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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Polarizer design for millimeter-wave plasma diagnostics

Radiation from magnetized plasmas is in general elliptically polarized. In order to convert the elliptical polarization to linear polarization, mirrors with grooved surfaces are currently employed in our collective Thomson scattering diagnostic at ASDEX Upgrade. If these mirrors can be substituted by birefringent windows, the microwave receivers can be designed to be more compact at lower cost. Sapphire windows (a-cut) as well as grooved high density polyethylene windows can serve this purpose. The sapphire window can be designed such that the calculated transmission of the wave energy is better than 99%, and that of the high density polyethylene can be better than 97%.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

PLASMA DIAGNOSTIC POTENTIAL OF 2p4f IN N{sup +}—ACCURATE WAVELENGTHS AND OSCILLATOR STRENGTHS

Radiative emission lines from nitrogen and its ions are often observed in nebula spectra, where the N{sup 2+} abundance can be inferred from lines of the 2p4f configuration. In addition, intensity ratios between lines of the 2p3p-2p3s and 2p4f-2p3d transition arrays can serve as temperature diagnostics. To aid abundance determinations and plasma diagnostics, wavelengths and oscillator strengths were calculated with high precision for electric dipole (E1) transitions from levels in the 2p4f configuration of N{sup +}. Electron correlation and relativistic effects, including the Breit interaction, were systematically taken into account within the framework of the multiconfiguration Dirac-Hartree-Fock method. Except for the 2p4f-2p4d transitions with quite large wavelengths and the two-electron-one-photon 2p4f-2s2p {sup 3} transitions, the uncertainties of the present calculations were controlled to within 3% and 5% for wavelengths and oscillator strengths, respectively. We also compared our results with other theoretical and experimental values when available. Discrepancies were found between our calculations and previous calculations due to the neglect of relativistic effects in the latter.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Polarization-separated double-imaging spectroscopy for weakly-ionized plasma diagnostics

Laser Thomson scattering, which provides thermal properties of electrons, has been extensively utilized in plasma diagnostics. However, being a non-resonant linear light scattering technique, it often encounters several challenges in weakly-ionized plasma diagnostics due to spectral overlap with different scatterings induced from other existing species, including Mie, Rayleigh, and rotational Raman scatterings. To address this challenge, we propose an imaging spectroscopy technique, polarization-separated double-imaging spectroscopy (PoDIS), which selectively separates specific scatterings based on their polarization characteristics. Using an atmospheric plasma jet as a plasma source for demonstration, we show that PoDIS can effectively separate rotational Raman and Thomson scatterings from a superimposed spectrum without prior knowledge or assumptions about the thermal properties of neutrals or electrons. This separation enables independent fitting of the rotational Raman and Thomson scattering spectra, allowing for precise determination of the thermal properties of neutral particles and electrons separately.

Bak, Junhwi [Texas A&M University, College Station↗
NASA NTRS1972

A comparative study of electrical probe techniques for plasma diagnostics

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.

Szuszczewicz, E. P.↗
DOE OSTI2018

Millimeter-wave system-on-chip advancement for fusion plasma diagnostics

Recent advances in radio-frequency system-on-chip technology have provided mm-wave fusion plasma diagnostics with the capability to overcome major challenges such as space inefficiency, inflexible installation, sensitivity, susceptibility to EMI, and prohibitively high cost of conventional discrete component assemblies as higher imaging resolution and data accuracy are achieved by increasing the number of channels. Nowadays, shrinking transistor gate lengths on fabrication techniques have enabled hundreds of GHz operation, which is suitable for millimeter-wave diagnostics on current and future tokamaks. The Davis Millimeter Wave Research Center (DMRC) has successfully developed V-band (55-75 GHz) transmitter and receiver chips for Microwave Imaging Reflectometer (MIR) instruments. The transmitter can illuminate 8 different frequencies simultaneously within 55-75 GHz. Moreover, the receiver has the capability to amplify the reflected signal (>30 dB) while offering 10-30× reduction in noise temperature compared to current MIR instruments. Plasma diagnostics requires ultra-wideband (more than 20 GHz) operation which is approximately nine times wider bandwidth than the recent commercial impetus for communication systems. Current efforts are underway for gallium-arsenide monolithic microwave integrated circuit receiver chips at W-band (75-110 GHz) and F-band (90–140 GHz) permitting measurements at higher toroidal magnetic fields.

47 OTHER INSTRUMENTATION↗
DOE OSTI2014

THz time-domain spectroscopy for tokamak plasma diagnostics

The technology is now becoming mature for diagnostics using large portions of the electromagnetic spectrum simultaneously, in the form of THz pulses. THz radiation-based techniques have become feasible for a variety of applications, e.g., spectroscopy, imaging for security, medicine and pharmaceutical industry. In particular, time-domain spectroscopy (TDS) is now being used also for plasma diagnostics in various fields of application. This technique is promising also for plasmas for fusion applications, where plasma characteristics are non-uniform and/or evolve during the discharge This is because THz pulses produced with femtosecond mode-locked lasers conveniently span the spectrum above and below the plasma frequency and, thus, can be used as very sensitive and versatile probes of widely varying plasma parameters. The short pulse duration permits time resolving plasma characteristics while the large frequency span permits a large dynamic range. The focus of this work is to present preliminary experimental and simulation results demonstrating that THz TDS can be realistically adapted as a versatile tokamak plasma diagnostic technique.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Plasma diagnostics of low pressure high power impulse magnetron sputtering assisted by electron cyclotron wave resonance plasma

This paper reports on an investigation of the hybrid pulsed sputtering source based on the combination of electron cyclotron wave resonance (ECWR) inductively coupled plasma and high power impulse magnetron sputtering (HiPIMS) of a Ti target. The plasma source, operated in an Ar atmosphere at a very low pressure of 0.03 Pa, provides plasma where the major fraction of sputtered particles is ionized. It was found that ECWR assistance increases the electron temperature during the HiPIMS pulse. The discharge current and electron density can achieve their stable maximum 10 {mu}s after the onset of the HiPIMS pulse. Further, a high concentration of double charged Ti{sup ++} with energies of up to 160 eV was detected. All of these facts were verified experimentally by time-resolved emission spectroscopy, retarding field analyzer measurement, Langmuir probe, and energy-resolved mass spectrometry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Preface to the Proceedings of the 25th Topical Conference on High-Temperature Plasma Diagnostics

The 25th Topical Conference on High-Temperature Plasma Diagnostics (HTPD 2024) was held in Asheville, NC, USA, at the Renaissance Asheville Downtown Hotel from 21 to 25 April 2024. This biennial conference brings together scientists and engineers from a variety of fields, including magnetic confinement fusion, inertial confinement fusion, space plasmas, astrophysics, and industrial applications, to discuss mutual problems in the development of instrumentation and experimental techniques for the characterization of high-temperature plasmas. As the 25th meeting, HTPD 2024 represents ∼50 years of ongoing international collaboration on these topics.

Biewer, Theodore [ORNL] (ORCID:0000000174563509)↗
DOE OSTI2013

Plasma diagnostic method using intermodulation frequencies in a Langmuir probe

A plasma diagnostic method using intermodulation frequencies is developed. When dual-frequency (ω{sub 1},ω{sub 2}) voltage signals are applied to a probe, the intermodulation frequencies (ω{sub 2}±ω{sub 1}, ω{sub 2}±2ω{sub 1}) between the signals are generated due to the nonlinearity of the sheath. From the analysis of the intermodulation frequencies, the plasma parameters, such as the electron temperature and the plasma density, can be obtained. The measured plasma parameters from this method are compared to the results from the measured electron energy distribution function, and they are in good agreement. Because the intermodulation currents originated from the plasma not from the stray component of the measurement system, an accurate measurement of the plasma parameters is achievable.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1977

Cold plasma diagnostics using satellite measurements of VLF signals from ground transmitters

A diagnostic technique to obtain the cold-plasma density profile in the magnetosphere is introduced. This method uses satellite measurements of group delay and pulse duration of VLF signals from ground transmitters in conjunction with a detailed ray-tracing analysis. An iterative method is involved which starts with an approximate density profile, computes the ray paths for that profile, and then compares the properties of the rays that reach the satellite location with the actual satellite measurements. The density profile is then modified to account for any discrepancies between the two results. The same process is repeated with the new profile until one has reasonable agreement between the data and ray-tracing results. This method is applied to the case of an Imp 6 pass, where strong signals from the Siple VLF transmitter were observed for over 25 min. Good agreement is found between the results of the proposed technique and the well-known ground whistler techniques of cold-plasma diagnostics. The results also serve to illustrate the wide diversity of propagation paths from ground transmitters to high-altitude satellites during VLF wave-injection experiments.

Inan, U. S.↗
DOE OSTI2012

Influence of excited state spatial distributions on plasma diagnostics: Atmospheric pressure laser-induced He-H{sub 2} plasma

Atmospheric pressure plasmas in helium-hydrogen mixtures with H{sub 2} molar concentrations ranging from 0.13% to 19.7% were investigated at times from 1 to 25 {mu}s after formation by a Q-switched Nd:YAG laser. Spatially integrated electron density values are obtained using time resolved optical emission spectroscopic techniques. Depending on mixture concentration and delay time, electron densities vary from almost 10{sup 17} cm{sup -3} to about 10{sup 14} cm{sup -3}. Helium based results agree reasonably well with each other, as do values extracted from the H{sub {alpha}} and H{sub {beta}} emission lines. However, in particular for delays up to about 7 {mu}s and in mixtures with less than 1% hydrogen, large discrepancies are observed between results obtained from the two species. Differences decrease with increasing hydrogen partial pressure and/or increasing delay time. In mixtures with molecular hydrogen fraction of 7% or more, all methods yield electron densities that are in good agreement. These findings seemingly contradict the well-established idea that addition of small amounts of hydrogen for diagnostic purposes does not perturb the plasma. Using Abel inversion analysis of the experimental data and a semi-empirical numerical model, we demonstrate that the major part of the detected discrepancies can be traced to differences in the spatial distributions of excited helium and hydrogen neutrals. The model yields spatially resolved emission intensities and electron density profiles that are in qualitative agreement with experiment. For the test case of a 1% H{sub 2} mixture at 5 {mu}s delay, our model suggests that high electron temperatures cause an elevated degree of ionization and thus a reduction of excited hydrogen concentration relative to that of helium near the plasma center. As a result, spatially integrated analysis of hydrogen emission lines leads to oversampling of the plasma perimeter and thus to lower electron density values compared to those obtained from helium lines.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1972

Material injection alleviation and plasma diagnostic measurements during the RAM C-III flight.

The results of a material injection RF blackout alleviation experiment and of plasma diagnostic measurements using electrostatic probes and an S-band reflectometer in a 25,000 ft/sec reentry flight are presented. Significant alleviation of RF blackout is observed at altitudes of from 270,000 feet to 120,000 feet due to injection of water and Freon E-3 on VHF, S-band, C-band, and X-band frequencies. Electrostatic probe data, attenuation data, and S-band diagnostic data show consistent plasma results. The relative effectiveness of water and Freon E-3 is discussed.

Schroeder, L. C.↗
DOE OSTI2021

Design of microwave broadband CMOS transmitter and receiver circuits for MIR and ECEI plasma diagnostics

To efficiently determine the plasma electron density fluctuations using the MIR diagnostic technique, a 55–75 GHz 65 nm-CMOS transmitter has been developed where four separate intermediate frequency (IF) signals are up-converted, amplified, and then combined to generate an 8-tone RF output; a broadband 90 nm-CMOS receiver has also been constructed, which consists of an RF-low noise amplifier (LNA), mixer, and IF amplifier. The circuits and their corresponding modules will soon be deployed on the DIII-D and NSTX-U fusion devices. A 110–140 GHz 65 nm-CMOS receiver has also been designed, which is suitable for measuring the deep-core temperature fluctuations in the DIII-D tokamak using the electron cyclotron emission imaging diagnostic system. In addition to the RF-LNA/balun, mixer, and IF amplifier, an LO balun/tripler and driving amplifier are now included in this highly integrated circuit chip. By adopting the microwave and millimeterwave system-on-chip concept in the front-end system design, this paper demonstrates that compact transmitter and receiver modules can be easily built, which, in turn, facilitates array implementation and maintenance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1986

Plasma diagnostics package measurements of ionospheric ions and Shuttle-induced perturbations

The plasma diagnostics package (PDP) on the Space Shuttle STS-3 mission in March 1982 carried among its instrument complement a retarding potential analyzer. This instrument measured both the ambient ion plasma density and temperature, and perturbations to the plasma produced by Shuttle Orbiter effects. Whenever the plasma flow streamline at the instrument was more than a distance of the order of thermal ion gyroradii away from any Orbiter surface, the measurements were characteristic of the ambient ionosphere. In several situations, the PDP was positioned so as to scan the wake in the plasma flow produced by Orbiter surfaces. The density profile of the major species O(+) was consistent with a classic Mach cone. However, strong perturbations extended for several meters outside the Mach cone, which resulted in failure of flowing Maxwellian distributions to represent the data. Configurations where the plasma-flow-impacted Orbiter surfaced downstream of the PDP resulted in generation of a suprathermal ion component. The observations are discussed in terms of a recent model of the mechanism for generation of Shuttle glow.

Reasoner, David L.↗