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Sample records for c-mod motional stark

  1. Design of a new optical system for Alcator C-Mod motional Stark effect diagnostic

    SciTech Connect

    Ko, Jinseok; Scott, Steve; Bitter, Manfred; Lerner, Scott

    2008-10-15

    The motional Stark effect (MSE) diagnostic on Alcator C-Mod uses an in-vessel optical system (five lenses and three mirrors) to relay polarized light to an external polarimeter because port access limitations on Alcator C-Mod preclude a direct view of the diagnostic beam. The system experiences unacceptable, spurious drifts of order several degrees in measured pitch angle over the course of a run day. Recent experiments illuminated the MSE diagnostic with polarized light of fixed orientation as heat was applied to various optical elements. A large change in measured angle was observed as two particular lenses were heated, indicating that thermal-stress-induced birefringence is a likely cause of the spurious variability. Several new optical designs have been evaluated to eliminate the affected in-vessel lenses and to replace the focusing they provide with curved mirrors; however, ray tracing calculations imply that this method is not feasible. A new approach is under consideration that utilizes in situ calibrations with in-vessel reference polarized light sources.

  2. Design of a New Optical System for Alcator C-Mod Motional Stark Effect Diagnostic

    SciTech Connect

    Ko, Jinseok; Scott, Steve; Manfred, Bitter; Lerner, Lerner

    2009-11-12

    The motional Stark effect (MSE) diagnostic on Alcator C-Mod uses an in-vessel optical system (five lenses and three mirrors) to relay polarized light to an external polarimeter because port access limitations on Alcator C-Mod preclude a direct view of the diagnostic beam. The system experiences unacceptable, spurious drifts of order several degrees in measured pitch angle over the course of a run day. Recent experiments illuminated the MSE diagnostic with polarized light of fixed orientation as heat was applied to various optical elements. A large change in measured angle was observed as two particular lenses were heated, indicating that thermal-stress-induced birefringence is a likely cause of the spurious variability. Several new optical designs have been evaluated to eliminate the affected in-vessel lenses and to replace the focusing they provide with curved mirrors; however, ray tracing calculations imply that this method is not feasible. A new approach is under consideration that utilizes in situ calibrations with in-vessel reference polarized light sources. 2008 American Institute of Physics.

  3. 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.

  4. 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.

  5. 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.

  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. Performance evaluation of MSE on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Scott, S.; Mumgaard, R.; Granetz, R.; Shugayev, R.; Chung, M.

    2011-10-01

    Performance of the Motional Stark Effect (MSE) diagnostic has been compared to first-principle numerical simulations by moving the Stark-split beam spectrum past MSE's narrow bandpass filters. The relative position of the Stark spectrum to the filters was varied by ramping the toroidal field at fixed q; changing the filter temperature; and swapping one filter for another. We compare the signal strength and polarization fraction of beam emission to simulations that model the MSE emission using a modified version of the PERF code (NC Hawkes et al., Rev. Sci. Instrum. 70, 894 (1999)). The simulation includes models for beam attenuation, beam excitation, Stark emission, aperture broadening, the measured filter response function, and background visible Bremsstrahlung emission. This work confirms analytic comparisons of the expected MSE signal strength between C-Mod and other tokamaks which suggest that the polarized signal intensity on C-Mod is unexpectedly low by a factor of several. Measurements of the beam performance using calorimeters, beam-target neutron production during deuterium beam injection, and IR measurements of a stainless steel target heated by the beam will be discussed. Supported by US DoE awards DE-FC02-99-ER54512 and DE-AC02-09CH11446.

  8. 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.

  9. Performance of spectral MSE diagnostic on C-Mod and ITER

    NASA Astrophysics Data System (ADS)

    Liao, Ken; Rowan, William; Mumgaard, Robert; Granetz, Robert; Scott, Steve; Marchuk, Oleksandr; Ralchenko, Yuri; Alcator C-Mod Team

    2015-11-01

    Magnetic field was measured on Alcator C-mod by applying spectral Motional Stark Effect techniques based on line shift (MSE-LS) and line ratio (MSE-LR) to the H-alpha emission spectrum of the diagnostic neutral beam atoms. The high field of Alcator C-mod allows measurements to be made at close to ITER values of Stark splitting (~ Bv⊥) with similar background levels to those expected for ITER. Accurate modeling of the spectrum requires a non-statistical, collisional-radiative analysis of the excited beam population and quadratic and Zeeman corrections to the Stark shift. A detailed synthetic diagnostic was developed and used to estimate the performance of the diagnostic at C-Mod and ITER parameters. Our analysis includes the sensitivity to view and beam geometry, aperture and divergence broadening, magnetic field, pixel size, background noise, and signal levels. Analysis of preliminary experiments agree with Kinetic+(polarization)MSE EFIT within ~2° in pitch angle and simulations predict uncertainties of 20 mT in | B | and <2° in pitch angle. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Fusion Energy Sciences under Award Number DE-FG03-96ER-54373 and DE-FC02-99ER54512.

  10. 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.

  11. Motional Stark effect diagnostic pilot experiment for MAST

    SciTech Connect

    Kuldkepp, M.; Walsh, M. J.; Carolan, P. G.; Conway, N. J.; Hawkes, N. C.; McCone, J.; Rachlew, E.; Wearing, G.

    2006-10-15

    Exploiting the motional Stark effect (MSE) in the low magnetic fields of spherical tokamaks such as MAST is complicated by the Doppler smearing of the relatively closely spaced Stark components. Extensive modeling of MSE spectra and the subsequent polarized fraction ({approx}20%) of spectrally filtered light and signal to noice ratios have been performed taking account of real experimental conditions including neutral beam parameters, port sizes, optical losses, filter characteristics, etc. A design is selected which uses high throughput interference filters (0.1 nm bandpass) for separation of the spectral components. An accuracy of {approx}0.5 deg. compared with typically 15 deg. is estimated for field angle measurements. The design allows for early implementation, starting with a pilot two chord system, and for an economic expansion to a multiplicity of chords. Matching the Doppler shifted D{sub {alpha}} from the beam neutrals will be accomplished by a combination of filter selection and fine-tuning of the beam voltage. Avoiding filter tuning in the design greatly simplifies the diagnostic. Calibration results of the diagnostic support the calculations.

  12. 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.

  13. 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.

  14. Improved spectral analysis for the motional Stark effect diagnostica)

    NASA Astrophysics Data System (ADS)

    Ko, J.; Klabacha, J.

    2012-10-01

    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.

  15. Ab initio modeling of the motional Stark effect on MAST

    SciTech Connect

    De Bock, M. F. M.; Conway, N. J.; Walsh, M. J.; Carolan, P. G.; Hawkes, N. C.

    2008-10-15

    A multichord motional Stark effect (MSE) system has recently been built on the MAST tokamak. In MAST the {pi} and {sigma} lines of the MSE spectrum overlap due to the low magnetic field typical for present day spherical tokamaks. Also, the field curvature results in a large change in the pitch angle over the observation volume. The measured polarization angle does not relate to one local pitch angle but to an integration over all pitch angles in the observation volume. The velocity distribution of the neutral beam further complicates the measurement. To take into account volume effects and velocity distribution, an ab initio code was written that simulates the MSE spectrum on MAST. The code is modular and can easily be adjusted for other tokamaks. The code returns the intensity, polarized fraction, and polarization angle as a function of wavelength. Results of the code are presented, showing the effect on depolarization and wavelength dependence of the polarization angle. The code is used to optimize the design and calibration of the MSE diagnostic.

  16. 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.

  17. Charge exchange recombination spectroscopy on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Eisner, E. C.; Rowan, William L.

    2001-01-01

    The optical systems for charge-exchange recombination spectroscopy (CXRS) on Alcator C-Mod have been developed and installed. They will provide measurements of Ti, νθ, and νφ. With the addition of the motional Stark effect diagnostic to determine Bp, Er can be inferred from the ion pressure balance equation, Er=(Zenz)-1∇rpz+νφzBθ-νθzBφ. The optical systems are simple and have high throughput. In particular, the toroidally viewing systems must be designed for invessel installation close to the plasma where they are subject to large forces and are inaccessible between vacuum vents. Two optical systems, located invessel, provide 20 channels of Ti and νφ data from 67.3 cm

  18. Optical coherence-based techniques for motional Stark effect measurements of magnetic field pitch angle

    NASA Astrophysics Data System (ADS)

    Howard, John

    1999-02-01

    The motional Stark effect measurement of magnetic field pitch angle in tokamaks is a mature and powerful technique for estimating plasma current density in tokamaks. However, its range of applicability is limited by the requirement that 0741-3335/41/2/012/img3 and 0741-3335/41/2/012/img4 manifolds are spectrally sufficiently well separated (high magnetic fields, high beam energies) to ensure adequate net polarization for a successful measurement. This paper proposes alternative schemes based on the optical coherence properties of the Stark multiplet that are somewhat more versatile than the standard method and better suited to measurements on low-field toroidal confinement devices. An interference filter is used to transmit the Stark multiplet to a polarimeter (which uses a single photoelastic plate) that modulates the light temporal coherence and/or its first spectral moment. This light is subsequently processed using a novel electro-optically modulated solid-state interferometer that is sensitive to low-order spectral moments. The modulation of these quantities conveys information about the orientation of the light polarization and hence the magnetic field pitch angle.

  19. Motional Stark Effect measurements of the local magnetic field in high temperature fusion plasmas

    NASA Astrophysics Data System (ADS)

    Wolf, R. C.; Bock, A.; Ford, O. P.; Reimer, R.; Burckhart, A.; Dinklage, A.; Hobirk, J.; Howard, J.; Reich, M.; Stober, J.

    2015-10-01

    The utilization of the Motional Stark Effect (MSE) experienced by the neutral hydrogen or deuterium injected into magnetically confined high temperature plasmas is a well established technique to infer the internal magnetic field distribution of fusion experiments. In their rest frame, the neutral atoms experience a Lorentz electric field, EL = v × B, which results in a characteristic line splitting and polarized line emission. The different properties of the Stark multiplet allow inferring, both the magnetic field strength and the orientation of the magnetic field vector. Besides recording the full MSE spectrum, several types of polarimeters have been developed to measure the polarization direction of the Stark line emission. To test physics models of the magnetic field distribution and dynamics, the accuracy requirements are quite demanding. In view of these requirements, the capabilities and issues of the different techniques are discussed, including the influence of the Zeeman Effect and the sensitivity to radial electric fields. A newly developed Imaging MSE system, which has been tested on the ASDEX Upgrade tokamak, is presented. The sensitivity allows to resolve sawtooth oscillations. A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics

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

    NASA Astrophysics Data System (ADS)

    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° for the magnitude and direction angle. These values are sufficient to provide significant constraints on magnetic equilibrium reconstructions.

  1. 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.

  2. 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.

  3. 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.

  4. q-profile measurements with motional stark effect in DIII-D

    SciTech Connect

    Rice, B.W.

    1996-07-01

    Motional Stark Effect (MSE) has emerged as the most reliable technique for the measurement of q profiles in tokamaks equipped with neutral beams. On DIII-D, two separate 8-channel MSE instruments are utilized, giving 16 radial measurements. The viewing geometry for each instrument is designed to optimize radial resolution (1.5 cm < {delta}R < 6 cm) over the measurement range. Dual-frequency polarization modulators combined with lock-in detection provides maximum signal-to-noise with a time response of {approximately}1 ms. Special consideration has gone into the design of the collection optics to minimize undesirable polarization effects on reflectors and Faraday rotation in lenses. Examples of data from negative central magnetic shear, VH-mode, and sawtoothing discharges highlight the capabilities of the DIII-D MSE diagnostic.

  5. First mirror contamination studies for polarimetry motional Stark effect measurements for ITER

    SciTech Connect

    Kuldkepp, M.; Rachlew, E.; Hawkes, N.C.; Schunke, B.

    2004-10-01

    The motional Stark effect (MSE) diagnostic on the International Thermonuclear Experimental Reactor will need to guide the light through a labyrinth of mirrors to provide neutron shielding. Knowledge of how the mirrors change the polarization is essential for accurate determination of the q profile. The optical properties of the plasma facing mirror are also expected to change with time due to deposition/erosion. For the purpose of examining this experimentally a detector system, identical to the JET MSE system, using twin photoelastic modulators was constructed. Measurements have been performed on freshly prepared mirrors, on mirrors after exposure to plasmas in Tore Supra, and labyrinth designs. The result shows a significant effect on the optical properties and demonstrate the need for in situ monitoring. The measured properties of the labyrinth closely follow the Mueller matrix formalism. With a correct choice of material the angle change introduced by the four mirrors furthest away from the plasma will be below 1 deg.

  6. Motional Stark effect plasma equilibria during LHCD experiments on PBX-M

    NASA Astrophysics Data System (ADS)

    Paoletti, F.; Batha, S.; Bernabei, S.; Fishman, H.; Hatcher, R.; Hirshman, S.; Ignat, D.; Jones, S.; Kaita, R.; Kaye, S.; Kesner, J.; Kessel, C.; LeBlanc, B.; Lee, D.; Levinton, F.; Luckhardt, S.; Okabayashi, M.; Takahashi, H.; Sesnic, S.; Sun, Y.; von Goeler, S.

    1994-10-01

    The magnetic field pitch angle measurements from the multichannel Motional Stark Effect (MSE) polarimeter system, together with the external poloidal flux values, toroidal plasma current, coil currents, and plasma pressure profile, as computed by the TRANSP code, are used to constrain the numerical solution of the Grad-Shafranov equation. The experimental results from the soft x-ray diagnostic and hard x-ray bremsstrahlung radiation profiles show clear signatures of a change in the current density profile during Lower hybrid injection. Indications of a variation in the q-profile are supported by the behavior of the measured sawtooth inversion radius. Modifications in the current density profiles, induced by Lower Hybrid waves, are discussed in terms of their effect on q-profiles and volume-averaged quantities like Ii.

  7. 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.

  8. The motional Stark effect diagnostic for ITER using a line-shift approach

    SciTech Connect

    Foley, E. L.; Levinton, F. M.; Yuh, H. Y.; Zakharov, L. E.

    2008-10-15

    The United States has been tasked with the development and implementation of a motional Stark effect (MSE) system on ITER. In the harsh ITER environment, MSE is particularly susceptible to degradation, as it depends on polarimetry, and the polarization reflection properties of surfaces are highly sensitive to thin film effects due to plasma deposition and erosion of a first mirror. Here we present the results of a comprehensive study considering a new MSE-based approach to internal plasma magnetic field measurements for ITER. The proposed method uses the line shifts in the MSE spectrum (MSE-LS) to provide a radial profile of the magnetic field magnitude. To determine the utility of MSE-LS for equilibrium reconstruction, studies were performed using the ESC-ERV code system. A near-term opportunity to test the use of MSE-LS for equilibrium reconstruction is being pursued in the implementation of MSE with laser-induced fluorescence on NSTX. Though the field values and beam energies are very different from ITER, the use of a laser allows precision spectroscopy with a similar ratio of linewidth to line spacing on NSTX as would be achievable with a passive system on ITER. Simulation results for ITER and NSTX are presented, and the relative merits of the traditional line polarization approach and the new line-shift approach are discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2006-10-01

    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 0.5-1MHz. 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 0.69-2.2km/s along the MSE measurement points, the time lag and distance between adjacent channels being 67±35μs and 70mm, respectively.

  10. 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.

  11. Measurements of LHCD current profile and efficiency for simulation validation on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Mumgaard, Robert T.

    2014-10-01

    Lower hybrid current drive (LHCD) is an effective tool to significantly modify the magnetic equilibrium by driving off-axis, non-inductive current. On Alcator C-Mod, an upgraded Motional Stark Effect (MSE) diagnostic enables the current profile to be accurately reconstructed during plasmas with strong LHCD and a hard X-ray camera measures the fast electron Bremsstrahlung profile. LHCD is applied for >4 current relaxation times, producing fully-relaxed magnetic equilibria in plasmas with non-inductive current fraction up to unity at currents up to 1.0 MA. C-Mod has developed an extensive database of LHCD performance, spanning a wide range in plasma current, launched n||, LHCD power, Te and plasma density. This dataset provides a unique platform for validation of LHCD current drive simulations with the plasma shape, density, field and LH frequency range envisioned for ITER and future reactors. In these conditions the measured current drive efficiencies are similar to that assumed for ITER with values up to 0.4*1020A/Wm2 despite being in a weak single-pass absorption regime. The driven current is observed to be off-axis, broadening the current profile, raising q0 above 1, suppressing sawteeth, decreasing/reversing the magnetic shear and sometimes destabilizing MHD modes and/or triggering internal transport barriers. Measurements indicate increased efficiency at increased temperature and plasma current but with a complicated dependence on launched n||. The MSE-constrained reconstructions show a loss in current drive efficiency as the plasma density is increased above =1.0×1020 m-3 consistent with previous observations of a precipitous drop in hard x-ray emission. Additionally, the measured driven current profile moves radially outward as the density is increased. Ray tracing simulations using GENRAY-CQL3D qualitatively reproduce these trends showing the rays make many passes through the plasma at high density and predicting a narrower current and HXR profile

  12. 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.

  13. Non-resonant dynamic stark control of vibrational motion with optimized laser pulses.

    PubMed

    Thomas, Esben F; Henriksen, Niels E

    2016-06-28

    The term dynamic Stark control (DSC) has been used to describe methods of quantum control related to the dynamic Stark effect, i.e., a time-dependent distortion of energy levels. Here, we employ analytical models that present clear and concise interpretations of the principles behind DSC. Within a linearly forced harmonic oscillator model of vibrational excitation, we show how the vibrational amplitude is related to the pulse envelope, and independent of the carrier frequency of the laser pulse, in the DSC regime. Furthermore, we shed light on the DSC regarding the construction of optimal pulse envelopes - from a time-domain as well as a frequency-domain perspective. Finally, in a numerical study beyond the linearly forced harmonic oscillator model, we show that a pulse envelope can be constructed such that a vibrational excitation into a specific excited vibrational eigenstate is accomplished. The pulse envelope is constructed such that high intensities are avoided in order to eliminate the process of ionization. PMID:27369515

  14. Non-resonant dynamic stark control of vibrational motion with optimized laser pulses

    NASA Astrophysics Data System (ADS)

    Thomas, Esben F.; Henriksen, Niels E.

    2016-06-01

    The term dynamic Stark control (DSC) has been used to describe methods of quantum control related to the dynamic Stark effect, i.e., a time-dependent distortion of energy levels. Here, we employ analytical models that present clear and concise interpretations of the principles behind DSC. Within a linearly forced harmonic oscillator model of vibrational excitation, we show how the vibrational amplitude is related to the pulse envelope, and independent of the carrier frequency of the laser pulse, in the DSC regime. Furthermore, we shed light on the DSC regarding the construction of optimal pulse envelopes - from a time-domain as well as a frequency-domain perspective. Finally, in a numerical study beyond the linearly forced harmonic oscillator model, we show that a pulse envelope can be constructed such that a vibrational excitation into a specific excited vibrational eigenstate is accomplished. The pulse envelope is constructed such that high intensities are avoided in order to eliminate the process of ionization.

  15. Measurements with magnetic field in the National Spherical Torus Experiment using the motional Stark effect with laser induced fluorescence diagnostic

    SciTech Connect

    Foley, E. L.; Levinton, F. M.

    2013-04-15

    The motional Stark effect with laser-induced fluorescence diagnostic (MSE-LIF) has been installed and tested on the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Lab. The MSE-LIF diagnostic will be capable of measuring radially resolved profiles of magnetic field magnitude or pitch angle in NSTX plasmas. The system includes a diagnostic neutral hydrogen beam and a laser which excites the n = 2 to n = 3 transition. A viewing system has been implemented which will support up to 38 channels from the plasma edge to past the magnetic axis. First measurements of MSE-LIF signals in the presence of small applied magnetic fields in neutral gas are reported.

  16. 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.

  17. Measurements with magnetic field in the National Spherical Torus Experiment using the motional Stark effect with laser induced fluorescence diagnostic

    NASA Astrophysics Data System (ADS)

    Foley, E. L.; Levinton, F. M.

    2013-04-01

    The motional Stark effect with laser-induced fluorescence diagnostic (MSE-LIF) has been installed and tested on the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Lab. The MSE-LIF diagnostic will be capable of measuring radially resolved profiles of magnetic field magnitude or pitch angle in NSTX plasmas. The system includes a diagnostic neutral hydrogen beam and a laser which excites the n = 2 to n = 3 transition. A viewing system has been implemented which will support up to 38 channels from the plasma edge to past the magnetic axis. First measurements of MSE-LIF signals in the presence of small applied magnetic fields in neutral gas are reported.

  18. 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.

  19. Performance Assessment of the C-Mod Multi-Spectral Line Polarization MSE (MSE-MSLP) Diagnostic

    NASA Astrophysics Data System (ADS)

    Scott, Steven; Mumgaard, Robert; Khoury, Matthew

    2015-11-01

    The accuracy of the Alcator C-Mod Motional Stark Effect (MSE) diagnostic is limited primarily by partially polarized background light that varies rapidly both in time (1 ms) and space - factor 10 variations are observed between adjacent spatial channels. ITER is likely to operate in a similar regime. Visible Bremsstrahlung, divertor molecular D2 emission, and glowing invessel structures generate unpolarized light that becomes partially polarized upon reflection. Because all three sources are broadband, the background light can be measured in real-time at wavelengths close to the MSE spectrum, thereby allowing the background to be interpolated in wavelength rather than in time. A 10-spatial-channel, 4-wavelength MSE-MSLP system has been developed using polarization polychromators that measure simultaneously the MSE pi- and sigma- lines as well as two nearby wavelengths that were chosen to avoid both the MSE spectrum and all known impurity lines on each sightline. Initial performance evaluation indicates that the background channel measurements faithfully track the background light in the pi- and sigma- lines. The improvement in accuracy of pitch-angle measurements and increased diagnostic flexibility over a wide range of plasma conditions will be reported. This work is supported by USDoE awards DE-FC02-99ER54512 and DE-AC02-09CH11466.

  20. Axisymmetric Control in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Tinios, Gerasimos

    1995-01-01

    This thesis investigates the degree to which linear axisymmetric modeling of the response of a tokamak plasma can reproduce observed experimental behavior. The emphasis is on the vertical instability. The motivation for this work lies in the fact that, once dependable models have been developed, modern control theory methods can be used to design feedback laws for more effective and efficient tokamak control. The models are tested against experimental data from the Alcator C-Mod tokamak. A linear model for each subsystem of the closed-loop system constituting an Alcator C-Mod discharge under feedback control has been constructed. A non-rigid, approximately flux-conserving, perturbed equilibrium plasma response model is used in the comparison to experiment. A detailed toroidally symmetric model of the vacuum vessel and the supporting superstructure is used. Modeling of the power supplies feeding the active coils has been included. Experiments have been conducted with vertically unstable plasmas where the feedback was turned off and the plasma response was observed in an open -loop configuration. The closed-loop behavior has been examined by injecting step perturbations into the desired vertical position of the plasma. The agreement between theory and experiment in the open-loop configuration was very satisfactory, proving that the perturbed equilibrium plasma response model and a toroidally symmetric electromagnetic model of the vacuum vessel and the structure can be trusted for the purpose of calculations for control law design. When the power supplies and the feedback computer hardware are added to the system, however, as they are in the closed-loop configuration, they introduce nonlinearities that make it difficult to explain observed behavior with linear theory. Nonlinear simulation of the time evolution of the closed-loop experiments was able to account for the discrepancies between linear theory and experiment. (Copies available exclusively from MIT Libraries

  1. Edge Turbulence Imaging in the Alcator C-Mod Tokamak

    SciTech Connect

    S.J. Zweben; D.P. Stotler; J.L. Terry; B. LaBombard; M. Greenwald; M. Muterspaugh; C.S. Pitcher; the Alcator C-Mod Group; K. Hallatschek; R.J. Maqueda; B. Rogers; J.L. Lowrance; V.J. Mastrocola; G.F. Renda

    2001-11-26

    The 2-D radial vs. poloidal structure of edge turbulence in the Alcator C-Mod tokamak [I.H. Hutchinson, R. Boivin, P.T. Bonoli et al., Nuclear Fusion 41(2001) 1391] was measured using fast cameras and compared with 3-D numerical simulations of edge plasma turbulence. The main diagnostic is Gas Puff Imaging (GPI), in which the visible D(subscript alpha) emission from a localized D(subscript 2) gas puff is viewed along a local magnetic field line. The observed D(subscript alpha) fluctuations have a typical radial and poloidal scale of approximately 1 cm, and often have strong local maxima (''blobs'') in the scrape-off layer. The motion of this 2-D structure motion has also been measured using an ultra-fast framing camera with 12 frames taken at 250,000 frames/sec. Numerical simulations produce turbulent structures with roughly similar spatial and temporal scales and transport levels as that observed in the experiment; however, some differences are also noted, perhaps requiring diagnostic improvement and/or additional physics in the numerical model.

  2. SOL Reflectometer for Alcator C-Mod

    SciTech Connect

    Hanson, Gregory R; Wilgen, John B; Wukitch, Dr. Steve; Lin, Dr. Yijun; Lau, Cornwall H; Wallace, Gregory M

    2008-01-01

    A two-frequency x-mode reflectometer operating from 100 146 GHz is being deployed on Alcator C-Mod to measure the density profile and fluctuations in the scrape-off layer (SOL) immediately in-front of the new J-port ICRF antenna and the new B-port Lower Hybrid launcher. The reflectometer will cover densities from 1016 to 1020 m-3 at 5 5.4 T. To provide the greatest flexibility and capability to deal with density fluctuations approaching 100% peak to peak in the SOL, both full-phase and differential-phase measurement capabilities with sweep speeds of ~10 s to >1 ms are being implemented. The differential-phase measurement will use a difference-frequency of 500 MHz, corresponding to cutoff layer separations ranging from about 0.1 mm to 1 mm. The reflectometer will have 6 sets of launchers: 3 on the J-port ICRF antenna and 3 on the B-port LHRF launcher. The ICRF and LHRF antennas will incorporate reflectometer antennas at their top, bottom and mid-plane locations.

  3. SOL Reflectometer for Alcator C-MOD

    SciTech Connect

    Lau, Cornwall H; Hanson, Gregory R; Wilgen, John B; Lin, Dr. Yijun; Wukitch, Dr. Steve

    2010-10-01

    A swept-frequency X-mode reflectometer is being built for Alcator C-Mod to measure the scrape-off layer density profiles at the top, middle, and bottom locations in front of both the new lower hybrid launcher and the new ion cyclotron range of frequencies antenna. The system is planned to operate between 100 and 146 GHz at sweep rates from 10 {micro}s to 1 ms, and will cover a density range of approximately 10{sup 16}-10{sup 20} m{sup -3} at B{sub 0} = 5-5.4 T. To minimize the effects of density fluctuations, both differential phase and full phase reflectometry will be employed. Design, test data, and calibration results of this electronics system will be discussed. To reduce attenuation losses, tallguide (TE{sub 01}) will be used for most of the transmission line system. Simulations of high mode conversion in tallguide components, such as e-plane hyperbolic secant radius of curvature bends, tapers, and horn antennas will be shown. Experimental measurements of the total attenuation losses of these components in the lower hybrid waveguide run will also be presented.

  4. 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.

  5. Stark Spectroscopy on Photoactive Yellow Protein, E46Q, and a Nonisomerizing Derivative, Probes Photo-Induced Charge Motion

    PubMed Central

    Premvardhan, L. L.; van der Horst, M. A.; Hellingwerf, K. J.; van Grondelle, R.

    2003-01-01

    The change in the electrostatic properties on excitation of the cofactor of wild-type photoactive yellow protein (WT-PYP) have been directly determined using Stark-effect spectroscopy. We find that, instantaneously on photon absorption, there is a large change in the permanent dipole moment, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\vert}{\\Delta}{\\vec{{\\mu}}}{\\vert},\\end{equation*}\\end{document} (26 Debye) and in the polarizability, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}\\overline{{\\Delta}{\\alpha}},\\end{equation*}\\end{document} (1000 Å3). We expect such a large degree of charge motion to have a significant impact on the photocycle that is associated with the important blue-light negative phototactic response of Halorhodospira halophila. Furthermore, changing E46 to Q in WT-PYP does not significantly alter its electrostatic properties, whereas, altering the chromophore to prevent it from undergoing trans-cis isomerization results in a significant diminution of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\vert}{\\Delta}{\\vec{{\\mu}}}{\\vert}\\end{equation*}\\end{document} and \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}\\overline{{\\Delta}{\\alpha}}.\\end{equation*}\\end{document} We

  6. 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.

  7. Disruptions and halo currents in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Granetz, R. S.; Hutchinson, I. H.; Sorci, J.; Irby, J. H.; La Bombard, B.; Gwinn, D.

    1996-05-01

    Disruptions in Alcator C-Mod can generate large eddy currents in the highly conducting vacuum vessel and internal structures, including a significant poloidal component due to halo currents. In order to understand better the stresses arising from the resulting J*B forces, Alcator C-Mod has been fitted with a comprehensive set of sensors to measure the spatial distribution and temporal behaviour of the halo currents. It is found that they are toroidally asymmetric, with a typical peaking factor of 2. The asymmetric pattern usually rotates toroidally at a few kilohertz, thus ruling out first wall non-uniformities as the cause of the asymmetry. Analysis of the information compiled in the C-Mod disruption database indicates that the maximum halo current during a disruption scales roughly as either Ip2/Bphi or Ip/q95, but that there is a large amount of variation that is not yet understood

  8. Divertor bypass in the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    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.

  9. 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. PMID:21034041

  10. 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.

  11. 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.

  12. Analysis tools for turbulence studies at Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Burns, C.; Shehata, S.; White, A. E.; Cziegler, I.; Dominguez, A.; Terry, J. L.; Pace, D. C.

    2010-11-01

    A new suite of analysis tools written in IDL is being developed to support experimental investigation of turbulence at Alcator C-Mod. The tools include GUIs for spectral analysis (coherence, cross-phase and bicoherence) and characteristic frequency calculations. A user-friendly interface for the GENRAY code, to facilitate in-between shot ray-tracing analysis, is also being developed. The spectral analysis tool is being used to analyze data from existing edge turbulence diagnostics, such as the O-mode correlation reflectometer and Gas Puff Imaging, during I-mode, ITB and EDA H-mode plasmas. GENRAY and the characteristic frequency tool are being used to study diagnostic accessibility limits set by wave propagation and refraction for X-mode Doppler Backscattering and Correlation Electron Cyclotron Emission (CECE) systems that are being planned for core turbulence studies at Alcator C-Mod.

  13. Assessment of ICRF Antenna Performance in Alcator C-Mod

    SciTech Connect

    G. Schilling; S.J. Wukitch; Y. Lin; N. Basse; P.T. Bonoli; E. Edlund; L. Lin; A. Parisot; M. Porkolab

    2004-08-10

    The Alcator C-Mod has presented a challenge to install high-power ICRF antennas in a tight space. Modifications have been made to the antenna plasma-facing surfaces and the internal current-carrying structure in order to overcome performance limitations. At the present time, the antennas have exceeded 5 MW into plasma with heating phasing, up to 2.7 MW with current-drive phasing, with good efficiency and no deleterious effects

  14. Turbulent Impurity Transport Modeling for C-Mod

    NASA Astrophysics Data System (ADS)

    Fu, Xiangrong; Horton, Wendell; Rowan, William; Bespamyatnov, Igor; Benkadda, Sadruddin; Fiore, Catherine

    2012-03-01

    Turbulent particle transport is investigated by analyzing boron impurity transport experiments in the Alcator C-Mod transport experiments with a quasilinear theory. Eigenvalue problems for sets of reduced fluid equations for the multi-component plasmas are solved to get the fluctuating field vector composed of the electric potential φ, the main ion density δni, the impurity density δnz and the ion temperature fluctuation δTi(for ITG). For Alcator C-Mod parameters, we investigate three drift waves models (1) the usual drift waves driven by density gradients, (2)impurity drift waves supported by the impurity density gradients and (3)turbulence driven by ITG mode. With turbulent spectrum obtained from simulations or nonlinear theories, we calculate particle transport coefficients and compare with the experiment and the neoclassical theory. This procedure results in a fast code that could run in real-time on the transport time scale to give the particle fluxes as a function of the state of the plasma. The code may be extended to include multiple modes for a more complete description of plasmas. Examples for the particle fluxes are given for C-Mod in the H modes and newly discovered I modes. Recent experiments reported on LHD are briefly discussed.

  15. 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.

  16. 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).

  17. Correlation ECE diagnostic in Alcator C-Mod

    DOE PAGESBeta

    Sung, C.; White, A. E.; Howard, N. T.; Mikkelsen, D.; Irby, J.; Leccacorvi, R.; Vieira, R.; Oi, C.; Rice, J.; Reinke, M.; et al

    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

  18. Implementation of LHCD Experiments on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

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

    2005-09-01

    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° phasing, the n∥ spectrum is sharply peaked at 2.3 and the range 1.5 < n∥ < 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 ˜20 kW and pulse length to 10 ms. Early results from plasma operation are discussed.

  19. Non-axisymmetric Field Effects on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Wolfe, S.; Hutchinson, I.; Granetz, R.; Rice, J.; Hubbard, A.; Irby, J.; Vieira, R.; Cochran, W.; Gwinn, D.; Rosati, J.; Lynn, A.

    2003-10-01

    A set of coils capable of producing non-axisymmetric, predominantly n=1, fields with different toroidal phase and a range of poloidal mode (m) spectra has been installed on Alcator C-Mod. This coilset has been used to suppress locked modes during low density or high current operation and also to induce locked modes in normally stable configurations in order to study error field effects. Locked modes are observed to result in braking of core toroidal rotation, modification of sawtooth activity, and significant reduction in energy and particle confinement. The inferred value of the threshold perturbation for producing a locked mode is of order B_21/B_T ˜ 10-4, where B_21 is the helically resonant m/n=2/1 field evaluated at the q=2 surface. This value is comparable to extrapolations based on experiments on JET and DIII-D, but is inconsistent with stronger BT and size scaling inferred from Compass-D results(R. J. Buttery, et al., 17th Fusion Energy Conference, Oct. 1998, Yokohama (IAEA-CN-69) EX8/5). The C-Mod result therefore has favorable implications for the locked mode threshold in ITER.

  20. Extended pulse-length operation of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Wolfe, S.; Irby, J.; Terry, J.; Labombard, B.; Wukitch, S.; Marmar, E.; Cochran, W.; Dekow, G.; Gwinn, D.; Maqueda, R.

    2001-10-01

    The C-Mod Advanced Tokamak program depends on the unique capability of the C-Mod facility to operate with plasma pulse lengths corresponding to multiple skin times with high performance parameters. Specifically, pulse lengths with current and toroidal field flattops of order 5 seconds, with toroidal field of 4 tesla, are proposed. In the case of the AT program, these plasmas would have current sustained non-inductively, i.e. by a combination of RF (lower hybrid) current drive and pressure-driven current. Experiments during the 2001 experimental campaign will extend the plasma pulse length to the maximum possible with only inductive current drive. The purpose of these experiments is to test and demonstrate the long-pulse capability of the coils, power system, control system, etc., and to test power and particle handling performance under long pulse conditions. In support of the latter goal, we will benchmark divertor surface heating during medium-power operation and assess the effectiveness of X-point sweeping and N2 puffing for dissipating the divertor heat loads. Results of these experiments will be presented.

  1. 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.

  2. 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.

  3. 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.

  4. 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.; Nelson-Melby, E.; Porkolab, M.; Wukitch, S. J.

    1999-09-20

    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. (c) 1999 American Institute of Physics.

  5. 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.

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

    SciTech Connect

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

    2012-12-15

    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.

  7. 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.

  8. Lower Hybrid Coupling Experiments on Alcator C-Mod

    SciTech Connect

    Wallace, G.; Bonoli, P.; Parisot, A.; Parker, R.; Schmidt, A.; Wilson, J. R.

    2007-09-28

    The Alcator C-Mod Lower Hybrid Current Drive experiment launches RF waves at 4.6 GHz via 4 rows of 22 phased waveguides. Forward and reflected power is measured with 156 directional couplers in the launcher structure. Langmuir probes mounted to the front of the antenna monitor density at the plasma edge and act as RF probes for the observation of parametric decay instability. Measurements of the coupling of lower hybrid waves have been performed at power levels approaching 1 MW. Edge density, launched n{sub parallel} spectrum, and plasma shape have been adjusted to optimize coupling in L-mode plasmas. Experimentally observed coupling results will be compared to simulations from the Brambilla Grill code [1].

  9. Two dimensional radiated power diagnostics on Alcator C-Mod.

    PubMed

    Reinke, M L; Hutchinson, I H

    2008-10-01

    The radiated power diagnostics for the Alcator C-Mod tokamak have been upgraded to measure two dimensional structure of the photon emissivity profile in order to investigate poloidal asymmetries in the core radiation. Commonly utilized unbiased absolute extreme ultraviolet (AXUV) diode arrays view the plasma along five different horizontal planes. The layout of the diagnostic set is shown and the results from calibrations and recent experiments are discussed. Data showing a significant, 30%-40%, inboard/outboard emissivity asymmetry during ELM-free H-mode are presented. The ability to use AXUV diode arrays to measure absolute radiated power is explored by comparing diode and resistive bolometer-based emissivity profiles for highly radiative L-mode plasmas seeded with argon. Emissivity profiles match in the core but disagree radially outward resulting in an underprediction of P(rad) of nearly 50% by the diodes compared to P(rad) determined using resistive bolometers. PMID:19044619

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

    SciTech Connect

    Niemczewski, A.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. 146 refs., 82 figs., 14 tabs.

  11. 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.

  12. Gyrokinetic Simulations of Impurity Seeded C-Mod Ohmic Plasmas

    NASA Astrophysics Data System (ADS)

    Porkolab, Miklos; Ennever, Paul; Rice, John; Rost, J. Chris; Davis, Evan; Ernst, Darin; Fiore, Catherine; Hubbard, Amanda; Hughes, Jerry; Terry, Jim; Tsujii, Naoto; Candy, Jeff; Staebler, Gary; Reinke, Matthew; Alcator C-Mod Team

    2014-10-01

    Ohmic plasmas on C-Mod were seeded with nitrogen to study the impact of dilution in the LOC (linear ohmic) and SOC (saturated ohmic) regimes. The seeding decreased ion diffusivity and caused the rotation to reverse in certain cases. TGLF, TGYRO, and global GYRO simulations were performed on these plasmas, simulating both the transport and the density fluctuations. TGYRO simulations using TGLF showed that the ion temperature profile only needed slight modification to get agreement with the heat flux, and the electron temperature profile needed almost no modification. However, when these TGYRO modified profiles were simulated with global GYRO the ion and electron fluxes were much lower than the experimental measurements and the TGLF simulated fluxes. The average of the TGYRO and experimental profiles gave ion fluxes that agreed with the experimental fluxes, and the density fluctuations agreed with PCI measurements. The electron flux from GYRO is below experimental levels, and since these plasmas have little TEM turbulence ETG simulations are being performed to make up the difference. Results will be presented. Work supported by US DOE awards DE-FG02-94-ER54235 and DE-FC02-99-ER54512.

  13. 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.

  14. Scrape-off layer reflectometer for Alcator C-Mod.

    PubMed

    Lau, Cornwall; Hanson, Greg; Wilgen, John; Lin, Yijun; Wukitch, Steve

    2010-10-01

    A swept-frequency X-mode reflectometer is being built for Alcator C-Mod to measure the scrape-off layer density profiles at the top, middle, and bottom locations in front of both the new lower hybrid launcher and the new ion cyclotron range of frequencies antenna. The system is planned to operate between 100 and 146 GHz at sweep rates from 10 μs to 1 ms, and will cover a density range of approximately 10(16)-10(20) m(-3) at B(0)=5-5.4 T. To minimize the effects of density fluctuations, both differential phase and full phase reflectometry will be employed. Design, test data, and calibration results of this electronics system will be discussed. To reduce attenuation losses, tallguide (TE(01)) will be used for most of the transmission line system. Simulations of high mode conversion in tallguide components, such as e-plane hyperbolic secant radius of curvature bends, tapers, and horn antennas will be shown. Experimental measurements of the total attenuation losses of these components in the lower hybrid waveguide run will also be presented. PMID:21033950

  15. Scrape-off layer reflectometer for Alcator C-Mod

    SciTech Connect

    Lau, Cornwall; Lin Yijun; Wukitch, Steve; Hanson, Greg; Wilgen, John

    2010-10-15

    A swept-frequency X-mode reflectometer is being built for Alcator C-Mod to measure the scrape-off layer density profiles at the top, middle, and bottom locations in front of both the new lower hybrid launcher and the new ion cyclotron range of frequencies antenna. The system is planned to operate between 100 and 146 GHz at sweep rates from 10 {mu}s to 1 ms, and will cover a density range of approximately 10{sup 16}-10{sup 20} m{sup -3} at B{sub 0}=5-5.4 T. To minimize the effects of density fluctuations, both differential phase and full phase reflectometry will be employed. Design, test data, and calibration results of this electronics system will be discussed. To reduce attenuation losses, tallguide (TE{sub 01}) will be used for most of the transmission line system. Simulations of high mode conversion in tallguide components, such as e-plane hyperbolic secant radius of curvature bends, tapers, and horn antennas will be shown. Experimental measurements of the total attenuation losses of these components in the lower hybrid waveguide run will also be presented.

  16. Scrape-off layer reflectometer for Alcator C-Mod.

    PubMed

    Hanson, G R; Wilgen, J B; Lau, C; Lin, Y; Wallace, G M; Wukitch, S J

    2008-10-01

    A two-frequency x-mode reflectometer operating from 100 to 146 GHz is deployed on Alcator C-Mod to measure the density profile and fluctuations in the scrape-off layer (SOL) immediately in front of the new J-port ICRF antenna and the new C-port lower hybrid launcher. The reflectometer covers densities from 10(16) to 10(20) m(-3) at 5-5.4 T. To provide the greatest flexibility and capability to deal with density fluctuations approaching 100% peak-to-peak in the SOL, both full-phase and differential-phase measurement capabilities with sweep speeds of approximately 10 micros to >1 ms are implemented. The differential-phase measurement uses a difference frequency of 500 MHz, corresponding to cutoff layer separations ranging from about 0.1 to 1 mm. The reflectometer has six sets of launchers: three on the ICRF antenna and three on the lower hybrid launcher. Both the ICRF antenna and the lower hybrid launcher incorporate reflectometer antennas at their top, bottom, and midplane locations. PMID:19044598

  17. Scrape-off layer reflectometer for Alcator C-Mod

    SciTech Connect

    Hanson, G. R.; Wilgen, J. B.; Lau, C.; Lin, Y.; Wallace, G. M.; Wukitch, S. J.

    2008-10-15

    A two-frequency x-mode reflectometer operating from 100 to 146 GHz is deployed on Alcator C-Mod to measure the density profile and fluctuations in the scrape-off layer (SOL) immediately in front of the new J-port ICRF antenna and the new C-port lower hybrid launcher. The reflectometer covers densities from 10{sup 16} to 10{sup 20} m{sup -3} at 5-5.4 T. To provide the greatest flexibility and capability to deal with density fluctuations approaching 100% peak-to-peak in the SOL, both full-phase and differential-phase measurement capabilities with sweep speeds of {approx}10 {mu}s to >1 ms are implemented. The differential-phase measurement uses a difference frequency of 500 MHz, corresponding to cutoff layer separations ranging from about 0.1 to 1 mm. The reflectometer has six sets of launchers: three on the ICRF antenna and three on the lower hybrid launcher. Both the ICRF antenna and the lower hybrid launcher incorporate reflectometer antennas at their top, bottom, and midplane locations.

  18. 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

  19. 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.

  20. 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).

  1. 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.

  2. 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.

  3. 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.

  4. Overview of the Alcator C-Mod Research Program

    NASA Astrophysics Data System (ADS)

    Marmar, E.; Bader, A.; Bakhtiari, M.; Barnard, H.; Beck, W.; Bespamyatnov, I.; Binus, A.; Bonoli, P.; Bose, B.; Bitter, M.; Cziegler, I.; Dekow, G.; Dominguez, A.; Duval, B.; Edlund, E.; Ernst, D.; Ferrara, M.; Fiore, C.; Fredian, T.; Graf, A.; Granetz, R.; Greenwald, M.; Grulke, O.; Gwinn, D.; Harrison, S.; Harvey, R.; Hender, T. C.; Hosea, J.; Hill, K.; Howard, N.; Howell, D. F.; Hubbard, A.; Hughes, J. W.; Hutchinson, I.; Ince-Cushman, A.; Irby, J.; Izzo, V.; Kanojia, A.; Kessel, C.; Ko, J. S.; Koert, P.; La Bombard, B.; Lau, C.; Lin, L.; Lin, Y.; Lipschultz, B.; Liptac, J.; Ma, Y.; Marr, K.; May, M.; McDermott, R.; Meneghini, O.; Mikkelsen, D.; Ochoukov, R.; Parker, R.; Phillips, C. K.; Phillips, P.; Podpaly, Y.; Porkolab, M.; Reinke, M.; Rice, J.; Rowan, W.; Scott, S.; Schmidt, A.; Sears, J.; Shiraiwa, S.; Sips, A.; Smick, N.; Snipes, J.; Stillerman, J.; Takase, Y.; Terry, D.; Terry, J.; Tsujii, N.; Valeo, E.; Vieira, R.; Wallace, G.; Whyte, D.; Wilson, J. R.; Wolfe, S.; Wright, G.; Wright, J.; Wukitch, S.; Wurden, G.; Xu, P.; Zhurovich, K.; Zaks, J.; Zweben, S.

    2009-10-01

    This paper summarizes highlights of research results from the Alcator C-Mod tokamak covering the period 2006-2008. Active flow drive, using mode converted ion cyclotron waves, has been observed for the first time in a tokamak plasma, using a mix of D and 3He ion species; toroidal and poloidal flows are driven near the location of the mode conversion layer. ICRF induced edge sheaths are implicated in both the erosion of thin boron coatings and the generation of metallic impurities. Lower hybrid range of frequencies (LHRF) microwaves have been used for efficient current drive, current profile modification and toroidal flow drive. In addition, LHRF has been used to modify the H-mode pedestal, increasing temperature, decreasing density and lowering the pedestal collisionality. Studies of hydrogen isotope retention in solid metallic plasma facing components reveal significantly higher retention than expected from ex situ laboratory studies; a model to explain the results, based on plasma/neutral induced lattice damage, has been developed and tested. During gas-puff mitigation of disruptions, induced MHD instabilities cause the magnetic field to become stochastic, resulting in reduction of halo currents, spreading of plasma power loading and loss of runaway electrons before they cause damage. Detailed pedestal rotation profile measurements have been used to infer Er profiles, and correlation with global H-mode confinement. An improved L-mode regime, obtained at q95 <= 3 with ion drift away from the active X-point, shows very good energy confinement with a strong temperature pedestal, a weak density pedestal, and no evidence of particle or impurity accumulation, without the need for ELMs or any additional edge density regulation mechanism.

  5. Alcator C-Mod: A high-field divertor tokamak

    NASA Astrophysics Data System (ADS)

    Lipschultz, B.; Becker, H.; Bonoli, P.; Coleman, J.; Fiore, C.; Golovato, S.; Granetz, R.; Greenwald, M.; Gwinn, D.; Humphries, D.; Hutchinson, I.; Irby, J.; Marmar, E.; Montgomery, D. B.; Najmabadi, F.; Parker, R.; Porkolab, M.; Rice, J.; Sevillano, E.; Takase, Y.; Terry, J.; Watterson, R.; Wolfe, S.

    1989-04-01

    The Alcator C-Mod tokamak is a new device presently under construction at Massachusetts Institute of Technology (M.I.T.) which is scheduled to begin operation in mid-1990. The projected operating parameters are as follows: Toroidal field of 9 T; Ip ≤ 3 MA, R = 66.5 cm, a = 21 cm, κ ≤ 2.0, δ ≤ 0.5, ne ≤ 10 21m-3, PICRF ≤ 6 MW. The divertor configuration includes mechanical baffling as opposed to an 'open' geometry. Under strictly ohmic heating conditions, central Ti and Te are predicted to be in the range 2.5-3.5 keV over the density range (4-8) × 10 20m-3. With the addition of 6 MW of ICRF heating, Ti should vary from 4-8 keV over the same density range (assuming either Kaye-Goldston or Neo-Alcator scalings for electron confinement). Based on edge plasma characterizations from Alcator-C and divertor tokamaks, the scrape-off layer (SOL) properties are predicted to be: λn ≈ 10mm, density at the divertor plate < 2 × 10 21m-3, H 0 ionization mean free path between 1 and 10 mm. Maximum heat loads on various internal components are predicted to be in the range 5-10 MW/m 2. The flexibility of the poloidal field system in forming a number of flux surface geometries will provide further comparisons of the relative impurity control capabilities of double-null, single-null and limiter plasmas.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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

  12. Design of a Compact Lower Hybrid Coupler for Alcator C-Mod

    SciTech Connect

    Bernabei, Stefano; Hosea, Joel C.; Kung, Chun Chieh; Loesser, George D.; Rushinski, Joseph; Wilson, James R.; Parker, Ronald R.; Porkolab, Miklos

    2003-03-15

    Princeton Plasma Physics Laboratory and the Massachusetts Institute of Technology are preparing an experiment of current profile control using lower hybrid waves to produce and sustain advanced tokamak regimes in steady-state conditions in Alcator C-Mod. Unlike the Joint European Torus, ToreSupra, and JT60 couplers, the C-Mod lower hybrid coupler does not employ the now conventional multijunction design but will have similar characteristics, compactness, and internal power division while retaining full control of the antenna element phasing. This is achieved by using 3-dB vertical power splitters and a stack of laminated plates with the waveguides milled in them. Construction is simplified and allows easy control and maintenance of all parts. Many precautions are taken to avoid arcing. Special care is also taken to avoid the recycling of reflected power, which could affect the coupling and the launched n.

  13. ICRF Heating with {omega}<{omega}{sub ci} in Alcator C-Mod

    SciTech Connect

    Phillips, C. K.; Hosea, J. C.; Valeo, E. J.; Wilson, J. R.; Bonoli, P. T.; Lin, Y.; Porkolab, M.; Wright, J. C.; Wukitch, S. J.

    2007-09-28

    The TORIC 2D full wave simulation code has been used to study the dynamics of waves with {omega}<{omega}{sub ci} everywhere for all ions in the Alcator C-Mod tokamak. This potential heating regime can be accessed uniquely on C-Mod, because of its high magnetic field capability, B{sub T}{<=}8 T, and variable ICRF source frequency, 40-80 MHz. The simulations indicate that the launched fast waves can mode convert to a short wavelength slow wave on the high field side of the discharge that damps primarily on electrons. The degree to which the mode converted wave penetrates into the core of the plasma is found to depend on the equilibrium density profile.

  14. ECE Temperature Fluctuations associated with EDA H-Mode discharges in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Phillips, P. E.; Lynn, A. G.

    2006-10-01

    Alcator C-Mod exhibits an ELM-free H-mode with ``enhanced,,lpha'' emission accompanied by a quasi-coherent mode (QCM) edge relaxation mechanism. This steady state H-mode lowers the peak heat load to the diverters which is advantageous for reactor operations. A high-resolution heterodyne electron-cyclotron-emission (ECE) radiometer with 32 channels (δR˜7mm) and a bandwidth up to 1MHz covering the full radius of C-Mod has observed spatial resolved temperature fluctuations that are highly correlated with the edge QCM mode. The QCM mode is also directly observed by the edge ECE channels though the changes in optical depth due to the large density fluctuations in the QCM (˜30%). Details of these measurements will be presented in this poster.

  15. 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.

  16. 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.

  17. Correlation ECE and Doppler Backscattering Diagnostics for Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    White, A. E.; Hubbard, A.; Phillips, P.; Irby, J.; Greenwald, M.; Mikkelsen, D. R.; Howard, N. T.

    2010-11-01

    A Correlation Electron Cyclotron Emission (CECE) diagnostic and an X-mode reflectometer system are being developed to measure long wavelength (kθρs) core electron temperature fluctuations and density fluctuations, respectively, at Alcator C-Mod. These new diagnostics will allow for detailed two-field core turbulence measurements and validation studies. Adjustable optics will allow the reflectometer to be configured as a Doppler backscattering system. Global, nonlinear gyrokinetic turbulence simulations (GYRO) and synthetic diagnostics are used to model the diagnostics' expected responses to turbulence in a variety of operating regimes. The challenges associated with the high frequency systems required for core turbulence studies at C-Mod and the feasibility of combining these complementary diagnostics into a single transmission system will be assessed. Accessibility limits, expected wavenumber sensitivity and waveguide/antennae configurations are discussed.

  18. New correlation electron cyclotron emission temperature fluctuation diagnositc for Alcator C-mod

    NASA Astrophysics Data System (ADS)

    Sung, C.; White, A. E.; Irby, J.; Peebles, W. A.; Nguyen, X.

    2011-10-01

    A new Correlation Electron Cyclotron Emission (CECE) system for the measurement of electron temperature fluctuation is planned for Alcator C-mod. The multi-channel CECE radiometer will use the spectral decorrelation technique to measure turbulent fluctuations that are below thermal noise levels. The design of the optics and Intermediate Frequency (IF) section was constrained using predictions from nonlinear gyrokinetic turbulence simulations using the GYRO code. A Gaussian optical system will provide high poloidal spatial resolution (ω0 < 0 . 5 cm) needed to measure long-wavelength core turbulence at C-Mod, kθρs < 0 . 5 . The IF section will employ tunable band-pass filters to optimize turbulence measurements. We will present details of the new CECE system design and laboratory tests of the optics and IF section.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Davis, Evan; Porkolab, Miklos; Hughes, Jerry; Tsujii, Naoto; Ennever, Paul; Golfinopoulos, Ted; Gyou Baek, Seung; Terry, Jim; Xu, Xueqiao

    2012-10-01

    Energy confinement in tokamaks is believed to be strongly controlled by plasma transport in the edge region, just inside the last closed magnetic flux surface. The Boundary-plasma Turbulence (BOUT++) code is capable of simulating nonlinear fluid turbulence in this region and is well-suited to Alcator C-Mod's Enhanced D-Alpha (EDA) H-mode (&*circ;>1). The EDA H-mode is always accompanied by the quasi-coherent mode (QCM), an edge fluctuation believed to reduce impurity confinement and allow steady-state H-mode operation. Using experimentally measured profiles as input, BOUT++ calculations show that typical C-Mod EDA H-modes are ideal MHD stable but become linearly unstable when the pedestal resistivity is included (η>10-7 φ-m). The computed growth rate in these resistive ballooning modes is found to be consistent with theory, while incorporation of experimentally measured flow profiles has allowed the self-consistent temporal evolution of the edge radial electric field. Nonlinear simulations have reached turbulent steady state, and the computed turbulence spectrum will be compared with measurements from relevant C-Mod diagnostics, such as phase contrast imaging (PCI), reflectometry, gas puff imaging (GPI), and magnetic probes.

  1. The Stark II reality.

    PubMed

    Memel, Sherwin L; Grosvenor, John C

    2003-02-01

    The long awaited final regulations in Phase I of a two-phase rulemaking process under the Stark II law were published on January 4, 2001. The Phase I final rules govern interpretation of the Stark law as it is applied to referrals by a physician for designated categories of health services to entities in which the referring physician has a financial interest. These new regulations are of particular concern to specialists, such as orthopaedic surgeons, whose practices are oriented to ancillary services that are considered designated health services, such as radiology, physical therapy and durable medical equipment, and where the availability of clear guidance is essential to ensure that medically necessary care is provided in a manner that complies with law. However, rather than the "brightline" guidance that the healthcare community sought, the new regulations create uncertainty in areas that had not existed before. The new regulations require physicians to evaluate the full range of their business and professional relationships to avoid the risk of nonpayment of claims, civil money penalties, or program exclusion after the effective date of the new regulations. PMID:12567126

  2. 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.

  3. 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

  4. Production of internal transport barriers via self-generated mean flows in Alcator C-Mod

    SciTech Connect

    Fiore, C. L.; Ernst, D. R.; Podpaly, Y. A.; Howard, N. T.; Lee, Jungpyo; Reinke, M. L.; Rice, J. E.; Hughes, J. W.; Ma, Y.; Mikkelsen, D.; Rowan, W. L.; Bespamyatnov, I.

    2012-05-15

    New results suggest that changes observed in the intrinsic toroidal rotation influence the internal transport barrier (ITB) formation in the Alcator C-Mod tokamak [E. S. Marmar and Alcator C-Mod group, Fusion Sci. Technol. 51, 261 (2007)]. These arise when the resonance for ion cyclotron range of frequencies (ICRF) minority heating is positioned off-axis at or outside of the plasma half-radius. These ITBs form in a reactor relevant regime, without particle or momentum injection, with Ti Almost-Equal-To Te, and with monotonic q profiles (q{sub min} < 1). C-Mod H-mode plasmas exhibit strong intrinsic co-current rotation that increases with increasing stored energy without external drive. When the resonance position is moved off-axis, the rotation decreases in the center of the plasma resulting in a radial toroidal rotation profile with a central well which deepens and moves farther off-axis when the ICRF resonance location reaches the plasma half-radius. This profile results in strong E Multiplication-Sign B shear (>1.5 Multiplication-Sign 10{sup 5} rad/s) in the region where the ITB foot is observed. Gyrokinetic analyses indicate that this spontaneous shearing rate is comparable to the linear ion temperature gradient (ITG) growth rate at the ITB location and is sufficient to reduce the turbulent particle and energy transport. New and detailed measurement of the ion temperature demonstrates that the radial profile flattens as the ICRF resonance position moves off axis, decreasing the drive for the ITG the instability as well. These results are the first evidence that intrinsic rotation can affect confinement in ITB plasmas.

  5. 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.

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

    DOE PAGESBeta

    Diallo, A.; Hughes, J. W.; Baek, S-G.; LaBombard, Brian; Terry, J.; Cziegler, I.; Hubbard, A.; Davis, E.; Walk, J.; Delgado-Aparicio, L.; et al

    2015-01-01

    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. 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.

  7. 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.

  8. Preliminary results from the soft x-ray crystal spectrometer on Alcator C-Mod

    SciTech Connect

    Ince-Cushman, A.; Rice, J. E.; Lee, S. G.; Bitter, M.; Reinke, M.; Podpaly, Y.

    2006-10-15

    A high resolution ({lambda}/{delta}{lambda}{approx}2000) soft x-ray spectrometer has been installed on the Alcator C-Mod tokamak. The system was designed to measure emission line spectra from heliumlike neon (1s{sup 1}2p{sup 1}{yields}1s{sup 2}) in a narrow spectral band centered on {lambda}=13.5 A (920 eV). The instrument is mounted with a poloidal view 20 cm below the midplane (r/a{approx}0.85). In addition to the neon emission lines, strong fluorine, xenon, iron, and manganese lines have been observed.

  9. Edge Temperature Gradient as Intrinsic Rotation Drive in Alcator C-Mod Tokamak Plasmas

    SciTech Connect

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

    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 {nabla}T, but completely different edge {nabla}n, it may be concluded that the drive of the intrinsic rotation is the edge {nabla}T rather than {nabla}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.

  10. High density LHRF experiments in Alcator C-Mod and implications for reactor scale devices

    NASA Astrophysics Data System (ADS)

    Baek, S. G.; Parker, R. R.; Bonoli, P. T.; Shiraiwa, S.; Wallace, G. M.; LaBombard, B.; Faust, I. C.; Porkolab, M.; Whyte, D. G.

    2015-04-01

    Parametric decay instabilities (PDI) appear to be an ubiquitous feature of lower hybrid current drive (LHCD) experiments at high density. In density ramp experiments in Alcator C-Mod and other machines the onset of PDI activity has been well correlated with a decrease in current drive efficiency and production of fast electron bremsstrahlung. However whether PDI is the primary cause of the ‘density limit’, and if so by exactly what mechanism (beyond the obvious one of pump depletion) has not been clearly established. In order to further understand the connection, the frequency spectrum of PDI activity occurring during Alcator C-Mod LHCD experiments has been explored in detail by means of a number of RF probes distributed around the periphery of the C-Mod tokamak including a probe imbedded in the inner wall. The results show that (i) the excited spectra consists mainly of a few discrete ion cyclotron (IC) quasi-modes, which have higher growth than the ion sound branch; (ii) PDI activity can begin either at the inner or outer wall, depending on magnetic configuration; (iii) the frequencies of the IC quasi-modes correspond to the magnetic field strength close to the low-field side (LFS) or high-field side separatrix; and (iv) although PDI activity may initiate near the inner separatrix, the loss in fast electron bremsstrahlung is best correlated with the appearance of IC quasi-modes characteristic of the magnetic field strength near the LFS separatrix. These data, supported by growth rate calculations, point to the importance of the LFS scrape-off layer (SOL) density in determining PDI onset and degradation in current drive efficiency. By minimizing the SOL density it is possible to extend the core density regime over which PDI can be avoided, thus potentially maximizing the effectiveness of LHCD at high density. Increased current drive efficiency at high density has been achieved in FTU and EAST through lithium coating and special fuelling methods, and in recent

  11. Vertical localization of phase contrast imaging diagnostic in Alcator C-Mod

    SciTech Connect

    Lin, L.; Edlund, E. M.; Porkolab, M.; Lin, Y.; Wukitch, S. J.

    2006-10-15

    Phase contrast imaging (PCI) diagnostic has been used to study mode conversion physics of ion cyclotron range of frequency waves [E. Nelson-Melby et al., Phys. Rev. Lett. 90, 155004 (2003)], plasma turbulence [A. Mazurenko et al., Phys. Rev. Lett. 89, 225004 (2002); N. Basse et al., Phys. Plasmas 12, 052512 (2005)], and Alfven Cascades [M. Porkolab et al., IEEE Trans. Plasma Sci. 34, 229 (2006)] in Alcator C-Mod. The C-Mod PCI system measures line integrated electron density fluctuations along 32 vertical chords with a sampling frequency of 10 MHz and wavenumber resolution up to 30 cm{sup -1}. Although PCI normally lacks localization along the chords, the vertical variation of the magnetic field pitch angle allows for localized measurements for large k{sub perpendicular} fluctuations. A system consisting of a partially masked phase plate on a rotatable stage has been installed and quasicoherent modes with wave number {approx}5 cm{sup -1} associated with the enhanced D{alpha}H mode at the top and bottom of the plasma have been differentiated. In future experiments, for k{approx}30 cm{sup -1}, a spatial resolution of r/a{approx}0.3 can be achieved under ideal conditions.

  12. Spectroscopic measurement of impurity transport coefficients and penetration efficiencies in Alcator C-Mod plasmas

    NASA Astrophysics Data System (ADS)

    Graf, M. A.; Rice, J. E.; Terry, J. L.; Marmar, E. S.; Goetz, J. A.; McCracken, G. M.; Bombarda, F.; May, M. J.

    1995-01-01

    Impurity transport coefficients and the penetration efficiencies of intrinsic and injected impurities through the separatrix of diverted Alcator C-Mod discharges have been measured using x-ray and vacuum ultraviolet (VUV) spectroscopic diagnostics. The dominant low Z intrinsic impurity in C-Mod is carbon which is found to be present in concentrations of less than 0.5%. Molybdenum, from the plasma facing components, is the dominant high Z impurity and is typically found in concentrations of about 0.02%. Trace amounts of medium and high Z nonrecycling impurities can be injected at the midplane using the laser blow-off technique and calibrated amounts of recycling, gaseous impurities can be introduced through fast valves either at the midplane or at various locations in the divertor chamber. A five chord crystal x-ray spectrometer array with high spectral resolution is used to provide spatial profiles of high charge state impurities. An absolutely calibrated, grazing incidence VUV spectrograph with high time resolution and a broad spectral range allows for the simultaneous measurement of many impurity lines. Various filtered soft x-ray diode arrays allow for spatial reconstructions of plasma emissivity. The observed brightnesses and emissivities from a number of impurity lines are used together with the mist transport code and a collisional-radiative atomic physics model to determine charge state density profiles and impurity transport coefficients. Comparisons of the deduced impurity content with the measured Zeff and total radiated power of the plasma are made.

  13. 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. PMID:19256643

  14. Fuel retention measurements in Alcator C-Mod using accelerator-based in situ materials surveillance

    NASA Astrophysics Data System (ADS)

    Hartwig, Zachary S.; Barnard, Harold S.; Sorbom, Brandon N.; Lanza, Richard C.; Lipschultz, Bruce; Stahle, Peter W.; Whyte, Dennis G.

    2015-08-01

    This paper presents the first in situ time- and space-resolved measurements of deuterium (D) fuel retention in plasma-facing component (PFC) surfaces using Accelerator-based In-situ Materials Surveillance (AIMS) on the Alcator C-Mod tokamak. AIMS is a novel in situ materials diagnostic technique based on the spectroscopic analysis of nuclear reaction products induced in PFC surfaces using an ∼MeV beam of deuterons from a compact linear accelerator in between plasma shots. AIMS measurements of D retention on inner wall PFCs were acquired during diverted and limited plasma operations and during wall conditioning experiments. Intershot measurements demonstrate the local erosion and codeposition of boron films on PFC surfaces with a constant D / B ratio. This is consistent with previous results suggesting that D codeposition with boron is insufficient to account for the net retention observed in Alcator C-Mod. Changes in deuterium concentration during boronization, electron cyclotron and glow cleanings were also measured.

  15. 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.

  16. PCI measurements of Turbulence and Transport in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Ennever, P.; Porkolab, M.; Dorris, J.; Tsujii, N.; Davis, E.; Alcator C-Mod Team

    2011-10-01

    Measurements of turbulent density fluctuations on C-Mod using Phase Contrast Imaging (PCI) are reported. PCI is an interferometric technique that measures line-integrated density fluctuations at frequencies up to 2 MHz in the wave number range 0.5-30 cm-1. The PCI system on C-Mod consists of a beam that passes vertically through the plasma core and images onto a 1-D array of 32 HgCdTe detectors. Owing to lack of localization along the beam path, the signal includes contributions from the plasma edge as well as the core. To distinguish edge turbulence from that emanating from the core, we compare the spectrum to other edge localized turbulence measurements (ie, GPI, reflectometry). The core turbulence spectrum is modeled by a synthetic PCI diagnostic and nonlinear global GYRO analysis. Fluctuation spectra predicted by GYRO will be compared with those measured with PCI in different modes of plasma operation. Supported by US DoE awards DE-FG02-94-ER54235 and DE-FC02-99-ER54512.

  17. Design and operation of a novel divertor cryopumping system in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Labombard, B.; Beck, B.; Bosco, J.; Childs, R.; Gwinn, D.; Irby, J.; Leccacorvi, R.; Marazita, S.; Mucic, N.; Pierson, S.; Rokhman, Y.; Titus, P.; Vieira, R.; Zaks, J.; Zhukovsky, A.

    2007-11-01

    C-Mod's recently installed upper-divertor cryopump is unique among the world's tokamaks, employing an array of gas-pumping slots that penetrate the upper divertor target. This geometry enables the use of a single toroidal loop of liquid helium, operating in an efficient heat transfer regime with low or no helium flow. A system pumping speed of 9,600 l/sec for D2 gas has been achieved, matching that of a full-scale prototype system. Neutral pressures in the pumping slots during upper-null plasmas (USN) are found to meet or exceed pressures in the lower divertor's private flux region during lower-null (LSN) -- evidence that the pumping-slot geometry is performing as intended. Very high steady-state pumping throughputs (exceeding ˜140 torr-l/s) have been demonstrated in USN. Reliable and efficient operation of the pump has been established, synchronized with the C-Mod shot cycle and consuming 60 to 90 liters of liquid helium during a full day of operation.

  18. Advanced Tokamak Regimes in Alcator C-Mod with Lower Hybrid Current Drive

    NASA Astrophysics Data System (ADS)

    Parker, R.; Bonoli, P.; Gwinn, D.; Hutchinson, I.; Porkolab, M.; Ramos, J.; Bernabei, S.; Hosea, J.; Wilson, R.

    1999-11-01

    Alcator C-Mod has been proposed as a test-bed for developing advanced tokamak scenarios owing to its strong shaping, relatively long pulse length capability at moderate field, e.g. t ~ L/R at B = 5T and T_eo ~ 7keV, and the availability of strong ICRF heating. We plan to exploit this capability by installing up to 4 MW RF power at 4.6 GHz for efficient off-axis current drive by lower hybrid waves. By launching LH waves with a grill whose n_xx spectrum can be dynamically controlled over the range 2 < n_xx < 3.5, the driven current profile can be modified so that, when combined with bootstrap current in high ɛβ_pol regimes, q_min > 2. Such reversed or nearly zero shear regimes have already been proposed as the basis of an advanced tokamak burning-plasma experiment-ATBX (M. Porkolab et al, IAEA-CN-69/FTP/13, IAEA,Yokohama 1998.), and could provide the basis for a demonstration power reactor. Theoretical and experimental basis for this advanced tokamak research program on C-Mod, including design of the lower hybrid coupler, its spectrum and current drive capabilities will be presented.

  19. Second Harmonics of Reversed Shear TAE in Alcator C-Mod Geometry

    NASA Astrophysics Data System (ADS)

    Chen, Eugene; Berk, Herbert; Breizman, Boris; Zheng, Linjin

    2009-11-01

    Experiments on Alcator C-Mod, operating with reversed magnetic shear, reveal Toroidal Alfven Eigenmodes (TAE) together with signals at twice the mode frequency. The double frequency signals can be viewed as second harmonic sidebands driven by quadratic non-linear terms in the MHD equations, in analogy with a corresponding theory for Alfven Cascades [1]. However, these nonlinear sidebands have not yet been quantified by any of the existing codes. In this work, we extend AEGIS code [2] to capture nonlinear effects iteratively by treating the nonlinear terms as a driving source in the linear MHD solver. We first compute the TAE mode structure for realistic geometry and q-profile and then use it to find the spatial structure of the second harmonic density perturbation, which can be directly compared with PCI measurements at Alcator C-Mod. [1] H. Smith, B. N. Breizman, M. Lisak and D. Anderson, Physics of Plasmas 13 042504 (2006) [2] L. J. Zheng and M. Kotschenreuther, Journal of Computational Physics 211 (2006) 748-766

  20. Applications of visible CCD cameras on the Alcator C-Mod tokamak

    NASA Astrophysics Data System (ADS)

    Boswell, C. J.; Terry, J. L.; Lipschultz, B.; Stillerman, J.

    2001-01-01

    Five 7 mm diameter remote-head visible charge-coupled device (CCD) cameras are being used on Alcator C-Mod for several different diagnostic purposes. All of the cameras' detectors and optics are placed inside a magnetic field of up to 4 T. Images of the cameras are recorded simultaneously using two three-channel color framegrabber cards. Two CCD cameras are used typically to generate two-dimensional emissivity profiles of deuterium line radiation from the divertor. Interference filters are used to select the spectral line to be measured. The local emissivity is obtained by inverting the measured brightnesses assuming toroidal symmetry of the emission. Another use of the cameras is the identification and localization of impurity sources generated by the ion cyclotron radio frequency (ICRF) antennas, which supply the auxiliary heating on Alcator C-Mod. The impurities generated by the antennas are identified by correlating in time the injections seen at the cameras with measurements made with core diagnostics. Fibers whose views aligned with the camera views and whose outputs are coupled to a visible spectrometer are also used to identify the species of the impurities injected.

  1. 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.

  2. First measurements of core electron temperature fluctuations in Alcator C-Mod via Correlation ECE

    NASA Astrophysics Data System (ADS)

    Sung, C.; White, A.; Howard, N.; Oi, C.; Rice, J.; Gao, C.; Ennever, P.; Porkolab, M.; Hubbard, A.; Greenwald, M.

    2012-10-01

    A new Correlation Electron Cyclotron Emission (CECE) diagnostic has been installed at Alcator C-Mod to measure broadband, turbulent electron temperature fluctuations in the core region (ρ<0.9). This diagnostic has high poloidal resolution (φ0< 0.5cm ), and can measure long wavelength turbulence (kθρs< 0.4). We obtained the first electron temperature fluctuation data in Ohmic and ICRH plasmas. It was observed that the core (ρ˜0.8) electron temperature fluctuation level decreases as the Ohmic confinement regime transitions from Linear Ohmic Confinement (LOC) to Saturated Ohmic Confinement (SOC), while edge fluctuation levels (ρ> 0.9) stay similar in amplitude. These first quantitative, local electron temperature fluctuation measurements in C-Mod demonstrate that core turbulence characteristics change between LOC and SOC. In order to interpret the data, linear stability analysis is being performed, and the relation between fluctuation level and other plasma parameters is being investigated. This talk will describe the new CECE diagnostic, the SOC/LOC measurements, and associated gyrokinetic analyses.

  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. Ion Temperature and Plasma Rotation in EDA H-Mode and ITB Discharges in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Rowan, William L.; Bravenec, R. V.; Phillips, P. E.; Sampsell, M. B.; Granetz, R. S.; Lipschultz, B.; McDermott, R. M.

    2004-11-01

    In the course of the 2004 campaign on Alcator C-Mod, extensive ion temperature and plasma rotation measurements were made in the outer half of the plasma via CXRS and spectroscopy of ambient species. The most significant of these results are for the unique C-Mod modes: the EDA H-Mode and the RF induced internal transport barrier. The CXRS data was taken with a 50 ms beam pulse which occurs just once during the typical 1.5 s C-Mod discharge. Ion temperature and rotation are inferred from measurements of ambient spectra to fill out the time series for a discharge. Due regard is given to spatial averaging in using this data. Consistency of the data is checked where possible via the momentum balance equation. Thermal transport analysis (TRANSP) is included as well. A long pulse beam is planned for installation in fall 2004. Expected improvements in CXRS will be discussed.

  5. Design of a CO{sub 2}-laser Thomson scattering ion-tail diagnostic for Alcator C-Mod

    SciTech Connect

    Richards, R.K.; Hutchinson, D.P.; Ma, C.H.

    1994-09-01

    A CO{sub 2}-laser Thomson scattering diagnostic has been designed for the measurement of the ICRH-produced ion tail on Alcator C-Mod. The plasma parameters and port access require that the detection of scattered radiation be made at small angles, typically one degree or less. The receiver system consists of five heterodyne detectors and the source laser produces an energy of 10 Joules per pulse with a 1 to 5 microsecond pulse length. The scattering system is currently being installed on the Alcator C-Mod experiment. Details of the diagnostic, calculations of the expected measurements, and application of the diagnostic for ITER are presented.

  6. 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.

  7. Effects of the q Profile on Toroidal Rotation in Alcator C-Mod LHCD Plasmas

    NASA Astrophysics Data System (ADS)

    Rice, John

    2015-11-01

    Changes in the core toroidal rotation velocity profiles following injection of lower hybrid (LH) waves have been documented in Alcator C-Mod plasmas. Shot by shot scans of LH input power have been performed at fixed magnetic field and electron density for several plasma currents. If the input power is low enough that there are still sawtooth oscillations, the change in the core rotation is in the counter-current direction, consistent in sign and magnitude with direct momentum input from the LH waves. If the power level is high enough that there are significant changes to the q profile, the change in the toroidal rotation is in the co-current direction, consistent with changes in the residual stress through its dependence on the current density profile. The direction of the rotation changes depends on the whether q0 is below or above unity, and seemingly not on the magnetic shear.

  8. Molybdenum density profiles on C-Mod using FAC generated cooling curves

    NASA Astrophysics Data System (ADS)

    Reinke, M.

    2005-10-01

    For tokamaks with high-Z plasma facing components, maintaining a low impurity content is necessary to produce high quality, repeatable discharges. A GENeral Impurity Emissivity (GENIE) method is outlined for determining impurity profiles using experimental spectroscopy data, an impurity transport code, and the atomic physics package, Flexible Atomic Code (FAC). Modular programming is emphasized in order to make the method extendable to arbitrary impurities, diagnostic sets and tokamaks. Development of GENIE is ongoing, but a necessary first step is to verify FAC. A testing stage of GENIE that ignores transport is demonstrated and the results are validated against the published molybdenum cooling-curve generated using HULLAC. Bolometry and Thomson scattering data are used to determine molybdenum density profiles on Alcator C-Mod using the Mo cooling-curve. Instances where this method fails are shown as well to illustrate the need for a more advanced version of GENIE that generates and uses charge state distributions that assume transport.

  9. 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.

  10. A Lower Hybrid Current Drive System for Alcator C-Mod

    SciTech Connect

    S. Bernabei; J.C. Hosea; D. Loesser; J. Rushinski; J.R. Wilson; P. Bonoli; M. Grimes; R. Parker; M. Porkolab; D. Terry; P. Woskov

    2001-05-04

    A Lower Hybrid Current Drive system is being constructed jointly by Plasma Science and Fusion Center (PSFC) and Princeton Plasma Physics Laboratory (PPPL) for installation on the Alcator C-Mod tokamak, with the primary goal of driving plasma current in the outer region of the plasma. The Lower Hybrid (LH) system consists of 3 MW power at 4.6 GHz with a maximum pulse length of 5 seconds. Twelve klystrons will feed an array of 4-vertical and 24-horizontal waveguides mounted in one equatorial port. The coupler will incorporate some compact characteristics of the multijunction power splitting while retaining full control of the toroidal phase. In addition a dynamic phase control system will allow feedback stabilization of MHD modes. The desire to avoid possible waveguide breakdown and the need for compactness have resulted in some innovative technical solution which will be presented.

  11. Divertor heat flux footprints in EDA H-mode discharges on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Labombard, B.; Terry, J. L.; Hughes, J. W.; Brunner, D.; Payne, J.; Reinke, M. L.; Lin, Y.; Wukitch, S.

    2011-08-01

    The physics that sets the width of the power exhaust channel in a tokamak scrape-off layer and its scaling with engineering parameters is of fundamental importance for reactor design, yet it remains to be understood. An extensive array of divertor heat flux diagnostics was recently commissioned in Alcator C-Mod with the aim of improving our understanding. Initial results are reported from EDA H-mode discharges in which plasma current, input power, toroidal field and magnetic topology were varied. The integral width of the outer divertor heat flux footprint is found to lie in the range of 3-5 mm mapped to the mid-plane. Widths are insensitive to single versus double-null topology and the magnitude of toroidal field. Pedestal physics appears to largely determine these widths; a dependence of width on plasma thermal energy is noted, yielding a reduction in width as plasma current is increased for the best EDA H-modes.

  12. First results of the SOL reflectometer on Alcator C-Mod.

    PubMed

    Lau, C; Hanson, G; Lin, Y; Wilgen, J; Wukitch, S; Labombard, B; Wallace, G

    2012-10-01

    A swept-frequency X-mode reflectometer has been built on Alcator C-Mod to measure the scrape-off layer (SOL) density profiles adjacent to the lower hybrid launcher. The reflectometer system operates between 100 and 146 GHz at sweep rates from 10 μs to 1 ms and covers a density range of ∼10(16)-10(20) m(-3) at B(0) = 5-5.4 T. This paper discusses the analysis of reflectometer density profiles and presents first experimental results of SOL density profile modifications due to the application of lower hybrid range-of-frequencies power to L-mode discharges. Comparison between density profiles measured by the X-mode reflectometer and scanning Langmuir probes is also shown. PMID:23126969

  13. 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.

  14. 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.

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

    PubMed

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

    2012-10-01

    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(θ) ≤ 4.8 cm(-1) (k(θ)ρ(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. PMID:23126971

  16. First Results From the Alcator C-Mod Lower Hybrid Experiment

    NASA Astrophysics Data System (ADS)

    Parker, Ronald; Bernabei, Stefano; Grimes, Montgomery; Hosea, Joel; Johnson, David; Wilson, Randy

    2005-10-01

    A lower hybrid system operating at 4.6 GHz and capable of 3 MW source power has been installed on Alcator C-Mod. The grill facing the plasma consists of 4 rows of 24 waveguides. Electronic control of the amplitude and phase of the 12 klystrons supplying the RF power enables the launcher's n|| spectrum to be dynamically controlled over a wide range with a time response of 1 ms. Since the deposition of current depends on n|| as well as the temperature profile, the spatial distribution of the driven current can be varied with the same time response. Detection of fast electron Bremsstrahlung is the primary means of monitoring the driven current profile. Initial measurements at the 100 kW power level show that reflection coefficients as low as 7% are obtained at optimal phasing and density at the grill mouth. Comparison of these results with modeling predictions will be presented in a companion paper.

  17. 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.

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    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.

    2015-06-01

    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.

  1. 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.

  2. 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.

  3. 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.

  4. Studies of Electron Temperature Fluctuations in the Core of Alcator C-Mod Plasmas via Correlation ECE

    NASA Astrophysics Data System (ADS)

    Oi, C.; Sung, C.; Howard, N.; White, A. E.; Irby, J.; Leccacorvi, R.; Vieira, R.; Rice, J.; Gao, C.

    2012-10-01

    A correlation electron cyclotron emission (CECE) diagnostic has been designed and installed at the Alcator C-Mod tokamak to measure long wavelength fluctuations in electron temperature [C. Sung, this conference, C-Mod oral session]. It is important to characterize turbulent fluctuations in the plasma in order to better understand and predict transport, since the cross-magnetic field transport of particles and energy in fusion plasmas exceeds the values predicted by neoclassical theory. The first electron temperature fluctuation data collected from Alcator C-Mod ohmic plasmas has shown that as the ohmic confinement regime transitions from Linear Ohmic Confinement (LOC) to Saturated Ohmic Confinement (SOC) there is a decrease in the core electron temperature fluctuation level. The edge electron temperature fluctuations are similar between the two modes, suggesting that mainly the core turbulence characteristics change when there is a shift between LOC and SOC regimes. In both ohmic and ICRH plasmas, the measured spectrum is seen to broaden in response to increases in plasma rotation; and fluctuation level increases with radius. A description of the C-Mod CECE diagnostic will be presented, along with the initial measurements of turbulent electron temperature fluctuations.

  5. Edge radial electric field structure and its connections to H-mode confinement in Alcator C-Mod plasmas

    SciTech Connect

    McDermott, R. M.; Lipschultz, B.; Hughes, J. W.; Catto, P. J.; Hubbard, A. E.; Hutchinson, I. H.; Granetz, R. S.; Greenwald, M.; LaBombard, B.; Marr, K.; Reinke, M. L.; Rice, J. E.; Whyte, D.

    2009-05-15

    High-resolution charge-exchange recombination spectroscopic measurements of B{sup 5+} ions have enabled the first spatially resolved calculations of the radial electric field (E{sub r}) in the Alcator C-Mod pedestal region [E. S. Marmar, Fusion Sci. Technol. 51, 261 (2006)]. These observations offer new challenges for theory and simulation and provide for important comparisons with other devices. Qualitatively, the field structure observed on C-Mod is similar to that on other tokamaks. However, the narrow high-confinement mode (H-mode) E{sub r} well widths (5 mm) observed on C-Mod suggest a scaling with machine size, while the observed depths (up to 300 kV/m) are unprecedented. Due to the strong ion-electron thermal coupling in the C-Mod pedestal, it is possible to infer information about the main ion population in this region. The results indicate that in H-mode the main ion pressure gradient is the dominant contributor to the E{sub r} well and that the main ions have significant edge flow. C-Mod H-mode data show a clear correlation between deeper E{sub r} wells, higher confinement plasmas, and higher electron temperature pedestal heights. However, improved L-mode (I-mode) plasmas exhibit energy confinement equivalent to that observed in similar H-mode discharges, but with significantly shallower E{sub r} wells. I-mode plasmas are characterized by H-mode-like energy barriers, but with L-mode-like particle barriers. The decoupling of energy and particle barrier formation makes the I-mode an interesting regime for fusion research and provides for a low collisionality pedestal without edge localized modes.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. Operation of Alcator C-Mod with high-Z plasma facing components and implications

    SciTech Connect

    Lipschultz, B.; Lin, Y.; Reinke, M.L.; Hubbard, A.; Hutchinson, I.H.; Irby, J.; LaBombard, B.; Marmar, E.S.; Marr, K.; Terry, J.L.; Wolfe, S.M.; Whyte, D.

    2006-05-15

    Studies of potential plasma facing component (PFC) materials for a magnetic fusion reactor generally conclude that tungsten is the best choice due to its low tritium (T) retention, capability to handle high heat fluxes with low erosion, and robustness to nuclear damage and activation. ITER [F. Perkins et al., Nucl. Fusion 39, 2137 (1999)] may operate with all tungsten PFCs to provide the necessary operational experience for a reactor. Alcator C-Mod [I. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] operates with molybdenum (Mo) high-Z PFCs, which have very similar properties to tungsten. The experiments described herein have provided a unique comparison of operation with or without in situ boron coatings applied to the molybdenum PFCs; the latter are likely most relevant to ITER and beyond. ICRF-heated H-modes were readily achieved without boron coatings although the resultant enhancement in energy confinement was typically small (H{sub ITER,89}{approx}1). Molybdenum concentrations, n{sub Mo}/n{sub e}, rise rapidly after the H-mode transition up to 0.1%, cooling the plasma by line radiation, reducing energy confinement, and/or causing a back H/L transition. Surprisingly, the primarily molybdenum PFC surfaces retain 3.5-5.0x10{sup 20} of injected D{sub 2} molecules per discharge, corresponding to 50% of the injected gas. Plasma current disruptions, both randomly occurring over the course of a day, or planned, reduce the retained D long term. After applying boron coatings, n{sub Mo}/n{sub e} was reduced by a factor of 10-20 with H{sub ITER,89} approaching 2. A world-record volume-average plasma pressure of 1.8 atm at 5.4 T was achieved at the ITER normalized {beta}. The effects of each boronization are found to be limited in time, correlated to time-integrated input energy. Intra- and inter-discharge boronization techniques have been developed with the latter being the most successful. This initial study indicates that a low-Z coating over at least a fraction of

  11. 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.

  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. Imaging of X-point turbulence in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Ballinger, Sean; Terry, James; White, Anne; Zweben, Stewart

    2015-11-01

    A nearly tangential view of the lower X-point region of Alcator C-Mod has been coupled to a high-speed camera filtered for D-alpha line emission. Recording at ~400,000 frames per second, the system detects filaments propagating in the private flux region that are approximately aligned with the local magnetic field. This behavior appears similar to what has recently been observed in the MAST tokamak. Turbulence and transport into the private flux region is potentially important. It may be a mechanism to spread heat across field lines and reduce peak heat fluxes on divertor targets. It may also explain how transport-driven flows seen in the high-field side scrape-off layer are accommodated, being otherwise too large compared to the particle flux arriving at the inner divertor target plates. The dynamics of these filaments are analyzed, as is the rate at which they are generated. Correlation analysis is used to determine the speed and trajectories of the filaments. Radial speeds of ~1 km/s are found. Clear changes are observed in the X-point-region fluctuations at the L-to-H-mode transition.

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

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

    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.

  15. 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.

  16. Collisionality dependence of impurity transport in Alcator C-Mod H-modes

    NASA Astrophysics Data System (ADS)

    Chilenski, M. A.; Greenwald, M.; Howard, N. T.; Reinke, M. L.; Rice, J.; White, A. E.; Marzouk, Y.

    2014-10-01

    Understanding and actuating impurity transport is of particular interest for future machines because of the concern that core accumulation of heavy impurities will lead to radiative collapse and higher disruptivity. This problem is expected to be especially pronounced at low collisionality, where a strong peaking of the electron density profile has previously been observed (Greenwald et al., Nucl. Fusion 47, L26 (2007)). To investigate this issue several experiments have been performed in Alcator C-Mod to measure the behavior of mid-Z (Ar, Ca) and high-Z (Mo, W) impurities in H-mode plasmas of varying collisionality (2 <νeff < 40). These plasmas are of particular interest to this problem because they are entirely RF heated and lack core particle sources. Impurities are injected using laser blow-off or gas injection and the evolution of the impurity density profile is constrained with an X-ray imaging crystal spectrometer. These diagnostics combined with analysis using STRAHL allows detailed study of the transport. Furthermore, analysis of the background ne, Te profiles is conducted using advanced techniques including Gaussian process regression. An outline of this analysis scheme will be presented and recent results obtained from its application will be shown. Supported by USDOE Award DE-FC02-99ER54512.

  17. Effects of the q profile on toroidal rotation in Alcator C-Mod LHCD plasmas

    NASA Astrophysics Data System (ADS)

    Rice, J. E.; Gao, C.; Mumgaard, R.; Parker, R. R.; Scott, S. D.; Shiraiwa, S.; Wallace, G. M.; Bonoli, P. T.; Delgado-Aparicio, L.; Fenzi, C.; Granetz, R. S.; Greenwald, M. J.; Hubbard, A. E.; Hughes, J. W.; Irby, J. H.; Lee, J. P.; Marmar, E. S.; Reinke, M. L.; Wolfe, S. M.

    2016-03-01

    Changes in the core toroidal rotation profiles following injection of lower hybrid (LH) waves have been documented in Alcator C-Mod plasmas. Shot by shot scans of LH input power have been performed at fixed magnetic field and electron density for several plasma currents. For sawtoothing target plasmas, if the input power is low enough that the central safety factor q 0 remains below 1, the change in the core rotation is in the counter-current direction, consistent in sign, magnitude and LH power scaling with direct momentum input from the LH waves. If the power level is high enough that there are significant changes to the q profile, including the termination of sawtooth oscillations, the change in the toroidal rotation is in the co-current direction, consistent with changes in the momentum flux through its dependence on the current density profile. The direction of the rotation changes depends on whether q 0 is below or above unity, and seemingly not on the magnetic shear, nor the Ohmic confinement regime of the target plasma.

  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. ICRF heating in Alcator C-Mod: Present status and future prospects

    SciTech Connect

    Porkolab, M.; Fiore, C.; Greenwald, M.; Hosea, J. C.; Hubbard, A.; Hutchinson, I.; Irby, J.; Nelson-Melby, E.; Marmar, E.; Phillips, C. K.

    1999-09-20

    Alcator C-Mod, the high field, high density, diverted, compact tokamak in the world's portfolio of high performance plasma fusion devices, is heated exclusively with ICRF auxiliary power. In this paper an overview of recent results is summarized, with particular attention given to the importance of RF operation and the flexibility afforded by different heating scenarios. Besides the routine minority heating operation, results in the mode conversion heating regime are also presented (mainly direct electron heating through mode converted ion Bernstein waves). Recent attempts at improving plasma performance by establishing internal transport barriers (ITBs) by various transient profile control techniques (the so-called Advanced Tokamak mode of operation) are also presented. Future improvements in performance afforded by the recent addition of a new 4-strap antenna and 4 MW of tunable (40-80 MHz) ICRF power are also discussed. Mode-conversion current drive (MCCD) and fast wave current drive (FWCD) will be among the many new options that will be tested with the goal of improving plasma performance. (c) 1999 American Institute of Physics.

  20. 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.

  1. Analysis of 4-strap ICRF Antenna Performance in Alcator C-Mod

    SciTech Connect

    G. Schilling; S.J. Wukitch; R.L. Boivin; J.A. Goetz; J.C. Hosea; J.H. Irby; Y. Lin; A. Parisot; M. Porkolab; J.R. Wilson; the Alcator C-Mod Team

    2003-07-31

    A 4-strap ICRF antenna was designed and fabricated for plasma heating and current drive in the Alcator C-Mod tokamak. Initial upgrades were carried out in 2000 and 2001, which eliminated surface arcing between the metallic protection tiles and reduced plasma-wall interactions at the antenna front surface. A boron nitride septum was added at the antenna midplane to intersect electric fields resulting from radio-frequency sheath rectification, which eliminated antenna corner heating at high power levels. The current feeds to the radiating straps were reoriented from an E||B to E parallel B geometry, avoiding the empirically observed {approx}15 kV/cm field limit and raising antenna voltage holding capability. Further modifications were carried out in 2002 and 2003. These included changes to the antenna current strap, the boron nitride tile mounting geometry, and shielding the BN-metal interface from the plasma. The antenna heating efficiency, power, and voltage characteristics under these various configurations will be presented.

  2. Status of the Alcator C-MOD scanning two-dimensional Thomson scattering diagnostic

    SciTech Connect

    Watterson, R. ); Chen, K. )

    1990-10-01

    The detailed study of noncircular tokamak discharges will require measurements of local {ital T}{sub {ital e}} and {ital n}{sub {ital e}} over a two-dimensional region. A novel scanning Thomson scattering system is under construction for use on the Alcator C-Mod device. A multipulse (50 Hz pulse rate) Nd:YAG laser (1 J, 15 nS) will be used to scan the plasma major radius within a 14 cm range during a 160 mS period with a spatial step size of 2 cm. The laser beam sweep, which is limited by the size of the diagnostic ports, will cover {approximately}50% of the plasma discharge cross section. The scattered laser light spectra at various positions along the vertical laser beam path will be analyzed by a set of up to 11 (initial operation is planned for six) Wadsworth spectrometers. A prototype spectrometer with associated light collection optics has been tested and the total Thomson system optical transmission has been measured to be {approximately}12--15%. System details and performance measurements will be presented.

  3. Design of off-midplane launcher (LH3) for Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Shiraiwa, S.; Bonoli, P. T.; Hillairet, J.; Meneghini, O.; Parker, R. R.; Wallace, G. M.; Wilson, J. R.; Harvey, R. W.; Smirnov, A. P.

    2012-10-01

    Improving LHCD efficiency at density above 10^20m-3 is crucial for approaching AT regimes on Alcator C-Mod. In this density regime, an unexpected loss of LHCD efficency has been observed. Modeling and experiments suggest that such loss is intrinsic to the strong multipass absorption regime and can be overcome by improving the wave single pass absorption. For this purpose, an additional launcher (LH3) was designed. Besides doubling total injected LH power, LH3 will be located off-midplane and will enhance the waves single pass absorption by velocity space synergy with the existing launcher (LH2). The poloidal location and launched N// were selected based on a large parameter scan using a ray-tracing code. About 300kA of LH driven current was predicted at 1.4e20m-3 using 1.3MW of forward power. LH3 has a grill of 4x16 active waveguides and is based on a eight-way splitter design, which splits the microwave power into four ways in the poloidal direction and two ways in the toroidal direction. Coupling studies using commercial FEM software and the ALOHA code predict good coupling in a wide range of N// (from 2.2 to 2.7). Details of RF design and progress of launcher fabrication will be reported.

  4. Rapid shutdown experiments with one and two gas jets on Alcator C-Mod

    SciTech Connect

    OlynykPlasma Scien, G.; Granetz, R. S.; Reinke, M. L.; Whyte, D. G.; Golfinopoulos, T.; Hughes, J.; Walk, J.; Izzo, V. A.; Combs, Stephen Kirk; Milora, Stanley L; Brookman, M. W.

    2013-01-01

    Massive gas injection rapid shutdown experiments have been conducted on the Alcator C-Mod tokamak using two toroidally separated gas injectors, in order to investigate the effect of multiple gas injection locations on the toroidal asymmetry in the radiated power. Toroidal radiation asymmetry is diagnosed by an array of six single-channel photodiodes mounted on the vessel wall. The presence of magnetohydrodynamic (MHD) activity is diagnosed using an array of magnetic pickup (Mirnov) coils, mounted on stalks on the vessel wall. Scans were conducted of the relative timing between the two jets, of the 95th percentile safety factor, and of the plasma elongation. It is observed that firing the two gas jets so that the injected impurities arrive at the plasma at nearly the same time produced an increase in the toroidal radiation asymmetry. In addition, the radiation asymmetry in the thermal quench phase correlates with the growth rate of low toroidal mode number MHD modes, indicating that these mode(s) are playing a role in setting the radiation asymmetry.

  5. Excitation of unstable TAEs and stable n=0 modes in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Sears, J.; Bader, A.; Parker, R. R.; Kramer, G. J.

    2009-11-01

    Toroidicity-induced Alfv'en Eigenmodes (TAEs) are weakly damped MHD modes in tokamak plasmas. The modes occur at discrete frequencies near φTAE=vA/2qR, ( vA=B/√μ0ρ ) in a gap of the continuous spectrum of Alfv'en waves. Unstable TAEs are excited by ICRF heating of at least 3.5 MW in Alcator C-Mod L-mode plasmas. These unstable modes have toroidal mode numbers in the range of n=-6 to n=6. In contrast, stable resonant modes that are observed in these plasmas at similar and lower ICRF powers by the Active MHD diagnostic in the TAE frequency range commonly have toroidal mode numbers of n=0, which precludes a TAE or EAE identity. The origin of these modes is explored with the NOVA-K code, and the destabilizing role of the energetic hydrogen tail as measured by the Neutral Particle Analyzer is presented.

  6. Tomography of Light Emission from the Plasma Edge of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Kurz, Christian

    1995-01-01

    This thesis focuses on the development of a tomographic technique used on the Alcator C-Mod tokamak to reconstruct local emissivity profiles from line-of-sight integrated brightness measurements of H_{alpha } and low-Z plasma impurities. The knowledge of H_{alpha} emissivity profiles in particular opens up the possibility to calculate important plasma parameters such as the particle confinement time, parallel plasma flow velocities in the edge, and local neutral densities. These calculations depend on the knowledge of plasma temperature and density in the respective regions. A simple plasma model for the edge region is developed to interpolate between measurement data of Langmuir probes at the divertor target and upstream. The neutral density profile along the outer divertor target plate is examined during attached and detached divertor plasma conditions. The neutral densities found in the divertor are consistent with neutral pressure data from pressure gauges at the midplane and at the bottom of the divertor. Application of the inversion algorithm to CII and CIII impurity radiation is successfully demonstrated. Total radiation profiles measured by bolometers are examined during methane impurity gas puffing and plasma detachment, and found to agree well with reconstructed CIII profiles. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253 -1690.).

  7. 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.

  8. 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.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

    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 et al., Phys. Plasmas 1, 1511 (1994)] is modeled and analyzed with the multi-fluid code UEDGE [T. D. Rognlien et al., J. Nucl. Mater. 196-198, 347 (1992)]. Matching the experimental plasma density profiles in the scrape-off layer (SOL) requires a spatially dependent effective anomalous diffusion coefficient D⊥ growing rapidly towards the wall. The midplane pressure of neutral gas, Pmid, 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 Pmid˜0.3 mTorr when the main wall provides ˜70% of recycling neutrals in the main chamber. In the upper SOL (well above the 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 Pmid case, heat conduction by CX neutrals along with radial heat convection by plasma carries most of the power flux (˜75%) across the last closed flux surface. Even in the low Pmid case, heat conduction by CX neutrals dominates the radial heat flux far out in the SOL.

  11. Upgrades to the 4-strap ICRF antenna in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

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

    2001-10-01

    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 2/2000, 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 7/2000, with the installation of BN plasma-facing tiles and radiofrequency 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 2/2001 and will be completed by this meeting. All the above upgrades and their effect on antenna performance will be presented.

  12. First ion temperature profiles in the boundary of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Brunner, Dan; Labombard, Brian; Churchill, Michael; Lipschultz, Bruce; Ochoukov, Roman; Theiler, Christian; Whyte, Dennis

    2012-10-01

    The ion temperature is an important parameter in the boundary of magnetic fusion devices, playing a role in the sheath heat flux, total plasma pressure, plasma potential, and sound speed. High spatial resolution measurements of Ti and Te profiles are needed to evaluate these quantities and to unfold the rates of cross-field heat transport in each species. To this end, we have developed two specialized scanning probes: an Ion Sensitive Probe (ISP) and a Retarding Field Analyzer (RFA). Alcator C-Mod is a challenging environment for probes, with parallel heat fluxes comparable to that expected in reactors, 100's MW/m^2, necessitating the use of refractory materials in compact, optimized geometries. The two probes, along with Charge-eXchange Recombination Spectroscopy (CXRS) measurements of B^5+ ions, allow important cross-checks to be performed. Preliminary results indicate good agreement between the ISP and RFA. Comparison with B^5+ CXRS is also favorable. In ohmic-heated, sheath-limited plasmas the ratio of Ti/Te is ˜3 (150 and 50 eV) at the seperatrix and increases to ˜5 (50 and 10 eV) at the limiter boundary. Experiments with conduction-limited plasma conditions are planned and will be reported. Implications for boundary electron and ion heat transport will also be discussed.

  13. 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.

  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. Validation study of gyrokinetic simulation (GYRO) near the edge in Alcator C-Mod ohmic discharges

    NASA Astrophysics Data System (ADS)

    Sung, C.; White, A.; Howard, N.; Mikkelsen, D.; Holland, C.; Rice, J.; Reinke, M.; Gao, C.; Ennever, P.; Porkolab, M.; Churchill, R.; Theiler, C.; Walk, J.; Hughes, J.; Hubbard, A.; Greenwald, M.

    2014-10-01

    A validation study of local gyrokinetic simulations (GYRO) near the edge region (r / a ~ 0 . 85) has been performed for two C-Mod ohmic discharges, namely one that is in the Linear Ohmic Confinement (LOC) regime and the other one in the Saturated Ohmic Confinement (SOC) regime. Comparing the simulated heat fluxes and synthetic Te fluctuations with the experiments, it is found that GYRO can reproduce the ion heat flux and the Te fluctuation level measured by the Correlation ECE (CECE) diagnostic within their uncertainties, while the simulated electron heat flux is under-predicted. Furthermore, the synthetic Te spectral shape is not matched with the measured spectrum in both LOC/SOC discharges. We have also performed global simulations to consider the interaction of turbulence within the sampling volume of the CECE diagnostic, enabling us to evaluate the importance of global simulations in applying a synthetic CECE diagnostic in this study. The LOC/SOC transition physics will be also explored. Research supported by USDoE Awards DE-SC0006419, DE-FC02-99ER54512.

  16. Effects of the q profile on toroidal rotation in Alcator C-Mod LHCD plasmas

    SciTech Connect

    Rice, J. E.; Mumgaard, R.; Parker, R.; Scott, S.; Shiraiwa, S.; Wallace, G. M.; Bonoli, P. T.; Delgado-Aparicio, L.; Fenzi, C.; Granetz, R. S.; Greenwald, M. J.; Hubbard, A. E.; Hughes, J. W.; Irby, J.; Lee, J. P.; Marmar, E. S.; Wolfe, S. M.

    2016-01-01

    Changes in the core toroidal rotation profiles following injection of lower hybrid (LH) waves have been documented in Alcator C-Mod plasmas. Shot by shot scans of LH input power have been performed at fixed magnetic field and electron density for several plasma currents. For sawtoothing target plasmas, if the input power is low enough that the central safety factor q0 remains below 1, the change in the core rotation is in the counter-current direction, consistent in sign, magnitude and LH power scaling with direct momentum input from the LH waves. If the power level is high enough that there are significant changes to the q profile, including the termination of sawtooth oscillations, the change in the toroidal rotation is in the co-current direction, consistent with changes in the momentum flux through its dependence on the current density profile. The direction of the rotation changes depends on whether q0 is below or above unity, and seemingly not on the magnetic shear, nor the Ohmic confinement regime of the target plasma.

  17. Disruption Mitigation Experiments with Two Gas Jets on Alcator C-Mod, and Implications for ITER

    NASA Astrophysics Data System (ADS)

    Granetz, R. S.; Olynyk, G. M.; Reinke, M. L.; Whyte, D. G.; Terry, J. L.; Lipschultz, B. L.; Combs, S. K.

    2012-10-01

    Until recently, all disruption mitigation experiments with massive gas injection have used one injection location at a time, and measurements have shown that the resulting radiated power is often toroidally asymmetric, which could lead to melting of first wall surfaces in ITER. Therefore, the proposed ITER MGI system has multiple gas jets distributed around the torus, but the effectiveness of this needs to be demonstrated on current machines. On Alcator C-Mod, a 2nd gas jet has been installed 154^o around the torus from the existing gas jet. The hardware components of both gas jets are nominally identical. A toroidally-distributed set of six AXUV detectors has been added to better measure the toroidal peaking factor (TPF) of the radiated power. Experiments have been carried out to characterize the effect of two jets on the radiation TPF by varying the relative timing between the firing of the gas jets shot-to-shot. Measurements of the radiation asymmetry during the pre-thermal quench, thermal quench, and current quench phases will be presented, as well as correlations with the growth rate of n=1 MHD modes. It will also be shown that very slight differences in hardware between the two gas jet systems are important. Implications for the ITER MGI system will be discussed.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The efficiency of LHCD on Alcator C-Mod drops exponentially with line average density. At reactor relevant densities (> 1 . 1020 [m-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||-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.

  20. 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.

  1. Effects of the q profile on toroidal rotation in Alcator C-Mod LHCD plasmas

    DOE PAGESBeta

    Rice, J. E.; Gao, C.; Mumgaard, R.; Parker, R. R.; Scott, S. D.; Shiraiwa, S.; Wallace, G. M.; Bonoli, P. T.; Delgado-Aparicio, L.; Fenzi, C.; et al

    2016-02-09

    Changes in the core toroidal rotation profiles following injection of lower hybrid (LH) waves have been documented in Alcator C-Mod plasmas. Shot by shot scans of LH input power have been performed at fixed magnetic field and electron density for several plasma currents. For sawtoothing target plasmas, if the input power is low enough that the central safety factor q0 remains below 1, the change in the core rotation is in the counter-current direction, consistent in sign, magnitude and LH power scaling with direct momentum input from the LH waves. If the power level is high enough that there aremore » significant changes to the q profile, including the termination of sawtooth oscillations, the change in the toroidal rotation is in the co-current direction, consistent with changes in the momentum flux through its dependence on the current density profile. Furthermore, the direction of the rotation changes depends on whether q0 is below or above unity, and seemingly not on the magnetic shear, nor the Ohmic confinement regime of the target plasma.« less

  2. 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.

  3. Initial Operation of the Alcator C-Mod ICRF Antennas with High-Z Metal Antenna Guards

    SciTech Connect

    Schilling, G.; Wukitch, S.J.; Lin, Y.; Parisot, A.; Porkolab, M.

    2005-09-26

    The Alcator C-Mod ICRF antennas have been operated with BN antenna guards since 2000. This modification had followed the observation that metallic impurities in the plasma increased with increasing ICRF power. Systematic improvements to the antenna structure have allowed the launched power to be raised to the 6 MW level, with good heating efficiency and few deleterious effects on the plasma. BN is inherently fragile, and disruption mechanical shocks have resulted in fracturing of the antenna tiles, exposing the supporting metal structure. Since the antennas are now electrically in reasonable shape, and one of C-Mod's goals is to study the behavior of plasmas with all-metal plasma facing components, it was decided to replace the BN tiles with molybdenum. High power operation was resumed in March, 2005, and the behavior of the antennas during the present run campaign will be reported.

  4. 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.

  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. 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.

  7. 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. PMID:21456742

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

    SciTech Connect

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

    2011-03-15

    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 {approx}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.

  9. First operation of a high-heat flux, flush mounted ``rail'' Langmuir probe array on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Kuang, Adam Q.; Brunner, Dan; Labombard, Brian; Leccacorvi, Rick; Vieira, Rui

    2015-11-01

    Divertor Langmuir probes are typically built proud of the divertor surface for an accurate measurement of the plasma flux. However, under the high heat flux conditions seen in Alcator C-Mod, proud tungsten probes that present a 10 degree attack angle to the incident heat flux can experience melt damage with less then 1 second plasma exposure time. A similar situation is anticipated for ITER. It is therefore desirable to develop a flush probe system that can both survive reactor-level fluxes and take accurate measurements. A poloidal array of 21 flush-mounted ``rail'' probes have been installed in the C-Mod outer divertor plate, which are toroidally-extended and field-aligned to minimize sheath expansion effects. Initial results indicate that the ``rail'' probes have a well-defined ion saturation current, reporting similar density and temperature measurements as proud probes. However, uncertainty in the projected area becomes significant when the incident magnetic field angle becomes less than ~0.5 degrees. Additionally, because the flush probes are conformal to the divertor surface, they are ideally suited to measure the poloidal distribution of halo currents during disruptions. Supported by USDoE C-Mod award DE-FC02-99ER54512.

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

    SciTech Connect

    Urbahn, J.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.

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

    SciTech Connect

    Garnier, D.T.

    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 ({ell}{sub p} {le} 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{sup +} 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 = {infinity} and the n = 1 marginal stability limits.

  12. 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.

  13. 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.

  14. 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.

  15. Development of Absolute Calibration of the Phase Contrast Imaging Diagnostic and Experimental Tests in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Tsujii, N.; Porkolab, M.; Edlund, E. M.; Lin, L.

    2007-11-01

    The Phase Contrast Imaging (PCI) system in Alcator C-Mod is used to measure density perturbations from MHD modes, turbulence and RF waves. Recently, an absolutely calibrated system has been installed. This system consists of a set of transducers which cover frequency from 30 kHz to 200 kHz, and wavenumber from 5.5 cm-1 to 36.6 cm-1. The amplitude and phase of the transducer wavefronts are measured using a calibrated microphone. We will present the system design and modeling of this calibration system. Initial results, including a comparison with experimental measurements will also be discussed, if available.

  16. Observation of Reversed Shear Alfvén Eigenmodes between Sawtooth Crashes in the Alcator C-Mod Tokamak

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

    Groups of frequency chirping modes observed between sawtooth crashes in the Alcator C-Mod tokamak are interpreted as reversed shear Alfvén eigenmodes near the q=1 surface. These modes indicate that a reversed shear q profile is generated during the relaxation phase of the sawtooth cycle. Two important parameters, qmin⁡ and its radial position, are deduced from comparisons of measured density fluctuations with calculations from the ideal MHD code NOVA. These studies provide valuable constraints for further modeling of the sawtooth cycle.

  17. 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.

  18. Comparison of GS2 Turbulence Simulations with Phase Contrast Imaging in Alcator C-Mod Internal Transport Barriers

    NASA Astrophysics Data System (ADS)

    Long, Andrew; Ernst, Darin

    2005-10-01

    Trapped electron mode (TEM) turbulence arises in gyrokinetic simulations of internal transport barriers in Alcator C-mod experiments [1]. C-mod is equipped with a PCI (phase contrast imaging) diagnostic which measures density fluctuations along 32 vertical chords passing near the magnetic axis. The GS2 density fluctuations are output as an integral along field lines. The GS2 poloidal wavelength spectrum is upshifted relative to the PCI spectrum [1]. To make the comparison more direct, we have modified GS2 [2] to calculate electron density fluctuations at the poloidal angles observed by PCI. The longer wavelength modes are more extended along field lines, so that when viewed off the midplane, they are weighted more strongly. Nonlinear simulations are underway, and results will be presented. [1] D. R. Ernst et al., 20th IAEA Fusion Energy Conf. IAEA-CN-116/TH/4-1. also Phys. Plasmas 11(5) 2637 (2004). http://www-naweb.iaea.org/napc/physics/fec/fec2004/datasets/TH4-1.html [2] W. Dorland et al., Phys. Rev. Lett. 85(26) 5579 (2000). funding: Contract number DE-AC02-76CH03073.

  19. Reduced-model (SOLT) simulations of an EDA H-mode shot at Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Russell, D. A.; D'Ippolito, D. A.; Myra, J. R.; Labombard, B.; Terry, J. L.; Zweben, S. J.

    2011-10-01

    Reduced-model scrape-off layer turbulence (SOLT) simulations of an Enhanced D-Alpha (EDA) H-mode observed at C-Mod were conducted to explore observed variations in scrape-off-layer (SOL) width. The amplitude of a mean poloidal flow was varied to control the level of turbulence in the simulation and to reproduce the observed heat flux across the separatrix. SOL width decreased with increasing input power and with increasing separatrix temperature in both experiment and simulation, consistent with the strong temperature dependence of collision-limited parallel heat flux. A persistent quasi-coherent mode (QCM) dominates the SOLT turbulence. The wavelength of the SOLT QCM is comparable to that of the QCM consistently observed on C-Mod during EDA operation. The SOLT QCM consists of a quasi-stationary string of vortices, located just inside the separatrix, poloidally convected by the mean flow and occasionally emitting blobs into the SOL. The mode frequency is dominated by the Doppler shift of this convected pattern. Analysis reveals underlying drift-interchange and Kelvin-Helmholtz instabilities. Supported by USDOE under DE-FG02-97ER54392, DE-AC02-09CH11466, DE-FC02-99ER54512 and S009625-F.

  20. Comparison of electron temperature fluctuations with gyrokinetic sumulations across the ohmic energy confinement transition in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Sung, C.; White, A.; Howard, N.; Mikkelsen, D.; Rice, J.; Reinke, M.; Gao, C.; Ennever, P.; Porkolab, M.; Churchill, R.; Theiler, C.; Hubbard, A.; Greenwald, M.

    2013-10-01

    Long wavelength electron temperature fluctuations (kyρs < 0 . 3) near the edge (r / a ~ 0 . 85) are reduced across the ohmic confinement transition from Linear Ohmic Confinement(LOC) regime to Saturated Ohmic Confinement(SOC) regime in Alcator C-Mod. Linear stability analysis shows that the dominant mode of long wavelength turbulence near the edge is changed from Trapped Electron Mode(TEM) to Ion Temperature Gradient(ITG) mode while the dominant mode is not changed deeper in the core (r / a ~ 0 . 5). This indicates that local turbulence changes near the edge might be responsible for the change of global energy confinement in ohmic plasmas. Further study using nonlinear gyrokinetic simulations is being performed to clarify the relation between the change of local turbulence and global ohmic energy confinement. Through nonlinear gyrokinetic simulation (GYRO), we will investigate the change of fluctuating quantities (T~ , ñ , ϕ~) and their phase relations across ohmic confinement transitions, and relate them to the change of energy transport. A synthetic CECE diagnostic for C-Mod has been developed, and it will be used to validate the gyrokinetic simulations. Research supported by USDoE awards DE-SC0006419, DE-FC02-99ER54512.

  1. 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.

  2. Measurements of relativistic emission from runaway electrons in Alcator C-Mod: spectrum, polarization, and spatial structure

    NASA Astrophysics Data System (ADS)

    Granetz, Robert; Mumgaard, Robert

    2014-10-01

    At low densities, runaway electrons (RE's) can be generated during the flattop of Alcator C-Mod discharges with highly relativistic energies, γ >> 1 , allowing careful study under steady conditions. These RE's emit light in a narrow forward-peaked cone which is detected with a number of diagnostics, including spectrometers, a video imaging camera, and polarimetry (using the MSE system), in addition to the standard hard x-ray detectors. These measurements of the relativistic emission can provide information about the RE energy distribution, pitch angle distribution, and spatial distribution. Unlike most other tokamaks, C-Mod's high magnetic field shifts the peak of the continuum emission into the visible, due to the smaller gyroradius and higher gyro-frequency, allowing for excellent spectral coverage with standard spectrometers, and thus detailed comparison to theoretical predictions of synchrotron and bremsstrahlung spectra. Additionally, camera images occasionally show highly structured formations. Profiles of the polarization fraction and polarization angle show radial structure, including a jump of 90° outboard of the magnetic axis, in qualitative agreement with recent theoretical calculations for relativistic electrons in a tokamak field. This work is supported by the U.S. Department of Energy.

  3. Stark broadening of B IV spectral lines

    NASA Astrophysics Data System (ADS)

    Dimitrijević, Milan S.; Christova, Magdalena; Simić, Zoran; Kovačević, Andjelka; Sahal-Bréchot, Sylvie

    2016-08-01

    Stark broadening parameters for 157 multiplets of helium-like boron (B IV) have been calculated using the impact semiclassical perturbation formalism. Obtained results have been used to investigate the regularities within spectral series. An example of the influence of Stark broadening on B IV lines in DO white dwarfs is given.

  4. Stark broadening of B IV spectral lines

    NASA Astrophysics Data System (ADS)

    Dimitrijević, Milan S.; Christova, Magdalena; Simić, Zoran; Kovačević, Andjelka; Sahal-Bréchot, Sylvie

    2016-05-01

    Stark broadening parameters for 157 multiplets of helium like boron (B IV) have been calculated using the impact semiclassical perturbation formalism. Obtained results have been used to investigate the regularities within spectral series. An example of the influence of Stark broadening on B IV lines in DO white dwarfs is given.

  5. 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.

  6. The multiphoton AC Stark effect

    NASA Astrophysics Data System (ADS)

    Rudolph, T. G.; Ficek, Z.; Freedhoff, H. S.

    1998-02-01

    We study the interaction of a two-level atom with two intense lasers: a strong laser of Rabi frequency 2Ω on resonance with the atomic transition, and a weaker laser detuned by 2Ω/n, i.e. by a subharmonic of the Rabi frequency of the first. The second laser "dresses" the dressed states created by the first in an n-photon process. We calculate the energy levels and eigenstates of this "doubly-dressed" atom, and find a new phenomenon: the splitting of the energy levels due to an n-photon coupling between them, resulting in a multiphoton AC Stark effect. We illustrate this effect in the fluorescence spectrum, and show that the spectrum contains triplets at the subharmonic as well as harmonic resonance frequencies with a clear dependence on the order n of the resonance and the ratio α of the Rabi frequencies of the lasers

  7. 3. SANDY RIVER (STARK ST.) BRIDGE, SOUTH END, LOOKING 295 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. SANDY RIVER (STARK ST.) BRIDGE, SOUTH END, LOOKING 295 DEGREES WEST-SOUTHWEST. - Historic Columbia River Highway, Stark Street Bridge, Spanning Sandy River on Stark Street at Historic Columbia River Highway, Troutdale, Multnomah County, OR

  8. 1. SANDY RIVER (STARK ST.) BRIDGE, NORTH END, LOOKING 135 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. SANDY RIVER (STARK ST.) BRIDGE, NORTH END, LOOKING 135 DEGREES SOUTHEAST. - Historic Columbia River Highway, Stark Street Bridge, Spanning Sandy River on Stark Street at Historic Columbia River Highway, Troutdale, Multnomah County, OR

  9. 5. SANDY RIVER (STARK ST.) BRIDGE, EAST ELEVATION, LOOKING 194 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. SANDY RIVER (STARK ST.) BRIDGE, EAST ELEVATION, LOOKING 194 DEGREES SOUTH. - Historic Columbia River Highway, Stark Street Bridge, Spanning Sandy River on Stark Street at Historic Columbia River Highway, Troutdale, Multnomah County, OR

  10. 4. SANDY RIVER (STARK ST.) BRIDGE, WEST ELEVATION, LOOKING 118 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. SANDY RIVER (STARK ST.) BRIDGE, WEST ELEVATION, LOOKING 118 DEGREES EAST-SOUTHEAST. - Historic Columbia River Highway, Stark Street Bridge, Spanning Sandy River on Stark Street at Historic Columbia River Highway, Troutdale, Multnomah County, OR

  11. 2. SANDY RIVER (STARK ST.) BRIDGE, NORTH END, LOOKING 163 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. SANDY RIVER (STARK ST.) BRIDGE, NORTH END, LOOKING 163 DEGREES SOUTH. - Historic Columbia River Highway, Stark Street Bridge, Spanning Sandy River on Stark Street at Historic Columbia River Highway, Troutdale, Multnomah County, OR

  12. 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.

  13. 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…

  14. 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…

  15. Comparisons of Measurements and Gyrokinetic Simulations of Turbulence and Transport in Alcator C-Mod EDA H-Mode Discharges.

    NASA Astrophysics Data System (ADS)

    Sampsell, M. B.; Bravenec, R. V.; Candy, J.; Ernst, D. R.; Alcator C-Mod Team Nevins

    2004-11-01

    Beam-emission spectroscopy (BES) on Alcator C-Mod has observed long wavelength broadband fluctuations and a `quasi-coherent mode' (the latter exclusive to enhanced D_α H modes) in the plasma edge. However, it has not observed broadband fluctuations at the top of the H-mode pedestal or farther in. In an attempt to understand this, we have run the GYRO gyrokinetic code [J. Candy, J. Comput. Phys. 186, 545 (2003)] for this region, applied `synthetic BES' to the fluctuating density output, and compared with the data. The synthetic BES is composed of i) an anti-aliasing filter in GYRO itself, ii) a conversion from density fluctuations to emissivity fluctuations, and iii) a spatial filter to model the finite viewing area of the diagnostic. We find significant attenuation of the density fluctuations. Transport results from GYRO are also compared to data to validate the simulations.

  16. 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.

  17. 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)

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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 kθρs < 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.

  19. 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.

  20. Response to ""comment on 'magnetic topology effects on alcator C-mod scrape-off layer flow'

    SciTech Connect

    Sinakov, 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.

  1. 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.

  2. EMC3-EIRENE modeling of toroidally-localized divertor gas injection experiments on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    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 modeling, with the simulation yielding a toroidal asymmetry in the heat flow to the outer strike point. 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

  3. 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)].

  4. Parallel transport studies of high-Z impurities in the core of Alcator C-Mod plasmasa)

    NASA Astrophysics Data System (ADS)

    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.

    2013-05-01

    Measurements of poloidal variation, ñz/⟨nz⟩, 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 -0.20, 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, -0.050 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, nzZ2/ni≪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, vθ ,z. Artificially modifying main-ion flow in parallel transport simulations is shown to impact both n˜z/⟨nz⟩ and vθ ,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.

  5. Stark profiles of forbidden and allowed transitions in a dense, laser produced helium plasma.

    NASA Technical Reports Server (NTRS)

    Ya'akobi, B.; George, E. V.; Bekefi, G.; Hawryluk, R. J.

    1972-01-01

    Comparisons of experimental and theoretical Stark profiles of the allowed 2(1)P-3(1)D helium line at 6678 A and of the forbidden 2(1)P-3(1)P component at 6632 A in a dense plasma were carried out. The plasma was produced by optical breakdown of helium by means of a repetitive, high power CO2 laser. The allowed line shows good agreement with conventional theory, but discrepancies are found around the centre of the forbidden component. When normally neglected ion motions are taken into consideration, the observed discrepancies are partially removed. Tables of the Stark profiles for the pair of lines are given.

  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. 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.

  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. Impact of dilution of deuterium on ion thermal diffusivity and turbulence in C-Mod Ohmic plasmas

    NASA Astrophysics Data System (ADS)

    Porkolab, Miklos; Ennever, P.; Edlund, E.; Rice, J.; Rost, J. C.; Ernst, D.; Fiore, C.; Hubbard, A.; Hughes, J.; Terry, J.; Reinke, M. L.; Staebler, G.; Candy, J.; Alcator C-Mod Team

    2015-11-01

    Past experiments on C-Mod and gyrokinetic studies indicated that dilution of the deuterium ion species decreases the ion diffusivity in Ohmically heated deuterium plasmas. Comparison of recent controlled seeding experiments to TGLF and GYRO simulations shows that main ion dilution reduces the ion transport in low density (LOC) plasmas by increasing the critical gradient, while in high density (SOC) plasmas ion dilution primarily decreased the stiffness (1). Meanwhile, there is still a deficit in the predicted electron transport in simulations that are restricted to wavenumbers kρs <= 1 . Importantly, measurements of the turbulent spectrum were also carried out with a Phase Contrast Imaging (PCI) diagnostic with a new detector array with an improved frequency response (now up to 1 MHz), and the results are in good agreement with synthetic diagnostic predictions. References: (1) Paul Ennever, Invited Talk at this meeting. Work supported by US DOE awards DE-FG02-94-ER54235 and DE-FC02-99-ER54512.

  11. Experimental Investigation of RF Sheath Rectification in ICRF and LH Heated Plasmas on Alcator C-Mod

    SciTech Connect

    Ochoukov, R.; Whyte, D. G.; Faust, I.; LaBombard, B.; Lipschultz, B.; Meneghini, O.; Wallace, G.; Wukitch, S.; Myra, J.

    2011-12-23

    Radio frequency (RF) rectification of the plasma sheath is being actively studied on C-Mod as a likely mechanism that leads to prohibitively high molybdenum levels in the plasma core of ion cyclotron RF (ICRF) heated discharges. We installed emissive, ion sensitive, Langmuir, and 3-D B-dot probes to quantify the plasma potentials ({Phi}{sub P}) in ICRF and lower hybrid (LH) heated discharges. Two probe sets were mounted on fixed limiter surfaces and one set of probes was mounted on a reciprocating (along the major radius) probe. Initial results showed that RF rectification is strongly dependent on the local plasma density and not on the local RF fields. The RF sheaths had a threshold-like appearance at the local density of {approx}10{sup 16} m-{sup 3}. Radial probe scans revealed that the RF sheaths peaked in the vicinity of the ICRF limiter surface, agreeing with a recent theory. The highest {Phi}{sub P}'s were observed on magnetic field lines directly mapped to the active ICRF antenna. Measurements in LH heated plasmas showed a strong {Phi}{sub P} dependence on the parallel index of refraction n{sub ||} of the launched LH waves: {Phi}{sub P} is greater at lower n{sub ||}. Little dependence was observed on the local plasma density.

  12. 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.

  13. Surface thermocouples for measurement of pulsed heat flux in the divertor of the Alcator C-Mod tokamak

    SciTech Connect

    Brunner, D.; LaBombard, B.

    2012-03-15

    A novel set of thermocouple sensors has been developed to measure heat fluxes arriving at divertor surfaces in the Alcator C-Mod tokamak, a magnetic confinement fusion experiment. These sensors operate in direct contact with the divertor plasma, which deposits heat fluxes in excess of {approx}10 MW/m{sup 2} over an {approx}1 s pulse. Thermoelectric EMF signals are produced across a non-standard bimetallic junction: a 50 {mu}m thick 74% tungsten-26% rhenium ribbon embedded in a 6.35 mm diameter molybdenum cylinder. The unique coaxial geometry of the sensor combined with its single-point electrical ground contact minimizes interference from the plasma/magnetic environment. Incident heat fluxes are inferred from surface temperature evolution via a 1D thermal heat transport model. For an incident heat flux of 10 MW/m{sup 2}, surface temperatures rise {approx}1000 deg. C/s, corresponding to a heat flux flowing along the local magnetic field of {approx}200 MW/m{sup 2}. Separate calorimeter sensors are used to independently confirm the derived heat fluxes by comparing total energies deposited during a plasma pulse. Langmuir probes in close proximity to the surface thermocouples are used to test plasma-sheath heat transmission theory and to identify potential sources of discrepancies among physical models.

  14. 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.

  15. BOUT simulations of the Quasi-Coherent Mode in the EDA Regime of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Xu, X. Q.; Nevins, W. M.; Mazurenko, A.; Porkolab, M.; Mossessian, D.

    2001-10-01

    The Quasi-Coherent (QC) mode is always seen by the phase contrast imaging (PCI) diagnostic during the EDA H-mode(Greenwald, M., et al, Phys. Plasmas 6, 1943 (1999).) in the Alcator C-Mod tokamak. The typical QC mode is characterized by a high frequency ( ~100kHz) ``quasi-coherent'' density fluctuation with high poloidal wavenumber, k_θ~= 5cm-1 (near the X-point region) localized in the edge steep density gradient region (pedestal). In order to understand the QC mode, simulations have been carried out using the BOUT code(Xu, X.Q., et al, J.R., Phys. of Plasmas, Vol.7, 1951 (2000).). The measured dispersion and mode stability is in good agreement with the resistive X-point ballooning mode predicted by the BOUT code. The principal results are: (1) Frequency spectrum of BOUT simulation resembles that of PCI, magnetic probe and reflectometer measurements; (2) Magnetic fluctuations peak near the separatrix and rapidly decay radially; (3) Radial particle flux shows maximum near the X-point region.

  16. 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.

  17. 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.

  18. 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.

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

    DOE PAGESBeta

    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 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

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

    PubMed

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

    2014-11-01

    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 kθρs < 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. PMID:25430224

  1. 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.

  2. 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.

  3. 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.

  4. 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. PMID:26931846

  5. 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.

  6. 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…

  7. Simulation of 3D effects on partially detached divertor conditions in NSTX and Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Lore, Jeremy

    2014-10-01

    Establishing a validated, predictive capability for the divertor plasma is critical for future fusion reactors, which must operate with detached divertors to reduce peak heat fluxes to the plasma facing components (PFC) and to mitigate net material erosion. This is challenging even for existing 2D codes, and is complicated further by non-axisymmetric effects due to divertor-localized gas injection, 3D magnetic fields, and 3D PFCs, modeling of which requires 3D simulations. New experiments performed on C-Mod at the request of the ITER organization to examine the consequence of localized nitrogen gas injection, show clear toroidal asymmetries in radiated power, impurity radiation, and divertor pressure. The 3D plasma/neutral transport code EMC3-EIRENE has been applied to model these experiments in the first attempt to benchmark the code against tokamak experimental data under detached conditions. The measured pressure modulation and the impurity radiation trends in the edge are qualitatively reproduced by the simulations, which also predict a ~2x modulation in heat flux at the outer strike point. Discrepancies are found in comparison with the measured private region radiation, and the simulations also indicate colder, denser divertor conditions than measured, suggesting that drifts and kinetic corrections may be required for more quantitative agreement. In separate experiments on NSTX, detached divertor plasmas are observed to reattach when 3D fields are applied. Modeling of the NSTX experiments reproduces these trends, with an increased peak heat flux with 3D fields and qualitative agreement of the striated flux patterns. The experimental identification of toroidal asymmetries in detached plasmas highlights the need for reliable 3D models for projecting the impact for ITER and beyond. Support from USDOE DE-AC05-00OR22725, DE-AC02-09CH11466, DE-FC02-99ER54512.

  8. Local gas injection as a scrape-off layer diagnostic on the Alcator C-Mod tokamak

    SciTech Connect

    Jablonski, D.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.

  9. Helium ELMy H-modes in Alcator C-Mod in Support of ITER Helium Operating Phases

    NASA Astrophysics Data System (ADS)

    Kessel, C. E.; Wolfe, S. M.; Chilenski, M. A.; Hughes, J. W.; Lin, Y.; Reinke, M. L.; Wukitch, S. J.; C-Mod Team

    2015-11-01

    ITER will operate helium majority plasmas in its earlier phases to shakedown the facility and provide plasmas in both L-mode and H-mode for commissioning and preparation for DT burning plasma operation. Part of this activity is to produce ELMy H-modes to test ELM mitigation schemes and observe the ELM impacts on the plasma facing components. It is of interest to characterize helium ELMy H-modes on present experiments to provide some basis to project to ITER and anticipate the plasma performance and ability to obtain H-modes with sufficient performance. ELMy H-mode is accessed in C-Mod by using LSN with an elongation of about 1.55, and with high lower triangularity and low upper triangularity. These regimes were produced with 1.5-4.0 MW of ICRF heating, and with H-mode line average densities of 2.0-3.2x1020 /m3, producing higher frequency repetitive to large infrequent ELMs, respectively. The infrequent ELM regime showed a cross between EDA and ELMy H-mode, with the EDA signature of a quasi-coherent mode at about 200 kHz. Tungsten laser blow-off was done. The pedestal features, energy confinement, ELM character, L-H threshold (1.7-2.5 MW) and W confinement will be discussed. Comparisons with deuterium ELMy H-modes will be made. Work supported by DOE DE-AC02-09CH11466 and DE-FC02-99ER54512.

  10. 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.

  11. Differential Stark shifts in the hydrogen maser

    SciTech Connect

    Stuart, J.G.; Larson, D.J.; Ramsey, N.F.

    1980-11-01

    The theory of the Stark shift of hydrogen ground-state hyperfine levels has been tested at the 2.4% level of accuracy in a hydrogen maser. The quadratic-Stark-shift coefficient for the hyperfine-transition frequency was experimentally found to be delta..nu.. x 10/sup -14/ Hz (V/m)/sup -2/, where the electric field was perpendicular to the axis of quantization. The quoted uncertainty corresponds to one standard deviation. The uncertainty has contributions from the statistics of the data and from systematic effects. A number of possible sources of systematic error or unwanted frequency shifts has been tested. The theoretically predicted coefficient delta..nu.. x 10/sup -14/ Hz (V/m)/sup -2/ is in reasonable agreement with the present experimental result.

  12. 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.}

  13. 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…

  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. 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.

  16. Science Translator: An Interview with Louisa Stark.

    PubMed

    Stark, Louisa A

    2015-07-01

    The Genetics Society of America's Elizabeth W. Jones Award for Excellence in Education recognizes significant and sustained impact on genetics education. The 2015 awardee, Louisa Stark, has made a major impact on global access to genetics education through her work as director of the University of Utah Genetic Science Learning Center. The Center's Learn.Genetics and Teach.Genetics websites are the most widely used online genetic education resources in the world. In 2014, they were visited by 18 million students, educators, scientists, and members of the public. With over 60 million page views annually, Learn.Genetics is among the most used sites on the Web. PMID:26170441

  17. 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

    NASA Astrophysics Data System (ADS)

    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.

    2015-08-01

    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-3He 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.

  18. 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.

  19. 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.

  20. Optical Stark effect in 2D semiconductors

    NASA Astrophysics Data System (ADS)

    Sie, Edbert J.; McIver, James W.; Lee, Yi-Hsien; Fu, Liang; Kong, Jing; Gedik, Nuh

    2016-05-01

    Semiconductors that are atomically thin can exhibit novel optical properties beyond those encountered in the bulk compounds. Monolayer transition-metal dichalcogenides (TMDs) are leading examples of such semiconductors that possess remarkable optical properties. They obey unique selection rules where light with different circular polarization can be used for selective photoexcitation at two different valleys in the momentum space. These valleys constitute bandgaps that are normally locked in the same energy. Selectively varying their energies is of great interest for applications because it unlocks the potential to control valley degree of freedom, and offers a new promising way to carry information in next-generation valleytronics. In this proceeding paper, we show that the energy gaps at the two valleys can be shifted relative to each other by means of the optical Stark effect in a controllable valley-selective manner. We discuss the physics of the optical Stark effect, and we describe the mechanism that leads to its valleyselectivity in monolayer TMD tungsten disulfide (WS2).

  1. 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

  2. Stark beats of Ar Rydberg states

    NASA Astrophysics Data System (ADS)

    Morioka, Y.; Aoto, T.; Yoshii, H.

    2001-11-01

    Vacuum ultraviolet fluorescence decay spectra of Ar atom resonance lines excited by pulsed vacuum ultraviolet light in a synchrotron single bunch operation were obtained under a static electric field. When an atom under the static electric field was excited simultaneously to both the magnetic sublevels M=0 and \\|M\\|=1 by polarized light and the observation area was asymmetric, Stark beats were observed in the fluorescent decay spectra. All observed beat frequencies varied proportionally to the square of the external electric field. The results for 8d and 9d doublet lines were compared with those obtained by the usual second order perturbation theory, assuming mixing ratios between three jl coupling scheme d-type states. The beat frequencies were also measured for other resonance lines.

  3. Science Translator: An Interview with Louisa Stark

    PubMed Central

    Stark, Louisa A.

    2015-01-01

    The Genetics Society of America’s Elizabeth W. Jones Award for Excellence in Education recognizes significant and sustained impact on genetics education. The 2015 awardee, Louisa Stark, has made a major impact on global access to genetics education through her work as director of the University of Utah Genetic Science Learning Center. The Center’s Learn.Genetics and Teach.Genetics websites are the most widely used online genetic education resources in the world. In 2014, they were visited by 18 million students, educators, scientists, and members of the public. With over 60 million page views annually, Learn.Genetics is among the most used sites on the Web. PMID:26170441

  4. Quantitative calibration of radiofrequency NMR Stark effects

    NASA Astrophysics Data System (ADS)

    Tarasek, Matthew R.; Kempf, James G.

    2011-10-01

    Nuclear magnetic resonance (NMR) Stark responses can occur in quadrupolar nuclei for an electric field oscillating at twice the usual NMR frequency (2ω0). Calibration of responses to an applied E field is needed to establish nuclear spins as probes of native E fields within material and molecular systems. We present an improved approach and apparatus for accurate measurement of quadrupolar Stark effects. Updated values of C14 (the response parameter in cubic crystals) were obtained for both 69Ga and 75As in GaAs. Keys to improvement include a modified implementation of voltage dividers to assess the 2ω0 amplitude, |E|, and the stabilization of divider response by reduction of stray couplings in 2ω0 circuitry. Finally, accuracy was enhanced by filtering sets of |E| through a linear response function that we established for the radiofrequency amplifier. Our approach is verified by two types of spectral results. Steady-state 2ω0 excitation to presaturate NMR spectra yielded C14 = (2.59 ± 0.06) × 1012 m-1 for 69Ga at room-temperature and 14.1 T. For 75As, we obtained (3.1 ± 0.1) × 1012 m-1. Both values reconcile with earlier results from 77 K and below 1 T, whereas current experiments are at room temperature and 14.1 T. Finally, we present results where few-microsecond pulses of the 2ω0 field induced small (tens of Hz) changes in high-resolution NMR line shapes. There too, spectra collected vs |E| agree with the model for response, further establishing the validity of our protocols to specify |E|.

  5. 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.

  6. Measurements of Mode Converted Ion Cyclotron Wave with Phase Contrast Imaging in Alcator C-Mod and Comparisons with Synthetic PCI Simulations in TORIC

    SciTech Connect

    Tsujii, N.; Porkolab, M.; Edlund, E. M.; Lin, L.; Lin, Y.; Wright, J. C.; Wukitch, S. J.

    2009-11-26

    Mode converted ion cyclotron wave (ICW) has been observed with phase contrast imaging (PCI) in D-{sup 3}He plasmas in Alcator C-Mod. The measurements were carried out with the optical heterodyne technique using acousto-optic modulators which modulate the CO2 laser beam intensity near the ion cyclotron frequency. With recently improved calibration of the PCI system using a calibrated sound wave source, the measurements have been compared with the full-wave code TORIC, as interpreted by a synthetic diagnostic. Because of the line-integrated nature of the PCI signal, the predictions are sensitive to the exact wave field pattern. The simulations are found to be in qualitative agreement with the measurements.

  7. 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.

  8. The effects of main-ion dilution on turbulence in low q95 C-Mod ohmic plasmas, and comparisons with nonlinear GYRO

    NASA Astrophysics Data System (ADS)

    Ennever, P.; Porkolab, M.; Candy, J.; Staebler, G.; Reinke, M. L.; Rice, J. E.; Rost, J. C.; Ernst, D.; Hughes, J.; Baek, S. G.

    2016-08-01

    Recent experiments on C-mod seeding nitrogen into ohmic plasmas with q95 = 3.4 found that the seeding greatly reduced long-wavelength (ITG-scale) turbulence. The long-wavelength turbulence that was reduced by the nitrogen seeding was localized to the region of r /a ≈0.85 , where the turbulence is well above marginal stability (as evidenced by Qi/QGB≫1 ). The nonlinear gyrokinetic code GYRO was used to simulate the expected turbulence in these plasmas, and the simulated turbulent density fluctuations and turbulent energy fluxes quantitatively agreed with the experimental measurements both before and after the nitrogen seeding. Unexpectedly, the intrinsic rotation of the plasma was also found to be affected by the nitrogen seeding, in a manner apparently unrelated to a change in the electron-ion collisionality that was proposed by other experiments.

  9. 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.

  10. 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.

  11. A new fast two-color interferometer at Alcator C-Mod for turbulence measurements and comparison with phase contrast imaging

    SciTech Connect

    Kasten, C. P. White, A. E.; Irby, J. H.

    2014-04-15

    Accurately predicting the turbulent transport properties of magnetically confined plasmas is a major challenge of fusion energy research. Validation of transport models is typically done by applying so-called “synthetic diagnostics” to the output of nonlinear gyrokinetic simulations, and the results are compared to experimental data. As part of the validation process, comparing two independent turbulence measurements to each other provides the opportunity to test the synthetic diagnostics themselves; a step which is rarely possible due to limited availability of redundant fluctuation measurements on magnetic confinement experiments. At Alcator C-Mod, phase-contrast imaging (PCI) is a commonly used turbulence diagnostic. PCI measures line-integrated electron density fluctuations with high sensitivity and wavenumber resolution (1.6 cm{sup −1}≲|k{sub R}|≲11 cm{sup −1}). A new fast two-color interferometry (FTCI) diagnostic on the Alcator C-Mod tokamak measures long-wavelength (|k{sub R}|≲3.0 cm{sup −1}) line-integrated electron density fluctuations. Measurements of coherent and broadband fluctuations made by PCI and FTCI are compared here for the first time. Good quantitative agreement is found between the two measurements. This provides experimental validation of the low-wavenumber region of the PCI calibration, and also helps validate the low-wavenumber portions of the synthetic PCI diagnostic that has been used in gyrokinetic model validation work in the past. We discuss possibilities to upgrade FTCI, so that a similar comparison could be done at higher wavenumbers in the future.

  12. 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.

  13. 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.

  14. Laser stark spectroscopy of SO2 with the HCN laser

    NASA Technical Reports Server (NTRS)

    Sarker, J. C.; Johnston, L. H.; Bhattacharjee, R. L.; Sudhakaran, G. R.

    1991-01-01

    The far infrared laser Stark spectrum of SO2 was investigated using the 337-micron line of the HCN laser. Two distinct families, one originating at low field and the other at high field, were observed. The high field transition is identified. A significant fourth-order Stark shift was observed for this transition in the presence of a large second-order Stark shift. The zero-field frequency of the assigned transition was obtained by accounting for the fourth-order contribution.

  15. Stark Widths of Spectral Lines of Neutral Neon

    NASA Astrophysics Data System (ADS)

    Dimitrijević, Milan S.; Simić, Zoran; Kovačević, Andjelka; Valjarević, Aleksandar; Sahal-Bréchot, Sylvie

    2015-12-01

    In order to complete Stark broadening data for Ne I spectral lines which are needed for analysis of stellar atmospheres, collisional widths and shifts (the so-called Stark broadening parameters) of 29 isolated spectral lines of neutral neon have been determined within the impact semiclassical perturbation method. Calculations have been performed for the broadening by collisions with electrons, protons and ionized helium for astrophysical applications, and for collisions with ionized neon and argon for laboratory plasma diagnostics. The shifts have been compared with existing experimental values. The obtained data will be included in the STARK-B database, which is a part of the Virtual Atomic and Molecular Data Center - VAMDC.

  16. 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

  17. 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

  18. Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod

    DOE PAGESBeta

    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 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

  19. 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.

  20. 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.

  1. 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, J. D.; Reinke, M. L.; Lipschultz, B.; Brunner, D.; LaBombard, B.; Terry, J.; Pitts, R. A.; Feng, Y.

    2015-05-15

    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-mode plasmas. This is in contrast to similar experiments in Ohmically heated L-mode plasmas, 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. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Three-dimensional simulation of H-mode plasmas with localized divertor impurity injection on Alcator C-Mod using the edge transport code EMC3-EIRENE

    DOE PAGESBeta

    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 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

  6. 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.

  7. 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.

  8. Surfing Stark II: prohibition against self-referrals.

    PubMed

    Swibel, H J; Zaremski, M J

    1995-02-01

    In 1989, the Chairman of the House Ways and Means Subcommittee on Health, Fortney (Pete) Stark (D.-Calif.), turned the health care industry on its ear by introducing the "Ethics in Patient Referrals Act" to Congress. The bill, commonly known as "Stark I," prohibited physician referrals to entities in which they held a financial interest. As Stark's bill made its way through Congress, its substance was dramatically reduced by the legislative process. Ultimately, the law was incorporated as part of the Omnibus Budget Reconciliation Act of 1990. Stark I's main thrust is that it bars physicians from referring Medicare patients to clinical laboratories with which they have a financial relationship. Furthermore, laboratories providing those services must report information concerning any ownership arrangements between the referring physician and the laboratory. Now, to complicate the picture, providers must contend with amendments to the original law that extend the reach of its prohibitions. Called "Stark II," these amendments took effect on January 1, 1995. In this article, guidelines for dealing successfully with the requirements of the law are outlined. PMID:10140213

  9. Comparison of three Stark problem solution techniques for the bounded case

    NASA Astrophysics Data System (ADS)

    Hatten, Noble; Russell, Ryan P.

    2015-01-01

    Three methods of obtaining solutions to the Stark problem—one developed by Lantoine and Russell using Jacobi elliptic and related functions, one developed by Biscani and Izzo using Weierstrass elliptic and related functions, and one developed by Pellegrini, Russell, and Vittaldev using and Taylor series extended to the Stark problem—are compared qualitatively and quantitatively for the bounded motion case. For consistency with existing available code for the series solution, Fortran routines of the Lantoine method and Biscani method are newly implemented and made available. For these implementations, the Lantoine formulation is found to be more efficient than the Biscani formulation in the propagation of a single trajectory segment. However, for applications for which acceptable accuracy may be achieved by orders up to 16, the Pellegrini series solution is shown to be more efficient than either analytical method. The three methods are also compared in the propagation of sequentially connected trajectory segments in a low-thrust orbital transfer maneuver. Separate tests are conducted for discretizations between 8 and 96 segments per orbit. For the series solution, the interaction between order and step size leads to computation times that are nearly invariable to discretization for a given truncation error tolerance over the tested range of discretizations. This finding makes the series solution particularly attractive for mission design applications where problems may require both coarse and fine discretizations. Example applications include the modeling of low-thrust propulsion and time-varying perturbations—problems for which the efficient propagation of relatively short Stark segments is paramount because the disturbing acceleration generally varies continuously.

  10. On the Stark Broadening of Lu III Spectral Lines

    NASA Astrophysics Data System (ADS)

    Majlinger, Zlatko; Simić, Zoran; Dimitrijević, Milan S.

    2015-12-01

    The electron-impact widths for 27 Lu III spectral lines have been calculated by using the modified semiempirical method. Calculations have been also performed with the published relativistic Hartree-Fock oscillator strengths and additionally, with the approximate formula of Cowley. With the obtained results, the influence of Stark broadening on Lu III lines was investigated in the spectra of A-type stars. The obtained data will be included in the STARK-B database, which is part of the Virtual Atomic and Molecular Data Center - VAMDC.

  11. Studies of turbulence and transport in Alcator C-Mod H-mode plasmas with phase contrast imaging and comparisons with GYRO

    SciTech Connect

    Lin, L.; Porkolab, M.; Edlund, E. M.; Rost, J. C.; Fiore, C. L.; Greenwald, M.; Lin, Y.; Tsujii, N.; Wukitch, S. J.; Mikkelsen, D. R.

    2009-01-15

    Recent advances in gyrokinetic simulation of core turbulence and associated transport requires an intensified experimental effort to validate these codes using state of the art synthetic diagnostics to compare simulations with experimental data. A phase contrast imaging (PCI) diagnostic [M. Porkolab, J. C. Rost, N. Basse et al., IEEE Trans. Plasma Sci. 34, 229 (2006)] is used to study H-mode plasmas in Alcator C-Mod [M. Greenwald, D. Andelin, N. Basse et al., Nucl. Fusion 45, S109 (2005)]. The PCI system is capable of measuring density fluctuations with high temporal (2 kHz-5 MHz) and wavenumber (0.5-55 cm{sup -1}) resolution. Recent upgrades have enabled PCI to localize the short wavelength turbulence in the electron temperature gradient range and resolve the direction of propagation (i.e., electron versus ion diamagnetic direction) of the longer wavelength turbulence in the ion temperature gradient (ITG) and trapped electron mode range. The studies focus on plasmas before and during internal transport barrier formation in an enhanced D{sub {alpha}} H-mode plasma assisted with ion cyclotron resonance frequency heating. Nonlinear GYRO simulations have also been performed [J. Candy and R. E. Waltz, Phys. Rev. Lett. 91, 045001 (2003)] and the predicted fluctuation is compared against experimental measurements through a synthetic PCI diagnostic method. The simulated fluctuations from GYRO agree with experimental measurements in the ITG regime. GYRO also shows good agreement in transport predictions with experimental measurements after reducing the ion temperature gradient ({approx}15%) and adding ExB shear suppression, all within the experimental uncertainty.

  12. 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)].

  13. 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.

  14. 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. PMID:24784610

  15. 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.

  16. 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.

  17. ac Stark shift of the Cs microwave atomic clock transitions

    NASA Astrophysics Data System (ADS)

    Rosenbusch, P.; Ghezali, S.; Dzuba, V. A.; Flambaum, V. V.; Beloy, K.; Derevianko, A.

    2009-01-01

    We analyze the ac Stark shift of the Cs microwave atomic clock transition theoretically and experimentally. Theoretical and experimental data are in good agreement with each other. Results indicate the absence of a magic wavelength at which there would be no differential shift of the clock states having zero projections of the total angular momentum.

  18. Criteria for SLI: The Stark and Tallal Legacy and Beyond.

    ERIC Educational Resources Information Center

    Plante, Elena

    1998-01-01

    A review of the literature finds that the criteria developed by Stark and Tallal (1981) for the selection of children with specific language impairment for research purposes continue to be used, in part or in whole, in current research. Additional information on the use of norm-referenced tests with this population is also provided. (Author/DB)

  19. 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.

  20. Virtual laboratory astrophysics : The STARK-B database

    NASA Astrophysics Data System (ADS)

    Sahal-Bréchot, S.; Dimitrijević, M. S.; Moreau, N.

    2012-02-01

    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. This requires the knowledge of numerous collisional line profiles, especially for very low abundant atoms and ions which are used as probes for modern spectroscopic diagnostics in astrophysics. Nowadays, the access to such data via an on line database becomes essential. STARK-B (stark-b.obspm.fr">http://stark-b.obspm.fr) is a collaborative project between the Astronomical Observatory of Belgrade and the Laboratoire d'Étude 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 (impacts). It is devoted to modelling and spectroscopic diagnostics of stellar atmospheres and envelopes, laboratory plasmas, laser equipments and technological plasmas. Hence, the domain of temperatures and densities covered by the tables is wide and depends on the ionization degree of the considered ion. The STARK-B database is a part of VAMDC (Virtual Atomic and Molecular Data Centre, http://www.vamdc.eu), which is an 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.

  1. The Stark truth: what your physician clients should know about Stark Law and the Anti-Kickback Statute.

    PubMed

    Taormina, Melissa

    2013-01-01

    This article summarizes key features of Stark Law and the Anti-Kickback Statute, statutes used to fight health care fraud and abuse within Medicare and Medicaid, and explains how attorneys can help health care providers comply with these laws. PMID:23614270

  2. 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/).

  3. 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. PMID:11580613

  4. Atom-interferometric measurement of Stark level splittings

    NASA Astrophysics Data System (ADS)

    Wang, Limei; Zhang, Hao; Zhang, Linjie; Raithel, Georg; Zhao, Jianming; Jia, Suotang

    2015-09-01

    Mixed adiabatic and diabatic passages through avoided crossings in the Stark map of cesium Rydberg atoms 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. The adiabatic state transformation in the interferometer's beam splitters enables the spectroscopy of states that are, due to selection rules, inaccessible to direct laser-spectroscopic observation. 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.

  5. Measurement of the electronic momentum distributions of Rydberg Stark states

    SciTech Connect

    Murray-Krezan, J.; Jones, R. R.

    2007-06-15

    Approximate momentum distributions of Rydberg electrons in static electric fields have been obtained using an improved impulsive momentum retrieval (IMR) technique. An imaging detector enables the measurement of half-cycle pulse (HCP) ionization probability across the spatial profile of a focused half-cycle pulse beam. By modulating the HCP amplitude we directly measure the derivative of the ionization vs HCP impulse curve, enabling the recovery of momentum distributions with better resolution than previously demonstrated with IMR. For example, for Stark states with small dipole moments, we observe predicted fine-structure in the projection of the momentum distribution along the Stark field axis. We use a semiclassical model to simulate the effect that the nonzero HCP duration has on our measurements. Good agreement between simulated and measured momentum distributions is obtained.

  6. Stark Spectroscopy of Rubrene. I. Electroabsorption Spectroscopy and Molecular Parameters.

    PubMed

    Iimori, Toshifumi; Ito, Ryuichi; Ohta, Nobuhiro; Nakano, Hideyuki

    2016-06-30

    Electroabsorption spectroscopy investigation and the determination of molecular parameters for rubrene dispersed in a poly(methyl methacrylate) (PMMA) matrix are reported. The features of the band system in the absorption spectrum in PMMA are analogous to those in solutions. The changes in the electric dipole moment and the polarizability between the excited and ground states are determined from analysis of the Stark effect in the absorption band. The change in the transition dipole moment in the presence of an external electric field is also observed. Although rubrene is predicted to be classified as a nonpolar molecule, there is a contribution of the difference in the electric dipole moment between the excited and ground states to the electroabsorption spectrum. The origin of the nonzero difference in the electric dipole moment is argued. Stark fluorescence spectroscopy investigation is reported in Part II of this series. PMID:27257765

  7. 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.

  8. Optical stark effect in the 2-photon spectrum of NO

    NASA Technical Reports Server (NTRS)

    Huo, W. M.; Gross, K. P.; Mckenzie, R. L.

    1984-01-01

    A large optical Stark effect has been observed in the two-photon spectrum X(2)Pi yields A(2)Sigma(+)_ in NO. It is explained as a near-resonant process in which the upper state of the two-photon transition is perturbed by interactions with higher-lying electronic states coupled by the laser field. A theoretical analysis is presented along with coupling parameters determined from ab initio wave functions. The synthetic spectrum reproduces the major experimental features.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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).

  14. Anisotropic stark effect and electric-field noise suppression for phosphorus donor qubits in silicon.

    PubMed

    Sigillito, A J; Tyryshkin, A M; Lyon, S A

    2015-05-29

    We report the use of novel, capacitively terminated coplanar waveguide resonators to measure the quadratic Stark shift of phosphorus donor qubits in Si. We confirm that valley repopulation leads to an anisotropic spin-orbit Stark shift depending on electric and magnetic field orientations relative to the Si crystal. By measuring the linear Stark effect, we estimate the effective electric field due to strain in our samples. We show that in the presence of this strain, electric-field sources of decoherence can be non-negligible. Using our measured values for the Stark shift, we predict magnetic fields for which the spin-orbit Stark effect cancels the hyperfine Stark effect, suppressing decoherence from electric-field noise. We discuss the limitations of these noise-suppression points due to random distributions of strain and propose a method for overcoming them. PMID:26066457

  15. Density measurements using coherence imaging spectroscopy based on Stark broadening

    SciTech Connect

    Lischtschenko, O.; Bystrov, K.; De Temmerman, G.; Howard, J.; Jaspers, R. J. E.; Koenig, R.

    2010-10-15

    A coherence imaging camera has been set up at Pilot-PSI. The system is to be used for imaging the plasma density through the Stark effect broadening of the H{sub {gamma}} line. Local density values are then obtained by the Abel inversion of the measured interferometric fringe contrast. This report will present the instrument setup and proof-of-principle demonstration. The inverted spatial electron density profiles obtained near the cascaded arc source of Pilot-PSI in discharges with axial magnetic field of B=0.4 T are compared with an independent measurement of electron density by Thomson scattering and good agreement is found.

  16. 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.

  17. Modeling of Stark-Zeeman Lines in Magnetized Hydrogen Plasmas

    NASA Astrophysics Data System (ADS)

    Rosato, J.; Bufferand, H.; Capes, H.; Koubiti, M.; Godbert-Mouret, L.; Marandet, Y.; Stamm, R.

    2015-12-01

    The action of electric and magnetic fields on atomic species results in a perturbation of the energy level structure, which alters the shape of spectral lines. In this work, we present the Zeeman-Stark line shape simulation method and perform new calculations of hydrogen Lyman and Balmer lines, in the framework of magnetic fusion research. The role of the Zeeman effect, fine structure and the plasma's non-homogeneity along the line-of-sight are investigated. Under specific conditions, our results are applicable to DA white dwarf atmospheres.

  18. Influence of Stark shift and atomic coherence on entanglement of two qubits

    NASA Astrophysics Data System (ADS)

    Bashkirov, Eugene K.; Mastuygin, Michail

    2015-03-01

    In this paper we have investigated the atom-atom entanglement for degenerate two-photon Tavis-Cummings model with taking into account Stark shift and initial atomic coherence. Considering different initial coherent states we have derived that the atom-atom entanglement can be greatly increased or decreased due to the presence of the Stark shift. In addition, we have derived that the entanglement sudden death effect vanishes due to the presence of Stark shift for some initial states.

  19. Dynamic Stark broadening as the Dicke narrowing effect

    NASA Astrophysics Data System (ADS)

    Calisti, A.; Mossé, C.; Ferri, S.; Talin, B.; Rosmej, F.; Bureyeva, L. A.; Lisitsa, V. S.

    2010-01-01

    A very fast method to account for charged particle dynamics effects in calculations of spectral line shape emitted by plasmas is presented. This method is based on a formulation of the frequency fluctuation model (FFM), which provides an expression of the dynamic line shape as a functional of the static distribution of frequencies. Thus, the main numerical work rests on the calculation of the quasistatic Stark profile. This method for taking into account ion dynamics allows a very fast and accurate calculation of Stark broadening of atomic hydrogen high- n series emission lines. It is not limited to hydrogen spectra. Results on helium- β and Lyman- α lines emitted by argon in microballoon implosion experiment conditions compared with experimental data and simulation results are also presented. The present approach reduces the computer time by more than 2 orders of magnitude as compared with the original FFM with an improvement of the calculation precision, and it opens broad possibilities for its application in spectral line-shape codes.

  20. 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.

  1. Hyperfine Stark effect of shallow donors in silicon

    NASA Astrophysics Data System (ADS)

    Pica, Giuseppe; Wolfowicz, Gary; Urdampilleta, Matias; Thewalt, Mike L. W.; Riemann, Helge; Abrosimov, Nikolai V.; Becker, Peter; Pohl, Hans-Joachim; Morton, John J. L.; Bhatt, R. N.; Lyon, S. A.; Lovett, Brendon W.

    2014-11-01

    We present a complete theoretical treatment of Stark effects in bulk doped silicon, whose predictions are supported by experimental measurements. A multivalley effective mass theory, dealing nonperturbatively with valley-orbit interactions induced by a donor-dependent central cell potential, allows us to obtain a very reliable picture of the donor wave function within a relatively simple framework. Variational optimization of the 1 s donor binding energies calculated with a new trial wave function, in a pseudopotential with two fitting parameters, allows an accurate match of the experimentally determined donor energy levels, while the correct limiting behavior for the electronic density, both close to and far from each impurity nucleus, is captured by fitting the measured contact hyperfine coupling between the donor nuclear and electron spin. We go on to include an external uniform electric field in order to model Stark physics: with no extra ad hoc parameters, variational minimization of the complete donor ground energy allows a quantitative description of the field-induced reduction of electronic density at each impurity nucleus. Detailed comparisons with experimental values for the shifts of the contact hyperfine coupling reveal very close agreement for all the donors measured (P, As, Sb, and Bi). Finally, we estimate field ionization thresholds for the donor ground states, thus setting upper limits to the gate manipulation times for single qubit operations in Kane-like architectures: the Si:Bi system is shown to allow for A gates as fast as ≈10 MHz.

  2. 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. PMID:27341859

  3. Stark and Zeeman Deceleration of Neutral Atoms and Molecules

    NASA Astrophysics Data System (ADS)

    Hogan, S. D.; Vliegen, E.; Sprecher, D.; Vanhaecke, N.; Andrist, M.; Schmutz, H.; Meier, U.; Meier, B. H.; Merkt, F.

    2008-04-01

    Argon and hydrogen atoms excited to Rydberg Stark states in supersonic expansions have been decelerated using inhomogeneous electric fields. In the case of hydrogen, the atoms have been decelerated from an initial velocity of 700 m/s to zero velocity in the lab frame using time-dependent inhomogeneous electric fields and subsequently stored in two- and three-dimensional traps. The dynamics of the Rydberg atoms in the traps and the phase-space characteristics of the decelerated atoms have been characterized by pulsed field ionization and imaging techniques. Multi-stage Zeeman deceleration of ground state H and D atoms has been demonstrated. Using this technique H atoms, traveling at 420 m/s, have been decelerated to half of their initial kinetic energy.

  4. Valley selective optical Stark effect in monolayer WS2

    NASA Astrophysics Data System (ADS)

    Sie, Edbert J.; McIver, James W.; Lee, Yi-Hsien; Fu, Liang; Kong, Jing; Gedik, Nuh

    2015-03-01

    Monolayer semiconductors, such as WS2, have a pair of valleys that, by time-reversal symmetry, are energetically degenerate. Lifting the valley degeneracy in these materials is of great interest because it would allow for valley specific band engineering and offer additional control in valleytronic applications. Here we show that circularly polarized light, which breaks time-reversal symmetry, can be used to lift the valley degeneracy by means of the optical Stark effect. We demonstrate that this effect is capable of raising the exciton level in monolayer WS2 by as much as 18 meV in a controllable valley selective manner. The resulting energy shift is extremely large, comparable to the shift that would be obtained using a very high magnetic field (200 Tesla). These results offer a novel way to control valley degree of freedom, and may provide a means to realize new valley-selective Floquet topological state of matter.

  5. 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.

  6. 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.

  7. 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. PMID:21770639

  8. Measurement of Linear Stark Interference in Hg199

    NASA Astrophysics Data System (ADS)

    Loftus, T. H.; Swallows, M. D.; Griffith, W. C.; Romalis, M. V.; Heckel, B. R.; Fortson, E. N.

    2011-06-01

    We present measurements of Stark interference in the 6S01→6P13 transition in Hg199, 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, aSI=(aM1+aE2)=(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 Hg199 EDM search apparatus to resolve nontrivial, controlled, and sub-nHz Larmor frequency shifts with EDM-like characteristics.

  9. Valley-selective optical Stark effect in monolayer WS2

    NASA Astrophysics Data System (ADS)

    Gedik, Nuh

    Monolayer semiconducting transition-metal dichalcogenides (TMDs) have a pair of valleys that, by time-reversal symmetry, are energetically degenerate. Lifting the valley degeneracy in these materials is of great interest because it would allow for valley specific band engineering and offer additional control in valleytronic applications. In this talk, I will show that circularly polarized light, which breaks time-reversal symmetry, can be used to lift the valley degeneracy by means of the optical Stark effect. We demonstrate that this effect is capable of raising the exciton level in monolayer TMD WS2 by as much as 18 meV in a controllable valley-selective manner. The resulting energy shift is extremely large, comparable to the shift that would be obtained using a very high magnetic field (approximately 100 Tesla). These results offer a novel way to control valley degree of freedom, and may provide a means to realize new valley-selective Floquet topological state of matter.

  10. 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.

  11. 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.

  12. 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%.

  13. 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.

  14. 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.

  15. 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.

  16. New features of a single-mode nonlinear Stark shift in the presence of phase damping

    NASA Astrophysics Data System (ADS)

    Obada, A.-S. F.; Khalil, E. M.; Abdel-Khalek, S.; Ali, S. I.

    2012-05-01

    The influence of the nonlinear Stark shift, for the multi-quanta JCM in the presence of phase damping is studied. In particular the temporal evolution of the atomic inversion, the linear entropy and the entropy squeezing are investigated. The linear entropy is used as an indicator of the degree of entanglement between the atom and the field. The results indicate the sensitivity of these aspects to changes either in the decay parameter or the Stark shift parameter.

  17. Influence of Stark Shift on Entanglement of Two Qubits in the Two-Photon Tavis-Cummings Model

    NASA Astrophysics Data System (ADS)

    Mastyugin, M. S.; Bashkirov, E. K.

    2015-09-01

    Considering two-atom degenerate two-photon Tavis-Cummings model, we investigate the entanglement between two atoms prepared initially in the coherent disentangled states and cavity field prepared in few-photon Fock state, and study the effect of the Stark shift on entanglement. The results show that the atom-atom negativity evolve periodically with time and the periods are affected by the Stark shift and initial coherent atomic state and that the atom-atom entanglement can be greatly enhanced due to the presence of Stark shift. We also have shown that entanglement sudden death effect vanishes for some parameters of the considered system due to the presence of Stark shift. In addition, the entanglement sudden death effect vanishes due to the presence of Stark shift. We have derived that the dynamic Stark shift can be used to control entanglement between two initially disentangled atoms.

  18. Higher-order motion sensitivity in fly visual circuits.

    PubMed

    Lee, Yu-Jen; Nordström, Karin

    2012-05-29

    In higher-order motion stimuli, the direction of object motion does not follow the direction of luminance change. Such stimuli could be generated by the wing movements of a flying butterfly and further complicated by its motion in and out of shadows. Human subjects readily perceive the direction of higher-order motion, although this stands in stark contrast to prevailing motion vision models. Flies and humans compute motion in similar ways, and because flies behaviorally track bars containing higher-order motion cues, they become an attractive model system for investigating the neurophysiology underlying higher-order motion sensitivity. We here use intracellular electrophysiology of motion-vision-sensitive neurons in the hoverfly lobula plate to quantify responses to stimuli containing higher-order motion. We show that motion sensitivity can be broken down into two separate streams, directionally coding for elementary motion and figure motion, respectively, and that responses to Fourier and theta motion can be predicted from these. The sensitivity is affected both by the stimulus' time course and by the neuron's underlying receptive field. Responses to preferred-direction theta motion are sexually dimorphic and particularly robust along the visual midline. PMID:22586123

  19. Higher-order motion sensitivity in fly visual circuits

    PubMed Central

    Lee, Yu-Jen; Nordström, Karin

    2012-01-01

    In higher-order motion stimuli, the direction of object motion does not follow the direction of luminance change. Such stimuli could be generated by the wing movements of a flying butterfly and further complicated by its motion in and out of shadows. Human subjects readily perceive the direction of higher-order motion, although this stands in stark contrast to prevailing motion vision models. Flies and humans compute motion in similar ways, and because flies behaviorally track bars containing higher-order motion cues, they become an attractive model system for investigating the neurophysiology underlying higher-order motion sensitivity. We here use intracellular electrophysiology of motion-vision–sensitive neurons in the hoverfly lobula plate to quantify responses to stimuli containing higher-order motion. We show that motion sensitivity can be broken down into two separate streams, directionally coding for elementary motion and figure motion, respectively, and that responses to Fourier and theta motion can be predicted from these. The sensitivity is affected both by the stimulus’ time course and by the neuron’s underlying receptive field. Responses to preferred-direction theta motion are sexually dimorphic and particularly robust along the visual midline. PMID:22586123

  20. Laser-assisted Stark deceleration of polar diatomic molecules in the Χ1Σ state

    NASA Astrophysics Data System (ADS)

    Huang, Yunxia; Xu, Shuwu; Yang, Xiaohua

    2016-07-01

    The traditional Stark deceleration method is difficult to apply in chemically stable polar diatomic molecules in their ground (Χ1Σ) state because the Χ1Σ state normally experiences little Stark shift and the rovibronic ground level is mostly high-field-seeking. To solve this problem, we propose a laser-assisted Stark deceleration scheme to decelerate such molecules in the present paper. Our results show that, owing to the transverse bunching effect of the applied red-detuning laser beam, the molecules of the high-field-seeking level |J = 0, M = 0> in the Χ1Σ state can be effectively decelerated. Furthermore, the present scheme is more effective because the interaction between the molecules and the combined fields can produce the pseudo-first-order Stark effect, and thus increase the depth of the effective potential. Compared to those molecules in the low-field-seeking state |J = 1, MΩ = ‑1> in the usual electrostatic Stark deceleration, a higher molecular density and lower velocity can be achieved under an equivalent initial phase angle.

  1. Wannier-Stark localization in InAs/(GaIn)Sb superlattice diodes

    NASA Astrophysics Data System (ADS)

    Bürkle, L.; Fuchs, F.; Ahlswede, E.; Pletschen, W.; Schmitz, J.

    2001-07-01

    We present experimental evidence for the formation of localized Wannier-Stark states in the depletion region of low band-gap InAs/(GaIn)Sb superlattice (SL) infrared photodiodes. In the photocurrent spectra of reverse-biased photodiodes, maxima are observed, that spectrally shift when the strength of the electric field in the depletion region of the diode is changed. Taking into account the spatially indirect type-II nature of interband transitions in InAs/(GaIn)Sb SL's, the spectral positions of the observed maxima can be explained in the framework of localized Wannier-Stark states. Besides photocurrent spectra, the current-voltage (I-V) characteristics of the diodes were investigated. In the reverse-bias regime dominated by Zener tunneling the differential resistance of the diodes reveals an oscillatory behavior. These oscillations are due to a resonant enhancement of the Zener tunneling current by Wannier-Stark states in the depletion region of the SL diode. A model is presented that quantitatively describes the occurrence of the oscillations in the I-V curves. In addition, the influence of a magnetic field on the Wannier-Stark oscillations in the Zener current was investigated. While the period of the oscillations in the I-V curves is conserved, the resonances are shifted, reflecting the energy shift introduced in the Wannier-Stark states by the magnetic field. This voltage shift exhibits a strong dependence on the magnetic-field orientation.

  2. Molecular collision studies with Stark-decelerated beams

    NASA Astrophysics Data System (ADS)

    Meijer, Gerard

    2008-03-01

    Molecular scattering behaviour has generally proven difficult to study at low collision energies. We formed a molecular beam of OH radicals with a narrow velocity distribution and a tunable velocity by passing the beam through a Stark decelerator [1]. The transition probabilities for inelastic scattering of the OH radicals with Xe atoms were measured as a function of the collision energy in the range of 50 to 400 wavenumbers. The behaviour of the cross-sections for inelastic scattering near the energetic thresholds was accurately measured, and excellent agreement was obtained with cross-sections derived from coupled- channel calculations on ab initio computed potential energy surfaces [2]. For collision studies at lower energies, the decelerated beams of molecules can be loaded into a variety of traps. In these traps, electric fields are used to keep the molecules confined in a region of space where they can be studied in complete isolation from the (hot) environment. Typically, 10^5 state- selected molecules can be trapped for times up to several seconds at a density of 10^7 mol/cm^3 and at a temperature of several tens of mK [3]. The long interaction time afforded by the trap has been exploited to measure the infrared radiative lifetime of vibrationally excited OH radicals, for instance, as well as to study the far-infrared optical pumping of these polar molecules due to blackbody radiation [4]. As an alternative to these traps, we have demonstrated an electrostatic storage ring for neutral molecules. In its simplest form, a storage ring is a trap in which the molecules - rather than having a minimum potential energy at a single location in space - have a minimum potential energy on a circle. To fully exploit the possibilities offered by a ring structure, it is imperative that the molecules remain in a bunch as they revolve around the ring. This ensures a high density of stored molecules, moreover, this makes it possible to inject multiple - either co-linear or

  3. Experimental Stark halfwidths of the ionized oxygen and silicon spectral lines

    NASA Astrophysics Data System (ADS)

    Gavanski, L.; Belmonte, M. T.; Savić, I.; Djurović, S.

    2016-04-01

    In this paper, we present experimental Stark halfwidths of spectral lines of singly ionized oxygen and singly and double ionized silicon. The observed spectral lines were emitted from plasma produced in a small electromagnetically driven T-tube. The plasma electron density was 1.45 × 1023 m-3 and the electron temperature was 15 000 K. The obtained results were compared with the available experimental results of other authors, as well as with some theoretical Stark halfwidth values. The obtained results, the analysis of experimental results and the comparison with theoretical results might be of interest in astrophysics. For example, the obtained Stark halfwidths can be useful for abundance determination, the calculation of stellar opacities, the interpretation and modelling of stellar spectra, the estimation of the relative transfer through the stellar plasma, etc.

  4. 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. PMID:22481773

  5. Stark width measurements of Fe II lines with wavelengths in the range 230-260 nm

    NASA Astrophysics Data System (ADS)

    Aguilera, J. A.; Manrique, J.; Aragón, C.

    2011-12-01

    The experimental Stark widths of 26 Fe II lines with wavelengths in the range 230-260 nm have been determined by laser-induced breakdown spectroscopy. These measurements complete the data reported previously for the wavelength range 260-300 nm. The laser-induced plasmas have been generated from Fe-Cu and Fe-Ni samples. The curve-of-growth methodology is used to determine the iron concentration required to avoid self-absorption. The electron density at the different instants of the plasma lifetime, determined from the Stark broadening of the Hα line, is in the range (1.6-7.4) × 1017 cm-3. The plasma temperature is in the range 12 900-15 200 K. The Stark widths obtained are compared with previous experimental and theoretical data.

  6. 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.

  7. Large polarization-dependent exciton optical Stark effect in lead iodide perovskites.

    PubMed

    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

  8. Time Evolution of High-l Stark States in Cold Rydberg Atoms

    NASA Astrophysics Data System (ADS)

    Wang, Limei; Zhang, Hao; Zhang, Linjie; Wang, Yong; Bao, Shanxia; Li, Changyong; Zhao, Jianming; Jia, Suotang

    2014-11-01

    The high-l Rydberg Stark states are populated by the state transfer from initial prepared nS Rydberg state via avoided crossings induced by a weak electric-field pulse, and investigated by the state selective field ionization method in a cesium standard magneto-optical trap. The dependences of the transfer rate, given by the ratio of the number of high-l Stark states to all atoms, on the strength and holding time of electric-field pulse are investigated and compared with those with additional ions. The results show that the time evolution of high-l Stark states strongly depends on the electric-field strength, and is affected by the additional ions at relatively weaker field (1.51 V/cm here). The density of Rydberg atoms has a minor effect on the characteristic time of evolution process.

  9. Interplay of Bias-Driven Charging and the Vibrational Stark Effect in Molecular Junctions.

    PubMed

    Li, Yajing; Zolotavin, Pavlo; Doak, Peter; Kronik, Leeor; Neaton, Jeffrey B; Natelson, Douglas

    2016-02-10

    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 C60-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 C60 junctions. PMID:26814562

  10. Stark effect in the J = 3 4 microwave line of tert-butyl chloride molecule

    NASA Astrophysics Data System (ADS)

    Gierszal, S.; Mis-Kuzminska, E.; Stankowski, J.; Galica, J.

    1984-03-01

    Stark effect in the J = 3 - 4 transition spectrum of the tert-butyl chloride has been investigated. The perturbation of the rotational levels by combined effect of the quadrupole and an intermediate electric fields was calculated and used for identify the Stark components. The rotational spectrum of tert-butyl chloride /CH 3/ 3CCl is characterised by the rotational constants A = 4518.70 MHz[1] and B = 3017.85 MHz, dipole moment U= 2.12 D, and quadrupole interaction constant eqQ = -67.58 MHz [2,3]. The energy of rotational states of the tert-butyl chloride molecule is described by the Hamiltonian ? where H 0 is the unperturbed rotational energy, H Q that of interaction of the angular momentum and quadrupole moment of the chlorine nucleus, and H E the Stark energy. Since H Q ˜ H E for the electric field strengths applied during the present investigation, we are dealing with the case of intermediate fields. To solve the problem theoretically we had recourse to the representation in F-space and calculated the energy for the perturbation H Q + H E as done by Low and Townes [4]. The theoretical distances of the Stark components from the absorption line of tert-butyl chloride for various electric field strengths at J = 3 - 4 and ΔM F = 0 is shown in Fig. 1a and 1b. We applied the theoretically calculated distances of the Stark components from the absorption line of /CH 3/ 3CCl as function of the electric field strength as well as the relative intensities of the components in order to interpret our experimental results concerning the Stark effect.

  11. Sub-Doppler Stark Spectroscopy in the A−X (1,0) Band of CN

    SciTech Connect

    Hall, G.E.; Hause, M.L.; Sears, T.J.

    2009-11-26

    The effect of external electric fields has been measured in hyperfine-resolved sub-Doppler transitions in the A {sup 2}{Pi}-X {sup 2}{Sigma} (1,0) band of the CN radical near 10900 cm{sup -1}. Static electric fields less than 1 kV/cm are sufficient to mix the most closely spaced {Lambda}-dpublets in the A state, leading to Stark spectra with both new and shifted resonances. Simulations of the saturation-dip Stark spectral line profiles allow extraction of the A-state permanent electric dipole moment with a magnitude of 0.06 {+-} 0.02 D.

  12. 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.

  13. Measurement of electron density by Stark broadening in an ablative pulsed plasma thruster

    SciTech Connect

    Liu Feng; Nie Zongfu; Xu Xu; Zhou Qianhong; Li Linsen; Liang Rongqing

    2008-09-15

    Electron density was measured by Stark broadening in an ablative pulsed plasma thruster. The asymmetrical deconvolution is used to obtain Stark broadening. The result shows that the electron density in the discharge channel is 2.534x10{sup 22} m{sup -3} when the discharge energy is 5 J and the measured electron temperature is 18 000 K, and it is in excellent agreement with other experimental and theoretical data. The electron density in the discharge channel increases very minimally with increasing discharge energy.

  14. Possibility of Stark-insensitive cotrapping of two atomic species in optical lattices

    SciTech Connect

    Morrison, Muir J.; Derevianko, A.; Dzuba, V. A.

    2011-01-15

    Much effort has been devoted to removing differential Stark shifts for atoms trapped in specially tailored ''magic'' optical lattices, but thus far work has focused on a single trapped atomic species. In this work, we extend these ideas to include two atomic species sharing the same optical lattice. We show qualitatively that, in particular, scalar J=0 divalent atoms paired with nonscalar state atoms have the necessary characteristics to achieve such Stark shift cancellation. We then present numerical results on ''magic'' trapping conditions for {sup 27}Al paired with {sup 87}Sr, as well as several other divalent atoms.

  15. Possibility of Stark-insensitive cotrapping of two atomic species in optical lattices

    NASA Astrophysics Data System (ADS)

    Morrison, Muir J.; Dzuba, V. A.; Derevianko, A.

    2011-01-01

    Much effort has been devoted to removing differential Stark shifts for atoms trapped in specially tailored “magic” optical lattices, but thus far work has focused on a single trapped atomic species. In this work, we extend these ideas to include two atomic species sharing the same optical lattice. We show qualitatively that, in particular, scalar J=0 divalent atoms paired with nonscalar state atoms have the necessary characteristics to achieve such Stark shift cancellation. We then present numerical results on “magic” trapping conditions for Al27 paired with Sr87, as well as several other divalent atoms.

  16. Quantum-confined Stark effect measurements in Ge/SiGe quantum-well structures.

    PubMed

    Chaisakul, Papichaya; Marris-Morini, Delphine; Isella, Giovanni; Chrastina, Daniel; Le Roux, Xavier; Gatti, Eleonora; Edmond, Samson; Osmond, Johann; Cassan, Eric; Vivien, Laurent

    2010-09-01

    We investigate the room-temperature quantum-confined Stark effect in Ge/SiGe multiple quantum wells (MQWs) grown by low-energy plasma-enhanced chemical vapor deposition. The active region is embedded in a p-i-n diode, and absorption spectra at different reverse bias voltages are obtained from optical transmission, photocurrent, and differential transmission measurements. The measurements provide accurate values of the fraction of light absorbed per well of the Ge/SiGe MQWs. Both Stark shift and reduction of exciton absorption peak are observed. Differential transmission indicates that there is no thermal contribution to these effects. PMID:20808367

  17. Possibility of Stark-insensitive cotrapping of two atomic species in optical lattices

    NASA Astrophysics Data System (ADS)

    Morrison, Muir; Dzuba, V. A.; Derevianko, A.

    2011-05-01

    Much effort has been devoted to removing differential Stark shifts for atoms trapped in specially tailored ``magic'' optical lattices, but thus far work has focused on a single trapped atomic species. In this work, we extend these ideas to include two atomic species sharing the same optical lattice. We show qualitatively that, in particular, scalar J = 0 divalent atoms paired with non-scalar state atoms have the necessary characteristics to achieve such Stark shift cancellation. We then present numerical results on ``magic'' trapping conditions for 27Al paired with 87Sr, as well as several other divalent atoms.

  18. 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.

  19. Measurements of Hbeta Stark central asymmetry and its analysis through standard theory and computer simulations.

    PubMed

    Djurović, S; Cirisan, M; Demura, A V; Demchenko, G V; Nikolić, D; Gigosos, M A; González, M A

    2009-04-01

    Experimental measurements of the center of the H_{beta} Stark profile on three different installations have been done to study its asymmetry in wide ranges of electron density, temperature, and plasma conditions. Theoretical calculations for the analysis of experimental results have been performed using the standard theory and computer simulations and included separately quadrupolar and quadratic Stark effects. Earlier experimental results and theoretical calculations of other authors have been reviewed as well. The experimental results are well reproduced by the calculations at high and moderate densities. PMID:19518354

  20. 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. PMID:26840424

  1. 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.

  2. Precision test of the ac Stark shift in a rubidium atomic vapor

    NASA Astrophysics Data System (ADS)

    Levi, F.; Camparo, J.; Francois, B.; Calosso, C. E.; Micalizio, S.; Godone, A.

    2016-02-01

    The ac Stark shift (also known as the "light shift") is one of the most important physical processes that arises in precision spectroscopy, affecting the basic understanding of field-matter interactions, measurements of fundamental constants, and even the atomic clocks onboard GPS satellites. Although the theory of the ac Stark shift was fully developed by the 1960s and 1970s, precision tests of theory have, for the most part, been few. Taking advantage of recent developments in atomic clock technology, specifically the pulsed approach to atomic signal generation, which allows frequency measurements with a resolution of ˜10-15 , we demonstrate a methodology for measuring the ac Stark shift. Here, we report results from a precision examination of the ac Stark shift in a vapor phase system, examining the resonant frequency of the 87Rb 0-0 hyperfine transition for a perturbing laser tuned over a broad optical frequency range (18 GHz) around the D1 absorption resonance. Over the full frequency range the agreement between semiclassical theory and experiment is very good (better than 5 ×10-2 ), and in our experiments we test both the frequency dependence of the scalar and tensor components of the light shift.

  3. Calculation of the Vibrational Stark Effect Using a First-Principles QM/MM Approach

    PubMed Central

    Ringer, Ashley L.; MacKerell, Alexander D.

    2011-01-01

    The proper description of the electric environment of condensed phases is a critical challenge for force field methods. To test and validate the ability of the CHARMM additive force field to describe the electric environment in aqueous solution combined QM/MM calculations have been used to calculate the vibrational Stark effect (VSE). We utilized a first principles methodology using correlated electronic structure techniques to compute the Stark shift between the gas phase and solvent environments and between two different solvent environments of three VSE probes containing acetonitrile or fluorine functionalities which have been well-characterized experimentally. Reasonable agreement with the experimentally determined Stark shifts is obtained when the MM atoms are described by the CHARMM additive force field, though it is essential to employ an anharmonic correction in the frequency calculation. In addition, the electric field created by the solvent is computed along the CN bond and a theoretical Stark tuning rate is determined for acetonitrile and shown to be in satisfactory agreement with experiment. PMID:21423871

  4. 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.

  5. DEVELOPING AN INTEGRATED BIOMASS PROCESSING PLAN FOR WAYNE AND STARK COUNTIES, OHIO

    EPA Science Inventory

    Ohio's Wayne and Stark counties are home to unique combination of biomass waste materials that offer interesting P3 opportunities. Biomass materials from 42 food manufacturing facilities, 72 wood manufacturing operations, large livestock farms, and residential land use for ne...

  6. On the Road to Expansion: Canton Public/Stark County District Library 1929-1997.

    ERIC Educational Resources Information Center

    Croston, Kendel R.

    This paper covers the history of the Canton Public/Stark County District Library (CPL), focusing on the years 1929-1997. The paper focuses on the broadening of the library's services, including the development of reference services, service to young adults, and a variety of outreach activities. A literature review discusses the history of the…

  7. Constructive and destructive interferences of Stark resonances induced by an ac field in atomic hydrogen

    SciTech Connect

    Pawlak, Mariusz; Bylicki, Miroslaw; Moiseyev, Nimrod; Sindelka, Milan

    2010-12-15

    We study theoretically the problem of a hydrogen atom exposed both to a static dc field and to a monochromatic ac field. We show that, in the presence of an ac field, a constructive (or destructive) interference occurs between the excited (Rydberg) Stark resonance states and the hydrogenic ground state. This mechanism is responsible for dramatic enhancement (or suppression) of the corresponding photoionization rates.

  8. 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. PMID:21102917

  9. Stark width measurements of Fe II lines with wavelengths in the range 260-300 nm

    NASA Astrophysics Data System (ADS)

    Aragón, C.; Vega, P.; Aguilera, J. A.

    2011-03-01

    The Stark widths of 21 Fe II lines with wavelengths in the range 260-300 nm have been measured using laser-induced plasmas as spectroscopic sources. A set of Fe-Cu samples has been employed to generate the plasmas. To reduce self-absorption, each line has been measured using a different sample, with an iron concentration determined by means of the curve-of-growth methodology. The remaining error due to self-absorption has been estimated to be lower than 10%. Different instants of the plasma evolution, from 0.84 to 2.5 µs, are included in the measurements. The electron density, in the range (1.6-7.3) × 1017 cm-3, is determined by the Stark broadening of the Hα line. Within this range, the Stark widths are found to be proportional to the electron density. The Boltzmann plot method is used to obtain the plasma temperature, which is in the range 12 900-15 200 K. The Stark widths obtained have been compared with available experimental and theoretical data.

  10. The Stark-B database VAMDC node for spectral line broadening by collisions with charged particles

    NASA Astrophysics Data System (ADS)

    Sahal-Bréchot, S.; Dimitrijević, M. S.; Moreau, N.; Ben Nessib, N.

    2014-12-01

    ``Stark broadening" theories and calculations have been extensively developed for about 50 years. Accurate spectroscopic diagnostics and modeling require the knowledge of numerous collisional line profiles. Nowadays, the access to such data via an on line database becomes essential. The aim of STARK-B is satisfy this need. It is a collaborative project between the Astronomical Observatory of Belgrade (AOB) and the LERMA at Observatory of Paris. It is a database of widths and shifts of isolated lines of atoms and ions due to electron and ion impacts that we have calculated and published in international refereed journals. It is devoted to spectroscopic diagnostics and modeling of stellar atmospheres and envelopes, laboratory plasmas, laser equipments and technological plasmas. Hence, the domain of temperatures and densities covered by the tables is wide and depends on the ionization degree of the considered ion. STARK-B has been fully opened to the international community since fall 2008 and is a node of VAMDC. VAMDC (Virtual Atomic and Molecular Data Centre) is an European Union funded collaboration between groups involved in the generation and use of atomic and molecular data. In the present paper, we will present STARK-B, its state of development, our current projects and future plans.

  11. Radiofrequency quadrupolar NMR stark spectroscopy: steady state response calibration and tensorial mapping.

    PubMed

    Tarasek, Matthew R; Kempf, James G

    2010-10-01

    Radiofrequency electric (E) fields oscillating at twice the usual NMR frequency (2ω(0)) can induce double-quantum transitions in quadrupolar nuclei, an NMR Stark effect. Characterization of such is of interest to aid understanding of electrostatic effects in NMR spectra. Calibration of Stark responses to an applied electric field may also be used to assess native fields within molecules and materials. We present high-field (14.1 T), room-temperature NMR experiments to calibrate the 2ω(0) Stark response in crystalline GaAs. This system presents an important test of current techniques and conditions, as historical studies at low field (500-900 mT) and low temperature (77 K) provide a basis for comparison. Our measurements of steady state response reveal the quadrupolar Stark tuning rate for (69)Ga in this material. The value, β(Q) = (11.5 ± 0.1) × 10(12) m(-1), is 3.6 times larger than the most-reliable prior result. In the process, we also uncovered a previously unobserved double-quantum steady state coherence. It appears as a completely separable dispersive signal component in quadrature-detected presaturation spectra versus offset from 2ω(0). The new component may eventually afford an independent route to calibrating β(Q). Finally, we demonstrated exceptional agreement with theory of the orientation-dependent Stark response for rotation of the sample relative to B(0) over a range of 90° and for E-field amplitudes from 30-180 V/cm. PMID:20839890

  12. 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

  13. Measurement of atomic Stark parameters of many Mn I and Fe I spectral lines using GMAW process

    NASA Astrophysics Data System (ADS)

    Zielinska, S.; Pellerin, S.; Dzierzega, K.; Valensi, F.; Musiol, K.; Briand, F.

    2010-11-01

    The particular character of the welding arc working in pure argon, whose emission spectrum consists of many spectral lines strongly broadened by the Stark effect, has allowed measurement, sometimes for the first time, of the Stark parameters of 15 Mn I and 10 Fe I atomic spectral lines, and determination of the dependence on temperature of normalized Stark broadening in Ne = 1023 m-3 of the 542.4 nm atomic iron line. These results show that special properties of the MIG plasma may be useful in this domain because composition of the wire-electrode may be easily adapted to the needs of an experiment.

  14. On the Stark effect in open shell complexes exhibiting partially quenched electronic angular momentum: Infrared laser Stark spectroscopy of OH-C2H2, OH-C2H4, and OH-H2O

    NASA Astrophysics Data System (ADS)

    Moradi, Christopher P.; Douberly, Gary E.

    2015-08-01

    The Stark effect is considered for polyatomic open shell complexes that exhibit partially quenched electronic angular momentum. Matrix elements of the Stark Hamiltonian represented in a parity conserving Hund's case (a) basis are derived for the most general case, in which the permanent dipole moment has projections on all three inertial axes of the system. Transition intensities are derived, again for the most general case, in which the laser polarization has projections onto axes parallel and perpendicular to the Stark electric field, and the transition dipole moment vector is projected onto all three inertial axes in the molecular frame. Simulations derived from this model are compared to experimental rovibrational Stark spectra of OH-C2H2, OH-C2H4, and OH-H2O complexes formed in helium nanodroplets.

  15. 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.

  16. Reactive intermediates in {sup 4}He nanodroplets: Infrared laser Stark spectroscopy of dihydroxycarbene

    SciTech Connect

    Broderick, Bernadette M.; Moradi, Christopher P.; Douberly, Gary E.; McCaslin, Laura; Stanton, John F.

    2015-04-14

    Singlet dihydroxycarbene (HOC{sup ¨}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 (μ{sub a}, μ{sub b}) = (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 HOC{sup ¨}OH torsional interconversion and tautomerization barriers.

  17. Spectroscopic Studies of DB White Dwarfs: Improved Stark Profiles for Optical Transitions of Neutral Helium

    NASA Astrophysics Data System (ADS)

    Beauchamp, A.; Wesemael, F.; Bergeron, P.

    1997-02-01

    New Stark profiles for 21 He I lines and their forbidden components have been calculated for electron densities ranging from 1014 to 6 × 1017 cm-3, and for temperatures ranging from 10,000 K to 40,000 K. The profiles include quasi-static broadening by ions as well as electron broadening--the latter treated within the impact approximation near the core, and within the one-perturber approximation in the far wings. The calculated profiles also allow for line dissolution. These new profiles are the cornerstone of a recent reanalysis of the optical spectrum of a large sample of DB white dwarfs. Our calculations provide a very good match to the observed profiles of all the lines, provided that Stark broadening dominates other broadening mechanisms.

  18. Full color modulation of firefly luciferase through engineering with unified Stark effect.

    PubMed

    Cai, Duanjun; Marques, Miguel A L; Nogueira, Fernando

    2013-11-01

    The firefly luciferase has been a unique marking tool used in various bioimaging techniques. Extensive color modulation is strongly required to meet special marking demands; however, intentional and accurate wavelength tuning has yet to be achieved. Here, we demonstrate that the color shift of the firefly chromophore (OxyLH2-1) by internal and external fields can be described as a unified Stark shift. Electrostatic microenvironmental effects on fluorescent spectroscopy are modeled in vacuo through effective electric fields by using time-dependent density functional theory. A complete visible fluorescence spectrum of firefly chromophore is depicted, which enables one to control the emission in a specific color. As an application, the widely observed pH-correlated color shift is proved to be associated with the local Stark field generated by the trace water-ions (vicinal hydronium and hydroxide ions) at active sites close to the OxyLH2-1. PMID:24087879

  19. Shift and width measurements of the Stark-broadened ionized helium line at 1215 A

    NASA Technical Reports Server (NTRS)

    Van Zandt, J. R.; Adcock, J. C., Jr.; Griem, H. R.

    1976-01-01

    Time-resolved photoelectric measurements were made of the shifts of helium plasma lines at 1640 A and 1215 A and of the Stark profile of the 1215 A line, using an electromagnetic shock tube as a light source. These red shifts are consistent with a plasma polarization shift, where the interaction energy between the radiating ion and the perturbing plasma electrons corresponds to the Coulomb interaction near the excited state Bohr radius. No significant shifts were observed for the 1640 A line, while the 1215 A line underwent a red shift of about 0.5 A. The measured Stark width of the 1215 A line was 10-45% greater than the calculated width based on the measured width of the 4686 A line.

  20. Significance of decay mechanism into continuum in dynamical Wannier-Stark ladder

    SciTech Connect

    Nemoto, Yuya; Maeshima, Nobuya; Hino, Ken-ichi

    2013-12-04

    We examine the resonance structure of photodressed electron states of laser-driven Wannier-Stark ladder, namely, dynamic Wannier-Stark ladder, in terms of the excess density of states (DOS) closely related to a lifetime of the state of concern. It is revealed that the resonance structure in the strong laser-field region shows clear dependence on the ratio, η, of a Bloch-frequency to a laser frequency. As the laser strength increases, for η = 1, the excess DOS becomes involved with a lot of newly-growing resonance peaks. This result would be understood from the viewpoint of a Fano-like decay-mechanism caused by a multichannel continuum effect, in marked contrast to the cases of larger η’s; for η = 3, the excess DOS just is found to show a pronounced red-shift of a single dominant peak caused by a single-channel continuum effect.

  1. Multiphoton ac Stark effect in a bichromatically driven two-level atom

    NASA Astrophysics Data System (ADS)

    Rudolph, T. G.; Freedhoff, H. S.; Ficek, Z.

    1998-08-01

    We study the interaction of a two-level atom with two lasers of different frequencies and amplitudes: a strong laser of Rabi frequency 2Ω1 on resonance with the atomic transition, and a weaker laser detuned by subharmonics (2Ω1/n) of the Rabi frequency of the first. We find that under these conditions the second laser couples the dressed states created by the first in an n-photon process, resulting in ``doubly dressed'' states and in a ``multiphoton ac Stark'' effect. We calculate the eigenstates of the doubly dressed atom and their energies, and illustrate the role of this multiphoton ac Stark effect in its fluorescence, absorption, and Autler-Townes spectra.

  2. Magic polarization for optical trapping of atoms without Stark-induced dephasing.

    PubMed

    Kim, Huidong; Han, Hyok Sang; Cho, D

    2013-12-13

    We demonstrate that the differential ac-Stark shift of a Zeeman-sensitive ground hyperfine transition in an optical trap can be eliminated by using properly polarized trapping light. We use the vector polarizability of an alkali-metal atom to produce a polarization-dependent ac-Stark shift that resembles a Zeeman shift. We study a transition from the |2S1/2,F=2,mF=-2> to the |2S1/2,F=1,mF=-1> state of 7Li to observe 0.59±0.02  Hz linewidth with interrogation time of 2 s and 0.82±0.06  s coherence time of a superposition state. Implications of the narrow linewidth and the long coherence time for precision spectroscopy and quantum information processing using atoms in an optical lattice are discussed. PMID:24483653

  3. Magic Polarization for Optical Trapping of Atoms without Stark-Induced Dephasing

    NASA Astrophysics Data System (ADS)

    Kim, Huidong; Han, Hyok Sang; Cho, D.

    2013-12-01

    We demonstrate that the differential ac-Stark shift of a Zeeman-sensitive ground hyperfine transition in an optical trap can be eliminated by using properly polarized trapping light. We use the vector polarizability of an alkali-metal atom to produce a polarization-dependent ac-Stark shift that resembles a Zeeman shift. We study a transition from the |2S1/2,F=2,mF=-2⟩ to the |2S1/2,F=1,mF=-1⟩ state of Li7 to observe 0.59±0.02Hz linewidth with interrogation time of 2 s and 0.82±0.06s coherence time of a superposition state. Implications of the narrow linewidth and the long coherence time for precision spectroscopy and quantum information processing using atoms in an optical lattice are discussed.

  4. Differential Stark shift measurement of clock states of Yb+ using an optical frequency comb

    NASA Astrophysics Data System (ADS)

    Quraishi*, Qudsia; Hayes, David; Hucul, David; Matsukevich, Dzmitry; Debnath, Shantanu; Clark, Susan; Monroe, Chris

    2011-03-01

    Quantum information processing with trapped ions has traditionally involved state preparation, manipulation (eg. quantum gates) and detection using CW lasers. Quantum gates implemented with ions typically involve optical Raman transitions between two atomic levels. An optical frequency comb, emitted by a pulsed laser, is an excellent tool for bridging atomic frequency differences. Previously, we demonstrated quantum gates and separately, ultrafast spin manipulation, using pulsed lasers [1,2]. Unlike the CW case, employing pulsed lasers has the marked advantage of both low spontaneous emission and low AC Stark shifts, because the high powers available from pulsed lasers allow for larger detunings from optical resonance. Here, we show both experimentally and theoretically the scaling of the differential Stark shift with detuning (6 THz to 20 THz) of the Raman fields, achieving values of 10-3 of the Rabi frequency.

  5. Trapped ion 88Sr+ optical clock systematic uncertainties - AC Stark shift determination

    NASA Astrophysics Data System (ADS)

    Barwood, GP; Huang, G.; King, SA; Klein, HA; Gill, P.

    2016-06-01

    A recent comparison between two trapped-ion 88Sr+ optical clocks at the UK. National Physical Laboratory demonstrated agreement to 4 parts in 1017. One of the uncertainty contributions to the optical clock absolute frequency arises from the blackbody radiation shift which in turn depends on uncertainty in the knowledge of the differential polarisability between the two clocks states. Whilst a recent NRC measurement has determined the DC differential polarisability to high accuracy, there has been no experimental verification to date of the dynamic correction to the DC Stark shift. We report a measurement of the scalar AC Stark shift at 1064 nm with measurements planned at other wavelengths. Our preliminary result using a fibre laser at 1064 nm agrees with calculated values to within ∼3%.

  6. Optical spin readout method in a quantum dot using the ac Stark effect

    NASA Astrophysics Data System (ADS)

    Flagg, Edward B.; Solomon, Glenn S.

    2015-12-01

    We propose a method to read out the spin state of an electron in a quantum dot in a Voigt geometry magnetic field using cycling transitions induced by the ac Stark effect. We show that cycling transitions can be made possible by a red-detuned, circularly polarized cw laser, which modifies the spin eigenstates and polarization selection rules via the ac Stark effect. A Floquet-Liouville supermatrix approach is used to calculate the time evolution of the density matrix under the experimental conditions of a spin readout operation. With an overall detection efficiency of 2.5%, the readout is a single-shot measurement with a fidelity of 76.2%.

  7. 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.

  8. Stark line broadening of the n=4 to 3 transitions in high-Z heliumlike ions

    SciTech Connect

    Loboda, P. A.; Lykov, V. A.; Popova, V. V.

    1995-05-01

    Stark line broadening of the n=4 to 3 transitions of He-like Ne, Mg, and Al in multicharged ion plasmas is considered. Line profiles calculations involved quasi-static ion broadening, impact electron broadening, natural, and Doppler broadening. Considerable effect of Stark line broadening due to plasma ions for the 4F-3D transitions of He-like Ne is demonstrated at the Ne-plasma parameters yielding a maximum gain in the theoretical modeling of the resonantly photopumped Na-Ne x-ray laser scheme under the conditions of the Saturn experiments. The sensitivity of the calculated line profiles to the intermediate coupling effects and different energy level data is also investigated. Calculated line profiles of the 4F-3D transitions in He-like Mg and Al are compared to the experimental and other theoretical data.

  9. Engineering Stark Potentials for Precision Measurements: Optical Lattice Clock and Electrodynamic Surface Trap

    SciTech Connect

    Katori, Hidetoshi; Takamoto, Masao; Hachisu, Hidekazu; Fujiki, Jun; Higashi, Ryoichi; Yasuda, Masami; Kishimoto, Tetsuo

    2005-05-05

    Employing the engineered electric fields, we demonstrate novel platforms for precision measurements with neutral atoms. (1) Applying the light shift cancellation technique, atoms trapped in an optical lattice reveal 50-Hz-narrow optical spectrum, yielding nearly an order of magnitude improvement over existing neutral-atom-based clocks. (2) Surface Stark trap has been developed to manipulate scalar atoms that are intrinsically robust to decoherence.

  10. Static multipole polarisabilities and second-order Stark shift in francium.

    PubMed

    Khan, F; Khandelwal, G S; Wilson, J W

    1988-01-01

    The multipole polarisability of the ground state of francium is calculated by utilising both the variational technique of Davison and the quantum defect theory underlying the Bates-Damgaard method. This approach is also shown to yield reasonable results for other alkali atoms. Second-order Stark shift for the ground state of francium is presented as a function of field strength for possible future experimental comparison. PMID:11539071

  11. Static multipole polarisabilities and second-order Stark shift in francium

    NASA Technical Reports Server (NTRS)

    Khan, F.; Khandelwal, G. S.; Wilson, J. W.

    1988-01-01

    The multipole polarizability of the ground state of francium is calculated by utilizing both the variational technique of Davison and the quantum defect theory underlying the Bates-Damgaard method. This approach is also shown to yield reasonable results for other alkali atoms. Second-order Stark shift for the ground state of francium is presented as a function of field strength for possible future experimental comparison.

  12. NMR Stark Spectroscopy: New Methods to Calibrate NMR Sensitivity to Electric Fields

    NASA Astrophysics Data System (ADS)

    Tarasek, Matthew R.

    The influence of electrostatics on NMR parameters is well accepted. Thus, NMR is a promising route to probe electrical features within molecules and materials. However, applications of NMR Stark effects (E-field induced changes in spin energy levels) have been elusive. I have developed new approaches to resolve NMR Stark effects from an applied E field. This calibrates nuclear probes whose spectral response might later be used to evaluate internal E fields that are critical to function, such as those due to local charge distributions or sample structure. I will present two novel experimental approaches for direct calibration of NMR quadrupolar Stark effects (QSEs). In the first, steady-state (few-second) excitation by an E field at twice the NMR frequency (2ω 0) is used to saturate spin magnetization. The extent of saturation vs. E-field amplitude calibrates the QSE response rate, while measurements vs sample orientation determine tensorial character. The second method instead synchronizes short (few µs) pulses of the 2ω0 E field with a multiple-pulse NMR sequence. This, “POWER” (Perturbations Observed With Enhanced Resolution) approach enables more accurate measure of small QSEs (i.e. few Hz spectral changes). A 2nd key advantage is the ability to define tensorial response without reorienting the sample, but instead varying the phase of the 2ω0 field. I will describe these experiments and my home-built NMR “Stark probe”, employed on a conventional wide-bore solid-state NMR system. Results with GaAs demonstrate each method, while extensions to a wider array of molecular and material systems may now be possible using these methods.

  13. Stark-shift-chirped rapid-adiabatic-passage technique among three states

    SciTech Connect

    Rangelov, A. A.; Vitanov, N. V.; Yatsenko, L. P.; Shore, B. W.; Halfmann, T.; Bergmann, K.

    2005-11-15

    We show that the technique of Stark-chirped rapid adiabatic passage (SCRAP), hitherto used for complete population transfer between two quantum states, offers a simple and robust method for complete population transfer amongst three states in atoms and molecules. In this case SCRAP uses three laser pulses: a strong far-off-resonant pulse modifies the transition frequencies by inducing dynamic Stark shifts and thereby creating time-dependent level crossings amongst the three diabatic states, while near-resonant and moderately strong pump and Stokes pulses, appropriately offset in time, drive the population between the initial and final states via adiabatic passage. The population transfer efficiency is robust to variations in the intensities of the lasers, as long as these intensities are sufficiently large to enforce adiabatic evolution. With suitable pulse timings the population in the (possibly decaying) intermediate state can be minimized, as with stimulated Raman adiabatic passage (STIRAP). This technique applies to one-photon as well as multiphoton transitions and it is also applicable to media exhibiting inhomogeneous broadening; these features represent clear advantages over STIRAP by overcoming the inevitable dynamical Stark shifts that accompany multiphoton transitions as well as unwanted detunings, e.g., induced by Doppler shifts.

  14. ac Stark shifts for cesium and their effect on ionization line shapes

    SciTech Connect

    Pindzola, M.S.; Glasser, A.H.; Payne, M.G.

    1984-10-01

    The influence of ac Stark shifts on the three-photon ionization of cesium in a moderate-intensity laser beam is investigated. The ionization process involves a two-photon resonance with the 8d fine-structure levels. The work consists of two related parts. In the first part, atomic parameters, such as the two-photon Rabi rate and the ac Stark shift, are calculated in the nonrelativistic Hartree-Fock approximation. In the second part, the atomic parameters thus obtained are used as coefficients in a system of coupled differential equations representing the time evolution of the density matrix. Ionization line shapes are generated for a transform-limited pulsed laser of moderate intensity with a single-mode transverse structure. As the time history of the intensity profile is varied from square to smooth, the ionization line shape becomes asymmetric due to the time dependence of the ac Stark shift. The effects of varying the spatial intensity distribution of the laser light to

  15. Investigation of ac Stark shifts in excited states of dysprosium relevant to testing fundamental symmetries

    NASA Astrophysics Data System (ADS)

    Weber, C. T. M.; Leefer, N.; Budker, D.

    2013-12-01

    We report on measurements of the differential polarizability between the nearly degenerate, opposite parity states in atomic dysprosium at 19 797.96 cm-1, and the differential blackbody radiation induced Stark shift of these states. The differential scalar and tensor polarizabilities due to additional states were measured for the |M|=7,⋯,10 sublevels in 164Dy and 162Dy and determined to be α¯BA(0)=180(45)stat(8)sys mHz/(V/cm)2 and α¯BA(2)=-163(65)stat(5)sys mHz/(V/cm)2, respectively. The average blackbody radiation induced Stark shift of the Zeeman spectrum was measured around 300 K and found to be -34(4) mHz/K and +29(4) mHz/K for 164Dy and 162Dy, respectively. We conclude that ac Stark related systematics will not limit a search for variation of the fine-structure constant, using dysprosium, down to the level of |α˙/α|=2.6×10-17 yr-1, for two measurements of the transition frequency one year apart.

  16. [Calculating the stark broadening of welding arc spectra by Fourier transform method].

    PubMed

    Pan, Cheng-Gang; Hua, Xue-Ming; Zhang, Wang; Li, Fang; Xiao, Xiao

    2012-07-01

    It's the most effective and accurate method to calculate the electronic density of plasma by using the Stark width of the plasma spectrum. However, it's difficult to separate Stark width from the composite spectrum linear produced by several mechanisms. In the present paper, Fourier transform was used to separate the Lorentz linear from the spectrum observed, thus to get the accurate Stark width. And we calculated the distribution of the TIG welding arc plasma. This method does not need to measure arc temperature accurately, to measure the width of the plasma spectrum broadened by instrument, and has the function to reject the noise data. The results show that, on the axis, the electron density of TIG welding arc decreases with the distance from tungsten increasing, and changes from 1.21 X 10(17) cm(-3) to 1.58 x 10(17) cm(-3); in the radial, the electron density decreases with the distance from axis increasing, and near the tungsten zone the biggest electronic density is off axis. PMID:23016315

  17. On the Stark Effect in Open Shell Complexes Exhibiting Partially Quenched Electronic Angular Momentum

    NASA Astrophysics Data System (ADS)

    Douberly, Gary E.; Moradi, Christopher P.

    2015-06-01

    The Stark effect is considered for polyatomic open shell complexes that exhibit partially quenched electronic angular momentum. Specifically, a zero-field model Hamiltonian is employed that accounts for the partial quenching of electronic orbital angular momentum in hydroxyl radical containing molecular complexes. Spherical tensor operator formalism is employed to derive matrix elements of the Stark Hamiltonian in a parity conserving, Hund's case (a) basis for the most general case, in which the permanent dipole moment has projections on all three inertial axes of the system. Ro-vibrational transition intensities are derived, again for the most general case; namely, the laser polarization is projected onto axes parallel and perpendicular to the Stark electric field, and the transition dipole moment vector is projected onto all three inertial axes in the molecular frame. The model discussed here is compared to experimental spectra of OH-(C2H2), OH-(C2H4), and OH-(H2O) complexes formed in He nanodroplets. M. D. Marshall and M. I. Lester, J. Chem. Phys. 121, 3019 (2004). G. E. Douberly, P. L. Raston, T. Liang, and M. D. Marshall, J. Chem. Phys. in press

  18. Stark effect modeling in the detailed opacity code SCO-RCG

    NASA Astrophysics Data System (ADS)

    Pain, J.-C.; Gilleron, F.; Gilles, D.

    2016-05-01

    The broadening of lines by Stark effect is an important tool for inferring electron density and temperature in plasmas. Stark-effect calculations often rely on atomic data (transition rates, energy levels,...) not always exhaustive and/or valid for isolated atoms. We present a recent development in the detailed opacity code SCO-RCG for K-shell spectroscopy (hydrogen- and helium-like ions). This approach is adapted from the work of Gilles and Peyrusse. Neglecting non-diagonal terms in dipolar and collision operators, the line profile is expressed as a sum of Voigt functions associated to the Stark components. The formalism relies on the use of parabolic coordinates within SO(4) symmetry. The relativistic fine-structure of Lyman lines is included by diagonalizing the hamiltonian matrix associated to quantum states having the same principal quantum number n. The resulting code enables one to investigate plasma environment effects, the impact of the microfield distribution, the decoupling between electron and ion temperatures and the role of satellite lines (such as Li-like 1snℓn'ℓ' — 1s 2 nℓ, Be-like, etc.). Comparisons with simpler and widely-used semi-empirical models are presented.

  19. Stark Profiles In Plasmas Interacting With A Strong Oscillatory Quasi-Monochromatic Electric Field

    SciTech Connect

    Sauvan, P.; Oks, E.; Renner, O.; Weber, S.

    2010-10-29

    This paper presents an advanced analysis of the spectroscopic signatures of the interaction of a strong oscillating Quasi-monochromatic Electric Field (QEF), generated by a high-power short-pulse laser, with a preformed laser-produced plasma. The computation of a synthetic spectrum emitted by such plasmas requires the calculation of the Stark line shape in the presence of a QEF and the evaluation of the QEF intensity profile throughout the line of sight in the plasma. As for the Stark profiles in hot dense plasmas submitted to a strong QEF, they are calculated using the so-called Floquet-Liouville formalism. In this formalism, the Liouville space, usually used for the calculation of Stark profiles in dense plasmas, and the Floquet theory, developed to solve time-periodic problems, have been joined together to solve the time-dependent Liouville equation. A second kind of simulations involving Particle-In-Cell PIC kinetic simulations is required for the calculation of the QEF inhomogeneous intensity and the exotic features exhibited in the spectroscopic diagnostic. The global synthetic profile is obtained integrating all individual contributions for every time and location in the plasma. Finally, a spectroscopic analysis of the experimental Al He {beta} line is performed using the tools presented in this work. The spectroscopic signatures of the QEF show up as prominent satellites, non symmetrical with respect to the unperturbed line and distinguishable from the di-electronic satellites.

  20. A Simultaneous Discovery: The Case of Johannes Stark and Antonino Lo Surdo

    NASA Astrophysics Data System (ADS)

    Leone, Matteo; Paoletti, Alessandro; Robotti, Nadia

    2004-09-01

    In 1913 the German physicist Johannes Stark (1874 1957) and the Italian physicist Antonino Lo Surdo (1880 1949)discovered virtually simultaneously and independently that hydrogen spectral lines are split into components by an external electric field. Both of their discoveries ensued from studies on the same phenomenon, the Doppler effect in canal rays, but they arose in different theoretical contexts. Stark had been working within the context of the emerging quantum theory, following a research program aimed at studying the effect of an electric field on spectral lines. Lo Surdo had been working within the context of the classical theory, and his was an accidental discovery. Both discoveries, however, played important roles in the history of physics: Stark’s discovery contributed to the establishment of both the old and the new quantum theories; Lo Surdo’s discovery led Antonio Garbasso (1871 1933)to introduce research on the quantum theory into Italian physics. Ironically, soon after their discoveries, both Stark and Lo Surdo rejected developments in modern physics and allied themselves with the political and racial programs of Hitler and Mussolini.

  1. Circular motion

    NASA Astrophysics Data System (ADS)

    Newton, Isaac; Henry, Richard Conn

    2000-07-01

    An extraordinarily simple and transparent derivation of the formula for the acceleration that occurs in uniform circular motion is presented, and is advocated for use in high school and college freshman physics textbooks.

  2. Polar motion

    NASA Technical Reports Server (NTRS)

    Kolenkiewicz, R.

    1973-01-01

    Tracking of the Beacon Explorer-C satellite by a precision laser system was used to measure the polar motion and solid earth tide. The tidal perturbation of satellite latitude is plotted as variation in maximum latitude in seconds of arc on earth's surface as a function of the date, and polar motion is shown by plotting the variation in latitude of the laser in seconds of arc along the earth's surface as a function of date

  3. Asteroid Motions

    NASA Astrophysics Data System (ADS)

    Sykes, Mary V.; Moynihan, P. Daniel

    1996-12-01

    Equations are derived which describe the apparent motion of an asteroid traveling on an elliptical orbit in geocentric ecliptic coordinates. At opposition, the equations are identical to those derived by Bowellet al. (Bowell, E., B. Skiff, and L. Wasserman 1990. InAsteroids, Comets, Meteors III(C.-I. Lagerkvist, M. Rickman, B. A. Lindblad, and M. Lindgren, Eds.), pp. 19-24. Uppsala Universitet, Uppsala, Sweden). These equations can be an important component in the optimization of search strategies for specific asteroid populations based on their apparent motions relative to other populations when observed away from opposition.

  4. What's Motion Sickness?

    MedlinePlus

    ... Homework? Here's Help White House Lunch Recipes What's Motion Sickness? KidsHealth > For Kids > What's Motion Sickness? Print ... motion sickness might get even worse. continue Avoiding Motion Sickness To avoid motion sickness: Put your best ...

  5. Brownian Motion.

    ERIC Educational Resources Information Center

    Lavenda, Bernard H.

    1985-01-01

    Explains the phenomenon of Brownian motion, which serves as a mathematical model for random processes. Topics addressed include kinetic theory, Einstein's theory, particle displacement, and others. Points out that observations of the random course of a particle suspended in fluid led to the first accurate measurement of atomic mass. (DH)

  6. [The reconstruction of welding arc 3D electron density distribution based on Stark broadening].

    PubMed

    Zhang, Wang; Hua, Xue-Ming; Pan, Cheng-Gang; Li, Fang; Wang, Min

    2012-10-01

    The three-dimensional electron density is very important for welding arc quality control. In the present paper, Side-on characteristic line profile was collected by a spectrometer, and the lateral experimental data were approximated by a polynomial fitting. By applying an Abel inversion technique, the authors obtained the radial intensity distribution at each wavelength and thus constructed a profile for the radial positions. The Fourier transform was used to separate the Lorentz linear from the spectrum reconstructed, thus got the accurate Stark width. And we calculated the electronic density three-dimensional distribution of the TIG welding are plasma. PMID:23285847

  7. Passive stabilization of a hole spin qubit using the optical Stark effect

    NASA Astrophysics Data System (ADS)

    Ramsay, A. J.

    2016-02-01

    The extrinsic dephasing of a hole spin confined to a self-assembled quantum dot is dominated by charge noise acting on an electric-field-dependent g -factor. Here we propose the use of the optical Stark effect to reduce the sensitivity of the effective hole Zeeman energy to fluctuations in the local electric field. Calculations using measured quantum dot parameters are presented, and they demonstrate a factor of 10-100 reduction in the extrinsic dephasing. Compared to active stabilization methods, this technique should benefit from reduced experimental complexity.

  8. Stark Effect Spectroscopy of Mono- and Few-Layer MoS2.

    PubMed

    Klein, J; Wierzbowski, J; Regler, A; Becker, J; Heimbach, F; Müller, K; Kaniber, M; Finley, J J

    2016-03-01

    We demonstrate electrical control of the A-exciton interband transition in mono- and few-layer MoS2 crystals embedded into photocapacitor devices via the DC Stark effect. Electric field-dependent low-temperature photoluminescence spectroscopy reveals a significant tuneability of the A-exciton transition energy up to ∼ 16 meV from which we extract the mean DC exciton polarizability ⟨β̅N⟩ = (0.58 ± 0.25) × 10(-8) Dm V(-1). The exciton polarizability is shown to be layer-independent, indicating a strong localization of both electron and hole wave functions in each individual layer. PMID:26845085

  9. Deterministic implementations of quantum gates with circuit QEDs via Stark-chirped rapid adiabatic passages

    NASA Astrophysics Data System (ADS)

    Chen, Jingwei; Wei, L. F.

    2015-10-01

    We show that a set of universal quantum gates could be implemented robustly in a circuit QED system by using Stark-chirped rapid adiabatic passage (SCRAP) technique. Under the adiabatic limit we find that the population transfers could be deterministically passaged from one selected quantum states to the others, and thus the desired quantum gates can be implemented. The proposed SCRAP-based gates are insensitive to the details of the operations and thus relax the designs of the applied pulses, operational imperfections, and the decoherence of the system.

  10. [Determination of electron density in atmospheric pressure radio frequency dielectric barrier discharges by Stark broadening].

    PubMed

    Li, Sen; Liu, Zhong-wei; Chen, Qiang; Liu, Fu-ping; Wang, Zheng-duo; Yang, Li-zhen

    2012-01-01

    The use of high frequency power to generate plasma at atmospheric pressure is a relatively new development. An apparatus of atmospheric pressure radio frequency dielectric barrier discharge was constructed. Plasma emission based measurement of electron density in discharge columns from Stark broadening Ar is discribed. The spacial profile of electron density was studied. In the middle of the discharge column, as the input power increases from 138 to 248 W, the electron density rises from 4.038 x 10(21) m(-3) to 4.75 x 10(21) m(-3). PMID:22497121

  11. Transition probabilities and Stark-broadening parameters of neutral and singly ionized lead

    NASA Technical Reports Server (NTRS)

    Miller, M. H.; Bengston, R. D.; Lindsay, J. M.

    1979-01-01

    Strengths and Stark widths of the prominent visible PbI and PbII lines are measured in emission by means of a gas-driven shock tube. Absolute ionic line strengths for 7s-7p and 7p-7d arrays conform well to quantum-mechanical sum rules and agree with theoretical predictions, but 6d-5f results differ markedly from central-field approximations. Neutral-line strengths agree satisfactorily with available comparison data. Semiempirical theory predicts the widths of PbII lines with characteristic reliability of better than 25%.

  12. Excitation-induced Quantum Confined Stark Effect in a Coupled Double Quantum Wells

    NASA Astrophysics Data System (ADS)

    Shin, Y. H.; Park, Y. H.; Kim, Yongmin; Perry, C. H.

    2011-12-01

    We report a photoluminescence detected anticrossing of the energy levels in an undoped asymmetric coupled-double-quantum-well buried in a p-i-n structure. Due to the built-in electric field, the quantum wells are tilted in such a way that the symmetric energy level is higher than that of the antisymmetric one in the conduction band. Keeping the laser excitation energy below the barrier, with increasing laser power, the level anticrossing and the quantum confined Stark effect were observed due to decreasing built-in electric field by the photogenerated electron and hole pairs.

  13. Two attosecond pulse transient absorption spectroscopy and extraction of the instantaneous AC Stark shift in helium

    NASA Astrophysics Data System (ADS)

    Bækhøj, Jens E.; Bojer Madsen, Lars

    2016-07-01

    In two attosecond pulse absorption spectroscopy (TAPAS) the use of two attosecond XUV pulses allows the extraction of atomic and molecular quantum mechanical dipole phases from spectroscopic measurements. TAPAS relies on interference between processes that individually only include a single XUV photon, and therefore does not rely on high intensity attosecond pulses. To show the usefulness and limitations of the TAPAS method we investigate its capability of capturing the instantaneous AC Stark shift induced by a midinfrared 3200 nm pulse in the | 1{{s}}2{{p}}> state of helium.

  14. Revisiting the Stark Broadening by fluctuating electric fields using the Continuous Time Random Walk Theory

    NASA Astrophysics Data System (ADS)

    Capes, H.; Christova, M.; Boland, D.; Catoire, F.; Godbert-Mouret, L.; Koubiti, M.; Mekkaoui, A.; Rosato, J.; Marandet, Y.; Stamm, R.

    2010-10-01

    Stark broadening of atomic lines in plasmas is calculated by modelling the plasma stochastic electric field using the CTRW approach [1,2]. This allows retaining non Markovian terms in the Schrödinger equation averaged over the electric field fluctuations. As an application we consider a special case of a non separable CTRW process, the so called Kangaroo process [3]. An analytic expression for the line profile is presented for arbitrary waiting time distribution functions. A preliminary application to the hydrogen Lyman α line is discussed.

  15. Effects of the Stark Shift on the Evolution of the Field Entropy and Entanglement in the Two-Photon Jaynes-Cummings Model

    NASA Technical Reports Server (NTRS)

    Fang, Mao Fa

    1996-01-01

    The evolution of the field entropy in the two-photon JCM in the presence of the Stark shift is investigated, and the effects of the dynamic Stark shift on the evolution of the field entropy and entanglement between the atom and field, are examined. The results show that the dynamic Stark shift plays an important role in the evolution of the field entropy in two-photon processes.

  16. Structure and motion of edge turbulence in the National Spherical Torus Experiment and Alcator C-Moda)

    NASA Astrophysics Data System (ADS)

    Zweben, S. J.; Maqueda, R. J.; Terry, J. L.; Munsat, T.; Myra, J. R.; D'Ippolito, D.; Russell, D. A.; Krommes, J. A.; LeBlanc, B.; Stoltzfus-Dueck, T.; Stotler, D. P.; Williams, K. M.; Bush, C. E.; Maingi, R.; Grulke, O.; Sabbagh, S. A.; White, A. E.

    2006-05-01

    In this paper we compare the structure and motion of edge turbulence observed in L-mode vs. H-mode plasmas in the National Spherical Torus Experiment (NSTX) [M. Ono, M. G. Bell, R. E. Bell et al., Plasma Phys. Controlled Fusion 45, A335 (2003)]. The radial and poloidal correlation lengths are not significantly different between the L-mode and the H-mode in the cases examined. The poloidal velocity fluctuations are lower and the radial profiles of the poloidal turbulence velocity are somewhat flatter in the H-mode compared with the L-mode plasmas. These results are compared with similar measurements Alcator C-Mod [E. Marmar, B. Bai, R. L. Boivin et al., Nucl. Fusion 43, 1610 (2003)], and with theoretical models.

  17. Compositional dependence of room-temperature Stark splitting of Yb³⁺ in several popular glass systems.

    PubMed

    Yang, Binhua; Liu, Xueqiang; Wang, Xin; Zhang, Junjie; Hu, Lili; Zhang, Liyan

    2014-04-01

    The room-temperature Stark splitting properties of Yb3+ are practical and valuable for lasers because the working temperature of the gain media intensively increases with the laser output. In this Letter, the room-temperature Stark splitting properties of Yb3+ in several popular laser glasses are contrastively studied. Yb3+-doped germanate (Ge), borate (B), silicate (Si), bismuthate (Bi), tellurite (Te), and fluorophosphate (FP) glasses exhibit large Stark splitting and tend to operate close to the quasi-four-level scheme, whereas phosphate (P) glass shows the weakest Stark splitting and tends to operate close to the quasi-three-level one. Due to the low thermal conductivity of the glass matrix, Yb3+-doped P glass suffers from serious thermal problems and is difficult to achieve high laser output. The Stark splitting is also used to estimate the crystal-field strength of glass hosts and local Yb3+ ligand asymmetry degree. The results show that P glass shows weaker crystal-field effect and lower Yb3+ ligand asymmetry than Ge, Si, and B glasses. PMID:24686601

  18. Theoretical study of the Stark broadening for Mg IV spectral lines of astrophysical interest

    NASA Astrophysics Data System (ADS)

    de Andrés-García, I.; You, C.; Alonso-Medina, A.; Colón, C.

    2016-08-01

    Emission lines of Mg IV have been detected in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of LS V +46º21 star and in the Space Telescope Imaging Spectrograph (STIS) spectrum of BD +28º4211 star. This fact justifies our interest in providing spectroscopic parameters of Mg IV. Stark broadening parameters for 169 spectral lines of Mg IV have been calculated by using the Griem semi-empirical approach. The matrix elements used in these calculations has been determined from 13 configurations of Mg IV: 2s12p6, 2s22p4ns (n = 3-5), 2s22p4nd (n = 3-5) and 2s22p45g for even parity and 2s22p5, 2s22p4np (n = 3, 4) and 2s22p4nf (n = 4, 5) for odd parity. Our calculations were made by using the Cowan code. Data are presented for an electron density of 1017 cm-3 and temperatures T = 1.0-10.0 (104 K). Also we present calculated values of transition probabilities for 30 spectral lines and radiative lifetimes corresponding to its upper levels. These values were analyzed using the data found in the literature. Theoretical trends of the Stark broadening parameters versus the temperature for several lines of astrophysical interest are presented.

  19. Stark effect of interfering electronic states: Localization of the nπ* excitations in toluquinone

    NASA Astrophysics Data System (ADS)

    Galaup, J. P.; Trommsdorff, H. P.

    1984-04-01

    High-precision Stark measurements on oriented single crystals of toluquinone at low temperatures have been performed and lead to an assessment of the electronic parenthood of the levels giving rise to the complex spectral region of interference between the two nearby nπ* excited states. The origin bands of the lowest excited singlet and triplet states are characterized by a measure of their factor-group splittings and an evaluation of the change in dipole moment and in polarizability upon excitation. The value of the change in dipole moment is shown to vary strongly between different vibrational levels of the lower state and an evaluation of the degree of localization of the electronic excitation on one CO group is made. The previous assignment of the second nπ* state is confirmed by the sign of the corresponding Stark shift. From measurements on crystals having been oriented in an electric field the absolute orientation of the polar crystal as well as the sign of the pyroelectric coefficient are proposed.

  20. SPECTROSCOPIC ANALYSIS OF DA WHITE DWARFS: STARK BROADENING OF HYDROGEN LINES INCLUDING NONIDEAL EFFECTS

    SciTech Connect

    Tremblay, P.-E.; Bergeron, P. E-mail: bergeron@astro.umontreal.ca

    2009-05-10

    We present improved calculations for the Stark broadening of hydrogen lines in dense plasmas typical of white dwarf atmospheres. Our new model is based on the unified theory of Stark broadening from Vidal, Cooper, and Smith. For the first time, we account for the nonideal effects in a consistent way directly inside the line profile calculations. The Hummer and Mihalas theory is used to describe the nonideal effects due to perturbations on the absorber from protons and electrons. We use a truncation of the electric microfield distribution in the quasi-static proton broadening to take into account the fact that high electric microfields dissociate the upper state of a transition. This approach represents a significant improvement over previous calculations that relied on the use of an ad hoc parameter to mimic these nonideal effects. We obtain the first model spectra with line profiles that are consistent with the equation of state. We revisit the properties of DA stars in the range 40,000 K >T {sub eff}> 13,000 K by analyzing the optical spectra with our improved models. The updated atmospheric parameters are shown to differ substantially from those published in previous studies, with a mean mass shifted by +0.034 M {sub sun}. We also show that these revised atmospheric parameters yield absolute visual magnitudes that remain in excellent agreement with trigonometric parallax measurements.

  1. Transient Conformational Changes of Sensory Rhodopsin II Investigated by Vibrational Stark Effect Probes.

    PubMed

    Mohrmann, Hendrik; Kube, Ines; Lórenz-Fonfría, Víctor A; Engelhard, Martin; Heberle, Joachim

    2016-05-19

    Sensory rhodopsin II (SRII) is the primary light sensor in the photophobic reaction of the halobacterium Natronomonas pharaonis. Photoactivation of SRII results in a movement of helices F and G of this seven-helical transmembrane protein. This conformational change is conveyed to the transducer protein (HtrII). Global changes in the protein backbone have been monitored by IR difference spectroscopy by recording frequency shifts in the amide bands. Here we investigate local structural changes by judiciously inserting thiocyanides at different locations of SRII. These vibrational Stark probes absorb in a frequency range devoid of any protein vibrations and respond to local changes in the dielectric, electrostatics, and hydrogen bonding. As a proof of principle, we demonstrate the use of Stark probes to test the conformational changes occurring in SRII 12 ms after photoexcitation and later. Thus, a methodology is provided to trace local conformational changes in membrane proteins by a minimal invasive probe at the high temporal resolution inherent to IR spectroscopy. PMID:27111635

  2. Laser control of the radiationless decay in pyrazine using the dynamic Stark effect

    SciTech Connect

    Sala, Matthieu Guérin, Stéphane; Saab, Mohamad; Lasorne, Benjamin; Gatti, Fabien

    2014-05-21

    The laser control of the radiationless decay between the B{sub 3u}(nπ*) and B{sub 2u}(ππ*) states of pyrazine using the dynamic Stark effect has been investigated. A vibronic coupling model Hamiltonian in diabatic representation, including potential energy, transition dipole, and static polarizability surfaces as a function of the four most important vibrational modes of the molecule has been parametrized using multi-reference electronic structure calculations. The interaction of the molecule with a strong non-resonant laser pulse has been analyzed in terms of dressed potential energy surfaces. Because of the large polarizability difference between the vibronically coupled B{sub 3u}(nπ*) and B{sub 2u}(ππ*) states, the Stark effect induced by the non-resonant laser pulse shifts the conical intersection away from the Franck-Condon region. We have shown, by solving the time-dependent Schrödinger equation for the molecule interacting with a relatively weak pump pulse driving the electronic excitation from the ground state to the B{sub 2u}(ππ*) state, and a strong non-resonant control pulse, that this control mechanism can be used to trap the wavepacket on the B{sub 2u}(ππ*) potential energy surface for a much longer time than the natural B{sub 2u}(ππ*) lifetime.

  3. Quantm confined stark effect of single photon emitters in atomically thin semiconductors

    NASA Astrophysics Data System (ADS)

    Chakraborty, Chitraleema; Goodfellow, Kenneth; Dhara, Sajal; Vamivakas, Nick

    The optical properties of semiconducting monolayer materials have been widely studied since the isolation of monolayer transition metal dichalcogenides (TMDCs). They have rich opto-electronic properties owing to their large direct bandgap, the interplay between the spin and the valley degree of freedom of charge carriers, and the recently discovered localized excitonic states giving rise to single photon emission. We study quantum confined Stark shift from these localized emitters present on the edges of monolayer tungsten diselenide. We employ a vertically stacked van der Waals heterostructure to fabricate a field effect device using hexagonal boron nitride as the tunnel barrier on either side of the TMDC and few layer graphene as top and bottom electrical contacts. We report the Stark shift of different defect centers to have linear or both linear and quadratic behavior with electric field. Further, evaluation of the spectral shift in the photoluminescence signal as a function of the applied voltage enables us to extract the polarizability as well as information on the dipole moment of an individual defect center.

  4. Propagation of vector solitons in a quasi-resonant medium with stark deformation of quantum states

    SciTech Connect

    Sazonov, S. V.; Ustinov, N. V.

    2012-11-15

    The nonlinear dynamics of a vector two-component optical pulse propagating in quasi-resonance conditions in a medium of nonsymmetric quantum objects is investigated for Stark splitting of quantum energy levels by an external electric field. We consider the case when the ordinary component of the optical pulse induces {sigma} transitions, while the extraordinary component induces the {pi} transition and shifts the frequencies of the allowed transitions due to the dynamic Stark effect. It is found that under Zakharov-Benney resonance conditions, the propagation of the optical pulse is accompanied by generation of an electromagnetic pulse in the terahertz band and is described by the vector generalization of the nonlinear Yajima-Oikawa system. It is shown that this system (as well as its formal generalization with an arbitrary number of optical components) is integrable by the inverse scattering transformation method. The corresponding Darboux transformations are found for obtaining multisoliton solutions. The influence of transverse effects on the propagation of vector solitons is investigated. The conditions under which transverse dynamics leads to self-focusing (defocusing) of solitons are determined.

  5. Collective electronic excitations in a semiconductor superlattice in the Landau and Wannier-Stark ladder regime

    NASA Astrophysics Data System (ADS)

    Margulis, Vl. A.; Makarov, S. V.; Piterimova, T. V.; Gaiduk, E. A.

    2003-05-01

    Using a mean-field approximation, we have developed a systematic treatment of collective electronic modes in a semiconductor superlattice (SL) in the presence of strong electric and magnetic fields parallel to the SL axis. The spectrum of collective modes with zero wavevector along the SL axis is shown to consist of a principle magnetoplasmon mode and an infinite set of Bernstein-like modes. For non-zero wavevector along the SL axis, in addition to the cyclotron modes, extra collective modes are found at the frequencies \\vert Nω_c± Mω_s\\vert, which we call cyclotron-Stark modes (ω_c and ω_s are respectively the cyclotron and Stark frequencies, N and M are integer numbers). The frequencies of the modes propagating in “oblique” direction with respect to the SL axis show oscillatory behavior as a function of electric field strength. All the modes considered have very weak spatial dispersion and they are not Landau damped. The specific predictions made for the dispersion relations of the collective excitations should be observable in resonant Raman scattering experiments.

  6. Heterostructure quantum confined Stark effect electrooptic modulators operating at 938 nm

    NASA Astrophysics Data System (ADS)

    Hayduk, Michael J.; Krol, Mark F.; Boncek, Raymond K.

    1993-12-01

    Electro-optics modulators are a necessary component of emerging optical fiber based local area interconnects. One type of modulator, suitable for use in optical interconnects, is an asymmetric Fabry-Perot reflection modulator (ARM). This type of an intensity modulator uses an electro-optic material as the spacer material to balance the normally unequal front and back mirror reflectances. The quantum confined Franz-Keldysh and Stark effects shift the absorption edge of semiconductor multiple quantum well (MQW) materials to longer wavelengths in the presence of an external electric field applied perpendicular to the MQW layers, thereby changing the reflectance of the etalon. The combined coherence effects of the etalon coupled with the quantum effects of the MQW materials result in a large modulation depth and a low insertion loss. P-I-N diode structures using an In Ha As/GaAs MQW structure as the intrinsic region were fabricated for the purpose of characterizing the electro-absorption associated with different applied electric fields. Quantum confined Franz-Keldysh and Stark shifts were observed for applied electric fields as large as 6.58 x 10000 V/cm. The resulting change in the absorption coefficient was found to be -3.7 x 1000 cm to the minus 1st power which is sufficient to design a high-speed ARM with a large modulation depth and a low insertion loss.

  7. Full-dimensional control of the radiationless decay in pyrazine using the dynamic Stark effect

    SciTech Connect

    Saab, Mohamad Lasorne, Benjamin Gatti, Fabien; Sala, Matthieu; Guérin, Stéphane

    2014-10-07

    We present a full quantum-mechanical study of the laser control of the radiationless decay between the B{sub 3u}(nπ{sup *}) and B{sub 2u}(ππ{sup *}) 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 B{sub 2u}(ππ{sup *}) potential energy surface due to the Stark effect for a longer time than the “non-resonant field-free” B{sub 2u}(ππ{sup *}) lifetime.

  8. High-accuracy time- and space-resolved Stark shift measurements

    SciTech Connect

    Bailey, J.E.; Adams, R.; Carlson, A.L.; Ching, C.H.; Filuk, A.B.; Lake, P.

    1996-07-01

    Stark-shift measurements using emission spectroscopy are a powerful tool for advancing understanding in many plasma physics experiments. The authors use simultaneous 2-D-spatial and time-resolved spectra to study the electric field evolution in the 20 TW Particle Beam Fusion Accelerator II ion diode acceleration gap. Fiber optic arrays transport light from the gap to remote streaked spectrographs operated in a multiplexed mode that enables recording time-resolved spectra from eight spatial locations on a single instrument. Design optimization and characterization measurements of the multiplexed spectrograph properties include the astigmatism, resolution, dispersion variation, and sensitivity. A semi-automated line-fitting procedure determines the Stark shift and the related uncertainties. Fields up to 10 MV/cm are measured with an accuracy {+-}2--4%. Detailed tests of the fitting procedure confirm that the wavelength shift uncertainties are accurate to better than {+-}20%. Development of an active spectroscopy probe technique that uses laser-induced fluorescence from an injected atomic beam to obtain 3-D space- and time-resolved measurements of the electric and magnetic fields is in progress.

  9. High-precision Stark shift measurements in excited states of indium using an atomic beam

    NASA Astrophysics Data System (ADS)

    Majumder, P. K.; Carter, A. L.; Augenbraun, B. L.; Rupasinghe, P. M.; Vilas, N. B.

    2016-05-01

    A recent precision measurement in our group of the indium scalar polarizability within the 410 nm 5p1 / 2 --> 6s1 / 2 transition showed excellent agreement with ab initio atomic theory. We are now completing a measurement of the polarizability within the 6s1 / 2 --> 6p1 / 2 excited-state transition. In our experiment, two external cavity semiconductor diode lasers interact transversely with a collimated indium atomic beam. We tune the 410 nm laser to the 5p1 / 2 --> 6s1 / 2 transition, keeping the laser locked to the exact Stark-shifted resonance frequency. We overlap a 1343 nm infrared laser to reach the 6p1 / 2 state. The very small infrared absorption in our atomic beam is detected using two-tone FM spectroscopy. Monitoring the two-step excitation signal in a field-free supplemental vapor cell provides frequency reference and calibration. Precisely calibrated electric fields of 5 - 15 kV/cm produce Stark shifts of order 100 MHz for this excited state. Experimental details, latest results, and comparison to theory will be discussed. In the near future, The same infrared laser will be tuned to 1291 nm to study the scalar and tensor polarizability of the 6p3 / 2 excited state providing a distinct test of atomic theory. Work supported by NSF Grant # 1404206.

  10. Spectroscopic Analysis of DA White Dwarfs: Stark Broadening of Hydrogen Lines Including Nonideal Effects

    NASA Astrophysics Data System (ADS)

    Tremblay, P.-E.; Bergeron, P.

    2009-05-01

    We present improved calculations for the Stark broadening of hydrogen lines in dense plasmas typical of white dwarf atmospheres. Our new model is based on the unified theory of Stark broadening from Vidal, Cooper, and Smith. For the first time, we account for the nonideal effects in a consistent way directly inside the line profile calculations. The Hummer and Mihalas theory is used to describe the nonideal effects due to perturbations on the absorber from protons and electrons. We use a truncation of the electric microfield distribution in the quasi-static proton broadening to take into account the fact that high electric microfields dissociate the upper state of a transition. This approach represents a significant improvement over previous calculations that relied on the use of an ad hoc parameter to mimic these nonideal effects. We obtain the first model spectra with line profiles that are consistent with the equation of state. We revisit the properties of DA stars in the range 40,000 K >T eff> 13,000 K by analyzing the optical spectra with our improved models. The updated atmospheric parameters are shown to differ substantially from those published in previous studies, with a mean mass shifted by +0.034 M sun. We also show that these revised atmospheric parameters yield absolute visual magnitudes that remain in excellent agreement with trigonometric parallax measurements.

  11. The application of weak electric field pulses to measure the pseudo-Stark split by photon echo beating

    NASA Astrophysics Data System (ADS)

    Lisin, V. N.; Shegeda, A. M.; Samartsev, V. V.

    2016-07-01

    A novel scheme for determining the pseudo-Stark splitting of optical lines has been suggested and tested in experiment. The scheme allows one to observe the beating of a photon echo waveform under conditions of overlap in time between a weak electric pulse and its echo-pulse. The pseudo-Stark splitting is equal to the inverse average modulation period of the echo waveform. The photon echo beating of the R1-line in Ruby has been observed. The dependence of the inverse average modulation period of the echo waveform on the average value of the electric field over the optically excited volume has been found. The obtained values of the pseudo-Stark parameter are in good agreement with known literature data.

  12. Enhanced Stark Tuning of Single InAs (211 )B Quantum Dots due to Nonlinear Piezoelectric Effect in Zincblende Nanostructures

    NASA Astrophysics Data System (ADS)

    Germanis, S.; Katsidis, C.; Tsintzos, S.; Stavrinidis, A.; Konstantinidis, G.; Florini, N.; Kioseoglou, J.; Dimitrakopulos, G. P.; Kehagias, Th.; Hatzopoulos, Z.; Pelekanos, N. T.

    2016-07-01

    We report enhanced Stark tuning of single exciton lines in self-assembled (211 )B InAs quantum dots (QDs) as a consequence of pronounced piezoelectric effects in polar orientations, making this QD system particularly sensitive to relatively "small" applied external fields. The Stark shifts in the first hundreds of kilovolts per centimeter of applied external field are at least 2.5 times larger, compared to those observed in nonpiezoelectric (100) InAs QDs of similar size. To account quantitatively for the observed transition energies and Stark shifts, we utilize a graded In-composition potential profile, as deduced from local strain analysis performed on high-resolution transmission microscopy images of the QDs. Our results provide a direct demonstration of the importance of nonlinear piezoelectric effects in zincblende semiconductors.

  13. Stark parameters irregularities of Xe II lines obtained by transitions from ({sup 3}P{sub 1})6plevels

    SciTech Connect

    Mar, S.; Pelaez, R. J.; Rodriguez, F.; Aparicio, J. A.

    2008-10-22

    Stark widths and shifts of some Xe II lines belonging to the supermultiplets with upper levels ({sup 3}P{sub 1})6p were measured using a pulsed discharge lamp. Plasma parameters, i.e. electron density and temperature, in this experiment were in the range from 0.2 to 1.4x10{sup 23} m{sup -3} and from 18000 to 23000 K, respectively. Lines obtained by transitions from levels ({sup 3}P{sub 1})6p show some strong intra-supermultiplet irregularities in their Stark widths and shifts. These results and the measurements obtained in previous works were used here to analyse the main irregularities that can appear in the case of Xe II. This study may be very useful for obtaining Stark parameters of non-measured lines, using the known parameters of other lines belonging to similar transitions.

  14. Rb atoms in a blue-detuned dipole trap: Coherence and ground-state differential ac Stark shift

    NASA Astrophysics Data System (ADS)

    Sheng, D.; Zhang, J.; Orozco, L. A.

    2013-06-01

    Blue-detuned dipole traps and their ability to preserve atomic coherences are interesting for precision measurement applications. In this paper, we present experimental studies on the differential ac Stark shift of the ground-state hyperfine splitting in 87Rb atoms confined in a dynamic blue-detuned dipole trap. We systematically study the power and detuning effects on the Rabi resonance frequency (differential ac Stark shift) and its linewidth (coherence) and find that their performance is compatible with future parity violation experiments in Fr.

  15. POP Experiment of Laser Stripping via a Broad Stark State Using BNL 200MeV H- Beams

    SciTech Connect

    Yamane, I.; Mimashi, T.; Nakayama, H.; Suzuki, T.; Takayama, K.; Tawada, M.; Satoh, K.; Raparia, D.; Alessi, J.; Blaskiewicz, M.; Cameron, P.; Connoly, R.; Hershcovitch, A.; Lee, Y.Y.; LoDestro, V.; Ritter, J.; Wei, J.

    2005-06-08

    Present status of the project of the POP (proof of principle) experiment of laser stripping using BNL 200MeV H- is presented. First, the principle of the laser stripping via a broad Stark state and the role of the broad Stark state are introduced. Then, the scheme of the POP experiment using 200MeV H- is given. Then, the concrete plan of experimental setup in the REF beam line of the BNL 200MeV H- Linac and present status of construction are given.

  16. Surface acoustic BLOCH oscillations, the Wannier-Stark ladder, and Landau-Zener tunneling in a solid.

    PubMed

    de Lima, M M; Kosevich, Yu A; Santos, P V; Cantarero, A

    2010-04-23

    We present the experimental observation of Bloch oscillations, the Wannier-Stark ladder, and Landau-Zener tunneling of surface acoustic waves in perturbed grating structures on a solid substrate. A model providing a quantitative description of our experimental observations, including multiple Landau-Zener transitions of the anticrossed surface acoustic Wannier-Stark states, is developed. The use of a planar geometry for the realization of the Bloch oscillations and Landau-Zener tunneling allows a direct access to the elastic field distribution. The vertical surface displacement has been measured by interferometry. PMID:20482064

  17. Generation of Stark spectral components in Nd:YAP and Nd:YAG lasers by using volume Bragg gratings

    SciTech Connect

    Vorob'ev, Nikolai S; Glebov, L B

    2009-01-31

    Generation of Stark spectral components in free-running Q-switched Nd:YAP (1064 nm and 1073 nm) and Nd:YAG (1062 nm) lasers is obtained. For this purpose reflecting volume Bragg gratings placed into the laser resonator and permitting to tune the laser emission spectrum were used. Stable generation of Stark components in both lasers is obtained. The possibility of obtaining two-frequency generation in an Nd-glass laser with the help of these gratings is shown. (control of laser radiation parameters)

  18. A simple formula for estimating Stark widths of neutral lines. [of stellar atmospheres

    NASA Technical Reports Server (NTRS)

    Freudenstein, S. A.; Cooper, J.

    1978-01-01

    A simple formula for the prediction of Stark widths of neutral lines similar to the semiempirical method of Griem (1968) for ion lines is presented. This formula is a simplification of the quantum-mechanical classical path impact theory and can be used for complicated atoms for which detailed calculations are not readily available, provided that the effective position of the closest interacting level is known. The expression does not require the use of a computer. The formula has been applied to a limited number of neutral lines of interest, and the width obtained is compared with the much more complete calculations of Bennett and Griem (1971). The agreement generally is well within 50% of the published value for the lines investigated. Comparisons with other formulas are also made. In addition, a simple estimate for the ion-broadening parameter is given.

  19. Vibrational stark effects to identify ion pairing and determine reduction potentials in electrolyte-free environments

    DOE PAGESBeta

    Mani, Tomoyasu; Grills, David C.; Miller, John R.

    2015-01-02

    A recently-developed instrument for time-resolved infrared detection following pulse radiolysis has been used to measure the ν(C≡N) IR band of the radical anion of a CN-substituted fluorene in tetrahydrofuran. Specific vibrational frequencies can exhibit distinct frequency shifts due to ion-pairing, which can be explained in the framework of the vibrational Stark effect. Measurements of the ratio of free ions and ion-pairs in different electrolyte concentrations allowed us to obtain an association constant and free energy change for ion-pairing. As a result, this new method has the potential to probe the geometry of ion-pairing and allows the reduction potentials of moleculesmore » to be determined in the absence of electrolyte in an environment of low dielectric constant.« less

  20. Hydrogen atoms under magnification: direct observation of the nodal structure of Stark states.

    PubMed

    Stodolna, A S; Rouzée, A; Lépine, F; Cohen, S; Robicheaux, F; Gijsbertsen, A; Jungmann, J H; Bordas, C; Vrakking, M J J

    2013-05-24

    To describe the microscopic properties of matter, quantum mechanics uses wave functions, whose structure and time dependence is governed by the Schrödinger equation. In atoms the charge distributions described by the wave function are rarely observed. The hydrogen atom is unique, since it only has one electron and, in a dc electric field, the Stark Hamiltonian is exactly separable in terms of parabolic coordinates (η, ξ, φ). As a result, the microscopic wave function along the ξ coordinate that exists in the vicinity of the atom, and the projection of the continuum wave function measured at a macroscopic distance, share the same nodal structure. In this Letter, we report photoionization microscopy experiments where this nodal structure is directly observed. The experiments provide a validation of theoretical predictions that have been made over the last three decades. PMID:23745864

  1. Vibrational stark effects to identify ion pairing and determine reduction potentials in electrolyte-free environments

    SciTech Connect

    Mani, Tomoyasu; Grills, David C.; Miller, John R.

    2015-01-02

    A recently-developed instrument for time-resolved infrared detection following pulse radiolysis has been used to measure the ν(C≡N) IR band of the radical anion of a CN-substituted fluorene in tetrahydrofuran. Specific vibrational frequencies can exhibit distinct frequency shifts due to ion-pairing, which can be explained in the framework of the vibrational Stark effect. Measurements of the ratio of free ions and ion-pairs in different electrolyte concentrations allowed us to obtain an association constant and free energy change for ion-pairing. As a result, this new method has the potential to probe the geometry of ion-pairing and allows the reduction potentials of molecules to be determined in the absence of electrolyte in an environment of low dielectric constant.

  2. Modulation-assisted tunneling in laser-fabricated photonic Wannier-Stark ladders

    NASA Astrophysics Data System (ADS)

    Mukherjee, Sebabrata; Spracklen, Alexander; Choudhury, Debaditya; Goldman, Nathan; Öhberg, Patrik; Andersson, Erika; Thomson, Robert R.

    2015-11-01

    We observe Wannier-Stark (W-S) localization in curved photonic lattices, realized using arrays of evanescently coupled optical waveguides. By correctly tuning the strength of inter-site coupling in the lattice, we observe that W-S states become increasingly localized, and eventually fully localized to one site, as the curvature of the lattice is increased. We then demonstrate that tunneling can be successfully restored in the lattice by applying a resonant sinusoidal modulation to the lattice position, an effect that is a direct analogue of photon-assisted tunneling. This precise tuning of the tunneling matrix elements, through resonant modulation-assisted tunneling, opens a novel route for the creation of gauge fields in laser-fabricated photonic lattices.

  3. Measurement of the ac Stark shift with a guided matter-wave interferometer

    NASA Astrophysics Data System (ADS)

    Deissler, B.; Hughes, K. J.; Burke, J. H. T.; Sackett, C. A.

    2008-03-01

    The dynamic polarizability of Rb87 atoms was measured using a guided-wave Bose-Einstein condensate interferometer. Taking advantage of the large arm separations obtainable in our device, a well-calibrated laser beam is applied to one atomic packet and not the other, inducing a differential phase shift. The technique requires relatively low laser intensity and works for arbitrary optical frequencies. For off-resonant light, the ac polarizability is obtained with a statistical accuracy of 3% and a calibration uncertainty of 6%. On resonance, the dispersion-shaped behavior of the Stark shift is observed, but with a broadened linewidth that is attributed to collective light scattering effects. The resulting nonlinearity may prove useful for the production and control of squeezed quantum states.

  4. Stark spectroscopy of CuPc organic semiconductor with a submicron metal-electrode grating

    NASA Astrophysics Data System (ADS)

    Blinov, L. M.; Lazarev, V. V.; Yudin, S. G.; Palto, S. P.

    2016-02-01

    The optical and electro-optical properties of organic copper phthalocyanine semiconductor (α- CuPc) have been investigated by Stark (electroabsorption) spectroscopy using a metal electrode grating with a submicron (0.88 μm) interelectrode distance. Differences between dipole moments (Δμ) and polarizabilities (Δα) in the excited and ground states of α-CuPc are measured for a nanoscale semiconductor film. It is concluded that the extremely high values of Δμ and Δα are in principle not parameters of individual α-CuPc molecules: they are determined by exciton effects specifically in the polycrystalline medium with a characteristic morphology of hyperfine films, which depends on the structure of the samples and their fabrication technology.

  5. Vibrational solvatochromism of nitrile infrared probes: beyond the vibrational Stark dipole approach.

    PubMed

    Błasiak, Bartosz; Ritchie, Andrew W; Webb, Lauren J; Cho, Minhaeng

    2016-07-21

    Systematic probing of local environments around biopolymers is important for understanding their functions. Therefore, there has been growing interest in in situ measurements of molecular granularity and heterogeneity through the systematic analysis of vibrational frequency shifts of carbonyl and nitrile infrared probes by vibrational Stark dipole theory. However, here we show that the nitrile vibrational frequency shift induced by its interaction with the surrounding molecules cannot be solely described by electric field-based theory because of the exchange-repulsion and dispersion interaction contributions. Considering a variety of molecular environments ranging from bulk solutions to protein environments, we explore the distinct scenarios of solute-environment contacts and their traces in vibrational frequency shifts. We believe that the present work could provide a set of clues that could be potentially used to design a rigorous theoretical model linking vibrational solvatochromism and molecular topology in complex heterogeneous environments. PMID:27326899

  6. Study of the Stark effect in the resonance lines of sodium by an atomic jet method

    NASA Technical Reports Server (NTRS)

    Duong, H. T.; Picque, J.-L.

    1972-01-01

    The reversal of the magnetic moment of a part of the atoms of a consecutive jet with optical excitation and on the return to the fundamental level is applied to the case of sodium, in order to complete previous results dealing with the alkalis. A conventional atomic jet apparatus consisting of two electromagnets with Rabi-type poles which produce magnetic field gradients of the same sense was used. The accuracy of measurement of the Stark effect by excitation of an atomic jet of high collimation is limited by the Doppler width of the lines emitted by the source or, if this width is diminished with the help of a connected process, by the luminous power available. The results make it possible to extend the experiments to the measurement of isotopic displacements of sodium.

  7. A switched ring Stark decelerator for both light and heavy polar molecules

    NASA Astrophysics Data System (ADS)

    Hou, Shunyong; Wang, Qin; Deng, Lianzhong; Yin, Jianping

    2016-03-01

    There is increasing interest in cold heavy polar molecular species for their applications in fundamental physics, such as the tests of the electron’s electric dipole moment. Here we propose a switched ring Stark decelerator suitable for slowing both light and heavy polar molecules. Two typical polar molecular species, ND3 and 205TlF, are employed to test the feasibility of our scheme with the help of trajectory calculation. Our proposed scheme is found to share many advantages with the state-of-the-art traveling wave decelerator, yet with relatively simple electronics and flexible operation modes. Sub-millikelvin molecular samples can be conveniently obtained in our decelerator using a combined operation mode. These monochromatic beams are ideal starting points for precise studies of molecular collision, cold chemistry and high-resolution spectroscopy.

  8. Fast optical cooling of a nanomechanical cantilever by a dynamical Stark-shift gate

    PubMed Central

    Yan, Leilei; Zhang, Jian-Qi; Zhang, Shuo; Feng, Mang

    2015-01-01

    The efficient cooling of nanomechanical resonators is essential to exploration of quantum properties of the macroscopic or mesoscopic systems. We propose such a laser-cooling scheme for a nanomechanical cantilever, which works even for the low-frequency mechanical mode and under weak cooling lasers. The cantilever is coupled by a diamond nitrogen-vacancy center under a strong magnetic field gradient and the cooling is assisted by a dynamical Stark-shift gate. Our scheme can effectively enhance the desired cooling efficiency by avoiding the off-resonant and undesired carrier transitions, and thereby cool the cantilever down to the vicinity of the vibrational ground state in a fast fashion. PMID:26455901

  9. Computation of the Stark effect in P impurity states in silicon

    NASA Astrophysics Data System (ADS)

    Debernardi, A.; Baldereschi, A.; Fanciulli, M.

    2006-07-01

    We compute within the effective-mass theory and without adjustable parameters the Stark effect for shallow P donors in Si with anisotropic band structure. Valley-orbit coupling is taken into account in a nonperturbative way and scattering effects of the impurity core are included to properly describe low-lying impurity states. The ground-state energy slightly decreases with increasing electric field up to a critical value Ecr˜25keV/cm , at which the donor can be ionized by tunneling due to a field-induced mixing of the “ 1s -like” singlet ground state with a “ 2p0 -like” excited state in zero field. The resulting ground-state wave function at high field extends significantly outside the potential barrier surrounding the impurity. Calculations of the hyperfine splitting and of the A -shell superhyperfine coupling constants as a function of the electric field complete the work.

  10. Plasma density characterization at SPARC_LAB through Stark broadening of Hydrogen spectral lines

    NASA Astrophysics Data System (ADS)

    Filippi, F.; Anania, M. P.; Bellaveglia, M.; Biagioni, A.; Chiadroni, E.; Cianchi, A.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Mostacci, A.; Palumbo, L.; Pompili, R.; Shpakov, V.; Vaccarezza, C.; Villa, F.; Zigler, A.

    2016-09-01

    Plasma-based acceleration techniques are of great interest for future, compact accelerators due to their high accelerating gradient. Both particle-driven and laser-driven Plasma Wakefield Acceleration experiments are foreseen at the SPARC_LAB Test Facility (INFN National Laboratories of Frascati, Italy), with the aim to accelerate high-brightness electron beams. In order to optimize the efficiency of the acceleration in the plasma and preserve the quality of the accelerated beam, the knowledge of the plasma electron density is mandatory. The Stark broadening of the Hydrogen spectral lines is one of the candidates used to characterize plasma density. The implementation of this diagnostic for plasma-based experiments at SPARC_LAB is presented.

  11. Perturbed wavefunctions of the excited states of hydrogen atom in Stark effect

    SciTech Connect

    Sapra, G.K.; Bhasin, V.S.; Kothari, L.S. . Dept. of Physics Astrophysics)

    1994-03-15

    The authors extend the procedure originally suggested by Dalgarno and Lewis in studying the second-order Stark effect for the ground-state hydrogen atom to the excited states. They solve the perturbation equations for the excited states of hydrogen atom placed in an external electric field to obtain expressions for the perturbed wavefunctions. Here the emphasis is on studying in detail the nature of the perturbed wavefunction rather than energy shifts as investigated in most of the attempts made so far. The effect of the electric field on these wavefunctions is analyzed and the values of the electric polarizability of the hydrogen atom in the excited states obtained in this way are compared with the earlier work.

  12. Tables of stark level transition probabilities and branching ratios in hydrogen-like atoms

    NASA Technical Reports Server (NTRS)

    Omidvar, K.

    1980-01-01

    The transition probabilities which are given in terms of n prime k prime and n k are tabulated. No additional summing or averaging is necessary. The electric quantum number k plays the role of the angular momentum quantum number l in the presence of an electric field. The branching ratios between stark levels are also tabulated. Necessary formulas for the transition probabilities and branching ratios are given. Symmetries are discussed and selection rules are given. Some disagreements for some branching ratios are found between the present calculation and the measurement of Mark and Wierl. The transition probability multiplied by the statistical weight of the initial state is called the static intensity J sub S, while the branching ratios are called the dynamic intensity J sub D.

  13. Motion Simulator

    NASA Technical Reports Server (NTRS)

    1993-01-01

    MOOG, Inc. supplies hydraulic actuators for the Space Shuttle. When MOOG learned NASA was interested in electric actuators for possible future use, the company designed them with assistance from Marshall Space Flight Center. They also decided to pursue the system's commercial potential. This led to partnership with InterActive Simulation, Inc. for production of cabin flight simulators for museums, expositions, etc. The resulting products, the Magic Motion Simulator 30 Series, are the first electric powered simulators. Movements are computer-guided, including free fall to heighten the sense of moving through space. A projection system provides visual effects, and the 11 speakers of a digital laser based sound system add to the realism. The electric actuators are easier to install, have lower operating costs, noise, heat and staff requirements. The U.S. Space & Rocket Center and several other organizations have purchased the simulators.

  14. AC Stark effect in a spin-orbit mixed quantum states in a five-level molecular system coupled by three lasers

    NASA Astrophysics Data System (ADS)

    Qi, Jianbing

    2016-05-01

    The interaction of the spin orbital motion of electrons can mix quantum states with different spin multiplicity. Thus the mixed states can carry both characteristics of the two states depending on the mixing coefficients. The spin-orbit coupled rovibrational levels in diatomic alkali are ubiquitous. These levels are classified as singlet states (if the total spin is zero) and triplet states (if the total spin is one), respectively. A transition from a singlet level can only go to singlet levels and a triplet only to triplet levels. The spin-orbit coupled states can be used as a gateway to access some normally prohibited transitions. By coupling the mixed states to an auxiliary quantum state with lasers, the coupling coefficient of two mixed singlet-triplet molecular states can be modified by ac Stark effect via varying the Rabi frequency of the coupling lasers and the detuning of the laser frequency, 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 enhance the probability of accessing target quantum states.

  15. Quantum mechanical calculation of electric fields and vibrational Stark shifts at active site of human aldose reductase.

    PubMed

    Wang, Xianwei; Zhang, John Z H; He, Xiao

    2015-11-14

    Recent advance in biophysics has made it possible to directly measure site-specific electric field at internal sites of proteins using molecular probes with C = O or C≡N groups in the context of vibrational Stark effect. These measurements directly probe changes of electric field at specific protein sites due to, e.g., mutation and are very useful in protein design. Computational simulation of the Stark effect based on force fields such as AMBER and OPLS, while providing good insight, shows large errors in comparison to experimental measurement due to inherent difficulties associated with point charge based representation of force fields. In this study, quantum mechanical calculation of protein's internal electrostatic properties and vibrational Stark shifts was carried out by using electrostatically embedded generalized molecular fractionation with conjugate caps method. Quantum calculated change of mutation-induced electric field and vibrational Stark shift is reported at the internal probing site of enzyme human aldose reductase. The quantum result is in much better agreement with experimental data than those predicted by force fields, underscoring the deficiency of traditional point charge models describing intra-protein electrostatic properties. PMID:26567650

  16. Quantum mechanical calculation of electric fields and vibrational Stark shifts at active site of human aldose reductase

    NASA Astrophysics Data System (ADS)

    Wang, Xianwei; Zhang, John Z. H.; He, Xiao

    2015-11-01

    Recent advance in biophysics has made it possible to directly measure site-specific electric field at internal sites of proteins using molecular probes with C = O or C≡N groups in the context of vibrational Stark effect. These measurements directly probe changes of electric field at specific protein sites due to, e.g., mutation and are very useful in protein design. Computational simulation of the Stark effect based on force fields such as AMBER and OPLS, while providing good insight, shows large errors in comparison to experimental measurement due to inherent difficulties associated with point charge based representation of force fields. In this study, quantum mechanical calculation of protein's internal electrostatic properties and vibrational Stark shifts was carried out by using electrostatically embedded generalized molecular fractionation with conjugate caps method. Quantum calculated change of mutation-induced electric field and vibrational Stark shift is reported at the internal probing site of enzyme human aldose reductase. The quantum result is in much better agreement with experimental data than those predicted by force fields, underscoring the deficiency of traditional point charge models describing intra-protein electrostatic properties.

  17. Expanding College Opportunity: An Annual Report on Dual Credit and Other Post Secondary Opportunities for Stark County High School Students

    ERIC Educational Resources Information Center

    Rochford, Joseph A.; O'Neill, Adrienne; Gelb, Adele; Ross, Kimberly J.; Ughrin, Tina

    2014-01-01

    This is the eighth annual report by the Stark Education Partnership on dual enrollment and other post secondary opportunities (PSOs) for the county's high school students. In addition to dual enrollment, this report looks at a portfolio of the county's PSOs that includes Canton Early College High School, and the opportunity to bank future college…

  18. Reaching for 80%: How Post Secondary Opportunities in High Schools Are Changing the College Going Culture in Stark County, Ohio

    ERIC Educational Resources Information Center

    Rochford, Joseph A.; O'Neill, Adrienne; Gelb, Adele; Ross, Kimberly J.

    2011-01-01

    In 2002, the Stark County Preschool through College (P-16) Compact set the goal of achieving an 80% college going rate. Such a goal seemed both audacious and daunting for a community where in 2001 only 17.9% of the adults held a Bachelor's Degree, or higher, and where only 49% of all high school graduates went directly to college. Nine years have…

  19. Quantum mechanical calculation of electric fields and vibrational Stark shifts at active site of human aldose reductase

    SciTech Connect

    Wang, Xianwei; Zhang, John Z. H.; He, Xiao

    2015-11-14

    Recent advance in biophysics has made it possible to directly measure site-specific electric field at internal sites of proteins using molecular probes with C = O or C≡N groups in the context of vibrational Stark effect. These measurements directly probe changes of electric field at specific protein sites due to, e.g., mutation and are very useful in protein design. Computational simulation of the Stark effect based on force fields such as AMBER and OPLS, while providing good insight, shows large errors in comparison to experimental measurement due to inherent difficulties associated with point charge based representation of force fields. In this study, quantum mechanical calculation of protein’s internal electrostatic properties and vibrational Stark shifts was carried out by using electrostatically embedded generalized molecular fractionation with conjugate caps method. Quantum calculated change of mutation-induced electric field and vibrational Stark shift is reported at the internal probing site of enzyme human aldose reductase. The quantum result is in much better agreement with experimental data than those predicted by force fields, underscoring the deficiency of traditional point charge models describing intra-protein electrostatic properties.

  20. Collective motion

    NASA Astrophysics Data System (ADS)

    Vicsek, Tamás; Zafeiris, Anna

    2012-08-01

    We review the observations and the basic laws describing the essential aspects of collective motion - being one of the most common and spectacular manifestation of coordinated behavior. Our aim is to provide a balanced discussion of the various facets of this highly multidisciplinary field, including experiments, mathematical methods and models for simulations, so that readers with a variety of background could get both the basics and a broader, more detailed picture of the field. The observations we report on include systems consisting of units ranging from macromolecules through metallic rods and robots to groups of animals and people. Some emphasis is put on models that are simple and realistic enough to reproduce the numerous related observations and are useful for developing concepts for a better understanding of the complexity of systems consisting of many simultaneously moving entities. As such, these models allow the establishing of a few fundamental principles of flocking. In particular, it is demonstrated, that in spite of considerable differences, a number of deep analogies exist between equilibrium statistical physics systems and those made of self-propelled (in most cases living) units. In both cases only a few well defined macroscopic/collective states occur and the transitions between these states follow a similar scenario, involving discontinuity and algebraic divergences.

  1. Auditory motion affects visual biological motion processing.

    PubMed

    Brooks, A; van der Zwan, R; Billard, A; Petreska, B; Clarke, S; Blanke, O

    2007-02-01

    The processing of biological motion is a critical, everyday task performed with remarkable efficiency by human sensory systems. Interest in this ability has focused to a large extent on biological motion processing in the visual modality (see, for example, Cutting, J. E., Moore, C., & Morrison, R. (1988). Masking the motions of human gait. Perception and Psychophysics, 44(4), 339-347). In naturalistic settings, however, it is often the case that biological motion is defined by input to more than one sensory modality. For this reason, here in a series of experiments we investigate behavioural correlates of multisensory, in particular audiovisual, integration in the processing of biological motion cues. More specifically, using a new psychophysical paradigm we investigate the effect of suprathreshold auditory motion on perceptions of visually defined biological motion. Unlike data from previous studies investigating audiovisual integration in linear motion processing [Meyer, G. F. & Wuerger, S. M. (2001). Cross-modal integration of auditory and visual motion signals. Neuroreport, 12(11), 2557-2560; Wuerger, S. M., Hofbauer, M., & Meyer, G. F. (2003). The integration of auditory and motion signals at threshold. Perception and Psychophysics, 65(8), 1188-1196; Alais, D. & Burr, D. (2004). No direction-specific bimodal facilitation for audiovisual motion detection. Cognitive Brain Research, 19, 185-194], we report the existence of direction-selective effects: relative to control (stationary) auditory conditions, auditory motion in the same direction as the visually defined biological motion target increased its detectability, whereas auditory motion in the opposite direction had the inverse effect. Our data suggest these effects do not arise through general shifts in visuo-spatial attention, but instead are a consequence of motion-sensitive, direction-tuned integration mechanisms that are, if not unique to biological visual motion, at least not common to all types of

  2. Limited range of motion

    MedlinePlus

    Limited range of motion is a term meaning that a joint or body part cannot move through its normal range of motion. ... Motion may be limited because of a problem within the joint, swelling of tissue around the joint, ...

  3. Self Motion Perception and Motion Sickness

    NASA Technical Reports Server (NTRS)

    Fox, Robert A. (Principal Investigator)

    1991-01-01

    The studies conducted in this research project examined several aspects of motion sickness in animal models. A principle objective of these studies was to investigate the neuroanatomy that is important in motion sickness with the objectives of examining both the utility of putative models and defining neural mechanisms that are important in motion sickness.

  4. Asymmetry of Drosophila ON and OFF motion detectors enhances real-world velocity estimation.

    PubMed

    Leonhardt, Aljoscha; Ammer, Georg; Meier, Matthias; Serbe, Etienne; Bahl, Armin; Borst, Alexander

    2016-05-01

    The reliable estimation of motion across varied surroundings represents a survival-critical task for sighted animals. How neural circuits have adapted to the particular demands of natural environments, however, is not well understood. We explored this question in the visual system of Drosophila melanogaster. Here, as in many mammalian retinas, motion is computed in parallel streams for brightness increments (ON) and decrements (OFF). When genetically isolated, ON and OFF pathways proved equally capable of accurately matching walking responses to realistic motion. To our surprise, detailed characterization of their functional tuning properties through in vivo calcium imaging and electrophysiology revealed stark differences in temporal tuning between ON and OFF channels. We trained an in silico motion estimation model on natural scenes and discovered that our optimized detector exhibited differences similar to those of the biological system. Thus, functional ON-OFF asymmetries in fly visual circuitry may reflect ON-OFF asymmetries in natural environments. PMID:26928063

  5. Comment on "Test of the Stark-effect theory using photoionization microscopy"

    NASA Astrophysics Data System (ADS)

    Giannakeas, P.; Robicheaux, F.; Greene, Chris H.

    2015-06-01

    An article by Zhao et al. [Phys. Rev. A 86, 053413 (2012), 10.1103/PhysRevA.86.053413] tests the local frame transformation (LFT) theory by comparing it with benchmark coupled-channel calculations. The system under consideration is an alkali-metal atom that is two-photon ionized in the presence of a static external electric field. Zhao et al. state that the differential cross sections computed in the LFT theory disagree with their supposedly more accurate coupled-channel calculations. They went on to diagnose the discrepancy and claimed that it originates in an inaccurate correspondence between the irregular functions in spherical and parabolic-cylindrical coordinates, a correspondence that lies at the heart of LFT theory. We have repeated the same tests and find that our calculations rule out the discrepancies that were claimed in Zhao et al. [Phys. Rev. A 86, 053413 (2012), 10.1103/PhysRevA.86.053413] to exist between the LFT approximation and the exact calculations. This Comment thus helps to clarify the accuracy of the Harmin-Fano theory and demonstrates that it is in fact remarkably accurate not only for the total photoionization cross section in the Stark effect, but also for the differential cross section in photoionization microscopy.

  6. Beyond Zeeman spectroscopy: Magnetic-field diagnostics with Stark-dominated line shapes

    SciTech Connect

    Tessarin, S.; Mikitchuk, D.; Doron, R.; Stambulchik, E.; Kroupp, E.; Maron, Y.; Hammer, D. A.; Jacobs, V. L.; Seely, J. F.; Oliver, B. V.; Fisher, A.

    2011-09-15

    A recently suggested spectroscopic approach for magnetic-field determination in plasma is employed to measure magnetic fields in an expanding laser-produced plasma plume in an externally applied magnetic field. The approach enables the field determination in a diagnostically difficult regime for which the Zeeman-split patterns are not resolvable, as is often encountered under the conditions characteristic of high-energy-density plasmas. Here, such conditions occur in the high-density plasma near the laser target, due to the dominance of Stark broadening. A pulsed-power system is used to generate magnetic fields with a peak magnitude of 25 T at the inner-electrode surface in a coaxial configuration. An aluminum target attached to the inner electrode surface is then irradiated by a laser beam to produce the expanding plasma that interacts with the applied azimuthal magnetic field. A line-shape analysis of the Al III 4s-4p doublet (5696 and 5722 A) enables the simultaneous determination of the magnetic field and the electron density. The measured magnetic fields are generally found to agree with those expected in a vacuum based on the pulsed-power system current. Examples of other transitions that can be used to diagnose a wide range of plasma and magnetic field parameters are presented.

  7. State-to-state inelastic scattering of Stark-decelerated OH radicals with Ar atoms.

    PubMed

    Scharfenberg, Ludwig; Kłos, Jacek; Dagdigian, Paul J; Alexander, Millard H; Meijer, Gerard; van de Meerakker, Sebastiaan Y T

    2010-09-28

    The Stark deceleration method exploits the concepts of charged particle accelerator physics to produce molecular beams with a tunable velocity. These tamed molecular beams offer interesting perspectives for precise crossed beam scattering studies as a function of the collision energy. The method has advanced sufficiently to compete with state-of-the-art beam methods that are used for scattering studies throughout. This is demonstrated here for the scattering of OH radicals (X(2)Pi(3/2), J = 3/2, f) with Ar atoms, a benchmark system for the scattering of open-shell molecules with atoms. Parity-resolved integral state-to-state inelastic scattering cross sections are measured at collision energies between 80 and 800 cm(-1). The threshold behavior and collision energy dependence of 13 inelastic scattering channels is accurately determined. Excellent agreement is obtained with the cross sections predicted by close-coupling scattering calculations based on the most accurate ab initio OH + Ar potential energy surfaces to date. PMID:20657906

  8. Stark Broadening of High-order Radio Recombination Lines toward the Orion Nebula

    NASA Astrophysics Data System (ADS)

    Alexander, J.; Gulyaev, S.

    2016-09-01

    We report the results of observations and analyses of 41 {{Δ }}n=1,\\ldots ,5 hydrogen radio recombination lines from the Orion nebula (M42) at 5.5 to 6.5 GHz, with a spectral sensitivity (channel-to-channel standard deviation) of ≈ 2 {mJy}. Observations were conducted at the Australia Telescope Compact Array. A 1 GHz bandwidth allowed simultaneous detection of up to 11 spectral lines of equal {{Δ }}n that were stacked to enable accurate measurement of line widths. Collisional widths in the range of principal quantum numbers n from 100 to 179 are found to be consistent with predictions of electron impact Stark broadening theory. An Orion nebula model with density inhomogeneities (clumps) and gradients of temperature and density is consistent with our data. We reanalyze the data of Smirnov et al. and Bell et al. and find excellent agreement between all statistically significant measurements and theory. Our findings confirm the absence of line narrowing for n = 100...179.

  9. Stark effect and dipole moments of the ammonia dimer in different vibration-rotation-tunneling states

    NASA Astrophysics Data System (ADS)

    Cotti, Gina; Linnartz, Harold; Meerts, W. Leo; van der Avoird, Ad; Olthof, Edgar H. T.

    1996-03-01

    In this paper we present Stark measurements on the G:K=-1 vibration-rotation-tunneling (VRT) transition, band origin 747.2 GHz, of the ammonia dimer. The observed splitting pattern and selection rules can be explained by considering the G36 and G144 symmetries of the inversion states involved, and almost complete mixing of these states by the applied electric field. The absolute values of the electric dipole moments of the ground and excited state are determined to be 0.763(15) and 0.365(10) D, respectively. From the theoretical analysis and the observed selection rules it is possible to establish that the dipole moments of the two interchange states must have opposite sign. The theoretical calculations are in good agreement with the experimental results: The calculated dipole moments are -0.74 D for the lower and +0.35 D for the higher state. Our results, in combination with the earlier dipole measurements on the G:K=0 ground state and the G:K=1 transition with band origin 486.8 GHz, confirm that the ammonia dimer is highly nonrigid. Its relatively small and strongly K-dependent dipole moment, which changes sign upon far-infrared excitation, originates from the difference in dynamical behavior of ortho and para NH3.

  10. Quantum confined stark effect in wide parabolic quantum wells: real density matrix approach

    NASA Astrophysics Data System (ADS)

    Zielińska-Raczyńska, Sylwia; Czajkowski, Gerard; Ziemkiewicz, David

    2015-12-01

    We show how to compute the optical functions of wide parabolic quantum wells (WPQWs) exposed to uniform electric F applied in the growth direction, in the excitonic energy region. The effect of the coherence between the electron-hole pair and the electromagnetic field of the propagating wave including the electron-hole screened Coulomb potential is adopted, and the valence band structure is taken into account in the cylindrical approximation. The role of the interaction potential and of the applied electric field, which mix the energy states according to different quantum numbers and create symmetry forbidden transitions, is stressed. We use the real density matrix approach (RDMA) and an effective e-h potential, which enable to derive analytical expressions for the WPQWs electrooptical functions. Choosing the susceptibility, we performed numerical calculations appropriate to a GaAs/GaAlAs WPQWs. We have obtained a red shift of the absorption maxima (quantum confined Stark effect), asymmetric upon the change of the direction of the applied field ( F → - F), parabolic for the ground state and strongly dependent on the confinement parameters (the QWs sizes), changes in the oscillator strengths, and new peaks related to the states with different parity for electron and hole.

  11. Dipole moment of methanol by microwave stark spectroscopy IV: 13CD316OH species

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Indra; Sastry, K. V. L. N.

    2015-10-01

    In this work, Stark effect measurements have been carried out on several transitions C-13 substituted species of triply-deuterated (D3) methanol. The analysis of the data allowed the determination of the dipole moment components in the first two torsional states of the ground vibrational state of this species. The extrapolated zero field frequencies of the transitions studied have been determined and found to be in excellent agreement with known values. For the torsional ground state the values {in Debye (D)} of μa = 0.9080(9) and μb = 1.4378(10) have been obtained for this species. These values increase for the first excited state as was observed for other species. The dipole moment values are considerably higher than the non-deuterated species. To our knowledge the present study represents the measurement of the most accurate dipole moment values of 13CD3OH for the first time. The results obtained will prove useful for radio astronomy and in understanding of large amplitude internal energy pathways in polyatomic molecules.

  12. Supersymmetry identifies molecular Stark states whose eigenproperties can be obtained analytically

    NASA Astrophysics Data System (ADS)

    Lemeshko, Mikhail; Mustafa, Mustafa; Kais, Sabre; Friedrich, Bretislav

    2011-06-01

    We made use of supersymmetric (SUSY) quantum mechanics to find the condition under which the Stark effect problem for a polar and polarizable closed-shell diatomic molecule subjected to collinear electrostatic and nonresonant radiative fields becomes exactly solvable. The condition \\Delta \\omega = \\frac{\\omega^2}{4 (m+1)^2 } connects values of the dimensionless parameters ω and Δω that characterize the strengths of the permanent and induced dipole interactions of the molecule with the respective fields. The exact solutions are obtained for the \\vert \\skew5\\tilde{J}=m,m;\\omega,\\Delta \\omega\\rangle family of 'stretched' states. The field-free and strong-field limits of the combined-fields problem were found to exhibit supersymmetry and shape invariance, which is indeed the reason why they are analytically solvable. By making use of the analytic form of the \\vert \\skew5\\tilde{J}=m,m;\\omega,\\Delta \\omega\\rangle wavefunctions, we obtained simple formulae for the expectation values of the space-fixed electric dipole moment, the alignment cosine and the angular momentum squared, and derived a 'sum rule' that combines the above expectation values into a formula for the eigenenergy. The analytic expressions for the characteristics of the strongly oriented and aligned states provide direct access to the values of the interaction parameters required for creating such states in the laboratory.

  13. Stark Broadening Analysis Using Optical Spectroscopy of the Dense Plasma Focus

    NASA Astrophysics Data System (ADS)

    Ross, Patrick; Bennett, Nikki; Dutra, Eric; Hagen, E. Chris; Hsu, Scott; Hunt, Gene; Koch, Jeff; Waltman, Tom; NSTec DPF Team

    2015-11-01

    To aid in validating numerical modeling of MA-class dense plasma focus (DPF) devices, spectroscopic measurements of the Gemini Dense Plasma Focus (DPF) were performed using deuterium and deuterium/dopant (argon/krypton) gas. The spectroscopic measurements were made using a fiber-coupled spectrometer and streak camera. Stark line-broadening analysis was applied to the deuterium beta emission (486 nm) in the region near the breakdown of the plasma and during the run-down and run-in phases of the plasma evolution. Densities in the range of 1e17 to low 1e18 cm-3 were obtained. These values are in agreement with models of the DPF performed using the LSP code. The spectra also show a rise and fall with time, indicative of the plasma sheath passing by the view port. Impurity features were also identified in the spectra which grew in intensity as the gas inside the DPF was discharged repeatedly without cycling. Implications of this impurity increase for D-T discharges (without fresh gas fills between every discharge) will be discussed. This work was done by National Security Technologies, LLC, under Contract No. DE-AC52-06NA25946, and by Los Alamos National Laboratory, under Contract no. DE-AC52-06NA25396 with the U.S. Department of Energy. DOE/NV/25946-2515.

  14. Valley-selective optical Stark effect in monolayer WS2.

    PubMed

    Sie, Edbert J; McIver, James W; Lee, Yi-Hsien; Fu, Liang; Kong, Jing; Gedik, Nuh

    2015-03-01

    Breaking space-time symmetries in two-dimensional crystals can markedly influence their macroscopic electronic properties. Monolayer transition metal dichalcogenides (TMDs) are prime examples where the intrinsically broken crystal inversion symmetry permits the generation of valley-selective electron populations, even though the two valleys are energetically degenerate, locked by time-reversal symmetry. Lifting the valley degeneracy in these materials is of great interest because it would allow for valley-specific band engineering and offer additional control in valleytronic applications. Although applying a magnetic field should, in principle, accomplish this task, experiments so far have not shown valley-selective energy level shifts in fields accessible in the laboratory. Here, we show the first direct evidence of lifted valley degeneracy in the monolayer TMD WS2. By applying intense circularly polarized light, which breaks time-reversal symmetry, we demonstrate that the exciton level in each valley can be selectively tuned by as much as 18 meV through the optical Stark effect. These results offer a new way to control the valley degree of freedom, and may provide a means to realize new Floquet topological phases in two-dimensional TMDs. PMID:25502098

  15. Ultrafast laser produced zinc plasma: Stark broadening of emission lines in nitrogen ambient

    NASA Astrophysics Data System (ADS)

    Rao, Kavya H.; Smijesh, N.; Nivas, Jijil JJ; Philip, Reji

    2016-04-01

    The effect of ambient pressure on Stark broadening of emission lines from neutrals and ions in an ultrafast laser (100 fs, 800 nm) produced zinc plasma is investigated. Measured spectra reveal that the full width at half maximum (δλ) of neutral lines remains unchanged in the pressure range of 10-6 to 10-1 Torr, shows an even fluctuation in the pressure range of 0.1 to 100 Torr, and then increases with pressure. On the other hand, δλ of ion lines is nearly a constant from 10-6 to 10-3 Torr, and then increases consistently with ambient pressure. A line narrowing of neutral emissions observed in the region of 1 to 100 Torr can be attributed to larger plasma temperatures, whereas the consistent increase in δλ with pressure seen for ion emission results from the prevalence of additional broadening mechanisms related to Coulomb interactions, ion-ion interaction, and Debye shielding. An accurate knowledge of emission line width is crucial for unambiguously calculating number density values for any given ambient pressure. Moreover, it can be relevant for the design of narrow line width, bright plasma sources for various applications.

  16. Self-Motion Perception and Motion Sickness

    NASA Technical Reports Server (NTRS)

    Fox, Robert A.

    1991-01-01

    Motion sickness typically is considered a bothersome artifact of exposure to passive motion in vehicles of conveyance. This condition seldom has significant impact on the health of individuals because it is of brief duration, it usually can be prevented by simply avoiding the eliciting condition and, when the conditions that produce it are unavoidable, sickness dissipates with continued exposure. The studies conducted examined several aspects of motion sickness in animal models. A principle objective of these studies was to investigate the neuroanatomy that is important in motion sickness with the objectives of examining both the utility of putative models and defining neural mechanisms that are important in motion sickness.

  17. The AC-Stark Effect in Nitric Oxide Induced by Rapidly Swept Continuous Wave Quantum Cascade Lasers

    SciTech Connect

    Duxbury, Geoffrey; Kelly, James F.; Blake, Thomas A.; Langford, Nigel

    2012-05-07

    A large AC Stark effect has been observed when nitric oxide, at low pressure in a long optical path (100 m) Herriot cell, is subjected to infrared radiation from a rapidly swept, continuous wave infrared quantum cascade laser. As the frequency sweep rate of the laser is increased, an emission signal induced by rapid passage, occurs after the laser frequency has passed through the resonance of a molecular absorption line. At very high sweep rates a laser field-induced splitting of the absorptive part of the signal is observed, due to the AC Stark effect. This splitting is related to the Autler-Townes mixing of the hyperfine transitions, which lie within the lambda doublet components of the transition, under the Doppler broadened envelope.

  18. Shift measurements of the stark-broadened ionized helium lines at 1640 and 1215 angstrom. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Vanzandt, J. R.

    1976-01-01

    Time-resolved measurements were made of the shifts of the ionized helium lines at 1,640 A (n = 3 approaches 2) and 1,215 A (n = 4 approaches 2), and of the Stark profile of the 1,215 A wavelength line. An electromagnetic shock tube was used as a light source. The plasma conditions corresponded to electron temperatures of approximately 3.5 eV and electron densities of 0.8 to 1.8 x 10 to the 17th power/cubic cm. The measured shifts fell between two previous estimates of plasma polarization shifts. The measured Stark width of the 1,215 A wavelength line was up to 30% greater than the theoretical width.

  19. Nanocathodoluminescence Reveals Mitigation of the Stark Shift in InGaN Quantum Wells by Si Doping

    PubMed Central

    2015-01-01

    Nanocathodoluminescence reveals the spectral properties of individual InGaN quantum wells in high efficiency light emitting diodes. We observe a variation in the emission wavelength of each quantum well, in correlation with the Si dopant concentration in the quantum barriers. This is reproduced by band profile simulations, which reveal the reduction of the Stark shift in the quantum wells by Si doping. We demonstrate nanocathodoluminescence is a powerful technique to optimize doping in optoelectronic devices. PMID:26488912

  20. Nanocathodoluminescence Reveals Mitigation of the Stark Shift in InGaN Quantum Wells by Si Doping.

    PubMed

    Griffiths, James T; Zhang, Siyuan; Rouet-Leduc, Bertrand; Fu, Wai Yuen; Bao, An; Zhu, Dandan; Wallis, David J; Howkins, Ashley; Boyd, Ian; Stowe, David; Kappers, Menno J; Humphreys, Colin J; Oliver, Rachel A

    2015-11-11

    Nanocathodoluminescence reveals the spectral properties of individual InGaN quantum wells in high efficiency light emitting diodes. We observe a variation in the emission wavelength of each quantum well, in correlation with the Si dopant concentration in the quantum barriers. This is reproduced by band profile simulations, which reveal the reduction of the Stark shift in the quantum wells by Si doping. We demonstrate nanocathodoluminescence is a powerful technique to optimize doping in optoelectronic devices. PMID:26488912

  1. Determination of Stark parameters by cross-calibration in a multi-element laser-induced plasma

    PubMed Central

    Liu, Hao; Truscott, Benjamin S.; Ashfold, Michael N. R.

    2016-01-01

    We illustrate a Stark broadening analysis of the electron density Ne and temperature Te in a laser-induced plasma (LIP), using a model free of assumptions regarding local thermodynamic equilibrium (LTE). The method relies on Stark parameters determined also without assuming LTE, which are often unknown and unavailable in the literature. Here, we demonstrate that the necessary values can be obtained in situ by cross-calibration between the spectral lines of different charge states, and even different elements, given determinations of Ne and Te based on appropriate parameters for at least one observed transition. This approach enables essentially free choice between species on which to base the analysis, extending the range over which these properties can be measured and giving improved access to low-density plasmas out of LTE. Because of the availability of suitable tabulated values for several charge states of both Si and C, the example of a SiC LIP is taken to illustrate the consistency and accuracy of the procedure. The cross-calibrated Stark parameters are at least as reliable as values obtained by other means, offering a straightforward route to extending the literature in this area. PMID:27170026

  2. Determination of Stark parameters by cross-calibration in a multi-element laser-induced plasma

    NASA Astrophysics Data System (ADS)

    Liu, Hao; Truscott, Benjamin S.; Ashfold, Michael N. R.

    2016-05-01

    We illustrate a Stark broadening analysis of the electron density Ne and temperature Te in a laser-induced plasma (LIP), using a model free of assumptions regarding local thermodynamic equilibrium (LTE). The method relies on Stark parameters determined also without assuming LTE, which are often unknown and unavailable in the literature. Here, we demonstrate that the necessary values can be obtained in situ by cross-calibration between the spectral lines of different charge states, and even different elements, given determinations of Ne and Te based on appropriate parameters for at least one observed transition. This approach enables essentially free choice between species on which to base the analysis, extending the range over which these properties can be measured and giving improved access to low-density plasmas out of LTE. Because of the availability of suitable tabulated values for several charge states of both Si and C, the example of a SiC LIP is taken to illustrate the consistency and accuracy of the procedure. The cross-calibrated Stark parameters are at least as reliable as values obtained by other means, offering a straightforward route to extending the literature in this area.

  3. Stark shift and field ionization of arsenic donors in {sup 28}Si-silicon-on-insulator structures

    SciTech Connect

    Lo, C. C. Morton, J. J. L.; Simmons, S.; Lo Nardo, R.; Weis, C. D.; Schenkel, T.; Tyryshkin, A. M.; Lyon, S. A.; Meijer, J.; Rogalla, D.; Bokor, J.

    2014-05-12

    We develop an efficient back gate for silicon-on-insulator (SOI) devices operating at cryogenic temperatures and measure the quadratic hyperfine Stark shift parameter of arsenic donors in isotopically purified {sup 28}Si-SOI layers using such structures. The back gate is implemented using MeV ion implantation through the SOI layer forming a metallic electrode in the handle wafer, enabling large and uniform electric fields up to 2 V/μm to be applied across the SOI layer. Utilizing this structure, we measure the Stark shift parameters of arsenic donors embedded in the {sup 28}Si-SOI layer and find a contact hyperfine Stark parameter of η{sub a} = −1.9 ± 0.7 × 10{sup −3} μm{sup 2}/V{sup 2}. We also demonstrate electric-field driven dopant ionization in the SOI device layer, measured by electron spin resonance.

  4. Determination of Stark parameters by cross-calibration in a multi-element laser-induced plasma.

    PubMed

    Liu, Hao; Truscott, Benjamin S; Ashfold, Michael N R

    2016-01-01

    We illustrate a Stark broadening analysis of the electron density Ne and temperature Te in a laser-induced plasma (LIP), using a model free of assumptions regarding local thermodynamic equilibrium (LTE). The method relies on Stark parameters determined also without assuming LTE, which are often unknown and unavailable in the literature. Here, we demonstrate that the necessary values can be obtained in situ by cross-calibration between the spectral lines of different charge states, and even different elements, given determinations of Ne and Te based on appropriate parameters for at least one observed transition. This approach enables essentially free choice between species on which to base the analysis, extending the range over which these properties can be measured and giving improved access to low-density plasmas out of LTE. Because of the availability of suitable tabulated values for several charge states of both Si and C, the example of a SiC LIP is taken to illustrate the consistency and accuracy of the procedure. The cross-calibrated Stark parameters are at least as reliable as values obtained by other means, offering a straightforward route to extending the literature in this area. PMID:27170026

  5. Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch

    SciTech Connect

    Vogman, G. V.; Shumlak, U.

    2011-10-13

    Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian function associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. As a result, these measurements are used to gain a better understanding of Z-pinch equilibria.

  6. Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch

    DOE PAGESBeta

    Vogman, G. V.; Shumlak, U.

    2011-10-13

    Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian functionmore » associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. As a result, these measurements are used to gain a better understanding of Z-pinch equilibria.« less

  7. Measuring electric fields and noncovalent interactions using the vibrational stark effect.

    PubMed

    Fried, Stephen D; Boxer, Steven G

    2015-04-21

    Over the past decade, we have developed a spectroscopic approach to measure electric fields inside matter with high spatial (<1 Å) and field (<1 MV/cm) resolution. The approach hinges on exploiting a physical phenomenon known as the vibrational Stark effect (VSE), which ultimately provides a direct mapping between observed vibrational frequencies and electric fields. Therefore, the frequency of a vibrational probe encodes information about the local electric field in the vicinity around the probe. The VSE method has enabled us to understand in great detail the underlying physical nature of several important biomolecular phenomena, such as drug-receptor selectivity in tyrosine kinases, catalysis by the enzyme ketosteroid isomerase, and unidirectional electron transfer in the photosynthetic reaction center. Beyond these specific examples, the VSE has provided a conceptual foundation for how to model intermolecular (noncovalent) interactions in a quantitative, consistent, and general manner. The starting point for research in this area is to choose (or design) a vibrational probe to interrogate the particular system of interest. Vibrational probes are sometimes intrinsic to the system in question, but we have also devised ways to build them into the system (extrinsic probes), often with minimal perturbation. With modern instruments, vibrational frequencies can increasingly be recorded with very high spatial, temporal, and frequency resolution, affording electric field maps correspondingly resolved in space, time, and field magnitude. In this Account, we set out to explain the VSE in broad strokes to make its relevance accessible to chemists of all specialties. Our intention is not to provide an encyclopedic review of published work but rather to motivate the underlying framework of the methodology and to describe how we make and interpret the measurements. Using certain vibrational probes, benchmarked against computer models, it is possible to use the VSE to measure

  8. Identification of Ion-Pair Structures in Solution by Vibrational Stark Effects.

    PubMed

    Hack, John; Grills, David C; Miller, John R; Mani, Tomoyasu

    2016-02-18

    Ion pairing is a fundamental consideration in many areas of chemistry and has implications in a wide range of sciences and technologies that include batteries and organic photovoltaics. Ions in solution are known to inhabit multiple possible states, including free ions (FI), contact ion pairs (CIP), and solvent-separated ion pairs (SSIP). However, in solutions of organic radicals and nonmetal electrolytes, it is often difficult to distinguish between these states. In the first part of this work, we report evidence for the formation of SSIPs in low-polarity solvents and distinct measurements of CIP, SSIP, and FI, by using the ν(C≡N) infrared (IR) band of a nitrile-substituted fluorene radical anion. Use of time-resolved IR detection following pulse radiolysis allowed us to unambiguously assign the peak of the FI. In the presence of nonmetal electrolytes, two distinct red-shifted peaks were observed and assigned to the CIP and SSIP. The assignments are interpreted in the framework of the vibrational Stark effect (VSE) and are supported by (1) the solvent dependence of ion-pair populations, (2) the observation of a cryptand-separated sodium ion pair that mimics the formation of SSIPs, and (3) electronic structure calculations. In the second part of this work, we show that a blue-shift of the ν(C≡N) IR band due to the VSE can be induced in a nitrile-substituted fluorene radical anion by covalently tethering it to a metal-chelating ligand that forms an intramolecular ion pair upon reduction and complexation with sodium ion. This adds support to the conclusion that the shift in IR absorptions by ion pairing originates from the VSE. These results combined show that we can identify ion-pair structures by using the VSE, including the existence of SSIPs in a low-polarity solvent. PMID:26807492

  9. Effect of higher-order multipole moments on the Stark line shape

    NASA Astrophysics Data System (ADS)

    Gomez, T. A.; Nagayama, T.; Kilcrease, D. P.; Montgomery, M. H.; Winget, D. E.

    2016-08-01

    Spectral line shapes are sensitive to plasma conditions and are often used to diagnose electron density of laboratory plasmas as well as astrophysical plasmas. Stark line-shape models take into account the perturbation of the radiator's energy structure due to the Coulomb interaction with the surrounding charged particles. Solving this Coulomb interaction is challenging and is commonly approximated via a multipole expansion. However, most models include only up to the second term of the expansion (the dipole term). While there have been studies on the higher-order terms due to one of the species (i.e., either ions or electrons), there is no model that includes the terms beyond dipole from both species. Here, we investigate the importance of the higher-order multipole terms from both species on the Hβ line shape. First, we find that it is important to include higher-order terms consistently from both ions and electrons to reproduce measured line-shape asymmetry. Next, we find that the line shape calculated with the dipole-only approximation becomes inaccurate as density increases. It is necessary to include up to the third (quadrupole) term to compute the line shape accurately within 2%. Since most existing models include only up to the dipole terms, the densities inferred with such models are in question. We find that the model without the quadrupole term slightly underestimates the density, and the discrepancy becomes as large as 12% at high densities. While the case of study is limited to Hβ, we expect similar impact on other lines.

  10. Identification of ion-pair structures in solution by vibrational stark effects

    DOE PAGESBeta

    Hack, John; Mani, Tomoyasu; Grills, David C.; Miller, John R.

    2016-01-25

    Here, ion pairing is a fundamental consideration in many areas of chemistry and has implications in a wide range of sciences and technologies that include batteries and organic photovoltaics. Ions in solution are known to inhabit multiple possible states, including free ions (FI), contact ion pairs (CIP), and solvent-separated ion pairs (SSIP). However, in solutions of organic radicals and nonmetal electrolytes, it is often difficult to distinguish between these states. In the first part of this work, we report evidence for the formation of SSIPs in low-polarity solvents and distinct measurements of CIP, SSIP, and FI, by using the ν(C≡N)more » infrared (IR) band of a nitrile-substituted fluorene radical anion. Use of time-resolved IR detection following pulse radiolysis allowed us to unambiguously assign the peak of the FI. In the presence of nonmetal electrolytes, two distinct red-shifted peaks were observed and assigned to the CIP and SSIP. The assignments are interpreted in the framework of the vibrational Stark effect (VSE) and are supported by (1) the solvent dependence of ion-pair populations, (2) the observation of a cryptand-separated sodium ion pair that mimics the formation of SSIPs, and (3) electronic structure calculations. In the second part of this work, we show that a blue-shift of the ν(C≡N) IR band due to the VSE can be induced in a nitrile-substituted fluorene radical anion by covalently tethering it to a metal-chelating ligand that forms an intramolecular ion pair upon reduction and complexation with sodium ion. This adds support to the conclusion that the shift in IR absorptions by ion pairing originates from the VSE. These results combined show that we can identify ion-pair structures by using the VSE, including the existence of SSIPs in a low-polarity solvent.« less

  11. Effect of higher-order multipole moments on the Stark line shape

    NASA Astrophysics Data System (ADS)

    Gomez, T. A.; Nagayama, T.; Kilcrease, D. P.; Montgomery, M. H.; Winget, D. E.

    2016-08-01

    Spectral line shapes are sensitive to plasma conditions and are often used to diagnose electron density of laboratory plasmas as well as astrophysical plasmas. Stark line-shape models take into account the perturbation of the radiator's energy structure due to the Coulomb interaction with the surrounding charged particles. Solving this Coulomb interaction is challenging and is commonly approximated via a multipole expansion. However, most models include only up to the second term of the expansion (the dipole term). While there have been studies on the higher-order terms due to one of the species (i.e., either ions or electrons), there is no model that includes the terms beyond dipole from both species. Here, we investigate the importance of the higher-order multipole terms from both species on the H β line shape. First, we find that it is important to include higher-order terms consistently from both ions and electrons to reproduce measured line-shape asymmetry. Next, we find that the line shape calculated with the dipole-only approximation becomes inaccurate as density increases. It is necessary to include up to the third (quadrupole) term to compute the line shape accurately within 2%. Since most existing models include only up to the dipole terms, the densities inferred with such models are in question. We find that the model without the quadrupole term slightly underestimates the density, and the discrepancy becomes as large as 12% at high densities. While the case of study is limited to H β , we expect similar impact on other lines.

  12. Collectively Induced Quantum-Confined Stark Effect in Monolayers of Molecules Consisting of Polar Repeating Units

    PubMed Central

    2011-01-01

    The electronic structure of terpyrimidinethiols is investigated by means of density-functional theory calculations for isolated molecules and monolayers. In the transition from molecule to self-assembled monolayer (SAM), we observe that the band gap is substantially reduced, frontier states increasingly localize on opposite sides of the SAM, and this polarization in several instances is in the direction opposite to the polarization of the overall charge density. This behavior can be analyzed by analogy to inorganic semiconductor quantum-wells, which, as the SAMs studied here, can be regarded as semiperiodic systems. There, similar observations are made under the influence of a, typically external, electric field and are known as the quantum-confined Stark effect. Without any external perturbation, in oligopyrimidine SAMs one encounters an energy gradient that is generated by the dipole moments of the pyrimidine repeat units. It is particularly strong, reaching values of about 1.6 eV/nm, which corresponds to a substantial electric field of 1.6 × 107 V/cm. Close-lying σ- and π-states turn out to be a particular complication for a reliable description of the present systems, as their order is influenced not only by the docking groups and bonding to the metal, but also by the chosen computational approach. In the latter context we demonstrate that deliberately picking a hybrid functional allows avoiding pitfalls due to the infamous self-interaction error. Our results show that when aiming to build a monolayer with a specific electronic structure one can not only resort to the traditional technique of modifying the molecular structure of the constituents, but also try to exploit collective electronic effects. PMID:21955058

  13. Refinement of the semiclassical theory of the Stark broadening of hydrogen spectral lines in plasmas

    NASA Astrophysics Data System (ADS)

    Oks, Eugene

    2015-02-01

    Stark broadening (SB) of hydrogen, deuterium, and tritium lines (H-lines) is an important diagnostic tool for many applications. The most "user-friendly" are semiclassical theories of the SB of H-lines: their results can be expressed analytically in a relatively simple form for any H-line. The simplest semiclassical theory is the so-called Conventional Theory (CT), which is frequently referred to as Griem's theory. While by now there are several significantly more advanced semiclassical "non-CT" theories of the SB, Griem's CT is still used by a number of groups performing laboratory experiments or astrophysical observations for the comparison with their experimental or observational results. In the present study we engage unexplored capabilities of the CT for creating analytically a more accurate CT. First, we take into account that the perturbing electrons actually do not move as free particles: rather they move in a dipole potential V=·r/r3, where r is the radius-vector of the perturbing electrons and is the mean value of the radius vector of the atomic electron. Second, Griem's definition of the so-called Weisskopf radius was not quite accurate. Third, in his book of year 1974, Griem suggested changing so-called strong collision constant without changing the Weisskopf radius, while in reality the choices of the Weisskopf radius and of the strong collision constant are interrelated. We show that the above refinements of the CT increase the electron broadening - especially for warm dense plasmas emitting H-lines. By comparison with benchmark experiments concerning the Hα line we demonstrate that the effect of the ion dynamics (neglected in any CT) might be slightly smaller than previously thought, while the effect of the acceleration of perturbing electrons by the ion field in the vicinity of the radiating atom (neglected in any CT) might be greater than previously thought.

  14. Laser-induced fluorescence and Optical/Stark spectroscopy of PtC

    SciTech Connect

    Beaton, S. A.; Steimle, T. C.

    1999-12-22

    Optical/Stark measurements have been performed on the (0,0) bands of both the A{sup ''} {sup 1}{sigma}{sup +}-X {sup 1}{sigma}{sup +} system ({nu}{sub 0}{approx_equal}12 643 cm{sup -1}) and the A{sup '} {sup 1}{pi}-X {sigma}{sup +} system ({nu}{sub 0}{approx_equal}13 196 cm{sup -1}) of platinum monocarbide. The PtC molecules were produced in a pulsed supersonic molecular beam source following the reaction of laser ablated platinum vapor with a mixture of a few percent of methane in argon. The newly determined permanent electric dipole moments obtained are 1.94(2)D (A{sup ''} {sup 1}{sigma}{sup +}) and 1.919(9)D (A{sup '} {sup 1}{pi}). These results are discussed in terms of a proposed molecular orbital correlation diagram for platinum containing diatomics. The laser-induced fluorescence spectrum of the (0,0)A{sup ''} {sup 1}{sigma}{sup +}-X {sup 1}{sigma}{sup +} transition of PtC has been re-recorded at high resolution (full width of half-maximum {approx}40 MHz) and analyzed to yield rotational constants for the four most abundant isotopomers of PtC, extending the previous analysis [Appelblad, Nilsson, and Scullman, Phys. Scr. 7, 65 (1973)]. The anomalously large value ({approx}15 MHz) for the newly derived nuclear-spin rotation parameter, C{sub I}({sup 195}Pt), for the A{sup ''} {sup 1}{sigma}{sup +} state is discussed. (c) 1999 American Institute of Physics.

  15. Mixed Exciton–Charge-Transfer States in Photosystem II: Stark Spectroscopy on Site-Directed Mutants

    PubMed Central

    Romero, Elisabet; Diner, Bruce A.; Nixon, Peter J.; Coleman, Wiliam J.; Dekker, Jan P.; van Grondelle, Rienk

    2012-01-01

    We investigated the electronic structure of the photosystem II reaction center (PSII RC) in relation to the light-induced charge separation process using Stark spectroscopy on a series of site-directed PSII RC mutants from the cyanobacterium Synechocystis sp. PCC 6803. The site-directed mutations modify the protein environment of the cofactors involved in charge separation (PD1, PD2, ChlD1, and PheD1). The results demonstrate that at least two different exciton states are mixed with charge-transfer (CT) states, yielding exciton states with CT character: (PD2δ+PD1δ−ChlD1)∗673nm and (ChlD1δ+PheD1δ−)∗681nm (where the subscript indicates the wavelength of the electronic transition). Moreover, the CT state PD2+PD1− acquires excited-state character due to its mixing with an exciton state, producing (PD2+PD1−)δ∗684nm. We conclude that the states that initiate charge separation are mixed exciton-CT states, and that the degree of mixing between exciton and CT states determines the efficiency of charge separation. In addition, the results reveal that the pigment-protein interactions fine-tune the energy of the exciton and CT states, and hence the mixing between these states. This mixing ultimately controls the selection and efficiency of a specific charge separation pathway, and highlights the capacity of the protein environment to control the functionality of the PSII RC complex. PMID:22853895

  16. Static imaging of motion: motion texture

    NASA Astrophysics Data System (ADS)

    Arimura, Koichi

    1992-05-01

    This paper describes how motion segmentation can be achieved by analyzing of a single static image that is created from a series of picture frames. The key idea is motion imaging; in other words, motion is expressed in static images by integrating, frame after frame, the spatiotemporal fluctuations of the gradient gray level at each local area. This tends to create blurred or attached line images (images with lines that show the path of movement of an object through space) on moving objects. We call this 'motion texture'. We computed motion texture images based on the animation of a natural scene and on a number of computer synthesized animations containing groups of moving objects (random dots). Moreover, we applied two different texture analyses to the motion textured images for segmentation: a texture analysis based on the local homogeneity of gray level gradation in similarly textured regions and another based on the structural feature of gray level gradation in motion texture. Experiments showed that subjective visual impressions of segmentation were quite different for these animations. The texture segmentation described here successfully grouped moving objects coincident to subjective impressions. In our random dot animations, the density of the basic motion vectors extracted from each pair of successive frames was set at a constant to compensate for the dot grouping effect based on the vector density. The dot appearance period (lifetime) is varied across the animations. In a long lifetime random dot animation, region boundaries can be more clearly perceived than in a short one. The different impressions may be explained by analyzing the motion texture elements, but can not always be represented successfully using the motion vectors between two successive frames whose density is set at a constant between the animations with the different lifetime.

  17. Electron Transport Dominated Regimes in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Porkolab, M.; Dorris, J.; Bonoli, P. T.; Ennever, P.; Fiore, C.; Greenwald, M.; Hubbard, A.; Ma, Y.; Reinke, M. L.; Rice, J.; Rost, J.; Tsujii, N.; Lin, L.; Candy, J.; Waltz, R.; Diamond, P.; Lee, C. J.

    2010-11-01

    In ohmically heated low density plasmas where τE ne, the so-called neo-Alcator regime, TRANSP results indicate that χi<< χe, while nonlinear gyrokinetic analysis for the measured profiles predicts the opposite inequality [1]. This regime is of great interest for transport studies since Ti < Te, and the electron and ion transport channels can be separated and studied separately. At the same time, measurements of turbulent fluctuations with Phase Contrast Imaging diagnostic (PCI) indicated reasonable agreement with GYRO predictions at frequencies 80-250 kHz, corresponding to core ITG turbulence. The turbulent spectrum at lower frequencies could not be identified since the PCI technique does not allow separation of the core plasma fluctuations from those at the edge. Here we present measurements and analysis from a more extensive set of plasma regimes than previously. Of particular current interest is the role of electron drift wave turbulence driven by ohmic electron drift, U [2], since in these low density regimes U/Cs <= 6, and experimentally we find that the global confinement τE Cs/U where Cs = (Te/mi)^1/2. [1] L. Lin, Invited talk, APS-DPP, 11, 2009, Atlanta, GA. [2] C.J. Lee, P. Diamond, M. Porkolab, presented at TTF workshop, 2010.

  18. Stark broadening for diagnostics of the electron density in non-equilibrium plasma utilizing isotope hydrogen alpha lines

    SciTech Connect

    Yang, Lin; Tan, Xiaohua; Wan, Xiang; Chen, Lei; Jin, Dazhi; Qian, Muyang; Li, Gongping

    2014-04-28

    Two Stark broadening parameters including FWHM (full width at half maximum) and FWHA (full width at half area) of isotope hydrogen alpha lines are simultaneously introduced to determine the electron density of a pulsed vacuum arc jet. To estimate the gas temperature, the rotational temperature of the C{sub 2} Swan system is fit to 2500 ± 100 K. A modified Boltzmann-plot method with b{sub i}-factor is introduced to determine the modified electron temperature. The comparison between results of atomic and ionic lines indicates the jet is in partial local thermodynamic equilibrium and the electron temperature is close to 13 000 ± 400 K. Based on the computational results of Gig-Card calculation, a simple and precise interpolation algorithm for the discrete-points tables can be constructed to obtain the traditional n{sub e}-T{sub e} diagnostic maps of two Stark broadening parameters. The results from FWHA formula by the direct use of FWHM = FWHA and these from the diagnostic map are different. It can be attributed to the imprecise FWHA formula form and the deviation between FWHM and FWHA. The variation of the reduced mass pair due to the non-equilibrium effect contributes to the difference of the results derived from two hydrogen isotope alpha lines. Based on the Stark broadening analysis in this work, a corrected method is set up to determine n{sub e} of (1.10 ± 0.08) × 10{sup 21} m{sup −3}, the reference reduced mass μ{sub 0} pair of (3.30 ± 0.82 and 1.65 ± 0.41), and the ion kinetic temperature of 7900 ± 1800 K.

  19. Essay on Gyroscopic Motions.

    ERIC Educational Resources Information Center

    Tea, Peter L., Jr.

    1988-01-01

    Explains gyroscopic motions to college freshman or high school seniors who have learned about centripetal acceleration and the transformations of a couple. Contains several figures showing the direction of forces and motion. (YP)

  20. A simplified method for calculating the ac Stark shift of hyperfine levels of alkali-metal atoms

    NASA Astrophysics Data System (ADS)

    Xu, Xia; Qing, Bo; Chen, Xuzong; Zhou, Xiaoji

    2015-07-01

    The ac Stark shift of hyperfine levels of neutral atoms can be calculated using the third order perturbation theory (TOPT), where the third order corrections are quadratic in the atom-photon interaction and linear in the hyperfine interaction. In this paper, we use Green's function to derive the E [ 2 + ɛ ] method which can give close values to those of TOPT for the differential light shift between two hyperfine levels. It comes with a simple form and easy incorporation of theoretical and experimental atomic structure data. Furthermore, we analyze the order of approximation and give the condition under which E [ 2 + ɛ ] method is valid.