tokamaks, including ITER, will be presented.

  13. Far-infrared polarimetry diagnostic for measurement of internal magnetic field dynamics and fluctuations in the C-MOD Tokamak (invited).

    PubMed

    Bergerson, W F; Xu, P; Irby, J H; Brower, D L; Ding, W X; Marmar, E S

    2012-10-01

    A laser-based (2.55 THz) mulitchord polarimeter is now operational on Alcator C-Mod and is used to make measurements of the internal magnetic field structure as well as plasma fluctuations. The polarimeter is designed to measure the Faraday effect for high-field (up to 8.3 T) and high-density (up to 5 × 10(20) m(-3)) ITER relevant plasma conditions. Initial 3 chord tests are consistent with magnetic equilibrium reconstructions and indicate no measurable contamination from the toroidal magnetic field due to the Cotton-Mouton effect or misalignment. Time response of <1 μs enables the measurement of fast equilibrium temporal dynamics as well as high-frequency fluctuations.

  14. Application of PILATUS II Detector Modules for High Resolution X-Ray Imaging Crystal Spectrometers on the Alcator C-Mod Tokamak

    SciTech Connect

    M.L. Bitter, Ch. Borennimann, E.F. Eikenberry, K.W. Hill, A. Ince-Chushman, S.G. Lee, J.E. Rice, and S. Scott.

    2007-07-23

    A new type of X-ray imaging crystal spectrometer for Doppler measurements of the radial profiles of the ion temperature and plasma rotation velocity in tokamak plasmas is presently being developed in a collaboration between various laboratories. The spectrometer will consist of a spherically bent crystal and a two-dimensional position sensitive detector; and it will record temporally and spatially resolved X-ray line spectra from highly-charged ions. The detector must satisfy challenging requirements with respect to count rate and spatial resolution. The paper presents the results from a recent test of a PILATUS II detector module on Alcator C-Mod, which demonstrate that the PILATUS II detector modules will satisfy these requirements.

  15. Spatial structure of scrape-off-layer filaments near the midplane and X-point regions of Alcator C-Mod

    SciTech Connect

    Terry, J L; Zweben, S J; Umansky, M V; Cziegler, I; Grulke, O; LaBombard, B; Stotler, D P

    2008-05-22

    Movies of edge turbulence at both the outboard midplane and the region outboard of the typical lower X-point location in C-Mod have been obtained using Gas-Puff-Imaging together with fast-framing cameras. Intermittent turbulent structures, typically referred to as blobs or filaments, are observed in both locations. Near the midplane the filaments are roughly circular in cross-section, while in the X-point region they are highly elongated. Filament velocities in this region are {approx}3x faster than the radial velocities at the midplane, in a direction roughly normal to the local flux surfaces. The observations are consistent with the picture that the filaments arise in outboard region and, as a consequence of the rapid parallel diffusion of the potential perturbations, map along field lines. A simulation using the 3D BOUT turbulence code has been made, with the result that reproduces many of the spatial features observed in the experiment.

  16. Pedestal and Transport Properties of Steady-state I-mode Plasmas over Expanded Operational Space in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Marmar, Earl

    2011-10-01

    I-mode operation on Alcator C-Mod combines a strong edge thermal transport barrier with L-mode levels of particle and impurity transport, allowing access to very high performance discharges with low pedestal collisionality and central temperatures up to 8 keV, and without large ELMs or other intermittent edge instabilities. In recent campaigns, C-Mod I-modes have been extended to quasi-steady-state, with access in both favorable and unfavorable ion drift directions and typical normalized energy confinement quality factor H98 ~ 1.0 to 1.2. Adding ICRF mode-conversion flow-drive enhances toroidal flow shear near the plasma edge and confinement is further enhanced. I-mode has been maintained with input power up to nearly 2x the I-mode threshold power, with the largest accessible range in closed divertor geometry at modest triangularity. Simple extrapolations at fixed field imply that ITER in unfavorable drift could access I-mode with available power, and stay in I-mode with alpha-dominant heating. Detailed pedestal fluctuation measurements reveal changes in the turbulence, with decreases in the power at some frequencies and size scales, and growth of a weakly coherent mode (WCM) (kθ ~ 1.5 cm-1, δf/f ~.3) which propagates in the electron diamagnetic direction in the plasma frame. The WCM, which has density, temperature and magnetic signatures, appears to play a key role in pedestal density and impurity regulation, and detailed experimental results and associated modeling are presented. The distribution of divertor exhaust power depends on ion drift direction; new measurements of I-mode heat flux footprints on the outer divertor are compared with those in H-mode. Pedestal stability analyses will be shown for I-modes, including some which exhibited small ELMs. Supported by USDOE Award DE-FC02-99-ER54512.

  17. The Stark Effect in Linear Potentials

    ERIC Educational Resources Information Center

    Robinett, R. W.

    2010-01-01

    We examine the Stark effect (the second-order shifts in the energy spectrum due to an external constant force) for two one-dimensional model quantum mechanical systems described by linear potentials, the so-called quantum bouncer (defined by V(z) = Fz for z greater than 0 and V(z) = [infinity] for z less than 0) and the symmetric linear potential…

  18. The Stark Effect in Linear Potentials

    ERIC Educational Resources Information Center

    Robinett, R. W.

    2010-01-01

    We examine the Stark effect (the second-order shifts in the energy spectrum due to an external constant force) for two one-dimensional model quantum mechanical systems described by linear potentials, the so-called quantum bouncer (defined by V(z) = Fz for z greater than 0 and V(z) = [infinity] for z less than 0) and the symmetric linear potential…

  19. Stark broadening effect and zirconium conflict problem

    NASA Astrophysics Data System (ADS)

    Dimitrijević, Milan S.; Popović, Luka Č.; Milovanović, Nenad

    2001-04-01

    Using the Modified Semiempirical Method we have calculated the electron-impact widths for four singly and doubly ionized zirconium UV lines of astrophysical importance. Using the SYNTH and ATLAS9 codes for stellar atmospheres similar to that of the HgMn star χ Lupi we have synthesized the line profiles and found equivalent widths for these lines. The influence of the Stark broadening effect on abundance determination and its contribution to the so-called ``zirconium conflict'' are discussed. .

  20. Atomic Landau-Zener tunneling and Wannier-Stark ladders in optical potentials

    SciTech Connect

    Niu, Q.; Zhao, X.; Georgakis, G.; Raizen, M.

    1996-06-01

    We calculate the quantum motion of ultracold atoms in an accelerating optical potential, and show how they may be used to observe Landau-Zener tunneling and Wannier-Stark ladders, two fundamental quantum effects in solid state physics. The optical potential is spatially periodic, yielding an energy spectrum of Bloch bands for the atoms. The acceleration provides an inertial force in the moving frame, emulating an electric force on Bloch electrons. {copyright} {ital 1996 The American Physical Society.}

  1. Application of a PILATUS II Detector to an X-Ray Imaging Crystal Spectrometer for fast Measurement of Ti and Rotation-Velocity Profiles on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Hill, K. W.; Bitter, M. L.; Scott, S. D.; Ince-Cushman, A.; Rice, J. E.; Lee, S. G.; Broennimann, C.; Eikenberry, E. F.

    2006-10-01

    A high resolution imaging x-ray crystal spectrometer (XICS) is being developed for Doppler measurement of radial profiles of ion temperature, Ti, and rotation velocity on Alcator C-mod. The XICS consists of a spherically bent crystal and a 2D imaging x-ray detector, and provides x-ray spectra from highly charged ions from multiple plasma sightlines. The proof of principle of the XICS was demonstrated by measurement of Ar XVII Kα spectral images from +/- 8 cm of the plasma height in Alcator C-Mod and +/- 40 cm in NSTX. However, the time resolution was limited to values >100 ms by the ˜400 kHz global count-rate limit of the available 2D gas detector. A silicon pixel array detector, PILATUS II, with a count-rate capability of 1 MHz PER PIXEL, was tested on C-Mod by recording spectra of ArXVII at 3.1 keV, and should enable XICS time resolution < 10 ms. The detector test results and C-Mod XICS design and expected performance will be presented.

  2. The STARK-B database VAMDC node

    NASA Astrophysics Data System (ADS)

    Sahal-Bréchot, S.; Dimitrijević, M. S.; Moreau, N.; Nessib, N. Ben

    2017-03-01

    Accurate spectroscopic diagnostics and modelling require the knowledge of numerous collisional line profiles. The access to such data via an on line database is essential. The aim of STARK-B is to meet these needs for widths and shifts of "isolated" lines of neutral and ionized atoms due to electron and ion impacts. It is devoted to modelling and spectroscopic diagnostics of stellar atmospheres and envelopes, laboratory plasmas, laser equipments and technological plasmas. So, the range of temperatures and densities covered by the tables is broad and depends on the ionization degree of the radiating atom. STARK-B is a collaborative project between the Astronomical Observatory of Belgrade (AOB) and the laboratory LERMA at Observatory of Paris, which started at the end of 2008. STARK-B is a database of LERMA and a node of VAMDC (Virtual Atomic and Molecular Data Centre) and thus complies with the standards of the Virtual Observatories. This database opened at the end of 2008. Today, the database contains our calculated data for a various number of transitions of neutral or ionized atoms, published in more than 150 papers in international refereed journals. We continue to implement our previously published data, and the new ones as soon as they are published. A summary of the scientific objectives, the key points of the impact-semiclassical-perturbation method used for the calculations, the current state of development of our ongoing work and our plans for the future objectives of the database are presented. Finally, an example of the results of a query is displayed.

  3. External Excitation of a Drift-Alfvén Wave Response in the Alcator C-Mod Edge Plasma and its Relationship to the Quasi-Coherent Mode

    NASA Astrophysics Data System (ADS)

    Golfinopoulos, Theodore

    2013-10-01

    Experiments indicate that short-wavelength, k⊥ρs ~ 0 . 1 , drift-Alfvénic turbulence plays an important role in C-Mod edge plasma transport. A Quasi-Coherent Mode (QCM, 50 < f < 150 kHz, k⊥ ~ 1 . 5 cm-1) regulates particle and impurity transport in C-Mod's EDA H-modes. A Weakly Coherent Mode (WCM, 150 < f < 500 kHz, k⊥ ~ 1 . 5 cm-1) plays a similar role in I-mode discharges, suppressing the formation of a density pedestal while maintaining a temperature pedestal. ELMs are not present in either confinement regime. With the idea of exciting, probing, and perhaps exploiting this transport behavior, we have developed a novel antenna system to excite drift-Alfvén-like modes at the outer midplane. A winding with a ``shoelace'' geometry is placed ~ 3 - 5 mm from the LCFS. The principal design parameters, k⊥ = 1 . 5 +/- 0 . 1 cm-1 and 45 < f < 300 kHz, match the QCM and WCM properties, so that the antenna induces parallel currents in the boundary plasma that mimic those observed for the intrinsic modes. Phase-locking to intrinsic modes is also accomplished via a custom circuit. The antenna produces perturbations in density and field comparable to amplitudes of the intrinsic QCM. The plasma response exhibits a resonance near the natural QCM frequency, which generally satisfies the drift wave dispersion relation. While a driven B~θ fluctuation is visible throughout the discharge, the driven ñe is only observed during H-mode, though it precedes the onset of the intrinsic QCM. Like the QCM, the driven mode propagates in the electron diamagnetic drift direction and is approximately field-aligned. Recent mirror probe measurements show the intrinsic QCM structure is predominantly drift-Alfvénic, and we might expect the same of the driven mode. However, the induced perturbation is not global, but is localized to field lines which map to the antenna, suggesting a damped response, and direct measurements of the damping rate indicate γ /ω0 ~ 5 %. If the antenna

  4. Dielectric waveguide gas-filled stark shift modulator

    DOEpatents

    Hutchinson, Donald P.; Richards, Roger K.

    2003-07-22

    An optical modulator includes a dielectric waveguide for receiving an optical beam and coupling energy of the optical beam into the waveguide. At least one Stark material is provided in the waveguide. A bias circuit generates a bias signal to produce an electrical field across the Stark material to shift at least one of the Stark absorption frequencies towards the frequency of the optical beam. A circuit for producing a time varying electric field across the Stark material modulates the optical beam. At least a portion of the bias field can be generated by an alternating bias signal, such as a square wave. A method of modulating optical signals includes the steps of providing a dielectric waveguide for receiving an optical beam and coupling energy of the optical beam into the waveguide, the waveguide having at least one Stark material disposed therein, and varying an electric field imposed across the Stark material.

  5. Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod

    SciTech Connect

    Russell, D. A.; Myra, J. R.; D'Ippolito, D. A.; LaBombard, B.; Hughes, J. W.; Terry, J. L.; Zweben, S. J.

    2016-06-10

    Two-dimensional scrape-off layer turbulence (SOLT) code simulations are compared with an L-mode discharge on the Alcator C-Mod tokamak [M. Greenwald, et al., Phys. Plasmas 21, 110501 (2014)]. Density and temperature profiles for the simulations were obtained by smoothly fitting Thomson scattering and mirror Langmuir probe (MLP) data from the shot. Simulations differing in turbulence intensity were obtained by varying a dissipation parameter. Mean flow profiles and density fluctuation amplitudes are consistent with those measured by MLP in the experiment and with a Fourier space diagnostic designed to measure poloidal phase velocity. Blob velocities in the simulations were determined from the correlation function for density fluctuations, as in the analysis of gas-puff-imaging (GPI) blobs in the experiment. In the simulations, it was found that larger blobs moved poloidally with the ExB flow velocity, vE , in the near-SOL, while smaller fluctuations moved with the group velocity of the dominant linear (interchange) mode, vE + 1/2 vdi, where vdi is the ion diamagnetic drift velocity. Comparisons are made with the measured GPI correlation velocity for the discharge. The saturation mechanisms operative in the simulation of the discharge are also discussed. In conclusion, it is found that neither sheared flow nor pressure gradient modification can be excluded as saturation mechanisms.

  6. Three-dimensional simulation of H-mode plasmas with localized divertor impurity injection on Alcator C-Mod using the edge transport code EMC3-EIRENE

    DOE PAGES

    Lore, Jeremy D.; Reinke, M. L.; Brunner, D.; ...

    2015-04-28

    We study experiments in Alcator C-Mod to assess the level of toroidal asymmetry in divertor conditions resulting from poloidally and toroidally localized extrinsic impurity gas seeding show a weak toroidal peaking (~1.1) in divertor electron temperatures for high-power enhanced D-alpha H-modeplasmas. This is in contrast to similar experiments in Ohmically heated L-modeplasmas, which showed a clear toroidal modulation in the divertor electron temperature. Modeling of these experiments using the 3D edge transport code EMC3-EIRENE [Y. Feng et al., J. Nucl. Mater. 241, 930 (1997)] qualitatively reproduces these trends, and indicates that the different response in the simulations is due tomore » the ionization location of the injected nitrogen. Low electron temperatures in the private flux region (PFR) in L-mode result in a PFR plasma that is nearly transparent to neutral nitrogen, while in H-mode the impurities are ionized in close proximity to the injection location, with this latter case yielding a largely axisymmetric radiation pattern in the scrape-off-layer. In conclusion, the consequences for the ITER gas injection system are discussed. Quantitative agreement with the experiment is lacking in some areas, suggesting potential areas for improving the physics model in EMC3-EIRENE.« less

  7. Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod

    DOE PAGES

    Russell, D. A.; Myra, J. R.; D'Ippolito, D. A.; ...

    2016-06-10

    Two-dimensional scrape-off layer turbulence (SOLT) code simulations are compared with an L-mode discharge on the Alcator C-Mod tokamak [M. Greenwald, et al., Phys. Plasmas 21, 110501 (2014)]. Density and temperature profiles for the simulations were obtained by smoothly fitting Thomson scattering and mirror Langmuir probe (MLP) data from the shot. Simulations differing in turbulence intensity were obtained by varying a dissipation parameter. Mean flow profiles and density fluctuation amplitudes are consistent with those measured by MLP in the experiment and with a Fourier space diagnostic designed to measure poloidal phase velocity. Blob velocities in the simulations were determined from themore » correlation function for density fluctuations, as in the analysis of gas-puff-imaging (GPI) blobs in the experiment. In the simulations, it was found that larger blobs moved poloidally with the ExB flow velocity, vE , in the near-SOL, while smaller fluctuations moved with the group velocity of the dominant linear (interchange) mode, vE + 1/2 vdi, where vdi is the ion diamagnetic drift velocity. Comparisons are made with the measured GPI correlation velocity for the discharge. The saturation mechanisms operative in the simulation of the discharge are also discussed. In conclusion, it is found that neither sheared flow nor pressure gradient modification can be excluded as saturation mechanisms.« less

  8. Time-Dependent Distribution Functions in C-Mod Calculated with the CQL3D-Hybrid-FOW, AORSA Full-Wave, and DC Lorentz Codes

    NASA Astrophysics Data System (ADS)

    Harvey, R. W. (Bob); Petrov, Yu. V.; Jaeger, E. F.; Berry, L. A.; Bonoli, P. T.; Bader, A.

    2015-11-01

    A time-dependent simulation of C-Mod pulsed ICRF power is made calculating minority hydrogen ion distribution functions with the CQL3D-Hybrid-FOW finite-orbit-width Fokker-Planck code. ICRF fields are calculated with the AORSA full wave code, and RF diffusion coefficients are obtained from these fields using the DC Lorentz gyro-orbit code. Prior results with a zero-banana-width simulation using the CQL3D/AORSA/DC time-cycles showed a pronounced enhancement of the H distribution in the perpendicular velocity direction compared to results obtained from Stix's quasilinear theory, in general agreement with experiment. The present study compares the new FOW results, including relevant gyro-radius effects, to determine the importance of these effects on the the NPA synthetic diagnostic time-dependence. The new NPA results give increased agreement with experiment, particularly in the ramp-down time after the ICRF pulse. Funded, through subcontract with Massachusetts Institute of Technology, by USDOE sponsored SciDAC Center for Simulation of Wave-Plasma Interactions.

  9. Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Russell, D. A.; Myra, J. R.; D'Ippolito, D. A.; LaBombard, B.; Hughes, J. W.; Terry, J. L.; Zweben, S. J.

    2016-06-01

    Two-dimensional scrape-off layer turbulence (SOLT) code simulations are compared with an L-mode discharge on the Alcator C-Mod tokamak [Greenwald et al., Phys. Plasmas 21, 110501 (2014)]. Density and temperature profiles for the simulations were obtained by smoothly fitting Thomson scattering and mirror Langmuir probe (MLP) data from the shot. Simulations differing in turbulence intensity were obtained by varying a dissipation parameter. Mean flow profiles and density fluctuation amplitudes are consistent with those measured by MLP in the experiment and with a Fourier space diagnostic designed to measure poloidal phase velocity. Blob velocities in the simulations were determined from the correlation function for density fluctuations, as in the analysis of gas-puff-imaging (GPI) blobs in the experiment. In the simulations, it was found that larger blobs moved poloidally with the E × B flow velocity, vE, in the near-SOL, while smaller fluctuations moved with the group velocity of the dominant linear (interchange) mode, vE + 1/2 vdi, where vdi is the ion diamagnetic drift velocity. Comparisons are made with the measured GPI correlation velocity for the discharge. The saturation mechanisms operative in the simulation of the discharge are also discussed. It is found that neither sheared flow nor pressure gradient modification can be excluded as saturation mechanisms.

  10. Mean Flows and Blob Velocities in Scrape-Off Layer (SOLT) Simulations of an L-mode discharge on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Russell, D. A.; Myra, J. R.; D'Ippolito, D. A.; Labombard, B.; Terry, J. L.; Zweben, S. J.

    2015-11-01

    Two-dimensional scrape-off layer turbulence (SOLT) code simulations are compared with an L-mode discharge on Alcator C-Mod. Density and temperature profiles for the simulations were obtained by smoothly fitting Thomson scatter and mirror Langmuir probe (MLP) data from the shot. Simulations differing in turbulence intensity were obtained by varying a dissipation parameter. Mean flow profiles and density fluctuation amplitudes are consistent with those measured by MLP in the experiment. Blob velocities in the simulations were determined from the correlation function for density fluctuations, as in the analysis of gas-puff-imaging (GPI) blobs in the experiment. In the simulations, it was found that larger blobs moved poloidally with the ExB flow velocity, vE , in the near-SOL, while smaller fluctuations moved with the group velocity of the dominant linear (interchange) mode, vE + 1/2 vdi, where vdi is the ion diamagnetic drift velocity. Comparisons are made with the measured GPI correlation velocity. The saturation mechanisms operative in the simulation of the discharge are explored. Work supported by the U.S. Department of Energy Office of Science, Office of Fusion Energy Sciences, under Agreement DE-FC02-99ER54512, Contract DE-AC02-09CH11466, and Princeton Plasma Physics Laboratory Subcontract S013429-U.

  11. New insights on boundary plasma turbulence and the quasi-coherent mode in Alcator C-Mod using a Mirror Langmuir Probe

    SciTech Connect

    LaBombard, B.; Golfinopoulos, T.; Terry, J. L.; Brunner, D.; Davis, E.; Greenwald, M.; Hughes, J. W.

    2014-05-15

    A new “Mirror Langmuir Probe” diagnostic, combined with a double-coil scanning magnetic probe, is used to interrogate Alcator C-Mod's quasi-coherent mode (QCM) with unprecedented detail. In ohmic EDA H-modes, the QCM is found to reside in a region of positive radial electric field, with a radial width (∼3 mm) that spans open and closed field line regions. Large amplitude, in-phase sinusoidal bursts (∼100 kHz) in density, electron temperature, and plasma potential are observed, with potential lagging density by ∼16°, producing an outward radial transport velocity of ∼10 m/s. Mode propagation corresponds to the sum of local E × B and electron diamagnetic drift velocities. Poloidal magnetic field fluctuations project to current filaments carrying peak current densities of ∼25 A/cm{sup 2}. An evaluation of parallel electron force balance (Ohm's law) over a fluctuation cycle indicates a significant electromotive component. Interchange drive is also a contributor in the current continuity (vorticity) equation. Thus, the QCM is primarily a separatrix-spanning electron drift-wave with interchange and electromagnetic contributions.

  12. Inboard and outboard radial electric field wells in the H- and I-mode pedestal of Alcator C-Mod and poloidal variations of impurity temperature

    NASA Astrophysics Data System (ADS)

    Theiler, C.; Churchill, R. M.; Lipschultz, B.; Landreman, M.; Ernst, D. R.; Hughes, J. W.; Catto, P. J.; Parra, F. I.; Hutchinson, I. H.; Reinke, M. L.; Hubbard, A. E.; Marmar, E. S.; Terry, J. T.; Walk, J. R.; the Alcator C-Mod Team

    2014-08-01

    We present inboard (HFS) and outboard (LFS) radial electric field (Er) and impurity temperature (Tz) measurements in the I-mode and H-mode pedestal of Alcator C-Mod. These measurements reveal strong Er wells at the HFS and the LFS midplane in both regimes and clear pedestals in Tz, which are of similar shape and height for the HFS and LFS. While the H-mode Er well has a radially symmetric structure, the Er well in I-mode is asymmetric, with a stronger ExB shear layer at the outer edge of the Er well, near the separatrix. Comparison of HFS and LFS profiles indicates that impurity temperature and plasma potential are not simultaneously flux functions. Uncertainties in radial alignment after mapping HFS measurements along flux surfaces to the LFS do not, however, allow direct determination as to which quantity varies poloidally and to what extent. Radially aligning HFS and LFS measurements based on the Tz profiles would result in substantial inboard-outboard variations of plasma potential and electron density. Aligning HFS and LFS Er wells instead also approximately aligns the impurity poloidal flow profiles, while resulting in a LFS impurity temperature exceeding the HFS values in the region of steepest gradients by up to 70%. Considerations based on a simplified form of total parallel momentum balance and estimates of parallel and perpendicular heat transport time scales seem to favor an approximate alignment of the Er wells and a substantial poloidal asymmetry in impurity temperature.

  13. Three-dimensional simulation of H-mode plasmas with localized divertor impurity injection on Alcator C-Mod using the edge transport code EMC3-EIRENE

    SciTech Connect

    Lore, Jeremy D.; Reinke, M. L.; Brunner, D.; LaBombard, B. A.; Lipschultz, B.; Terry, J. L.; Pitts, R. A.; Feng, Y.

    2015-04-28

    We study experiments in Alcator C-Mod to assess the level of toroidal asymmetry in divertor conditions resulting from poloidally and toroidally localized extrinsic impurity gas seeding show a weak toroidal peaking (~1.1) in divertor electron temperatures for high-power enhanced D-alpha H-modeplasmas. This is in contrast to similar experiments in Ohmically heated L-modeplasmas, which showed a clear toroidal modulation in the divertor electron temperature. Modeling of these experiments using the 3D edge transport code EMC3-EIRENE [Y. Feng et al., J. Nucl. Mater. 241, 930 (1997)] qualitatively reproduces these trends, and indicates that the different response in the simulations is due to the ionization location of the injected nitrogen. Low electron temperatures in the private flux region (PFR) in L-mode result in a PFR plasma that is nearly transparent to neutral nitrogen, while in H-mode the impurities are ionized in close proximity to the injection location, with this latter case yielding a largely axisymmetric radiation pattern in the scrape-off-layer. In conclusion, the consequences for the ITER gas injection system are discussed. Quantitative agreement with the experiment is lacking in some areas, suggesting potential areas for improving the physics model in EMC3-EIRENE.

  14. Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod

    SciTech Connect

    Russell, D. A.; Myra, J. R.; D'Ippolito, D. A.; LaBombard, B.; Hughes, J. W.; Terry, J. L.; Zweben, S. J.

    2016-06-10

    Two-dimensional scrape-off layer turbulence (SOLT) code simulations are compared with an L-mode discharge on the Alcator C-Mod tokamak [M. Greenwald, et al., Phys. Plasmas 21, 110501 (2014)]. Density and temperature profiles for the simulations were obtained by smoothly fitting Thomson scattering and mirror Langmuir probe (MLP) data from the shot. Simulations differing in turbulence intensity were obtained by varying a dissipation parameter. Mean flow profiles and density fluctuation amplitudes are consistent with those measured by MLP in the experiment and with a Fourier space diagnostic designed to measure poloidal phase velocity. Blob velocities in the simulations were determined from the correlation function for density fluctuations, as in the analysis of gas-puff-imaging (GPI) blobs in the experiment. In the simulations, it was found that larger blobs moved poloidally with the ExB flow velocity, vE , in the near-SOL, while smaller fluctuations moved with the group velocity of the dominant linear (interchange) mode, vE + 1/2 vdi, where vdi is the ion diamagnetic drift velocity. Comparisons are made with the measured GPI correlation velocity for the discharge. The saturation mechanisms operative in the simulation of the discharge are also discussed. In conclusion, it is found that neither sheared flow nor pressure gradient modification can be excluded as saturation mechanisms.

  15. Comparison of Edge Turbulence Imaging at Two Different Poloidal Locations in the Scrape-off Layer of Alcator C-Mod

    SciTech Connect

    S.J. Zweben, et. al.

    2013-03-29

    This paper describes 2-D imaging measurements of plasma turbulence made in the scrape-off layer of the Alcator C-Mod tokamak simultaneously at two different poloidal locations, one near the outer midplane and the other near the divertor X-point region. These images were made with radial and poloidal resolution using two gas puff imaging (GPI) diagnostics, which were not directly connected along a B field line. The turbulence correlation structure has a significantly different tilt angle with respect to the local flux surfaces for the midplane and X-regions, and a slightly different ellipticity and size. The time-averaged turbulence velocities can be different in the midplane and Xregions, even within the same flux surface in the same shot, and in most cases the fluctuations in poloidal velocity in these two regions were not correlated. These structures are partially consistent with a magnetic flux tube mapping model, and the velocities are compared with various poloidal flow models.

  16. 1. VIEW LOOKING WEST AT STARK MILL WAREHOUSES FROM ROOF ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. VIEW LOOKING WEST AT STARK MILL WAREHOUSES FROM ROOF OF MILL. THE WAREHOUSES WERE BUILT USING SLOW-BURNING TIMBER AND BRICK CONSTRUCTION AND INCLUDED THE PICKER ROOM. NOTE ORIGINAL WATER TANK ON LEFT AND BOILER STACK IN RIGHT BACKGROUND. - Stark Mill, Warehouses, 117 Corinth Road, Hogansville, Troup County, GA

  17. 1. VIEW FROM ROOF OF MILL LOOKING SOUTHWEST AT STARK ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. VIEW FROM ROOF OF MILL LOOKING SOUTHWEST AT STARK MILL HOUSING ON CORINTH ROAD. THESE FRONT GABLE BUNGALOWS WERE BUILT AS OVERSEERS HOUSES FOR NEW ENGLAND SOUTHERN MILLS IN HOGANSVILLE IN 1923-1924. THE MILL ENGINEERS FOR STARK MILL, LOCKWOOD GREENE COMPANY, ALSO BUILT THE NEW WORKER HOUSING. - 110 Corinth Road (House), 110 Corinth Road, Hogansville, Troup County, GA

  18. Stark effect applicable to optically pumped far-infrared laser

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Koo, K. P.

    1976-01-01

    Absorption measurements at CO2 laser frequencies were carried out as a function of Stark fields and CH3OH gas pressures to assess the effect of low electric field Stark tuning on methanol absorption at the P(12) 9.4 micron CO2 laser line, in a continuing search for coherent emitters at submillimeter wavelengths (far infrared). The line center absorption coefficient is found to increase five-fold with a 2.3 kV/cm Stark field at the 220 mtorr methanol pressure optimal for methanol far infrared lasing. The low electric field Stark tuning encourages efforts to enhance the pumping efficiency of a methanol far infrared laser at its normal optimum operating pressure, and suggests that significant Stark field induced frequency modulation of the far IR laser output is feasible.

  19. Optical control of coupled molecular states by ac Stark effect

    NASA Astrophysics Data System (ADS)

    Qi, Jianbing

    2014-05-01

    Quantum states with different spin multiplicity can be coupled through the interaction of the spin orbital motion of electrons. For example, the spin-orbit coupled rovibrational levels in diatomic alkali, which have different multiplicity in terms of total spin quantum number, and are classified as singlet states (if the total spin is zero) and triplet states (if the total spin is one), respectively. A transition from the singlet level can only go to singlet levels and a triplet only to triplet levels. Due to the spin-orbit coupling, however, the coupled states mix each other, therefore both states have singlet as well as triplet character. By coherently coupling the pair to an auxiliary quantum state, varying the Rabi frequency of the coupling laser and the detuning of the laser frequency, the coupling of the two mixed singlet-triplet molecular rovibrational levels can be modified by ac Stark effect. We use density matrix equations and a five-level molecular model to show that a coupled singlet-triplet pair of rovibrational levels can be used as a channel to optically control quantum states.

  20. Polarization dependence of n = 2 positronium transition rates to Stark-split n = 30 levels via crossed-beam spectroscopy

    NASA Astrophysics Data System (ADS)

    Jones, A. C. L.; Hisakado, T. H.; Goldman, H. J.; Tom, H. W. K.; Mills, A. P., Jr.

    2016-03-01

    We produce Rydberg Ps by a two-step laser excitation from {1}3S\\to {2}3P and from {2}3P to states of principal quantum level n=30+/- 1 that are Stark split by a motionally induced electric field. Our measurements are largely free of first-order Doppler shifts such that we are able to investigate the impact of laser polarization on the population of the closely spaced Stark levels. We find a variation in the distribution that is primarily dependent on the IR laser polarization with respect to the direction of the motionally induced electric field. With the IR light polarized parallel to the electric field F, the ratio of excitation probability to the levels of maximal Stark splitting compared to that of excitation to the states of minimal Stark splitting is found to be 3.37 ± 0.51, whereas with the IR light polarized perpendicular to F, the excitation ratio is 0.87 ± 0.64. Our results agree with those of Wall et al (2015 Phys. Rev. Lett. 114 173001) obtained with n = 11 and will be useful in the preparation of high-n states of Ps for a variety of experiments, including measuring the interaction of Ps with gravity, in precision time-of-flight (TOF) energy spectroscopy, and precision optical spectroscopy of Ps.

  1. External excitation of a short-wavelength fluctuation in the Alcator C-Mod edge plasma and its relationship to the quasi-coherent mode

    SciTech Connect

    Golfinopoulos, T.; LaBombard, B.; Parker, R. R.; Burke, W.; Davis, E.; Granetz, R.; Greenwald, M.; Irby, J.; Leccacorvi, R.; Marmar, E.; Parkin, W.; Porkolab, M.; Terry, J.; Vieira, R.; Wolfe, S.

    2014-05-15

    A novel “Shoelace” antenna has been used to inductively excite a short-wavelength edge fluctuation in a tokamak boundary layer for the first time. The principal design parameters, k{sub ⊥}=1.5±0.1 cm{sup −1} and 45C-Mod, responsible for exhausting impurities in the steady-state, ELM-free Enhanced D{sub α} H-mode. In H-mode, whether or not there is a QCM, the antenna drives coherent, field-aligned perturbations in density, n{sup ~}{sub e}, and field, B{sup ~}{sub θ}, which are guided by field lines, propagate in the electron diamagnetic drift direction, and exhibit a weakly damped (γ/ω{sub 0}∼5%−10%) resonance near the natural QCM frequency. This result is significant, offering the possibility that externally driven modes may be used to enhance particle transport. In L-mode, the antenna drives only a non-resonant B{sup ~}{sub θ} response. The facts that the driven mode has the same wave number and propagation direction as the QCM, and is resonant at the QCM frequency, suggest the antenna may couple to this mode, which we have shown elsewhere to be predominantly drift-mode-like [B. LaBombard et al., Phys. Plasmas 21, 056108 (2014)].

  2. Characterization of core and edge turbulence in L- and enhanced D{sub {alpha}} H-mode Alcator C-Mod plasmas

    SciTech Connect

    Basse, N.P.; Edlund, E.M.; Ernst, D.R.; Fiore, C.L.; Greenwald, M.J.; Hubbard, A.E.; Hughes, J.W.; Irby, J.H.; Lin, L.; Lin, Y.; Marmar, E.S.; Mossessian, D.A.; Porkolab, M.; Rice, J.E.; Snipes, J.A.; Stillerman, J.A.; Terry, J.L.; Wolfe, S.M.; Wukitch, S.J.; Zhurovich, K.

    2005-05-15

    The recently upgraded phase-contrast imaging (PCI) diagnostic is used to characterize the transition from the low (L) to the enhanced D{sub {alpha}} (EDA) high (H) confinement mode in Alcator C-Mod [I. H. Hutchinson, R. Boivin, F. Bombarda et al., Phys. Plasmas 1, 1511 (1994)] plasmas. PCI yields information on line integrated density fluctuations along vertical chords. The number of channels has been increased from 12 to 32 and the sampling rate from 1 MHz to 10 MHz. This expansion of diagnostic capabilities is used to study broadband turbulence in L and EDA H mode and to analyze the quasicoherent (QC) mode associated with EDA H mode. Changes in broadband turbulence at the transition from L to EDA H mode can be interpreted as an effect of the Doppler rotation of the bulk plasma. Additional fluctuation measurements of D{sub {alpha}} light and the poloidal magnetic field show features correlated with PCI in two different frequency ranges at the transition. The backtransition from EDA H to L mode, the so-called enhanced neutron (EN) mode, is investigated by new high frequency (132 and 140 GHz) reflectometer channels operating in the ordinary (O) mode. This additional hardware has been installed in an effort to study localized turbulence associated with internal transport barriers (ITBs). The EN mode is a suitable candidate for this study, since an ITB exists transiently as the outer density decreases much faster than the core density in this mode. The fact that the density decays from the outside inward allows us to study fluctuations progressing towards the plasma core. Our results mark the first localized observation of the QC mode at medium density: 2.2x10{sup 20} m{sup -3} (132 GHz). Correlating the reflectometry measurements with other fluctuating quantities provides some insight regarding the causality of the EN-mode development.

  3. Characterization of neo-classical tearing modes in high-performance I-mode plasmas with ICRF mode conversion flow drive on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Lin, Yijun; Granetz, R.; Reinke, M. L.; Rice, J. E.; Wolfe, S. M.; Wukitch, S. J.

    2012-10-01

    Neo-classical tearing modes (NTM's) have been observed on Alcator C-Mod in high performance I-mode plasmas (Bt0˜5.2 T) that are heated by a combination of ICRF D(H) minority heating at 80 MHz and D(He3) mode conversion (MC) heating at 50 MHz. Due to the stabilizing effect by the energetic minority hydrogen ions, long sawtooth (>=40 ms) and large sawtooth crashes (δTe0>=3 keV) are produced in these hot (Te0<=9 keV) plasmas. NTMs with (m=4, n=3), (5, 4), (3, 2) and (2, 1) have been observed. The onset criteria of the (3, 2) NTMs, βp˜0.4-0.7, βN˜1.0-1.4, βN/ρi^*˜200-350, ν NTM (q=3/2)˜0.04-0.25, approximately follow the trend that obtained from DIII-D and ASDEX Upgrade. For the (3, 2) mode, the saturated width Wsat˜0.8-1 cm, which is 3-4 times the ion banana width. Although the NTMs have a small effect on confinement degradation (δβ/β˜ a few percent), they have significant effect on plasma rotation. MC flow drive generates large toroidal rotation above 100 km/sec in L-mode, and when the plasma enters I-mode, plasma rotation is expected to increase significantly due to the additional intrinsic rotation torque from the edge Te pedestal. The appearance of the (3, 2) mode usually rapidly reduces the rotation speed, and the (2, 1) mode, if it occurs, would completely halt the rotation.

  4. Wide-frequency range, dynamic matching network and power system for the “Shoelace” radio frequency antenna on the Alcator C-Mod tokamak

    SciTech Connect

    Golfinopoulos, Theodore LaBombard, Brian; Burke, William; Parker, Ronald R.; Parkin, William; Woskov, Paul

    2014-04-15

    A wide-frequency range (50–300 kHz) power system has been implemented for use with a new RF antenna – the “Shoelace” antenna – built to drive coherent plasma fluctuations in the edge of the Alcator C-Mod tokamak. A custom, dynamically tunable matching network allows two commercial 1 kW, 50-Ω RF amplifiers to drive the low-impedance, inductive load presented by the antenna. This is accomplished by a discretely variable L-match network, with 81 independently selected steps available for each of the series and parallel legs of the matching configuration. A compact programmable logic device provides a control system that measures the frequency with better than 1 kHz accuracy and transitions to the correct tuning state in less than 1 ms. At least 85% of source power is dissipated in the antenna across the operational frequency range, with a minimum frequency slew rate of 1 MHz/s; the best performance is achieved in the narrower band from 80 to 150 kHz which is of interest in typical experiments. The RF frequency can be run with open-loop control, following a pre-programmed analog waveform, or phase-locked to track a plasma fluctuation diagnostic signal in real time with programmable phase delay; the amplitude control is always open-loop. The control waveforms and phase delay are programmed remotely. These tools have enabled first-of-a-kind measurements of the tokamak edge plasma system response in the frequency range and at the wave number at which coherent fluctuations regulate heat and particle transport through the plasma boundary.

  5. Wide-frequency range, dynamic matching network and power system for the "Shoelace" radio frequency antenna on the Alcator C-Mod tokamak.

    PubMed

    Golfinopoulos, Theodore; LaBombard, Brian; Burke, William; Parker, Ronald R; Parkin, William; Woskov, Paul

    2014-04-01

    A wide-frequency range (50-300 kHz) power system has been implemented for use with a new RF antenna - the "Shoelace" antenna - built to drive coherent plasma fluctuations in the edge of the Alcator C-Mod tokamak. A custom, dynamically tunable matching network allows two commercial 1 kW, 50-Ω RF amplifiers to drive the low-impedance, inductive load presented by the antenna. This is accomplished by a discretely variable L-match network, with 81 independently selected steps available for each of the series and parallel legs of the matching configuration. A compact programmable logic device provides a control system that measures the frequency with better than 1 kHz accuracy and transitions to the correct tuning state in less than 1 ms. At least 85% of source power is dissipated in the antenna across the operational frequency range, with a minimum frequency slew rate of 1 MHz/s; the best performance is achieved in the narrower band from 80 to 150 kHz which is of interest in typical experiments. The RF frequency can be run with open-loop control, following a pre-programmed analog waveform, or phase-locked to track a plasma fluctuation diagnostic signal in real time with programmable phase delay; the amplitude control is always open-loop. The control waveforms and phase delay are programmed remotely. These tools have enabled first-of-a-kind measurements of the tokamak edge plasma system response in the frequency range and at the wave number at which coherent fluctuations regulate heat and particle transport through the plasma boundary.

  6. Wide-frequency range, dynamic matching network and power system for the "Shoelace" radio frequency antenna on the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Golfinopoulos, Theodore; LaBombard, Brian; Burke, William; Parker, Ronald R.; Parkin, William; Woskov, Paul

    2014-04-01

    A wide-frequency range (50-300 kHz) power system has been implemented for use with a new RF antenna - the "Shoelace" antenna - built to drive coherent plasma fluctuations in the edge of the Alcator C-Mod tokamak. A custom, dynamically tunable matching network allows two commercial 1 kW, 50-Ω RF amplifiers to drive the low-impedance, inductive load presented by the antenna. This is accomplished by a discretely variable L-match network, with 81 independently selected steps available for each of the series and parallel legs of the matching configuration. A compact programmable logic device provides a control system that measures the frequency with better than 1 kHz accuracy and transitions to the correct tuning state in less than 1 ms. At least 85% of source power is dissipated in the antenna across the operational frequency range, with a minimum frequency slew rate of 1 MHz/s; the best performance is achieved in the narrower band from 80 to 150 kHz which is of interest in typical experiments. The RF frequency can be run with open-loop control, following a pre-programmed analog waveform, or phase-locked to track a plasma fluctuation diagnostic signal in real time with programmable phase delay; the amplitude control is always open-loop. The control waveforms and phase delay are programmed remotely. These tools have enabled first-of-a-kind measurements of the tokamak edge plasma system response in the frequency range and at the wave number at which coherent fluctuations regulate heat and particle transport through the plasma boundary.

  7. Stark Tuning of Donor Electron Spins of Silicon

    SciTech Connect

    Bradbury, Forrest R.; Tyryshkin, Alexei M.; Sabouret, Guillaume; Bokor, Jeff; Schenkel, Thomas; Lyon, Stephen A.

    2006-03-23

    We report Stark shift measurements for {sup 121}Sb donor electron spins in silicon using pulsed electron spin resonance. Interdigitated metal gates on top of a Sb-implanted {sup 28}Si epi-layer are used to apply electric fields. Two Stark effects are resolved: a decrease of the hyperfine coupling between electron and nuclear spins of the donor and a decrease in electron Zeeman g-factor. The hyperfine term prevails at X-band magnetic fields of 0.35T, while the g-factor term is expected to dominate at higher magnetic fields. A significant linear Stark effect is also resolved presumably arising from strain.

  8. Stark tuning of donor electron spins in silicon

    SciTech Connect

    Bradbury, F.R.; Tyryshkin, A.M.; Sabouret, G.; Bokor, J.; Schenkel, T.; Lyon, S.A.

    2006-03-12

    We report Stark shift measurements for 121Sb donor electronspins in silicon using pulsed electron spin resonance. Interdigitatedmetal gates on top of a Sb-implanted 28Si epi-layer are used to applyelectric fields. Two Stark effects are resolved: a decrease of thehyperfine coupling between electron and nuclear spins of the donor and adecrease in electron Zeeman g-factor. The hyperfine term prevails atX-band magnetic fields of 0.35T, while the g-factor term is expected todominate at higher magnetic fields. A significant linear Stark effect isalso resolved presumably arising from strain.

  9. Optical Stark Spectroscopy of Gold Chrolride

    NASA Astrophysics Data System (ADS)

    Zhang, Ruohan; Steimle, Timothy

    2014-06-01

    The bonding and electrostatic properties of gold containing molecules are highly influenced by relativistic effects and electron correlation. Hence it is difficult to predict those properties via electron structure calculation, and such calculation are guided by experimental observations. Here we report on the A(Ω=1)-X1Σ+ and B(Ω=0)-X1Σ+ bands of AuCl, which have been previously recorded at Doppler limited resolution. A cold molecular beam sample was generated and the bands were recorded at high resolution (FWHM =35 MHz) using laser excitation spectroscopy, both field-free and in the presence of a static electric field. An improved set of spectroscopic parameters for the A(Ω=1) and B(Ω=0) states were obtained. The Stark induced shifts were analyzed to determine the permanent electric dipole moments for the X, A, and B states. A comparison with AuF and theory will be made. P. Pyykko; Angew Chem. Int {43} 4412, 2004. L. C. O'Brien, A. L. Elliott, and M. Dulick; J. Mol. Spectrosc, 194, 124, 1999.

  10. Stark Widths Of Ionized Xenon UV Lines Of Low Intensity

    SciTech Connect

    Cirisan, M.; Djurovic, S.; Pelaez, R. J.; Aparicio, J. A.; Mar, S.

    2007-04-23

    Stark width measurements of several low intensity Xe II spectral lines (5d - 4f transitions) in UV region, are presented here for the first time. These measurements were obtained from helium - xenon pulsed arc plasma.

  11. Measurements of some ZnII Stark widths

    SciTech Connect

    Mayo, R.; Ortiz, M.

    2008-10-22

    The Stark broadening parameters of six lines of Zn II (4 measured for the first time) have been measured in a plasma produced by ablation of a Cd-Zn alloy with a Nd:YAG laser. The broadening parameters were obtained in molecular Argon at 6 Torr. A Boltzmann plot was used to obtain the plasma temperature and published values of the Stark broadening in Cd II and Saha's equation to obtain the electron density. The Local Thermodynamic Equilibrium condition was checked. Contributions to broadening arising from a mechanism different from the Stark broadening as well as self-absorption influence were estimated for every studied line. A comparison is made with previous experimental values and recent theoretical estimates of the Stark broadening where possible.

  12. Multiphoton Rabi oscillations between highly excited Stark states of potassium

    SciTech Connect

    He Yonglin

    2011-11-15

    We have applied a nonperturbative resonant theory to study the Rabi frequency of microwave multiphoton transitions between two Rydberg states of potassium in a static electric field. The Stark electric dipole moments used to calculate the Rabi frequency are determined by the Stark states' wave functions, which are obtained by the diagonalization method. The frequencies of the Rabi oscillations are in good agreement with either experimental ones or ones calculated by the time-dependent close-coupling method and the Floquet theory. Furthermore, we are able to show that the size of avoided crossings between the (n+2)s and (n,3) states can be predicted from the Stark electric dipole moment and the difference of the two Stark states' energy at a given resonance.

  13. Spectral broadening and its effect in Stark spectra of carotenoids

    NASA Astrophysics Data System (ADS)

    Krawczyk, Stanisław; Olszówka, Dorota

    2001-04-01

    Electrooptical parameters of eight carotenoids with different molecular structures were determined from the absorption and electroabsorption (Stark) spectra in glassy solvents and in poly(methyl methacrylate) films at temperatures 108-115 K. The results point to a limited significance of solvent-induced dipole moments in carotenoids resulting from local electric fields generated by solvent molecules, and indicate that the features in Stark spectra related to apparent dipole moments display a correlation with the bandwidth of individual vibronic transitions in absorption spectra. Model calculations show that it is possible to describe the Stark spectra by assuming a close link between the molecular polarizability and the inhomogeneous spectral shift. It is postulated that the dipole-related features in Stark spectra and the inhomogeneous broadening have a common origin in the distortions of molecular geometry in the form of torsional deformations about the single C-C bonds.

  14. Diffusive suppression of AC-Stark shifts in atomic magnetometers

    PubMed Central

    Sulai, I. A.; Wyllie, R.; Kauer, M.; Smetana, G. S.; Wakai, R. T.; Walker, T. G.

    2016-01-01

    In atomic magnetometers, the vector AC-Stark shift associated with circularly polarized light generates spatially varying effective magnetic fields, which limit the magnetometer response and serve as sources of noise. We describe a scheme whereby optically pumping a small subvolume of the magnetometer cell and relying on diffusion to transport polarized atoms allows a magnetometer to be operated with minimal sensitivity to the AC-Stark field. © 2013 Optical Society of America PMID:23503278

  15. Solid state optical refrigeration using stark manifold resonances in crystals

    DOEpatents

    Seletskiy, Denis V.; Epstein, Richard; Hehlen, Markus P.; Sheik-Bahae, Mansoor

    2017-02-21

    A method and device for cooling electronics is disclosed. The device includes a doped crystal configured to resonate at a Stark manifold resonance capable of cooling the crystal to a temperature of from about 110K to about 170K. The crystal host resonates in response to input from an excitation laser tuned to exploit the Stark manifold resonance corresponding to the cooling of the crystal.

  16. Stark laws and fair market value exceptions: an introduction.

    PubMed

    Siebrasse, Paul B

    2007-01-01

    This article will focus on one aspect of complexity in modern healthcare, namely the implications of Stark laws and other fraud and abuse provisions, including anti-kickback statutes and HIPAA. Also, this article explores the prevalence of fair market value as an exception in the Stark laws and discusses the meanings of those exceptions. Finally, the article explores basic approaches to assessing fair market value, including cost, income, and marketing approaches.

  17. Diffusive suppression of AC-Stark shifts in atomic magnetometers

    NASA Astrophysics Data System (ADS)

    Sulai, I. A.; Wyllie, R.; Kauer, M.; Smetana, G. S.; Wakai, R. T.; Walker, T. G.

    2013-03-01

    In atomic magnetometers, the vector AC-Stark shift associated with circularly polarized light generates spatially varying effective magnetic fields which limit the magnetometer response and serve as sources of noise. We describe a scheme whereby optically pumping a small sub-volume of the magnetometer cell and relying on diffusion to transport polarized atoms allows a magnetometer to be operated with minimal sensitivity to the AC-Stark field.

  18. 1. VIEW LOOKING NORTHWEST AT MAIN ELEVATION OF STARK MILL, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. VIEW LOOKING NORTHWEST AT MAIN ELEVATION OF STARK MILL, A REINFORCED CONCRETE MILL BUILT BY NEW ENGLAND SOUTHERN MILLS IN 1923-24. THE MILL WAS DESIGNED BY LOCKWOOD GREENE ENGINEERS, AND CONTAINED 35,000 SPINDLES FOR MAKING TIRE FABRICS. PART OF THE WEAVING WOULD TAKE PLACE AT HOGANSVILLE MILL (BUILT c. 1900), ANOTHER NEW ENGLAND SOUTHERN MILL NEARBY, UNTIL THE DEMOLITION OF THAT MILL IN THE 1970s. - Stark Mill, 117 Corinth Road, Hogansville, Troup County, GA

  19. Dynamic Stark effect and forbidden-transition spectrallineshapes

    SciTech Connect

    Stalnaker, Jason E.; Budker, D.; Freedman, S.J.; Guzman, J.S.; Rochester, S.M.; Yashchuk, V.V.

    2005-12-15

    We report on an experimental and theoretical study of thedynamic (ac) Stark effect on a for bidden transition. A general frameworkfor parameterizing and describing off-resonant ac-Stark shifts ispresented. A model is developed to calculate spectral line shapesresulting from resonant excitation of atoms in an intense standinglight-wave in the presence of off-resonant ac-Stark shifts. The model isused in the analysis and interpretation of a measurement of the ac-Starkshifts of the static-electric-field-induced 6s2 1S0 -->5d6s 3D1transition at 408 nm in atomic Yb. The results are in agreement withestimates of the ac-Stark shift of the transition under the assumptionthat the shift is dominated by that of the 6s2 1S0 ground state. Adetailed description of the experiment and analysis is presented. Abi-product of this work is an ind ependent determination (from thesaturation behavior of the 408-nm transition) of the Stark transitionpolarizability, which is found to be in agreement with our earliermeasurement. This work is part of the ongoing effort aimed at a precisionmeasurement of atomic parity-violation effects in Yb.

  20. Stark Broadening Parameters for Neutral Oxygen Spectral Lines

    NASA Astrophysics Data System (ADS)

    Alonizan, N.; Qindeel, R.; Nessib, N. Ben; Sahal-Bréchot, S.; Dimitrijević, Milan S.

    2015-12-01

    Stark broadening parameters for nine neutral oxygen (O I) lines have been determined within the impact approximation and the semiclassical perturbation method. The atomic data have been taken from the TOPbase and NIST atomic databases. The electron and proton Stark widths and shifts and ion broadening parameter values for these O I lines have been calculated for electron density of 10 16 cm -3 and for 4 different electron temperatures in the range of 5000 K to 40000 K. These Stark broadening parameters are compared with our previous results (Ben Nessib, N. et al. 1996, Physica Scripta, 54, 603-613), where we calculated Stark broadening parameters for only four O I spectral lines and where Stark widths and shifts were compared with experimental and theoretical data available in the literature. In the present paper, we have also compared our results with the Griem's book (Griem, H. R. 1974, Spectral line broadening by plasmas) and VALD (Ryabchikova, T. et al. 2015, Physica Scripta, 90, 054005) values.

  1. High confinement/high radiated power H-mode experiments in Alcator C-Mod and consequences for International Thermonuclear Experimental Reactor (ITER) Q{sub DT} = 10 operation

    SciTech Connect

    Loarte, A.; Hughes, J. W.; Reinke, M. L.; Terry, J. L.; LaBombard, B.; Brunner, D.; Greenwald, M.; Lipschultz, B.; Ma, Y.; Wukitch, S.; Wolfe, S.

    2011-05-15

    Experiments in Alcator C-Mod in (Enhanced D-alpha) EDA H-modes with extrinsic impurity seeding (N{sub 2}, Ne, and Ar) have demonstrated a direct correlation between plasma energy confinement and edge power flow, achieving values of H{sub 98{>=}} 1 for edge power flows only marginally exceeding the scaled power for access to H-mode confinement in these conditions. For lower Z impurity seeding (N{sub 2} and Ne), plasmas with high energy confinement are obtained with a radiative power fraction of 85% or larger and a reduction of the peak heat flux at the divertor by more than a factor of 5 compared to similar attached conditions. The H-mode plasmas thus achieved in Alcator C-Mod meet or exceed the requirements both in terms of divertor heat flux handling and energy confinement for ITER Q{sub DT} = 10 operation and with an edge power flow only marginally above the H-mode threshold power (by 1.0-1.4) as expected in ITER.

  2. Sideband excitation of trapped ions by rapid adiabatic passage for manipulation of motional states

    SciTech Connect

    Watanabe, T.; Nomura, S.; Toyoda, K.; Urabe, S.

    2011-09-15

    We describe an analysis and experimental results of the manipulation of motional states of a single trapped {sup 40}Ca{sup +} ion based on sideband excitation by rapid adiabatic passage. When the sideband transition is excited by rapid adiabatic passage, adiabaticity may be affected by ac Stark shifts. We investigate the influence of ac Stark shifts and compensate for these shifts with an additional laser field. This makes the population transfer by rapid adiabatic passage more robust with respect to experimental parameters. Finally, we manipulate the motional states and generate motional Fock states of a single {sup 40}Ca{sup +} ion by rapid adiabatic passage with ac Stark compensation.

  3. Experimental Stark widths and shifts of Ti II spectral lines

    NASA Astrophysics Data System (ADS)

    Manrique, J.; Aguilera, J. A.; Aragón, C.

    2016-10-01

    Stark widths and shifts of Ti II lines with wavelengths in the range 2500-4600 Å have been determined by laser-induced breakdown spectroscopy. The temperature and electron density of the plasma vary in the ranges 11 970-15 520 K and (2.0-7.2) × 1017 cm-3, respectively, for the different measurement instants from 0.6 to 1.8 μs. The samples used are fused glass discs with different titanium concentrations, selected to control the self-absorption of the lines. The Stark widths and shifts are compared with the experimental and theoretical data available in the literature.

  4. Graphene mediated Stark shifting of quantum dot energy levels

    SciTech Connect

    Kinnischtzke, Laura; Badolato, Antonio; Goodfellow, Kenneth M.; Vamivakas, A. Nick; Chakraborty, Chitraleema; Lai, Yi-Ming; Fält, Stefan; Wegscheider, Werner

    2016-05-23

    We demonstrate an optoelectronic device comprised of single InAs quantum dots in an n-i-Schottky diode where graphene has been used as the Schottky contact. Deterministic electric field tuning is shown using Stark-shifted micro-photoluminescence from single quantum dots. The extracted dipole moments from the Stark shifts are comparable to conventional devices where the Schottky contact is a semi-transparent metal. Neutral and singly charged excitons are also observed in the well-known Coulomb-blockade plateaus. Our results indicate that graphene is a suitable replacement for metal contacts in quantum dot devices which require electric field control.

  5. Stark effect and polarizability of graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Pedersen, Thomas Garm

    2017-09-01

    The properties of graphene quantum dots can be manipulated via lateral electric fields. Treating electrons in such structures as confined massless Dirac fermions, we derive an analytical expression for the quadratic Stark shift valid for arbitrary angular momentum and quantum dot size. Moreover, we determine the perturbative regime, beyond which higher-order field effects are observed. The Dirac approach is validated by comparison with atomistic tight-binding simulations. Finally, we study the influence on the Stark effect of band gaps produced by, e.g., interaction with the substrate.

  6. Stark broadening of hydrogen lines in magnetic fusion plasmas

    NASA Astrophysics Data System (ADS)

    Rosato, J.; Godbert-Mouret, L.; Koubiti, M.; Marandet, Y.; Stamm, R.

    2017-03-01

    We report on a Stark line shape model for the diagnostic of tokamak edge plasmas. In specific scenarios, plasma discharges are carried out at high density regimes, sufficiently so that the spectral lines emitted by the neutral atoms present in the edge and in the divertor region are affected by the plasma microscopic electric field (Stark broadening). We present new line shape calculations, carried out for diagnostic purposes in the context of the MST1 (Medium Sized Tokamak) European campaign. The role of the magnetic field (Zeeman effect) on line spectra is discussed.

  7. Experimental Stark Shift of Some Xe II UV Lines

    SciTech Connect

    Djurovic, S.; Cirisan, M.; Pelaez, R. J.; Aparicio, J. A.; Mar, S.

    2008-10-22

    Stark broadening and shift of Xe II lines have been the subject of many experimental and theoretical studie. Here, the results of Stark shift measurements for six Xe II lines are presented. All given results are here reported for the first time. Two lines belong to 5d-6p, two to 5d-7p and one to 5d-4f transition. In this experiment pulsed arc plasma made of mixture of 95% helium and 5% xenon was used. Measured electron densities and temperatures were in the range of (0.2-1.8)10{sup 23}m{sup -3} and 18300-25500 K respectively.

  8. Graphene mediated Stark shifting of quantum dot energy levels

    NASA Astrophysics Data System (ADS)

    Kinnischtzke, Laura; Goodfellow, Kenneth M.; Chakraborty, Chitraleema; Lai, Yi-Ming; Fält, Stefan; Wegscheider, Werner; Badolato, Antonio; Vamivakas, A. Nick

    2016-05-01

    We demonstrate an optoelectronic device comprised of single InAs quantum dots in an n-i-Schottky diode where graphene has been used as the Schottky contact. Deterministic electric field tuning is shown using Stark-shifted micro-photoluminescence from single quantum dots. The extracted dipole moments from the Stark shifts are comparable to conventional devices where the Schottky contact is a semi-transparent metal. Neutral and singly charged excitons are also observed in the well-known Coulomb-blockade plateaus. Our results indicate that graphene is a suitable replacement for metal contacts in quantum dot devices which require electric field control.

  9. On the Stark Broadening of Single Ionized Argon Lines

    NASA Astrophysics Data System (ADS)

    Dimitrijević, M. S.; Truong-Bach

    1986-06-01

    Using a semi-classical formalism which includes Debye shielding, Stark broadening parameters of various components within the 4 s 2P - 4 p ´ 2P0 multiplet and the 4 p - 4 d (2P 0 - 2P, 2D0 - 2 P, 2D0 - 2D) supermutiplet of Ar II are computed. We show that when various components of a multiplet (supermultiplet or transition array) are broadened inequally by an embedded closelying perturbing level, use of a perturber param eter cut-off at the Debye length can restrain the calculated differences between Stark widths within the multiplet.

  10. The Stark anomalous dispersion optical filter: The theory

    NASA Technical Reports Server (NTRS)

    Yin, B.; Shay, T. M.

    1994-01-01

    The Stark anomalous dispersion optical filter is a wide-frequency-tunable ultra-narrow-bandwidth optical filter. The first theoretical investigation of this filter matched to the wavelength of a doubled Nd:YAG laser is reported. The calculations show that such a filter may provide above 80 percent transmission, and a noise equivalent bandwidth of 3 GHz.

  11. Stark Broadening Parameters For White Dwarf Atmospheres Research

    NASA Astrophysics Data System (ADS)

    Larbi-Terzi, N.; Sahal-Brechot, S.; Nessib, N. B.; Dimitrijevic, M. S.

    2010-07-01

    Stark broadening parameters of C II lines were determined within 3d-nf series using semiclassical perturbation method. The atomic energy levels needed for calculations were taken from TOPBASE as well as the oscillator strengths, which were additionally calculated using the method of Bates and Damgaard. The both results were compared and only insignificant differences were found. Calculations were performed for plasma conditions relevant for atmospheres of DQ white dwarfs and for a new type of white dwarfs, with surface composed mostly of carbon, discovered in 2007 by Dufour et al. The aim of this work is to provide accurate C II Stark broadening data, which are crucial for this type of white dwarf atmosphere modellisation. Obtained results will be included in STARK-B database (http://stark-b.obspm.fr/), entering in the FP7 project of European Virtual Atomic and Molecular Data Center VAMDC aiming at building an interoperable e- Infrastructure for the exchange of atomic and molecular data (http://www.vamdc.org/).

  12. VAMDC FP7 project and STARK-B database: C II Stark broadening parameters for white dwarf atmospheres research

    NASA Astrophysics Data System (ADS)

    Larbi-Terzi, Neila; Sahal-Bréchot, Sylvie; Ben Nessib, Nebil; Dimitrijević, Milan S.

    2010-11-01

    Stark broadening parameters of C II lines were determined within 3s-np spectral series within the semiclassical perturbation method. The atomic energy levels needed for calculations were taken from TOPBASE as well as the oscillator strengths, calculated additionally using the Coulomb approximation (the method of Bates and Damgaard). The both results were compared and the disagreement is found only in one case where the configuration mixing allows a forbidden transition to a close perturbing energy level. Calculations were performed for plasma conditions relevant for atmospheres of DQ white dwarfs and for a new type of white dwarfs, with surface composed mostly of carbon, discovered in 2007 by Dufour et al.. The aim of this work is to provide accurate C II Stark broadening data, which are crucial for this type of white dwarf atmosphere modellisation. Obtained results will be included in STARK-B database (http://stark-b.obspm.fr/), entering in the FP7 project of European Virtual Atomic and Molecular Data Center VAMDC aiming at building an interoperable e-Infrastructure for the exchange of atomic and molecular data (http://www.vamdc.org/).

  13. VAMDC FP7 project and STARK-B database: C II Stark broadening parameters for white dwarf atmospheres research

    SciTech Connect

    Larbi-Terzi, Neila; Ben Nessib, Nebil; Sahal-Brechot, Sylvie; Dimitrijevic, Milan S.

    2010-11-23

    Stark broadening parameters of C II lines were determined within 3s-np spectral series within the semiclassical perturbation method. The atomic energy levels needed for calculations were taken from TOPBASE as well as the oscillator strengths, calculated additionally using the Coulomb approximation (the method of Bates and Damgaard). The both results were compared and the disagreement is found only in one case where the configuration mixing allows a forbidden transition to a close perturbing energy level. Calculations were performed for plasma conditions relevant for atmospheres of DQ white dwarfs and for a new type of white dwarfs, with surface composed mostly of carbon, discovered in 2007 by Dufour et al.. The aim of this work is to provide accurate C II Stark broadening data, which are crucial for this type of white dwarf atmosphere modellisation. Obtained results will be included in STARK-B database (http://stark-b.obspm.fr/), entering in the FP7 project of European Virtual Atomic and Molecular Data Center VAMDC aiming at building an interoperable e-Infrastructure for the exchange of atomic and molecular data (http://www.vamdc.org/).

  14. Reconstruction in 3D of the fast wave fields in ITER, DIII-D, C-Mod and NSTX, including the coupling of full-wave and particle codes to resolve finite orbit effects

    SciTech Connect

    Green, David L; Jaeger, Erwin Frederick; Berry, Lee A; Choi, M.

    2009-01-01

    The rf-SciDAC collaboration is developing computer simulations to predict the damping of radio frequency (rf) waves in fusion plasmas. Here we extend self-consistent quasi-linear calculations of ion cyclotron resonant heating to include the finite drift of ions from magnetic flux surfaces and rf induced spatial transport. The all-orders spectral wave solver AORSA is iteratively coupled with a particle based update of the plasma distribution function using a quasi-linear diffusion tersor representative of the (k) over right arrow spectrum. Initial results are presented for a high power minority heating scenario on the Alcator C-Mod tokamak and a high harmonic beam heating scenario on DIII-D. Finite orbit effects are shown to give a less peaked perpendicular energy profile and rf induced transport.

  15. A Newtonian Description of the Linear Stark Effect

    NASA Astrophysics Data System (ADS)

    Woodyard, James; Espinosa, James

    2010-10-01

    After the discovery of the magnetic effect on spectral lines by Zeeman, it was only natural that physicists should look for a similar effect when an electric field was applied. A nonlinear model of the hydrogen atom developed by Woldemar Voigt was investigated and predicted a second order effect that would require huge electric fields in the ten of millions of volts per centimeter. Fortunately, Johannes Stark ignored this ominous prediction by a leading theoretician and discovered a linear electric effect that would quickly be named after himself. Soon after Bohr introduced his quantum theory of the Hydrogen Atom, Schwarzschild and Epstein independently utilized Sommerfeld's extension of Bohr's theory to arrive at an empirically correct formula. We will show how our classical theory of the hydrogen atom can account for the linear Stark effect.

  16. Stark effect for Si:Li spin qubits

    NASA Astrophysics Data System (ADS)

    Pendo, Luke; Handberg, Erin; Smelyanskiy, Vadim; Petukhov, Andre

    2010-03-01

    We study the effect of a static electric field on lithium donors in silicon. Our treatment is based on a variational procedure utilizing a large set of basis functions similar to those used by Faulkner [1]. We take into account the valley-orbit splitting, arbitrary external stress and magnetic field as well as spin-orbit interaction. We believe that our variational method captures the effects of higher energy excited states as well as non-linear E-field contributions to the energy level splitting and the electrical dipole moment. The anisotropy of the effective mass in a single valley leads to an anisotropy of the quadratic Stark susceptibility. This anisotropy could be used to manipulate and control Si:Li spin qubits because it causes a nontrivial interplay of the Stark and Zeeman effects due to the unique inverted electronic structure of the Li donor in Si. [1] R.A. Faulkner, Phys. Rev. 184, 713 (1969).

  17. Stark Shift Measurement of Some Xe III Lines

    SciTech Connect

    Djurovic, S.; Cirisaif, M.; Pelaez, R. J.; Aparicio, J. A.; Mar, S.

    2008-10-22

    Examination of ionized xenon spectrum is of a great interest for plasma diagnostic purposes, theory testing and different applications. In this paper, we present Stark shift data for one blue and five UV Xe III lines. One line belongs to the 5d-6p transition, while all other lines belong to 6s-6p transition. Most of the existing papers are devoted to Stark width measurements and only one paper deals with shift data of the lines studied herein. A low-pressure pulsed arc with 95% of helium and 5% of xenon was used as a plasma source. All measurements were performed under following plasma conditions: electron density (0.2-1.4)10{sup 23}m{sup -3} and electron temperature 18000-23000 K.

  18. Acoustically induced stark effect for excitons in intrinsic semiconductors.

    PubMed

    Ivanov, A L; Littlewood, P B

    2001-09-24

    A Stark effect for excitons parametrically driven by coherent acoustic phonons is proposed. Our scheme refers to a low-temperature intrinsic semiconductor or semiconductor nanostructure pumped by an acoustic wave (frequency band nu(ac) approximately equal to 1-40 GHz and intensity range I(ac) approximately equal to 10(-2)-10(2) W/cm(2)) and probed by low-intensity light. Tunable optical band gaps, which strongly change the spectral shape of the exciton line, are induced in the polariton spectrum by acoustic pumping. We develop an exactly solvable model of the acoustic Stark effect and apply our results to GaAs driven by bulk or surface acoustic waves.

  19. Hydrogen Stark broadening by different kinds of model microfields

    NASA Astrophysics Data System (ADS)

    Seidel, J.

    1980-07-01

    A new model microfield is defined (the theta process) which in conjunction with the kangaroo process, is used to demonstrate the effects of different model microfields on hydrogen line profiles. The differences in the statistical features of the models give an estimate of the uncertainties associated with the method of model microfields. Stark broadening of hydrogen Lyman lines by either electrons or ions is investigated specifically.

  20. Exceptional points in bichromatic Wannier-Stark systems

    NASA Astrophysics Data System (ADS)

    Elsen, C.; Rapedius, K.; Witthaut, D.; Korsch, H. J.

    2011-11-01

    The resonance spectrum of a tilted periodic quantum system for a bichromatic periodic potential is investigated. For such a bichromatic Wannier-Stark system, exceptional points, degeneracies of the spectrum, can be localized in parameter space by means of an efficient method for computing resonances. Berry phases and Petermann factors are analysed. Finally, the influence of a nonlinearity of the Gross-Pitaevskii type on the resonance crossing scenario is briefly discussed.

  1. On the Absolutely Continuous Spectrum of Stark Operators

    NASA Astrophysics Data System (ADS)

    Perelman, Galina

    The stability of the absolutely continuous spectrum of the one-dimensional Stark operator under perturbations of the potential is discussed. The focus is on proving this stability under minimal assumptions on smoothness of the perturbation. A general criterion is presented together with some applications. These include the case of periodic perturbations where we show that any perturbation vL1()∩H-1/2() preserves the a.c. spectrum.

  2. Some properties of Stark states of hydrogenic atoms and ions

    NASA Astrophysics Data System (ADS)

    Hey, J. D.

    2007-10-01

    The motivation for this work is the problem of providing accurate values of the atomic transition matrix elements for the Stark components of Rydberg Rydberg transitions in atomic hydrogen and hydrogenic ions, for use in spectral line broadening calculations applicable to cool, low-density plasmas, such as those found in H II regions. Since conventional methods of calculating these transition matrix elements cannot be used for the high principal quantum numbers now easily attained in radio astronomical spectra, we attempt to show that the recurrence relation (ladder operator) method recently employed by Watson (2006 J. Phys. B: At. Mol. Opt. Phys. 39 1889 97) and Hey (2006 J. Phys. B: At. Mol. Opt. Phys. 39 2641 64) can be taken over into the parabolic coordinate system used to describe the Stark states of the atomic (ionic) radiators. The present method is therefore suggested as potentially useful for extending the work of Griem (1967 Astrophys. J. 148 547 58, 2005 Astrophys. J. 620 L133 4), Watson (2006), Stambulchik et al (2007 Phys. Rev. E 75 016401(9 pp) on Stark broadening in transitions between states of high principal quantum number, to physical conditions where the binary, impact approximation is no longer strictly applicable to both electron and ion perturbers. Another possible field of application is the study of Stark mixing transitions in 'ultracold' Rydberg atoms perturbed by long-range interactions with slow atoms and ions. Preparatory to the derivation of recurrence relations for states of different principal quantum number, a number of properties and recurrence relations are also found for states of identical principal quantum number, including the analogue in parabolic coordinates to the relations of Pasternack (1937 Proc. Natl Acad. Sci. USA 23 91 4, 250) in spherical polar coordinates.

  3. Molecular Beam Optical Stark Spectroscopy of Magnesium Deuteride

    NASA Astrophysics Data System (ADS)

    Steimle, Timothy; Zhang, Ruohan; Wang, Hailing

    2014-06-01

    Light polar, paramagnetic molecules, such as magnesium hydride, MgH, are attractive for slowing and trapping experiments because these molecules have both non-zero permanent electric dipole, μel, and magnetic dipole, μm moments. The permanent electric dipole moment is particularly relevant to Stark deceleration which depends on the ratio of the Stark shift to molecular mass. Here we report on the Stark effect in the (0,0) A2Π - X 2Σ+ band system of a cold molecular beam sample of magnesium deuteride, MgD. The lines associated with the lowest rotational levels are detected for the first time. The field-free spectrum was analyzed to produce an improved set of fine structure parameters for the A2Π(v = 0) state. The observed electric field induced splittings and shifts were analyzed to produce permanent electric dipole moments, μel,of 2.561(10)D and 1.34(8)D for A2Π(v = 0) and X2Σ+(v=0)states, respectively. This is the first molecular beam study of MgD.

  4. Supersonic Molecular Beam Optical Stark Spectroscopy of MnH.

    NASA Astrophysics Data System (ADS)

    Gengler, Jamie; Ma, Tongmei; Harrison, Jeremy; Steimle, Timothy

    2006-03-01

    The large moment of inertia, large magnetic moment, and possible large permanent electric dipole moment of manganese monohydride, MnH, makes it a prime candidate for ultra-cold molecule production via Stark deceleration and magnetic trapping. Here we report the first molecular beam production of MnH and the analysis of the Stark effect in the (0,0) A^7 π -- X^ 7σ^+ band. The sample was prepared by laser ablation of solid Mn in an H2 supersonic expansion. The low rotational temperature (<50 K) and near natural linewidth resolution (˜50 MHz) facilitated analysis of the ^55Mn (I=5/2) and ^1H (I=1/2) hyperfine structure. A comparison of the derived field-free parameters with those obtained from sub- Doppler optical measurements will be made. Progress on the analysis of the Stark effect will be given. J.R. Bochinski, E.R. Hudson, H.J. Lewandowski, and J. Ye, Phys. Rev. A 70, 043410 (2004). S.Y.T. van de Meerakker, R.T. Jongma, H.L. Bethlem, and G. Meijer, Phys. Rev. A 64, 041401(R) (2001) report the first molecular beam production of MnH and the analysis of T.D. Varberg, J.A. Gray, R.W. Field, and A.J. Merer, J. Mol. Spec. 156, 296-318 (1992). I.E. Gordon, D.R.T. Appadoo, A. Shayesteh, K.A. Walker, and P.F. Bernath, J. Mol. Spec., 229, 145-149 (2005).

  5. Stark widths and shifts for spectral lines of Sn IV

    NASA Astrophysics Data System (ADS)

    de Andrés-García, I.; Alonso-Medina, A.; Colón, C.

    2016-01-01

    In this paper, we present theoretical Stark widths and shifts calculated corresponding to 66 spectral lines of Sn IV. We use the Griem semi-empirical approach and the COWAN computer code. For the intermediate coupling calculations, the standard method of least-squares fitting from experimental energy levels was used. Data are presented for an electron density of 1017 cm-3 and temperatures T = 1.1-5.0 (104 K). The matrix elements used in these calculations have been determined from 34 configurations of Sn IV: 4d10ns(n = 5-10), 4d10nd(n = 5-8), 4d95s2, 4d95p2, 4d95s5d, 4d85s5p2 and 4d105g for even parity and 4d10np(n = 5-8), 4d10nf (n = 4-6), 4d95snp(n = 5-8), 4d85s25p and 4d95snf (n = 4-10) for odd parity. Also, in order to test the matrix elements used in our calculations, we present calculated values of radiative lifetimes of 14 levels of Sn IV. There is good agreement between our calculations and the experimental radiative lifetimes obtained from the bibliography. The spectral lines of Sn IV are observed in UV spectra of HD 149499 B obtained with the Far Ultraviolet Spectroscopic Explorer, the Goddard High Resolution Spectrograph and the International Ultraviolet Explorer. Theoretical trends of the Stark broadening parameter versus the temperature for relevant lines are presented. Also our values of Stark broadening parameters have been compared with the data available in the bibliography.

  6. Stark shift and broadening of FI and ClI lines

    NASA Astrophysics Data System (ADS)

    Djurović, S.; Konjević, N.

    1988-12-01

    We report measured Stark shifts and widths of neutral flourine and chlorine lines. Wall stabilized arc is used as a plasma source. Electron densities 2 4×1022 m-3 are determined from the width of the H β line and electron temperatures 9500 10 000 K from plasma composition data. Experimental results for FI and ClI Stark widths and FI Stark shifts agree within 10% with semiclassical calculations. ClI Stark shifts are systematically smaller for about 20% than theoretical data with the only exception of the line from multiplet no. 15 where the discrepancy goes up to 49%. Results of investigation of similarities and regularities of Stark widths are in agreement with the study of Wiese and Konjević. Comparison of experimental Stark shifts shows certain types of regularities.

  7. Stark broadening and shift of neutral iodine lines and regularities for analogous transitions of halogene atoms

    NASA Astrophysics Data System (ADS)

    Djurović, S.; Konjević, N.

    1988-06-01

    We report results of an experimental study of the Stark broadening and shift of fourteen and eight neutral iodine lines, respectively, in a plasma wall stabilized arc. An electron density of about 2 × 1022 m-3 was determined from the width of Hα line, while an electron temperature about 9300 K was derived from plasma composition data. The agreement within 40% of both experimental Stark widths and shifts with results of simple theoretical approach by Dimitrijević and Konjević is found. Results of the investigation of similarities of neutral iodine Stark widths are in agreement with the study of Wiese and Konjević. Comparison of experimental Stark shift shows similar types of regularities. Comparisons of Stark widths along analogous transitions of halogene atoms show an increase of widths from fluorine to iodine. It has been demonstrated also that Stark shifts for the same transitions show similar behaviour.

  8. Self-Induced Transparency with the Stark Pulse Technique

    SciTech Connect

    Basharov, A.M.; Kashurnikova, O.V.

    2005-11-15

    A theory based on the method of the inverse scattering problem is presented describing propagation of an ultrashort light pulse under the condition that resonant interaction with atoms of the medium is initially switched on by an additional Stark pulse. A Hamiltonian form of the Maxwell-Bloch equation is found without redefining the spatiotemporal variables. The method of the inverse scattering problem is based on a special spectral problem. Equations of the Gel'fand-Levitan-Marchenko type and a soliton solution are obtained.

  9. Stark cell optoacoustic detection of constituent gases in sample

    NASA Technical Reports Server (NTRS)

    Margolis, J. S.; Shumate, M. S. (Inventor)

    1980-01-01

    An optoacoustic detector for gas analysis is implemented with Stark effect cell modulation for switching a beam in and out of coincidence with a spectral line of a constituent gas in order to eliminate the heating effect of laser energy in the cell as a source of background noise. By using a multiline laser, and linearly sweeping the DC bias voltage while exciting the cell with a multiline laser, it is possible to obtain a spectrum from which to determine the combinations of excited constituents and determine their concentrations in parts per million.

  10. Time-dependent distribution functions and resulting synthetic NPA spectra in C-Mod calculated with the CQL3D-Hybrid-FOW, AORSA full-wave, and DC Lorentz codes

    NASA Astrophysics Data System (ADS)

    Harvey, R. W.; Petrov, Yu.; Jaeger, E. F.; Berry, L. A.; Bonoli, P. T.; Bader, A.

    2015-12-01

    A time-dependent simulation of C-Mod pulsed TCRF power is made obtaining minority hydrogen ion distributions with the CQL3D-Hybrid-FOW finite-orbit-width Fokker-Planck code. Cyclotron-resonant TCRF fields are calculated with the AORSA full wave code. The RF diffusion coefficients used in CQL3D are obtained with the DC Lorentz gyro-orbit code for perturbed particle trajectories in the combined equilibrium and TCRF electromagnetic fields. Prior results with a zero-banana-width simulation using the CQL3D/AORSA/DC time-cycles showed a pronounced enhancement of the H distribution in the perpendicular velocity direction compared to results obtained from Stix's quasilinear theory, and this substantially increased the rampup rate of the observed vertically-viewed neutral particle analyzer (NPA) flux, in general agreement with experiment. However, ramp down of the NPA flux after the pulse, remained long compared to the experiment. The present study compares the new FOW results, including relevant gyro-radius effects, to determine the importance of these new effects on the the NPA time-dependence.

  11. The Stark effect in atomic Rydberg states through a quantum defect approach

    NASA Astrophysics Data System (ADS)

    Menéndez, J. M.; Martín, I.; Velasco, A. M.

    A basis set of quantum defect orbitals (QDOs) has been adopted for the diagonalization of the Hamiltonian matrix of nonhydrogenic atoms in the presence of an external electric field, so that the Stark structure of the Rydberg states has been possible to determine. The presently obtained Stark maps are in excellent agreement with those resulting from theory and experiment, as reported in the literature for a few representative atoms. The adequacy of the Stark quantum defect orbital (SQDO) procedure for accurately dealing with properties related to the Stark effect in atoms is suggested.

  12. Stark broadening experiments on a vacuum arc discharge in tin vapor.

    PubMed

    Kieft, E R; van der Mullen, J J A M; Kroesen, G M W; Banine, V; Koshelev, K N

    2004-12-01

    Pinched discharge plasmas in tin vapor are candidates for application in future semiconductor lithography tools. This paper presents time-resolved measurements of Stark broadened linewidths in a pulsed tin discharge. Stark broadening parameters have been determined for four lines of the Sn III spectrum in the range from 522 to 538 nm, based on a cross-calibration to a Sn II line with a previously known Stark width. The influence of the electron temperature on the Stark widths is discussed. Results for the electron densities in the discharge are presented and compared to Thomson scattering results.

  13. Si 6142 and 6155 Å lines in stellar atmospheres: Stark broadening effect

    NASA Astrophysics Data System (ADS)

    Dimitrijević, M. S.; Popović, L. Č.; Ryabchikova, T.

    2002-07-01

    We study the influence of Stark broadening effect on Si I lines in the roAp 10 Aql star, where the lines are asymmetrical and shifted. First we have calculated Stark broadening parameters using by the semi-classical method for two Si I lines: 6142.48 Å and 6155.13 Å. We have adopted SYNTH code to include into account both Stark width and shift for these lines. From comparison of our calculation data with observations we found that Stark broadening plus stratification effect can explain the width and the asymmetry of the Si I lines in the atmosphere of roAp 10 Aql star.

  14. On the Stark broadening of Cr VI spectral lines in astrophysical plasma

    NASA Astrophysics Data System (ADS)

    Dimitrijević, M. S.; Simić, Z.; Sahal-Bréchot, S.

    2017-02-01

    Stark broadening parameters for Cr VI lines have been calculated using semiclassical perturbation method for conditions of interest for stellar plasma. Here are presented, as an example of obtained results, Stark broadening parameters for electron- and proton-impact broadening for Cr VI 4s 2S-4p 2P° λ = 1430 Å and Cr VI 4p 2P°-5s 2S λ = 611.8 Å multiplets. The obtained results are used to demonstrate the importance of Stark broadening of Cr VI in DO white dwarf atmospheres. Also the obtained results will enter in STARK-B database which is included in Virtual Atomic and Molecula Data Center - VAMDC.

  15. Optical Stark Spectroscopy of Chloro-Methylene HCCl

    NASA Astrophysics Data System (ADS)

    Zhuang, Xiujuan; Steimle, Timothy C.; Wang, Zhong

    2011-06-01

    The optical spectrum of chloro-methylene, HCCl, has been studied for more than 40 years by both conventional and laser-based spectroscopy. Surprisingly, numerous visible bands have yet to be characterized, due in part to known perturbations. Furthermore, the permanent electric dipole moment, μEl, for any state has yet to be determined. Here we report on the field-free and optical Stark spectrum of the tilde{A}1A'' (060)- tilde{X}1A '(000) band system. A cold molecular beam sample was produced by skimming the output of a pulsed discharge source and the spectrum recorded at a resolution of approximately 30 MHz via LIF detection. The field-free spectrum was analyzed to produce an improved set of spectroscopic parameters for the tilde{A}1A''(060)state. The Stark induced shifts were analyzed to determine the values of the a-component of μEl for the tilde{X}1A^ {'}(000)state of 0.498(8)D. Small perturbations in the tilde{A}1A''(060)state will be described. A. J. Merer and D.N. Travis Can. J. Phys., 44, 525 1966. M.Kakimoto, S.Saito and E. Hirota J.Mol.Spectrosc., 97, 194 1983. B.-C.Chang and T. Sears J.Mol.Spectrosc., 173, 391 1995. H. Fan, I. Ionescu, C. Annesley, J. Cummins, M. Bowers and S. A. Reid J.Mol.Spectrosc., 225, 43 2004.

  16. Individual Optical Addressing of Atomic Clock Qubits With Stark Shifts

    NASA Astrophysics Data System (ADS)

    Lee, Aaron; Smith, Jacob; Richerme, Phillip; Neyenhuis, Brian; Hess, Paul; Zhang, Jiehang; Monroe, Chris

    2016-05-01

    In recent years, trapped ions have proven to be a versatile quantum information platform, enabled by their long lifetimes and high gate fidelities. Some of the most promising trapped ion systems take advantage of groundstate hyperfine ``clock'' qubits, which are insensitive to background fields to first order. This same insensitivity also makes σz manipulations of the qubit impractical, eliminating whole classes of operations. We prove there exists a fourth-order light shift, or four-photon Stark shift, of the clock states derived from two coherent laser beams whose beatnote is close to the qubit splitting. Using a mode-locked source generates a large light shift with only modest laser powers, making it a practical σz operation on a clock qubit. We experimentally verify and measure the four-photon Stark shift and demonstrate its use to coherently individually address qubits in a chain of 10 Yb 171 ions with low crosstalk. We use this individual addressing to prepare arbitrary product states with high fidelity and also to apply independent σz terms transverse to an Ising Hamiltonian. This work is supported by the ARO Atomic Physics Program, the AFOSR MURI on Quantum Measurement and Verification, and the NSF Physics Frontier Center at JQI.

  17. Radial Stark Effect in (In,Ga)N Nanowires.

    PubMed

    Lähnemann, Jonas; Corfdir, Pierre; Feix, Felix; Kamimura, Jumpei; Flissikowski, Timur; Grahn, Holger T; Geelhaar, Lutz; Brandt, Oliver

    2016-02-10

    We study the luminescence of unintentionally doped and Si-doped InxGa1-xN nanowires with a low In content (x < 0.2) grown by molecular beam epitaxy on Si substrates. The emission band observed at 300 K from the unintentionally doped samples is centered at much lower energies (800 meV) than expected from the In content measured by X-ray diffractometry and energy dispersive X-ray spectroscopy. This discrepancy arises from the pinning of the Fermi level at the sidewalls of the nanowires, which gives rise to strong radial built-in electric fields. The combination of the built-in electric fields with the compositional fluctuations inherent to (In,Ga)N alloys induces a competition between spatially direct and indirect recombination channels. At elevated temperatures, electrons at the core of the nanowire recombine with holes close to the surface, and the emission from unintentionally doped nanowires exhibits a Stark shift of several hundreds of meV. The competition between spatially direct and indirect transitions is analyzed as a function of temperature for samples with various Si concentrations. We propose that the radial Stark effect is responsible for the broadband absorption of (In,Ga)N nanowires across the entire visible range, which makes these nanostructures a promising platform for solar energy applications.

  18. Stark effect, polarizability, and electroabsorption in silicon nanocrystals

    NASA Astrophysics Data System (ADS)

    Bulutay, Ceyhun; Kulakci, Mustafa; Turan, Raşit

    2010-03-01

    Demonstrating the quantum-confined Stark effect (QCSE) in silicon nanocrystals (NCs) embedded in oxide has been rather elusive, unlike the other materials. Here, the recent experimental data from ion-implanted Si NCs is unambiguously explained within the context of QCSE using an atomistic pseudopotential theory. This further reveals that the majority of the Stark shift comes from the valence states which undergo a level crossing that leads to a nonmonotonic radiative recombination behavior with respect to the applied field. The polarizability of embedded Si NCs including the excitonic effects is extracted over a diameter range of 2.5-6.5 nm, which displays a cubic scaling, α=cDNC3 , with c=2.436×10-11C/(Vm) , where DNC is the NC diameter. Finally, based on intraband electroabsorption analysis, it is predicted that p -doped Si NCs will show substantial voltage tunability, whereas n -doped samples should be almost insensitive. Given the fact that bulk silicon lacks the linear electro-optic effect as being a centrosymmetric crystal, this may offer a viable alternative for electrical modulation using p -doped Si NCs.

  19. Stark Spectroscopy of Rubrene. II. Stark Fluorescence Spectroscopy and Fluorescence Quenching Induced by an External Electric Field.

    PubMed

    Iimori, Toshifumi; Ito, Ryuichi; Ohta, Nobuhiro

    2016-07-21

    We report Stark fluorescence spectroscopy investigation of rubrene dispersed in a poly(methyl methacrylate) film. The features of the fluorescence spectrum are analogous to those in solutions. In the Stark fluorescence spectrum, the decrease of the fluorescence quantum yield in the presence of an external electric field is observed. This result shows that the yield of nonradiative decay processes is increased by the application of an external electric field. It is known that the fluorescence quantum yield for rubrene, which is nearly unity at room temperature, depends on temperature, and a major nonradiative decay process in photoexcited rubrene is ascribed to a thermally activated intersystem crossing (ISC). Equations that express the field-induced fluorescence quenching in terms of the molecular parameters are derived from the ensemble average of electric field effects on the activation energy of the reaction rate constant in random orientation systems. The molecular parameters are then extracted from the observed data. It is inferred that the field-induced increase in the yield of other intramolecular and intermolecular photophysical processes in addition to the ISC should be taken into account.

  20. Measurement of linear stark interference in 199Hg.

    PubMed

    Loftus, T H; Swallows, M D; Griffith, W C; Romalis, M V; Heckel, B R; Fortson, E N

    2011-06-24

    We present measurements of Stark interference in the (61)S(0)→6(3)P(1) transition in (199)Hg, a process whereby a static electric field E mixes magnetic dipole and electric quadrupole couplings into an electric dipole transition, leading to E-linear energy shifts similar to those produced by a permanent atomic electric dipole moment (EDM). The measured interference amplitude, a(SI) = (a(M1) + a(E2)) = (5.8 ± 1.5) × 10(-9) (kV / cm)(-1), agrees with relativistic, many-body predictions and confirms that earlier central-field estimates are a factor of 10 too large. More importantly, this study validates the capability of the (199)Hg EDM search apparatus to resolve nontrivial, controlled, and sub-nHz Larmor frequency shifts with EDM-like characteristics.

  1. Measurement of Linear Stark Interference in {sup 199}Hg

    SciTech Connect

    Loftus, T. H.; Swallows, M. D.; Griffith, W. C.; Romalis, M. V.; Heckel, B. R.; Fortson, E. N.

    2011-06-24

    We present measurements of Stark interference in the 6{sup 1}S{sub 0}{yields}6{sup 3}P{sub 1} transition in {sup 199}Hg, a process whereby a static electric field E mixes magnetic dipole and electric quadrupole couplings into an electric dipole transition, leading to E-linear energy shifts similar to those produced by a permanent atomic electric dipole moment (EDM). The measured interference amplitude, a{sub SI}=(a{sub M1}+a{sub E2})=(5.8{+-}1.5)x10{sup -9} (kV/cm){sup -1}, agrees with relativistic, many-body predictions and confirms that earlier central-field estimates are a factor of 10 too large. More importantly, this study validates the capability of the {sup 199}Hg EDM search apparatus to resolve nontrivial, controlled, and sub-nHz Larmor frequency shifts with EDM-like characteristics.

  2. Stark parameter measurement of Ar II UV spectral lines

    NASA Astrophysics Data System (ADS)

    Djurović, S.; Belmonte, M. T.; Peláez, R. J.; Aparicio, J. A.; Mar, S.

    2013-08-01

    In this paper, we present results of experimental determination of Stark parameters of Ar II spectral lines. We report 126 half-width and 111 shift results, 53 half-widths and 44 shifts of which are presented here for the first time. The obtained data may be of astrophysical interest. The results were compared with available experimental results of other authors and with calculated ones in the cases where it was possible. A low-pressure pulsed arc, filled with pure argon, was used as a plasma source. All measurements were done under electron density which ranges from 0.20 × 1023 to 1.15 × 1023 m-3 and electron temperature from 16 000 to 26 000 K.

  3. Excitonic Stark effect in MoS2 monolayers

    NASA Astrophysics Data System (ADS)

    Scharf, Benedikt; Frank, Tobias; Gmitra, Martin; Fabian, Jaroslav; Žutić, Igor; Perebeinos, Vasili

    2016-12-01

    We theoretically investigate excitons in MoS2 monolayers in an applied in-plane electric field. Tight-binding and Bethe-Salpeter equation calculations predict a quadratic Stark shift, of the order of a few meV for fields of 10 V/μ m , in the linear absorption spectra. The spectral weight of the main exciton peaks decreases by a few percent with an increasing electric field due to the exciton field ionization into free carriers as reflected in the exciton wave functions. Subpicosecond exciton decay lifetimes at fields of a few tens of V/μ m could be utilized in solar energy harvesting and photodetection. We find simple scaling relations of the exciton binding, radius, and oscillator strength with the dielectric environment and an electric field, which provides a path to engineering the MoS2 electro-optical response.

  4. Quantum-confined Stark effect in band-inverted junctions

    NASA Astrophysics Data System (ADS)

    Díaz-Fernández, A.; Domínguez-Adame, F.

    2017-09-01

    Topological phases of matter are often characterized by interface states, which were already known to occur at the boundary of a band-inverted junction in semiconductor heterostructures. In IV-VI compounds such interface states are properly described by a two-band model, predicting the appearance of a Dirac cone in single junctions. We study the quantum-confined Stark effect of interface states due to an electric field perpendicular to a band-inverted junction. We find a closed expression to obtain the interface dispersion relation at any field strength and show that the Dirac cone widens under an applied bias. Thus, the Fermi velocity can be substantially lowered even at moderate fields, paving the way for tunable band-engineered devices based on band-inverted junctions.

  5. Quantum-confined Stark effects in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Wen, G. W.; Lin, J. Y.; Jiang, H. X.; Chen, Z.

    1995-08-01

    Quantum-confined Stark effects (QCSE) on excitons, i.e., the influence of a uniform electric field on the confined excitons in semiconductor quantum dots (QD's), have been studied by using a numerical matrix-diagonalization scheme. The energy levels and the wave functions of the ground and several excited states of excitons in CdS and CdS1-xSex quantum dots as functions of the size of the quantum dot and the applied electric field have been obtained. The electron and hole distributions and wave function overlap inside the QD's have also been calculated for different QD sizes and electric fields. It is found that the electron and hole wave function overlap decreases under an electric field, which implies an increased exciton recombination lifetime due to QCSE. The energy level redshift and the enhancement of the exciton recombination lifetime are due to the polarization of the electron-hole pair under the applied electric field.

  6. Stark ladder in a one-dimensional quasiperiodic system

    NASA Astrophysics Data System (ADS)

    Niizeki, K.; Matsumura, A.

    1993-08-01

    We have investigated the effect of a uniform field F on the energy spectrum of the Harper model, which includes an irrational ω and the phase variable cphi as parameters. The energy levels Ei(cphi), iEopenZ, are periodic on cphi, Ei(cphi+1)=Ei(cphi), and form a two-dimensional (2D) pattern in the cphi-E plane. The pattern which we term a 2D Wannier-Stark ladder (2DWSL) has 2D periodicity because of the equalities Ei(cphi)=iF+E0(cphi+iω), i∈openZ . The energy spectrum is a vertical section of the 2DWSL through the specified cphi and represents a quasiperiodic WSL.

  7. Atom-interferometric measurement of Stark level splittings

    NASA Astrophysics Data System (ADS)

    Zhao, Jianming; Raithel, Georg

    2016-05-01

    Rydberg atoms are highly sensitive to external electric fields due to their large polarizability, scaling as n7 (n is the principal quantum number). In cesium, nS Rydberg levels mix with nearby (n-4) high- l states, forming sequences of avoided crossings. Mixed adiabatic/diabatic passages through these crossings are employed as beam splitters and recombiners in an atom-interferometric measurement of energy level splittings. We subject cold cesium atoms to laser-excitation, electric-field and detection sequences that constitute an (internal-state) atom interferometer. For the read-out of the interferometer we utilize state-dependent collisions, which selectively remove atoms of one kind from the detected signal. We investigate the dependence of the interferometric signal on timing and field parameters, and find good agreement with quantum simulations of the interferometer. Fourier analysis of the interferometric signals yield coherence frequencies that agree with corresponding energy-level differences in calculated Stark maps.

  8. Ionization spectra of highly Stark-shifted rubidium Rydberg states

    NASA Astrophysics Data System (ADS)

    Grimmel, Jens; Stecker, Markus; Kaiser, Manuel; Karlewski, Florian; Torralbo-Campo, Lara; Günther, Andreas; Fortágh, József

    2017-07-01

    We report on the observation and numerical calculation of ionization spectra of highly Stark-shifted Rydberg states of rubidium beyond the classical ionization threshold. In the numerical calculations, a complex absorbing potential (CAP) allows us to predict the energy levels and ionization rates of Rydberg states in this regime. Our approach of adjusting the CAP to the external electric field reduces the number of free parameters from one per resonance to a single one. Furthermore, we have measured the ionization spectra of magneto-optically trapped rubidium atoms which are excited to principal quantum numbers of 43 and 70 at various electric fields. The emerging ions are detected using an ion optics. We find good agreement between the numerically and experimentally obtained spectra.

  9. Investigation of the Stark broadening of Balmer beta

    NASA Astrophysics Data System (ADS)

    Helbig, V.; Nick, K.-P.

    1981-10-01

    The Stark broadening of the Balmer line Hβ was studied in a high-current wall-stabilized arc at electron densities between 1.75 and 14.4 × 1016 cm-3. The electron density was obtained by means of a two-wavelength Michelson interferometer. The reduced half-widths of Hβ were compared with the theories of Griem et al, Vidal et al and Seidel. A slight increase in the reduced half-widths with increasing electron density was observed, just as predicted by theory. The absolute values, however, were smaller than the theoretical ones. There was good agreement with the experimental data of Bässler and Kock. The results of Wiese, Kelleher and Paquette differ from our data by 5-10% depending on the electron density.

  10. The influence of Stark broadening on Cr II spectral line shapes in stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Dimitrijević, M. S.; Ryabchikova, T.; Simić, Z.; Popović, L. Č.; Dačić, M.

    2007-07-01

    Aims:We consider the effect of Stark broadening on the shapes of Cr ii spectral lines observed in stellar atmospheres of the middle part of the main sequence. Methods: Stark broadening parameters were calculated by the semiclassical perturbation approach. For stellar spectra synthesis, the improved version synth3 of the code synth for synthetic spectrum calculations was used. Results: Stark broadening parameters for Cr ii spectral lines of seven multiplets belonging to 4s-4p transitions were calculated. New calculated Stark parameters were applied to the analysis of Cr ii line profiles observed in the spectrum of Cr-rich star HD 133792. Conclusions: We found that Stark broadening mechanism is very important and should be taken into account, especially in the study of Cr abundance stratification.

  11. Cold Ion-Molecule Chemistry with a Stark Decelerator Beamline

    NASA Astrophysics Data System (ADS)

    Oldham, James M.; Bell, Martin T.; Harper, Lee D.; Softley, Timothy P.

    2012-06-01

    We describe an experimental method for studying ion-molecule reactive collisions at very low energies. Building on our previous work using an electrostatic quadrupole guide as a source of cold neutral molecules, we discuss a proof of principle study of the charge-exchange reaction between cold xenon ions and Stark decelerated ammonia molecules. Ammonia molecules from a pulsed supersonic expansion are produced at low velocities using the Stark deceleration technique of Meijer and co-workers. The decelerated molecules are focussed using pulsed electrostatic hexapoles into the centre of a radiofrequency ion trap where they collide with cold xenon ions. A fast-opening vacuum-compatible mechanical shutter installed in the beamline is used to prevent transmission of the undecelerated molecules and carrier gas into the ion trap chamber. To prepare the target ions, the ion trap is loaded with calcium ions, which are Doppler laser cooled to form a low-temperature ordered ``Coulomb crystal'' phase. Xenon ions formed by resonant multiphoton ionisation are subsequently loaded and sympathetically cooled through their Coulomb interaction with the laser-cooled ions. The spatial distribution of fluorescence emitted by the laser-cooled ions in the multicomponent crystal is imaged; reactive collisions of Xe^+ with ND_3 are observed and quantified through changes in this distribution. By varying the high voltage switching sequence applied to the decelerator, the velocity of the ammonia molecules can be tuned from around 250 m/s to 35 m/s. For collisions with trapped xenon ions, this corresponds to collision energies (expressed in temperature units) from 65 K down to close to 1 K.

  12. Stark-induced adiabatic Raman passage for preparing polarized molecules.

    PubMed

    Mukherjee, Nandini; Zare, Richard N

    2011-07-14

    We propose a method based on Stark-induced adiabatic Raman passage (SARP) for preparing vibrationally excited molecules with known orientation and alignment for future dynamical stereochemistry studies. This method utilizes the (J, M)-state dependent dynamic Stark shifts of rovibrational levels induced by delayed but overlapping pump and Stokes pulses of unequal intensities. Under collision-free conditions, our calculations show that we can achieve complete population transfer to an excited vibrational level (v > 0) of the H(2) molecule in its ground electronic state. Specifically, the H(2) (v = 1, J = 2, M = 0) level can be prepared with complete population transfer from the (v = 0, J = 0, M = 0) level using the S(0) branch of the Raman transition with visible pump and Stoke laser pulses, each polarized parallel to the z axis (uniaxial π-π Raman pumping). Similarly, H(2) (v = 1, J = 2, M = ±2) can be prepared using SARP with a left circularly polarized pump and a right circularly (or vice versa) polarized Stokes wave propagating along the z axis (σ(±)-σ(∓) Raman pumping). This technique requires phase coherent nanosecond pulses with unequal intensity between the pump and the Stokes pulses, one being four or more times greater than the other. A peak intensity of ~16 GW/cm(2) for the stronger pulse is required to generate the desirable sweep of the Raman resonance frequency. These conditions may be fulfilled using red and green laser pulses with the duration of a few nanoseconds and optical energies of ~12 and 60 mJ within a focused beam of diameter ~0.25 mm. Additionally, complete population transfer to the v = 4 vibrational level is predicted to be possible using SARP with a 355-nm pump and a near infrared Stokes laser with accessible pulse energies.

  13. Electron Stark Broadening Database for Atomic N, O, and C Lines

    NASA Technical Reports Server (NTRS)

    Liu, Yen; Yao, Winifred M.; Wray, Alan A.; Carbon, Duane F.

    2012-01-01

    A database for efficiently computing the electron Stark broadening line widths for atomic N, O, and C lines is constructed. The line width is expressed in terms of the electron number density and electronatom scattering cross sections based on the Baranger impact theory. The state-to-state cross sections are computed using the semiclassical approximation, in which the atom is treated quantum mechanically whereas the motion of the free electron follows a classical trajectory. These state-to-state cross sections are calculated based on newly compiled line lists. Each atomic line list consists of a careful merger of NIST, Vanderbilt, and TOPbase line datasets from wavelength 50 nm to 50 micrometers covering the VUV to IR spectral regions. There are over 10,000 lines in each atomic line list. The widths for each line are computed at 13 electron temperatures between 1,000 K 50,000 K. A linear least squares method using a four-term fractional power series is then employed to obtain an analytical fit for each line-width variation as a function of the electron temperature. The maximum L2 error of the analytic fits for all lines in our line lists is about 5%.

  14. Static Properties and Stark Effect of the Ground State of the HD Molecular Ion

    NASA Technical Reports Server (NTRS)

    Bhatia, A. K.; Drachman, Richard J.

    1999-01-01

    We have calculated static properties of the ground state of the HD(+) ion and its lowest-lying P-state without making use of the Born-Oppenheimer approximation, as was done in the case of H2(+) and D2(+) [Phys. Rev. A 58, 2787 (1998)]. The ion is treated as a three-body system whose ground state is spherically symmetric. The wavefunction is of generalized Hylleraas type, but it is necessary to include high powers of the internuclear distance to localize the nuclear motion. We obtain good values of the energies of the ground S-state and lowest P-state and compare them with earlier calculations. Expectation values are obtained for various operators, the Fermi contact parameters, and the permanent quadrupole moment. The cusp conditions are also calculated. The polarizability was then calculated using second-order perturbation theory with intermediate P pseudostates. Since the nuclei in HD(+) are not of equal mass there is dipole coupling between the lowest two rotational states, which are almost degenerate. This situation is carefully analyzed, and the Stark shift is calculated variationally as a function of the applied electric field.

  15. Observation and Measurement of MHD Activity Using Motional Stark Effect (MSE) Diagnostic

    SciTech Connect

    Jayakumar, R; Makowski, M; Allen, S; Moller, J; Rhodes, T

    2004-06-25

    In a new mode of measurement, the amplitude of a tearing mode rotating at frequencies of up to tens of KHz has been obtained using the spectral features of high frequency MSE data. A formulation has been developed to calculate the pitch angle oscillations associated with these instabilities, from the MSE spectrum. Density fluctuations can be simultaneously obtained from MSE measurements if the intensity response to density variation can be calibrated. Examples of observations are given and detection limits are explored.

  16. Many-body and stark effects in transition metal dichalcogenides monolayers (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Scharf, Benedikt; Frank, Tobias; Gmitra, Martin; Fabian, Jaroslav; Zutic, Igor; Perebeinos, Vasili

    2016-10-01

    Inversion symmetry breaking combined with strong spin-orbit coupling in transition metal dichalcogenides such as MoS2 offers important opportunities for spintronics. We investigate excitons in MoS2 monolayers in an applied in-plane electric field. Tight-binding and Bethe-Salpeter equation calculations predict a large quadratic Stark shift. The scaling of the Stark shifts with the exciton binding energy and the dielectric environment provides a path to engineering the MoS2 electro-optical response. Our results suggest that the excitonic Stark effect can be observed experimentally in a MoS2 monolayer and we explain its implications for spintronic devices.

  17. Stark II and physician compensation models: integrating business and legal issues.

    PubMed

    Pursell, David; Marsh, Jennifer; Thompson, David; Potter, Keith

    2005-01-01

    In March of 2004, the Centers for Medicare & Medicaid Services released new regulations that interpreted the Federal Physician Self Referral Act, otherwise known as Stark II. The new regulations, commonly referred to as the Phase II regulations, must be carefully considered when structuring physician compensation models. Stark II generally holds that physicians may not make a referral for designated health services to an entity with which they have a direct or indirect financial relationship. This Article outlines the provisions of Stark II that are applicable to physician compensation methodologies. In addition, the authors evaluate hypothetical transactions involving physician groups seeking viable compensation schemes and explore the validity and risks of each.

  18. Observation and cancellation of a perturbing dc stark shift in strontium optical lattice clocks.

    PubMed

    Lodewyck, Jérôme; Zawada, Michal; Lorini, Luca; Gurov, Mikhail; Lemonde, Pierre

    2012-03-01

    We report on the observation of a dc Stark frequency shift at the 10-(13) level by comparing two strontium optical lattice clocks. This frequency shift arises from the presence of electric charges trapped on dielectric surfaces placed under vacuum close to the atomic sample. We show that these charges can be eliminated by shining UV light on the dielectric surfaces, and characterize the residual dc Stark frequency shift on the clock transition at the 10-(18) level by applying an external electric field. This study shows that the dc Stark shift can play an important role in the accuracy budget of lattice clocks, and should be duly taken into account.

  19. Electrostatically Shielded Quantum Confined Stark Effect Inside Polar Nanostructures

    PubMed Central

    2009-01-01

    The effect of electrostatic shielding of the polarization fields in nanostructures at high carrier densities is studied. A simplified analytical model, employing screened, exponentially decaying polarization potentials, localized at the edges of a QW, is introduced for the ES-shielded quantum confined Stark effect (QCSE). Wave function trapping within the Debye-length edge-potential causes blue shifting of energy levels and gradual elimination of the QCSE red-shifting with increasing carrier density. The increase in the e−h wave function overlap and the decrease of the radiative emission time are, however, delayed until the “edge-localization” energy exceeds the peak-voltage of the charged layer. Then the wave function center shifts to the middle of the QW, and behavior becomes similar to that of an unbiased square QW. Our theoretical estimates of the radiative emission time show a complete elimination of the QCSE at doping densities ≥1020 cm−3, in quantitative agreement with experimental measurements. PMID:20596407

  20. Giant Stark effect in double-stranded porphyrin ladder polymers

    NASA Astrophysics Data System (ADS)

    Pramanik, Anup; Kang, Hong Seok

    2011-03-01

    Using the first-principles calculations, we have investigated the stability and the electronic structure of two types of recently synthesized one-dimensional nanoribbons, i.e., double-stranded zinc(II) porphyrin ladder polymer (LADDER) arrays. First, electronic structure calculations were used to show that the LADDER is a semiconductor. Most importantly, the application of a transverse electric field significantly reduces the band gap of the LADDER, ultimately converting the LADDER to a metal at a field strength of 0.1 V/Å. The giant Stark effect in this case is almost as strong as that in boron nitride nanotubes and nanoribbons. In the presence of an electric field, hole conduction and electronic conduction will occur entirely through spatially separated strands, rendering these materials useful for nanoelectronic devices. Second, the substitution of hydrogen atoms in the porphyrin units or that of zinc ions with other kinds of chemical species is found to increase the binding strength of the LADDER and reduce the band gap.

  1. Stark-shift based quantum dot-cavity electrometer

    NASA Astrophysics Data System (ADS)

    Tsukanov, Alexander V.; Chekmachev, Vadim G.

    2016-12-01

    In this paper we propose the scheme of an optical quantum sensor of external electric field which design based on a double quantum dot (DQD) placed in a high quality optical semiconductor microcavity (MC). The characteristic DQD frequencies of the observed nontrivial single-electron dynamics are determined using spectroscopic simulation in the steady-state regime. Due to Stark shifts of excited energy levels of DQD located at the edge of microdisk the hybrid electron-photon spectrum changes depending on the strength and direction of electric field. Probe laser with tunable wavelength excites the structure in single-photon regime and photon spectrum from MC is detected. We analyze the system's behavior with the use of a standard technique based on solving the Lindblad equation for the density matrix of an electron-phonon system with regard to the escape of photons from the cavity to the continuum and the relaxation of an excited electron with the emission of a photon or phonon. It will be shown that due to the design features, such a device has several advantages: high sensitivity, availability of different channels for excitation and measuring, the ability to accurately detect the spatial distribution of the field.

  2. Nanoscale spin rectifiers controlled by the Stark effect

    NASA Astrophysics Data System (ADS)

    Rossella, Francesco; Bertoni, Andrea; Ercolani, Daniele; Rontani, Massimo; Sorba, Lucia; Beltram, Fabio; Roddaro, Stefano

    2014-12-01

    The control of orbitals and spin states of single electrons is a key ingredient for quantum information processing and novel detection schemes and is, more generally, of great relevance for spintronics. Coulomb and spin blockade in double quantum dots enable advanced single-spin operations that would be available even for room-temperature applications with sufficiently small devices. To date, however, spin operations in double quantum dots have typically been observed at sub-kelvin temperatures, a key reason being that it is very challenging to scale a double quantum dot system while retaining independent field-effect control of individual dots. Here, we show that the quantum-confined Stark effect allows two dots only 5 nm apart to be independently addressed without the requirement for aligned nanometre-sized local gating. We thus demonstrate a scalable method to fully control a double quantum dot device, regardless of its physical size. In the present implementation we present InAs/InP nanowire double quantum dots that display an experimentally detectable spin blockade up to 10 K. We also report and discuss an unexpected re-entrant spin blockade lifting as a function of the magnetic field intensity.

  3. DC and subcycle-resolved AC Stark shifts in Helium

    NASA Astrophysics Data System (ADS)

    Liu, Aihua; Thumm, Uwe

    2012-06-01

    We are developing a finite element discrete variable representation (FE-DVR) code to model the response of two-electron atoms to ultra-short pulses of EM radiation. Our first numerical results for the DC stark shift of helium deviate significantly from previous [1] single-active-electron (SAE), but are in close agreement with improved SAE calculations that include the effect of core polarization in the external field. For 3x10^14 W/cm^2 infra red fields, we calculate sub-IR-cycle- resolved instantaneous (AC) level shifts of low-lying bound He states that also strongly deviate from the SAE prediction [1]. We plan to apply our code to model recently measured subcycle time-resolved absorption spectra [2].[4pt] [1] F. He, C. Ruiz, A. Becker, and U. Thumm, J. Phys. B 44, 211001 (2011).[0pt] [2] H. Wang, M. Chini, S. Chen, C.-H. Zhang, F. He, Y. Cheng, Y. Wu, U. Thumm, and Z. Chang, Phys. Rev. Lett. 105, 143002 (2010); M. Chini, Z. Chang et al., to be published.

  4. DLTS study of the Wannier-Stark effect in Ge/Si QD superlattices

    NASA Astrophysics Data System (ADS)

    Sobolev, Mikhail M.; Cirlin, Georgii E.; Tonkikh, Alexander A.

    2007-12-01

    Deep-level transient spectroscopy (DLTS) has been applied to study the emission of electrons from quantum states in a 20-layer quantum-dot superlattice (QDSL) of Ge in a Ge/Si p-n heterostructure. Changes in the DLTS spectra of this structure strongly depend on the applied bias Ur. There are three bias ranges corresponding to three modes of the Wannier-Stark effect: Wannier-Stark ladder mode, Wannier-Stark localization and non-resonant Zener tunneling. The DLTS peaks for all the three modes are associated with emission of electrons from deep-level defects into the Wannier-Stark localized states resulting from the splitting of the electron miniband of the Ge/Si QDSL.

  5. A study of Stark broadening for the diagnostic of runaway electrons in ITER

    NASA Astrophysics Data System (ADS)

    Rosato, J.; Pandya, S. P.; Logeais, Ch.; Meireni, M.; Hannachi, I.; Reichle, R.; Barnsley, R.; Marandet, Y.; Stamm, R.

    2017-03-01

    We investigate the Stark broadening of hydrogen lines in tokamak edge plasma conditions in the presence of a beam of relativistic "runaway" electrons. The possibility for a diagnostic involving passive spectroscopy is discussed.

  6. Examining the impact of the new Stark rules on joint ventures.

    PubMed

    Washlick, John R

    2008-11-01

    The new Stark rules will affect joint ventures involving physicians and hospitals in four primary areas: Services provided "under arrangement". "Per click" lease arrangements. Percentage-based compensation. "Stand-in-the-shoes" provisions.

  7. Stark broadening of Zr IV spectral lines in the atmospheres of chemically peculiar stars

    NASA Astrophysics Data System (ADS)

    Majlinger, Zlatko; Simić, Zoran; Dimitrijević, Milan S.

    2017-09-01

    Stark widths for 18 Zr IV spectral lines have been calculated by using the modified semi-empirical method. The obtained results have been used to investigate the influence of Stark broadening on the spectra of atmospheres of chemically peculiar stars of A spectral type and hydrogen-rich DA and helium-rich DB white dwarfs. Our results have been used also to test possibility to predict new data using some approximate methods developed on the basis on regularities and systematic trends.

  8. VizieR Online Data Catalog: Stark broadening of Cd I spectral lines (Simic+, 2005)

    NASA Astrophysics Data System (ADS)

    Simic, Z.; Dimitrijevic, M. S.; Milovanovic, N.; Sahal-Brechot, S.

    2005-09-01

    Stark broadening parameters, widths, and shifts for 33 CdI singlets and 37 triplets were calculated using the semiclassical perturbation method. The results were compared with available experimental and theoretical data. Also, regularity in the spectral series 5s2 1S-np 1Po was investigated. The influence of Stark broadening was analyzed in A-type stellar atmospheres. (2 data files).

  9. Optimizing the Stark-decelerator beamline for the trapping of cold molecules using evolutionary strategies

    SciTech Connect

    Gilijamse, Joop J.; Kuepper, Jochen; Hoekstra, Steven; Vanhaecke, Nicolas; Meerakker, Sebastiaan Y. T. van de; Meijer, Gerard

    2006-06-15

    We demonstrate feedback control optimization for the Stark deceleration and trapping of neutral polar molecules using evolutionary strategies. In a Stark-decelerator beamline, pulsed electric fields are used to decelerate OH radicals and subsequently store them in an electrostatic trap. The efficiency of the deceleration and trapping process is determined by the exact timings of the applied electric field pulses. Automated optimization of these timings yields an increase of 40% of the number of trapped OH radicals.

  10. Regularities And Irregularities Of The Stark Parameters For Single Ionized Noble Gases

    NASA Astrophysics Data System (ADS)

    Peláez, R. J.; Djurovic, S.; Cirišan, M.; Aparicio, J. A.; Mar S.

    2010-07-01

    Spectroscopy of ionized noble gases has a great importance for the laboratory and astrophysical plasmas. Generally, spectra of inert gases are important for many physics areas, for example laser physics, fusion diagnostics, photoelectron spectroscopy, collision physics, astrophysics etc. Stark halfwidths as well as shifts of spectral lines are usually employed for plasma diagnostic purposes. For example atomic data of argon krypton and xenon will be useful for the spectral diagnostic of ITER. In addition, the software used for stellar atmosphere simulation like TMAP, and SMART require a large amount of atomic and spectroscopic data. Availability of these parameters will be useful for a further development of stellar atmosphere and evolution models. Stark parameters data of spectral lines can also be useful for verification of theoretical calculations and investigation of regularities and systematic trends of these parameters within a multiplet, supermultiplet or transition array. In the last years, different trends and regularities of Stark parameters (halwidths and shifts of spectral lines) have been analyzed. The conditions related with atomic structure of the element as well as plasma conditions are responsible for regular or irregular behaviors of the Stark parameters. The absence of very close perturbing levels makes Ne II as a good candidate for analysis of the regularities. Other two considered elements Kr II and Xe II with complex spectra present strong perturbations and in some cases an irregularities in Stark parameters appear. In this work we analyze the influence of the perturbations to Stark parameters within the multiplets.

  11. Classifying Motion.

    ERIC Educational Resources Information Center

    Duzen, Carl; And Others

    1992-01-01

    Presents a series of activities that utilizes a leveling device to classify constant and accelerated motion. Applies this classification system to uniform circular motion and motion produced by gravitational force. (MDH)

  12. Classifying Motion.

    ERIC Educational Resources Information Center

    Duzen, Carl; And Others

    1992-01-01

    Presents a series of activities that utilizes a leveling device to classify constant and accelerated motion. Applies this classification system to uniform circular motion and motion produced by gravitational force. (MDH)

  13. QM/MM Prediction of the Stark Shift in the Active Site of a Protein.

    PubMed

    Sandberg, Daniel J; Rudnitskaya, Aleksandra N; Gascón, José A

    2012-08-14

    Recent developments in the biophysical characterization of proteins have provided a means of directly measuring electrostatic fields by introducing a probe molecule to the system of interest and interpreting photon absorption in the context of the Stark effect. To fully account for this effect, the development of accurate atomistic models is of paramount importance. However, suitable computational protocols for evaluating Stark shifts in proteins are yet to be established. In this work, we present a comprehensive computational method to predict the change in absorption frequency of a probe functional group as a direct result of a perturbation in its surrounding electrostatic field created by a protein environment, i.e., the Stark shift. We apply the method to human aldose reductase, a key protein enzyme that catalyzes the reduction of monosaccharides. We develop a protocol based on a combination of molecular dynamics and moving-domain QM/MM methods, which achieves quantitative agreement with experiment. We outline the difficulties in predicting localized electrostatic field changes within a protein environment, and by extension the Stark shift, due to a protein site mutation. Furthermore, the combined use of Stark effect spectroscopy and computational modeling is used to predict the protonation state of ionizable residues in the vicinity of the electrostatic probe.

  14. Optical Stark Effects in J -Aggregate-Metal Hybrid Nanostructures Exhibiting a Strong Exciton-Surface-Plasmon-Polariton Interaction

    NASA Astrophysics Data System (ADS)

    Vasa, P.; Wang, W.; Pomraenke, R.; Maiuri, M.; Manzoni, C.; Cerullo, G.; Lienau, C.

    2015-01-01

    We report on the observation of optical Stark effects in J -aggregate-metal hybrid nanostructures exhibiting strong exciton-surface-plasmon-polariton coupling. For redshifted nonresonant excitation, pump-probe spectra show short-lived dispersive line shapes of the exciton-surface-plasmon-polariton coupled modes caused by a pump-induced Stark shift of the polariton resonances. For larger coupling strengths, the sign of the Stark shift is reversed by a transient reduction in normal mode splitting. Our studies demonstrate an approach to coherently control and largely enhance optical Stark effects in strongly coupled hybrid systems. This may be useful for applications in ultrafast all-optical switching.

  15. Interplay of Bias-Driven Charging and the Vibrational Stark Effect in Molecular Junctions

    SciTech Connect

    Li, Yajing; Zolotavin, Pavlo; Doak, Peter; Kronik, Leeor; Neaton, Jeffrey B.; Natelson, Douglas

    2016-01-27

    We observe large, reversible, bias driven changes in the vibrational energies of PCBM based on simultaneous transport and surface-enhanced Raman spectroscopy (SERS) measurements on PCBM-gold junctions. A combination of linear and quadratic shifts in vibrational energies with voltage is analyzed and compared with similar measurements involving C-60-gold junctions. A theoretical model based on density functional theory (DFT) calculations suggests that both a vibrational Stark effect and bias-induced charging of the junction contribute to the shifts in vibrational energies. In the PCBM case, a linear vibrational Stark effect is observed due to the permanent electric dipole moment of PCBM. The vibrational Stark shifts shown here for PCBM junctions are comparable to or larger than the charging effects that dominate in C-60 junctions.

  16. Interplay of Bias-Driven Charging and the Vibrational Stark Effect in Molecular Junctions

    DOE PAGES

    Li, Yajing; Zolotavin, Pavlo; Doak, Peter; ...

    2016-01-27

    We observe large, reversible, bias driven changes in the vibrational energies of PCBM based on simultaneous transport and surface-enhanced Raman spectroscopy (SERS) measurements on PCBM-gold junctions. A combination of linear and quadratic shifts in vibrational energies with voltage is analyzed and compared with similar measurements involving C-60-gold junctions. A theoretical model based on density functional theory (DFT) calculations suggests that both a vibrational Stark effect and bias-induced charging of the junction contribute to the shifts in vibrational energies. In the PCBM case, a linear vibrational Stark effect is observed due to the permanent electric dipole moment of PCBM. The vibrationalmore » Stark shifts shown here for PCBM junctions are comparable to or larger than the charging effects that dominate in C-60 junctions.« less

  17. Quantum interferometry of degenerate Rydberg states using a temporary dc Stark splitting

    NASA Astrophysics Data System (ADS)

    Ryabtsev, I. I.; Beterov, I. M.

    2000-06-01

    A method for quantum interferometry and phase control of degenerate Rydberg states has been proposed and realized experimentally. Phase control was carried out by a pulse of a weak dc electric field which caused a Stark splitting of degenerate Rydberg sublevels for a short time. A strong interference dependence of the probability of the microwave transition 37P3/2-->37S1/2 in sodium Rydberg atoms on a phase difference between the Stark sublevels of the 37P3/2 state has been detected. Changes in the probability were measured directly by a pulsed resonant microwave radiation applied after the electric-field pulse. Records of the quantum interference signals and Stark spectra of the microwave transition are presented and discussed. An influence of the laboratory magnetic field has been analyzed.

  18. Enhanced Quantum Confined Stark Effect in a mesoporous hybrid multifunctional system

    NASA Astrophysics Data System (ADS)

    Gogoi, M.; Deb, P.; Sen, D.; Mazumder, S.; Kostka, A.

    2014-06-01

    Quantum Confined Stark Effect in hybrid of CdTe quantum dot with superparamagnetic iron oxide nanoparticles in both nonporous and mesoporous silica matrix has been realized. The observed QCSE is due to the local electric field induced by charge dispersion at SiO2/polar solvent interface. Enhanced Stark shift of 89.5 meV is observed in case of mesoporous hybrid structure and the corresponding local electric field has been evaluated as 4.38×104 V/cm. The enhancement is assumed to be caused by greater density of charge in the mesoporous hybrid. The conjugation of superparamagnetic nanoparticles in this tailored hybrid microstructure has not imparted any alteration to the Stark shift, but has added multifunctional attribute. The present study on the local electric field induced enhanced QCSE with wavelength modulation towards red end paves the way of developing magneto-fluorescent hybrid systems for biomedical imaging application.

  19. Large polarization-dependent exciton optical Stark effect in lead iodide perovskites

    SciTech Connect

    Yang, Ye; Yang, Mengjin; Zhu, Kai; Johnson, Justin C.; Berry, Joseph J.; van de Lagemaat, Jao; Beard, Matthew C.

    2016-08-31

    A strong interaction of a semiconductor with a below-bandgap laser pulse causes a blue-shift of the bandgap transition energy, known as the optical Stark effect. The energy shift persists only during the pulse duration with an instantaneous response time. The optical Stark effect has practical relevance for applications, including quantum information processing and communication, and passively mode-locked femtosecond lasers. Here we demonstrate that solution-processable lead-halide perovskites exhibit a large optical Stark effect that is easily resolved at room temperature resulting from the sharp excitonic feature near the bandedge. We also demonstrate that a polarized pump pulse selectively shifts one spin state producing a spin splitting of the degenerate excitonic states. Such selective spin manipulation is an important prerequisite for spintronic applications. Lastly, our result implies that such hybrid semiconductors may have great potential for optoelectronic applications beyond photovoltaics.

  20. Virtual Atomic and Molecular Data Center (VAMDC) and Stark-B Database

    NASA Astrophysics Data System (ADS)

    Dimitrijevic, M. S.; Sahal-Brechot, S.; Kovacevic, A.; Jevremovic, D.; Popovic, L. C.; VAMDC Consortium; Dubernet, Marie-Lise

    2012-01-01

    Virtual Atomic and Molecular Data Center (VAMDC) is an European FP7 project with aims to build a flexible and interoperable e-science environment based interface to the existing Atomic and Molecular data. The VAMDC will be built upon the expertise of existing Atomic and Molecular databases, data producers and service providers with the specific aim of creating an infrastructure that is easily tuned to the requirements of a wide variety of users in academic, governmental, industrial or public communities. In VAMDC will enter also STARK-B database, containing Stark broadening parameters for a large number of lines, obtained by the semiclassical perturbation method during more than 30 years of collaboration of authors of this work (MSD and SSB) and their co-workers. In this contribution we will review the VAMDC project, STARK-B database and discuss the benefits of both for the corresponding data users.

  1. Large polarization-dependent exciton optical Stark effect in lead iodide perovskites

    PubMed Central

    Yang, Ye; Yang, Mengjin; Zhu, Kai; Johnson, Justin C.; Berry, Joseph J.; van de Lagemaat, Jao; Beard, Matthew C.

    2016-01-01

    A strong interaction of a semiconductor with a below-bandgap laser pulse causes a blue-shift of the bandgap transition energy, known as the optical Stark effect. The energy shift persists only during the pulse duration with an instantaneous response time. The optical Stark effect has practical relevance for applications, including quantum information processing and communication, and passively mode-locked femtosecond lasers. Here we demonstrate that solution-processable lead-halide perovskites exhibit a large optical Stark effect that is easily resolved at room temperature resulting from the sharp excitonic feature near the bandedge. We also demonstrate that a polarized pump pulse selectively shifts one spin state producing a spin splitting of the degenerate excitonic states. Such selective spin manipulation is an important prerequisite for spintronic applications. Our result implies that such hybrid semiconductors may have great potential for optoelectronic applications beyond photovoltaics. PMID:27577007

  2. Large polarization-dependent exciton optical Stark effect in lead iodide perovskites

    NASA Astrophysics Data System (ADS)

    Yang, Ye; Yang, Mengjin; Zhu, Kai; Johnson, Justin C.; Berry, Joseph J.; van de Lagemaat, Jao; Beard, Matthew C.

    2016-08-01

    A strong interaction of a semiconductor with a below-bandgap laser pulse causes a blue-shift of the bandgap transition energy, known as the optical Stark effect. The energy shift persists only during the pulse duration with an instantaneous response time. The optical Stark effect has practical relevance for applications, including quantum information processing and communication, and passively mode-locked femtosecond lasers. Here we demonstrate that solution-processable lead-halide perovskites exhibit a large optical Stark effect that is easily resolved at room temperature resulting from the sharp excitonic feature near the bandedge. We also demonstrate that a polarized pump pulse selectively shifts one spin state producing a spin splitting of the degenerate excitonic states. Such selective spin manipulation is an important prerequisite for spintronic applications. Our result implies that such hybrid semiconductors may have great potential for optoelectronic applications beyond photovoltaics.

  3. Large polarization-dependent exciton optical Stark effect in lead iodide perovskites

    DOE PAGES

    Yang, Ye; Yang, Mengjin; Zhu, Kai; ...

    2016-08-31

    A strong interaction of a semiconductor with a below-bandgap laser pulse causes a blue-shift of the bandgap transition energy, known as the optical Stark effect. The energy shift persists only during the pulse duration with an instantaneous response time. The optical Stark effect has practical relevance for applications, including quantum information processing and communication, and passively mode-locked femtosecond lasers. Here we demonstrate that solution-processable lead-halide perovskites exhibit a large optical Stark effect that is easily resolved at room temperature resulting from the sharp excitonic feature near the bandedge. We also demonstrate that a polarized pump pulse selectively shifts one spinmore » state producing a spin splitting of the degenerate excitonic states. Such selective spin manipulation is an important prerequisite for spintronic applications. Lastly, our result implies that such hybrid semiconductors may have great potential for optoelectronic applications beyond photovoltaics.« less

  4. A new questionnaire for measuring quality of life - the Stark QoL.

    PubMed

    Hardt, Jochen

    2015-10-26

    The Stark questionnaire measures health-related quality of life (QoL) using pictures almost exclusively. It is supplemented by a minimum of words. It comprises a mental and a physical health component. A German sample of n = 500 subjects, age and gender stratified, filled out the Stark Qol questionnaire along with various other questionnaires via internet. The physical component shows good reliability (Cronbach's alpha = McDonalds Omega = greatest lower bound = .93), the mental component can be improved (Cronbach's alpha = .63, McDonalds Omega = .72, greatest lower bound = .77). Confirmatory factor analysis shows a good fit (Bentlers CFI = .97). Construct validity was proven. The Stark QoL is a promising new development in measuring QoL, it is a short and easy to apply questionnaire. Additionally, it is particularly promising for international research.

  5. New and rapid analytical procedure for water content determination: microwave accelerated Dean-Stark.

    PubMed

    Veillet, Sébastien; Tomao, Valérie; Visinoni, Franco; Chemat, Farid

    2009-01-26

    Development of new procedures in analytical chemistry is currently increasingly focussed on reducing the time, cost and energy to carry out routine analyses. The conventional Dean-Stark (CDS) distillation to determine the water content is one of the most commonly used analytical methods and uses large amounts of solvent and energy. A new microwave accelerated Dean-Stark (MADS) distillation is presented as an alternative procedure. Microwaves were applied to a mixture of toluene, Weflon stir bar and olives, and the corresponding water was collected in a Dean-Stark receiver. This procedure permits fast and efficient determination of the water content of olives. Reliability and reproducibility were evaluated using statistical analyses. Different matrices were then used with MADS and the results were compared to CDS. Water determination from olives with MADS was better than that with CDS in terms of energy saving, rapidity (10 min versus 120 min), reproducibility, and cleanliness.

  6. On spectral line Stark broadening parameters needed for stellar and laboratory plasma investigations.

    NASA Astrophysics Data System (ADS)

    Dimitrijević, M. S.

    1995-03-01

    This paper presents a review of semiclassical calculations of Stark broadening parameters and a comparison of different semiclassical procedures is discussed, as well as the agreement with critically selected experimental data and more sophisticated, close coupling calculations. Approximate methods for the calculation of Stark broadening parameters, useful especially in such astrophysical problems where large scale calculations and analyses must be performed and where a good average accuracy is expected, have also been discussed. The beginning and development of line shapes investigations in Yugoslavia has been described as well.

  7. A Stark-tuned, far-infrared laser for high frequency plasma diagnostics

    SciTech Connect

    Mansfield, D.K.; Vocaturo, M.; Guttadora, L.; Rockmore, M.; Micai, K. . Plasma Physics Lab.); Krug, P.A. . School of Physics)

    1992-03-01

    A Stark-tuned optically pumped far-infrared methanol laser operating at 119 micrometers has been built. The laser is designed to operate at high power while exhibiting a well-separated Stark doublet. At a pump power of 65 Watts and electric field of 1 kV/cm the laser has delivered over 100 mW c.w. while exhibiting a frequency splitting of 34 MHz. These parameters indicate that this laser would be suitable for use in the present generation of modulated interferometers on large thermonuclear plasma devices. The achieved modulation frequency is more than an order of magnitude higher than could be achieved using standard techniques.

  8. A Riemann-Hilbert approach to the inverse problem for the Stark operator on the line

    NASA Astrophysics Data System (ADS)

    Its, A.; Sukhanov, V.

    2016-05-01

    The paper is concerned with the inverse scattering problem for the Stark operator on the line with a potential from the Schwartz class. In our study of the inverse problem, we use the Riemann-Hilbert formalism. This allows us to overcome the principal technical difficulties which arise in the more traditional approaches based on the Gel’fand-Levitan-Marchenko equations, and indeed solve the problem. We also produce a complete description of the relevant scattering data (which have not been obtained in the previous works on the Stark operator) and establish the bijection between the Schwartz class potentials and the scattering data.

  9. Experimental transition probabilities and Stark-broadening parameters of neutral and single ionized tin

    NASA Technical Reports Server (NTRS)

    Miller, M. H.; Roig, R. A.; Bengtson, R. D.

    1979-01-01

    Strengths and Stark-effect widths of the Sn I and Sn II lines prominent between 3200 and 7900 A are measured with a spectroscopic shock tube. Absolute strengths of 17 ionic lines are obtained with estimated (22-50)% accuracy and conform to appropriate quantum-mechanical sum rules. Relative transition probabilities for nine prominent neutral tin lines, normalized to radiative-lifetime data, are compared with other experiments and theoretical predictions. Parameters for Stark-effect broadening are measured over a range of plasma electron densities. Broadening data (with accuracies of 15-35%) for one neutral and ten ionic lines of tin are compared to theoretical predictions.

  10. Controlling the Excited-State Dynamics of Nuclear Spin Isomers Using the Dynamic Stark Effect.

    PubMed

    Waldl, Maria; Oppel, Markus; González, Leticia

    2016-07-14

    Stark control of chemical reactions uses intense laser pulses to distort the potential energy surfaces of a molecule, thus opening new chemical pathways. We use the concept of Stark shifts to convert a local minimum into a local maximum of the potential energy surface, triggering constructive and destructive wave-packet interferences, which then induce different dynamics on nuclear spin isomers in the electronically excited state of a quinodimethane derivative. Model quantum-dynamical simulations on reduced dimensionality using optimized ultrashort laser pulses demonstrate a difference of the excited-state dynamics of two sets of nuclear spin isomers, which ultimately can be used to discriminate between these isomers.

  11. Stark Broadening Of Heavy Metal Spectral Lines In Atmospheres Of Chemically Peculiar Stars

    NASA Astrophysics Data System (ADS)

    Simic, Z.

    2010-07-01

    Data on the Stark broadening of heavy metal spectral lines are of interest not only for laboratory but also for astrophysical plasma research as e.g. for stellar spectra analysis and synthesis. Here, we investigated theoretically the influence of collisions with charged particles on heavy metal spectral line profiles for Te I, Cr II, Mn II, Au II, Cu III, Zn III, Se III, In III and Sn III in spectra of A stars and white dwarfs. We applied semiclassical theory of Sahal-Bréchot since the most of published results in literature until now are determined using this method. When it can not be applied in an adequate way, due to the lack of reliable atomic data, we used modified semiempirical theory of Dimitrijevic & Konjevic, Dimitrijevic & Králjanin. Stark broadening parameters, widths and shifts, were obtained for spectral lines of neutral emitter Te I, singly charged emitters Cr II, Mn II and Au II and doubly charged emitters Cu III, Zn III, Se III, In III and Sn III. We considered as well the contributions of different collision processes to the total Stark width in comparison with Doppler one. In this case we obtained distributions for elastic, strong, inelastic collisions from upper and lower levels. For example, chromium lines are interesting due to their presence in stellar atmospheres, so that they give possibility to determine chromium abundance and investigate chromium stratification in stelar atmospheres and to be used for the diagnostics of stellar plasma and for more rafined synthesis of stellar spectra. We consider the effect of Stark broadening on the shapes of Cr II spectral lines observed in the spectra of stars in the middle part of the main sequence. Stark broadening parameters were calculated by the semic- lassical perturbation approach. For stellar spectra synthesis, the improved version SYNTH3 of the code SYNTH for synthetic spectrum calculations was used. Stark broadening parameters for Cr II spectral lines of seven multiplets belonging to 4s-4p

  12. Stark broadening of heavy metal spectral lines in atmospheres of chemically peculiar stars

    NASA Astrophysics Data System (ADS)

    Simić, Zoran

    2010-11-01

    Data on the Stark broadening of heavy metal spectral lines are of interest not only for laboratory but also for astrophysical plasma research as e.g. for stellar spectra analysis and synthesis. Here, we investigated theoretically the influence of collisions with charged particles on heavy metal spectral line profiles for Te I, Cr II, Mn II, Au II, Cu III, Zn III, Se III, In III and Sn III in spectra of A stars and white dwarfs. We applied semiclassical theory of Sahal-Bréchot since the most of published results in literature until now are determined using this method. When it can not be applied in an adequate way, due to the lack of reliable atomic data, we used modified semiempirical theory of Dimitrijević & Konjević, Dimitrijević & Kršljanin. Stark broadening parameters, widths and shifts, were obtained for spectral lines of neutral emitter Te I, singly charged emitters Cr II, Mn II and Au II and doubly charged emitters Cu III, Zn III, Se III, In III and Sn III. We considered as well the contributions of different collision processes to the total Stark width in comparison with Doppler one. In this case we obtained contributions for elastic, strong and inelastic collisions for upper and lower levels. For example, chromium lines are interesting due to their presence in stellar atmospheres, so that they give possibility to determine chromium abundance and investigate chromium stratification in stelar atmospheres and to be used for the diagnostics of stellar plasma and for more refined synthesis of stellar spectra. We consider the effect of Stark broadening on the shapes of Cr II spectral lines observed in the spectra of stars in the middle part of the main sequence. Stark broadening parameters were calculated by the semiclassical perturbation approach. For stellar spectra synthesis, the improved version SYNTH3 of the code SYNTH for synthetic spectrum calculations was used. Stark broadening parameters for Cr II spectral lines of seven multiplets belonging to 4s

  13. Optical Stark decelerator for molecules with a traveling potential well

    NASA Astrophysics Data System (ADS)

    Deng, Lianzhong; Hou, Shunyong; Yin, Jianping

    2017-03-01

    We propose a versatile scheme to slow supersonically cooled molecules using a decelerating potential well, obtained by steering a focusing laser beam onto a pair of spinning reflective mirrors under a high-speed brake. The longitudinal motion of molecules in the moving red-detuned light field is analyzed and their corresponding phase-space stability is investigated. Trajectories of C H4 molecules under the influence of the potential well are simulated using the Monte Carlo method. For instance, with a laser beam of power 20 kW focused onto a spot of waist radius 40-100 μm, corresponding to a peak laser intensity on the order of ˜108W /c m2 , a C H4 molecule of ˜250 m /s can be decelerated to ˜10 m /s over a distance of a few centimeters on a time scale of hundreds of microseconds.

  14. Electron Capture from Linear Stark Rydberg States above the Matching Velocity

    NASA Astrophysics Data System (ADS)

    Ciocca, M.; Creasey, C.; MacAdam, K. B.

    1998-05-01

    The relative cross section for electron capture by singly charged ions from linear Stark Rydberg states of Na has been measured, both as a function of the angle of impact and of projectile velocity. The target, the topmost state of the n = 24 Stark manifold, was prepared by two-step laser excitation from the Na ground state, via 3p_3/2, in an electric field F_Stark= 160 V/cm. By means of a device perfected in our laboratory (the "Stark Barrel"), we aligned the target by adiabatically switching the electric field, after excitation, down to a preset low value and a desired direction in the plane determined by the ion and Na beams. Thermionic emission ion sources of Li and Na were operated at accelerating voltages 400-2000 V to allow study of electron capture in the reduced velocity range v = 1.0 - 2.5. This augments an earlier study by Homan footnote D. M. Homan, Ph. D. Dissertation, University of Kentucky 1997, unpublished. at lower velocities.

  15. Selectively tunable optical Stark effect of anisotropic excitons in atomically thin ReS2

    PubMed Central

    Sim, Sangwan; Lee, Doeon; Noh, Minji; Cha, Soonyoung; Soh, Chan Ho; Sung, Ji Ho; Jo, Moon-Ho; Choi, Hyunyong

    2016-01-01

    The optical Stark effect is a coherent light–matter interaction describing the modification of quantum states by non-resonant light illumination in atoms, solids and nanostructures. Researchers have strived to utilize this effect to control exciton states, aiming to realize ultra-high-speed optical switches and modulators. However, most studies have focused on the optical Stark effect of only the lowest exciton state due to lack of energy selectivity, resulting in low degree-of-freedom devices. Here, by applying a linearly polarized laser pulse to few-layer ReS2, where reduced symmetry leads to strong in-plane anisotropy of excitons, we control the optical Stark shift of two energetically separated exciton states. Especially, we selectively tune the Stark effect of an individual state with varying light polarization. This is possible because each state has a completely distinct dependence on light polarization due to different excitonic transition dipole moments. Our finding provides a methodology for energy-selective control of exciton states. PMID:27857053

  16. Stark broadening measurements in plasmas produced by laser ablation of hydrogen containing compounds

    NASA Astrophysics Data System (ADS)

    Burger, Miloš; Hermann, Jörg

    2016-08-01

    We present a method for the measurement of Stark broadening parameters of atomic and ionic spectral lines based on laser ablation of hydrogen containing compounds. Therefore, plume emission spectra, recorded with an echelle spectrometer coupled to a gated detector, were compared to the spectral radiance of a plasma in local thermal equilibrium. Producing material ablation with ultraviolet nanosecond laser pulses in argon at near atmospheric pressure, the recordings take advantage of the spatially uniform distributions of electron density and temperature within the ablated vapor. By changing the delay between laser pulse and detector gate, the electron density could be varied by more than two orders of magnitude while the temperature was altered in the range from 6,000 to 14,000 K. The Stark broadening parameters of transitions were derived from their simultaneous observation with the hydrogen Balmer alpha line. In addition, assuming a linear increase of Stark widths and shifts with electron density for non-hydrogenic lines, our measurements indicate a change of the Stark broadening-dependence of Hα over the considered electron density range. The presented results obtained for hydrated calcium sulfate (CaSO4ṡ2H2O) can be extended to any kind of hydrogen containing compounds.

  17. Quantum confined Stark effect in Gaussian quantum wells: A tight-binding study

    SciTech Connect

    Ramírez-Morales, A.; Martínez-Orozco, J. C.; Rodríguez-Vargas, I.

    2014-05-15

    The main characteristics of the quantum confined Stark effect (QCSE) are studied theoretically in quantum wells of Gaussian profile. The semi-empirical tight-binding model and the Green function formalism are applied in the numerical calculations. A comparison of the QCSE in quantum wells with different kinds of confining potential is presented.

  18. Experimental measurements of Stark widths for Mn I lines in long laser spark

    NASA Astrophysics Data System (ADS)

    Popov, Andrey M.; Akhmetzhanov, Timur F.; Labutin, Timur A.; Zaytsev, Sergey M.; Zorov, Nikita B.; Chekalin, Nikolay V.

    2016-11-01

    We report the experimental Stark widths of Mn I lines belonging to multiplets z6P° → a6S and z6D° → a6D in long spark induced by laser. We have used aluminum alloy containing 80 ppm of manganese as a target to avoid strong self-absorption of Mn I lines. Its absence was proved by the comparison of observed intensities with relative strengths of lines within multiplets. Electron density of plasma estimated by Mg I (5172.68 Å) and Al II (2816.18 Å) lines was within the range of (4-30) × 1016 cm- 3. The shortest possible gate allowed the observation of symmetric atomic and ionic lines. The spatial profiles of plasma temperature and electron density along the axis of long spark demonstrated that both values were lower than for spherical plasma. Measured Stark widths of resonance multiplet z6P° → a6S decrease from 0.075 Å for its first component to 0.055 Å for the last one, while Stark widths of components of multiplet z6D° → a6D increase from 0.095 Å to 0.125 Å. No Stark shifting was observed for the studied multiplets.

  19. Selectively tunable optical Stark effect of anisotropic excitons in atomically thin ReS2.

    PubMed

    Sim, Sangwan; Lee, Doeon; Noh, Minji; Cha, Soonyoung; Soh, Chan Ho; Sung, Ji Ho; Jo, Moon-Ho; Choi, Hyunyong

    2016-11-18

    The optical Stark effect is a coherent light-matter interaction describing the modification of quantum states by non-resonant light illumination in atoms, solids and nanostructures. Researchers have strived to utilize this effect to control exciton states, aiming to realize ultra-high-speed optical switches and modulators. However, most studies have focused on the optical Stark effect of only the lowest exciton state due to lack of energy selectivity, resulting in low degree-of-freedom devices. Here, by applying a linearly polarized laser pulse to few-layer ReS2, where reduced symmetry leads to strong in-plane anisotropy of excitons, we control the optical Stark shift of two energetically separated exciton states. Especially, we selectively tune the Stark effect of an individual state with varying light polarization. This is possible because each state has a completely distinct dependence on light polarization due to different excitonic transition dipole moments. Our finding provides a methodology for energy-selective control of exciton states.

  20. On the Stark Widths and Shifts of Ar II 472.68 nm Spectral Line

    SciTech Connect

    Mijatovic, Z.; Gajo, T.; Vujicic, B.; Djurovic, S.; Kobilarov, R.

    2008-10-22

    Stark widths and shifts of Ar II 472.68 nm spectral line were measured from T-tube plasmas. Plasma electron density ranged 1.8-2.210{sup 17} cm{sup -3}, while temperature ranged 20000-43000 K. Obtained results of widths and shifts were compared with measured results of other authors.

  1. Dynamical effects of Stark-shifted quantum dots strongly coupled to photonic crystal cavities

    NASA Astrophysics Data System (ADS)

    Roy Choudhury, Kaushik; Bose, Ranojoy; Waks, Edo

    2013-03-01

    Single semiconductor quantum-dots (QDs) strongly coupled to photonic crystal cavities are a strong candidate for single photon generation, ultra-fast all optical switching and quantum information processing. Recent experiments on coupled-cavity quantum dot systems show possible manipulation of emission wavelength of the dot through optical Stark effect. Interesting dynamical features arise when the Stark pulse duration is comparable to QD-cavity interaction time. Here, we present a theoretical treatment of these dynamical effects and investigate dynamical emission spectrum, energy transfer and single photon generation. We study these effects through numerical solution of the full master equation. We demonstrate that dynamic Stark effects can be used to generate ultra-fast indistinguishable single photons using rapid Stark tuning of the quantum dot. The theoretical limit for the speed is shown to be faster than adiabatic rapid passage technique used for microwave photon generation in circuit QED. A systematic study of role of device parameters such as pulse-shape, dot-cavity coupling and incoherent losses on the efficiency and speed of single photon generation is also presented for possible experimental realization.

  2. Stark broadening corrections to laser-induced fluorescence temperature measurements in a hydrogen arcjet plume.

    PubMed

    Storm, P V; Cappelli, M A

    1996-08-20

    Laser-induced fluorescence of the H(α) transition of atomic hydrogen has previously been performed in the plume of a hydrogen arcjet thruster. Measurements of plasma velocity and temperature, based on the Doppler shift and broadening of the H(α) line shape, were previously published [Appl. Opt. 32, 6117 (1993)]. In that paper the Stark broadening of the H(α) transition was estimated from static-ion calculations performed in the early 1970's and found to be negligible in comparison with the Doppler broadening. However, more recent dynamic-ion calculations have shown the Stark broadening to be considerably larger than was previously assumed, resulting in inaccurate temperature measurements. We present a reanalysis of the fluorescence data, taking into account the improved Stark broadening calculations. The correct atomic hydrogen translation temperature and electron number density are obtained from the Doppler and Stark broadening components of the measured line shape. The results indicate a substantial drop in temperature from those previously reported.

  3. Motion Sickness

    MedlinePlus

    Motion sickness is a common problem in people traveling by car, train, airplanes, and especially boats. Anyone ... children, pregnant women, and people taking certain medicines. Motion sickness can start suddenly, with a queasy feeling ...

  4. Infrared Stark and Zeeman spectroscopy of OH-CO: The entrance channel complex along the OH + CO → trans-HOCO reaction pathway

    NASA Astrophysics Data System (ADS)

    Brice, Joseph T.; Liang, Tao; Raston, Paul L.; McCoy, Anne B.; Douberly, Gary E.

    2016-09-01

    Sequential capture of OH and CO by superfluid helium droplets leads exclusively to the formation of the linear, entrance-channel complex, OH-CO. This species is characterized by infrared laser Stark and Zeeman spectroscopy via measurements of the fundamental OH stretching vibration. Experimental dipole moments are in disagreement with ab initio calculations at the equilibrium geometry, indicating large-amplitude motion on the ground state potential energy surface. Vibrational averaging along the hydroxyl bending coordinate recovers 80% of the observed deviation from the equilibrium dipole moment. Inhomogeneous line broadening in the zero-field spectrum is modeled with an effective Hamiltonian approach that aims to account for the anisotropic molecule-helium interaction potential that arises as the OH-CO complex is displaced from the center of the droplet.

  5. Case studies on recent Stark broadening calculations and STARK-B database development in the framework of the European project VAMDC (Virtual Atomic and Molecular Data Center)

    NASA Astrophysics Data System (ADS)

    Sahal-Bréchot, S.

    2010-11-01

    Stark broadening theories and calculations have been extensively developed for about 50 years. The theory can now be considered as mature for many applications, especially for accurate spectroscopic diagnostics and modelling. In astrophysics, with the increasing sensitivity of observations and spectral resolution, in all domains of wavelengths from far UV to infrared, it has become possible to develop realistic models of interiors and atmospheres of stars and interpret their evolution and the creation of elements through nuclear reactions. For hot stars, especially white dwarfs, Stark broadening is the dominant collisional line broadening process. This requires the knowledge of numerous profiles, especially for trace elements, which are used as useful probes for modern spectroscopic diagnostics. Hence, calculations based on a simple but enough accurate and fast method, are necessary for obtaining numerous results. Ab initio calculations are a growing domain of development. Nowadays, the access to such data via an on line database becomes crucial. This is the object of STARK-B, which is a collaborative project between the Paris Observatory and the Astronomical Observatory of Belgrade. It is a database of calculated widths and shifts of isolated lines of atoms and ions due to electron and ion collisions. It is devoted to modelling and spectroscopic diagnostics of stellar atmospheres and envelopes. In addition, it is relevant to laboratory plasmas, laser equipments and technological plasmas. It is a part of VAMDC (Virtual Atomic and Molecular Data Centre), which is an European Union funded collaboration between groups involved in the generation and use of atomic and molecular data.

  6. Plate motion

    SciTech Connect

    Gordon, R.G. )

    1991-01-01

    The motion of tectonic plates on the earth is characterized in a critical review of U.S. research from the period 1987-1990. Topics addressed include the NUVEL-1 global model of current plate motions, diffuse plate boundaries and the oceanic lithosphere, the relation between plate motions and distributed deformations, accelerations and the steadiness of plate motions, the distribution of current Pacific-North America motion across western North America and its margin, plate reconstructions and their uncertainties, hotspots, and plate dynamics. A comprehensive bibliography is provided. 126 refs.

  7. Case Studies On Recent Stark Broadening Calculations And Stark-B Database Development In The Framework Of The European Project Vamdc (Virtual Atomic And Molecular Data Center)

    NASA Astrophysics Data System (ADS)

    Sahal-Bréchot, S.

    2010-07-01

    Stark broadening theories and calculations have been extensively developed for about 50 years. The theory can now be considered as mature for many applications, especially for accurate spectroscopic diagnostics and modelisation. In astrophysics, with the increasing sensitivity of observations and spectral resolution, in all domains of wavelengths from far UV to infrared, it has become possible to develop realistic models of interiors and atmospheres of stars and interpret their evolution. For hot stars, especially white dwarfs, Stark broadening is the dominant collisional line broadening process. This requires the knowledge of numerous collisional line profiles, especially for very weakly abundant atoms and ions that are used as useful probes for modern spectroscopic diagnostics. Hence, calculations based on a simple but enough accurate and fast method is indispensable for obtaining numerous results. Ab initio quantum calculations are also a useful domain of development, especially for ion emitters. Nowadays, the access to such data via an on line database becomes indispensable. The Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu) is a European Union funded collaboration between groups involved in the generation and use of atomic and molecular data. VAMDC aims to build a secure, documented, flexible and interoperable e-science environment-based interface to existing atomic and molecular data. In this framework, the Stark-B (http://starkb.obspm.fr) database, which is a part of VAMDC, is a collaborative project between the Astronomical Observatory of Belgrade and the Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA). It is a database of calculated widths and shifts of isolated lines of atoms and ions due to electron and ion collisions (i.e. impacts are separated in time). This database is devoted to modelisation and spectroscopic diagnostics of stellar atmospheres and envelopes. In addition, it is relevant to

  8. Stark Widths and Shifts Dependence on the Rest Core Charge of the Emitters within ns-np Transition Arrays

    SciTech Connect

    Scepanovic, Mara; Puric, Jagos

    2010-01-21

    Stark width and shift simultaneous dependence on the upper level ionization potential and rest core charge of the emitter has been evaluated and discussed. It has been verified that the found relations, connecting Stark broadening parameters with upper level ionization potential and rest core charge of the emitters for particular electron temperature and density, can be used for prediction of Stark line width and shift data in case of ions for which observed data, or more detailed calculations, are not yet available. Stark widths and shifts published data are used to demonstrate the existence of other kinds of regularities within similar spectra of different elements and their ionization stages. The emphasis is on the Stark parameter dependence on the upper level ionization potential and on the rest core charge for the lines from similar spectra of multiply charged ions. The found relations connecting Stark widths and shift parameters with upper level ionization potential, rest core charge and electron temperature were used for a prediction of new Stark broadening data, thus avoiding much more complicated procedures.

  9. Stark parameter dependence of the rest core charge of the emitters for multiply charged ions spectral lines

    SciTech Connect

    Šćepanović, M.; Purić, J.

    2016-03-25

    Stark width and shift simultaneous dependence on the upper level ionization potential and rest core charge of the emitter has been evaluated and discussed. It has been verified that the found relations, connecting Stark broadening parameters with upper level ionization potential and rest core charge of the emitters for particular electron temperature and density, can be used for prediction of Stark line width and shift data in case of ions for which observed data, or more detailed calculations, are not yet available. Stark widths and shifts published data are used to demonstrate the existence of other kinds of regularities within similar spectra of different elements and their ionization stages. The emphasis is on the Stark parameter dependence on the upper level ionization potential and on the rest core charge for the lines from similar spectra of multiply charged ions. The found relations connecting Stark widths and shift parameters with upper level ionization potential, rest core charge and electron temperature were used for a prediction of new Stark broadening data, thus avoiding much more complicated procedures.

  10. Stark maps and Rydberg transitions in the presence of an electric field for Li, Na, and K. A quantum defect orbital approach

    NASA Astrophysics Data System (ADS)

    Menéndez, J. M.; Martín, I.; Velasco, A. M.

    2003-12-01

    The Stark structure of the Rydberg states of the lighter alkali atoms, Li, Na, and K, and the Stark oscillator strength distribution for Li have been calculated by diagonalization of the quantum defect orbital (QDO) Hamiltonian matrix. The presently obtained Stark maps are in excellent agreement with those resulting from theory and experiment, as reported in the literature by other authors. Good accord is also found for the presently calculated oscillator strength distribution, within a Stark manifold, with that of other theoretical approach and experimental measurements. The adequacy of the QDO procedure for accurately dealing with properties related to the Stark effect in atoms is suggested.

  11. Development of a wavy Stark velocity filter for studying interstellar chemistry

    NASA Astrophysics Data System (ADS)

    Okada, Kunihiro; Takada, Yusuke; Kimura, Naoki; Wada, Michiharu; Schuessler, Hans A.

    2017-08-01

    Cold polar molecules are key to both the understanding of fundamental physics and the characterization of the chemical evolution of interstellar clouds. To facilitate such studies over a wide range of temperatures, we developed a new type of Stark velocity filter for changing the translational and rotational temperatures of velocity-selected polar molecules without changing the output beam position. The translational temperature of guided polar molecules can be significantly varied by exchanging the wavy deflection section with one having a different radius of the curvature and a different deflection angle. Combining in addition a temperature variable gas cell with the wavy Stark velocity filter enables to observe the translational and rotational temperature dependence of the reaction-rate constants of cold ion-polar molecule reactions over the interesting temperature range of 10-100 K.

  12. Reactive intermediates in 4He nanodroplets: Infrared laser Stark spectroscopy of dihydroxycarbene

    NASA Astrophysics Data System (ADS)

    Broderick, Bernadette M.; McCaslin, Laura; Moradi, Christopher P.; Stanton, John F.; Douberly, Gary E.

    2015-04-01

    Singlet dihydroxycarbene ( HO C ̈ OH ) is produced via pyrolytic decomposition of oxalic acid, captured by helium nanodroplets, and probed with infrared laser Stark spectroscopy. Rovibrational bands in the OH stretch region are assigned to either trans,trans- or trans,cis-rotamers on the basis of symmetry type, nuclear spin statistical weights, and comparisons to electronic structure theory calculations. Stark spectroscopy provides the inertial components of the permanent electric dipole moments for these rotamers. The dipole components for trans, trans- and trans, cis-rotamers are (μa, μb) = (0.00, 0.68(6)) and (1.63(3), 1.50(5)), respectively. The infrared spectra lack evidence for the higher energy cis,cis-rotamer, which is consistent with a previously proposed pyrolytic decomposition mechanism of oxalic acid and computations of HO C ̈ OH torsional interconversion and tautomerization barriers.

  13. Asymmetric Stark shift in an impurity doped dome-shaped quantum dot with wetting layer

    NASA Astrophysics Data System (ADS)

    Niculescu, E. C.; Cristea, M.; Bejan, D.

    2017-02-01

    The effects of vertical electric field and donor impurity on the electronic properties of the dome-shaped InAs/GaAs quantum dot coupled to its wetting layer were investigated. The dependence of the electron density, energy and Stark shift of the S-, P- and WL-states on the applied electric field was studied with and without impurity. The S- and P-states have no significant qualitative changes in the shape of the wave functions with increasing the electric field, except that they become slightly shifted due to the competition between the field action and the quantum confinement. The wave function of the WL-state is strongly modified in polarized structures. Our results reveal that the Stark shift of electron energies can be fitted with a quadratic dependence on the electric field, the linear and quadratic terms corresponding to the dipole moment and static electron polarizability. Their estimated values reasonable agree with those calculated.

  14. Engineering large Stark shifts for control of individual clock state qubits

    NASA Astrophysics Data System (ADS)

    Lee, A. C.; Smith, J.; Richerme, P.; Neyenhuis, B.; Hess, P. W.; Zhang, J.; Monroe, C.

    2016-10-01

    In quantum information science, the external control of qubits must be balanced with the extreme isolation of the qubits from the environment. Atomic qubit systems typically mitigate this balance through the use of gated laser fields that can create superpositions and entanglement between qubits. Here we propose the use of high-order optical Stark shifts from optical fields to manipulate the splitting of atomic qubits that are insensitive to other types of fields. We demonstrate a fourth-order ac Stark shift in a trapped atomic ion system that does not require extra laser power beyond that needed for other control fields. We individually address a chain of tightly spaced trapped ions and show how these controlled shifts can produce an arbitrary product state of 10 ions as well as generate site-specific magnetic field terms in a simulated spin Hamiltonian.

  15. Exact expression of the impact broadening operator for hydrogen Stark broadening

    NASA Astrophysics Data System (ADS)

    Gigosos, M. A.; González, M. Á.; Talin, B.; Calisti, A.

    2007-05-01

    Aims:Recent measurements on the Stark broadening of radio recombination lines show values and trends in disagreement with conventional theories. Different attemps to explain those disagreements have not been successfull for any of the employed theoretical models. In particular, the impact model that describes well the physical conditions at which the studied broadenings occur, shows a functional trend upon the principal quantum number of the studied transitions that does not correspond to the experimental observations. Methods: High values of the principal quantum number require computable formulas for the calculation of transition probabilities. Some of those expressions have been published, leading to approximate formulas on the dependence of the line width versus the principal quantum number of the upper level of the transition. Results: In this work an exact expression for the hydrogen Stark width in the frame of impact approximation is given.

  16. Psychosocial response to disaster: the attacks on the Stark and the Cole.

    PubMed

    Kootte, Anton F

    2002-01-01

    The terrorist attack on the USS Cole on 12 October 2000 was remarkably similar to the 1987 attack on the USS Stark. This article discusses the psychosocial consequences of the attacks on the families and crews of the ships and the community response of the Navy to the attacks, particularly that of the Navy Family Service Centers. The impact of the attacks is compared to the impact of natural and man-made disasters on communities while the impact on the crew is examined in light of combat psychiatry and post-traumatic stress disorder (PTSD). Events such as these are very likely to produce PTSD despite early intervention efforts. Following the attack on the Stark greater attention was given to the grief of family members than to the trauma of the crew, while the crew of the Cole has received longer-term psychiatric assistance than in previous similar episodes.

  17. Atomic Clock with 1 ×10-18 Room-Temperature Blackbody Stark Uncertainty

    NASA Astrophysics Data System (ADS)

    Beloy, K.; Hinkley, N.; Phillips, N. B.; Sherman, J. A.; Schioppo, M.; Lehman, J.; Feldman, A.; Hanssen, L. M.; Oates, C. W.; Ludlow, A. D.

    2014-12-01

    The Stark shift due to blackbody radiation (BBR) is the key factor limiting the performance of many atomic frequency standards, with the BBR environment inside the clock apparatus being difficult to characterize at a high level of precision. Here we demonstrate an in-vacuum radiation shield that furnishes a uniform, well-characterized BBR environment for the atoms in an ytterbium optical lattice clock. Operated at room temperature, this shield enables specification of the BBR environment to a corresponding fractional clock uncertainty contribution of 5.5 ×10-19 . Combined with uncertainty in the atomic response, the total uncertainty of the BBR Stark shift is now 1 ×10-18. Further operation of the shield at elevated temperatures enables a direct measure of the BBR shift temperature dependence and demonstrates consistency between our evaluated BBR environment and the expected atomic response.

  18. Full-dimensional control of the radiationless decay in pyrazine using the dynamic Stark effect

    NASA Astrophysics Data System (ADS)

    Saab, Mohamad; Sala, Matthieu; Lasorne, Benjamin; Gatti, Fabien; Guérin, Stéphane

    2014-10-01

    We present a full quantum-mechanical study of the laser control of the radiationless decay between the B3u(nπ*) and B2u(ππ*) states of pyrazine using the dynamic Stark effect. In contrast to our previous study [Sala et al., J. Chem. Phys. 140, 194309 (2014)], where a four-dimensional model was used, all the 24 degrees of freedom are now included in order to test the robustness of the strategy of control. Using a vibronic coupling Hamiltonian model in a diabatic representation, the multi-layer version of the multi-configuration time-dependent Hartree method is exploited to propagate the corresponding wave packets. We still observe a trapping of the wavepacket on the B2u(ππ*) potential energy surface due to the Stark effect for a longer time than the "non-resonant field-free" B2u(ππ*) lifetime.

  19. Conditional control of donor nuclear spins in silicon using stark shifts.

    PubMed

    Wolfowicz, Gary; Urdampilleta, Matias; Thewalt, Mike L W; Riemann, Helge; Abrosimov, Nikolai V; Becker, Peter; Pohl, Hans-Joachim; Morton, John J L

    2014-10-10

    Electric fields can be used to tune donor spins in silicon using the Stark shift, whereby the donor electron wave function is displaced by an electric field, modifying the hyperfine coupling between the electron spin and the donor nuclear spin. We present a technique based on dynamic decoupling of the electron spin to accurately determine the Stark shift, and illustrate this using antimony donors in isotopically purified silicon-28. We then demonstrate two different methods to use a dc electric field combined with an applied resonant radio-frequency (rf) field to conditionally control donor nuclear spins. The first method combines an electric-field induced conditional phase gate with standard rf pulses, and the second one simply detunes the spins off resonance. Finally, we consider different strategies to reduce the effect of electric field inhomogeneities and obtain above 90% process fidelities.

  20. Internal Stark effect mediates intramolecular excited-state proton transfer in 3-hydroxyflavone derivatives

    NASA Astrophysics Data System (ADS)

    Klymchenko, Andriy S.; Demchenko, Alexander P.

    2002-12-01

    Internal Stark effect in electronic spectra is the effect that is observed when the electronic bands shift udner the influence of promixal charges. In order to study the possible involvement of this effect in modulating the intramolecular proton transfer reactions in the excited state, we designed and studied several derivatives of 3-hydroxyflavone. They include the species containing neutral and positively charged substituents in 6 position of chromone ring. These compounds were studied in solvents of different polarities. In these experiments the shifts of both normal and tautomer flurosence bands are clearly observed in a manner predicted by Stark effect theory. In addition, a dramatic effect of suppression by introduced charge of intramolecular excited-state proton transfer was observed.