Embedded calibration system for the DIII-D Langmuir probe analog fiber optic links

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watkins, J. G.; Rajpal, R.; Mandaliya, H.

2012-10-15

This paper describes a generally applicable technique for simultaneously measuring offset and gain of 64 analog fiber optic data links used for the DIII-D fixed Langmuir probes by embedding a reference voltage waveform in the optical transmitted signal before every tokamak shot. The calibrated data channels allow calibration of the power supply control fiber optic links as well. The array of fiber optic links and the embedded calibration system described here makes possible the use of superior modern data acquisition electronics in the control room.

A time-resolved Langmuir double-probe method for the investigation of pulsed magnetron discharges

NASA Astrophysics Data System (ADS)

Welzel, Th.; Dunger, Th.; Kupfer, H.; Richter, F.

2004-12-01

Langmuir probes are important means for the characterization of plasma discharges. For measurements in plasmas used for the deposition of thin films, the Langmuir double probe is especially suited. With the increasing popularity of pulsed deposition discharges, there is also an increasing need for time-resolved characterization methods. For Langmuir probes, several single-probe approaches to time-resolved measurements are reported but very few for the double probe. We present a time-resolved Langmuir double-probe technique, which is applied to a pulsed magnetron discharge at several 100 kHz used for MgO deposition. The investigations show that a proper treatment of the current measurement is necessary to obtain reliable results. In doing so, a characteristic time dependence of the charge-carrier density during the "pulse on" time containing maximum values of almost 2•1011cm-3 was found. This characteristic time dependence varies with the pulse frequency and the duty cycle. A similar time dependence of the electron temperature is only observed when the probe is placed near the magnesium target.

Operation of a swept Langmuir probe on a sounding rocket

NASA Astrophysics Data System (ADS)

Robertson, S. H.; Dickson, S.; Friedrich, M.; Sternovsky, Z.

2012-12-01

A swept cylindrical Langmuir probe was operated on two sounding rockets from ~ 60-120 km for the purpose of determining both the ambient electron density and the payload potential relative to the ambient plasma. The rockets were part of the CHAMPS (CHarge And mass of Meteoritic smoke ParticleS) rocket campaign and carried mass analyzers and various plasma probes to study charged meteoritic dust in the mesopause region. The payload potential is an important parameter for data interpretation. The rockets were launched in October of 2011 from Andøya Rocket Range, Norway. The launches were a few days apart with one taking place during the day and the other at night. The swept Langmuir probe data provided a current-voltage characteristic that had a distinct "knee" indicating the onset of electron collection; the probe voltage at this "knee" corresponds to the ambient plasma potential. The data indicate a payload potential of about -2 V to -1 V for both launches. The payload potential becomes less negative for altitudes above 80 km on the day launch due to photoemission. The probe current-voltage data are also compared with ion and electron density measurements from ion probes and Faraday rotation antennas, respectively. The data from the various instruments are in general agreement. Further consideration of the Langmuir probe performance shows that if the probe had been operated with feedback control to continuously collect electrons with a current of order 1 microamp, the probe potential would be an accurate, continuous indicator of the payload potential without the need for sweeping which could periodically alter the payload potential.

Magnetic and Langmuir Probe Measurements on the Plasmoid Thruster Experiment (PTX)

NASA Technical Reports Server (NTRS)

Koelfgen, Syri J.; Eskridge, Richard; Lee, Michael H.; Martin, Adam; Hawk, Clark W.; Fimognan, Peter

2004-01-01

The Plasmoid Thruster Experiment (PTX) operates by inductively producing plasmoids in a conical theta-pinch coil and ejecting them at high velocity. A plasmoid is a plasma with an imbedded closed magnetic field structure. The shape and magnetic field structure of the translating plasmoids have been measured with of an array of magnetic field probes. Six sets of two B-dot probes were constructed for measuring B(sub z) and B(sub theta), the axial and azimuthal components of the magnetic field. The probes are wound on a square G10 form, and have an average (calibrated) NA of 9.37 x l0(exp -5) square meters, where N is the number of turns and A is the cross-sectional area. The probes were calibrated with a Helmholtz coil, driven by a high-voltage pulser to measure NA, and by a signal generator to determine the probe's frequency response. The plasmoid electron number density n(sub e) electron temperature T(sub e), and velocity ratio v/c(sub m), (where v is the bulk plasma flow velocity and c(sub m), is the ion thermal speed) have also been measured with a quadruple Langmuir probe. The Langmuir probe tips are 10 mm long, 20-mil diameter stainless steel wire, housed in a 6-inch long 4-bore aluminum rod. Measurements on PTX with argon and hydrogen from the magnetic field probes and quadruple Langmuir probe will be presented in this paper.

Investigation of Coatings for Langmuir Probes in an Oxygen-Rich Space Environment

NASA Astrophysics Data System (ADS)

Samaniego, J. I.; Wang, X.; Andersson, L.; Malaspina, D.; Ergun, R.; Horanyi, M.

2017-12-01

The surface properties of the Langmuir probes, such as the one on the MAVEN mission, will change after exposure to upper planetary atmospheres where high concentrations of atomic oxygen and other oxidizing compounds are present. TiN (Titanium Nitride) or DAG (a resin based graphite dispersion) are the most common coatings for current Langmuir probes, yet both of these coatings pose issues when exposed to oxygen-rich space environment. TiN showed reduced surface conductivity while the DAG layers erode with exposure to oxygen. It is known that Iridium (Ir) and Rhenium (Rh) are difficult to oxidize and maintain high conductivity even in their oxidized forms, suggesting them to be good candidates for probe coatings. Oxidation of most metals creates a resistive layer on the surface of the probe that will affect the amount of current being collected at a given voltage during the probe sweep and therefore affect the accuracy of plasma parameters determined by the Langmuir probe (e.g. density, temperature). We present the results of the oxidation effect on the current-voltage curves (I-V curves) and therefore the resulting measured plasma parameters of Ir and Rh wire probes compared with other control metals and coatings (Cu, Ni, TiN) in controlled plasma environments. The oxidation process is performed in an oxygen plasma chamber in which both O+ and O2+ are created and accelerated toward the probes with energies < 10 eV. An argon plasma chamber is used to compare the probe's I-V curves before and after the oxidation process. Our preliminary results indicate that iridium shows the least effect of oxidation on the probe measurements. The second objective of this study is to identify methods that can be used in orbit to clean the surface of Langmuir probes to minimize the effect of exposure to oxidizing compounds.

Langmuir Probe Measurements in an Inductively Coupled GEC Reference Cell Plasma

NASA Technical Reports Server (NTRS)

Ji, J. S.; Kim, J. S.; Cappelli, M. A.; Sharma, S. P.; Arnold, J. O. (Technical Monitor)

1998-01-01

Measurements of electron number density, electron temperature, and electron energy distribution function (EEDF) using a compensated Langmuir probe have been performed on an inductively (transformer ) coupled Gaseous Electronics Conference (GEC) reference cell plasma. The plasma source is operated with CH4, CF4, or their mixtures with argon. The effect of independently driving the electrode supporting the wafer on the probe data is studied. In particular, we find that the plasma structure depends on the phase in addition to the magnitude of the power coupled to the electrode relative to that of the transformer coil. The Langmuir probe is translated in a plane parallel to the electrode to investigate the spatial structure of the plasma. The probe data is also compared with fluid model predictions.

HIT-SI Injector Voltage Measurements Using Injector Langmuir Probes

NASA Astrophysics Data System (ADS)

Aboul Hosn, Rabih; Smith, Roger; Jarboe, Thomas

2006-10-01

A pair of Langmuir probe arrays have been designed and built to measure floating potentials of the plasma at the injector mouth of the HIT-SI device. The Helicity Injected Torus using Steady Inductive Helicity Injection (HIT-SI) [1,2] is a ``bow tie'' spheromak using an electrodeless formation and sustainment concept. HIT-SI is powered by two inductive helicity injectors operated in quadrature to maintain a constant helicity injection rate. The electric probes consist of an array of four floating potential Langmuir probes measuring the voltage distribution in each injector from the shell to midpoint of the injector mouth. The probe measurements combine to determine the part of the injector loop voltage driving the n = 0 spheromak equilibrium region. Preliminary data suggest the spheromak voltage is the loop voltage minus the nearly constant injector voltage of 150-180 volts. These probe data will be used to calculate the helicity decay time of the spheromak. [1] T. R. Jarboe. Steady inductive helicity injection and its application to a high-beta spheromak. Fusion Technology, 36(1):85--91, July 1999. [2] P.E.Sieck et al., ``Demonstration of Steady Inductive Helicity Injection'', Nuc. Fusion, in press (2006).

Behavior of Triple Langmuir Probes in Non-Equilibrium Plasmas

NASA Technical Reports Server (NTRS)

Polzin, Kurt A.; Ratcliffe, Alicia C.

2018-01-01

The triple Langmuir probe is an electrostatic probe in which three probe tips collect current when inserted into a plasma. The triple probe differs from a simple single Langmuir probe in the nature of the voltage applied to the probe tips. In the single probe, a swept voltage is applied to the probe tip to acquire a waveform showing the collected current as a function of applied voltage (I-V curve). In a triple probe three probe tips are electrically coupled to each other with constant voltages applied between each of the tips. The voltages are selected such that they would represent three points on the single Langmuir probe I-V curve. Elimination of the voltage sweep makes it possible to measure time-varying plasma properties in transient plasmas. Under the assumption of a Maxwellian plasma, one can determine the time-varying plasma temperature T(sub e)(t) and number density n(sub e)(t) from the applied voltage levels and the time-histories of the collected currents. In the present paper we examine the theory of triple probe operation, specifically focusing on the assumption of a Maxwellian plasma. Triple probe measurements have been widely employed for a number of pulsed and timevarying plasmas, including pulsed plasma thrusters (PPTs), dense plasma focus devices, plasma flows, and fusion experiments. While the equilibrium assumption may be justified for some applications, it is unlikely that it is fully justifiable for all pulsed and time-varying plasmas or for all times during the pulse of a plasma device. To examine a simple non-equilibrium plasma case, we return to basic governing equations of probe current collection and compute the current to the probes for a distribution function consisting of two Maxwellian distributions with different temperatures (the two-temperature Maxwellian). A variation of this method is also employed, where one of the Maxwellians is offset from zero (in velocity space) to add a suprathermal beam of electrons to the tail of the

On the interpretation of Langmuir probe data inside a spacecraft sheath

NASA Astrophysics Data System (ADS)

Olson, J.; Brenning, N.; Wahlund, J.-E.; Gunell, H.

2010-10-01

If a Langmuir probe is located inside the sheath of a negatively charged spacecraft, there is a risk that the probe characteristic is modified compared to that of a free probe in the ambient plasma. We have studied this probe-in-spacecraft-sheath problem in the parameter range of a small Langmuir probe (with radius rLP<<λD) using a modified version of the orbit motion limited (OML) probe theory. We find that the ambient electron contribution Ie(ULP) to the probe characteristic is suitably analyzed in terms of three regions of applied probe potential ULP. In region I, where the probe is negatively charged (i.e., ULPprobe position), the probe characteristic Ie(ULP) is close to that of OML theory for a free probe in the ambient plasma. In the probe potential range ULP>U1, there is first a transition region II in applied potential, U1probe and the ambient plasma. This minimum gives the depth Upl-UM of a potential barrier that prevents the lowest energy ambient electrons from reaching the probe. For a high enough positive probe potential, in region III, the barrier becomes small. Here, Ie(ULP) again approaches OML theory for a free probe. The boundary U2 between regions II and III is somewhat arbitrary; we propose a condition on the barrier, Upl-UM<probe characteristic is likely to depart from usual OML in crucial respects: (1) the ambient plasma potential Upl falls into the transition region, but there is no obvious knee or other feature to identify it, (2) there is in this region no exponential part of Ie(ULP) that can be used to obtain Te, instead, (3) the probe

Langmuir probe surveys of an arcjet exhaust

NASA Technical Reports Server (NTRS)

Zana, Lynnette M.

1987-01-01

Electrostatic (Langmuir) probes of both spherical and cylindrical geometry have been used to obtain electron number density and temperature in the exhaust of a laboratory arcjet. The arcjet thruster operated on nitrogen and hydrogen mixtures to simulate fully decomposed hydrazine in a vacuum environment with background pressures less than 0.05 Pa. The exhaust appears to be only slightly ionized (less than 1 percent) with local plasma potentials near facility ground. The current-voltage characteristics of the probes indicate a Maxwellian temperature distribution. Plume data are presented as a function of arcjet operating conditions and also position in the exhaust.

The Fixed-bias Langmuir Probe on the Communication-navigation Outage Forecast System Satellite: Calibration and Validation

NASA Technical Reports Server (NTRS)

Klenzing, Jeffrey H.; Rowland, Douglas E.

2012-01-01

A fixed-bias spherical Langmuir probe is included as part of the Vector Electric Field Instrument (VEFI) suite on the Communication Navigation Outage Forecast System (CNOFS) satellite.CNOFS gathers data in the equatorial ionosphere between 400 and 860 km, where the primary constituent ions are H+ and O+. The ion current collected by the probe surface per unit plasmadensity is found to be a strong function of ion composition. The calibration of the collected current to an absolute density is discussed, and the performance of the spherical probe is compared to other in situ instruments on board the CNOFS satellite. The application of the calibration is discussed with respect to future xed-bias probes; in particular, it is demonstrated that some density fluctuations will be suppressed in the collected current if the plasma composition rapidly changes along with density. This is illustrated in the observation of plasma density enhancements on CNOFS.

High-spatial-resolution electron density measurement by Langmuir probe for multi-point observations using tiny spacecraft

NASA Astrophysics Data System (ADS)

Hoang, H.; Røed, K.; Bekkeng, T. A.; Trondsen, E.; Clausen, L. B. N.; Miloch, W. J.; Moen, J. I.

2017-11-01

A method for evaluating electron density using a single fixed-bias Langmuir probe is presented. The technique allows for high-spatio-temporal resolution electron density measurements, which can be effectively carried out by tiny spacecraft for multi-point observations in the ionosphere. The results are compared with the multi-needle Langmuir probe system, which is a scientific instrument developed at the University of Oslo comprising four fixed-bias cylindrical probes that allow small-scale plasma density structures to be characterized in the ionosphere. The technique proposed in this paper can comply with the requirements of future small-sized spacecraft, where the cost-effectiveness, limited space available on the craft, low power consumption and capacity for data-links need to be addressed. The first experimental results in both the plasma laboratory and space confirm the efficiency of the new approach. Moreover, detailed analyses on two challenging issues when deploying the DC Langmuir probe on a tiny spacecraft, which are the limited conductive area of the spacecraft and probe surface contamination, are presented in the paper. It is demonstrated that the limited conductive area, depending on applications, can either be of no concern for the experiment or can be resolved by mitigation methods. Surface contamination has a small impact on the performance of the developed probe.

The Fixed-Bias Langmuir Probe on the Communication-Navigation Outage Forecast System Satellite: Calibration and Validation

NASA Technical Reports Server (NTRS)

Klenzing, J.; Rowland, D.

2012-01-01

A fixed-bias spherical Langmuir probe is included as part of the Vector Electric Field Instrument (VEFI) suite on the Communication Navigation Outage Forecast System (CNOFS) satellite.CNOFS gathers data in the equatorial ionosphere between 400 and 860 km, where the primary constituent ions are H+ and O+. The ion current collected by the probe surface per unit plasma density is found to be a strong function of ion composition. The calibration of the collected current to an absolute density is discussed, and the performance of the spherical probe is compared to other in situ instruments on board the CNOFS satellite. The application of the calibration is discussed with respect to future fixed-bias probes; in particular, it is demonstrated that some density fluctuations will be suppressed in the collected current if the plasma composition rapidly changes along with density. This is illustrated in the observation of plasma density enhancements on CNOFS.

Mirror Langmuir probe: a technique for real-time measurement of magnetized plasma conditions using a single Langmuir electrode.

PubMed

LaBombard, B; Lyons, L

2007-07-01

A new method for the real-time evaluation of the conditions in a magnetized plasma is described. The technique employs an electronic "mirror Langmuir probe" (MLP), constructed from bipolar rf transistors and associated high-bandwidth electronics. Utilizing a three-state bias wave form and active feedback control, the mirror probe's I-V characteristic is continuously adjusted to be a scaled replica of the "actual" Langmuir electrode immersed in a plasma. Real-time high-bandwidth measurements of the plasma's electron temperature, ion saturation current, and floating potential can thereby be obtained using only a single electrode. Initial tests of a prototype MLP system are reported, proving the concept. Fast-switching metal-oxide-semiconductor field-effect transistors produce the required three-state voltage bias wave form, completing a full cycle in under 1 mus. Real-time outputs of electron temperature, ion saturation current, and floating potential are demonstrated, which accurately track an independent computation of these values from digitally stored I-V characteristics. The MLP technique represents a significant improvement over existing real-time methods, eliminating the need for multiple electrodes and sampling all three plasma parameters at a single spatial location.

Balloon-borne Langmuir probe measurement of stratospheric ions in low latitudes

NASA Astrophysics Data System (ADS)

Banerjee, A.; Somayajulu, Y. V.; Subrahmanyam, P.

1984-12-01

A balloon carrying a Langmuir probe payload for measuring the positive and negative ion densities in the stratosphere was flown around midnight IST on Mar. 23, 1982 from the National Balloon Facility at Hyderabad, a low latitude station. The Langmuir probe with a guard ring arrangement is given a symmetrical probe voltage of triangular waveform with amplitude + or - 4.2 V and with a repetition frequency of 0.28 Hz. The balloon reached a ceiling altitude of 33 km and data were taken from 15 km up to the ceiling altitude. The altitude profiles of the ion density show a peak around 18 km with densities decreasing with altitude. The results are discussed in terms of cosmic ray production and ion chemistry. The structures in the positive ion density profile are interpreted in terms of the presence of aerosol layers.

Behavior of a Single Langmuir Probe in a Magnetic Field.

ERIC Educational Resources Information Center

Pytlinski, J. T.; And Others

1978-01-01

Describes an experiment to demonstrate the influence of a magnetic field on the behavior of a single Langmuir probe. The experiment introduces the student to magnetically supported plasma and particle behavior in a magnetic field. (GA)

Electronegative plasma diagnostic by laser photo-detachment combined with negatively biased Langmuir probe

NASA Astrophysics Data System (ADS)

Oudini, N.; Sirse, N.; Taccogna, F.; Ellingboe, A. R.; Bendib, A.

2018-05-01

We propose a new technique for diagnosing negative ion properties using Langmuir probe assisted pulsed laser photo-detachment. While the classical technique uses a laser pulse to convert negative ions into electron-atom pairs and a positively biased Langmuir probe tracking the change of electron saturation current, the proposed method uses a negatively biased Langmuir probe to track the temporal evolution of positive ion current. The negative bias aims to avoid the parasitic electron current inherent to probe tip surface ablation. In this work, we show through analytical and numerical approaches that, by knowing electron temperature and performing photo-detachment at two different laser wavelengths, it is possible to deduce plasma electronegativity (ratio of negative ion to electron densities) α, and anisothermicity (ratio of electron to negative ion temperatures) γ-. We present an analytical model that links the change in the collected positive ion current to plasma electronegativity and anisothermicity. Particle-In-Cell simulation is used as a numerical experiment covering a wide range of α and γ- to test the new analysis technique. The new technique is sensitive to α in the range 0.5 < α < 10 and yields γ- for large α, where negative ion flux affects the probe sheath behavior, typically α > 1.

The Multi-Needle Langmuir Probe System on Board NorSat-1

NASA Astrophysics Data System (ADS)

Hoang, H.; Clausen, L. B. N.; Røed, K.; Bekkeng, T. A.; Trondsen, E.; Lybekk, B.; Strøm, H.; Bang-Hauge, D. M.; Pedersen, A.; Spicher, A.; Moen, J. I.

2018-06-01

On July 14th, 2017, the first Norwegian scientific satellite NorSat-1 was launched into a high-inclination (98∘), low-Earth orbit (600 km altitude) from Baikonur, Kazakhstan. As part of the payload package, NorSat-1 carries the multi-needle Langmuir probe (m-NLP) instrument which is capable of sampling the electron density at a rate up to 1 kHz, thus offering an unprecedented opportunity to continuously resolve ionospheric plasma density structures down to a few meters. Over the coming years, NorSat-1 will cross the equatorial and polar regions twice every 90 minutes, providing a wealth of data that will help to better understand the mechanisms that dissipate energy input from larger spatial scales by creating small-scale plasma density structures within the ionosphere. In this paper we describe the m-NLP system on board NorSat-1 and present some first results from the instrument commissioning phase. We show that the m-NLP instrument performs as expected and highlight its unique capabilities at resolving small-scale ionospheric plasma density structures.

Langmuir probe diagnostic suite in the C-2 field-reversed configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roche, T., E-mail: troche@trialphaenergy.com; Armstrong, S.; Knapp, K.

2014-11-15

Several in situ probes have been designed and implemented into the diagnostic array of the C-2 field-reversed configuration (FRC) at Tri Alpha Energy [M. Tuszewski et al. (the TAE Team), Phys. Rev. Lett. 108, 255008 (2012)]. The probes are all variations on the traditional Langmuir probe. They include linear arrays of triple probes, linear arrays of single-tipped swept probes, a multi-faced Gundestrup probe, and an ion-sensitive probe. The probes vary from 5 to 7 mm diameter in size to minimize plasma perturbations. They also have boron nitride outer casings that prevent unwanted electrical breakdown and reduce the introduction of impurities.more » The probes are mounted on motorized linear-actuators allowing for programmatic scans of the various plasma parameters over the course of several shots. Each probe has a custom set of electronics that allows for measurement of the desired signals. High frequency ( > 5MHz) analog optical-isolators ensure that plasma parameters can be measured at sub-microsecond time scales while providing electrical isolation between machine and data acquisition systems. With these probes time-resolved plasma parameters (temperature, density, spatial potential, flow, and electric field) can be directly/locally measured in the FRC jet and edge/scrape-off layer.« less

Plasma potential and electron temperature evaluated by ball-pen and Langmuir probes in the COMPASS tokamak

NASA Astrophysics Data System (ADS)

Dimitrova, M.; Popov, Tsv K.; Adamek, J.; Kovačič, J.; Ivanova, P.; Hasan, E.; López-Bruna, D.; Seidl, J.; Vondráček, P.; Dejarnac, R.; Stöckel, J.; Imríšek, M.; Panek, R.; the COMPASS Team

2017-12-01

The radial distributions of the main plasma parameters in the scrape-off-layer of the COMPASS tokamak are measured during L-mode and H-mode regimes by using both Langmuir and ball-pen probes mounted on a horizontal reciprocating manipulator. The radial profile of the plasma potential derived previously from Langmuir probes data by using the first derivative probe technique is compared with data derived using ball-pen probes. A good agreement can be seen between the data acquired by the two techniques during the L-mode discharge and during the H-mode regime within the inter-ELM periods. In contrast with the first derivative probe technique, the ball-pen probe technique does not require a swept voltage and, therefore, the temporal resolution is only limited by the data acquisition system. In the electron temperature evaluation, in the far scrape-off layer and in the limiter shadow, where the electron energy distribution is Maxwellian, the results from both techniques match well. In the vicinity of the last closed flux surface, where the electron energy distribution function is bi-Maxwellian, the ball-pen probe technique results are in agreement with the high-temperature components of the electron distribution only. We also discuss the application of relatively large Langmuir probes placed in parallel and perpendicularly to the magnetic field lines to studying the main plasma parameters. The results obtained by the two types of the large probes agree well. They are compared with Thomson scattering data for electron temperatures and densities. The results for the electron densities are compared also with the results from ASTRA code calculation of the electron source due to the ionization of the neutrals by fast electrons and the origin of the bi-Maxwellian electron energy distribution function is briefly discussed.

Payload charging events in the mesosphere and their impact on Langmuir type electric probes

NASA Astrophysics Data System (ADS)

Bekkeng, T. A.; Barjatya, A.; Hoppe, U.-P.; Pedersen, A.; Moen, J. I.; Friedrich, M.; Rapp, M.

2013-02-01

Three sounding rockets were launched from Andøya Rocket Range in the ECOMA campaign in December 2010. The aim was to study the evolution of meteoric smoke particles during a major meteor shower. Of the various instruments onboard the rocket payload, this paper presents the data from a multi-Needle Langmuir Probe (m-NLP) and a charged dust detector. The payload floating potential, as observed using the m-NLP instrument, shows charging events on two of the three flights. These charging events cannot be explained using a simple charging model, and have implications towards the use of fixed bias Langmuir probes on sounding rockets investigating mesospheric altitudes. We show that for a reliable use of a single fixed bias Langmuir probe as a high spatial resolution relative density measurement, each payload should also carry an additional instrument to measure payload floating potential, and an instrument that is immune to spacecraft charging and measures absolute plasma density.

A study of data analysis techniques for the multi-needle Langmuir probe

NASA Astrophysics Data System (ADS)

Hoang, H.; Røed, K.; Bekkeng, T. A.; Moen, J. I.; Spicher, A.; Clausen, L. B. N.; Miloch, W. J.; Trondsen, E.; Pedersen, A.

2018-06-01

In this paper we evaluate two data analysis techniques for the multi-needle Langmuir probe (m-NLP). The instrument uses several cylindrical Langmuir probes, which are positively biased with respect to the plasma potential in order to operate in the electron saturation region. Since the currents collected by these probes can be sampled at kilohertz rates, the instrument is capable of resolving the ionospheric plasma structure down to the meter scale. The two data analysis techniques, a linear fit and a non-linear least squares fit, are discussed in detail using data from the Investigation of Cusp Irregularities 2 sounding rocket. It is shown that each technique has pros and cons with respect to the m-NLP implementation. Even though the linear fitting technique seems to be better than measurements from incoherent scatter radar and in situ instruments, m-NLPs can be longer and can be cleaned during operation to improve instrument performance. The non-linear least squares fitting technique would be more reliable provided that a higher number of probes are deployed.

Langmuir probe measurements of double-layers in a pulsed discharge

NASA Technical Reports Server (NTRS)

Levine, J. S.; Crawford, F. W.

1980-01-01

Langmuir probe measurements were carried out which confirm the occurrence of double-layers in an argon positive column. Pulsing the discharge current permitted probe measurements to be performed in the presence of the double-layer. Supplementary evidence, obtained from DC and pulsed discharges, indicated that the double-layers formed in the two modes of operation were similar. The double-layers observed were weak and stable; their relation to other classes of double-layers are discussed, and directions for future work are suggested.

Hardware and software systems for the determination of charged particle parameters in low pressure plasmas using impedance-tuned Langmuir probes

NASA Astrophysics Data System (ADS)

Ye, Yuancai; Marcus, R. Kenneth

1997-12-01

A computer-controlled, impedance-tuned Langmuir probe data acquisition system and processing software package have been designed for the diagnostic study of low pressure plasmas. The combination of impedance-tuning and a wide range of applied potentials (± 100 V) provides a versatile system, applicable to a variety of analytical plasmas without significant modification. The automated probe system can be used to produce complete and undistorted current-voltage (i-V) curves with extremely low noise over the wide potential range. Based on these hardware and software systems, it is possible to determine all of the important charged particle parameters in a plasma; electron number density ( ne), ion number density ( ni), electron temperature ( Te), electron energy distribution function (EEDF), and average electron energy (<ɛ>). The complete data acquisition system and evaluation software are described in detail. A LabView (National Instruments Corporation, Austin, TX) application program has been developed for the Apple Macintosh line of microcomputers to control all of the operational aspects of the Langmuir probe experiments. The description here is mainly focused on the design aspects of the acquisition system with the targets of extremely low noise and reduction of the influence of measurement noise in the calculation procedures. This is particularly important in the case of electron energy distribution functions where multiple derivatives are calculated from the obtained i-V curves. A separate C-language data processing program has been developed and is included here to allow the reader to evaluate data obtained with the described hardware, or any i-V data imported in tab separated variable format. Both of the software systems are included on a Macintosh formatted disk for their use in other laboratories desiring these capabilities.

Langmuir Probe Spacecraft Potential End Item Specification Document

NASA Technical Reports Server (NTRS)

Gilchrist, Brian; Curtis, Leslie (Technical Monitor)

2001-01-01

This document describes the Langmuir Probe Spacecraft Potential (LPSP) investigation of the plasma environment in the vicinity of the ProSEDS Delta II spacecraft. This investigation will employ a group of three (3) Langmuir Probe Assemblies, LPAs, mounted on the Delta II second stage to measure the electron density and temperature (n(sub e) and T(sub e)), the ion density (n(sub i)), and the spacecraft potential (V(sub s)) relative to the surrounding ionospheric plasma. This document is also intended to define the technical requirements and flight-vehicle installation interfaces for the design, development, assembly, testing, qualification, and operation of the LPSP subsystem for the Propulsive Small Expendable Deployer System (ProSEDS) and its associated Ground Support Equipment (GSE). This document also defines the interfaces between the LPSP instrument and the ProSEDS Delta II spacecraft, as well as the design, fabrication, operation, and other requirements established to meet the mission objectives. The LPSP is the primary measurement instrument designed to characterize the background plasma environment and is a supporting instrument for measuring spacecraft potential of the Delta II vehicle used for the ProSEDS mission. Specifically, the LPSP will use the three LPAs equally spaced around the Delta II body to make measurements of the ambient ionospheric plasma during passive operations to aid in validating existing models of electrodynamic-tether propulsion. These same probes will also be used to measure Delta II spacecraft potential when active operations occur. When the electron emitting plasma contractor is on, dense neutral plasma is emitted. Effective operation of the plasma contactor (PC) will mean a low potential difference between the Delta II second stage and the surrounding plasma and represents one of the voltage parameters needed to fully characterize the electrodynamic-tether closed circuit. Given that the LP already needs to be well away from any

Resolving an anomaly in electron temperature measurement using double and triple Langmuir probes

NASA Astrophysics Data System (ADS)

Ghosh, Soumen; Barada, K. K.; Chattopadhyay, P. K.; Ghosh, J.; Bora, D.

2015-02-01

Langmuir probes with variants such as single, double and triple probes remain the most common method of electron temperature measurement in low-temperature laboratory plasmas. However, proper estimation of electron temperature mainly using triple probe configuration requires the proper choice of compensation factor (W). Determination of the compensating factor is not very straightforward as it depends heavily on plasma floating potential (Vf), electron temperature (Te), the type of gas used for plasma production and the bias voltage applied to probe pins, especially in cases where there are substantial variations in floating potential. In this paper we highlight the anomaly in electron temperature measurement using double and triple Langmuir probe techniques as well as the proper determination of the compensation factor (W) to overcome this anomaly. Experiments are carried out with helicon antenna producing inductive radiofrequency plasmas, where significant variation of floating potential along the axis enables a detailed study of deviations introduced in Te measurements using triple probes compared to double and single probes. It is observed that the bias voltage between the probe pins of the triple probes plays an important role in the accurate determination of the compensating factor (W) and should be in the range (5Vd2 < Vd3 < 10Vd2), where Vd2 and Vd3 are the voltage between floating probe pins 2 and 1 and the bias voltage, respectively.

Comparison of Langmuir probe and multipole resonance probe measurements in argon, hydrogen, nitrogen, and oxygen mixtures in a double ICP discharge

NASA Astrophysics Data System (ADS)

Fiebrandt, Marcel; Oberberg, Moritz; Awakowicz, Peter

2017-07-01

The results of a Multipole Resonance Probe (MRP) are compared to a Langmuir probe in measuring the electron density in Ar, H2, N2, and O2 mixtures. The MRP was designed for measurements in industry processes, i.e., coating or etching. To evaluate a possible influence on the MRP measurement due to molecular gases, different plasmas with increasing molecular gas content in a double inductively coupled plasma at 5 Pa and 10 Pa at 500 W are used. The determined electron densities from the MRP and the Langmuir probe slightly differ in H2 and N2 diluted argon plasmas, but diverge significantly with oxygen. In pure molecular gas plasmas, electron densities measured with the MRP are always higher than those measured with the Langmuir Probe, in particular, in oxygen containing mixtures. The differences can be attributed to etching of the tungsten wire in the Ar:O2 mixtures and rf distortion in the pure molecular discharges. The influence of a non-Maxwellian electron energy distribution function, negative ions or secondary electron emission seems to be of no or only minor importance.

The flush-mounted rail Langmuir probe array designed for the Alcator C-Mod vertical target plate divertor

NASA Astrophysics Data System (ADS)

Kuang, A. Q.; Brunner, D.; LaBombard, B.; Leccacorvi, R.; Vieira, R.

2018-04-01

An array of flush-mounted and toroidally elongated Langmuir probes (henceforth called rail probes) have been specifically designed for the Alcator C-Mod's vertical target plate divertor and operated over multiple campaigns. The "flush" geometry enables the tungsten electrodes to survive high heat flux conditions in which traditional "proud" tungsten electrodes suffer damage from melting. The toroidally elongated rail-like geometry reduces the influence of sheath expansion, which is an important effect to consider in the design and interpretation of flush-mounted Langmuir probes. The new rail probes successfully operated during C-Mod's FY2015 and FY2016 experimental campaigns with no evidence of damage, despite being regularly subjected to heat flux densities parallel to the magnetic field exceeding ˜1 GW m-2 for short periods of time. A comparison between rail and proud probe data indicates that sheath expansion effects were successfully mitigated by the rail design, extending the use of these Langmuir probes to incident magnetic field line angles as low as 0.5°.

Note: Measurement of the cathode layer thickness in glow discharges with a Langmuir probe

NASA Astrophysics Data System (ADS)

Wang, Hao; Hou, Xinyu; Zou, Xiaobing; Luo, Haiyun; Wang, Xinxin

2018-06-01

A method using a Langmuir probe to determine the thickness of the cathode layer for a glow discharge is developed. The method is based on the phenomenon that the curve of the voltage-current characteristics changes in shape as the Langmuir probe moves from the positive column into the cathode layer. The method was used to measure the thicknesses of the cathode layer in the normal glow discharges of argon and air with the cathodes made from stainless steel and aluminum. The results are in good agreement with those given in a book of gas discharge.

Rosetta Langmuir Probe Photoelectron Emission and Solar Ultraviolet Flux at Comet 67P

NASA Astrophysics Data System (ADS)

Johansson, F. L.; Odelstad, E.; Paulsson, J. J.; Harang, S. S.; Eriksson, A. I.; Mannel, T.; Vigren, E.; Edberg, N. J. T.; Miloch, W. J.; Simon Wedlund, C.; Thiemann, E.; Epavier, F.; Andersson, L.

2017-12-01

The Langmuir Probe instrument on Rosetta monitored the photoelectron emission current of the probes during the Rosetta mission at comet 67P/Churyumov-Gerasimenko, in essence acting as a photodiode monitoring the solar ultraviolet radiation at wavelengths below 250 nm. We have used three methods of extracting the photoelectron saturation current from the Langmuir probe measurements. The resulting dataset can be used as an index of the solar far and extreme ultraviolet at the Rosetta spacecraft position, including flares, in wavelengths that are important for photoionisation of the cometary neutral gas. Comparing the photoemission current to data measurements by MAVEN/EUVM and TIMED/SEE, we find good correlation when 67P was at large heliocentric distances early and late in the mission, but up to 50 percent decrease of the expected photoelectron current at perihelion. We discuss possible reasons for the photoemission decrease, including scattering and absorption by nanograins created by disintegration of cometary dust far away from the nucleus.

Accounting for Debye sheath expansion for proud Langmuir probes in magnetic confinement fusion plasmas

NASA Astrophysics Data System (ADS)

Tsui, C. K.; Boedo, J. A.; Stangeby, P. C.; TCV Team

2018-01-01

A Child-Langmuir law-based method for accounting for Debye sheath expansion while fitting the current-voltage I-V characteristic of proud Langmuir probes (electrodes that extend into the volume of the plasma) is described. For Langmuir probes of a typical size used in tokamak plasmas, these new estimates of electron temperature and ion saturation current density values decreased by up to 60% compared to methods that did not account for sheath expansion. Changes to the collection area are modeled using the Child-Langmuir law and effective expansion perimeter lp, and the model is thus referred to as the "perimeter sheath expansion method." lp is determined solely from electrode geometry, so the method may be employed without prior measurement of the magnitude of the sheath expansion effects for a given Langmuir probe and can be used for electrodes of different geometries. This method correctly predicts the non-saturating ΔI/ΔV slope for cold, low-density plasmas where sheath-expansion effects are strong, as well as for hot plasmas where ΔI/ΔV ˜ 0, though it is shown that the sheath can still significantly affect the collection area in these hot conditions. The perimeter sheath expansion method has several advantages compared to methods where the non-saturating current is fitted: (1) It is more resilient to scatter in the I-V characteristics observed in turbulent plasmas. (2) It is able to separate the contributions to the ΔI/ΔV slope from sheath expansion to that of the high energy electron tail in high Te conditions. (3) It calculates the change in the collection area due to the Debye sheath for conditions where ΔI/ΔV ˜ 0 and for V = Vf.

Accounting for Debye sheath expansion for proud Langmuir probes in magnetic confinement fusion plasmas.

PubMed

Tsui, C K; Boedo, J A; Stangeby, P C

2018-01-01

A Child-Langmuir law-based method for accounting for Debye sheath expansion while fitting the current-voltage I-V characteristic of proud Langmuir probes (electrodes that extend into the volume of the plasma) is described. For Langmuir probes of a typical size used in tokamak plasmas, these new estimates of electron temperature and ion saturation current density values decreased by up to 60% compared to methods that did not account for sheath expansion. Changes to the collection area are modeled using the Child-Langmuir law and effective expansion perimeter l p , and the model is thus referred to as the "perimeter sheath expansion method." l p is determined solely from electrode geometry, so the method may be employed without prior measurement of the magnitude of the sheath expansion effects for a given Langmuir probe and can be used for electrodes of different geometries. This method correctly predicts the non-saturating ΔI/ΔV slope for cold, low-density plasmas where sheath-expansion effects are strong, as well as for hot plasmas where ΔI/ΔV ∼ 0, though it is shown that the sheath can still significantly affect the collection area in these hot conditions. The perimeter sheath expansion method has several advantages compared to methods where the non-saturating current is fitted: (1) It is more resilient to scatter in the I-V characteristics observed in turbulent plasmas. (2) It is able to separate the contributions to the ΔI/ΔV slope from sheath expansion to that of the high energy electron tail in high Te conditions. (3) It calculates the change in the collection area due to the Debye sheath for conditions where ΔI/ΔV ∼ 0 and for V = V f .

The Use of Langmuir Probes in Non-Maxwellian Space Plasmas

NASA Technical Reports Server (NTRS)

Hoegy, Walter R.; Brace, Larry H.

1998-01-01

Disturbance of the Maxwellian plasma may occur in the vicinity of a spacecraft due to photoemission, interactions between the spacecraft and thermospheric gases, or electron emissions from other devices on the spacecraft. Significant non-maxwellian plasma distributions may also occur in nature as a mixture of ionospheric and magnetospheric plasmas or secondaries produced by photoionization in the thermosphere or auroral precipitation. The general formulas for current collection (volt-ampere curves) by planar, cylindrical, and spherical Langmuir probes in isotropic and anisotropic non-maxwellian plasmas are examined. Examples are given of how one may identify and remove the non-maxwellian components in the Langmuir probe current to permit the ionospheric parameters to be determined. Theoretical volt-ampere curves presented for typical examples of non-maxwellian distributions include: two-temperature plasmas and a thermal plasma with an energetic electron beam. If the non-ionospheric electrons are Maxwellian at a temperature distinct from that of the ionosphere electrons, the volt-ampere curves can be fitted directly to obtain the temperatures and densities of both electron components without resorting to differenting the current. For an arbitrary isotropic distribution, the current for retarded particles is shown to be identical for the three geometries. For anisotropic distributions, the three probe geometries are not equally suited for measuring the ionospheric electron temperature and density or for determining the distribution function in the presence of non-maxwellian back-round electrons.

Solving the Capacitive Effect in the High-Frequency sweep for Langmuir Probe in SYMPLE

NASA Astrophysics Data System (ADS)

Pramila; Patel, J. J.; Rajpal, R.; Hansalia, C. J.; Anitha, V. P.; Sathyanarayana, K.

2017-04-01

Langmuir Probe based measurements need to be routinely carried out to measure various plasma parameters such as the electron density (ne), the electron temperature (Te), the floating potential (Vf), and the plasma potential (Vp). For this, the diagnostic electronics along with the biasing power supplies is installed in standard industrial racks with a 2KV isolation transformer. The Signal Conditioning Electronics (SCE) system is populated inside the 4U-chassis based system with the front-end electronics, designed using high common mode differential amplifiers which can measure small differential signal in presence of high common mode dc- bias or ac ramp voltage used for biasing the probes. DC-biasing of the probe is most common method for getting its I-V characteristic but method of biasing the probe with a sweep at high frequency encounters the problem of corruption of signal due to capacitive effect specially when the sweep period and the discharge time is very fast and die down in the order of μs or lesser. This paper presents and summarises the method of removing such effects encountered while measuring the probe current.

Study of plasma parameters in a pulsed plasma accelerator using triple Langmuir probe

NASA Astrophysics Data System (ADS)

Borthakur, S.; Talukdar, N.; Neog, N. K.; Borthakur, T. K.

2018-01-01

A Triple Langmuir Probe (TLP) has been used to study plasma parameters of a transient plasma produced in a newly developed Pulsed Plasma Accelerator system. In this experiment, a TLP with a capacitor based current mode biasing circuit was used that instantaneously gives voltage traces in an oscilloscope which are directly proportional to the plasma electron temperature and density. The electron temperature (Te) and plasma density (ne) of the plasma are measured with the help of this probe and found to be 24.13 eV and 3.34 × 1021/m3 at the maximum energy (-15 kV) of the system, respectively. An attempt was also made to analyse the time-dependent fluctuations in plasma parameters detected by the highly sensitive triple probe. In addition to this, the variation of these parameters under different discharge voltages was studied. The information obtained from these parameters is the initial diagnostics of a new device which is to be dedicated to study the impact of high heat flux plasma stream upon material surfaces inside an ITER like tokamak.

Plasma monitoring of the RLVIP-process with a Langmuir probe

NASA Astrophysics Data System (ADS)

Huber, D.; Hallbauer, A.; Pulker, H. K.

2005-09-01

The aim of this investigation was to study the characteristics of a reactive-low-voltage-high-current-ion-plating plasma and to correlate the observed plasma data with the properties of films deposited under such conditions. A Langmuir probe system (Smart Probe - Scientific Systems) was inserted into a Balzers BAP 800 ion plating plant above the e-gun evaporation source close to the insulated substrate holder. In this position during RLVIP deposition, plasma potential, floating potential, self-bias voltage, electron temperature, ion current density, and particle number density were measured and calculated, respectively. All measurements were performed in dependence of arc current (20-80A) and oxygen partial pressure (1 - 36 x 10-4mbar). With rising arc current the number of charged particles, the self-bias voltage between plasma and substrates as well as the energy of the condensing and bombarding species were increased. These data explain the increase of density, refractive index and mechanical stress of RLVIP-metal-oxide-layers, like Ta2O5 and Nb2O5, deposited with higher arc currents. An increase of gas pressure decreased the energy of the particles and therefore reduced slightly film density and refractive index. However, it improved chemistry and eliminated unwanted residual optical absorption and also decreased compressive mechanical film stress.

A hemispherical Langmuir probe array detector for angular resolved measurements on droplet-based laser-produced plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gambino, Nadia, E-mail: gambinon@ethz.ch; Brandstätter, Markus; Rollinger, Bob

2014-09-15

In this work, a new diagnostic tool for laser-produced plasmas (LPPs) is presented. The detector is based on a multiple array of six motorized Langmuir probes. It allows to measure the dynamics of a LPP in terms of charged particles detection with particular attention to droplet-based LPP sources for EUV lithography. The system design permits to temporally resolve the angular and radial plasma charge distribution and to obtain a hemispherical mapping of the ions and electrons around the droplet plasma. The understanding of these dynamics is fundamental to improve the debris mitigation techniques for droplet-based LPP sources. The device hasmore » been developed, built, and employed at the Laboratory for Energy Conversion, ETH Zürich. The experimental results have been obtained on the droplet-based LPP source ALPS II. For the first time, 2D mappings of the ion kinetic energy distribution around the droplet plasma have been obtained with an array of multiple Langmuir probes. These measurements show an anisotropic expansion of the ions in terms of kinetic energy and amount of ion charge around the droplet target. First estimations of the plasma density and electron temperature were also obtained from the analysis of the probe current signals.« less

Analysis of wall-embedded Langmuir probe signals in different conditions on the Tokamak à Configuration Variable

NASA Astrophysics Data System (ADS)

Février, O.; Theiler, C.; De Oliveira, H.; Labit, B.; Fedorczak, N.; Baillod, A.

2018-05-01

This paper presents the current wall-embedded Langmuir probe system installed on the Tokamak à Configuration Variable (TCV), as well as the analysis tool chain used to interpret the current-voltage characteristic obtained when the probes are operated in swept-bias conditions. The analysis is based on a four-parameter fit combined with a minimum temperature approach. In order to reduce the effect of plasma fluctuations and measurement noise, several current-voltage characteristics are usually averaged before proceeding to the fitting. The impact of this procedure on the results is investigated, as well as the possible role of finite resistances in the circuitry, which could lead to an overestimation of the temperature. We study the application of the procedure in a specific regime, the plasma detachment, where results from other diagnostics indicate that the electron temperature derived from the Langmuir probes might be overestimated. To address this issue, we explore other fitting models and, in particular, an extension of the asymmetric double probe fit, which features effects of sheath expansion. We show that these models yield lower temperatures (up to approximately 60%) than the standard analysis in detached conditions, particularly for a temperature peak observed near the plasma strike point, but a discrepancy with other measurements remains. We explore a possible explanation for this observation, the presence of a fast electron population, and assess how robust the different methods are in such conditions.

Error analysis of multi-needle Langmuir probe measurement technique.

PubMed

Barjatya, Aroh; Merritt, William

2018-04-01

Multi-needle Langmuir probe is a fairly new instrument technique that has been flown on several recent sounding rockets and is slated to fly on a subset of QB50 CubeSat constellation. This paper takes a fundamental look into the data analysis procedures used for this instrument to derive absolute electron density. Our calculations suggest that while the technique remains promising, the current data analysis procedures could easily result in errors of 50% or more. We present a simple data analysis adjustment that can reduce errors by at least a factor of five in typical operation.

Error analysis of multi-needle Langmuir probe measurement technique

NASA Astrophysics Data System (ADS)

Barjatya, Aroh; Merritt, William

2018-04-01

Multi-needle Langmuir probe is a fairly new instrument technique that has been flown on several recent sounding rockets and is slated to fly on a subset of QB50 CubeSat constellation. This paper takes a fundamental look into the data analysis procedures used for this instrument to derive absolute electron density. Our calculations suggest that while the technique remains promising, the current data analysis procedures could easily result in errors of 50% or more. We present a simple data analysis adjustment that can reduce errors by at least a factor of five in typical operation.

Flame exposure time on Langmuir probe degradation, ion density, and thermionic emission for flame temperature.

PubMed

Doyle, S J; Salvador, P R; Xu, K G

2017-11-01

The paper examines the effect of exposure time of Langmuir probes in an atmospheric premixed methane-air flame. The effects of probe size and material composition on current measurements were investigated, with molybdenum and tungsten probe tips ranging in diameter from 0.0508 to 0.1651 mm. Repeated prolonged exposures to the flame, with five runs of 60 s, resulted in gradual probe degradations (-6% to -62% area loss) which affected the measurements. Due to long flame exposures, two ion saturation currents were observed, resulting in significantly different ion densities ranging from 1.16 × 10 16 to 2.71 × 10 19 m -3 . The difference between the saturation currents is caused by thermionic emissions from the probe tip. As thermionic emission is temperature dependent, the flame temperature could thus be estimated from the change in current. The flame temperatures calculated from the difference in saturation currents (1734-1887 K) were compared to those from a conventional thermocouple (1580-1908 K). Temperature measurements obtained from tungsten probes placed in rich flames yielded the highest percent error (9.66%-18.70%) due to smaller emission current densities at lower temperatures. The molybdenum probe yielded an accurate temperature value with only 1.29% error. Molybdenum also demonstrated very low probe degradation in comparison to the tungsten probe tips (area reductions of 6% vs. 58%, respectively). The results also show that very little exposure time (<5 s) is needed to obtain a valid ion density measurement and that prolonged flame exposures can yield the flame temperature but also risks damage to the Langmuir probe tip.

Upgrade of Langmuir probe diagnostic in ITER-like tungsten mono-block divertor on experimental advanced superconducting tokamak.

PubMed

Xu, J C; Wang, L; Xu, G S; Luo, G N; Yao, D M; Li, Q; Cao, L; Chen, L; Zhang, W; Liu, S C; Wang, H Q; Jia, M N; Feng, W; Deng, G Z; Hu, L Q; Wan, B N; Li, J; Sun, Y W; Guo, H Y

2016-08-01

In order to withstand rapid increase in particle and power impact onto the divertor and demonstrate the feasibility of the ITER design under long pulse operation, the upper divertor of the EAST tokamak has been upgraded to actively water-cooled, ITER-like tungsten mono-block structure since the 2014 campaign, which is the first attempt for ITER on the tokamak devices. Therefore, a new divertor Langmuir probe diagnostic system (DivLP) was designed and successfully upgraded on the tungsten divertor to obtain the plasma parameters in the divertor region such as electron temperature, electron density, particle and heat fluxes. More specifically, two identical triple probe arrays have been installed at two ports of different toroidal positions (112.5-deg separated toroidally), which can provide fundamental data to study the toroidal asymmetry of divertor power deposition and related 3-dimension (3D) physics, as induced by resonant magnetic perturbations, lower hybrid wave, and so on. The shape of graphite tip and fixed structure of the probe are designed according to the structure of the upper tungsten divertor. The ceramic support, small graphite tip, and proper connector installed make it possible to be successfully installed in the very narrow interval between the cassette body and tungsten mono-block, i.e., 13.5 mm. It was demonstrated during the 2014 and 2015 commissioning campaigns that the newly upgraded divertor Langmuir probe diagnostic system is successful. Representative experimental data are given and discussed for the DivLP measurements, then proving its availability and reliability.

Upgrade of Langmuir probe diagnostic in ITER-like tungsten mono-block divertor on experimental advanced superconducting tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, J. C.; Jia, M. N.; Feng, W.

2016-08-15

In order to withstand rapid increase in particle and power impact onto the divertor and demonstrate the feasibility of the ITER design under long pulse operation, the upper divertor of the EAST tokamak has been upgraded to actively water-cooled, ITER-like tungsten mono-block structure since the 2014 campaign, which is the first attempt for ITER on the tokamak devices. Therefore, a new divertor Langmuir probe diagnostic system (DivLP) was designed and successfully upgraded on the tungsten divertor to obtain the plasma parameters in the divertor region such as electron temperature, electron density, particle and heat fluxes. More specifically, two identical triplemore » probe arrays have been installed at two ports of different toroidal positions (112.5-deg separated toroidally), which can provide fundamental data to study the toroidal asymmetry of divertor power deposition and related 3-dimension (3D) physics, as induced by resonant magnetic perturbations, lower hybrid wave, and so on. The shape of graphite tip and fixed structure of the probe are designed according to the structure of the upper tungsten divertor. The ceramic support, small graphite tip, and proper connector installed make it possible to be successfully installed in the very narrow interval between the cassette body and tungsten mono-block, i.e., 13.5 mm. It was demonstrated during the 2014 and 2015 commissioning campaigns that the newly upgraded divertor Langmuir probe diagnostic system is successful. Representative experimental data are given and discussed for the DivLP measurements, then proving its availability and reliability.« less

Investigations in the ionosphere on Kosmos 378. VIII. Results of T/sub e/ measurements with an hf probe and a Langmuir probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afonin, V.V.; Gdalevich, G.L.; Sheronova, S.M.

1975-01-01

The results of T/sub e/ measurements with an hf probe and a spherical Langmuir probe with modulation are discussed. Both instruments give the same results for a Maxwellian electron velocity distribution in the ionosphere. The distribution of T/sub e/ along the satellite orbit is presented, and the behavior of T/sub e/ in the polar region and above the geomagnetic equator is analyzed.

Experimental evaluation of Langmuir probe sheath potential coefficient on the HL-2A tokamak

NASA Astrophysics Data System (ADS)

Nie, L.; Xu, M.; Ke, R.; Yuan, B. D.; Wu, Y. F.; Cheng, J.; Lan, T.; Yu, Y.; Hong, R. J.; Guo, D.; Ting, L.; Dong, Y. B.; Zhang, Y. P.; Song, X. M.; Zhong, W. L.; Wang, Z. H.; Sun, A. P.; Xu, J. Q.; Chen, W.; Yan, L. W.; Zou, X. L.; Duan, X. R.; HL-2A Team

2018-03-01

Systematic calibration experiment of Langmuir probe sheath potential coefficient Λ, which is a critical coefficient for estimating plasma sheath potential, has been carried out in the HL-2A tokamak deuterium plasmas. The electron energy probability function (EEPF) shows that electron outside last-closed-flux-surface (LCFS) is Maxwell distribution, but inside LCFS it changes to bi-Maxwell. Two kinds of plasma potential measuring method and three kinds Λ estmating method were compared. It is found that the estimated Λ coefficient is in the region of 2-3 outside LCFS and then increases to ~5 inside LCFS due to the high temperature electron effect. Fortunately, the results show that the commonly used value Λ  =  2.8 is still available to calculate plasma potential when we use the overestimated electron temperature measured by three-tip probe in bi-Maxwell case. Further analysis indicated this value should be corrected. Or it may lead to a error when we calculate the the electric field {{E}r} and its shear d{{E}r}/dr . The corrected value monotonically increased from ~2.2 to ~2.9 while Langmuir probe moved from 40 mm outside LCFS to 20 mm inside LCFS.

High heat flux Langmuir probe array for the DIII-D divertor platesa)

NASA Astrophysics Data System (ADS)

Watkins, J. G.; Taussig, D.; Boivin, R. L.; Mahdavi, M. A.; Nygren, R. E.

2008-10-01

Two modular arrays of Langmuir probes designed to handle a heat flux of up to 25 MW/m2 for 10 s exposures have been installed in the lower divertor target plates of the DIII-D tokamak. The 20 pyrolytic graphite probe tips have more than three times higher thermal conductivity and 16 times larger mass than the original DIII-D isotropic graphite probes. The probe tips have a fixed 12.5° surface angle to distribute the heat flux more uniformly than the previous 6 mm diameter domed collectors and a symmetric "rooftop" design to allow operation with reversed toroidal magnetic field. A large spring-loaded contact area improves heat conduction from each probe tip through a ceramic insulator into a cooled graphite divertor floor tile. The probe tips, brazed to molybdenum foil to ensure good electrical contact, are mounted in a ceramic tray for electrical isolation and reliable cable connections. The new probes are located 1.5 cm radially apart in a staggered arrangement near the entrance to the lower divertor pumping baffle and are linearly spaced 3 cm apart on the shelf above the in-vessel cryopump. Typical target plate profiles of Jsat, Te, and Vf with 4 mm spatial resolution are shown.

Measurements of plasma profiles using a fast swept Langmuir probe in the VINETA-II magnetic reconnection experiment

NASA Astrophysics Data System (ADS)

Shesterikov, I.; Von Stechow, A.; Grulke, O.; Stenzel, R.; Klinger, T.

2017-07-01

A fast-swept Langmuir probe capable to be biased at a high voltages has been constructed and successfully operated at the VINETA-II magnetic reconnection experiment. The presented circuit has two main features beneficial for fast transient parameter changes in laboratory experiments as, e.g., plasma guns or magnetic reconnection: the implementation simplicity and the high voltage sweep range. This work presents its design and performance for time-dependent measurements of VINETA-II plasmas. The probe is biased with a sinusoidal voltage at a fixed frequency. Current - voltage characteristics are measured along the falling and rising slopes of the probe bias. The sweep frequency is fsweep= 150 kHz. The spatiotemporal evolution of radial plasma profiles is obtained by evaluation of the probe characteristics. The plasma density measurements agree with those derived from a microwave interferometer, demonstrating the reliability of the measurements. As a model plasma system, a plasma gun discharge with typical pulse times of 60 μ s is chosen.

Removal of singularity in radial Langmuir probe models for non-zero ion temperature

NASA Astrophysics Data System (ADS)

Regodón, Guillermo Fernando; Fernández Palop, José Ignacio; Tejero-del-Caz, Antonio; Díaz-Cabrera, Juan Manuel; Carmona-Cabezas, Rafael; Ballesteros, Jerónimo

2017-10-01

We solve a radial theoretical model that describes the ion sheath around a cylindrical Langmuir probe with finite non-zero ion temperature in which singularity in an a priori unknown point prevents direct integration. The singularity appears naturally in fluid models when the velocity of the ions reaches the local ion speed of sound. The solutions are smooth and continuous and are valid from the plasma to the probe with no need for asymptotic matching. The solutions that we present are valid for any value of the positive ion to electron temperature ratio and for any constant polytropic coefficient. The model is numerically solved to obtain the electric potential and the ion population density profiles for any given positive ion current collected by the probe. The ion-current to probe-voltage characteristic curves and the Sonin plot are calculated in order to use the results of the model in plasma diagnosis. The proposed methodology is adaptable to other geometries and in the presence of other presheath mechanisms.

Plasma Potential and Langmuir Probe Measurements in the Near-field Plume of the NASA 300M Hall Thruster

NASA Technical Reports Server (NTRS)

Herman, Daniel A; Shastry, Rohit; Huang, Wensheng; Soulas, George C.; KamHawi, Hani

2012-01-01

In order to aid in the design of high-power Hall thrusters and provide experimental validation for existing modeling efforts, plasma potential and Langmuir probe measurements were performed in the near-field plume of the NASA 300M Hall thruster. A probe array consisting of a Faraday probe, Langmuir probe, and emissive probe was used to interrogate the plume from approximately 0.1 - 2.0 DT,m downstream of the thruster exit plane at four operating conditions: 300 V, 400 V, and 500 V at 20 kW as well as 300 V at 10 kW. Results show that the acceleration zone and high-temperature region were contained within 0.3 DT,m from the exit plane at all operating conditions. Isothermal lines were shown to strongly follow magnetic field lines in the nearfield, with maximum temperatures ranging from 19 - 27 eV. The electron temperature spatial distribution created large drops in measured floating potentials in front of the magnetic pole surfaces where the plasma density was small, which suggests strong sheaths at these surfaces. The data taken have provided valuable information for future design and modeling validation, and complements ongoing internal measurement efforts on the NASA 300 M.

Method for reducing measurement errors of a Langmuir probe with a protective RF shield

NASA Astrophysics Data System (ADS)

Riaby, V.; Masherov, P.; Savinov, V.; Yakunin, V.

2018-04-01

Probe measurements were conducted in the middle cross-section of an inductive, low-pressure xenon plasma using a straight cylindrical Langmuir probe with a bare metal shield that protected the probe from radio frequency interference. As a result, reliable radial distributions of the plasma parameters were obtained. Subsequent analyses of these measurements revealed that the electron energy distribution function (EEDF) deviated substantially from the Maxwellian functions and that this deviation depended on the length of the probe shield. To evaluate the shield's influence on the measurement results, in addition to the probe (which was moved radially as its shield length varied in the range of lsh1 = lmax-0), an additional L-shaped probe was inserted at a different location. This probe was moved differently from the first probe and provided confirmational measurements in the common special position where lsh1 = 0 and lsh2 ≠ 0. In this position, the second shield decreased all the plasma parameters. A comparison of the probe datasets identified the principles of the relationships between measurement errors and EEDF distortions caused by the bare probe shields. This dependence was used to correct the measurements performed using the first probe by eliminating the influence of its shield. Physical analyses based on earlier studies showed that these peculiarities are caused by a short-circuited double-probe effect that occurs in bare metal probe protective shields.

Shadowing effects on multi-step Langmuir probe array on HL-2A tokamak

NASA Astrophysics Data System (ADS)

Ke, R.; Xu, M.; Nie, L.; Gao, Z.; Wu, Y.; Yuan, B.; Chen, J.; Song, X.; Yan, L.; Duan, X.

2018-05-01

Multi-step Langmuir probe arrays have been designed and installed on the HL-2A tokamak [1]–[2] to study the turbulent transport in the edge plasma, especially for the measurement of poloidal momentum flux, Reynolds stress Rs. However, except the probe tips on the top step, all other tips on lower steps are shadowed by graphite skeleton. It is necessary to estimate the shadowing effects on equilibrium and fluctuation measurement. In this paper, comparison of shadowed tips to unshadowed ones is presented. The results show that shadowing can strongly reduce the ion and electron effective collection area. However, its effect is negligible for the turbulence intensity and coherence measurement, confirming that the multi-step LP array is proper for the turbulent transport measurement.

Langmuir probes for SPIDER (source for the production of ions of deuterium extracted from radio frequency plasma) experiment: Tests in BATMAN (Bavarian test machine for negative ions)

NASA Astrophysics Data System (ADS)

Brombin, M.; Spolaore, M.; Serianni, G.; Pomaro, N.; Taliercio, C.; Palma, M. Dalla; Pasqualotto, R.; Schiesko, L.

2014-11-01

A prototype system of the Langmuir probes for SPIDER (Source for the production of Ions of Deuterium Extracted from RF plasma) was manufactured and experimentally qualified. The diagnostic was operated in RF (Radio Frequency) plasmas with cesium evaporation on the BATMAN (BAvarian Test MAchine for Negative ions) test facility, which can provide plasma conditions as expected in the SPIDER source. A RF passive compensation circuit was realised to operate the Langmuir probes in RF plasmas. The sensors' holder, designed to better simulate the bias plate conditions in SPIDER, was exposed to a severe experimental campaign in BATMAN with cesium evaporation. No detrimental effect on the diagnostic due to cesium evaporation was found during the exposure to the BATMAN plasma and in particular the insulation of the electrodes was preserved. The paper presents the system prototype, the RF compensation circuit, the acquisition system (as foreseen in SPIDER), and the results obtained during the experimental campaigns.

Langmuir probes for SPIDER (Source for the production of Ions of Deuterium Extracted from Radio Frequency plasma) experiment: tests in BATMAN (BAvarian Test Machine for Negative ions).

PubMed

Brombin, M; Spolaore, M; Serianni, G; Pomaro, N; Taliercio, C; Dalla Palma, M; Pasqualotto, R; Schiesko, L

2014-11-01

A prototype system of the Langmuir probes for SPIDER (Source for the production of Ions of Deuterium Extracted from RF plasma) was manufactured and experimentally qualified. The diagnostic was operated in RF (Radio Frequency) plasmas with cesium evaporation on the BATMAN (BAvarian Test MAchine for Negative ions) test facility, which can provide plasma conditions as expected in the SPIDER source. A RF passive compensation circuit was realised to operate the Langmuir probes in RF plasmas. The sensors' holder, designed to better simulate the bias plate conditions in SPIDER, was exposed to a severe experimental campaign in BATMAN with cesium evaporation. No detrimental effect on the diagnostic due to cesium evaporation was found during the exposure to the BATMAN plasma and in particular the insulation of the electrodes was preserved. The paper presents the system prototype, the RF compensation circuit, the acquisition system (as foreseen in SPIDER), and the results obtained during the experimental campaigns.

Langmuir probes for SPIDER (source for the production of ions of deuterium extracted from radio frequency plasma) experiment: Tests in BATMAN (Bavarian test machine for negative ions)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brombin, M., E-mail: matteo.brombin@igi.cnr.it; Spolaore, M.; Serianni, G.

2014-11-15

A prototype system of the Langmuir probes for SPIDER (Source for the production of Ions of Deuterium Extracted from RF plasma) was manufactured and experimentally qualified. The diagnostic was operated in RF (Radio Frequency) plasmas with cesium evaporation on the BATMAN (BAvarian Test MAchine for Negative ions) test facility, which can provide plasma conditions as expected in the SPIDER source. A RF passive compensation circuit was realised to operate the Langmuir probes in RF plasmas. The sensors’ holder, designed to better simulate the bias plate conditions in SPIDER, was exposed to a severe experimental campaign in BATMAN with cesium evaporation.more » No detrimental effect on the diagnostic due to cesium evaporation was found during the exposure to the BATMAN plasma and in particular the insulation of the electrodes was preserved. The paper presents the system prototype, the RF compensation circuit, the acquisition system (as foreseen in SPIDER), and the results obtained during the experimental campaigns.« less

Langmuir probe measurements in the intense RF field of a helicon discharge

NASA Astrophysics Data System (ADS)

Chen, Francis F.

2012-10-01

Helicon discharges have extensively been studied for over 25 years both because of their intriguing physics and because of their utility in producing high plasma densities for industrial applications. Almost all measurements so far have been made away from the antenna region in the plasma ejected into a chamber where there may be a strong magnetic field (B-field) but where the radiofrequency (RF) field is much weaker than under the antenna. Inside the source region, the RF field distorts the current-voltage (I-V) characteristic of the probe unless it is specially designed with strong RF compensation. For this purpose, a thin probe was designed and used to show the effect of inadequate compensation on electron temperature (Te) measurements. The subtraction of ion current from the I-V curve is essential; and, surprisingly, Langmuir's orbital motion limited theory for ion current can be used well beyond its intended regime.

Comparative measurements of plasma potential with ball-pen and Langmuir probe in low-temperature magnetized plasma

NASA Astrophysics Data System (ADS)

Zanáška, M.; Adámek, J.; Peterka, M.; Kudrna, P.; Tichý, M.

2015-03-01

The ball-pen probe (BPP) is used for direct plasma potential measurements in magnetized plasma. The probe can adjust the ratio of the electron and ion saturation currents Isat-/Isat+ to be close to one and therefore its I-V characteristic becomes nearly symmetric. If this is achieved, the floating potential of the BPP is close to the plasma potential. Because of its rather simple construction, it offers an attractive probe for measurements in magnetized plasma. Comparative measurements of plasma potential by BPPs of different dimensions as well as one Langmuir probe (LP) in an argon discharge plasma of a cylindrical magnetron were performed at various experimental conditions. An additional comparison by an emissive probe was also performed. All these types of probes provide similar values of plasma potential in a wide range of plasma parameters. Our results for three different BPP dimensions indicate that the BPP can be operated in a cylindrical magnetron DC argon discharge if the value of the ratio of the magnetic field and neutral gas pressure, B/p, is greater than approximately 10 mT/Pa.

Modeling of current characteristics of segmented Langmuir probe on DEMETER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imtiaz, Nadia; Marchand, Richard; Lebreton, Jean-Pierre

We model the current characteristics of the DEMETER Segmented Langmuir probe (SLP). The probe is used to measure electron density and temperature in the ionosphere at an altitude of approximately 700 km. It is also used to measure the plasma flow velocity in the satellite frame of reference. The probe is partitioned into seven collectors: six electrically insulated spherical segments and a guard electrode (the rest of the sphere and the small post). Comparisons are made between the predictions of the model and DEMETER measurements for actual ionospheric plasma conditions encountered along the satellite orbit. Segment characteristics are computed numericallymore » with PTetra, a three-dimensional particle in cell simulation code. In PTetra, space is discretized with an unstructured tetrahedral mesh, thus, enabling a good representation of the probe geometry. The model also accounts for several physical effects of importance in the interaction of spacecraft with the space environment. These include satellite charging, photoelectron, and secondary electron emissions. The model is electrostatic, but it accounts for the presence of a uniform background magnetic field. PTetra simulation results show different characteristics for the different probe segments. The current collected by each segment depends on its orientation with respect to the ram direction, the plasma composition, the magnitude, and the orientation of the magnetic field. It is observed that the presence of light H{sup +} ions leads to a significant increase in the ion current branch of the I-V curves of the negatively polarized SLP. The effect of the magnetic field is demonstrated by varying its magnitude and direction with respect to the reference magnetic field. It is found that the magnetic field appreciably affects the electron current branch of the I-V curves of certain segments on the SLP, whereas the ion current branch remains almost unaffected. PTetra simulations are validated by comparing the

Langmuir probe diagnostics of an atmospheric pressure, vortex-stabilized nitrogen plasma jet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prevosto, L.; Mancinelli, B. R.; Kelly, H.

Langmuir probe measurements in an atmospheric pressure direct current (dc) plasma jet are reported. Sweeping probes were used. The experiment was carried out using a dc non-transferred arc torch with a rod-type cathode and an anode of 5 mm diameter. The torch was operated at a nominal power level of 15 kW with a nitrogen flow rate of 25 Nl min{sup -1}. A flat ion saturation region was found in the current-voltage curve of the probe. The ion saturation current to a cylindrical probe in a high-pressure non local thermal equilibrium (LTE) plasma was modeled. Thermal effects and ionization/recombination processesmore » inside the probe perturbed region were taken into account. Averaged radial profiles of the electron and heavy particle temperatures as well as the electron density were obtained. An electron temperature around 11 000 K, a heavy particle temperature around 9500 K and an electron density of about 4 Multiplication-Sign 10{sup 22} m{sup -3}, were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found throughout the plasma jet. The electron and heavy particle temperature profiles showed good agreement with those reported in the literature by using spectroscopic techniques. It was also found that the temperature radial profile based on LTE was very close to that of the electrons. The calculations have shown that this method is particularly useful for studying spraying-type plasma jets characterized by electron temperatures in the range 9000-14 000 K.« less

Plasma Potential and Langmuir Probe Measurements in the Near-field Plume of the NASA-457Mv2 Hall Thruster

NASA Technical Reports Server (NTRS)

Shastry, Rohit; Huang, Wensheng; Herman, Daniel A.; Soulas, George C.; Kamhawi, Hani

2012-01-01

In order to further the design of future high-power Hall thrusters and provide experimental validation for ongoing modeling efforts, plasma potential and Langmuir probe measurements were performed on the 50-kW NASA-457Mv2. An electrostatic probe array comprised of a near-field Faraday probe, single Langmuir probe, and emissive probe was used to interrogate the near-field plume from approximately 0.1 - 2.0 mean thruster diameters downstream of the thruster exit plane at the following operating conditions: 300 V, 400 V and 500 V at 30 kW and 500 V at 50 kW. Results have shown that the acceleration zone is limited to within 0.4 mean thruster diameters of the exit plane while the high-temperature region is limited to 0.25 mean thruster diameters from the exit plane at all four operating conditions. Maximum plasma potentials in the near-field at 300 and 400 V were approximately 50 V with respect to cathode potential, while maximum electron temperatures varied from 24 - 32 eV, depending on operating condition. Isothermal lines at all operating conditions were found to strongly resemble the magnetic field topology in the high-temperature regions. This distribution was found to create regions of high temperature and low density near the magnetic poles, indicating strong, thick sheath formation along these surfaces. The data taken from this study are considered valuable for future design as well as modeling validation.

High-resolution disruption halo current measurements using Langmuir probes in Alcator C-Mod

NASA Astrophysics Data System (ADS)

Tinguely, R. A.; Granetz, R. S.; Berg, A.; Kuang, A. Q.; Brunner, D.; LaBombard, B.

2018-01-01

Halo currents generated during disruptions on Alcator C-Mod have been measured with Langmuir ‘rail’ probes. These rail probes are embedded in a lower outboard divertor module in a closely-spaced vertical (poloidal) array. The dense array provides detailed resolution of the spatial dependence (~1 cm spacing) of the halo current distribution in the plasma scrape-off region with high time resolution (400 kHz digitization rate). As the plasma limits on the outboard divertor plate, the contact point is clearly discernible in the halo current data (as an inversion of current) and moves vertically down the divertor plate on many disruptions. These data are consistent with filament reconstructions of the plasma boundary, from which the edge safety factor of the disrupting plasma can be calculated. Additionally, the halo current ‘footprint’ on the divertor plate is obtained and related to the halo flux width. The voltage driving halo current and the effective resistance of the plasma region through which the halo current flows to reach the probes are also investigated. Estimations of the sheath resistance and halo region resistivity and temperature are given. This information could prove useful for modeling halo current dynamics.

Langmuir probe measurements and mass spectrometry of plasma plumes generated by laser ablation of La0.4Ca0.6MnO3

NASA Astrophysics Data System (ADS)

Chen, Jikun; Lunney, James G.; Lippert, Thomas; Ojeda-G-P, Alejandro; Stender, Dieter; Schneider, Christof W.; Wokaun, Alexander

2014-08-01

The plasma formed in vacuum by UV nanosecond laser ablation of La0.4Ca0.6MnO3 in the fluence range of 0.8 to 1.9 J cm-2 using both Langmuir probe analysis and energy-resolved mass spectrometry has been studied. Mass spectrometry shows that the main positive ion species are Ca+, Mn+, La+, and LaO+. The Ca+ and Mn+ energy distributions are quite broad and lie in the 0-100 eV region, with the average energies increasing with laser fluence. In contrast, the La+ and LaO+ distributions are strongly peaked around 10 eV. The net time-of-arrival signal derived from the measured positive ion energy distributions is broadly consistent with the positive ion signal measured by the Langmuir probe. We also detected a significant number of O- ions with energies in the range of 0 to 10 eV. The Langmuir probe was also used to measure the temporal variation of the electron density and temperature at 6 cm from the ablation target. In the period when O- ions are found at this position, the plasma conditions are consistent with those required for significant negative oxygen ion formation, as revealed by studies on radio frequency excited oxygen plasma.

Estimation of plasma ion saturation current and reduced tip arcing using Langmuir probe harmonics.

PubMed

Boedo, J A; Rudakov, D L

2017-03-01

We present a method to calculate the ion saturation current, I sat , for Langmuir probes at high frequency (>100 kHz) using the harmonics technique and we compare that to a direct measurement of I sat . It is noted that the I sat estimation can be made directly by the ratio of harmonic amplitudes, without explicitly calculating T e . We also demonstrate that since the probe tips using the harmonic method are oscillating near the floating potential, drawing little power, this method reduces tip heating and arcing and allows plasma density measurements at a plasma power flux that would cause continuously biased tips to arc. A multi-probe array is used, with two spatially separated tips employing the harmonics technique and measuring the amplitude of at least two harmonics per tip. A third tip, located between the other two, measures the ion saturation current directly. We compare the measured and calculated ion saturation currents for a variety of plasma conditions and demonstrate the validity of the technique and its use in reducing arcs.

Estimation of plasma ion saturation current and reduced tip arcing using Langmuir probe harmonics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boedo, J. A.; Rudakov, D. L.

Here we present a method to calculate the ion saturation current, I sat, for Langmuir probes at high frequency (>100 kHz) using the harmonics technique and we compare that to a direct measurement of I sat. It is noted that the Isat estimation can be made directly by the ratio of harmonic amplitudes, without explicitly calculating T e. We also demonstrate that since the probe tips using the harmonic method are oscillating near the floating potential, drawing little power, this method reduces tip heating and arcing and allows plasma density measurements at a plasma power flux that would cause continuouslymore » biased tips to arc. A multi-probe array is used, with two spatially separated tips employing the harmonics technique and measuring the amplitude of at least two harmonics per tip. A third tip, located between the other two, measures the ion saturation current directly. We compare the measured and calculated ion saturation currents for a variety of plasma conditions and demonstrate the validity of the technique and it’s use in reducing arcs.« less

Estimation of plasma ion saturation current and reduced tip arcing using Langmuir probe harmonics

DOE PAGES

Boedo, J. A.; Rudakov, D. L.

2017-03-20

Here we present a method to calculate the ion saturation current, I sat, for Langmuir probes at high frequency (>100 kHz) using the harmonics technique and we compare that to a direct measurement of I sat. It is noted that the Isat estimation can be made directly by the ratio of harmonic amplitudes, without explicitly calculating T e. We also demonstrate that since the probe tips using the harmonic method are oscillating near the floating potential, drawing little power, this method reduces tip heating and arcing and allows plasma density measurements at a plasma power flux that would cause continuouslymore » biased tips to arc. A multi-probe array is used, with two spatially separated tips employing the harmonics technique and measuring the amplitude of at least two harmonics per tip. A third tip, located between the other two, measures the ion saturation current directly. We compare the measured and calculated ion saturation currents for a variety of plasma conditions and demonstrate the validity of the technique and it’s use in reducing arcs.« less

Comparative measurements of plasma potential with ball-pen and Langmuir probe in low-temperature magnetized plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zanáška, M.; Kudrna, P.; Tichý, M.

The ball-pen probe (BPP) is used for direct plasma potential measurements in magnetized plasma. The probe can adjust the ratio of the electron and ion saturation currents I{sub sat}{sup −}/I{sub sat}{sup +} to be close to one and therefore its I-V characteristic becomes nearly symmetric. If this is achieved, the floating potential of the BPP is close to the plasma potential. Because of its rather simple construction, it offers an attractive probe for measurements in magnetized plasma. Comparative measurements of plasma potential by BPPs of different dimensions as well as one Langmuir probe (LP) in an argon discharge plasma ofmore » a cylindrical magnetron were performed at various experimental conditions. An additional comparison by an emissive probe was also performed. All these types of probes provide similar values of plasma potential in a wide range of plasma parameters. Our results for three different BPP dimensions indicate that the BPP can be operated in a cylindrical magnetron DC argon discharge if the value of the ratio of the magnetic field and neutral gas pressure, B/p, is greater than approximately 10 mT/Pa.« less

Langmuir probe measurements aboard the International Space Station

NASA Astrophysics Data System (ADS)

Kirov, B.; Asenovski, S.; Bachvarov, D.; Boneva, A.; Grushin, V.; Georgieva, K.; Klimov, S. I.

2016-12-01

In the current work we describe the Langmuir Probe (LP) and its operation on board the International Space Station. This instrument is a part of the scientific complex "Ostonovka". The main goal of the complex is to establish, on one hand how such big body as the International Space Station affects the ambient plasma and on the other how Space Weather factors influence the Station. The LP was designed and developed at BAS-SRTI. With this instrument we measure the thermal plasma parameters-electron temperature Te, electron and ion concentration, respectively Ne and Ni, and also the potential at the Station's surface. The instrument is positioned at around 1.5 meters from the surface of the Station, at the Russian module "Zvezda", located at the farthermost point of the Space Station, considering the velocity vector. The Multi- Purpose Laboratory (MLM) module is providing additional shielding for our instrument, from the oncoming plasma flow (with respect to the velocity vector). Measurements show that in this area, the plasma concentration is two orders of magnitude lower, in comparison with the unperturbed areas. The surface potential fluctuates between-3 and-25 volts with respect to the ambient plasma. Fast upsurges in the surface potential are detected when passing over the twilight zone and the Equatorial anomaly.

Comparison of currents predicted by NASCAP/LEO model simulations with elementary Langmuir-type bare probe models for an insulated cable containing a single pinhole

NASA Technical Reports Server (NTRS)

Galofaro, Joel T.

1990-01-01

The behavior of a defect in the insulation of a short biased section of cable in a Low Earth Orbit (LEO) space environment was examined. Such studies are of the utmost importance for large space power systems where great quantities of cabling will be deployed. An insulated probe containing a pinhole was placed into a hypothetical high speed LEO plasma. The NASA Charging Analyzer Program (NASCAP/LEO) was used to explore sheath growth about the probe as a function of applied voltage and to predict I-V behavior. A set of independent current calculations using Langmuir's formulations for concentric spheres and coaxial cylinders were also performed. The case of concentric spheres was here extended to include the case of concentric hemispheres. Several simple Langmuir-type models were then constructed to bracket the current collected by the cable. The space-charge sheath radius and impact parameters were used to determine the proper current regime. I-V curves were plotted for the models and comparisons were made with NASCAP/LEO results. Finally, NASCAP/LEO potential contours and surface cell potential plots were examined to explain interesting features in the NASCAP/LEO I-V curve.

Measurement of Electron Density Using the Multipole Resonance Probe, Langmuir Probe and Optical Emission Spectroscopy in Low Pressure Plasmas with Different Electron Energy Distribution Functions

NASA Astrophysics Data System (ADS)

Oberberg, Moritz; Bibinov, Nikita; Ries, Stefan; Awakowicz, Peter; Institute of Electrical Engineering; Plasma Technology Team

2016-09-01

In recently publication, the young diagnostic tool Multipole Resonance Probe (MRP) for electron density measurements was introduced. It is based on active plasma resonance spectroscopy (APRS). The probe was simulated und evaluated for different devices. The geometrical and electrical symmetry simplifies the APRS model, so that the electron density can be easily calculated from the measured resonance. In this work, low pressure nitrogen mixture plasmas with different electron energy distribution functions (EEDF) are investigated. The results of the MRP measurement are compared with measurements of a Langmuir Probe (LP) and Optical Emission Spectroscopy (OES). Probes and OES measure in different regimes of kinetic electron energy. Both probes measure electrons with low kinetic energy (<10 eV), whereas the OES is influenced by electrons with high kinetic energy which are needed for transitions of molecule bands. By the determination of the absolute intensity of N2(C-B) and N2+(B-X)electron temperature and density can be calculated. In a non-maxwellian plasma, all plasma diagnostics need to be combined.

Statistical results from 10 years of Cassini Langmuir probe plasma measurements

NASA Astrophysics Data System (ADS)

Holmberg, M.; Shebanits, O.; Wahlund, J. E.; Morooka, M.; Andre, N.

2016-12-01

We use a new analysis method to obtain 10 years of Cassini RPWS Langmuir probe (LP) measurements to study the structure and dynamics of the inner plasma disk of Saturn. The LP plasma density measurements show good agreement with electron densities derived from the RPWS electric field power spectra and confirms and/or improves a number of previous findings about the structure of the plasma disk. E.g., the Enceladus plume is detected as a localised density maximum at the orbit of Enceladus, but the peak density of the inner plasma disk, excluding Enceladus plume passages, is located closer to 4.7 Rs. No density peaks are recorded at the orbits of the moons Mimas, Tethys, Dione, and Rhea. We confirm the previously detected plasma density dayside/nightside asymmetry, which is likely due to a particle drift in the dusk to dawn direction. Presented is also the LP result on the seasonal dependence of the plasma disk within Enceladus' orbit.

Method for obtaining electron energy-density functions from Langmuir-probe data using a card-programmable calculator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Longhurst, G.R.

This paper presents a method for obtaining electron energy density functions from Langmuir probe data taken in cool, dense plasmas where thin-sheath criteria apply and where magnetic effects are not severe. Noise is filtered out by using regression of orthogonal polynomials. The method requires only a programmable calculator (TI-59 or equivalent) to implement and can be used for the most general, nonequilibrium electron energy distribution plasmas. Data from a mercury ion source analyzed using this method are presented and compared with results for the same data using standard numerical techniques.

On the Measurement of Electron Temperature by Single Langmuir Probes in High Recycling Divertors

NASA Astrophysics Data System (ADS)

Pitts, Richard; Horacek, Jan; Loarte, Alberto

2000-10-01

Under high recycling and detached conditions, divertor Langmuir probes often yield a significantly higher value of Te than expected. The influence of plasma turbulence and the effect of fast electrons/plasma collisionality are two reasons why this might occur. We concentrate on these two candidates, with particular reference to observations on the TCV tokamak. A systematic study of the effects of noise on simulated probe characteristics at low T_e, shows that the asymmetric, exponential nature of the characteristic favours electron collection such that fluctuations in Vf alone actually tend to reduce the derived Te from that which would otherwise be found. We have also studied the effects of correlated density and potential fluctuations, finding no effect on the fitted T_e. The sheath potential fall energetically filters electrons such that at high densities, the probe measured Te may be characteristic of hotter, more distant zones in the plasma. We use model parallel field profiles of Te and ne generated from B2-Eirene simulations of TCV discharges as input to the analytic theory of Wesson [1] to show how a divertor plate measurement of Te in TCV can exceed the expected value by factors of up to 6 as detachment is approached. [1] J. A. Wesson, Plasma Phys. and Contr. Fusion 37 (1995) 1459

Indium-chlorine and gallium-chlorine tetrasubstituted phthalocyanines in a bulk system, Langmuir monolayers and Langmuir-Blodgett nanolayers--spectroscopic investigations.

PubMed

Bursa, B; Wróbel, D; Biadasz, A; Kędzierski, K; Lewandowska, K; Graja, A; Szybowicz, M; Durmuş, M

2014-07-15

The paper deals with spectroscopic characterization of metallic phthalocyanines (Pc's) (indium and gallium) complexed with chlorine and substituted with four benzyloxyphenoxy peripheral groups in bulk systems, 2D Langmuir monolayers and Langmuir-Blodgett nanolayers. An influence of the molecular structure of dyes (the presence of metal and of substitutes attached to the phthalocyanine macroring) on the in situ measurements of light absorption is reported. Molecular arrangement of the phthalocyanine molecular skeleton in the Langmuir monolayers on water substrate and in the Langmuir-Blodgett nanolayers is evaluated. A comparison of the light absorption spectra of the phthalocyanine monolayers with the spectra of the dyes in solution supports the existence of dye aggregates in the monolayer. It was shown that the type of dye aggregates (oblique and H types) depends markedly on the dye molecular structures. The NIR-IR, IR reflection-absorption and Raman spectra are also monitored for Langmuir-Blodgett nanolayers in non-polarized and polarized light. It was shown that the dye molecules in the Langmuir-Blodgett layers are oriented nearly vertically with respect to a gold substrate. Copyright © 2014 Elsevier B.V. All rights reserved.

Langmuir Probe Measurements in an Inductively Coupled Ar/CF4 Plasmas

NASA Technical Reports Server (NTRS)

Rao, M. V. V. S.; Meyyappan, M.; Sharma, S. P.; Arnold, James O. (Technical Monitor)

2000-01-01

Technological advancement in the microelectronics industry requires an understanding of the physical and chemical processes occurring in plasmas of fluorocarbon gases, such as carbon tetrafluoride (CF4) which is commonly used as an etchant, and their mixtures to optimize various operating parameters. In this paper we report data on electron number density (ne), electron temperature'(Te), electron energy distribution function (EEDF), mean electron energy, ion number density (ni), and plasma potential (Vp) measured by using Langmuir probe in an inductively coupled 13.56 MHz radio frequency plasmas generated in 50%Ar:50%CF4 mixture in the GEC cell. The probe data were recorded at various radial positions providing radial profiles of these plasma parameters at 10-50 mTorr pressures and 200 W and 300 W of RF power. Present measurements indicate that the electron and ion number densities increase with increase in pressure and power. Whereas the plasma potential and electron temperature decrease with increase in pressure, and they weakly depend on RF power. The radial profiles exhibit that the electron and ion number densities and the plasma potential peak at the center of the plasma with an exponential fall away from it, while the electron temperature has a minimum at the center and it increases steadily towards the electrode edge. The EEDFs have a characteristic drop near the low energy end at all pressures and pressures and their shapes represent non-Maxwellian plasma and exhibit more like Druyvesteyn energy distribution.v

Effect of working power and pressure on plasma properties during the deposition of TiN films in reactive magnetron sputtering plasma measured using Langmuir probe measurement

NASA Astrophysics Data System (ADS)

How, Soo Ren; Nayan, Nafarizal; Khairul Ahmad, Mohd; Fhong Soon, Chin; Zainizan Sahdan, Mohd; Lias, Jais; Shuhaimi Abu Bakar, Ahmad; Arshad, Mohd Khairuddin Md; Hashim, Uda; Yazid Ahmad, Mohd

2018-04-01

The ion, electron density and electron temperature during formation of TiN films in reactive magnetron sputtering system have been investigated for various settings of radio frequency (RF) power and working pressure by using Langmuir probe measurements. The RF power and working pressure able to affect the densities and plasma properties during the deposition process. In this work, a working pressure (100 and 20 mTorr) and RF power (100, 150 and 200 W) have been used for data acquisition of probe measurement. Fundamental of studied on sputter deposition is very important for improvement of film quality and deposition rate. Higher working pressure and RF power able to produce a higher ion density and reduction of electron temperature.

Soft Particle Spectrometer, Langmuir Probe, and Data Analysis for Aerospace Magnetospheric/Thermospheric Coupling Rocket Program

NASA Technical Reports Server (NTRS)

Sharber, J. R.; Frahm, R. A.; Scherrer, J. R.

1997-01-01

Under this grant two instruments, a soft particle spectrometer and a Langmuir probe, were refurbished and calibrated, and flown on three instrumented rocket payloads as part of the Magnetosphere/Thermosphere Coupling program. The flights took place at the Poker Flat Research Range on February 12, 1994 (T(sub o) = 1316:00 UT), February 2, 1995 (T(sub o) = 1527:20 UT), and November 27, 1995 (T(sub o) = 0807:24 UT). In this report the observations of the particle instrumentation flown on all three of the flights are described, and brief descriptions of relevant geophysical activity for each flight are provided. Calibrations of the particle instrumentation for all ARIA flights are also provided.

Electron density and electron temperature measurement in a bi-Maxwellian electron distribution using a derivative method of Langmuir probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Ikjin; Chung, ChinWook; Youn Moon, Se

2013-08-15

In plasma diagnostics with a single Langmuir probe, the electron temperature T{sub e} is usually obtained from the slope of the logarithm of the electron current or from the electron energy probability functions of current (I)-voltage (V) curve. Recently, Chen [F. F. Chen, Phys. Plasmas 8, 3029 (2001)] suggested a derivative analysis method to obtain T{sub e} by the ratio between the probe current and the derivative of the probe current at a plasma potential where the ion current becomes zero. Based on this method, electron temperatures and electron densities were measured and compared with those from the electron energymore » distribution function (EEDF) measurement in Maxwellian and bi-Maxwellian electron distribution conditions. In a bi-Maxwellian electron distribution, we found the electron temperature T{sub e} obtained from the method is always lower than the effective temperatures T{sub eff} derived from EEDFs. The theoretical analysis for this is presented.« less

Design of a Miniaturized Langmuir Plasma Probe for the QuadSat/PnP

NASA Astrophysics Data System (ADS)

Landavazo, M.; Jorgensen, A. M.; Del Barga, C.; Ferguson, D.; Guillette, D.; Huynh, A.; Klepper, J.; Kuker, J.; Lyke, J. C.; Marohn, B.; Mason, J.; Quiroga, J.; Ravindran, V.; Yelton, C.; Zagrai, A. N.; Zufelt, B.

2011-12-01

We have developed a miniaturized Langmuir plasma probe for measuring plasma density in low-earth orbit. Measuring plasma density in the upper ionosphere is important as a diagnostic for the rest of the ionosphere and as an input to space weather forecasting models. Developing miniaturized instrumentation allows easier deployment of a large number of small satellites for monitoring space weather. Our instrument was designed for the Swedish QuadSat/PnP, with the following constraints: A volume constraint of 5x5x1.25cm for the electronics enclosure, a mass budget 100 g, and a power budget of 0.5 W. We met the volume and mass constraints and where able to use less power than budgeted, only 0.25 W. We designed the probe for a bias range of +/-15V and current measurements in the 1 nA to 1 mA range (6 orders of magnitude). Necessary voltage of +/- 15 V and 3.3 V were generated on-board from a single 5 V supply. The electronics suite is based off carefully selected yet affordable commercial components that exhibit low noise, low leakage currents and low power consumption. Size constraints, low noise and low leakage requirements called for a carefully designed four layer PCB with a properly guarded current path using surface mount components on both sides. An ultra-low power microcontroller handles instrument functionality and is fully controllable over i2c using SPA-1 space plug and play. We elected for a probe launched deployed, which required careful design to survive launch vibrations while staying within the mass budget. The QuadSat/PnP has not been launched at the time of writing. We will present details of the instrument design and initial calibration data.

Real-time control of divertor detachment in H-mode with impurity seeding using Langmuir probe feedback in JET-ITER-like wall

NASA Astrophysics Data System (ADS)

Guillemaut, C.; Lennholm, M.; Harrison, J.; Carvalho, I.; Valcarcel, D.; Felton, R.; Griph, S.; Hogben, C.; Lucock, R.; Matthews, G. F.; Perez Von Thun, C.; Pitts, R. A.; Wiesen, S.; contributors, JET

2017-04-01

Burning plasmas with 500 MW of fusion power on ITER will rely on partially detached divertor operation to keep target heat loads at manageable levels. Such divertor regimes will be maintained by a real-time control system using the seeding of radiative impurities like nitrogen (N), neon or argon as actuator and one or more diagnostic signals as sensors. Recently, real-time control of divertor detachment has been successfully achieved in Type I ELMy H-mode JET-ITER-like wall discharges by using saturation current (I sat) measurements from divertor Langmuir probes as feedback signals to control the level of N seeding. The degree of divertor detachment is calculated in real-time by comparing the outer target peak I sat measurements to the peak I sat value at the roll-over in order to control the opening of the N injection valve. Real-time control of detachment has been achieved in both fixed and swept strike point experiments. The system has been progressively improved and can now automatically drive the divertor conditions from attached through high recycling and roll-over down to a user-defined level of detachment. Such a demonstration is a successful proof of principle in the context of future operation on ITER which will be extensively equipped with divertor target probes.

Photo-detachment of negative ions in Ar-CO2 dc discharge employing Langmuir probe

NASA Astrophysics Data System (ADS)

Rodríguez, Jannet; Yousif, Farook Bashir; Fuentes, Beatriz E.; Vázquez, Federico; Rivera, Marco; López-Patiño, J.; Figueroa, Aldo; Martínez, Horacio

2018-05-01

The electronegativity of the A r - C O 2 gas mixture was investigated, and the total relative negative oxygen ion density O2- + O- in the bulk of a dc discharge has been determined employing Langmuir probe assisted laser photo-detachment. The relative electron density and absolute temperature were obtained for the mixture at discharge powers between 200 and 3000 mW and pressures between 0.2 and 0.6 mbar, employing the collisional radiative model for several Ar gas mixtures. The absolute metastable number density for 1s3 and 1s5 levels was measured, and both showed an increasing trend as a function of pressure and power. The absolute number density of the 1s5 level was found to be higher than that of the 1s3 level. Electronegativity was found to decrease as a function of power and as a function of the increasing Ar percentage in the gas mixture.

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

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

A seven-month solar cycle observed with the Langmuir probe on Pioneer Venus Orbiter

NASA Technical Reports Server (NTRS)

Hoegy, W. R.; Wolff, C. L.

1989-01-01

Data collected by the Langmuir probe aboard the Pioneer Venus orbiter (PVO) over the years 1979 though 1987 were normalized to remove the long-period 11-year solar maximum to minimum trend and were analyzed for periodicity. Results yield evidence for the existence of an approximately 7-month solar cycle, which was also observed from SME Lyman alpha and 2800-MHz radio flux measurements carried out from an earth-based platform. This coincidence suggests that the cycle is an intrinsic periodicity in the solar output. The cycle has a frequency independent of the orbital frequency of the PVO and is distinct from a 'rotating beacon' cycle whose period depends on the orbital motion of the PVO about the sun. The second most dominant cycle discovered was a 5-month period. Results of an oscillation model of solar periodicity indicate that the 7-month and 5-month cycles are caused by long-lived flux enhancements from nonlinear interactions of global oscillation modes in the sun's convective envelope (r modes) and radiative interior (g modes).

Combined Langmuir-magnetic probe measurements of type-I ELMy filaments in the EAST tokamak

NASA Astrophysics Data System (ADS)

Qingquan, YANG; Fangchuan, ZHONG; Guosheng, XU; Ning, YAN; Liang, CHEN; Xiang, LIU; Yong, LIU; Liang, WANG; Zhendong, YANG; Yifeng, WANG; Yang, YE; Heng, ZHANG; Xiaoliang, Li

2018-06-01

Detailed investigations on the filamentary structures associated with the type-I edge-localized modes (ELMs) should be helpful for protecting the materials of a plasma-facing wall on a future large device. Related experiments have been carefully conducted in the Experimental Advanced Superconducting Tokamak (EAST) using combined Langmuir-magnetic probes. The experimental results indicate that the radially outward velocity of type-I ELMy filaments can be up to 1.7 km s‑1 in the far scrape-off layer (SOL) region. It is remarkable that the electron temperature of these filaments is detected to be ∼50 eV, corresponding to a fraction of 1/6 to the temperature near the pedestal top, while the density (∼ 3× {10}19 {{{m}}}-3) of these filaments could be approximate to the line-averaged density. In addition, associated magnetic fluctuations have been clearly observed at the same time, which show good agreement with the density perturbations. A localized current on the order of ∼100 kA could be estimated within the filaments.

In the Footsteps of Irving Langmuir: Physical Chemistry in Service of Society

NASA Astrophysics Data System (ADS)

Carter, Emily

The approach that Irving Langmuir took during his scientific career in industry at General Electric exemplifies the best that we chemical physicists/physical chemists can offer the world. His name is associated with very fundamental concepts and phenomena (e.g., the Langmuir isotherm, Langmuir-Blodgett films) along with practical inventions (e.g., the Langmuir probe, Langmuir trough). He worked at the interface of physics, chemistry, and engineering, with much of his important work devoted to understanding surface and interface phenomena. I have - unintentionally - followed in his footsteps, trained as a physical chemist who now leads the engineering school at Princeton. In this talk, I will give examples from my research as to how fundamental physical chemistry techniques and concepts - based largely on quantum mechanics - can be harnessed to help the world transition to a sustainable energy future. In the footsteps of Irving, surface and interfacial phenomena will figure prominently in the examples chosen.

Divertor sheath power studies in DIII-D using fixed Langmuir probes and three-dimensional modeling of tile heat flows

NASA Astrophysics Data System (ADS)

Donovan, D.; Nygren, R.; Buchenauer, D.; Watkins, J.; Rudakov, D.; Leonard, A.; Wong, C. P. C.; Makowski, M.

2014-04-01

Experimental results are presented from the three-Langmuir probe (LP) diagnostic head of the divertor material evaluation system (DiMES) on DIII-D that confirm the size of the projected current collection area of the LPs, which is essential for properly measuring ion saturation current density (Jsat) and the sheath power transmission factor (SPTF). Also using the 3-LP DiMES head, the hypothesis that collisional effects on plasma density occurring in the magnetic sheath of the tile are responsible for a lower than expected SPTF is tested and deemed not to have a significant impact on the SPTF. Three-dimensional thermal modeling of wall tiles is presented that accounts for lateral heat conduction, temperature dependence of tile material properties and radiative heat loss from the tile surface. This modeling was developed to be used in the analysis of temperature profiles of the divertor embedded thermocouple (TC) array to obtain more accurate interpretations of TC temperature profiles to infer divertor surface heat flux than have previously been accomplished using more basic one-dimensional methods.

Tribology of Langmuir-Blodgett Films

DTIC Science & Technology

1992-03-01

poly - meric systems and the use of Langmuir - Blodgett films as lubricants. An, 1473 ESWnoW’oP’-oVsS osOLe UNCLASSIFIED SECUlRTV CLASSIFICATIONi O r ThIS...N/A N/A 4. TITLE (and Subtitle) S. TyPE OF REPORT & PERIOD COVERED Tribology of Langmuir - Blodgett Films Interim Technical Report 6. PERFORMING ORO...Co . - e o If neceesea mnd Identily by block number) Tribology, Langmuir - Blodgett Films 2 AerNACT t 44 Pem.e s* I peminp and tdolvart by block niber

Development of a Double Hemispherical Probe for Improved Space Plasma Measurements

NASA Astrophysics Data System (ADS)

Wang, X.; Samaniego, J. I.; Hsu, H.-W.; Horányi, M.; Wahlund, J.-E.; Ergun, R. E.; Bering, E. A.

2018-04-01

Langmuir probes have been widely used for space plasma measurements for decades. However, there are still challenges in the interpretation of their measurements. Due to the interaction of the ambient plasma with a spacecraft and an onboard probe itself, the local plasma conditions around the probe could be very different from the true ambient plasma of interest. These local plasma conditions are often anisotropic and/or inhomogeneous. Most of the Langmuir probes that are made of a single electrode have difficulties to remove these local plasma effects, introducing errors in the derived plasma characteristics. Directional probes are able to characterize anisotropic and inhomogeneous plasmas. The split Langmuir probe and the Segmented Langmuir Probe have been developed to characterize the plasma flow in the Earth's ionosphere. Here we introduce a new type of a directional Langmuir probe, the Double Hemispherical Probe (DHP), to improve the space plasma measurements in a broad range of scenarios: (a) low-density plasmas, (b) high surface-emission (photo and/or secondary electron emission) environments, (c) flowing plasmas, and (d) dust-rich plasma environments. The DHP consists of two identical hemispheres that are electrically insulated and swept with the same voltages simultaneously. The difference currents between the two hemispheres are used to characterize the anisotropic/inhomogeneous plasma conditions created around the probe, which will be then removed or minimized on the interpretation of their current-voltage curves. This paper describes the basic concept and design of the DHP sensor, as well as its initial results tested in the laboratory plasma environments.

Predictions of VRF on a Langmuir Probe under the RF Heating Spiral on the Divertor Floor on NSTX-U

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hosea, J C; Perkins, R J; Jaworski, M A

RF heating deposition spirals are observed on the divertor plates on NSTX as shown in for a NB plus RF heating case. It has been shown that the RF spiral is tracked quite well by the spiral mapping of the strike points on the divertor plate of magnetic field lines passing in front of the high harmonic fast wave (HHFW) antenna on NSTX. Indeed, both current instrumented tiles and Langmuir probes respond to the spiral when it is positioned over them. In particular, a positive increment in tile current (collection of electrons) is obtained when the spiral is over themore » tile. This current can be due to RF rectification and/or RF heating of the scrape off layer (SOL) plasma along the magnetic field lines passing in front of the the HHFW antenna. It is important to determine quantitatively the relative contributions of these processes. Here we explore the properties of the characteristics of probes on the lower divertor plate to determine the likelyhood that the primary cause of the RF heat deposition is RF rectification.« less

Laboratory plasma probe studies

NASA Technical Reports Server (NTRS)

Heikkila, W. J.

1975-01-01

Diagnostic experiments performed in a collisionless plasma using CO2 as the working gas are described. In particular, simultaneous measurements that have been performed by means of Langmuir- and RF-probes are presented. A resonance occurring above the parallel resonance in the frequency characteristic of a two electrode system is interpreted as being due to the resonant excitation of electroacoustic waves.

Langmuir probe measurements in a time-fluctuating-highly ionized non-equilibrium cutting arc: analysis of the electron retarding part of the time-averaged current-voltage characteristic of the probe.

PubMed

Prevosto, L; Kelly, H; Mancinelli, B

2013-12-01

This work describes the application of Langmuir probe diagnostics to the measurement of the electron temperature in a time-fluctuating-highly ionized, non-equilibrium cutting arc. The electron retarding part of the time-averaged current-voltage characteristic of the probe was analysed, assuming that the standard exponential expression describing the electron current to the probe in collision-free plasmas can be applied under the investigated conditions. A procedure is described which allows the determination of the errors introduced in time-averaged probe data due to small-amplitude plasma fluctuations. It was found that the experimental points can be gathered into two well defined groups allowing defining two quite different averaged electron temperature values. In the low-current region the averaged characteristic was not significantly disturbed by the fluctuations and can reliably be used to obtain the actual value of the averaged electron temperature. In particular, an averaged electron temperature of 0.98 ± 0.07 eV (= 11400 ± 800 K) was found for the central core of the arc (30 A) at 3.5 mm downstream from the nozzle exit. This average included not only a time-average over the time fluctuations but also a spatial-average along the probe collecting length. The fitting of the high-current region of the characteristic using such electron temperature value together with the corrections given by the fluctuation analysis showed a relevant departure of local thermal equilibrium in the arc core.

Diagnostics of capacitively-coupled hydrocarbon plasmas for deposition of diamond-like carbon films using quadrupole mass spectrometry and Langmuir probe

NASA Astrophysics Data System (ADS)

Oda, Akinori; Fukai, Shun; Kousaka, Hiroyuki; Ohta, Takayuki

2015-09-01

Diamond-like carbon (DLC) films are the hydrogenated amorphous carbon films, which contains a mixture of sp2- and sp3-bonded carbon. The DLC films have been widely used for various applications, such as automotive, semiconductors, medical devices, since have excellent material properties in lower friction, higher chemical stability, higher hardness, higher wear resistance. Until now, numerous investigations on the DLC films using plasma assisted chemical vapor deposition have been done. For precise control of coating technique of DLC films, it is enormously important to clarify the fundamental properties in hydrocarbon plasmas, as a source of hydrocarbon ions and radicals. In this paper, the fundamental properties in a low pressure radio-frequency hydrocarbon (Ar/CH4 (1 %) gas mixture) plasmas have been diagnosed using a quadrupole mass spectrometer (HIDEN ANARYTICAL Ltd., EQP-300) and Langmuir probe system (HIDEN ANARYTICAL Ltd., ESPion). This work was partly supported by KAKENHI (No.26420247), and a ``Grant for Advanced Industrial Technology Development (No.11B06004d)'' in 2011 from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Development progress of the Materials Analysis and Particle Probe

NASA Astrophysics Data System (ADS)

Lucia, M.; Kaita, R.; Majeski, R.; Bedoya, F.; Allain, J. P.; Boyle, D. P.; Schmitt, J. C.; Onge, D. A. St.

2014-11-01

The Materials Analysis and Particle Probe (MAPP) is a compact in vacuo surface science diagnostic, designed to provide in situ surface characterization of plasma facing components in a tokamak environment. MAPP has been implemented for operation on the Lithium Tokamak Experiment at Princeton Plasma Physics Laboratory (PPPL), where all control and analysis systems are currently under development for full remote operation. Control systems include vacuum management, instrument power, and translational/rotational probe drive. Analysis systems include onboard Langmuir probes and all components required for x-ray photoelectron spectroscopy, low-energy ion scattering spectroscopy, direct recoil spectroscopy, and thermal desorption spectroscopy surface analysis techniques.

Development progress of the Materials Analysis and Particle Probe.

PubMed

Lucia, M; Kaita, R; Majeski, R; Bedoya, F; Allain, J P; Boyle, D P; Schmitt, J C; Onge, D A St

2014-11-01

The Materials Analysis and Particle Probe (MAPP) is a compact in vacuo surface science diagnostic, designed to provide in situ surface characterization of plasma facing components in a tokamak environment. MAPP has been implemented for operation on the Lithium Tokamak Experiment at Princeton Plasma Physics Laboratory (PPPL), where all control and analysis systems are currently under development for full remote operation. Control systems include vacuum management, instrument power, and translational/rotational probe drive. Analysis systems include onboard Langmuir probes and all components required for x-ray photoelectron spectroscopy, low-energy ion scattering spectroscopy, direct recoil spectroscopy, and thermal desorption spectroscopy surface analysis techniques.

Chorus Waves Modulation of Langmuir Waves in the Radiation Belts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jinxing; Bortnik, Jacob; An, Xin

Using high-resolution waveforms measured by the Van Allen Probes, we report a novel observation in the radiation belts. Namely, we show that multiband, discrete, rising-tone whistler-mode chorus emissions exhibit a one-to-one correlation with Langmuir wave bursts. Moreover, the periodic Langmuir wave bursts are generally observed at the phase location where the chorus wave E || component is oriented opposite to its propagation direction. The electron measurements show a beam in phase space density at the particle velocity that matches the parallel phase velocity of the chorus waves. Based on this evidence, we conclude that the chorus waves accelerate the suprathermalmore » electrons via Landau resonance, and generate a localized electron beam in phase space density. Consequently, the Langmuir waves are excited locally and are modulated by the chorus wave phase. As a result, this microscale interaction between chorus waves and high frequency electrostatic waves provides a new insight into the nonlinear wave-particle interaction process.« less

Chorus Waves Modulation of Langmuir Waves in the Radiation Belts

DOE PAGES

Li, Jinxing; Bortnik, Jacob; An, Xin; ...

2017-11-20

Using high-resolution waveforms measured by the Van Allen Probes, we report a novel observation in the radiation belts. Namely, we show that multiband, discrete, rising-tone whistler-mode chorus emissions exhibit a one-to-one correlation with Langmuir wave bursts. Moreover, the periodic Langmuir wave bursts are generally observed at the phase location where the chorus wave E || component is oriented opposite to its propagation direction. The electron measurements show a beam in phase space density at the particle velocity that matches the parallel phase velocity of the chorus waves. Based on this evidence, we conclude that the chorus waves accelerate the suprathermalmore » electrons via Landau resonance, and generate a localized electron beam in phase space density. Consequently, the Langmuir waves are excited locally and are modulated by the chorus wave phase. As a result, this microscale interaction between chorus waves and high frequency electrostatic waves provides a new insight into the nonlinear wave-particle interaction process.« less

Characteristics of the Plasma Source for Ground Ionosphere Simulation Surveyed by Disk-Type Langmuir Probe

NASA Astrophysics Data System (ADS)

Ryu, Kwangsun; Lee, Junchan; Kim, Songoo; Chung, Taejin; Shin, Goo-Hwan; Cha, Wonho; Min, Kyoungwook; Kim, Vitaly P.

2017-12-01

A space plasma facility has been operated with a back-diffusion-type plasma source installed in a mid-sized vacuum chamber with a diameter of 1.5 m located in Satellite Technology Research Center (SaTReC), Korea Advanced Institute of Science and Technology (KAIST). To generate plasma with a temperature and density similar to the ionospheric plasma, nickel wires coated with carbonate solution were used as filaments that emit thermal electrons, and the accelerated thermal electrons emitted from the heated wires collide with the neutral gas to form plasma inside the chamber. By using a disk-type Langmuir probe installed inside the vacuum chamber, the generation of plasma similar to the space environment was validated. The characteristics of the plasma according to the grid and plate anode voltages were investigated. The grid voltage of the plasma source is realized as a suitable parameter for manipulating the electron density, while the plate voltage is suitable for adjusting the electron temperature. A simple physical model based on the collision cross-section of electron impact on nitrogen molecule was established to explain the plasma generation mechanism.

Note: Additionally refined new possibilities of plasma probe diagnostics

NASA Astrophysics Data System (ADS)

Riaby, V. A.; Savinov, V. P.; Masherov, P. E.; Yakunin, V. G.

2018-03-01

In two previous Notes published in this journal, a method of measuring probe sheath thickness and ion mass was described using Langmuir probe diagnostics in low pressure xenon plasma close to Maxwellian substance. According to the first Note, this method includes two stages: (i) in a special experiment with known ion mass, the Bohm and Child-Langmuir-Boguslavsky (CLB) equations for cylindrical Langmuir probes used in this xenon plasma were solved jointly to determine the probe sheath thicknesses and Bohm coefficient CBCyl ≈ 1.13; and (ii) in a general experiment, with known CBCyl, the same equations could be solved to obtain the probe sheath thicknesses and the mean ion mass. In the second Note, the (i) stage of this method was refined: the results of the CLB probe sheath model application, which were termed "evaluations," were corrected using the step-front probe sheath model, which was closer to reality in the special experiment with the xenon plasma. This process resulted in a Bohm coefficient of CBCyl ≈ 1.23 for the cylindrical probe. In the present Note, corrected xenon plasma parameters without the influence of the bare probe protective shield were used for the (i) stage of this diagnostic method. This action also refined the Bohm coefficient, lowering it to CBCyl ≈ 0.745 for cylindrical probes. This advance makes the new diagnostics method more objective and reliable.

Langmuir Probe Measurements Within the Discharge Channel of the 20-kW NASA-300M and NASA-300MS Hall Thrusters

NASA Technical Reports Server (NTRS)

Shastry, Rohit; Huang, Wensheng; Haag, Thomas W.; Kamhawi, Hani

2013-01-01

NASA is presently developing a high-power, high-efficiency, long-lifetime Hall thruster for the Solar Electric Propulsion Technology Demonstration Mission. In support of this task, studies have been performed on the 20-kW NASA-300M Hall thruster to aid in the overall design process. The ability to incorporate magnetic shielding into a high-power Hall thruster was also investigated with the NASA- 300MS, a modified version of the NASA-300M. The inclusion of magnetic shielding would allow the thruster to push existing state-of-the-art technology in regards to service lifetime, one of the goals of the Technology Demonstration Mission. Langmuir probe measurements were taken within the discharge channels of both thrusters in order to characterize differences at higher power levels, as well as validate ongoing modeling efforts using the axisymmetric code Hall2De. Flush-mounted Langmuir probes were also used within the channel of the NASA-300MS to verify that magnetic shielding was successfully applied. Measurements taken from 300 V, 10 kW to 600 V, 20 kW have shown plasma potentials near anode potential and electron temperatures of 4 to 12 eV at the walls near the thruster exit plane of the NASA-300MS, verifying magnetic shielding and validating the design process at this power level. Channel centerline measurements on the NASA-300M from 300 V, 10 kW to 500 V, 20 kW show the electron temperature peak at approximately 0.1 to 0.2 channel lengths upstream of the exit plane, with magnitudes increasing with discharge voltage. The acceleration profiles appear to be centered about the exit plane with a width of approximately 0.3 to 0.4 channel lengths. Channel centerline measurements on the NASA-300MS were found to be more challenging due to additional probe heating. Ionization and acceleration zones appeared to move downstream on the NASA-300MS compared to the NASA-300M, as expected based on the shift in peak radial magnetic field. Additional measurements or alternative

Note: Additionally refined new possibilities of plasma probe diagnostics.

PubMed

Riaby, V A; Savinov, V P; Masherov, P E; Yakunin, V G

2018-03-01

In two previous Notes published in this journal, a method of measuring probe sheath thickness and ion mass was described using Langmuir probe diagnostics in low pressure xenon plasma close to Maxwellian substance. According to the first Note, this method includes two stages: (i) in a special experiment with known ion mass, the Bohm and Child-Langmuir-Boguslavsky (CLB) equations for cylindrical Langmuir probes used in this xenon plasma were solved jointly to determine the probe sheath thicknesses and Bohm coefficient C BCyl ≈ 1.13; and (ii) in a general experiment, with known C BCyl , the same equations could be solved to obtain the probe sheath thicknesses and the mean ion mass. In the second Note, the (i) stage of this method was refined: the results of the CLB probe sheath model application, which were termed "evaluations," were corrected using the step-front probe sheath model, which was closer to reality in the special experiment with the xenon plasma. This process resulted in a Bohm coefficient of C BCyl ≈ 1.23 for the cylindrical probe. In the present Note, corrected xenon plasma parameters without the influence of the bare probe protective shield were used for the (i) stage of this diagnostic method. This action also refined the Bohm coefficient, lowering it to C BCyl ≈ 0.745 for cylindrical probes. This advance makes the new diagnostics method more objective and reliable.

Langmuir Turbulence

DTIC Science & Technology

2015-09-30

1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Langmuir Turbulence Eric A. D’Asaro, Ramsey Harcourt...definitive experimental tests of the hypothesis that Langmuir Turbulence , specifically the equations of motion with the addition of the Craik-Leibovich...vortex force and advection by the surface wave Stokes drift, can accurately describe turbulence in the upper ocean boundary layer under conditions of

Plasma characterization of the superconducting proton linear accelerator plasma generator using a 2 MHz compensated Langmuir probe.

PubMed

Schmitzer, C; Kronberger, M; Lettry, J; Sanchez-Arias, J; Störi, H

2012-02-01

The CERN study for a superconducting proton Linac (SPL) investigates the design of a pulsed 5 GeV Linac operating at 50 Hz. As a first step towards a future SPL H(-) volume ion source, a plasma generator capable of operating at Linac4 or nominal SPL settings has been developed and operated at a dedicated test stand. The hydrogen plasma is heated by an inductively coupled RF discharge e(-) and ions are confined by a magnetic multipole cusp field similar to the currently commissioned Linac4 H(-) ion source. Time-resolved measurements of the plasma potential, temperature, and electron energy distribution function obtained by means of a RF compensated Langmuir probe along the axis of the plasma generator are presented. The influence of the main tuning parameters, such as RF power and frequency and the timing scheme is discussed with the aim to correlate them to optimum H(-) ion beam parameters measured on an ion source test stand. The effects of hydrogen injection settings which allow operation at 50 Hz repetition rate are discussed.

Comparative analyses of plasma probe diagnostics techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Godyak, V. A.; Alexandrovich, B. M.

The subject of this paper is a comparative analysis of the plasma parameters inferred from the classical Langmuir probe procedure, from different theories of the ion current to the probe, and from measured electron energy distribution function (EEDF) obtained by double differentiation of the probe characteristic. We concluded that the plasma parameters inferred from the classical Langmuir procedure can be subjected to significant inaccuracy due to the non-Maxwellian EEDF, uncertainty of locating the plasma potential, and the arbitrariness of the ion current approximation. The plasma densities derived from the ion part of the probe characteristics diverge by as much asmore » an order of magnitude from the density calculated according to Langmuir procedure or calculated as corresponding integral of the measured EEDF. The electron temperature extracted from the ion part is always subjected to uncertainty. Such inaccuracy is attributed to modification of the EEDF for fast electrons due to inelastic electron collisions, and to deficiencies in the existing ion current theories; i.e., unrealistic assumptions about Maxwellian EEDFs, underestimation of the ion collisions and the ion ambipolar drift, and discounting deformation of the one-dimensional structure of the region perturbed by the probe. We concluded that EEDF measurement is the single reliable probe diagnostics for the basic research and industrial applications of highly non-equilibrium gas discharge plasmas. Examples of EEDF measurements point up importance of examining the probe current derivatives in real time and reiterate significance of the equipment technical characteristics, such as high energy resolution and wide dynamic range.« less

Comparative analyses of plasma probe diagnostics techniques

NASA Astrophysics Data System (ADS)

Godyak, V. A.; Alexandrovich, B. M.

2015-12-01

The subject of this paper is a comparative analysis of the plasma parameters inferred from the classical Langmuir probe procedure, from different theories of the ion current to the probe, and from measured electron energy distribution function (EEDF) obtained by double differentiation of the probe characteristic. We concluded that the plasma parameters inferred from the classical Langmuir procedure can be subjected to significant inaccuracy due to the non-Maxwellian EEDF, uncertainty of locating the plasma potential, and the arbitrariness of the ion current approximation. The plasma densities derived from the ion part of the probe characteristics diverge by as much as an order of magnitude from the density calculated according to Langmuir procedure or calculated as corresponding integral of the measured EEDF. The electron temperature extracted from the ion part is always subjected to uncertainty. Such inaccuracy is attributed to modification of the EEDF for fast electrons due to inelastic electron collisions, and to deficiencies in the existing ion current theories; i.e., unrealistic assumptions about Maxwellian EEDFs, underestimation of the ion collisions and the ion ambipolar drift, and discounting deformation of the one-dimensional structure of the region perturbed by the probe. We concluded that EEDF measurement is the single reliable probe diagnostics for the basic research and industrial applications of highly non-equilibrium gas discharge plasmas. Examples of EEDF measurements point up importance of examining the probe current derivatives in real time and reiterate significance of the equipment technical characteristics, such as high energy resolution and wide dynamic range.

Linear discrete systems with memory: a generalization of the Langmuir model

NASA Astrophysics Data System (ADS)

Băleanu, Dumitru; Nigmatullin, Raoul R.

2013-10-01

In this manuscript we analyzed a general solution of the linear nonlocal Langmuir model within time scale calculus. Several generalizations of the Langmuir model are presented together with their exact corresponding solutions. The physical meaning of the proposed models are investigated and their corresponding geometries are reported.

Measurement of electron density using reactance cutoff probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

You, K. H.; Seo, B. H.; Kim, J. H.

2016-05-15

This paper proposes a new measurement method of electron density using the reactance spectrum of the plasma in the cutoff probe system instead of the transmission spectrum. The highly accurate reactance spectrum of the plasma-cutoff probe system, as expected from previous circuit simulations [Kim et al., Appl. Phys. Lett. 99, 131502 (2011)], was measured using the full two-port error correction and automatic port extension methods of the network analyzer. The electron density can be obtained from the analysis of the measured reactance spectrum, based on circuit modeling. According to the circuit simulation results, the reactance cutoff probe can measure themore » electron density more precisely than the previous cutoff probe at low densities or at higher pressure. The obtained results for the electron density are presented and discussed for a wide range of experimental conditions, and this method is compared with previous methods (a cutoff probe using the transmission spectrum and a single Langmuir probe).« less

A comparative study of electrical probe techniques for plasma diagnostics

NASA Technical Reports Server (NTRS)

Szuszczewicz, E. P.

1972-01-01

Techniques for using electrical probes for plasma diagnostics are reviewed. Specific consideration is given to the simple Langmuir probe, the symmetric double probe of Johnson and Malter, the variable-area probe of Fetz and Oeschsner, and a floating probe technique. The advantages and disadvantages of each technique are discussed.

A brightness exceeding simulated Langmuir limit

NASA Astrophysics Data System (ADS)

Nakasuji, Mamoru

2013-08-01

When an excitation of the first lens determines a beam is parallel beam, a brightness that is 100 times higher than Langmuir limit is measured experimentally, where Langmuir limits are estimated using a simulated axial cathode current density which is simulated based on a measured emission current. The measured brightness is comparable to Langmuir limit, when the lens excitation is such that an image position is slightly shorter than a lens position. Previously measured values of brightness for cathode apical radii of curvature 20, 60, 120, 240, and 480 μm were 8.7, 5.3, 3.3, 2.4, and 3.9 times higher than their corresponding Langmuir limits, respectively, in this experiment, the lens excitation was such that the lens and the image positions were 180 mm and 400 mm, respectively. From these measured brightness for three different lens excitation conditions, it is concluded that the brightness depends on the first lens excitation. For the electron gun operated in a space charge limited condition, some of the electrons emitted from the cathode are returned to the cathode without having crossed a virtual cathode. Therefore, method that assumes a Langmuir limit defining method using a Maxwellian distribution of electron velocities may need to be revised. For the condition in which the values of the exceeding the Langmuir limit are measured, the simulated trajectories of electrons that are emitted from the cathode do not cross the optical axis at the crossover, thus the law of sines may not be valid for high brightness electron beam systems.

Electron temperature and heat load measurements in the COMPASS divertor using the new system of probes

NASA Astrophysics Data System (ADS)

Adamek, J.; Seidl, J.; Horacek, J.; Komm, M.; Eich, T.; Panek, R.; Cavalier, J.; Devitre, A.; Peterka, M.; Vondracek, P.; Stöckel, J.; Sestak, D.; Grover, O.; Bilkova, P.; Böhm, P.; Varju, J.; Havranek, A.; Weinzettl, V.; Lovell, J.; Dimitrova, M.; Mitosinkova, K.; Dejarnac, R.; Hron, M.; The COMPASS Team; The EUROfusion MST1 Team

2017-11-01

A new system of probes was recently installed in the divertor of tokamak COMPASS in order to investigate the ELM energy density with high spatial and temporal resolution. The new system consists of two arrays of rooftop-shaped Langmuir probes (LPs) used to measure the floating potential or the ion saturation current density and one array of Ball-pen probes (BPPs) used to measure the plasma potential with a spatial resolution of ~3.5 mm. The combination of floating BPPs and LPs yields the electron temperature with microsecond temporal resolution. We report on the design of the new divertor probe arrays and first results of electron temperature profile measurements in ELMy H-mode and L-mode. We also present comparative measurements of the parallel heat flux using the new probe arrays and fast infrared termography (IR) data during L-mode with excellent agreement between both techniques using a heat power transmission coefficient γ  =  7. The ELM energy density {{\\varepsilon }\\parallel } was measured during a set of NBI assisted ELMy H-mode discharges. The peak values of {{\\varepsilon }\\parallel } were compared with those predicted by model and with experimental data from JET, AUG and MAST with a good agreement.

Probing the Surface Tension of Ionic Liquids Using the Langmuir Principle

PubMed Central

2018-01-01

At 298 K, the surface tension of ionic liquids (ILs) of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide series, [CnC1Im][NTf2], ranges from around 35 mN·m–1 for [C2C1Im][NTf2] to just below 30 mN·m–1 for [C12C1Im][NTf2]. However, the decrease rate along the series is not constant: a large decrease from [C2C1Im][NTf2] to [C8C1Im][NTf2] is followed by almost constant values from [C8C1Im][NTf2] to [C12C1Im][NTf2]. Such behavior is hard to interpret from a molecular point of view without suitable information about the free-surface structure of the different ILs. In this work, we have successfully used the Langmuir principle in combination with structural data obtained from angle-resolved X-ray photoelectron spectroscopy experiments and molecular dynamics simulations, to predict the correct surface tension trend along the IL series. The concepts unveiled for this particular homologous IL family can be easily extended to other systems. PMID:29485882

Langmuir probe study of a magnetically enhanced RF plasma source at pressures below 0.1 Pa

NASA Astrophysics Data System (ADS)

Kousal, Jaroslav; Tichý, Milan; Šebek, Ondřej; Čechvala, Juraj; Biederman, Hynek

2011-08-01

The majority of plasma polymerization sources operate at pressures higher than 1 Pa. At these pressures most common deposition methods do not show significant directionality. One way of enhancing the directional effects is to decrease the working pressure to increase the mean free path of the reactive molecules. The plasma source used in this work was designed to study the plasma polymerization process at pressures below 0.1 Pa. The source consists of the classical radio frequency (RF) (13.56 MHz, capacitive coupled) tubular reactor enhanced by an external magnetic circuit. The working gas is introduced into the discharge by a capillary. This forms a relatively localized zone of higher pressure where the monomer is activated. Due to the magnetic field, the plasma is constricted near the axis of the reactor with nearly collisionless gas flow. The plasma parameters were obtained using a double Langmuir probe. Plasma density in the range ni = 1013-1016 m-3 was obtained in various parts of the discharge under typical conditions. The presence of the magnetic field led to the presence of relatively strong electric fields (103 V m-1) and relatively high electron energies up to several tens of eV in the plasma.

Spreading dynamics of 2D dipolar Langmuir monolayer phases.

PubMed

Heinig, P; Wurlitzer, S; Fischer, Th M

2004-07-01

We study the spreading of a liquid 2D dipolar droplet in a Langmuir monolayer. Interfacial tensions (line tensions) and microscopic contact angles depend on the scale on which they are probed and obey a scaling law. Assuming rapid equilibration of the microscopic contact angle and ideal slippage of the 2D solid/liquid and solid/gas boundary, the driving force of spreading is merely expressed by the shape-dependent long-range interaction integrals. We obtain good agreement between experiment and numerical simulations using this theory.

Investigating the role of hydrogen in silicon deposition using an energy-resolved mass spectrometer and a Langmuir probe in an Ar/H2 radio frequency magnetron discharge

NASA Astrophysics Data System (ADS)

Mensah, S. L.; Naseem, Hameed H.; Abu-Safe, Husam; Gordon, M. H.

2012-07-01

The plasma parameters and ion energy distributions (IED) of the dominant species in an Ar-H2 discharge are investigated with an energy resolved mass spectrometer and a Langmuir probe. The plasmas are generated in a conventional magnetron chamber powered at 150 W, 13.56 MHz at hydrogen flow rates ranging from 0 to 25 sccm with a fixed argon gas flow rate of 15 sccm. Various Hn+, SiHn+, SiHn fragments (with n = 1, 2, 3) together with Ar+ and ArH+ species are detected in the discharge. The most important species for the film deposition is SiHn (with n = 0, 1, 2). H fragments affect the hydrogen content in the material. The flux of Ar+ decreases and the flux of ArH+ increases when the hydrogen flow rate is increased; however, both fluxes saturate at hydrogen flow rates above 15 sccm. Electron density, ne, electron energy, Te, and ion density, ni, are estimated from the Langmuir probe data. Te is below 1.2 eV at hydrogen flow rates below 8 sccm, and about 2 eV at flow rates above 8 sccm. ne and ni decrease with increased hydrogen flow but the ratio of ni to ne increases. The formation of H+ ions with energies above 36 eV and electrons with energies greater than 2 eV contributes to the decrease in hydrogen content at hydrogen flow rates above 8 sccm. Analysis of the IEDs indicates an inter-dependence of the species and their contribution to the thin film growth and properties.

Long Awaited Fundamental Measurement of the Martian Upper Atmosphere from the Langmuir Probe and Waves Instrument on the MAVEN Mission.

NASA Astrophysics Data System (ADS)

Andersson, Laila; Andrews, David; Ergun, Bob; Delory, Greg; Morooka, Michiko; Fowler, Chris; McEnulty, Tess; Weber, Tristan; Eriksson, Anders; Malaspina, David; Crary, Frank; Mitchell, David; McFadden, Jim; Halekas, Jasper; Larson, Davin; Connerney, Jack; Espley, Jared; Eparvies, Frank

2015-04-01

Electron temperature and density are critical quantities in understanding an upper atmosphere. Approximately 40 years ago, the Viking landers reached the Martian surface, measuring the first (and only) two temperature profiles during it's descent. With the MAVEN mission arriving at Mars details of the Martian ionosphere can agin be studied by a complete plasma package. This paper investigates the first few months of data from the MAVEN mission when the orbit is below 500 km and around the northern hemisphere's terminator. The fo-cus of this presentation is on the different measure-ments that the Langmuir probe and Waves (LPW) in-strument is making on the MAVEN mission. Some of the LPW highlights that will be presented: (a) the long awaited new the electron temperature profiles; (b) the structures observed on the nightside ionosphere; (c) wave-particle insteractions observed below 500 km; and (d) the observed dusty environment at Mars. This presentation is supported by measurements from the other Particle and Fileds (PF) measurements on MAVEN.

Langmuir vacuum and superconductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Veklenko, B. A.

It is shown that, in the 'jelly' model of cold electron-ion plasma, the interaction between electrons and the quantum electromagnetic vacuum of Langmuir waves involves plasma superconductivity with an energy gap proportional to the energy of the Langmuir quantum.

Simple solutions for relativistic generalizations of the Child-Langmuir law and the Langmuir-Blodgett law

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang Yongpeng; Northwest Institute of Nuclear Technology, P.O. Box 69-13, Xi'an 710024; Liu Guozhi

In this paper, the Child-Langmuir law and Langmuir-Blodgett law are generalized to the relativistic regime by a simple method. Two classical laws suitable for the nonrelativistic regime are modified to simple approximate expressions applicable for calculating the space-charge-limited currents of one-dimensional steady-state planar diodes and coaxial diodes under the relativistic regime. The simple approximate expressions, extending the Child-Langmuir law and Langmuir-Blodgett law to fit the full range of voltage, have small relative errors less than 1% for one-dimensional planar diodes and less than 5% for coaxial diodes.

Langmuir Probe Analysis of Maser-Driven Alfven Waves Using New LaB6 Cathode in LaPD

NASA Astrophysics Data System (ADS)

Clark, Mary; Dorfman, Seth; Zhu, Ziyan; Rossi, Giovanni; Carter, Troy

2015-11-01

Previous research in the Large Plasma Device shows that specific conditions on the magnetic field and cathode discharge voltage allow an Alfven wave to develop in the cathode-anode region. When the speed of bulk electrons (dependent on discharge voltage) entering the region exceeds the Alfven speed, the electrons can excite a wave. This phenomenon mimics one proposed to exist in the Earth's ionosphere. Previous experiments used a cathode coated with Barium Oxide, and this project uses a new cathode coated with Lanthanum Hexaboride (LaB6). The experiment seeks to characterize the behavior of plasmas generated with the LaB6 source, as well as understand properties of the driven wave when using the new cathode. Langmuir probes are used to find electron temperature, ion saturation current, and plasma density. These parameters determine characteristics of the wave. Preliminary analysis implies that density increases with LaB6 discharge voltage until 170 V, where it levels off. A linear increase in density is expected; the plateau implies cathode power does not ionize the plasma after 170 V. It is possible the power is carried out by the generated Alfven wave, or heats the plasma or cathode. This ``missing'' power is currently under investigation. Work funded by DOE and NSF.

New insights on boundary plasma turbulence and the Quasi-Coherent Mode in Alcator C-Mod using a Mirror Langmuir Probe

NASA Astrophysics Data System (ADS)

Labombard, Brian

2013-10-01

A ``Mirror Langmuir Probe'' (MLP) diagnostic has been used to interrogate edge plasma profiles and turbulence in Alcator C-Mod with unprecedented detail, yielding fundamental insights on the Quasi-Coherent Mode (QCM) - a mode that regulates plasma density and impurities in EDA H-modes without ELMs. The MLP employs a fast-switching, self-adapting bias scheme, recording density, electron temperature and plasma potential simultaneously at high bandwidth (~1 MHz) on each of four separate electrodes on a scanning probe. Temporal dynamics are followed in detail; wavenumber-frequency spectra and phase relationships are readily deduced. Poloidal field fluctuations are recorded separately with a two-coil, scanning probe. Results from ohmic L-mode and H-mode plasmas are reported, including key observations of the QCM: The QCM lives in a region of positive radial electric field, with a mode width (~3 mm) that spans open and closed field line regions. Remarkably large amplitude (~30%), sinusoidal bursts in density, electron temperature and plasma potential fluctuations are observed that are in phase; potential lags density by at most 10 degrees. Propagation velocity of the mode corresponds to the sum of local E × B and electron diamagnetic drift velocities - quantities that are deduced directly from time-averaged profiles. Poloidal magnetic field fluctuations project to parallel current densities of ~5 amps/cm2 in the mode layer, with significant parallel electromagnetic induction. Electron force balance is examined, unambiguously identifying the mode type. It is found that fluctuations in parallel electron pressure gradient are roughly balanced by the sum of electrostatic and electromotive forces. Thus the primary mode structure of the QCM is that of a drift-Alfven wave. Work supported by US DoE award DE-FC02-99ER54512.

PAPERS DEVOTED TO THE MEMORY OF ACADEMICIAN A M PROKHOROV: Immunosensor systems with the Langmuir-film-based fluorescence detection

NASA Astrophysics Data System (ADS)

Chudinova, G. K.; Nagovitsyn, I. A.; Karpov, R. E.; Savranskii, V. V.

2003-09-01

A method is developed for detecting protein antigens for fluorescent immunoassay using a model system based on the technique for preparation of Langmuir films. Fluorescein isothiocyanate and donor-acceptor energy-transfer pairs of markers (the Yb complex of tetraphenyl porphyrin — benzoyl trifluoroacetoneisothiocyanate and derivatives of tetra(carboxyphenyl) porphyrin — cyanine dye containing a five-membered polyene chain), which were nor studied earlier, were used as markers for detecting the binding of an antigen on the surface of Langmuir films of antibodies. Fluorescence was detected in the near-IR region (for the first pair) and in the visible spectral range (for the second pair). To reduce the nonspecific sorption of a protein (antigen), a method was proposed for the preparation of a nonpolar surface by applying an even number of layers of stearic acid as a substrate for the Langmuir — Blodgett film. A high sensitivity of model systems to a protein antigen in solution was achieved (~10-11 M), the assay time being 6 — 8 min. The model system with the first donor — acceptor pair was tested in analysis of the blood plasma. The fluorescence of the Dy3+, Tm3+, and Yb3+ complexes of tetraphenyl porphyrin sensitised by diketonate complexes of lanthanides was studied for the first time and the enhancement of the IR fluorescence of these complexes in a Langmuir film was demonstrated.

On Floating Potential of Emissive Probes in a Partially-Magnetized Plasma

NASA Astrophysics Data System (ADS)

Raitses, Yevgeny; Kraus, Brian

2016-10-01

We compare measurements of plasma potential in a cross-field Penning discharge from two probes: swept biased Langmuir probe and floating emissive probe. The plasma potential was deduced from the first derivative of the Langmuir probe characteristic. In previous studies, the emissive and swept biased probes were placed at the channel exit of a Hall thruster (HT). Measurements showed that the emissive probe floats below the plasma potential, in agreement with conventional theories. However, recent measurements in the Penning discharge indicate a floating potential of a strongly-emitting hot probe above the plasma potential. In both probe applications, xenon plasmas have magnetized electrons and non-magnetized ions with similar plasma densities (1010 - 1011 cm-3) . Though their electron temperatures differ by an order of magnitude (Penning 5 eV, HT 50 eV), this difference cannot explain the difference in measurement values of the hot floating potential because both temperatures are much higher than the emitting wire. In this work, we investigate how the ion velocity and other plasma parameters affect this discrepancy between probe measurements of the plasma potential. This work was supported by DOE contract DE-AC02-09CH11466.

Child-Langmuir flow with periodically varying anode voltage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rokhlenko, A.

Using the Lagrangian technique, we study settled Child-Langmuir flows in a one dimensional planar diodes whose anode voltages periodically vary around given positive values. Our goal is to find analytically if the average currents in these systems can exceed the famous Child-Langmuir limit found for the stationary current a long time ago. The main result of our study is that in a periodic quasi-stationary regime the average current can be larger than the Child-Langmuir maximum even by 50% compared with its adiabatic average value. The cathode current in this case has the form of rectangular pulses which are formed bymore » a very special triangular voltage modulation. This regime, i.e., periodicity, shape of pulses, and their amplitude, needs to be carefully chosen for the best performance.« less

Dichromatic Langmuir waves in degenerate quantum plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dubinov, A. E., E-mail: dubinov-ae@yandex.ru; Kitayev, I. N.

2015-06-15

Langmuir waves in fully degenerate quantum plasma are considered. It is shown that, in the linear approximation, Langmuir waves are always dichromatic. The low-frequency component of the waves corresponds to classical Langmuir waves, while the high-frequency component, to free-electron quantum oscillations. The nonlinear problem on the profile of dichromatic Langmuir waves is solved. Solutions in the form of a superposition of waves and in the form of beatings of its components are obtained.

Investigating the role of hydrogen in silicon deposition using an energy-resolved mass spectrometer and a Langmuir probe in an Ar/H{sub 2} radio frequency magnetron discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mensah, S. L.; Naseem, Hameed H.; Abu-Safe, Husam

2012-07-15

The plasma parameters and ion energy distributions (IED) of the dominant species in an Ar-H{sub 2} discharge are investigated with an energy resolved mass spectrometer and a Langmuir probe. The plasmas are generated in a conventional magnetron chamber powered at 150 W, 13.56 MHz at hydrogen flow rates ranging from 0 to 25 sccm with a fixed argon gas flow rate of 15 sccm. Various H{sub n}{sup +}, SiH{sub n}{sup +}, SiH{sub n} fragments (with n = 1, 2, 3) together with Ar{sup +} and ArH{sup +} species are detected in the discharge. The most important species for the filmmore » deposition is SiH{sub n} (with n = 0, 1, 2). H fragments affect the hydrogen content in the material. The flux of Ar{sup +} decreases and the flux of ArH{sup +} increases when the hydrogen flow rate is increased; however, both fluxes saturate at hydrogen flow rates above 15 sccm. Electron density, n{sub e}, electron energy, T{sub e}, and ion density, n{sub i}, are estimated from the Langmuir probe data. T{sub e} is below 1.2 eV at hydrogen flow rates below 8 sccm, and about 2 eV at flow rates above 8 sccm. n{sub e} and n{sub i} decrease with increased hydrogen flow but the ratio of n{sub i} to n{sub e} increases. The formation of H{sup +} ions with energies above 36 eV and electrons with energies greater than 2 eV contributes to the decrease in hydrogen content at hydrogen flow rates above 8 sccm. Analysis of the IEDs indicates an inter-dependence of the species and their contribution to the thin film growth and properties.« less

An analytical model for floating probes in AC plasma and its application to double probes for high density, high power RF discharges

NASA Astrophysics Data System (ADS)

Caneses, Juan Francisco; Blackwell, Boyd; Plasma Research Laboratory Team

2013-10-01

In this work we provide an analytical model that allows one to quantitatively assess the RF compensation performance and suitability of the double probe technique for use in RF generated plasma. The model is based in the theory of the self-bias effect as described in Braithwaite's work, which we extend to include the time resolved behavior of floating probes. We provide experimental verification for this model and show that the theory of transient RF self-bias probes and harmonic current detection probes are limiting cases of this extended model. Furthermore, the model shows that the RF compensation is solely dependent on the sheath impedance, the probe's stray capacitance to ground and RF frequency. In addition, we use these results to implement a double probe system for use in high density helicon plasma where heat loads could potentially damage the intricate components in an RF compensating circuit. Finally we use this model to (1) recommend ways to extend the operational regime of double probes where the plasma conditions would render them unsuitable and to (2) comment on the use of this model to aid design of RF compensated Langmuir probes.

Periodic collapse and long-time evolution of strong Langmuir turbulence

NASA Astrophysics Data System (ADS)

Cheung, P. Y.; Wong, A. Y.

1985-10-01

Experimental measurements on the long-time evolution of strong Langmuir turbulence in a beam-plasma system reveal a picture of periodic, short bursts of Langmuir wave collapse instead of the existence of long-lived solitons. The remnants of density cavities from burnout cavitons are observed to curtail wave growth periodically, creating time intervals of low wave activity between successive cycles of wave collapse, and establishing three regimes of wave evolution.

Measurement and analysis of electron-neutral collision frequency in the calibrated cutoff probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

You, K. H.; Seo, B. H.; Kim, J. H.

2016-03-15

As collisions between electrons and neutral particles constitute one of the most representative physical phenomena in weakly ionized plasma, the electron-neutral (e-n) collision frequency is a very important plasma parameter as regards understanding the physics of this material. In this paper, we measured the e-n collision frequency in the plasma using a calibrated cutoff-probe. A highly accurate reactance spectrum of the plasma/cutoff-probe system, which is expected based on previous cutoff-probe circuit simulations [Kim et al., Appl. Phys. Lett. 99, 131502 (2011)], is obtained using the calibrated cutoff-probe method, and the e-n collision frequency is calculated based on the cutoff-probe circuitmore » model together with the high-frequency conductance model. The measured e-n collision frequency (by the calibrated cutoff-probe method) is compared and analyzed with that obtained using a Langmuir probe, with the latter being calculated from the measured electron-energy distribution functions, in wide range of gas pressure.« less

A Multi-ring Ionospheric Plasma Probe

NASA Technical Reports Server (NTRS)

Sheldon, J. W.

1972-01-01

An ionospheric plasma probe was constructed which consists of a long cylinder with the end facing the flow closed by an end plate made up of multiple annular rings and a center disk. A theoretical argument is given which yields the plasma potential and electron temperature in terms of known plasma parameters and the currents to the various rings of the end plate. This probe was successfully operated in an ionospheric flow simulation facility and the resulting plasma potential is in excellent agreement with the traditional Langmuir analysis (1.22 volts).

Influence of the liquid crystal behaviour on the Langmuir and Langmuir-Blodgett film supramolecular architecture of an ionic liquid crystal.

PubMed

Pérez-Gregorio, Víctor; Giner, Ignacio; López, M Carmen; Gascón, Ignacio; Cavero, Emma; Giménez, Raquel

2012-06-01

A new luminescent ionic liquid crystal, called Ipz-2, has been synthesised and its mesophase behaviour and also at the air-liquid interface has been studied and compared with Ipz, another ionic pyrazole derivative, with a similar molecular structure, previously studied. The X-ray diffraction pattern shows that Ipz-2 exhibits hexagonal columnar mesomorphism, while Ipz adopts lamellar mesophases. Langmuir films of both compounds are flat and homogeneous at large areas per molecule, but create different supramolecular structures under further compression. Ipz-2 Langmuir films have been transferred onto solid substrates, and Atomic Force Microscopy (AFM) images of the Langmuir-Blodgett films have shown that large columnar structures hundreds of nm in diameter are formed on top of the initial monolayer, in contrast with well-defined trilayer LB films obtained for Ipz. Our results show that Ipz-2 has a tendency to stack in columnar arrangements both in liquid crystalline bulk and in Langmuir and Langmuir-Blodgett films. Copyright © 2012 Elsevier Inc. All rights reserved.

Outer planet entry probe system study. Volume 4: Common Saturn/Uranus probe studies

NASA Technical Reports Server (NTRS)

1973-01-01

Results are summarized of a common scientific probe study to explore the atmospheres of Saturn and Uranus. This was a three-month follow-on effort to the Outer Planet Entry Probe System study. The report presents: (1) a summary, conclusions and recommendations of this study, (2) parametric analysis conducted to support the two system definitions, (3) common Saturn/Uranus probe system definition using the Science Advisory Group's exploratory payload and, (4) common Saturn/Uranus probe system definition using an expanded science complement. Each of the probe system definitions consists of detailed discussions of the mission, science, system and subsystems including telecommunications, data handling, power, pyrotechnics, attitude control, structures, propulsion, thermal control and probe-to-spacecraft integration. References are made to the contents of the first three volumes where it is feasible to do so.

Statistical models of global Langmuir mixing

NASA Astrophysics Data System (ADS)

Li, Qing; Fox-Kemper, Baylor; Breivik, Øyvind; Webb, Adrean

2017-05-01

The effects of Langmuir mixing on the surface ocean mixing may be parameterized by applying an enhancement factor which depends on wave, wind, and ocean state to the turbulent velocity scale in the K-Profile Parameterization. Diagnosing the appropriate enhancement factor online in global climate simulations is readily achieved by coupling with a prognostic wave model, but with significant computational and code development expenses. In this paper, two alternatives that do not require a prognostic wave model, (i) a monthly mean enhancement factor climatology, and (ii) an approximation to the enhancement factor based on the empirical wave spectra, are explored and tested in a global climate model. Both appear to reproduce the Langmuir mixing effects as estimated using a prognostic wave model, with nearly identical and substantial improvements in the simulated mixed layer depth and intermediate water ventilation over control simulations, but significantly less computational cost. Simpler approaches, such as ignoring Langmuir mixing altogether or setting a globally constant Langmuir number, are found to be deficient. Thus, the consequences of Stokes depth and misaligned wind and waves are important.

The multipole resonance probe: characterization of a prototype

NASA Astrophysics Data System (ADS)

Lapke, Martin; Oberrath, Jens; Schulz, Christian; Storch, Robert; Styrnoll, Tim; Zietz, Christian; Awakowicz, Peter; Brinkmann, Ralf Peter; Musch, Thomas; Mussenbrock, Thomas; Rolfes, Ilona

2011-08-01

The multipole resonance probe (MRP) was recently proposed as an economical and industry compatible plasma diagnostic device (Lapke et al 2008 Appl. Phys. Lett. 93 051502). This communication reports the experimental characterization of a first MRP prototype in an inductively coupled argon/nitrogen plasma at 10 Pa. The behavior of the device follows the predictions of both an analytical model and a numerical simulation. The obtained electron densities are in excellent agreement with the results of Langmuir probe measurements.

Limitations on the upconversion of ion sound to Langmuir turbulence

NASA Technical Reports Server (NTRS)

Vlahos, L.; Papadopoulos, K.

1982-01-01

The weak turbulence theory of Tsytovich, Stenflo and Wilhelmsson (1981) for evaluation of the nonlinear transfer of ion acoustic waves to Langmuir waves is shown to be limited in its region of validity to the level of ion acoustic waves. It is also demonstrated that, in applying the upconversion of ion sound to Langmuir waves for electron acceleration, nonlinear scattering should be self-consistently included, with a suppression of the upconversion process resulting. The impossibility of accelerating electrons by such a process for any reasonable physical system is thereby reaffirmed.

Bunker probe: A plasma potential probe almost insensitive to its orientation with the magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Costea, S., E-mail: stefan.costea@uibk.ac.at; Schneider, B. S.; Schrittwieser, R.

Due to their ability to suppress a large part of the electron current and thus measuring directly the plasma potential, ion sensitive probes have begun to be widely tested and used in fusion devices. For these probes to work, almost perfect alignment with the total magnetic field is necessary. This condition cannot always be fulfilled due to the curvature of magnetic fields, complex magnetic structure, or magnetic field reconnection. In this perspective, we have developed a plasma potential probe (named Bunker probe) based on the principle of the ion sensitive probe but almost insensitive to its orientation with the totalmore » magnetic field. Therefore it can be used to measure the plasma potential inside fusion devices, especially in regions with complex magnetic field topology. Experimental results are presented and compared with Ball-Pen probe measurements taken under identical conditions. We have observed that the floating potential of the Bunker probe is indeed little affected by its orientation with the magnetic field for angles ranging from 90° to 30°, in contrast to the Ball-Pen probe whose floating potential decreases towards that of a Langmuir probe if not properly aligned with the magnetic field.« less

Mass Spectrometric and Langmuir Probe Measurements in Inductively Coupled Plasmas in Ar, CHF3/Ar and CHF3/Ar/O2 Mixtures

NASA Technical Reports Server (NTRS)

Kim, J. S.; Rao, M. V. V. S.; Cappelli, M. A.; Sharma, S. P.; Meyyappan, M.; Arnold, Jim (Technical Monitor)

2000-01-01

Absolute fluxes and energy distributions of ions in inductively coupled plasmas of Ar, CHF3/Ar, and CHF3/Ar/O2 have been measured. These plasmas were generated in a Gaseous Electronics Conference (GEC) cell modified for inductive coupling at pressures 10-50 mTorr and 100-300 W of 13.56 MHz radio frequency (RF) power in various feedgas mixtures. In pure Ar plasmas, the Ar(+) flux increases linearly with pressure as well as RF-power. Total ion flux in CHF3 mixtures decreases with increase in pressure and also CHF3 concentration. Relative ion fluxes observed in the present studies are analyzed with the help of available cross sections for electron impact ionization and charge-exchange ion-molecule reactions. Measurements of plasma potential, electron and ion number densities, electron energy distribution function, and mean electron energy have also been made in the center of the plasma with a RF compensated Langmuir probe. Plasma potential values are compared with the mean ion energies determined from the measured ion energy distributions and are consistent. Electron temperature, plasma potential, and mean ion energy vary inversely with pressure, but increase with CHF3 content in the mixture.

Understanding the dimensional and mechanical properties of coastal Langmuir Circulations

NASA Astrophysics Data System (ADS)

Shrestha, Kalyan; Kuehl, Joseph; Anderson, William

2017-11-01

Non-linear interaction of surface waves and wind-driven shear instability in the upper ocean mixed layer form counter-rotating vortical structures called Langmuir Circulations. This oceanic microscale turbulence is one of the key contributors of mixing and vertical transport in the upper ocean mixed layer. Langmuir turbulence in the open (deep) ocean has already been the topic of a large research effort. However, coastal Langmuir cells are distinctly different from Langmuir cells in open-ocean regions, where additional bottom-boundary layer shear alters the kinematic properties of Langmuir cells. For this study, we have conducted a wide-ranging numerical study (solving the grid-filtered Craik-Leibovich equations) of coastal Langmuir turbulence, assessing which parameters affect Langmuir cells and defining the parametric hierarchy. The Stokes profile (aggregate velocity due to orbital wave motion) is functionally dependent on Stokes drift velocity and wavenumber of the surface waves. We explain that these parameters, which correspond to the environmental forcing variables, control the horizontal and vertical length scales of Langmuir cell respectively. This result is important in understanding the transport and dispersion of materials in the upper mixed layer of coastal ocean. We argue that wind stress is a parameter governing the strength of Langmuir cells.

Theory for low-frequency modulated Langmuir wave packets

NASA Technical Reports Server (NTRS)

Cairns, Iver H.; Robinson, P. A.

1992-01-01

Langmuir wave packets with low frequency modulations (or beats) observed in the Jovian foreshock are argued to be direct evidence for the Langmuir wave decay L yields L-prime + S. In this decay, 'pump' Langmuir waves L, driven by an electron beam, produce backscattered product Langmuir waves L-prime and ion sound waves S. The L and L-prime waves beat at the frequency and wavevector of the S waves, thereby modulating the wave packets. Beam speeds calculated using the modulated Jovian wave packets (1) are reasonable, at 4-10 times the electron thermal speed, (2) are consistent with theoretical limits on the decay process, and (3) decrease with increasing foreshock depth, as expected theoretically. These results strongly support the theory. The modulation depth of some wave packets suggests saturation by the decay L yields L-prime + S. Applications to modulated Langmuir packets in the Venusian and terrestrial foreshocks and in a type III radio source are proposed.

Shape modeling with family of Pearson distributions: Langmuir waves

NASA Astrophysics Data System (ADS)

Vidojevic, Sonja

2014-10-01

Two major effects of Langmuir wave electric field influence on spectral line shapes are appearance of depressions shifted from unperturbed line and an additional dynamical line broadening. More realistic and accurate models of Langmuir waves are needed to study these effects with more confidence. In this article we present distribution shapes of a high-quality data set of Langmuir waves electric field observed by the WIND satellite. Using well developed numerical techniques, the distributions of the empirical measurements are modeled by family of Pearson distributions. The results suggest that the existing theoretical models of energy conversion between an electron beam and surrounding plasma is more complex. If the processes of the Langmuir wave generation are better understood, the influence of Langmuir waves on spectral line shapes could be modeled better.

Langmuir and Langmuir-Blodgett films of multifunctional, amphiphilic polyethers with cholesterol moieties.

PubMed

Reuter, Sascha; Hofmann, Anna M; Busse, Karsten; Frey, Holger; Kressler, Jörg

2011-03-01

Langmuir films of multifunctional, hydrophilic polyethers containing a hydrophobic cholesterol group (Ch) were studied by surface pressure-mean molecular area (π-mmA) measurements and Brewster angle microscopy (BAM). The polyethers were either homopolymers or diblock copolymers of linear poly(glycerol) (lPG), linear poly(glyceryl glycidyl ether) (lPGG), linear poly(ethylene glycol) (lPEG), or hyperbranched poly(glycerol) (hbPG). Surface pressure measurements revealed that the homopolymers lPG and hbPG did not stay at the water surface after spreading and solvent evaporation, in contrast to lPEG. Because of the incorporation of the Ch group in the polymer structure, stable Langmuir films were formed by Ch-lPG(n), Ch-lPGG(n), and Ch-hbPG(n). The Ch-hbPG(n), Ch-lPEG(n), Ch-lPEG(n)-b-lPG(m), Ch-lPEG(n)-b-lPGG(m), and Ch-lPEG(n)-b-hbPG(m) systems showed an extended plateau region assigned to a phase transition involving the Ch groups. Typical hierarchically ordered morphologies of the LB films on hydrophilic substrates were observed for all Ch-initiated polymers. All LB films showed that Ch of the Ch-initiated homopolymers is able to crystallize. This strong tendency of self-aggregation then triggers further dewetting effects of the respective polyether entities. Fingerlike morphologies are observed for Ch-lPEG(69), since the lPEG(69) entity is able to undergo crystallization after transfer onto the silicon substrate.

Zero voltage mass spectrometry probes and systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cooks, Robert Graham; Wleklinski, Michael Stanley; Bag, Soumabha

The invention generally relates to zero volt mass spectrometry probes and systems. In certain embodiments, the invention provides a system including a mass spectrometry probe including a porous material, and a mass spectrometer (bench-top or miniature mass spectrometer). The system operates without an application of voltage to the probe. In certain embodiments, the probe is oriented such that a distal end faces an inlet of the mass spectrometer. In other embodiments, the distal end of the probe is 5 mm or less from an inlet of the mass spectrometer.

Diagnosing pure-electron plasmas with internal particle flux probes.

PubMed

Kremer, J P; Pedersen, T Sunn; Marksteiner, Q; Lefrancois, R G; Hahn, M

2007-01-01

Techniques for measuring local plasma potential, density, and temperature of pure-electron plasmas using emissive and Langmuir probes are described. The plasma potential is measured as the least negative potential at which a hot tungsten filament emits electrons. Temperature is measured, as is commonly done in quasineutral plasmas, through the interpretation of a Langmuir probe current-voltage characteristic. Due to the lack of ion-saturation current, the density must also be measured through the interpretation of this characteristic thereby greatly complicating the measurement. Measurements are further complicated by low densities, low cross field transport rates, and large flows typical of pure-electron plasmas. This article describes the use of these techniques on pure-electron plasmas in the Columbia Non-neutral Torus (CNT) stellarator. Measured values for present baseline experimental parameters in CNT are phi(p)=-200+/-2 V, T(e)=4+/-1 eV, and n(e) on the order of 10(12) m(-3) in the interior.

Development of the STPX Spheromak System

NASA Astrophysics Data System (ADS)

Williams, R. L.; Clark, J.; Weatherford, C. A.

2015-11-01

The progress made in starting up the STPX Spheromak system, which is now installed at the Florida A&M University, is reviewed. Experimental, computational and theoretical activities are underway. The control system for firing the magnetized coaxial plasma gun and for collecting data from the diagnostic probes, based on LabView, is being tested and adapted. Preliminary results of testing the installed magnetic field probes, Langmuir triple probes, cylindrical ion probes, and optical diagnostics will be discussed. Progress in modeling this spheromak using simulation codes, such as NIMROD, will be discussed. Progress in investigating the use of algebraic topology to describe this spheromak will be reported.

Outer planet entry probe system study. Volume 1: Summary

NASA Technical Reports Server (NTRS)

1972-01-01

General mission considerations and science prospectus, which are of a general nature that applies to several or all planetary applications, are presented. Five probe systems are defined: nominal Jupiter probe system, and Jupiter probe-dedicated alternative probe system, Jupiter spacecraft radiation-compatible alternative probe system, Saturn probe system, and Saturn probe applicability for Uranus. Parametric analysis is summarized for mission analysis of a general nature, and then for specific missions to Jupiter, Saturn, Uranus, and Neptune. The program is also discussed from the hardware availability viewpoint and the aspect of commonality.

Neutralizer Characterization of a NEXT Multi-Thruster Array With Electrostatic Probes

NASA Technical Reports Server (NTRS)

Foster, John E.; Patterson, Michael; Pencil, Eric; McEwen, Heather; Diaz, Esther

2006-01-01

Neutralizers in a multi-thruster array configuration were characterized using conventional diagnostics such as peak-to-peak keeper oscillation amplitude as well as unconventional methods which featured the application of electrostatic probes. The response of the array local plasma environment to neutralizer flow rate changes were documented using Langmuir probes and retarding potential analyzers. Such characterization is necessary for system efficiency and stability optimization. Because the local plasma environment was measured in conjunction with the neutralizer characterization, particle fluxes at the array and thus array lifetime impacts associated with neutralizer operating mode could also be investigated. Neutralizer operating condition was documented for a number of multithruster array configurations ranging from three-engines, three-neutralizers to a single engine, one-neutralizer all as a function of neutralizer flow rate.

Improved Estimation of Electron Temperature from Rocket-borne Impedance Probes

NASA Astrophysics Data System (ADS)

Rowland, D. E.; Wolfinger, K.; Stamm, J. D.

2017-12-01

The impedance probe technique is a well known method for determining high accuracy measurements of electron number density in the Earth's ionosphere. We present analysis of impedance probe data from several sounding rockets at low, mid-, and auroral latitudes, including high cadence estimates of the electron temperature, derived from analytical fits to the antenna impedance curves. These estimates compare favorably with independent estimates from Langmuir Probes, but at much higher temporal and spatial resolution, providing a capability to resolve small-scale temperature fluctuations. We also present some considerations for the design of impedance probes, including assessment of the effects of resonance damping due to rocket motion, effects of wake and spin modulation, and aspect angle to the magnetic field.

Effect of clay in controlling the non-fluorescence H-dimeric states of a cationic dye Nile Blue Chloride (NBC) in hybrid Langmuir-Blodgett (LB) film

NASA Astrophysics Data System (ADS)

Debnath, Chandan; Shil, Ashis; Hussain, S. A.; Bhattacharjee, D.

2018-01-01

Present communication reports the effect of amphiphilic matrices and nano-clay platelets on the aggregation properties of a water soluble cationic fluorescent dye Nile Blue Chloride (NBC) in Langmuir-Blodgett (LB) films. In-situ Brewster Angle Microscopic (BAM) studies showed distinct domain structures of complex and hybrid Langmuir monolayer at the air-water interface. UV-vis absorption spectra showed non-fluorescent H-dimeric band in concentrated aqueous solution of NBC and in complex LB film of NBC with stearic acid. By changing various parameters, a great control over H-dimeric states has been achieved in clay incorporated hybrid LB films. These films can act as efficient fluorescence probe.

Photon-assisted Beam Probes for Low Temperature Plasmas and Installation of Neutral Beam Probe in Helimak

NASA Astrophysics Data System (ADS)

Garcia de Gorordo, Alvaro; Hallock, Gary A.; Kandadai, Nirmala

2008-11-01

The Heavy Ion Beam Probe (HIBP) diagnostic has successfully measured the electric potential in a number of major plasma devices in the fusion community. In contrast to a Langmuir probe, the HIBP measures the exact electric potential rather than the floating potential. It is also has the advantage of being a very nonperturbing diagnostic. We propose a new photon-assisted beam probe technique that would extend the HIBP type of diagnostics into the low temperature plasma regime. We expect this method to probe plasmas colder than 10 eV. The novelty of the proposed diagnostic is a VUV laser that ionizes the probing particle. Excimer lasers produce the pulsed VUV radiation needed. The lasers on the market don't have a short enough wavelength too ionize any ion directly and so we calculate the population density of excited states in a NLTE plasma. These new photo-ionization techniques can take an instantaneous one-dimensional potential measurement of a plasma and are ideal for nonmagnitized plasmas where continuous time resolution is not required. Also the status of the Neutral Beam Probe installation on the Helimak experiment will be presented.

Mach Probe Measurements in a Large-Scale Helicon Plasma

NASA Astrophysics Data System (ADS)

Hatch, M. W.; Kelly, R. F.; Fisher, D. M.; Gilmore, M.; Dwyer, R. H.

2017-10-01

A new six-tipped Mach probe, that utilizes a fused-quartz insulator, has been developed and initially tested in the HelCat dual-source plasma device at the University of New Mexico. The new design allows for relatively long duration measurements of parallel and perpendicular flows that suffer less from thermal changes in conductivity and surface build-up seen in previous alumina-insulated designs. Mach probe measurement will be presented in comparison with ongoing laser induced fluorescence (LIF) measurements, previous Mach probe measurements, ExB flow estimates derived from Langmuir probes, and fast-frame CCD camera images, in an effort to better understand previous anomalous ion flow in HelCat. Additionally, Mach probe-LIF comparisons will provide an experimentally obtained Mach probe calibration constant, K, to validate sheath-derived estimates for the weakly magnetized case. Supported by U.S. National Science Foundation Award 1500423.

Transmission X-ray scattering as a probe for complex liquid-surface structures

DOE PAGES

Fukuto, Masafumi; Yang, Lin; Nykypanchuk, Dmytro; ...

2016-01-28

The need for functional materials calls for increasing complexity in self-assembly systems. As a result, the ability to probe both local structure and heterogeneities, such as phase-coexistence and domain morphologies, has become increasingly important to controlling self-assembly processes, including those at liquid surfaces. The traditional X-ray scattering methods for liquid surfaces, such as specular reflectivity and grazing-incidence diffraction, are not well suited to spatially resolving lateral heterogeneities due to large illuminated footprint. A possible alternative approach is to use scanning transmission X-ray scattering to simultaneously probe local intermolecular structures and heterogeneous domain morphologies on liquid surfaces. To test the feasibilitymore » of this approach, transmission small- and wide-angle X-ray scattering (TSAXS/TWAXS) studies of Langmuir films formed on water meniscus against a vertically immersed hydrophilic Si substrate were recently carried out. First-order diffraction rings were observed in TSAXS patterns from a monolayer of hexagonally packed gold nanoparticles and in TWAXS patterns from a monolayer of fluorinated fatty acids, both as a Langmuir monolayer on water meniscus and as a Langmuir–Blodgett monolayer on the substrate. The patterns taken at multiple spots have been analyzed to extract the shape of the meniscus surface and the ordered-monolayer coverage as a function of spot position. These results, together with continual improvement in the brightness and spot size of X-ray beams available at synchrotron facilities, support the possibility of using scanning-probe TSAXS/TWAXS to characterize heterogeneous structures at liquid surfaces.« less

Landau damping of Langmuir twisted waves with kappa distributed electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arshad, Kashif, E-mail: kashif.arshad.butt@gmail.com; Aman-ur-Rehman; Mahmood, Shahzad

2015-11-15

The kinetic theory of Landau damping of Langmuir twisted modes is investigated in the presence of orbital angular momentum of the helical (twisted) electric field in plasmas with kappa distributed electrons. The perturbed distribution function and helical electric field are considered to be decomposed by Laguerre-Gaussian mode function defined in cylindrical geometry. The Vlasov-Poisson equation is obtained and solved analytically to obtain the weak damping rates of the Langmuir twisted waves in a nonthermal plasma. The strong damping effects of the Langmuir twisted waves at wavelengths approaching Debye length are also obtained by using an exact numerical method and aremore » illustrated graphically. The damping rates of the planar Langmuir waves are found to be larger than the twisted Langmuir waves in plasmas which shows opposite behavior as depicted in Fig. 3 by J. T. Mendoça [Phys. Plasmas 19, 112113 (2012)].« less

Reproducibility of the cutoff probe for the measurement of electron density

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, D. W.; Oh, W. Y.; You, S. J., E-mail: sjyou@cnu.ac.kr

2016-06-15

Since a plasma processing control based on plasma diagnostics attracted considerable attention in industry, the reproducibility of the diagnostics using in this application has become a great interest. Because the cutoff probe is one of the potential candidates for this application, knowing the reproducibility of the cutoff probe measurement becomes quit important in the cutoff probe application research. To test the reproducibility of the cutoff probe measurement, in this paper, a comparative study among the different cutoff probe measurements was performed. The comparative study revealed remarkable result: the cutoff probe has a great reproducibility for the electron density measurement, i.e.,more » there are little differences among measurements by different probes made by different experimenters. The discussion including the reason for the result was addressed via this paper by using a basic measurement principle of cutoff probe and a comparative experiment with Langmuir probe.« less

Caviton dynamics in strong Langmuir turbulence

NASA Astrophysics Data System (ADS)

Dubois, Don; Rose, Harvey A.; Russell, David

Recent studies based on long time computer simulations of Langmuir turbulence as described by Zakharov's model will be reviewed. These show that for strong to moderate ion sound samping the turbulent energy is dominantly in nonlinear caviton excitations which are localized in space and time. A local caviton model will be presented which accounts for the nucleation collapse burnout cycles of individual cavitons as well as their space-time correlations. This model is in detailed agreement with many features of the electron density fluctuation spectra in the ionosphere modified by powerful HF waves as measured by incoherent scatter radar. Recently such observations have verified a prediction of the theory that free Langmuir waves are emitted in the caviton collapse process. These observations and theoretical considerations also strongly imply that cavitons in the heated ionosphere, under certain conditions, evolve to states in which they are ordered in space and time. The sensitivity of the high frequency Langmuir field dynamics to the low frequency ion density fluctuations and the related caviton nucleation process will be discussed.

Caviton dynamics in strong Langmuir turbulence

NASA Astrophysics Data System (ADS)

DuBois, Don; Rose, Harvey A.; Russell, David

1990-01-01

Recent studies based on long time computer simulations of Langmuir turbulence as described by Zakharov's model will be reviewed. These show that for strong to moderate ion sound damping the turbulent energy is dominantly in non-linear "caviton" excitations which are localized in space and time. A local caviton model will be presented which accounts for the nucleation-collapse-burnout cycles of individual cavitons as well as their space-time correlations. This model is in detailed agreement with many features of the electron density fluctuation spectra in the ionosphere modified by powerful HF waves as measured by incoherent scatter radar. Recently such observations have verified a prediction of the theory that "free" Langmuir waves are emitted in the caviton collapse process. These observations and theoretical considerations also strongly imply that cavitons in the heated ionosphere, under certain conditions, evolve to states in which they are ordered in space and time. The sensitivity of the high frequency Langmuir field dynamics to the low frequency ion density fluctuations and the related caviton nucleation process will be discussed.

Description of two-metal biosorption equilibria by Langmuir-type models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chong, K.H.; Volesky, B.

A biosorbent prepared from Ascophyllum nodosum seaweed biomass, FCAN2, was examined for its sorption capacity. Equilibrium batch sorption studies were performed using two-metal systems containing either (Cu+Zn), (Cu+Cd), or (Zn+Cd). In the evaluation of the two-metal sorption system performance, simple isotherm curves had to be replaced by three-dimensional sorption isotherm surfaces. In order to describe the isotherm surfaces mathematically, three Langmuir-type models were evaluated. The apparent one-parameter Langmuir constant (b) was used to quantify FCAN2 ``affinity`` for one metal in the presence of another one. The uptake of Zn decreased drastically when Cu of Cd were present. The uptake ofmore » Cd was much more sensitive to the presence of Cu than to that of Zn. The presence of Cd and Zn alter the ``affinity`` of FCAN2 for Cu the least at high Cu equilibrium concentrations. The mathematical model of the two-metal sorption system enabled quantitative estimation of one-metal (bio)sorption inhibition due to the influence of a second metal.« less

Fiberoptic probe and system for spectral measurements

DOEpatents

Dai, Sheng; Young, Jack P.

1998-01-01

A fused fiberoptic probe, a system, method and embodiments thereof for conducting spectral measurements are disclosed. The fused fiberoptic probe comprises a probe tip having a specific geometrical configuration, an exciting optical fiber and at least one collection optical fiber fused within a housing, preferrably silica. The specific geometrical configurations in which the probe tip can be shaped include a slanted probe tip with an angle greater than 0.degree., an inverted cone-shaped probe tip, and a lens head.

Fiberoptic probe and system for spectral measurements

DOEpatents

Dai, S.; Young, J.P.

1998-10-13

A fused fiberoptic probe, a system, method and embodiments thereof for conducting spectral measurements are disclosed. The fused fiberoptic probe comprises a probe tip having a specific geometrical configuration, an exciting optical fiber and at least one collection optical fiber fused within a housing, preferably silica. The specific geometrical configurations in which the probe tip can be shaped include a slanted probe tip with an angle greater than 0{degree}, an inverted cone-shaped probe tip, and a lens head. 12 figs.

Studies on probe measurements in presence of magnetic field in dust containing hydrogen plasma

NASA Astrophysics Data System (ADS)

Kalita, Deiji; Kakati, Bharat; Kausik, Siddhartha Sankar; Saikia, Bipul Kumar; Bandyopadhyay, Mainak

2018-04-01

The accuracy of plasma parameters measured by Langmuir probe in presence of magnetic field is studied in our present work. It is observed that the ratio of electron to ion saturation current shows almost identical behavior with that of unmagnetized hydrogen plasma when r L > 10 r p (here r L : Larmor radius and r p : probe radius). At magnetic field strength, B = 594 gauss, the electron temperature ( T e ) shows an overestimated value up to 35-40%, whereas at B ≤ 37 gauss, T e shows around ≤10% overestimated value w.r.t. unmagnetized case. A bi-Maxwellian electron energy probability function is observed for entire magnetic field range for both pristine and dust containing hydrogen plasma. The bulk (cold) electron collection by the Langmuir probe is strongly suppressed whereas the higher energetic electron collection remains unaffected in presence of magnetic field. In presence of dust grains, it is found that the low energy electron population decreases even more than the magnetized plasma and the high-energy tail slightly increases compared to the pristine plasma.

Magnetic dipole discharges. II. Cathode and anode spot discharges and probe diagnostics

NASA Astrophysics Data System (ADS)

Stenzel, R. L.; Urrutia, J. M.; Ionita, C.; Schrittwieser, R.

2013-08-01

The high current regime of a magnetron-type discharge has been investigated. The discharge uses a permanent magnet as a cold cathode which emits secondary electrons while the chamber wall or a grounded electrode serves as the anode. As the discharge voltage is increased, the magnet develops cathode spots, which are short duration arcs that provide copious electrons to increase the discharge current dramatically. Short (1 μs), high current (200 A) and high voltage (750 V) discharge pulses are produced in a relaxation instability between the plasma and a charging capacitor. Spots are also observed on a negatively biased plane Langmuir probe. The probe current pulses are as large as those on the magnet, implying that the high discharge current does not depend on the cathode surface area but on the properties of the spots. The fast current pulses produce large inductive voltages, which can reverse the electrical polarity of the magnet and temporarily operate it as an anode. The discharge current may also oscillate at the frequency determined by the charging capacitor and the discharge circuit inductance. Each half cycle of high-current current pulses exhibits a fast (≃10 ns) current rise when a spot is formed. It induces high frequency (10-100 MHz) transients and ringing oscillations in probes and current circuits. Most probes behave like unmatched antennas for the electromagnetic pulses of spot discharges. Examples are shown to distinguish the source of oscillations and some rf characteristics of Langmuir probes.

SUPRATHERMAL SOLAR WIND ELECTRONS AND LANGMUIR TURBULENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Sunjung; Yoon, Peter H.; Choe, G. S.

2016-09-01

The steady-state model recently put forth for the solar wind electron velocity distribution function during quiet time conditions, was originally composed of three population electrons (core, halo, and superhalo) with the core remaining nonresonant with any plasma waves while the halo and superhalo separately maintained steady-state resonance with whistler- and Langmuir-frequency range fluctuations, respectively. However, a recent paper demonstrates that whistler-range fluctuations in fact have no significant contribution. The present paper represents a consummation of the model in that a self-consistent model of the suprathermal electron population, which encompasses both the halo and the superhalo, is constructed solely on themore » basis of the Langmuir fluctuation spectrum. Numerical solutions to steady-state particle and wave kinetic equations are obtained on the basis of an initial trial electron distribution and Langmuir wave spectrum. Such a finding offers a self-consistent explanation for the observed steady-state electron distribution in the solar wind.« less

Terahertz generation by beating two Langmuir waves in a warm and collisional plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiao-Bo; Qiao, Xin; Cheng, Li-Hong

2015-09-15

Terahertz (THz) radiation generated by beating of two Langmuir waves in a warm and collisional plasma is discussed theoretically. The critical angle between the two Langmuir waves and the critical wave-length (wave vector) of Langmuir waves for generating THz radiation are obtained analytically. Furthermore, the maximum radiation energy is obtained. We find that the critical angle, the critical wave-length, and the generated radiation energy strongly depend on plasma temperature and wave-length of the Langmuir waves. That is, the THz radiation generated by beating of two Langmuir waves in a warm and collisional plasma can be controlled by adjusting the plasmamore » temperature and the Langmuir wave-length.« less

Observation of Langmuir Cascade in Single Hot Spot Laser-Plasma Experiments

NASA Astrophysics Data System (ADS)

Johnson, R. P.; Montgomery, D. S.; Fernandez, J. C.; Focia, R. J.

2001-10-01

We present results from the sixth in a series of experiments designed to investigate the interaction of a single laser hot spot, or speckle, with a preformed, quasi-homogeneous plasma. The experiments were conducted at the Los Alamos National Laboratory (LANL) using the TRIDENT laser. Thomson scattering was used to probe plasma waves driven by stimulated Raman scattering (SRS) and structure was observed in the scattered spectra consistent with multiple steps of the Langmuir decay instability (LDI).(R. J. Focia et al., PSFC Report PSFC/JA-01-17, M.I.T.) The experimental setup is described. The Thomson scattered spectra, resolved in both wavelength versus time and wavelength versus wave vector (effectively ω vs. k), are well-correlated with measurements of the backscattered SRS light and calculations based on linear theory. Parameter regimes are identified in which the LDI cascade exists.

Observed Coupling Between the International Space Station PCU Plasma and a FPMU Langmuir Probe Facilitated by the Geomagnetic Field

NASA Technical Reports Server (NTRS)

Hartman, William; Koontz, Steven L.

2010-01-01

Electrical charging of the International Space Station (ISS) is a matter of serious concern resulting from the possibility of vehicle arcing and electrical shock hazard to crew during extravehicular activity (EVA). A Plasma Contactor Unit (PCU) was developed and integrated into ISS in order to control the ISS floating potential, thereby, minimize vehicle charging and associated hazards. One of the principle factors affecting ISS electrical charging is the ionosphere plasma state (i.e., electron temperature and density). To support ISS electrical charging studies a Floating Potential Monitoring Unit (FPMU) is also integrated into ISS in order to measure the ionosphere properties using Langmuir probes (LP). The FPMU was located on the Starboard side of ISS. The PCU is located near the center of ISS with its plasma exhaust pointed to port. From its integration on ISS in 2006 through November of 2009, the FPMU data exhibited nominal characteristics during PCU operation. On November 21, 2009 the FPMU was relocated from the Starboard location to a new Port location. After relocation significant enhanced noise was observed in both the LP current-voltage sweeps and the derived electron temperature data. The enhanced noise only occurred when the PCU was in discharge and at unique and repeatable locations of the ISS orbit. The cause of this enhanced noise was investigated. It was found that there is coupling occurring between the PCU plasma and the FPMU LP. In this paper we shall 1) present the on-orbit data and the presence of enhanced noise, 2) demonstrate that the coupling of the PCU plasma and the FPMU measurements is geomagnetically organized, 3) show that coupling of the PCU plasma and the FPMU is primarily due to and driven by particle-wave interaction and 4) show that the ionosphere conditions are adequate for Alfven waves to be generated by the PCU plasma.

Langmuir-Blodgett Films of Supported Polyester Dendrimers

PubMed Central

Redón, Rocío; Carreón-Castro, M. Pilar; Mendoza-Martínez, F. J.

2012-01-01

Amphiphiles with a dendritic structure are attractive materials as they combine the features of dendrimers with the self-assembling properties and interfacial behavior of water-air affinities. We have synthesized three generations of polyester dendrimers and studied their interfacial properties on the Langmuir films. The behavior obtained was, as a rule, the lowest generation dendrimers behaving like traditional amphiphiles and the larger molecules presenting complicated isotherms. The Langmuir films of these compounds have been characterized by their surface pressure versus molecular area (π/A) and Brewster angle microscopy (BAM) observations. PMID:24052855

Experimental validation of the Helmoltz equation for the surface potential of Langmuir monolayers

NASA Astrophysics Data System (ADS)

El Abed, Abdel I.

2009-10-01

We show in this paper that monolayers of the nonhydrophilic F8H18 semifluorinated n -alkane constitute when spread on the hydrophobic top of an alamethicin Langmuir monolayer, a very good experimental system in order to check the validity of Helmoltz equation. This system allows for a good agreement between measured and calculated surface potentials of unionized Langmuir monolayers. We show also that the relative dielectric constant of the F8H18 monolayer does not vary upon compression of the monolayer, the measured 2.9 value is in a very good agreement with literature data. We attribute this behavior to the self-aggregation of F8H18 molecules in nanosized circular domains whose size remains constant upon compression as shown by atomic force microscopy.

Optical second-harmonic-generation probe of two-dimensional ferroelectricity.

PubMed

Aktsipetrov, O A; Misuryaev, T V; Murzina, T V; Blinov, L M; Fridkin, V M; Palto, S P

2000-03-15

Optical second-harmonic generation (SHG) is used as a noninvasive probe of two-dimensional (2D) ferroelectricity in Langmuir-Blodgett (LB) films of the copolymer vinylidene fluoride with trifluoroethylene. The surface 2D ferroelectric-paraelectric phase transition in the topmost layer of the LB films and a thickness-independent (almost 2D) transition in the bulk of these films are observed in temperature studies of SHG.

A Sixth-Form Teaching Unit on the Langmuir Adsorption Isotherm

ERIC Educational Resources Information Center

Walkley, G. H.

1973-01-01

Presents a teaching unit on the Langmuir absorption isotherm suitable for advanced secondary school chemistry classes. Describes the experimental investigation of the isothermal adsorption of sulfur dioxide on charcoal, and discusses the derivation of the Langmuir equation and some applications. (JR)

Identification of Langmuir wave turbulence-supercontinuum transition by application of von Neumann entropy

NASA Astrophysics Data System (ADS)

Kawamori, Eiichirou

2017-09-01

A transition from Langmuir wave turbulence (LWT) to coherent Langmuir wave supercontinuum (LWSC) is identified in one-dimensional particle-in-cell simulations as the emergence of a broad frequency band showing significant temporal coherence of a wave field accompanied by a decrease in the von Neumann entropy of classical wave fields. The concept of the von Neumann entropy is utilized for evaluation of the phase-randomizing degree of the classical wave fields, together with introduction of the density matrix of the wave fields. The transition from LWT to LWSC takes place when the energy per one plasmon (one wave quantum) exceeds a certain threshold. The coherent nature, which Langmuir wave systems acquire through the transition, is created by four wave mixings of the plasmons. The emergence of temporal coherence and the decrease in the phase randomization are considered as the development of long-range order and spontaneous symmetry breaking, respectively, indicating that the LWT-LWSC transition is a second order phase transition phenomenon.

The Floating Potential Probe (FPP) for ISS: Operations and Initial Results

NASA Technical Reports Server (NTRS)

Ferguson, Dale C.; Hillard, G. Barry; Morton, Thomas L.

2001-01-01

In this paper we report early results from the Floating Potential Probe (FPP) recently installed on the International Space Station (ISS). The data show that FPP properly measures the electrical potential of ISS structure with respect to the plasma it is flying through. FPP Langmuir probe data seem to give accurate measurements of the ambient plasma density, and are generally consistent with the IRI-90 model. FPP data are used to judge the performance of the ISS Plasma Contacting Units (PCUs), and to evaluate the extent of ISS charging in the absence of the PCUs.

Dynamics of cavitons in strong Langmuir turbulence

NASA Astrophysics Data System (ADS)

Dubois, D. F.; Rose, Harvey A.; Russell, David

Recent studies of Langmuir turbulence as described by Zakharov's model will be reviewed. For parameters of interest in laser-plasma experiments and for ionospheric hf heating experiments a significant fraction of the turbulent energy is in nonlinear caviton excitations which are localized in space and time. A local caviton model will be presented which accounts for the nucleation-collapse-burnout cycles of individual cavitons as well as their space-time correlations. This model is in detailed agreement with many features of the electron density fluctuation spectra in the ionosphere modified by powerful hf waves as measured by incoherent scatter radar. Recently such observations have verified a prediction of the theory that free Langmuir waves are emitted in the caviton collapse process. Observations and theoretical considerations also imply that when the pump frequency is slightly lower than the ambient electron plasma frequency cavitons may evolve to states in which they are ordered in space and time. The sensitivity of the high frequency Langmuir field dynamics to the low frequency ion density fluctuations and the related caviton nucleation process will be discussed.

Process Diagnostics and Monitoring Using the Multipole Resonance Probe (MRP)

NASA Astrophysics Data System (ADS)

Harhausen, J.; Awakowicz, P.; Brinkmann, R. P.; Foest, R.; Lapke, M.; Musch, T.; Mussenbrock, T.; Oberrath, J.; Ohl, A.; Rolfes, I.; Schulz, Ch.; Storch, R.; Styrnoll, T.

2011-10-01

In this contribution we present the application of the MRP in an industrial plasma ion assisted deposition (PIAD) chamber (Leybold optics SYRUS-pro). The MRP is a novel plasma diagnostic which is suitable for an industrial environment - which means that the proposed method is robust, calibration free, and economical, and can be used for ideal and reactive plasmas alike. In order to employ the MRP as process diagnostics we mounted the probe on a manipulator to obtain spatially resolved information on the electron density and temperature. As monitoring tool the MRP is installed at a fixed position. Even during the deposition process it provides stable measurement results while other diagnostic methods, e.g. the Langmuir probe, may suffer from dielectric coatings. In this contribution we present the application of the MRP in an industrial plasma ion assisted deposition (PIAD) chamber (Leybold optics SYRUS-pro). The MRP is a novel plasma diagnostic which is suitable for an industrial environment - which means that the proposed method is robust, calibration free, and economical, and can be used for ideal and reactive plasmas alike. In order to employ the MRP as process diagnostics we mounted the probe on a manipulator to obtain spatially resolved information on the electron density and temperature. As monitoring tool the MRP is installed at a fixed position. Even during the deposition process it provides stable measurement results while other diagnostic methods, e.g. the Langmuir probe, may suffer from dielectric coatings. Funded by the German Ministry for Education and Research (BMBF, Fkz. 13N10462).

Breaking Waves, Langmuir Circulation and Bubbles in the Mixed Layer

DTIC Science & Technology

1997-09-30

Langmuir circulation, derived from the acoustical imaging and is also in accord with predictions of Li et al., (1995) and Gnanadesikan , (1996), who...Structure of Langmuir Circulation. IUTAM Symposium - Physical Limnology, Broome,Australia, Sept. 10-14, 1995 Gnanadesikan , A., 1996: Mixing driven

MMS Observations of Langmuir Collapse and Emission?

NASA Astrophysics Data System (ADS)

Boardsen, S. A.; Che, H.; Wilder, F. D.; Ergun, R.; Le Contel, O.; Gershman, D. J.; Giles, B. L.; Moore, T. E.; Paterson, W.

2017-12-01

Through the two stream instability, electron beams accelerated by solar flares and nanoflares are believed to be responsible for several types of solar radio bursts observed in the corona and interplanetary medium, including flare-associated coronal Type J, U, and Type III radio bursts, and nanoflare-associated weak coronal type III bursts. However the duration of these radio bursts is several orders of magnitude longer than the linear saturation time of the electron two-stream instability. This discrepancy has been a long-standing puzzle. Recently Che et al. [2017, doi: 10.1073/pnas.1614055114] proposed a mechanism in which the plasma coherent emission is maintained by the cyclic Langmuir collapse. Wave coupling between Langmuir waves and electrostatic whistler waves is the key process necessary to close the feedback loop. In the magnetosphere, electron beams are commonly produced by acceleration processes such as magnetic reconnection, during which both whistlers and Langmuir waves are observed and thus provide possible in-situ observations to test and study the emission process near the acceleration source region. The high spatial and time resolution MMS fields and particle data are used to test aspects of this mechanism. In this presentation, we will present some preliminary results from MMS observations of electron beams near a reconnection region. We investigate, in the regions where the electron beams are observed, the coupling between high frequency Langmuir waves and low frequency electrostatic whistler waves, and the associated electromagnetic emissions, along with other possible specific features predicted by this model.

Traversing probe system

DOEpatents

Mashburn, Douglas N.; Stevens, Richard H.; Woodall, Harold C.

1977-01-01

This invention comprises a rotatable annular probe-positioner which carries at least one radially disposed sensing probe, such as a Pitot tube having a right-angled tip. The positioner can be coaxially and rotatably mounted within a compressor casing or the like and then actuated to orient the sensing probe as required to make measurements at selected stations in the annulus between the positioner and compressor casing. The positioner can be actuated to (a) selectively move the probe along its own axis, (b) adjust the yaw angle of the right-angled probe tip, and (c) revolve the probe about the axis common to the positioner and casing. A cam plate engages a cam-follower portion of the probe and normally rotates with the positioner. The positioner includes a first-motor-driven ring gear which effects slidable movement of the probe by rotating the positioner at a time when an external pneumatic cylinder is actuated to engage the cam plate and hold it stationary. When the pneumatic cylinder is not actuated, this ring gear can be driven to revolve the positioner and thus the probe to a desired circumferential location about the above-mentioned common axis. A second motor-driven ring gear included in the positioner can be driven to rotate the probe about its axis, thus adjusting the yaw angle of the probe tip. The positioner can be used in highly corrosive atmosphere, such as gaseous uranium hexafluoride.

Langmuir wave phase-mixing in warm electron-positron-dusty plasmas

NASA Astrophysics Data System (ADS)

Pramanik, Sourav; Maity, Chandan

2018-04-01

An analytical study on nonlinear evolution of Langmuir waves in warm electron-positron-dusty plasmas is presented. The massive dust grains of either positively or negatively charged are assumed to form a fixed charge neutralizing background. A perturbative analysis of the fluid-Maxwell's equations confirms that the excited Langmuir waves phase-mix and eventually break, even at arbitrarily low amplitudes. It is shown that the nature of the dust-charge as well as the amount of dust grains can significantly influence the Langmuir wave phase-mixing process. The phase-mixing time is also found to increase with the temperature.

Surface chemistry of lipid raft and amyloid Aβ (1-40) Langmuir monolayer.

PubMed

Thakur, Garima; Pao, Christine; Micic, Miodrag; Johnson, Sheba; Leblanc, Roger M

2011-10-15

Lipid rafts being rich in cholesterol and sphingolipids are considered to provide ordered lipid environment in the neuronal membranes, where it is hypothesized that the cleavage of amyloid precursor protein (APP) to Aβ (1-40) and Aβ (1-42) takes place. It is highly likely that the interaction of lipid raft components like cholesterol, sphingomylein or GM1 leads to nucleation of Aβ and results in aggregation or accumulation of amyloid plaques. One has investigated surface pressure-area isotherms of the lipid raft and Aβ (1-40) Langmuir monolayer. The compression-decompression cycles and the stability of the lipid raft Langmuir monolayer are crucial parameters for the investigation of interaction of Aβ (1-40) with the lipid raft Langmuir monolayer. It was revealed that GM1 provides instability to the lipid raft Langmuir monolayer. Adsorption of Aβ (1-40) onto the lipid raft Langmuir monolayer containing neutral (POPC) or negatively charged phospholipid (DPPG) was examined. The adsorption isotherms revealed that the concentration of cholesterol was important for adsorption of Aβ (1-40) onto the lipid raft Langmuir monolayer containing POPC whereas for the lipid raft Langmuir monolayer containing DPPG:cholesterol or GM1 did not play any role. In situ UV-vis absorption spectroscopy supported the interpretation of results for the adsorption isotherms. Copyright © 2011 Elsevier B.V. All rights reserved.

Using Weighted Least Squares Regression for Obtaining Langmuir Sorption Constants

USDA-ARS?s Scientific Manuscript database

One of the most commonly used models for describing phosphorus (P) sorption to soils is the Langmuir model. To obtain model parameters, the Langmuir model is fit to measured sorption data using least squares regression. Least squares regression is based on several assumptions including normally dist...

New effects in Langmuir and Langmuir-Blodgett monolayers from fluorescently labelled phospholipids and their possible use for water quality control

NASA Astrophysics Data System (ADS)

Ivanov, G. R.; Geshev, N. I.

2016-02-01

Secondary water contamination poses significant challenges to the sensitivity and selectivity of sensors used for its detection and monitoring. Currently only lab tests can detect these contaminants and by the time this happens the contaminated water has entered the city water supply system. Fluorescent chromophore NitroBenzoxaDiazole (NBD) is very suitable and had been successfully used in biosensor applications due to its high sensitivity to close proximity polarity of the medium. Over the years we have discovered 3 new effects in NBD- labelled phospholipids which can significantly improve the performance of biosensors. The phospholipid matrix provides flexible biocompatible environment for immobilization of selectively reacting enzymes, microorganisms, DNA, immunoagents, whole cells. Use of single layer (3.1 nm thickness) films at the air-water interface (Langmuir films) or deposited on solid support as Langmuir-Blodgett (LB) film gives fast response times for real time monitoring (no slow diffusion processes) and precise molecule ordering and orientation. The first new effect was fluorescence self-quenching in Langmuir and LB films. In the liquid phase films exhibit normal fluorescence. Upon transition to solid phase fluorescence intensity is almost completely self-quenched and fluorescence lifetimes in the nanosecond region decrease 2 times. This is easily measured. Usually large heavy metal atoms quench fluorescence. We observed the opposite new effect when LB film is deposited in the solid phase from a subphase containing heavy metals. The third new effect is the obtaining of nanosized cylinders with bilayer thickness, which remain stable at least for months, when LB monolayer is deposited in the phase coexistence region at thermodynamic equilibrium. This greatly increases reacting surface and sensitivity of possible sensors. Almost all possible optical experimental methods were used for this research. This includes polarized ATR FTIR and polarized UV

Investigating magnetospheric interaction effects on Titan's ionosphere with the Cassini orbiter Ion Neutral Mass Spectrometer, Langmuir Probe and magnetometer observations during targeted flybys

NASA Astrophysics Data System (ADS)

Luhmann, J. G.; Ulusen, D.; Ledvina, S. A.; Mandt, K.; Magee, B.; Waite, J. H.; Westlake, J.; Cravens, T. E.; Robertson, I.; Edberg, N.; Agren, K.; Wahlund, J.-E.; Ma, Y.-J.; Wei, H.; Russell, C. T.; Dougherty, M. K.

2012-06-01

In the ˜6 years since the Cassini spacecraft went into orbit around Saturn in 2004, roughly a dozen Titan flybys have occurred for which the Ion Neutral Mass Spectrometer (INMS) measured that moon's ionospheric density and composition. For these, and for the majority of the ˜60 close flybys probing to altitudes down to ˜950 km, Langmuir Probe electron densities were also obtained. These were all complemented by Cassini magnetometer observations of the magnetic fields affected by the Titan plasma interaction. Titan's ionosphere was expected to differ from those of other unmagnetized planetary bodies because of significant contributions from particle impact due to its magnetospheric environment. However, previous analyses of these data clearly showed the dominance of the solar photon source, with the possible exception of the nightside. This paper describes the collected ionospheric data obtained in the period between Cassini's Saturn Orbit Insertion in 2004 and 2009, and examines some of their basic characteristics with the goal of searching for magnetospheric influences. These influences might include effects on the altitude profiles of impact ionization by magnetospheric particles at the Titan orbit location, or by locally produced pickup ions freshly created in Titan's upper atmosphere. The effects of forces on the ionosphere associated with both the draped and penetrating external magnetic fields might also be discernable. A number of challenges arise in such investigations given both the observed order of magnitude variations in the magnetospheric particle sources and the unsteadiness of the magnetospheric magnetic field and plasma flows at Titan's (˜20Rs (Saturn Radius)) orbit. Transterminator flow of ionospheric plasma from the dayside may also supply some of the nightside ionosphere, complicating determination of the magnetospheric contribution. Moreover, we are limited by the sparse sampling of the ionosphere during the mission as the Titan interaction

Using a biased qubit to probe complex systems

NASA Astrophysics Data System (ADS)

Pollock, Felix A.; Checińska, Agata; Pascazio, Saverio; Modi, Kavan

2016-09-01

Complex mesoscopic systems play increasingly important roles in modern science, from understanding biological functions at the molecular level to designing solid-state information processing devices. The operation of these systems typically depends on their energetic structure, yet probing their energy landscape can be extremely challenging; they have many degrees of freedom, which may be hard to isolate and measure independently. Here, we show that a qubit (a two-level quantum system) with a biased energy splitting can directly probe the spectral properties of a complex system, without knowledge of how they couple. Our work is based on the completely positive and trace-preserving map formalism, which treats any unknown dynamics as a "black-box" process. This black box contains information about the system with which the probe interacts, which we access by measuring the survival probability of the initial state of the probe as function of the energy splitting and the process time. Fourier transforming the results yields the energy spectrum of the complex system. Without making assumptions about the strength or form of its coupling, our probe could determine aspects of a complex molecule's energy landscape as well as, in many cases, test for coherent superposition of its energy eigenstates.

A Robust Definition for the Turbulent Langmuir Number

NASA Astrophysics Data System (ADS)

Christensen, K. H.; Breivik, O.; Sutherland, G.; Belcher, S. E.; Gargett, A.

2016-02-01

The turbulent Langmuir number combines the water side friction velocity and the surface value of the Stokes drift, and is central to parameterizations of mixing by Langmuir turbulence. Making a direct comparison between such parameterizations and observations is difficult since the surface Stokes drift is sensitive to both the spectral tail and the directional spread of the waves. We propose a new definition for the turbulent Langmuir number based on low order moments of the one-dimensional frequency spectrum, hence eliminating most of the uncertainties associated with the diagnostic spectral tail. Comparison is made between the old and the new definitions using both observed and modeled wave spectra. The new definition has a higher variation around the mean and is better at resolving typical oceanic conditions. In addition, it is backwards compatible with the old definition for monochromatic waves, which means that scalings based on large eddy simulations with monochromatic wave forcing are still valid.

Extracting surface diffusion coefficients from batch adsorption measurement data: application of the classic Langmuir kinetics model.

PubMed

Chu, Khim Hoong

2017-11-09

Surface diffusion coefficients may be estimated by fitting solutions of a diffusion model to batch kinetic data. For non-linear systems, a numerical solution of the diffusion model's governing equations is generally required. We report here the application of the classic Langmuir kinetics model to extract surface diffusion coefficients from batch kinetic data. The use of the Langmuir kinetics model in lieu of the conventional surface diffusion model allows derivation of an analytical expression. The parameter estimation procedure requires determining the Langmuir rate coefficient from which the pertinent surface diffusion coefficient is calculated. Surface diffusion coefficients within the 10 -9 to 10 -6  cm 2 /s range obtained by fitting the Langmuir kinetics model to experimental kinetic data taken from the literature are found to be consistent with the corresponding values obtained from the traditional surface diffusion model. The virtue of this simplified parameter estimation method is that it reduces the computational complexity as the analytical expression involves only an algebraic equation in closed form which is easily evaluated by spreadsheet computation.

Fiber-optic temperature probe system for inner body

NASA Astrophysics Data System (ADS)

Liu, Bo; Deng, Xing-Zhong; Cao, Wei; Cheng, Xianping; Xie, Tuqiang; Zhong, Zugen

1991-08-01

The authors have designed a fiber-optic temperature probe system that can quickly insert its probe into bodies to measure temperature. Its thermometer unit has the function of program- controlled zeroing. The single-chip microcomputer is used to control the whole system and process data. The sample system has been tested in a coal furnace.

Observations of mesospheric turbulence by rocket probe and VHF radar, part 2.4A

NASA Astrophysics Data System (ADS)

Royrvik, O.; Smith, L. G.

1984-12-01

Data from the Jicamarca VHF radar and from a Languir probe fine-structure on a Nike Orion rocket launched from Punto Lobos, Peru, have been compared. A single mesospheric scattering layer was observed by the radar. The Langmuir probe detected irregularities in the electron-density profile in a narrow region between 85.2 and 86.6 km. It appears from a comparison between these two data sets that turbulence in the neutral atmosphere is the mechanism generating the refractive index irregularities.

Observations of Mesospheric Turbulence by Rocket Probe and VHF Radar, Part 2.4A

NASA Technical Reports Server (NTRS)

Royrvik, O.; Smith, L. G.

1984-01-01

Data from the Jicamarca VHF radar and from a Languir probe fine-structure on a Nike Orion rocket launched from Punto Lobos, Peru, have been compared. A single mesospheric scattering layer was observed by the radar. The Langmuir probe detected irregularities in the electron-density profile in a narrow region between 85.2 and 86.6 km. It appears from a comparison between these two data sets that turbulence in the neutral atmosphere is the mechanism generating the refractive index irregularities.

Pressure Anisotropy Probe for the Terrestrial Reconnection Experiment (TREX)

NASA Astrophysics Data System (ADS)

Myers, Rachel; Egedal, Jan; Olson, Joseph; Greess, Samuel; Clark, Michael; Nonn, Paul; Wallace, John; Forest, Cary

2016-10-01

The Terrestrial Reconnection Experiment (TREX) at the Wisconsin Plasma Astrophysics Laboratory (WiPAL) studies magnetic reconnection primarily in the collisionless regime. In this regime, electron pressure anisotropy is expected to develop, deviating from traditional Hall reconnection dynamics and driving formation of large-scale current layers. In order to measure the anisotropy, a multi-tip electromagnetic probe similar to the M-probe described by Shadman, consisting of 32 Langmuir probe tips and two magnetic coils, has been constructed. Each tip is biased to a different potential, simultaneously measuring discrete parts of the full I-V characteristic. Pulsing the coil then locally increases the magnetic field, creating a magnetic mirror force to reflect electrons with large values of v⊥ / v . The change in electron velocity modifies the I-V characteristics and can be used to infer p∥ /p⊥ . Analysis with the new probe will be presented. DOE Grant DE-SC0010463, University of Wisconsin-Madison University Fellowship.

LANGMUIR WAVE DECAY IN INHOMOGENEOUS SOLAR WIND PLASMAS: SIMULATION RESULTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krafft, C.; Volokitin, A. S.; Krasnoselskikh, V. V., E-mail: catherine.krafft@u-psud.fr

2015-08-20

Langmuir turbulence excited by electron flows in solar wind plasmas is studied on the basis of numerical simulations. In particular, nonlinear wave decay processes involving ion-sound (IS) waves are considered in order to understand their dependence on external long-wavelength plasma density fluctuations. In the presence of inhomogeneities, it is shown that the decay processes are localized in space and, due to the differences between the group velocities of Langmuir and IS waves, their duration is limited so that a full nonlinear saturation cannot be achieved. The reflection and the scattering of Langmuir wave packets on the ambient and randomly varying density fluctuationsmore » lead to crucial effects impacting the development of the IS wave spectrum. Notably, beatings between forward propagating Langmuir waves and reflected ones result in the parametric generation of waves of noticeable amplitudes and in the amplification of IS waves. These processes, repeated at different space locations, form a series of cascades of wave energy transfer, similar to those studied in the frame of weak turbulence theory. The dynamics of such a cascading mechanism and its influence on the acceleration of the most energetic part of the electron beam are studied. Finally, the role of the decay processes in the shaping of the profiles of the Langmuir wave packets is discussed, and the waveforms calculated are compared with those observed recently on board the spacecraft Solar TErrestrial RElations Observatory and WIND.« less

Electron acceleration by parametrically excited Langmuir waves. [in ionospheric modification

NASA Technical Reports Server (NTRS)

Fejer, J. A.; Graham, K. N.

1974-01-01

Simple physical arguments are used to estimate the downward-going energetic electron flux due to parametrically excited Langmuir waves in ionospheric modification experiments. The acceleration mechanism is a single velocity reversal as seen in the frame of the Langmuir wave. The flux is sufficient to produce the observed ionospheric airglow if focusing-type instabilities are invoked to produce moderate local enhancements of the pump field.

Simultaneous use of camera and probe diagnostics to unambiguously identify and study the dynamics of multiple underlying instabilities during the route to plasma turbulence.

PubMed

Thakur, S C; Brandt, C; Light, A; Cui, L; Gosselin, J J; Tynan, G R

2014-11-01

We use multiple-tip Langmuir probes and fast imaging to unambiguously identify and study the dynamics of underlying instabilities during the controlled route to fully-developed plasma turbulence in a linear magnetized helicon plasma device. Langmuir probes measure radial profiles of electron temperature, plasma density and potential; from which we compute linear growth rates of instabilities, cross-phase between density and potential fluctuations, Reynold's stress, particle flux, vorticity, time-delay estimated velocity, etc. Fast imaging complements the 1D probe measurements by providing temporally and spatially resolved 2D details of plasma structures associated with the instabilities. We find that three radially separated plasma instabilities exist simultaneously. Density gradient driven resistive drift waves propagating in the electron diamagnetic drift direction separate the plasma into an edge region dominated by strong, velocity shear driven Kelvin-Helmholtz instabilities and a central core region which shows coherent Rayleigh-Taylor modes propagating in the ion diamagnetic drift direction. The simultaneous, complementary use of both probes and camera was crucial to identify the instabilities and understand the details of the very rich plasma dynamics.

Study of Strongly Coupled Systems via Probe Brane Constructions

NASA Astrophysics Data System (ADS)

Chang, Han-Chih

In this thesis, we present our study towards better understanding of the strongly coupled systems with extra matter content in the fundamental representation of some prescribed global symmetry group in the quenched approximation, with the toolkit of holography via a probe brane construction. Specically, for the defect conformal systems, we unearth and quantify the phase trasition diagram, and novel supersymmetric vacua in the top-down model of the D3/D5 probe brane system. For further quantify various non-Fermi quantum liquid phases realized through the holographical probe brane construction, we then propose and verify the method to include the backreaction of entanglement entropy due to the probe branes at the leading order, which can potentially be used to detect topological phase transitions. We will recapitulate the main results of our works, in collaboration with Prof. Andreas Karch, published in the following journals: "Minimal Submanifolds asymptotic to AdS4 xS2 in AdS5xS5', JHEP, vol.1404, p.037, 2014; "The Novel Solutions of Finite-Density D3/D5 Probe Brane System and Their Implications for Stability'', JHEP, vol.1210, p.060, 2014; "Entanglement Entropy for Probe Branes'', JHEP, vol.1401, p.180, 2014.

Did Irving Langmuir Observe Langmuir Circulations?

NASA Astrophysics Data System (ADS)

D'Asaro, E. A.; Harcourt, R. R.; Shcherbina, A.; Thomson, J. M.; Fox-Kemper, B.

2012-12-01

Although surface waves are known to play an important role in mixing the upper ocean, the current generation of upper ocean boundary layer parameterizations does not include the explicit effects of surface waves. Detailed simulations using LES models which include the Craik-Leibovich wave-current interactions, now provide quantitative predictions of the enhancement of boundary layer mixing by waves. Here, using parallel experiments in Lake Washington and at Ocean Station Papa, we show a clear enhancement of vertical kinetic energy across the entire upper ocean boundary layer which can be attributed to surface wave effects. The magnitude of this effect is close to that predicted by LES models, but is not large, less than a factor of 2 on average, and increased by large Stokes drift and shallow mixed layers. Global estimates show the largest wave enhancements occur on the equatorial side of the westerlies in late Spring, due to the combination of large waves, shallow mixed layers and weak winds. In Lakes, however, the waves and the Craik-Leibovich interactions are weak, making it likely that the counter-rotating vortices famously observed by Irving Langmuir in Lake George were not driven by wave-current interactions.

Unbinding Transition of Probes in Single-File Systems

NASA Astrophysics Data System (ADS)

Bénichou, Olivier; Démery, Vincent; Poncet, Alexis

2018-02-01

Single-file transport, arising in quasi-one-dimensional geometries where particles cannot pass each other, is characterized by the anomalous dynamics of a probe, notably its response to an external force. In these systems, the motion of several probes submitted to different external forces, although relevant to mixtures of charged and neutral or active and passive objects, remains unexplored. Here, we determine how several probes respond to external forces. We rely on a hydrodynamic description of the symmetric exclusion process to obtain exact analytical results at long times. We show that the probes can either move as a whole, or separate into two groups moving away from each other. In between the two regimes, they separate with a different dynamical exponent, as t1 /4. This unbinding transition also occurs in several continuous single-file systems and is expected to be observable.

Measurement of electron density transients in pulsed RF discharges using a frequency boxcar hairpin probe

NASA Astrophysics Data System (ADS)

Peterson, David; Coumou, David; Shannon, Steven

2015-11-01

Time resolved electron density measurements in pulsed RF discharges are shown using a hairpin resonance probe using low cost electronics, on par with normal Langmuir probe boxcar mode operation. Time resolution of 10 microseconds has been demonstrated. A signal generator produces the applied microwave frequency; the reflected waveform is passed through a directional coupler and filtered to remove the RF component. The signal is heterodyned with a frequency mixer and rectified to produce a DC signal read by an oscilloscope. At certain points during the pulse, the plasma density is such that the applied frequency is the same as the resonance frequency of the probe/plasma system, creating reflected signal dips. The applied microwave frequency is shifted in small increments in a frequency boxcar routine to determine the density as a function of time. A dc sheath correction is applied for the grounded probe, producing low cost, high fidelity, and highly reproducible electron density measurements. The measurements are made in both inductively and capacitively coupled systems, the latter driven by multiple frequencies where a subset of these frequencies are pulsed. Measurements are compared to previous published results, time resolved OES, and in-line measurement of plasma impedance. This work is supported by the NSF DOE partnership on plasma science, the NSF GOALI program, and MKS Instruments.

Galileo probe battery system -- An update

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dagarin, B.P.; Taenaka, R.K.; Stofel, E.J.

NASA`s Galileo 6-year trip to Jupiter is in its final phase. The mission consists of a Jovian Orbiter and an atmospheric entry Probe. The Probe is designed to coast autonomously for up to 190 days and turn itself on 6 hours prior to entry. It will then descend through the upper atmosphere for 50 to 75 minutes with the aid of an 8-foot parachute. This paper discusses sources of electrical power for the Probe and battery testing at the systems level. Described are the final production phase, qualification, and systems testing prior to and following launch, as well as decisionsmore » made regarding the Probe separation Li/SO{sub 2} battery configuration. In addition, the paper briefly describes the thermal battery verification program. The main power source comprises three Li/SO{sub 2} battery modules containing 13 D-sized cell strings per module. These modules are required to retain capacity for 7.5 years and support a 150-day clock, ending with a 7-hour mission sequence of increasing loads from 0.15 A to 9.5 A during the last 30 minutes. The main power source is supplemented by two thermal batteries (CaCrO{sub 4}-Ca), which will be used for firing the pyrotechnic initiators during the atmospheric entry.« less

Probing the Solar System

ERIC Educational Resources Information Center

Wilkinson, John

2013-01-01

Humans have always had the vision to one day live on other planets. This vision existed even before the first person was put into orbit. Since the early space missions of putting humans into orbit around Earth, many advances have been made in space technology. We have now sent many space probes deep into the Solar system to explore the planets and…

Improved understanding of the ball-pen probe through particle-in-cell simulations

NASA Astrophysics Data System (ADS)

Murphy-Sugrue, S.; Harrison, J.; Walkden, N. R.; Bryant, P.; Bradley, J. W.

2017-05-01

Ball-pen probes (BPP) have been deployed in the SOL of numerous tokamak experiments and low-temperature magnetised plasmas to make direct measurements of the plasma potential and electron temperature. Despite strong empirical evidence for the success of the BPP it lacks a theoretical underpinning of its collection mechanism. In this paper we investigate the capability of the probe to measure the plasma potential by means of particle-in-cell simulations. The BPP is found to float at a potential offset from the plasma potential by a factor {T}{{e}}{α }{{BPP}}. By simulating BPPs and Langmuir probes, excellent agreement has been found between the measured electron temperature and the specified source temperature. The transport mechanism for both ions and electrons has been determined. E × B drifts are observed to drive electrons and ions down the tunnel. This mechanism is sensitive to the diameter of the probe.

Bimolecular recombination quenching in Langmuir Blodgett multilayers

NASA Astrophysics Data System (ADS)

Elliott, J. E.; Jeong, I. S.; Scott, K.; Donovan, K. J.; Wilson, E. G.

2000-11-01

A model is developed that describes bimolecular recombination of photogenerated carriers in two dimensional systems. Carriers are free to diffuse in two dimensions and undergo bimolecular recombination, while drifting under the influence of an electric field in the third dimension. The model describes a competition between carrier loss due to transiting and loss due to bimolecular recombination. This model of recombination quenching is then used to obtain information on microscopic parameters associated with photogeneration efficiency and charge transport in organic quantum wells formed from Langmuir Blodgett films of conjugated molecules. The ratio of the intralayer to interlayer tunneling rates is found along with the quantum efficiency for photocarrier generation for two bis-phthalocyanine amphiphilic molecules.

Structural investigation of Langmuir and Langmuir-Blodgett monolayers of semifluorinated alkanes.

PubMed

Dynarowicz Łatka, Patrycja; Pérez-Morales, Marta; Muñoz, Eulogia; Broniatowski, Marcin; Martín-Romero, María T; Camacho, Luis

2006-03-30

The behavior of a semi-fluorinated alkane (C(10)F(21)C(19)H(39)) has been studied at the air-water interface by using surface pressure and surface potential-area isotherms as well as infrared spectroscopy for the Langmuir-Blodgett films. In addition, based on the quantum chemical PM3 semiempirical approach, the dimer structure was investigated, and the double helix was found to be the most stable conformation of the dimer. The obtained results allow us to imply that the phase transition observed in the course of the surface pressure/area isotherm is due to a conformational change originating from the double helix to a vertical, single helix configuration.

Graphene Oxide-Polymer Composite Langmuir Films Constructed by Interfacial Thiol-Ene Photopolymerization

NASA Astrophysics Data System (ADS)

Luo, Xiaona; Ma, Kai; Jiao, Tifeng; Xing, Ruirui; Zhang, Lexin; Zhou, Jingxin; Li, Bingbing

2017-02-01

The effective synthesis and self-assembly of graphene oxide (GO) nanocomposites are of key importance for a broad range of nanomaterial applications. In this work, a one-step chemical strategy is presented to synthesize stable GO-polymer Langmuir composite films by interfacial thiol-ene photopolymerization at room temperature, without use of any crosslinking agents and stabilizing agents. It is discovered that photopolymerization reaction between thiol groups modified GO sheets and ene in polymer molecules is critically responsible for the formation of the composite Langmuir films. The film formed by Langmuir assembly of such GO-polymer composite films shows potential to improve the mechanical and chemical properties and promotes the design of various GO-based nanocomposites. Thus, the GO-polymer composite Langmuir films synthesized by interfacial thiol-ene photopolymerization with such a straightforward and clean manner, provide new alternatives for developing chemically modified GO-based hybrid self-assembled films and nanomaterials towards a range of soft matter and graphene applications.

The Langmuir isotherm: a commonly applied but misleading approach for the analysis of protein adsorption behavior.

PubMed

Latour, Robert A

2015-03-01

The Langmuir adsorption isotherm provides one of the simplest and most direct methods to quantify an adsorption process. Because isotherm data from protein adsorption studies often appear to be fit well by the Langmuir isotherm model, estimates of protein binding affinity have often been made from its use despite that fact that none of the conditions required for a Langmuir adsorption process may be satisfied for this type of application. The physical events that cause protein adsorption isotherms to often provide a Langmuir-shaped isotherm can be explained as being due to changes in adsorption-induced spreading, reorientation, clustering, and aggregation of the protein on a surface as a function of solution concentration in contrast to being due to a dynamic equilibrium adsorption process, which is required for Langmuir adsorption. Unless the requirements of the Langmuir adsorption process can be confirmed, fitting of the Langmuir model to protein adsorption isotherm data to obtain thermodynamic properties, such as the equilibrium constant for adsorption and adsorption free energy, may provide erroneous values that have little to do with the actual protein adsorption process, and should be avoided. In this article, a detailed analysis of the Langmuir isotherm model is presented along with a quantitative analysis of the level of error that can arise in derived parameters when the Langmuir isotherm is inappropriately applied to characterize a protein adsorption process. © 2014 Wiley Periodicals, Inc.

Saturation of Langmuir waves in laser-produced plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, K.L.

1996-04-01

This dissertation deals with the interaction of an intense laser with a plasma (a quasineutral collection of electrons and ions). During this interaction, the laser drives large-amplitude waves through a class of processes known as parametric instabilities. Several such instabilities drive one type of wave, the Langmuir wave, which involves oscillations of the electrons relative to the nearly-stationary ions. There are a number of mechanisms which limit the amplitude to which Langmuir waves grow. In this dissertation, these mechanisms are examined to identify qualitative features which might be observed in experiments and/or simulations. In addition, a number of experiments aremore » proposed to specifically look for particular saturation mechanisms. In a plasma, a Langmuir wave can decay into an electromagnetic wave and an ion wave. This parametric instability is proposed as a source for electromagnetic emission near half of the incident laser frequency observed from laser-produced plasmas. This interpretation is shown to be consistent with existing experimental data and it is found that one of the previous mechanisms used to explain such emission is not. The scattering version of the electromagnetic decay instability is shown to provide an enhanced noise source of electromagnetic waves near the frequency of the incident laser.« less

Topics in strong Langmuir turbulence

NASA Technical Reports Server (NTRS)

Nicholson, D. R.

1983-01-01

Progress in two approaches to the study of strong Langmuir turbulence is reported. In two spatial dimensions, numerical solution of the Zakharov equations yields a steady state involving linear growth, linear damping, and a collection of coherent, long-lived entities which might loosely be called solitons. In one spatial dimension, a statistical theory is applied to the cubically nonlinear Schroedinger equation and is solved analytically in a special case.

Topics in strong Langmuir turbulence

NASA Technical Reports Server (NTRS)

Nicholson, D. R.

1982-01-01

Progress in two approaches to the study of strong Langmuir turbulence is reported. In two spatial dimensions, numerical solution of the Zakharov equations yields a steady state involving linear growth, linear damping, and a collection of coherent, long-lived entities which might loosely be called solitons. In one spatial dimension, a statistical theory is applied to the cubically nonlinear Schroedinger equation and is solved analytically in a special case.

Situ soil sampling probe system with heated transfer line

DOEpatents

Robbat, Jr., Albert

2002-01-01

The present invention is directed both to an improved in situ penetrometer probe and to a heated, flexible transfer line. The line and probe may be implemented together in a penetrometer system in which the transfer line is used to connect the probe to a collector/analyzer at the surface. The probe comprises a heater that controls a temperature of a geologic medium surrounding the probe. At least one carrier gas port and vapor collection port are located on an external side wall of the probe. The carrier gas port provides a carrier gas into the geologic medium, and the collection port captures vapors from the geologic medium for analysis. In the transfer line, a flexible collection line that conveys a collected fluid, i.e., vapor, sample to a collector/analyzer. A flexible carrier gas line conveys a carrier gas to facilitate the collection of the sample. A system heating the collection line is also provided. Preferably the collection line is electrically conductive so that an electrical power source can generate a current through it so that the internal resistance generates heat.

Saturation of radiation-induced parametric instabilities by excitation of Langmuir turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dubois, D.F.; Rose, H.A.; Russell, D.

1995-12-01

Progress made in the last few years in the calculation of the saturation spectra of parametric instabilities which involve Langmuir daughter waves will be reviewed. These instabilities include the ion acoustic decay instability, the two plasmon decay instability (TPDI), and stimulated Raman scattering (SRS). In particular I will emphasize spectral signatures which can be directly compared with experiment. The calculations are based on reduced models of driven Laugmuir turbulence. Thomson scattering from hf-induced Langmuir turbulence in the unpreconditioned ionosphere has resulted in detailed agreement between theory and experiment at early times. Strong turbulence signatures dominate in this regime where themore » weak turbulence approximation fails completely. Recent experimental studies of the TPDI have measured the Fourier spectra of Langmuir waves as well as the angular and frequency, spectra of light emitted near 3/2 of the pump frequency again permitting some detailed comparisons with theory. The experiments on SRS are less detailed but by Thomson scattering the secondary decay of the daughter Langmuir wave has been observed. Scaling laws derived from a local model of SRS saturation are compared with full simulations and recent Nova experiments.« less

Study of new systems concepts for a Titan atmospheric probe

NASA Technical Reports Server (NTRS)

Bernard, Doug; Citron, Todd; Drean, Robert; Lewis, Scott; Lo, Martin; Mccarthy, John; Soderblom, Robert; Steffy, Dave; Vargas, Tina; Wolff, Marty

1986-01-01

Results of a systems concepts study for a Titan Probe were examined. The key tradeoffs performed are described in detail. Mass breakdown of each Probe subsystem or major element were given. The mission analysis performed to determine compliance with the high altitude sampling and descent time requirements are described. The baseline Descent Module design was derived. The element of the Probe System left on the Carrier after separation were described.

Evidence for Langmuir Envelope Solitons in Solar Type III Burst Source Regions

NASA Technical Reports Server (NTRS)

Thejappa, G.; Goldstein, M. L.; MacDowall, R. J.; Papadopoulos, K.; Stone, R. G.

1998-01-01

We present observational evidence for the generation of Langmuir envelope solitons in the source regions of solar type III radio bursts. The solitons appear to be formed by electron beams which excite either the modulational instability or oscillating two-stream instability (OTSI). Millisecond data from the Ulysses Unified Radio and Plasma Wave Experiment (URAP) show that Langmuir waves associated with type III bursts occur as broad intense peaks with time scales ranging from 15 to 90 milliseconds (6 - 27 km). These broad field structures have the properties expected of Langmuir envelope solitons, viz.: the normalized peak energy densities, W(sub L)/n(sub e)T(sub e) approximately 10(exp -5), are well above the modulational instability threshold; the spatial scales, L, which range from 1 - 5 Langmuir wavelengths, show a high degree of inverse correlation with (W(sub L)/n(sub e)T(sub e))(sup 1/2); and the observed widths of these broad peaks agree well with the predicted widths of envelope solitons. We show that the orientation of the Langmuir field structures is random with respect to the ambient magnetic field, indicating that they are probably isotropic structures that have evolved from initially pancake-like solitons. These observations suggest that strong turbulence processes, such as the modulational instability or the OTSI, stabilize the electron beams that produce type III bursts.

Photo-switching of a non-ionic azobenzene amphiphile in Langmuir and Langmuir-Blodgett films.

PubMed

Piosik, Emilia; Kotkowiak, Michał; Korbecka, Izabela; Galewski, Zbigniew; Martyński, Tomasz

2017-08-30

The concept of programmable and reconfigurable soft matter has emerged in science in the last few decades and can be realized by photoisomerization of azobenzene derivatives. This possibility results in great application potential of these compounds in optical storage devices, molecular junctions of electronic devices, command layers of liquid crystal displays or holographic gratings. In this paper, we present the results of a study on the organization and isomerization of the non-ionic and amphiphilic methyl 4-[(E)-2-[4-(nonyloxy)phenyl]diazen-1-yl]benzoate (LCA) in a 2D layer architecture of Langmuir and Langmuir-Blodgett (LB) films supported by spectroscopic studies on LCA chloroform solutions. Our investigation has shown a significantly different molecular organization of LCA depending on the ratio of trans and cis isomers in the monolayers. Taking advantage of a relatively low packing density and aggregation strength in the cis-LCA monolayer, we demonstrated the reversible isomerization in the LB film initially formed of LCA molecules in the cis form, while in the trans-LCA monolayer this effect was not observed. Our approach allows the formation of a switchable monolayer made of the amphiphilic LCA showing liquid crystalline properties without introducing an ionic group into the molecule structure, mixing with another compound or changing the subphase pH to provide free space for the molecules' isomerization.

Water penetration/accommodation and phase behaviour of the neutral Langmuir monolayer at the air/water interface probed with sum frequency generation vibrational spectroscopy (SFG-VS).

PubMed

Zhang, Zhen; Zheng, De-Sheng; Guo, Yuan; Wang, Hong-Fei

2009-02-14

A strong and broad hydrogen bonded O-H band around 3520 cm(-1) is observed in the insoluble monolayer of the neutral liquid crystal molecules of 4''-n-pentyl-4-p-cyanobiphenyl (5CB) and 4''-n-octyl-4-p-cyanobiphenyl (8CB) throughout the whole surface density range, but not in the 4-pentyl-4'-cyanoterphenyl (5CT) monolayer, at the air/water interface. This novel spectral feature suggests the existence of an oriented water cluster species which has penetrated or accommodated into the Langmuir monolayer of the 8CB and 5CB molecules. This finding provided a molecular level mechanism for the stark difference in the phase behaviour between the CB and CT insoluble Langmuir monolayers at the air/water interface. It also calls for attention to the details of the specific water-surface interaction in mediating the structure and the phase behaviour of the molecular assemblies at the heterogeneous aqueous interfaces.

Study on electrostatic and electromagnetic probes operated in ceramic and metallic depositing plasmas

NASA Astrophysics Data System (ADS)

Styrnoll, T.; Bienholz, S.; Lapke, M.; Awakowicz, P.

2014-04-01

This paper discusses plasma probe diagnostics, namely the multipole resonance probe (MRP) and Langmuir probe (LP), operated in depositing plasmas. The aim of this work is to show that the combination of both probes provides stable and robust measurements and clear determination of plasma parameters for metallic and ceramic coating processes. The probes use different approaches to determine plasma parameters, e.g. electron density ne and electron temperature Te. The LP is a well-established plasma diagnostic, and its applicability in technological plasmas is well documented. The LP is a dc probe that performs a voltage sweep and analyses the measured current, which makes it insensitive against conductive metallic coating. However, once the LP is dielectrically coated with a ceramic film, its functionality is constricted. In contrast, the MRP was recently presented as a monitoring tool, which is insensitive to coating with dielectric ceramics. It is a new plasma diagnostic based on the concept of active plasma resonance spectroscopy, which uses the universal characteristic of all plasmas to resonate on or near the electron plasma frequency. The MRP emits a frequency sweep and the absorption of the signal, the |S11| parameter, is analysed. Since the MRP concept is based on electromagnetic waves, which are able to transmit dielectrics, it is insensitive to dielectric coatings. But once the MRP is metallized with a thin conductive film, no undisturbed RF-signal can be emitted into the plasma, which leads to falsified plasma parameter. In order to compare both systems, during metallic or dielectric coating, the probes are operated in a magnetron CCP, which is equipped with a titanium target. We present measurements in metallic and dielectric coating processes with both probes and elaborate advantages and problems of each probe operated in each coating environment.

Impact of science objectives and requirements on probe mission and system design

NASA Technical Reports Server (NTRS)

Ledbetter, K. W.

1974-01-01

Problem areas in probe science technology are discussed that require a solution before probe systems can actually be designed. Considered are the effects of the model atmospheres on probe design; secondly, the effects of implementing the requirements to locate and measure the clouds and, trade-offs between descent sampling and measurement criteria as they affect probe system design.

Galileo probe battery systems design

NASA Technical Reports Server (NTRS)

Dagarin, B. P.; Van Ess, J. S.; Marcoux, L. S.

1986-01-01

NASA's Galileo mission to Jupiter will consist of a Jovian orbiter and an atmospheric entry probe. The power for the probe will be derived from two primary power sources. The main source is composed of three Li-SO2 battery modules containing 13 D-size cell strings per module. These are required to retain capacity for 7.5 years, support a 150 day clock, and a 7 hour mission sequence of increasing loads from 0.15 to 9.5 amperes for the last 30 minutes. This main power source is supplemented by two thermal batteries (CaCrO4-Ca) for use in firing the pyrotechnic initiators during the atmospheric staging events. This paper describes design development and testing of these batteries at the system level.

A practical model for pressure probe system response estimation (with review of existing models)

NASA Astrophysics Data System (ADS)

Hall, B. F.; Povey, T.

2018-04-01

The accurate estimation of the unsteady response (bandwidth) of pneumatic pressure probe systems (probe, line and transducer volume) is a common practical problem encountered in the design of aerodynamic experiments. Understanding the bandwidth of the probe system is necessary to capture unsteady flow features accurately. Where traversing probes are used, the desired traverse speed and spatial gradients in the flow dictate the minimum probe system bandwidth required to resolve the flow. Existing approaches for bandwidth estimation are either complex or inaccurate in implementation, so probes are often designed based on experience. Where probe system bandwidth is characterized, it is often done experimentally, requiring careful experimental set-up and analysis. There is a need for a relatively simple but accurate model for estimation of probe system bandwidth. A new model is presented for the accurate estimation of pressure probe bandwidth for simple probes commonly used in wind tunnel environments; experimental validation is provided. An additional, simple graphical method for air is included for convenience.

Langmuir-Blodgett deposition selects carboxylate headgroup coordination

NASA Astrophysics Data System (ADS)

Mukherjee, Smita; Datta, Alokmay

2011-10-01

Infrared reflection-absorption spectroscopy results on stearic acid Langmuir monolayers containing Mn, Co, and Cd ions show that on the water surface, the ions induce unidentate and bidentate (both chelate and bridged) coordination in the carboxylate headgroup with some trace of undissociated acid. Moreover, with Cd and Mn ions in subphase, the preferred coordination is found to be unidentate, whereas for Co, bidentate chelate is most preferred. After transfer onto amorphous substrate, not all coordinations are found to exist in the same ratio for the deposited metal stearate monolayers. More specifically, after transfer, Mn is found to coordinate with the carboxylate group as bidentate chelate, Cd as unidentate and bidentate bridged (with unidentate as the preferred coordination), and Co as preferably bidentate bridged (although all coordinations are present). Results suggest a specific interaction in each case, as the metal-carboxylate pair at the water surface is transferred to the substrate surface during Langmuir-Blodgett deposition.

Chemical Polymerization and Langmuir-Blodgett Techniques. 2. The Polymerization of Monolayers of 3-Substituted Pyrroles

DTIC Science & Technology

1993-09-12

the liquid -air interface could be monitored by changes in the surface area. Deposition of monolayers by Langmuir - Blodgett technique is possible and...polymerization product from the LB trough in chloroform solution. Figure 10 Langmuir - Blodgett transfer of poly (3-hexadecyl pyrrole) onto hydrophobized glass... Langmuir - Blodgett Techniques, 2: The Polymerization of Monolayers of 3-Substituted Pyrroles by W.M. Sigmund, C. Marestin, S. Keil, H. Zhou and R.S

A Statistical Analysis of Langmuir Wave-Electron Correlations Observed by the CHARM II Auroral Sounding Rocket

NASA Astrophysics Data System (ADS)

Dombrowski, M. P.; Labelle, J. W.; Kletzing, C.; Bounds, S. R.; Kaeppler, S. R.

2014-12-01

Langmuir-mode electron plasma waves are frequently observed by spacecraft in active plasma environments such as the ionosphere. Ionospheric Langmuir waves may be excited by the bump-on-tail instability generated by impinging beams of electrons traveling parallel to the background magnetic field (B). The Correlation of High-frequencies and Auroral Roar Measurement (CHARM II) sounding rocket was launched into a substorm at 9:49 UT on 17 February 2010, from the Poker Flat Research Range in Alaska. The primary instruments included the University of Iowa Wave-Particle Correlator (WPC), the Dartmouth High-Frequency Experiment (HFE), several charged particle detectors, low-frequency wave instruments, and a magnetometer. The HFE is a receiver system which effectively yields continuous (100% duty cycle) electric-field waveform measurements from 100 kHz to 5 MHz, and which had its detection axis aligned nominally parallel to B. The HFE output was fed on-payload to the WPC, which uses a phase-locked loop to track the incoming wave frequency with the most power, then sorting incoming electrons at eight energy levels into sixteen wave-phase bins. CHARM II encountered several regions of strong Langmuir wave activity throughout its 15-minute flight, and the WPC showed wave-lock and statistically significant particle correlation distributions during several time periods. We show results of an in-depth analysis of the CHARM II WPC data for the entire flight, including statistical analysis of correlations which show evidence of direct interaction with the Langmuir waves, indicating (at various times) trapping of particles and both driving and damping of Langmuir waves by particles. In particular, the sign of the gradient in particle flux appears to correlate with the phase relation between the electrons and the wave field, with possible implications for the wave physics.

Probe systems for static pressure and cross-stream turbulence intensity

NASA Technical Reports Server (NTRS)

Rossow, Vernon, J.

1991-01-01

A recent study of total-pressure probes for use in highly turbulent streams is extended herein by developing probe systems that measure time-averaged static or ambient pressure and turbulence intensity. Arrangements of tubular probes of circular and elliptical cross section are described that measure the pressure at orifices on the sides of the probes to obtain different responses to the cross-stream velocity fluctuations. When the measured data are combined to remove the effect of the presence of the probes on the local pressure, the time-averaged static pressure and the cross-stream components of turbulence intensity can be determined. If a system of total pressure tubes, as described in an accompanying paper, is added to the static pressure group to form a single cluster, redundant measurements are obtained that permit accuracy and consistency checks.

Effects of Langmuir Turbulence on Reactive Tracers in the Upper Ocean

NASA Astrophysics Data System (ADS)

Smith, K.; Hamlington, P.; Niemeyer, K.; Fox-Kemper, B.; Lovenduski, N. S.

2017-12-01

Reactive tracers such as carbonate chemical species play important roles in the oceanic carbon cycle, allowing the ocean to hold 60 times more carbon than the atmosphere. However, uncertainties in regional ocean sinks for anthropogenic CO2 are still relatively high. Many carbonate species are non-conserved, flux across the air-sea interface, and react on time scales similar to those of ocean turbulent processes, such as small-scale wave-driven Langmuir turbulence. All of this complexity gives rise to heterogeneous tracer distributions that are not fully understood and can greatly affect the rate at which CO2 fluxes across the air-sea interface. In order to more accurately model the biogeochemistry of the ocean in Earth system models (ESMs), a better understanding of the fundamental interactions between these reactive tracers and relevant turbulent processes is required. Research on reacting flows in other contexts has shown that the most significant tracer-flow couplings occur when coherent structures in the flow have timescales that rival reaction time scales. Langmuir turbulence, a 3D, small-scale, wave-driven process, has length and time scales on the order of O(1-100m) and O(1-10min), respectively. Once CO2 transfers across the air-sea interface, it reacts with seawater in a series of reactions whose rate limiting steps have time scales of 10-25s. This similarity in scales warrants further examination into interactions between these small-scale physical and chemical processes. In this presentation, large eddy simulations are used to examine the evolution of reactive tracers in the presence of realistic upper ocean wave- and shear-driven turbulence. The reactive tracers examined are those specifically involved in non-biological carbonate chemistry. The strength of Langmuir turbulence is varied in order to determine a relationship between the degree of enhancement (or reduction) of carbon that is fluxed across the air-sea interface due to the presence of Langmuir

Multi-function diamond film fiberoptic probe and measuring system employing same

DOEpatents

Young, Jack P.

1998-01-01

A fused fiberoptic probe having a protective cover, a fiberoptic probe system, and embodiments thereof for conducting electromagnetic spectral measurements are disclosed. The fused fiberoptic probe comprises a probe tip having a specific geometrical configuration, an exciting optical fiber and at least one collection optical fiber fused within a housing, preferrably silica, with a protective cover disposed over at least a portion of the probe tip. The specific geometrical configurations in which the probe tip can be shaped include a slanted probe tip with an angle greater than 0.degree., an inverted cone-shaped probe tip, and a lens head.

Molecular-Scale Investigation of Heavy Metal Ions at a Charged Langmuir Monolayer

NASA Astrophysics Data System (ADS)

Rock, William; Qiao, Baofu; Uysal, Ahmet; Bu, Wei; Lin, Binhua

Solvent extraction - the surfactant-aided preferential transfer of a species from an aqueous to an organic phase - is an important technique used in heavy and precious metal refining and reprocessing. Solvent extraction requires transfer through an oil/water interface, and interfacial interactions are expected to control transfer kinetics and phase stability, yet these key interactions are poorly understood. Langmuir monolayers with charged headgroups atop concentrated salt solutions containing heavy metal ions act as a model of solvent extraction interfaces; studies of ions at a charged surface are also fundamentally important to many other phenomena including protein solvation, mineral surface chemistry, and electrochemistry. We probe these charged interfaces using a variety of surface-sensitive techniques - vibrational sum frequency generation (VSFG) spectroscopy, x-ray reflectivity (XRR), x-ray fluorescence near total reflection (XFNTR), and grazing incidence diffraction (GID). We integrate experiments with Molecular Dynamics (MD) simulations to uncover the molecular-level interfacial structure. This work is supported by the U.S. DOE, BES, Contract DE-AC02-06CH11357. ChemMatCARS is supported by NSF/CHE-1346572.

Dynamic of Langmuir and Ion-Sound Waves in Type 3 Solar Radio Sources

NASA Technical Reports Server (NTRS)

Robinson, P. A.; Willes, A. J.; Cairns, I. H.

1993-01-01

The evolution of Langmuir and ion-sound waves in type 3 sources is investigated, incorporating linear growth, linear damping, and nonlinear electrostatic decay. Improved estimates are obtained for the wavenumber range of growing waves and the nonlinear coupling coefficient for the decay process. The resulting prediction for the electrostatic decay threshold is consistent with the observed high-field cutoff in the Langmuir field distribution. It is shown that the conditions in the solar wind do not allow a steady state to be attained; rather, bursty linear and nonlinear interactions take place, consistent with the highly inhomogeneous and impulsive waves actually observed. Nonlinear growth is found to be fast enough to saturate the growth of the parent Langmuir waves in the available interaction time. The resulting levels of product Langmuir and ion-sound waves are estimated theoretically and shown to be consistent with in situ ISEE 3 observations of type 3 events at 1 AU. Nonlinear interactions slave the growth and decay of product sound waves to that of the product Langmuir waves. The resulting probability distribution of ion-sound field strengths is predicted to have a flat tail extending to a high-field cutoff. This prediction is consistent with statistics derived here from ISEE 3 observations. Agreement is also found between the frequencies of the observed waves and predictions for the product S waves. The competing processes of nonlinear wave collapse and quasilinear relaxation are discussed, and it is concluded that neither is responsible for the saturation of Langmuir growth. When wave and beam inhomogeneities are accounted for, arguments from quasi-linear relaxation yield an upper bound on the Langmuir fields that is too high to be relevant. Nor are the criteria for direct wave collapse of the beam-driven waves met, consistent with earlier simulation results that imply that this process is not responsible for saturation of the beam instability. Indeed, even

Compensation of the sheath effects in cylindrical floating probes

NASA Astrophysics Data System (ADS)

Park, Ji-Hwan; Chung, Chin-Wook

2018-05-01

In cylindrical floating probe measurements, the plasma density and electron temperature are overestimated due to sheath expansion and oscillation. To reduce these sheath effects, a compensation method based on well-developed floating sheath theories is proposed and applied to the floating harmonic method. The iterative calculation of the Allen-Boyd-Reynolds equation can derive the floating sheath thickness, which can be used to calculate the effective ion collection area; in this way, an accurate ion density is obtained. The Child-Langmuir law is used to calculate the ion harmonic currents caused by sheath oscillation of the alternating-voltage-biased probe tip. Accurate plasma parameters can be obtained by subtracting these ion harmonic currents from the total measured harmonic currents. Herein, the measurement principles and compensation method are discussed in detail and an experimental demonstration is presented.

Local Environment and Interactions of Liquid and Solid Interfaces Revealed by Spectral Line Shape of Surface Selective Nonlinear Vibrational Probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Shun-Li; Fu, Li; Chase, Zizwe A.

Vibrational spectral lineshape contains important detailed information of molecular vibration and reports its specific interactions and couplings to its local environment. In this work, recently developed sub-1 cm-1 high-resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS) was used to measure the -C≡N stretch vibration in the 4-n-octyl-4’-cyanobiphenyl (8CB) Langmuir or Langmuir-Blodgett (LB) monolayer as a unique vibrational probe, and the spectral lineshape analysis revealed the local environment and interactions at the air/water, air/glass, air/calcium fluoride and air/-quartz interfaces for the first time. The 8CB Langmuir or LB film is uniform and the vibrational spectral lineshape of its -C≡N group hasmore » been well characterized, making it a good choice as the surface vibrational probe. Lineshape analysis of the 8CB -C≡N stretch SFG vibrational spectra suggests the coherent vibrational dynamics and the structural and dynamic inhomogeneity of the -C≡N group at each interface are uniquely different. In addition, it is also found that there are significantly different roles for water molecules in the LB films on different substrate surfaces. These results demonstrated the novel capabilities of the surface nonlinear spectroscopy in characterization and in understanding the specific structures and chemical interactions at the liquid and solid interfaces in general.« less

Supramolecular architectures of iron phthalocyanine Langmuir-Blodgett films: The role played by the solution solvents

NASA Astrophysics Data System (ADS)

Rubira, Rafael Jesus Gonçalves; Aoki, Pedro Henrique Benites; Constantino, Carlos José Leopoldo; Alessio, Priscila

2017-09-01

The developing of organic-based devices has been widely explored using ultrathin films as the transducer element, whose supramolecular architecture plays a central role in the device performance. Here, Langmuir and Langmuir-Blodgett (LB) ultrathin films were fabricated from iron phthalocyanine (FePc) solutions in chloroform (CHCl3), dichloromethane (CH2Cl2), dimethylformamide (DMF), and tetrahydrofuran (THF) to determine the influence of different solvents on the supramolecular architecture of the ultrathin films. The UV-vis absorption spectroscopy shows a strong dependence of the FePc aggregation on these solvents. As a consequence, the surface pressure vs. mean molecular area (π-A) isotherms and Brewster angle microscopy (BAM) reveal a more homogeneous (surface morphology) Langmuir film at the air/water interface for FePc in DMF. The same morphological pattern observed for the Langmuir films is preserved upon LB deposition onto solid substrates. The Raman and FTIR analyses indicate the DMF-FePc interaction relies on coordination bonds between N atom (from DMF) and Fe atom (from FePc). Besides, the FePc molecular organization was also found to be affected by the DMF-FePc chemical interaction. It is interesting to note that, if the DMF-FePc leads to less aggregated FePc either in solution or ultrathin films (Langmuir and LB), with time (one week) the opposite trend is found. Taking into account the N-Fe interaction, the performance of the FePc ultrathin films with distinct supramolecular architectures composing sensing units was explored as proof-of-principle in the detection of trace amounts of atrazine herbicide in water using impedance spectroscopy. Further statistical and computational analysis reveal not only the role played by FePc supramolecular architecture but also the sensitivity of the system to detect atrazine solutions down to 10-10 mol/L, which is sufficient to monitor the quality of drinking water even according to the most stringent international

Outer planet entry probe system study. Volume 2: Supporting technical studies

NASA Technical Reports Server (NTRS)

1972-01-01

The environment, science investigations, and general mission analysis considerations are given first. These data are followed by discussions of the studies pertaining to the planets Jupiter, Saturn, Uranus, and Neptune. Except for Neptune, each planet discussion is divided into two parts: (1) parametric activities and (2) probe definition for that planet, or the application of a given probe for that planet. The Neptune discussion is limited to parametrics in the area of science and mission analysis. Each of the probe system definitions consists of system and subsystem details including telecommunications, data handling, power pyrotechnics, attitude control, structures, propulsion, thermal control, and probe to spacecraft integration. The first configuration is discussed in detail and the subsequent configuration discussions are limited to the differences. Finally, the hardware availability to support a probe system and commonality of science, missions, and subsystems for use at the various planets are considered.

Two-dimensional electromagnetic Child-Langmuir law of a short-pulse electron flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, S. H.; Tai, L. C.; Liu, Y. L.

Two-dimensional electromagnetic particle-in-cell simulations were performed to study the effect of the displacement current and the self-magnetic field on the space charge limited current density or the Child-Langmuir law of a short-pulse electron flow with a propagation distance of {zeta} and an emitting width of W from the classical regime to the relativistic regime. Numerical scaling of the two-dimensional electromagnetic Child-Langmuir law was constructed and it scales with ({zeta}/W) and ({zeta}/W){sup 2} at the classical and relativistic regimes, respectively. Our findings reveal that the displacement current can considerably enhance the space charge limited current density as compared to the well-knownmore » two-dimensional electrostatic Child-Langmuir law even at the classical regime.« less

Solar Power System Design for the Solar Probe+ Mission

NASA Technical Reports Server (NTRS)

Landis, Geoffrey A.; Schmitz, Paul C.; Kinnison, James; Fraeman, Martin; Roufberg, Lew; Vernon, Steve; Wirzburger, Melissa

2008-01-01

Solar Probe+ is an ambitious mission proposed to the solar corona, designed to make a perihelion approach of 9 solar radii from the surface of the sun. The high temperature, high solar flux environment makes this mission a significant challenge for power system design. This paper summarizes the power system conceptual design for the solar probe mission. Power supplies considered included nuclear, solar thermoelectric generation, solar dynamic generation using Stirling engines, and solar photovoltaic generation. The solar probe mission ranges from a starting distance from the sun of 1 AU, to a minimum distance of about 9.5 solar radii, or 0.044 AU, from the center of the sun. During the mission, the solar intensity ranges from one to about 510 times AM0. This requires power systems that can operate over nearly three orders of magnitude of incident intensity.

Adsorption of 2-propanol on ice probed by ambient pressure X-ray photoelectron spectroscopy

DOE PAGES

Newberg, John T.; Bluhm, Hendrik

2015-08-18

The interaction of 2-propanol with ice was examined via ambient pressure X-ray photoelectron spectroscopy (APXPS), a surface sensitive technique that probes the adsorbed 2-propanol directly with submonolayer resolution. Isothermal uptake experiments were performed on vapor deposited ice at 227 K in the presence of the equilibrium water vapor pressure of 0.05 Torr and 2-propanol partial pressures ranging from 5 × 10 -5 to 2 × 10 -3 Torr. The C 1s APXPS spectra of adsorbed 2-propanol showed two characteristic peaks associated with the C OH alcohol group and C Me methyl groups in a 1 : 2 ratio, respectively. Coveragemore » increased with 2-propanol partial pressure and followed first order Langmuir kinetics with a Langmuir constant of K = 6.3 × 10 3 Torr -1. The 1 : 2 ratio of C OH : C Me remained constant with increasing coverage, indicating there is no chemical reaction upon adsorption. The observed Langmuir kinetics using APXPS is consistent with previous observations of other small chain alcohols via indirect adsorption methods using, e.g., Knudsen cell and coated wall flow tube reactors.« less

Graphical determination of metal bioavailability to soil invertebrates utilizing the Langmuir sorption model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donkin, S.G.

1997-09-01

A new method of performing soil toxicity tests with free-living nematodes exposed to several metals and soil types has been adapted to the Langmuir sorption model in an attempt at bridging the gap between physico-chemical and biological data gathered in the complex soil matrix. Pseudo-Langmuir sorption isotherms have been developed using nematode toxic responses (lethality, in this case) in place of measured solvated metal, in order to more accurately model bioavailability. This method allows the graphical determination of Langmuir coefficients describing maximum sorption capacities and sorption affinities of various metal-soil combinations in the context of real biological responses of indigenousmore » organisms. Results from nematode mortality tests with zinc, cadmium, copper, and lead in four soil types and water were used for isotherm construction. The level of agreement between these results and available literature data on metal sorption behavior in soils suggests that biologically relevant data may be successfully fitted to sorption models such as the Langmuir. This would allow for accurate prediction of soil contaminant concentrations which have minimal effect on indigenous invertebrates.« less

Parametric study of a pin-plane probe in moderately magnetized plasma

NASA Astrophysics Data System (ADS)

Binwal, S.; Gandhi, S.; Kabariya, H.; Karkari, S. K.

2015-12-01

The application of a planar Langmuir probe in magnetized plasma is found to be problematic due to significant perturbation of plasma along the magnetic field lines intercepting the probe surface. This causes the Ampere-Volts ‘I e(U)’ characteristics of the probe to deviate from its usual exponential law; in conjunction the electron saturation current I es is significantly reduced. Moreover estimating the electron temperature T e by considering the entire semi-log plot of I e(U) gives ambiguous values of T e. To address this problem, Pitts and Stangeby developed a formula for the reduction factor for I es. This formula depends on a number of uncertain parameters, namely; the ion temperature T +, electron cross-field diffusion coefficient {{D}\\bot ,\\text{e}} and the local potential hill V h estimated by applying a floating pin probe in the vicinity of the planar probe. Due to implicit dependence of these parameters on T e, the resulting analysis is not straightforward. This paper presents a parametric study of different parameters that influence the characteristics of a planar probe in magnetized plasma. For this purpose a pin-plane probe is constructed and applied in the magnetized plasma column. A comprehensive discussion is presented that highlights the practical methodology of using this technique for extracting useful information of plasma parameters in magnetized plasmas.

Langmuir Films of Flexible Polymers Transferred to Aqueous/Liquid Crystal Interfaces Induce Uniform Azimuthal Alignment of the Liquid Crystal

PubMed Central

Kinsinger, Michael I.; Buck, Maren E.; Meli, Maria-Victoria; Abbott, Nicholas L.; Lynn, David M.

2009-01-01

We reported recently that amphiphilic polymers can be assembled at interfaces created between aqueous phases and thermotropic liquid crystals (LCs) in ways that (i) couple the organization of the polymer to the order of the LC and (ii) respond to changes in the properties of aqueous phases that can be characterized as changes in the optical appearance of the LC. This investigation sought to characterize the behavior of aqueous-LC interfaces decorated with uniaxially compressed thin films of polymers transferred by Langmuir-Schaefer (LS) transfer. Here, we report physicochemical characterization of interfaces created between aqueous phases and the thermotropic LC 4-cyano-4’-pentylbiphenyl (5CB) decorated with Langmuir films of a novel amphiphilic polymer (polymer 1), synthesized by the addition of hydrophobic and hydrophilic side chains to poly(2-vinyl-4,4’-dimethylazlactone). Initial characterization of this system resulted in the unexpected observation of uniform azimuthal alignment of 5CB after LS transfer of the polymer films to aqueous-5CB interfaces. This paper describes characterization of Langmuir films of polymer 1 hosted at aqueous-5CB interfaces as well as the results of our investigations into the origins of the uniform ordering of the LC observed upon LS transfer. Our results, when combined, support the conclusion that uniform azimuthal alignment of 5CB is the result of long-range ordering of polymer chains in the Langmuir films (in a preferred direction orthogonal to the direction of compression) that is generated during uniaxial compression of the films prior to LS transfer. Although past studies of Langmuir films of polymers at aqueous-air interfaces have demonstrated that in-plane alignment of polymer backbones can be induced by uniaxial compression, these past reports have generally made use of polymers with rigid backbones. One important outcome of this current study is thus the observation of anisotropy and long-range order in Langmuir films

Theoretical study of the accuracy of the elution by characteristic points method for bi-langmuir isotherms.

PubMed

Ravald, L; Fornstedt, T

2001-01-26

The bi-Langmuir equation has recently been proven essential to describe chiral chromatographic surfaces and we therefore investigated the accuracy of the elution by characteristic points method (ECP) for estimation of bi-Langmuir isotherm parameters. The ECP calculations was done on elution profiles generated by the equilibrium-dispersive model of chromatography for five different sets of bi-Langmuir parameters. The ECP method generates two different errors; (i) the error of the ECP calculated isotherm and (ii) the model error of the fitting to the ECP isotherm. Both errors decreased with increasing column efficiency. Moreover, the model error was strongly affected by the weight of the bi-Langmuir function fitted. For some bi-Langmuir compositions the error of the ECP calculated isotherm is too large even at high column efficiencies. Guidelines will be given on surface types to be avoided and on column efficiencies and loading factors required for adequate parameter estimations with ECP.

The fine structure of Langmuir waves observed upstream of the bow shock at Venus

NASA Technical Reports Server (NTRS)

Hospodarsky, G. B.; Gurnett, D. A.; Kurth, W. S.; Kivelson, M. G.; Strangeway, R. J.; Bolton, S. J.

1994-01-01

Highly structured Langmuir waves, also known as electron plasma oscillations, have been observed in the foreshock of Venus using the plasma wave experiment on the Galileo spacecraft during the gravity assist flyby on February 10, 1990. The Galileo wideband sampling system provides digital electric field waveform measurements at sampling rates up to 201,600 samples per second, much higher than any previous instrument of this type. The main Langmuir wave emission band occurs near the local electron plasma frequency, which was approximately 43 kHz. The Langmuir waves are observed to shift above and below the plasma frequency, sometimes by as much as 20 kHz. The shifts in frequency are closely correlated with the downstream distance from the tangent field line, implying that the shifts are controlled by the electron beam velocity. Considerable fine structure is also evident, with time scales as short as 0.15 milliseconds, corresponding to spatial scales of a few tens of Debye lengths. The frequency spectrum often consists of beat-type waveforms, with beat frequencies ranging from 0.2 to 7 kHz, and in a few cases, isolated wavepackets. The peak electric field strengths are approximately 1 mV/m. These field strengths are too small for strongly nonlinear processes to be important. The beat-type waveforms are suggestive of a parametric decay process.

Immbolization of uricase enzyme in Langmuir and Langmuir-Blodgett films of fatty acids: possible use as a uric acid sensor.

PubMed

Zanon, Nathaly C M; Oliveira, Osvaldo N; Caseli, Luciano

2012-05-01

Preserving the enzyme structure in solid films is key for producing various bioelectronic devices, including biosensors, which has normally been performed with nanostructured films that allow for control of molecular architectures. In this paper, we investigate the adsorption of uricase onto Langmuir monolayers of stearic acid (SA), and their transfer to solid supports as Langmuir-Blodgett (LB) films. Structuring of the enzyme in β-sheets was preserved in the form of 1-layer LB film, which was corroborated with a higher catalytic activity than for other uricase-containing LB film architectures where the β-sheets structuring was not preserved. The optimized architecture was also used to detect uric acid within a range covering typical concentrations in the human blood. The approach presented here not only allows for an optimized catalytic activity toward uric acid but also permits one to explain why some film architectures exhibit a superior performance. Copyright © 2011 Elsevier Inc. All rights reserved.

Condensation of monovalent and divalent metal ions on a Langmuir monolayer

NASA Astrophysics Data System (ADS)

Bloch, J. Mati; Yun, Wenbing

1990-01-01

A system that consists of a monolayer spread on a solution containing a monovalent and a divalent ion is investigated. The solution of the Poisson-Boltzmann-Stern equation for this system indicates that the metal ions segregating to the surface can be found in two distinct states. Divalent ions are chemically condensed on the monolayer, while monovalent ions are electrically attracted to it. We derive simple expressions for the charge left on the surfactant monolayer and the amount of metal ions condensed on the monolayer. These formulas reproduce very accurately (to within pro milles) the values obtained using the nonlinear Grahame equation and eliminate the need to solve that equation. That permits a simple identification of the state of the surfactant monolayer and we propose a universal condensation chart that characterizes the state of the surfactant. We further derive a chemical equilibrium equation for the surface components that has considerable range of validity. This equation requires a knowledge of the bulk concentrations only, and thus allows in many cases the identification of the state of the monolayer, avoiding the need to solve the full nonlinear Poisson-Boltzmann equation. All existing experimental results on Langmuir systems are in good agreement with the one-dimensional Poisson-Boltzmann-Stern model with no adjustable parameters. Several of these fits are presented in this work and are also mapped on the condensation chart. Our calculations point to some characteristic differences between the monovalent and the divalent ions that explain why it is possible to build Langmuir-Blodgett multilayers from divalent compensated surfactants but not from monovalent ones.

Cometary Plasma Probed by Rosetta

NASA Astrophysics Data System (ADS)

Galand, Marina; Vigren, Erik; Raghuram, Susarla; Schwartz, Steve; Eriksson, Anders; Edberg, Niklas; Lebreton, Jean-Pierre; Henri, Pierre; Burch, Jim; Fuselier, Stephen; Haessig, Myrtha; Mandt, Kathy; Altwegg, Kathrin; Tzou, Chia-You

2015-04-01

In Fall 2014, comet 67P/Churyumov-Gerasimenko, the main target of the Rosetta mission, was at 3 AU from the Sun. Its outgassing rate was only of the order of 5×1025 s-1 based on Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) / Cometary Pressure Sensor (COPS). Despite such a thin coma, a plasma of cometary origin has been detected by Rosetta Plasma Consortium (RPC) sensors and ROSINA/ Double Focusing Mass Spectrometer (DFMS). Close to the comet they have revealed the presence of a cometary ionosphere, with a hot electron population, consistent with the deposition of Extreme UltraViolet (EUV) solar radiation. We will present a comparison between RPC sensors and an energy deposition model in terms of suprathermal electron intensities [RPC/ Ion and Electron Sensor (IES)] and electron temperature and density [RPC/ LAngmuir Probe (LAP) and RPC/ Mutual Impedance Probe (MIP)]. We will also compare ion composition among the main species, between our ionospheric model and ROSINA/DFMS. We will discuss effects of the space environment on the cometary plasma. Finally, we will highlight any evolution in the cometary plasma as the comet is getting closer to perihelion.

Improved analysis techniques for cylindrical and spherical double probes.

PubMed

Beal, Brian; Johnson, Lee; Brown, Daniel; Blakely, Joseph; Bromaghim, Daron

2012-07-01

A versatile double Langmuir probe technique has been developed by incorporating analytical fits to Laframboise's numerical results for ion current collection by biased electrodes of various sizes relative to the local electron Debye length. Application of these fits to the double probe circuit has produced a set of coupled equations that express the potential of each electrode relative to the plasma potential as well as the resulting probe current as a function of applied probe voltage. These equations can be readily solved via standard numerical techniques in order to determine electron temperature and plasma density from probe current and voltage measurements. Because this method self-consistently accounts for the effects of sheath expansion, it can be readily applied to plasmas with a wide range of densities and low ion temperature (T(i)/T(e) ≪ 1) without requiring probe dimensions to be asymptotically large or small with respect to the electron Debye length. The presented approach has been successfully applied to experimental measurements obtained in the plume of a low-power Hall thruster, which produced a quasineutral, flowing xenon plasma during operation at 200 W on xenon. The measured plasma densities and electron temperatures were in the range of 1 × 10(12)-1 × 10(17) m(-3) and 0.5-5.0 eV, respectively. The estimated measurement uncertainty is +6%∕-34% in density and +∕-30% in electron temperature.

Electron temperature and density probe for small aeronomy satellites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oyama, K.-I.; Institute of Space and Plasma Sciences, National Cheng Kung University, Tainan, Taiwan; International Center for Space Weather Study and education, Kyushu University, Fukuoka

2015-08-15

A compact and low power consumption instrument for measuring the electron density and temperature in the ionosphere has been developed by modifying the previously developed Electron Temperature Probe (ETP). A circuit block which controls frequency of the sinusoidal signal is added to the ETP so that the instrument can measure both T{sub e} in low frequency mode and N{sub e} in high frequency mode from the floating potential shift of the electrode. The floating potential shift shows a minimum at the upper hybrid resonance frequency (f{sub UHR}). The instrument which is named “TeNeP” can be used for tiny satellites whichmore » do not have enough conductive surface area for conventional DC Langmuir probe measurements. The instrument also eliminates the serious problems associated with the contamination of satellite surface as well as the sensor electrode.« less

Handheld probe for portable high frame photoacoustic/ultrasound imaging system

NASA Astrophysics Data System (ADS)

Daoudi, K.; van den Berg, P. J.; Rabot, O.; Kohl, A.; Tisserand, S.; Brands, P.; Steenbergen, W.

2013-03-01

Photoacoustics is a hybrid imaging modality that is based on the detection of acoustic waves generated by absorption of pulsed light by tissue chromophors. In current research, this technique uses large and costly photoacoustic systems with a low frame rate imaging. To open the door for widespread clinical use, a compact, cost effective and fast system is required. In this paper we report on the development of a small compact handset pulsed laser probe which will be connected to a portable ultrasound system for real-time photoacoustic imaging and ultrasound imaging. The probe integrates diode lasers driven by an electrical driver developed for very short high power pulses. It uses specifically developed highly efficient diode stacks with high frequency repetition rate up to 10 kHz, emitting at 800nm wavelength. The emitted beam is collimated and shaped with compact micro optics beam shaping system delivering a homogenized rectangular laser beam intensity distribution. The laser block is integrated with an ultrasound transducer in an ergonomically designed handset probe. This handset is a building block enabling for a low cost high frame rate photoacoustic and ultrasound imaging system. The probe was used with a modified ultrasound scanner and was tested by imaging a tissue mimicking phantom.

Linear analysis of time dependent properties of Child-Langmuir flow

NASA Astrophysics Data System (ADS)

Rokhlenko, A.

2013-01-01

We continue our analysis of the time dependent behavior of the electron flow in the Child-Langmuir system, removing an approximation used earlier. We find a modified set of oscillatory decaying modes with frequencies of the same order as the inverse of the electron transient time. This range (typically MHz) allows simple experimental detection and maybe exploitation. We then study the time evolution of the current in response to a slow change of the anode voltage where the same modes of oscillations appear too. The cathode current in this case is systematically advanced or retarded depending on the direction of the voltage change.

A fast and accurate Langmuir-type polymer microtensiometer.

PubMed

Gijsenbergh, Pieter; Puers, Robert

2018-05-01

A semi-flexible polymer microtensiometer for local surface pressure measurements of Langmuir monolayers is presented. The current device geometry and read-out method via image analysis result in a theoretical accuracy of ±0.02mN⋅m -1 for a dynamic range between 0 and 75mN⋅m -1 . The tensiometer sensitivity and dynamic range are easily tunable as they are solely based on the tensiometer spring dimensions. Finite element simulations are used to determine the response time of 20ms for a subphase viscosity of 1mPa⋅s. A poroviscomechanical model of the sensor is composed and the subphase viscosity is shown to dominate the transient behavior. The tensiometer performance is verified in a Langmuir trough by applying rapid local surface pressure oscillations. A Wilhelmy plate is used as an independent measurement tool and the results of both techniques correlate well. Copyright © 2017 Elsevier B.V. All rights reserved.

Spacecraft-level verification of the Van Allen Probes' RF communication system

NASA Astrophysics Data System (ADS)

Crowne, M. J.; Srinivasan, D.; Royster, D.; Weaver, G.; Matlin, D.; Mosavi, N.

This paper presents the verification process, lessons learned, and selected test results of the radio frequency (RF) communication system of the Van Allen Probes, formerly known as the Radiation Belt Storm Probes (RBSP). The Van Allen Probes mission is investigating the doughnut-shaped regions of space known as the Van Allen radiation belts where the Sun interacts with charged particles trapped in Earth's magnetic field. Understanding this dynamic area that surrounds our planet is important to improving our ability to design spacecraft and missions for reliability and astronaut safety. The Van Allen Probes mission features two nearly identical spacecraft designed, built, and operated by the Johns Hopkins University Applied Physics Laboratory (JHU/APL) for the National Aeronautics and Space Administration (NASA). The RF communication system features the JHU/APL Frontier Radio. The Frontier Radio is a software-defined radio (SDR) designed for spaceborne communications, navigation, radio science, and sensor applications. This mission marks the first spaceflight usage of the Frontier Radio. RF ground support equipment (RF GSE) was developed using a ground station receiver similar to what will be used in flight and whose capabilities provided clarity into RF system performance that was previously not obtained until compatibility testing with the ground segments. The Van Allen Probes underwent EMC, acoustic, vibration, and thermal vacuum testing at the environmental test facilities at APL. During this time the RF communication system was rigorously tested to ensure optimal performance, including system-level testing down to threshold power levels. Compatibility tests were performed with the JHU/APL Satellite Communication Facility (SCF), the Universal Space Network (USN), and the Tracking and Data Relay Satellite System (TDRSS). Successful completion of this program as described in this paper validated the design of the system and demonstrated that it will be able to me

Nonlinear, relativistic Langmuir waves in astrophysical magnetospheres

NASA Technical Reports Server (NTRS)

Chian, Abraham C.-L.

1987-01-01

Large amplitude, electrostatic plasma waves are relevant to physical processes occurring in the astrophysical magnetospheres wherein charged particles are accelerated to relativistic energies by strong waves emitted by pulsars, quasars, or radio galaxies. The nonlinear, relativistic theory of traveling Langmuir waves in a cold plasma is reviewed. The cases of streaming electron plasma, electronic plasma, and two-streams are discussed.

Probe Scanning Support System by a Parallel Mechanism for Robotic Echography

NASA Astrophysics Data System (ADS)

Aoki, Yusuke; Kaneko, Kenta; Oyamada, Masami; Takachi, Yuuki; Masuda, Kohji

We propose a probe scanning support system based on force/visual servoing control for robotic echography. First, we have designed and formulated its inverse kinematics the construction of mechanism. Next, we have developed a scanning method of the ultrasound probe on body surface to construct visual servo system based on acquired echogram by the standalone medical robot to move the ultrasound probe on patient abdomen in three-dimension. The visual servo system detects local change of brightness in time series echogram, which is stabilized the position of the probe by conventional force servo system in the robot, to compensate not only periodical respiration motion but also body motion. Then we integrated control method of the visual servo with the force servo as a hybrid control in both of position and force. To confirm the ability to apply for actual abdomen, we experimented the total system to follow the gallbladder as a moving target to keep its position in the echogram by minimizing variation of reaction force on abdomen. As the result, the system has a potential to be applied to automatic detection of human internal organ.

Investigating Langmuir films at the air-water interface using a planar array infrared reflection-absorption spectrograph

NASA Astrophysics Data System (ADS)

Kim, Young Shin

In this work, a new planar array infrared reflection-absorption spectrograph (PA-IRRAS) was developed to investigate a broad range of Langmuir films at the air-water interface. This instrument is capable of recording sample and reference spectra simultaneously with an optical setup that is the same as that of a single-beam instrument but splits the incident infrared beam into two sections on a plane mirror (H) or a water trough. With this design, the instrument could accommodate large infrared accessories, such as a water trough. In addition, water bands were subtracted to obtain a high quality spectrum for a poly(lactic acid) (PLA) Langmuir film on the water subphase with a resolution of about 8 cm-1 in 10.8 sec. With this instrument, two types of monolayer systems were studied; polymeric and lipid Langmuir films at the air-water interface. For the polymeric monolayer system, PA-IRRAS was used as a probe to follow the real-time conformational changes associated with intermolecular interactions of the polymer chains during the compression of the monolayers. It was found that the mixture of poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) (D/L) formed a stereocomplex when the mixed solution developed the two-dimensional monolayer at the air-water interface. The stereocomplexation occurred before film compression, indicating that there is no direct correlation between film compression and stereocomplexation. For the lipid monolayer system, PA-IRRAS was also used as a probe to investigate the origin of the disruption of a lipid monolayer upon protein adsorption at the air-water interface. Analysis of the time-resolved PA-IRRAS spectra revealed that Cu(II) ion-chelated DSIDA lipid monolayer (Cu 2+-DSIDA) was readily disrupted by myoglobin adsorption as demonstrated by a blue shift of 1.7 cm-1 and a lower intensity in the vas(CH2) stretch mode of the lipid monolayer over a period of five hours. To find the origin of the disruption of the lipid monolayer, a

Parametric decay of current-driven Langmuir waves in plateau plasmas: Relevance to solar wind and foreshock events

NASA Astrophysics Data System (ADS)

Sauer, Konrad; Malaspina, David M.; Pulupa, Marc; Salem, Chadi S.

2017-07-01

Langmuir amplitude modulation in association with type III radio bursts is a well-known phenomenon since the beginning of space observations. It is commonly attributed to the superposition of beam-excited Langmuir waves and their backscattered counterparts as a result of parametric decay. The dilemma, however, is the discrepancy between fast beam relaxation and long-lasting Langmuir wave activity. Instead of starting with an unstable electron beam, our focus in this paper is on the nonlinear response of Langmuir oscillations that are driven after beam stabilization by the still persisting current of the (stable) two-electron plasma. The velocity distribution function of the second population forms a plateau (index h) with a point at which ∂fh/∂v ˜0 associated with weak damping over a more or less extended wave number range k. As shown by particle-in-cell simulations, this so-called plateau plasma drives primarily Langmuir oscillations at the plasma frequency (ωe) with k = 0 over long times without remarkable change of the distribution function. These Langmuir oscillations act as a pump wave for parametric decay by which an electron-acoustic wave slightly below ωe and a counterstreaming ion-acoustic wave are generated. Both high-frequency waves have nearly the same amplitude, which is given by the product of plateau density and velocity. Beating of these two wave types leads to pronounced Langmuir amplitude modulation, in reasonable agreement with solar wind and terrestrial foreshock observations made by the Wind spacecraft.

Multi-function diamond film fiber optic probe and measuring system employing same

DOEpatents

Young, J.P.

1998-11-24

A fused fiber optic probe having a protective cover, a fiber optic probe system, and embodiments thereof for conducting electromagnetic spectral measurements are disclosed. The fused fiber optic probe comprises a probe tip having a specific geometrical configuration, an exciting optical fiber and at least one collection optical fiber fused within a housing, preferably silica, with a protective cover disposed over at least a portion of the probe tip. The specific geometrical configurations in which the probe tip can be shaped include a slanted probe tip with an angle greater than 0{degree}, an inverted cone-shaped probe tip, and a lens head. 9 figs.

Matched dipole probe for precise electron density measurements in magnetized and non-magnetized plasmas

NASA Astrophysics Data System (ADS)

Rafalskyi, Dmytro; Aanesland, Ane

2015-09-01

We present a plasma diagnostics method based on impedance measurements of a short matched dipole placed in the plasma. This allows measuring the local electron density in the range from 1012-1015 m-3 with a magnetic field of at least 0-50 mT. The magnetic field strength is not directly influencing the data analysis and requires only that the dipole probe is oriented perpendicularly to the magnetic field. As a result, the magnetic field can be non-homogeneous or even non-defined within the probe length without any effect on the final tolerance of the measurements. The method can be applied to plasmas of relatively small dimensions (< 10 cm) and doesn't require any special boundary conditions. The high sensitivity of the impedance measurements is achieved by using a miniature matching system installed close to the probe tip, which also allows to suppress sheath resonance effects. We experimentally show here that the tolerance of the electron density measurements reaches values lower than 1%, both with and without the magnetic field. The method is successfully validated by both analytical modeling and experimental comparison with Langmuir probes. The validation experiments are conducted in a low pressure (1 mTorr) Ar discharge sustained in a 10 cm size plasma chamber with and without a transversal magnetic field of about 20 mT. This work was supported by a Marie Curie International Incoming Fellowships within FP7 (NEPTUNE PIIF-GA-2012-326054).

Study of a high-resolution PET system using a Silicon detector probe

NASA Astrophysics Data System (ADS)

Brzeziński, K.; Oliver, J. F.; Gillam, J.; Rafecas, M.

2014-10-01

A high-resolution silicon detector probe, in coincidence with a conventional PET scanner, is expected to provide images of higher quality than those achievable using the scanner alone. Spatial resolution should improve due to the finer pixelization of the probe detector, while increased sensitivity in the probe vicinity is expected to decrease noise. A PET-probe prototype is being developed utilizing this principle. The system includes a probe consisting of ten layers of silicon detectors, each a 80 × 52 array of 1 × 1 × 1 mm3 pixels, to be operated in coincidence with a modern clinical PET scanner. Detailed simulation studies of this system have been performed to assess the effect of the additional probe information on the quality of the reconstructed images. A grid of point sources was simulated to study the contribution of the probe to the system resolution at different locations over the field of view (FOV). A resolution phantom was used to demonstrate the effect on image resolution for two probe positions. A homogeneous source distribution with hot and cold regions was used to demonstrate that the localized improvement in resolution does not come at the expense of the overall quality of the image. Since the improvement is constrained to an area close to the probe, breast imaging is proposed as a potential application for the novel geometry. In this sense, a simplified breast phantom, adjacent to heart and torso compartments, was simulated and the effect of the probe on lesion detectability, through measurements of the local contrast recovery coefficient-to-noise ratio (CNR), was observed. The list-mode ML-EM algorithm was used for image reconstruction in all cases. As expected, the point spread function of the PET-probe system was found to be non-isotropic and vary with position, offering improvement in specific regions. Increase in resolution, of factors of up to 2, was observed in the region close to the probe. Images of the resolution phantom showed

Systems-level study of a nonsurvivable Jupiter turbopause probe. Volume 1: Summary

NASA Technical Reports Server (NTRS)

Wiltshire, R. S.

1972-01-01

The design of a space probe to explore the atmosphere of the planet Jupiter is discussed. Five major areas were considered: (1) definition of science requirements, (2) mission evaluation, (3) definition of probe system, (4) definition of spacecraft support requirements, and (5) nonequilibrium flow field analysis for communications blackout evaluation. The overall mission and system design are emphasized. The integration of the various technologies into complete systems designs is described. Results showed that a nonsurvivable turbopause probe mission to Jupiter with adequate data return to meet the science objectives is feasible and practical.

Langmuir-Gibbs Surface Phases and Transitions

NASA Astrophysics Data System (ADS)

Ocko, Benjamin; Sloutskin, Eli; Sapir, Zvi; Tamam, Lilach; Deutsch, Moshe; Bain, Colin

2007-03-01

Recent synchrotron x-ray measurements reveal surface ordering transitions in films of medium-length linear hydrocarbons (alkanes), spread on the water surface. Alkanes longer than hexane do not spread on the free surface of water. However, sub-mM concentrations of some anionic surfactants (e.g. CTAB) induce formation of thermodynamically stable alkane monolayers, through a ``pseudo-partial wetting'' phenomenon[1]. The monolayers, incorporating both water-insoluble alkanes (Langmuir) and water-soluble CTAB molecules (Gibbs) are called Langmuir-Gibbs (LG) films. The films formed by alkanes with n <=17 exhibit ordering transition upon cooling [2], below which the molecules are normal to the water surface and hexagonally packed, with CTAB molecules randomly mixed inside the quasi-2D crystal. Alkanes with n>17 can not form ordered LG monolayers, due to the repulsion from the n=16 tails of CTAB. This repulsion arises from the two chains' length mismatch. A demixing transition occurs upon ordering, with a pure alkane quasi-2D crystal forming on top of disordered alkyl tails of CTAB molecules. [1] K.M. Wilkinson et al., Chem. Phys. Phys. Chem. 6, 547 (2005). [2] E. Sloutskin, Z. Sapir, L. Tamam, B.M. Ocko, C.D. Bain, and M. Deutsch, Thin Solid Films, in press; K.M. Wilkinson, L. Qunfang, and C.D. Bain, Soft Matter 2, 66 (2006).

Plasma Perturbations in High-Speed Probing of Hall Thruster Discharge Chambers: Quantification and Mitigation

NASA Technical Reports Server (NTRS)

Jorns, Benjamin A.; Goebel, Dan M.; Hofer, Richard R.

2015-01-01

An experimental investigation is presented to quantify the effect of high-speed probing on the plasma parameters inside the discharge chamber of a 6-kW Hall thruster. Understanding the nature of these perturbations is of significant interest given the importance of accurate plasma measurements for characterizing thruster operation. An array of diagnostics including a high-speed camera and embedded wall probes is employed to examine in real time the changes in electron temperature and plasma potential induced by inserting a high-speed reciprocating Langmuir probe into the discharge chamber. It is found that the perturbations onset when the scanning probe is downstream of the electron temperature peak, and that along channel centerline, the perturbations are best characterized as a downstream shift of plasma parameters by 15-20% the length of the discharge chamber. A parametric study is performed to investigate techniques to mitigate the observed probe perturbations including varying probe speed, probe location, and operating conditions. It is found that the perturbations largely disappear when the thruster is operated at low power and low discharge voltage. The results of this mitigation study are discussed in the context of recommended methods for generating unperturbed measurements of the discharge chamber plasma.

Evaluating polymeric biomaterial–environment interfaces by Langmuir monolayer techniques

PubMed Central

Schöne, Anne-Christin; Roch, Toralf; Schulz, Burkhard

2017-01-01

Polymeric biomaterials are of specific relevance in medical and pharmaceutical applications due to their wide range of tailorable properties and functionalities. The knowledge about interactions of biomaterials with their biological environment is of crucial importance for developing highly sophisticated medical devices. To achieve optimal in vivo performance, a description at the molecular level is required to gain better understanding about the surface of synthetic materials for tailoring their properties. This is still challenging and requires the comprehensive characterization of morphological structures, polymer chain arrangements and degradation behaviour. The review discusses selected aspects for evaluating polymeric biomaterial–environment interfaces by Langmuir monolayer methods as powerful techniques for studying interfacial properties, such as morphological and degradation processes. The combination of spectroscopic, microscopic and scattering methods with the Langmuir techniques adapted to polymers can substantially improve the understanding of their in vivo behaviour. PMID:28468918

Immobilization of alcohol dehydrogenase in phospholipid Langmuir-Blodgett films to detect ethanol.

PubMed

Caseli, Luciano; Perinotto, Angelo C; Viitala, Tapani; Zucolotto, Valtencir; Oliveira, Osvaldo N

2009-03-03

Enzyme immobilization in nanostructured films may be useful for a number of biomimetic systems, particularly if suitable matrixes are identified. Here we show that alcohol dehydrogenase (ADH) has high affinity toward a negatively charged phospholipid, dimyristoylphosphatidic acid (DMPA), which forms a Langmuir monolayer at an air-water interface. Incorporation of ADH into the DMPA monolayer was monitored with surface pressure measurements and polarization-modulation infrared reflection absorption spectroscopy, with the alpha-helices from ADH being mainly oriented parallel to the water surface. ADH remained at the interface even at high surface pressures, thus allowing deposition of Langmuir-Blodgett (LB) films from the DMPA-ADH film. Indeed, interaction with DMPA enhances the transfer of ADH, where the mass transferred onto a solid support increased from 134 ng for ADH on a Gibbs monolayer to 178 ng for an LB film with DMPA. With fluorescence spectroscopy it was possible to confirm that the ADH structure was preserved even after one month of the LB deposition. ADH-containing films deposited onto gold-interdigitated electrodes were employed in a sensor array capable of detecting ethanol at concentrations down to 10 ppb (in volume), using impedance spectroscopy as the method of detection.

Effects of Langmuir Circulations on the Plankton

DTIC Science & Technology

1999-09-30

remains the same as stated previously for this project. I wish to establish whether the plankton is affected by Langmuir Circulations (LCs). LCs are wind...particles from Optical Plankton Counter data) variables. This also has proved fruitful and has yielded results (below) different than those I originally...complement the standard, depth-integrated estimates of zooplankton abundance from bongo net deployments. This is proving to be a significant

Design and validation of the ball-pen probe for measurements in a low-temperature magnetized plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bousselin, G.; Cavalier, J.; Pautex, J. F.

Ball-pen probes have been used in fusion devices for direct measurements of the plasma potential. Their application in low-temperature magnetized plasma devices is still subject to studies. In this context, a ball-pen probe has been recently implemented on the linear plasma device Mirabelle. Produced by a thermionic discharge, the plasma is characterized by a low electron temperature and a low density. Plasma confinement is provided by an axial magnetic field that goes up to 100 mT. The principle of the ball-pen probe is to adjust the saturation current ratio to 1 by reducing the electron current contribution. In that case,more » the floating potential of the probe is close to the plasma potential. A thorough study of the ball-pen probe operation is performed for different designs of the probe over a large set of plasma conditions. Comparisons between ball-pen, Langmuir, and emissive probes are conducted in the same plasma conditions. The ball-pen probe is successfully measuring the plasma potential in these specific plasma conditions only if an adapted electronics and an adapted probe size to the plasma characteristic lengths ({lambda}{sub D}, {rho}{sub ce}) are used.« less

Cross Comparison of Electron Density and Electron Temperature Observations from the DICE CubeSat Langmuir Probes and the Millstone Hill Incoherent Scatter Radar.

NASA Astrophysics Data System (ADS)

Swenson, C.; Erickson, P. J.; Crowley, G.; Pilinski, M.; Barjatya, A.; Fish, C. S.

2014-12-01

The Dynamic Ionosphere CubeSat Experiment (DICE) consists of two identical 1.5U CubeSats deployed simultaneously from a single P-POD (Poly Picosatellite Orbital Deployer) into the same orbit. Several observational campaigns were planned between the DICE CubeSats and the mid-latitude Millstone Hill Incoherent Scatter Radar (ISR) in order to calibrate the DICE measurements of electron density and electron temperature. In this presentation, we compare in-situ observations from the Dynamic Ionosphere CubeSat Experiment (DICE) and from the Millstone Hill ISR. Both measurements are cross-calibrated against an assimilative model of the global ionospheric electron density. The electron density and electron temperature were obtained for three Millstone Hill DICE overflights (2013-03-12, 2013-03-15, 2013-03-17). We compare the data during quiet and geomagnetically disturbed conditions and find evidence of an storm enhanced density (SED) plume in the topside ionosphere on 2013-03-17 at 19? UTC. During this disturbed interval, American longitude sector high density plasma was convected near 15 SLT towards the noontime cusp. DICE was selected for flight under the NSF "CubeSat-based Science Mission for Space Weather and Atmospheric Research" program. The DICE twin satellites were launched on a Delta II rocket on October 28, 2011. The satellites are flying in a "leader-follower" formation in an elliptical orbit which ranges from 820 to 400 km in altitude. Each satellite carries a fixed-bias DC Langmuir Probe (DCP) to measure in-situ ionospheric plasma densities and a science grade magnetometer to measure DC and AC geomagnetic fields. The purpose of these measurements was to permit accurate identification of storm-time features such as the SED bulge and plume. The mission team combines expertise from ASTRA, Utah State University/Space Dynamics Laboratory (USU/SDL), and Embry-Riddle Aeronautical University. In this paper we present a comparison of data from DICE and Millstone Hill

Statistical Analysis of Bursty Langmuir Waves, Alfvén and Whistler Waves, and Precipitating Electrons Seen by the CHARM II Nightside Sounding Rocket

NASA Astrophysics Data System (ADS)

Dombrowski, M. P.; Labelle, J. W.; Kletzing, C.; Bounds, S. R.; Kaeppler, S. R.

2013-12-01

Bursty Langmuir waves have been interpreted as the result of the superposition of multiple Langmuir normal-mode waves, with the resultant modulation being the beat pattern between waves with e.g. 10 kHz frequency differences. The normal-mode waves could be generated either through wave-wave interactions with VLF waves, or through independent linear processes. The CHARM II sounding rocket was launched into a substorm at 9:49 UT on 15 February 2010, from the Poker Flat Research Range in Alaska. The primary instruments included the Dartmouth High-Frequency Experiment (HFE), a receiver system which effectively yields continuous (100% duty cycle) E-field waveform measurements up to 5 MHz, as well as a number of charged particle detectors, including a wave-particle correlator. The payload also included a magnetometer and several low-frequency wave instruments. CHARM II encountered several regions of strong Langmuir wave activity throughout its 15-minute flight, including several hundred discrete Langmuir-wave bursts. We show results of a statistical analysis of CHARM II data for the entire flight, comparing HFE data with the other payload instruments, specifically looking at timings and correlations between bursty Langmuir waves, Alfvén and whistler-mode waves, and electrons precipitating parallel to the magnetic field. Following a similar analysis on TRICE dayside sounding rocket data, we also calculate the fraction of correlated waves with VLF waves at appropriate frequencies to support the wave-wave interaction bursty Langmuir wave generation mechanism, and compare to results from CHARM II nightside data.

Linear analysis of time dependent properties of Child-Langmuir flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rokhlenko, A.

We continue our analysis of the time dependent behavior of the electron flow in the Child-Langmuir system, removing an approximation used earlier. We find a modified set of oscillatory decaying modes with frequencies of the same order as the inverse of the electron transient time. This range (typically MHz) allows simple experimental detection and maybe exploitation. We then study the time evolution of the current in response to a slow change of the anode voltage where the same modes of oscillations appear too. The cathode current in this case is systematically advanced or retarded depending on the direction of themore » voltage change.« less

Power loss in open cavity diodes and a modified Child-Langmuir law

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biswas, Debabrata; Kumar, Raghwendra; Puri, R.R.

Diodes used in most high power devices are inherently open. It is shown that under such circumstances, there is a loss of electromagnetic radiation leading to a lower critical current as compared to closed diodes. The power loss can be incorporated in the standard Child-Langmuir framework by introducing an effective potential. The modified Child-Langmuir law can be used to predict the maximum power loss for a given plate separation and potential difference as well as the maximum transmitted current for this power loss. The effectiveness of the theory is tested numerically.

Hall Probe Calibration System Design for the Mu2e Solenoid Field Mapping System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Orozco, Charles; Elementi, Luciano; Feher, Sandor

The goal of the Mu2e experiment at Fermilab is to search for charged-lepton flavor violation by looking for neutrino-less muon to electron conversion in the field of the nucleus. The Mu2e experimental apparatus utilizes a complex magnetic field in the muon generation and momentum and charge selection process. Precise knowledge of the magnetic field is crucial. It is planned to map the solenoid field with calibrated 3D Hall probes up to 10 -5 accuracy. Here, this article describes a new design of a Hall probe calibration system that will be used to calibrate 3D Hall probes to better than 10more » -5 accuracy for the Mu2e Solenoid Field Mapping System.« less

Hall Probe Calibration System Design for the Mu2e Solenoid Field Mapping System

DOE PAGES

Orozco, Charles; Elementi, Luciano; Feher, Sandor; ...

2018-02-22

The goal of the Mu2e experiment at Fermilab is to search for charged-lepton flavor violation by looking for neutrino-less muon to electron conversion in the field of the nucleus. The Mu2e experimental apparatus utilizes a complex magnetic field in the muon generation and momentum and charge selection process. Precise knowledge of the magnetic field is crucial. It is planned to map the solenoid field with calibrated 3D Hall probes up to 10 -5 accuracy. Here, this article describes a new design of a Hall probe calibration system that will be used to calibrate 3D Hall probes to better than 10more » -5 accuracy for the Mu2e Solenoid Field Mapping System.« less

Phase Coupling Between Spectral Components of Collapsing Langmuir Solitons in Solar Type III Radio Bursts

NASA Technical Reports Server (NTRS)

Thejappa, G.; MacDowall, R. J.; Bergamo, M.

2012-01-01

We present the high time resolution observations of one of the Langmuir wave packets obtained in the source region of a solar type III radio burst. This wave packet satisfies the threshold condition of the supersonic modulational instability, as well as the criterion of a collapsing Langmuir soliton, i.e., the spatial scale derived from its peak intensity is less than that derived from its short time scale. The spectrum of t his wave packet contains an intense spectral peak at local electron plasma frequency, f(sub pe) and relatively weaker peaks at 2f(sub pe) and 3f(sub pe). We apply the wavelet based bispectral analysis technique on this wave packet and compute the bicoherence between its spectral components. It is found that the bicoherence exhibits two peaks at (approximately f(sub pe), approximately f(sub pe)) and (approximately f(sub pe) approximately 2f(sub pe)), which strongly suggest that the spectral peak at 2f(sub pe) probably corresponds to the second harmonic radio emission, generated as a result of the merging of antiparallel propagating Langmuir waves trapped in the collapsing Langmuir soliton, and, the spectral peak at 3f(sub pe) probably corresponds to the third harmonic radio emission, generated as a result of merging of a trapped Langmuir wave and a second harmonic electromagnetic wave.

Polyaniline Langmuir-Blodgett film based aptasensor for ochratoxin A detection.

PubMed

Prabhakar, Nirmal; Matharu, Zimple; Malhotra, B D

2011-06-15

Ochratoxin A (OTA) produced by Aspergillus Ochraceus and Penicillium verrucosum is a very dangerous toxin due to its toxic effects in human beings and its presence in a wide range of food products and cereals. A Langmuir-Blodgett (polyaniline (PANI)-stearic acid (SA)) film based highly sensitive and robust impedimetric aptasensor has been developed for ochratoxin A (OTA) detection. DNA Aptamer (Apt-DNA) specific to OTA has been covalently immobilized onto mixed Langmuir-Blodgett (LB) monolayer comprising of PANI-SA deposited onto indium tin-oxide (ITO) coated glass plates. This Apt-DNA/PANI-SA/ITO aptaelectrode has been characterized using scanning electron microscopy, Fourier transform-infrared spectroscopy, contact angle measurements, cyclic voltammetry and electrochemical impedance spectroscopy, respectively. The Apt-DNA/PANI-SA/ITO aptasensor shows detection of OTA by electrochemical impedance spectroscopy in the linear range of 0.0001 μg/ml (0.1 ng/ml) to 0.01 μg/ml (10 ng/ml) and 1 μg/ml-25 μg/ml with detection limit of 0.1 ng/ml in 15 min. The Apt-DNA/PANI-SA/ITO aptasensor can be reused ∼13 times. The binding or affinity constant (K(a)) of aptamer with OTA, calculated using Langmuir adsorption isotherm, is found be 1.21×10(7) M(-1). Copyright © 2011 Elsevier B.V. All rights reserved.

General properties of the radiation spectra from relativistic electrons moving in Langmuir turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teraki, Yuto; Takahara, Fumio, E-mail: teraki@vega.ess.sci.osaka-u.ac.jp

2014-05-20

Using a numerical method, we examine the radiation spectra from relativistic electrons moving in Langmuir turbulence, which are expected to exist in high energy astrophysical objects. The spectral shape is characterized by the spatial scale λ, field strength σ, and frequency of the Langmuir waves, and in terms of frequency they are represented by ω{sub 0} = 2πc/λ, ω{sub st} = eσ/mc, and ω{sub p}, respectively. We normalize ω{sub st} and ω {sub p} by ω{sub 0} as a ≡ ω{sub st}/ω{sub 0} and b ≡ ω{sub p}/ω{sub 0}, and examine the spectral shape in the a–b plane. An earliermore » study based on the diffusive radiation in Langmuir turbulence (DRL) theory by Fleishman and Toptygin showed that the typical frequency is γ{sup 2}ω{sub p} and that the low frequency spectrum behaves as F {sub ω}∝ω{sup 1} for b > 1 irrespective of a. Here, we adopt the first principle numerical approach to obtain the radiation spectra in more detail. We generate Langmuir turbulence by superposing Fourier modes, injecting monoenergetic electrons, solving the equation of motion, and calculating the radiation spectra using a Lienard-Wiechert potential. We find different features from the DRL theory for a > b > 1. The peak frequency turns out to be γ{sup 2}ω{sub st}, which is higher than the γ{sup 2}ω{sub p} predicted by the DRL theory, and the spectral index of the low frequency region is not 1 but 1/3. This is because the typical deflection angle of electrons is larger than the angle of the beaming cone ∼1/γ. We call the radiation for this case 'wiggler radiation in Langmuir turbulence'.« less

Two-dimensional axisymmetric Child-Langmuir scaling law

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ragan-Kelley, Benjamin; Verboncoeur, John; Feng Yang

The classical one-dimensional (1D) Child-Langmuir law was previously extended to two dimensions by numerical calculation in planar geometries. By considering an axisymmetric cylindrical system with axial emission from a circular cathode of radius r, outer drift tube radius R>r, and gap length L, we further examine the space charge limit in two dimensions. Simulations were done with no applied magnetic field as well as with a large (100 T) longitudinal magnetic field to restrict motion of particles to 1D. The ratio of the observed current density limit J{sub CL2} to the theoretical 1D value J{sub CL1} is found to bemore » a monotonically decreasing function of the ratio of emission radius to gap separation r/L. This result is in agreement with the planar results, where the emission area is proportional to the cathode width W. The drift tube in axisymmetric systems is shown to have a small but measurable effect on the space charge limit. Strong beam edge effects are observed with J(r)/J(0) approaching 3.5. Two-dimensional axisymmetric electrostatic particle-in-cell simulations were used to produce these results.« less

Ultrasonic probe system for the bore-side inspection of tubes and welds therein

DOEpatents

Cook, K. Von; Koerner, Dan W.; Cunningham, Jr., Robert A.; Murrin, Jr., Horace T.

1977-07-26

A probe system is provided for the bore-side inspection of tube-to-header welds and the like for small diameter tubes. The probe head of the system includes an ultrasonic transmitter-receiver transducer, a separate ultrasonic receiver, a reflector associated with the transducer to properly orient the ultrasonic signal with respect to a tube wall, a baffle to isolate the receiver from the transducer, and means for maintaining the probe head against the tube wall under investigation. Since the probe head must rotate to inspect along a helical path, special ultrasonic signal connections are employed. Through the use of the probe, flaws at either the inner or outer surfaces may be detected.

Predicting heavy metals' adsorption edges and adsorption isotherms on MnO2 with the parameters determined from Langmuir kinetics.

PubMed

Hu, Qinghai; Xiao, Zhongjin; Xiong, Xinmei; Zhou, Gongming; Guan, Xiaohong

2015-01-01

Although surface complexation models have been widely used to describe the adsorption of heavy metals, few studies have verified the feasibility of modeling the adsorption kinetics, edge, and isotherm data with one pH-independent parameter. A close inspection of the derivation process of Langmuir isotherm revealed that the equilibrium constant derived from the Langmuir kinetic model, KS-kinetic, is theoretically equivalent to the adsorption constant in Langmuir isotherm, KS-Langmuir. The modified Langmuir kinetic model (MLK model) and modified Langmuir isotherm model (MLI model) incorporating pH factor were developed. The MLK model was employed to simulate the adsorption kinetics of Cu(II), Co(II), Cd(II), Zn(II) and Ni(II) on MnO2 at pH3.2 or 3.3 to get the values of KS-kinetic. The adsorption edges of heavy metals could be modeled with the modified metal partitioning model (MMP model), and the values of KS-Langmuir were obtained. The values of KS-kinetic and KS-Langmuir are very close to each other, validating that the constants obtained by these two methods are basically the same. The MMP model with KS-kinetic constants could predict the adsorption edges of heavy metals on MnO2 very well at different adsorbent/adsorbate concentrations. Moreover, the adsorption isotherms of heavy metals on MnO2 at various pH levels could be predicted reasonably well by the MLI model with the KS-kinetic constants. Copyright © 2014. Published by Elsevier B.V.

Boronate-Based Fluorescent Probes: Imaging Hydrogen Peroxide in Living Systems

PubMed Central

Lin, Vivian S.; Dickinson, Bryan C.; Chang, Christopher J.

2014-01-01

Hydrogen peroxide, a reactive oxygen species with unique chemical properties, is produced endogenously in living systems as a destructive oxidant to ward off pathogens or as a finely tuned second messenger in dynamic cellular signaling pathways. In order to understand the complex roles that hydrogen peroxide can play in biological systems, new tools to monitor hydrogen peroxide in its native settings, with high selectivity and sensitivity, are needed. Knowledge of organic synthetic reactivity provides the foundation for the molecular design of selective, functional hydrogen peroxide probes. A palette of fluorescent and luminescent probes that react chemoselectively with hydrogen peroxide has been developed, utilizing a boronate oxidation trigger. These indicators offer a variety of colors and in cellulo characteristics and have been used to examine hydrogen peroxide in a number of experimental setups, including in vitro fluorometry, confocal fluorescence microscopy, and flow cytometry. In this chapter, we provide an overview of the chemical features of these probes and information on their behavior to help researchers select the optimal probe and application. PMID:23791092

Proposed Solar Probe telecommunications system concept

NASA Astrophysics Data System (ADS)

Kellogg, K.; Devereaux, A.; Vacchione, J.; Kapoor, V.; Crist, R.

1992-01-01

A proposed telecommunications system concept for NASA's Solar Probe mission is described. Key system requirements include 70 kbps data rate at perihelion and operation at X-band (uplink/downlink) and Ka-band (downlink). A design control table is presented to demonstrate design compliance with telecommunication needs. The Ka-band feed is to be a hexagonal array of 37 active elements, each containing 1/4W HEMT amplifiers. The array is located at the Cassegrain point of a 0.75-m reflector. When compared to the TWTA-based system, the Ka-band active array feed provides advantages of reduced mass, increased dc power efficiency, enhanced reliability, graceful degradation, and reduced volume requirements.

Methylene blue adsorption on a DMPA lipid langmuir monolayer.

PubMed

Giner Casares, Juan José; Camacho, Luis; Martín-Romero, Maria Teresa; López Cascales, José Javier

2010-07-12

Adsorption of methylene blue (MB) onto a dimyristoylphosphatidic acid (DMPA) Langmuir air/water monolayer is studied by molecular dynamics (MD) simulations, UV reflection spectroscopy and surface potential measurements. The free-energy profile associated with MB transfer from water to the lipid monolayer shows two minima of -66 and -60 kJ mol(-1) for its solid and gas phase, respectively, corresponding to a spontaneous thermodynamic process. From the position of the free-energy minima, it is possible to predict the precise location of MB in the interior of the DMPA monolayer. Thus, MB is accommodated in the phosphoryl or carbonyl region of the DMPA Langmuir air/water interface, depending on the isomorphic state (solid or gas phase, respectively). Reorientation of MB, measured from the bulk solution to the interior of the lipid monolayer, passes from a random orientation in bulk solution to an orientation parallel to the surface of the lipid monolayer when MB is absorbed.

Self-consistent Langmuir waves in resonantly driven thermal plasmas

NASA Astrophysics Data System (ADS)

Lindberg, R. R.; Charman, A. E.; Wurtele, J. S.

2007-12-01

The longitudinal dynamics of a resonantly driven Langmuir wave are analyzed in the limit that the growth of the electrostatic wave is slow compared to the bounce frequency. Using simple physical arguments, the nonlinear distribution function is shown to be nearly invariant in the canonical particle action, provided both a spatially uniform term and higher-order spatial harmonics are included along with the fundamental in the longitudinal electric field. Requirements of self-consistency with the electrostatic potential yield the basic properties of the nonlinear distribution function, including a frequency shift that agrees closely with driven, electrostatic particle simulations over a range of temperatures. This extends earlier work on nonlinear Langmuir waves by Morales and O'Neil [G. J. Morales and T. M. O'Neil, Phys. Rev. Lett. 28, 417 (1972)] and Dewar [R. L. Dewar, Phys. Plasmas 15, 712 (1972)], and could form the basis of a reduced kinetic treatment of plasma dynamics for accelerator applications or Raman backscatter.

Fine Spectral Properties of Langmuir Waves Observed Upstream of the Saturn's Bowshock by the Cassini Wideband Receiver

NASA Astrophysics Data System (ADS)

Hospodarsky, G. B.; Pisa, D.; Santolik, O.; Kurth, W. S.; Soucek, J.; Basovnik, M.; Gurnett, D. A.; Arridge, C. S.

2015-12-01

Langmuir waves are commonly observed in the upstream regions of planetary and interplanetary shock. Solar wind electrons accelerated at the shock front are reflected back into the solar wind and can form electron beams. In regions with beams, the electron distribution becomes unstable and electrostatic waves can be generated. The process of generation and the evolution of electrostatic waves strongly depends on the solar wind electron distribution and generally exhibits complex behavior. Langmuir waves can be identified as intense narrowband emission at a frequency very close to the local plasma frequency and weaker broadband waves below and above the plasma frequency deeper in the downstream region. We present a detailed study of Langmuir waves detected upstream of the Saturnian bowshock by the Cassini spacecraft. Using data from the Radio and Plasma Wave Science (RPWS), Magnetometer (MAG) and Cassini Plasma Spectrometer (CAPS) instruments we have analyzed several periods containing the extended waveform captures by the Wideband Receiver. Langmuir waves are a bursty emission highly controlled by variations in solar wind conditions. Unfortunately due to a combination of instrumental field of view and sampling period, it is often difficult to identify the electron distribution function that is unstable and able to generate Langmuir waves. We used an electrostatic version of particle-in-cell simulation of the Langmuir wave generation process to reproduce some of the more subtle observed spectral features and help understand the late stages of the instability and interactions in the solar wind plasma.

The Multiple Resonance Probe: A Novel Device for Industry Compatible Plasma Diagnostics

NASA Astrophysics Data System (ADS)

Brinkmann, Ralf Peter; Storch, Robert; Lapke, Martin; Oberrath, Jens; Schulz, Christian; Styrnoll, Tim; Zietz, Christian; Awakowicz, Peter; Musch, Thomas; Mussenbrock, Thomas; Rolfes, Ilona

2012-10-01

To be useful for the supervision or control of technical plasmas, a diagnostic method must be i) robust and stable, ii) insensitive to perturbation by the process, iii) itself not perturbing the process, iv) clearly and easily interpretable without the need for calibration, v) compliant with the requirements of process integration, and, last but not least, vi) economical in terms of investment, footprint, and maintenance. Plasma resonance spectroscopy, exploiting the natural ability of plasmas to resonate on or near the electron plasma frequency, provides a good basis for such an ``industry compatible'' plasma diagnostics. The contribution will describe the general idea of active plasma resonance spectroscopy and introduce a mathematical formalism for its analysis. It will then focus on the novel multipole resonance probe (MRP), where the excited resonances can be classified explicitly and the connection between the probe response and the desired electron density can be cast as a simple formula. The current state of the MRP project will be described, including the experimental characterization of a prototype in comparison with Langmuir probes, and the development of a specialized measurement circuit.

Probe tip heating assembly

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmitz, Roger William; Oh, Yunje

A heating assembly configured for use in mechanical testing at a scale of microns or less. The heating assembly includes a probe tip assembly configured for coupling with a transducer of the mechanical testing system. The probe tip assembly includes a probe tip heater system having a heating element, a probe tip coupled with the probe tip heater system, and a heater socket assembly. The heater socket assembly, in one example, includes a yoke and a heater interface that form a socket within the heater socket assembly. The probe tip heater system, coupled with the probe tip, is slidably receivedmore » and clamped within the socket.« less

Langmuir wave damping decreases slowly

NASA Astrophysics Data System (ADS)

Rose, Harvey

2006-10-01

The onset of stimulated Raman scatter in a single laser speckle occurs (D. S. Montgomery et al., Phys. Plasmas, 9, 2311 (2002)) at lower laser intensity, I, than predicted by linear theory based on classical Landau damping, νL, of the SRS daughter Langmuir wave. Does this imply that SRS onset in a speckled laser beam, propagating through long scale length plasma, is also at odds with linear theory? It has been shown (Harvey A. Rose and D. F. DuBois, Phys. Rev. Lett. 72, 2883 (1994)) that linear convective gain in speckles with large fluctuations of I about the average, , leads to onset at a value of , Ic, small compared to that for onset in a uniform beam. While nonlinear electron trapping effects may occur in very intense speckles, whether or not these effects are sufficient to lower the onset value of below Ic depends on how strongly electrons must be trapped before there is significant reduction in νL. As the amplitude of an SRS daughter Langmuir wave increases, its νL decreases by the factor ν/φb, due to the competition between electron trapping, with electron bounce frequency, φb, and escape of these trapped electrons by advection out of a speckle's side, at rate ν. This result (Harvey A. Rose and David A. Russell, Phys. Plasmas, 8, 4784 (2001)) is valid for ν/φb 1. In this talk I present a nonlinear, transit time damping, calculation of νL and find that reduction by a factor of two does not occur until φb/ν 5. This slow turn on of trapping effects suggests that the linear calculation of Ic is NIF relevant.