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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

First observation of unlocking the locked mode by electrode biasing on J-TEXT tokamak

Major disruptions, often caused by locked m/n = 2/1 modes (m/n is the poloidal/toroidal mode number), are great threat to a tokamak fusion reactor and should be mitigated or avoided. The locked 2/1 modes have been unlocked by electrode biasing (EB) for the first time in J-TEXT tokamak experiments. Furthermore, the application of a sufficiently negative EB voltage in plasma edge region quickly changes the phase and amplitude of the locked 2/1 mode and drives the mode to rotate in about 10–30 ms. For a larger EB current or a smaller locked mode amplitude, the mode is more easily to be unlocked, revealing a new method for mode unlocking and avoiding plasma disruptions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

AETHER: A simulation platform for inductively coupled plasma

An in-house code is developed to simulate the inductively coupled plasma (ICP). The model comprises the fluid, electromagnetic and transformer submodels. Fluid equations are solved to evaluate the plasma flow parameters, including the plasma and neutral densities, ion and neutral velocities, electron flux, electron temperature, and electric potential. The model relies on the ambipolar approximation and offers the evaluation of plasma parameters without solving the sheath region. The electromagnetic model handles the calculation of the electric and magnetic fields using the magnetic vector potential. The transformer model captures the effect of the matching circuit utilized in laboratory experiments for RF power deposition. The continuity and momentum equations are solved using finite volume method. The energy, electric potential, and magnetic vector potential equations are solved using finite difference method. The resulting linear systems of equations are solved with iterative solvers including Jacobi and GMRES. The code is written using the C++ programming language, it works in parallel and has graphical user interface. The model is applied to study ICP characteristics of a plasma confined within a cylindrical chamber with dielectric walls for two different power deposition cases. The results obtained from the developed model are verified using the plasma module of COMSOL Multiphysics. The model is also applied to a plasma source configuration, and it is demonstrated that there is an overall increase in the plasma potential when current is extracted from ICP with a biased wall electrode.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Consumption of the electric power inside silent discharge reactors

An experimental study was made in this paper to investigate the relation between the places of the dielectric barriers, which cover the surfaces of the electrodes in the coaxial cylindrical reactors, and the rate of change of the electric power that is consumed in forming silent discharges. Therefore, silent discharges have been formed inside three coaxial cylindrical reactors. The dielectric barriers in these reactors were pasted on both the internal surface of the outer electrode in the first reactor and the external surface of the inner electrode in the second reactor as well as the surfaces of the two electrodes in the third reactor. The reactor under study has been fed by atmospheric air that flowed inside it with a constant rate at normal temperature and pressure, in parallel with the application of a sinusoidal ac voltage between the electrodes of the reactor. The electric power consumed in forming the silent discharges inside the three reactors was measured as a function of the ac peak voltage. The validity of the experimental results was investigated by applying Manley's equation on the same discharge conditions. The results have shown that the rate of consumption of the electric power relative to the ac peak voltage per unit width of the discharge gap improves by a ratio of either 26.8% or 80% or 128% depending on the places of the dielectric barriers that cover the surfaces of the electrodes inside the three reactors.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Modified quadrupole mass analyzer RGA-100 for beam plasma research in forevacuum pressure range

The industrial quadrupole RGA-100 residual gas analyzer was modified for the research of electron beam-generated plasma at forevacuum pressure range. The standard ionizer of the RGA-100 was replaced by three electrode extracting unit. We made the optimization of operation parameters in order to provide the maximum values of measured currents of any ion species. The modified analyzer was successfully tested with beam plasma of argon, nitrogen, oxygen, and hydrocarbons.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Femtosecond laser ablation particle introduction to a liquid sampling-atmospheric pressure glow discharge ionization source

This work describes the use of a compact, liquid sampling – atmospheric pressure glow discharge (LS-APGD) ionization source to ionize metal particles within a laser ablation aerosol. Mass analysis was performed with a Thermo Scientific Exactive Mass Spectrometer which utilizes an orbitrap mass analyzer capable of producing mass resolution exceeding M/ΔM > 160,000. The LS-APGD source generates a low-power plasma between the surface of an electrolytic solution flowing at several µl min-1 through a fused silica capillary and a counter electrode consisting of a stainless steel capillary employed to deliver the laser ablation particles into the plasma. Sample particles of approximately 100 nm were generated with an Applied Spectra femtosecond laser located remotely and transported through 25 meters of polyurethane tubing by means of argon carrier gas. Samples consisted of an oxygen free copper shard, a disk of solder, and a one-cent U.S. coin. Analyte signal onset was readily detectable relative to the background signal produced by the carrier gas alone. The high mass resolution capability of the orbitrap mass spectrometer was demonstrated on the solder sample with resolution exceeding 90,000 for Pb and 160,000 for Cu. In addition, results from a laser ablation depth-profiling experiment of a one cent coin revealed retention of the relative locations of the ~10 µm copper cladding and zinc rich bulk layers.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Axial mass fraction measurements in a 300kA dense plasma focus

The dynamics and characteristics of the plasma sheath during the axial phase in a ~300 kA, ~2 kJ dense plasma focus using a static gas load of Ne at 1–4 Torr are reported. The sheath, which is driven axially at a constant velocity ~10 5 m/s by the j × B force, is observed using optical imaging, to form an acute angle between the electrodes. This angle becomes more acute (more parallel to the axis) along the rundown. The average sheath thickness nearer the anode is 0.69 ± 0.02 mm and nearer the cathode is 0.95 ± 0.02 mm. The sheath total mass increases from 1 ± 0.02 μg to 6 ± 0.02 μg over the pressure range of 1–4 Torr. However, the mass fraction (defined as the sheath mass/total mass of cold gas between the electrodes) decreases from 7% to 5%. In addition, the steeper the plasma sheath, the more mass is lost from the sheath, which is consistent with radial and axial motion. Lastly, experimental results are compared to the Lee code when 100% of the current drives the axial and radial phase.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Experimental observation of the behaviour of cogenerated dusty plasma using a bipolar pulsed direct current power supply

We have experimentally observed the behaviour of cogenerated dusts in unmagnetized plasma produced using a bipolar pulsed dc power supply. In this experiment, the dust particles have been generated through sputtering of graphite cathode and were stratified between two electrodes. This stratification of dust clouds has obtained at a typical range of plasma parameters, namely, 650 V (peak-to-peak) with 0.2 mbar pressure. In above condition, we detected the Taylor-like instability at the interface of two dusty clouds with different densities. A very less dust density (void like) region inside the lesser dust density portion is also noted. Again, it has been observed that a self excited dust density wave propagates towards the higher density dust fluid inside the system as well as a stationary band structure of thin multiple layers of dust particles when we apply a higher voltage (750 V peak-to-peak). The wavelength, phase velocity, and frequency of the excited wave have also been estimated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Electron beam injection from a hollow cathode plasma into a downstream reactive environment: Characterization of secondary plasma production and Si 3 N 4 and Si etching

A material etching system was developed by combining beam electron injection from a direct current (DC) hollow-cathode (HC) electron source with the downstream reactive environment of a remote CF 4 /O 2 low temperature plasma. The energy of the injected beam electrons is controlled using an acceleration electrode biased positively relative to the HC Argon discharge. For an acceleration voltage greater than the ionization potential of Ar, the extracted primary electrons can produce a secondary plasma in the process chamber. We characterized the properties of the secondary plasma by performing Langmuir probe measurements of the electron energy probability function (EEPF) 2.5 cm below the extraction ring. The data indicate the existence of two major groups of electrons, including electrons with a primary beam electron energy which varies as the acceleration voltage is varied, along with low energy electrons produced by ionization of the Ar gas atoms in the process chamber by the injected beam electrons. When combining the HC Ar beam electron with a remote CF 4 /O 2 electron cyclotron wave resonance (ECWR) plasma, the EEPF of both the low energy plasma electron and beam electron components decreases. Additionally, we studied surface etching of Si3N4 and poly-crystalline Si (poly-Si) thin films as a function of process parameters, including the acceleration voltage (0-70 V), discharge current of the HC discharge (1-2 A), pressure (2- 100 mTorr), source to substrate distance (2.5 to 5 cm), and feed gas composition (with or without CF 4 /O 2 ). The direction of the incident beam electrons was perpendicular to the surface. Si 3 N 4 and poly-crystalline silicon etching are seen and indicate an electronneutral synergy effect. No/little remote plasma spontaneous etching was observed for the conditions used in this study, and the etching is confined to the substrate area irradiated by the injected beam electrons. The electron etched Si 3 N 4 surface etching rate profile distribution is confined within a ~30 mm diameter circle, which is slightly broader than the area for which poly-Si etching is seen, and coincides closely with the spatial profile of beam electrons as determined by the Langmuir probe measurements. The magnitude of poly-Si etching rate is by a factor of two times smaller than the Si 3 N 4 etching rate. In this paper, we discuss possible explanations of the data and the role of surface charging.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Dynamics of two discrete vortices with different circulations composed of pure electron plasmas

Two-dimensional dynamics of two vortex strings with different circulations were experimentally observed. The strings were composed of pure electron plasmas and were confined in a Malmberg–Penning trap. When one of the two vortices trapped in a conventional potential well had weak circulation, the orbits of the two vortices contradicted the point vortex theory. This disagreement stems from an unavoidable external electric field that exerts a different additional E × B drift velocity on each vortex. We resolved the discrepancy between observation and theory by applying a stepwise potential to the end electrodes, which produced a less non-ideal electric field.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Investigating instabilities in magnetized low-pressure capacitively coupled RF plasma using particle-in-cell (PIC) simulations

The effect of a uniform magnetic field on particle transport in low-pressure radio frequency (RF) capacitively coupled plasma (CCP) has been studied using a particle-in-cell model. Three distinct regimes of plasma behavior can be identified as a function of the magnetic field. In the first regime at low magnetic fields, asymmetric plasma profiles are observed within the CCP chamber due to the effect of $\overrightarrow{E}$ × $\overrightarrow{B}$ drift. As the magnetic field increases, instabilities develop and form self-organized spoke-shaped structures that are distinctly seen within the bulk plasma closer to the sheath. In this second regime, the spoke-shaped coherent structures rotate inside the plasma chamber in the -$\overrightarrow{E}$ × $\overrightarrow{B}$ direction, where $\overrightarrow{E}$ × $\overrightarrow{B}$ are the DC electric and magnetic field vectors, respectively, and the DC electric field exists in the sheath and pre-sheath regions. The spoke rotation frequency is in the megahertz range. As the magnetic field strength increases further, the rotating coherent spokes continue to exist near the sheath. The coherent structures are, however, accompanied by new small-scale incoherent structures originating and moving within the bulk plasma region away from the sheath. This is the third regime of plasma behavior. The threshold values of the magnetic field between these regimes were found not to vary with changing plasma reactor geometry (e.g., area ratio between ground and powered electrodes) or the use of an external capacitor between the RF-powered electrode and the RF source. The threshold values of the magnetic field between these regimes shift toward higher values with increasing gas pressure. Analysis of the results indicates that the rotating structures are due to the lower hybrid instability driven by density gradients and electron-neutral collisions. This paper provides guidance on the upper limit of the magnetic field for instability-free operation in low-pressure CCP-based semiconductor deposition and etch systems that use the external magnetic field for plasma uniformity control.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Absolute and relative emission spectroscopy study of 3 cm wide planar radio frequency atmospheric pressure bio-plasma source

The dynamics of low power atmospheric pressure radio frequency discharge generated in Ar gas in long gap of 3 cm is investigated. This plasma source is characterized and analyzed for possible large scale biomedical applications where low gas temperature and potential-less effluent are required. The discharge forms a homogenous glow-like afterglow in ambient air at input power of 30 W with low gas temperature of 330 K, which is desirable in biomedical applications. With absolute calibrated spectroscopy of the discharge, electron density of 0.4 × 10{sup 18} m{sup −3} and electron temperature of 1.5 eV are obtained from continuum Bremsstrahlung radiation of the source. Time and spatial resolved emission spectroscopy is used to analyze discharge generation mechanism and active species formation. It is found that discharge dynamics strongly correlates with the discharge current waveform. Strong Ar(2p) excited states emission is observed nearby the electrodes surface on a distance up to 200 μm in the plasma sheath region at 10 ns after the current peak, whereas OH(A) emission is uniform along of the interelectrode gap.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Modified Paschen curves for pulsed breakdown

The influence of the voltage rise time on the Paschen curves is analyzed using kinetic and fluid models. The Paschen curves, which describe the dependence of the breakdown voltage, U br , on the product pd of gas pressure p and the characteristic length d between the electrodes, have minima that correspond to optimal conditions for plasma generation. It is shown that both kinetic and fluid models predict the experimentally observed shift of the curves toward higher voltages and the shift of the Paschen minima toward higher values of pd with the decreasing voltage rise time τ. On the right branch of the Paschen curves, the agreement between both models is obtained for all τ. We confirm that the minimum of the Paschen curves corresponds to conditions of electron runaway. Finally on the left branch, the electron velocity distribution function is nonlocal in space and also nonlocal in time.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

System and method for alfvenic reconnecting plasmoid plasma acceleration

According to various embodiments, a system for using magnetic reconnection to accelerate plasma is disclosed. The system includes a pair of electrodes including two concentric rings separated by an electrode gap and held at different electrostatic potential by applying a voltage to generate an inter-electrode electric field. The system further includes a plurality of magnetic coils configured to produce magnetic field lines that connect the pair of electrodes. The system additionally includes a gas injector configured to inject gas into the electrode gap, the injected gas being partially ionized by the inter-electrode electric field to generate a poloidal current that flows along open magnetic field lines across the electrode gap. A total Lorentz force causes oppositely directed magnetic field lines to be expanded around a region of the gas injector to further create an azimuthal current in the form of an axially elongated current sheet that is unstable such that the axially elongated current sheet reconnects and breaks into plasmoids.

Ebrahimi, Fatima Arezu↗
DOE OSTI2015

Particle formation and its control in dual frequency plasma etching reactors

The behavior of a particle cloud in plasma etching reactors at the moment when radio frequency (RF) power changes, that is, turning off and transition steps, was observed using the laser-light-scattering method. Two types of reactors, dual-frequency capacitively coupled plasma (CCP) and the hybrid CCP/inductively coupled plasma (ICP), were set up for experiments. In the hybrid CCP/ICP reactor (hereafter ICP reactor), the position and shape of the cloud were strongly dependent on the RF frequency. The particle cloud becomes larger and approaches the electrode as the RF frequency increases. By turning the lower frequency power off later with a small delay time, the particle cloud is made to move away from the electrode. Maintaining lower frequency RF power only was also helpful to reduce the particle cloud size during this transition step. In the ICP reactor, a sufficient bias power is necessary to make a particle trap appear. A similar particle cloud to that in the CCP reactor was observed around the sheath region of the lower electrode. The authors can also use the low-frequency effect to move the particle cloud away from the substrate holder if two or more bias powers are applied to the substrate holder. The dependence of the particle behavior on the RF frequencies suggests that choosing the proper frequency at the right moment during RF power changes can reduce particle contamination effectively.

42 ENGINEERING↗
DOE OSTI2012

Ion beams extraction and measurements of plasma parameters on a multi-frequencies microwaves large bore ECRIS with permanent magnets

We have developed an all-permanent magnet large bore electron cyclotron resonance ion source (ECRIS) for broad ion beam processing. The cylindrically comb-shaped magnetic field configuration is adopted for efficient plasma production and good magnetic confinement. To compensate for disadvantages of fixed magnetic configuration, a traveling wave tube amplifier (TWTA) is used. In the comb-shaped ECRIS, it is difficult to achieve controlling ion beam profiles in the whole inside the chamber by using even single frequency-controllable TWTA (11-13GHz), because of large bore size with all-magnets. We have tried controlling profiles of plasma parameters and then those of extracted ion beams by launching two largely different frequencies simultaneously, i.e., multi-frequencies microwaves. Here we report ion beam profiles and corresponding plasma parameters under various experimental conditions, dependence of ion beams against extraction voltages, and influence of different electrode positions on the electron density profile.

43 PARTICLE ACCELERATORS↗
NASA NTRS1996

Charged body-plasma interaction research laboratory for the International Space Station

An experiment is proposed for the provision of a fundamental plasma physics facility onboard the International Space Station (ISS) for the investigation of the plasma processes governing the electron current collection processes on a charged electrode. The facility will allow the pre-sheath and sheath physics of a positively biased body to be investigated. These processes are important to the consideration of the use of electrodynamic tether lines for practical applications such as for electrical power generation and to the understanding of the physics of space plasma. A deployment mechanism is required to deploy the charged body to a distance of several 100 m from the space station. The possible solutions are a flexible boom or a short tether line.

Lebreton, Jean-Pierre↗
DOE OSTI2017

Electrostatically driven helical plasma state

A novel plasma state has been found in the presence of a uniformly applied axial magnetic field in periodic cylindrical geometry. This state is driven electrostatically by helical electrodes, providing a driving field that depends on the radius and mθ−nζ, where θ is the poloidal angle and ζ=z/R is the toroidal angle. We focus on m=n=1. The radial magnetic field at the wall is taken to be zero. With weak driving, the resulting distortion is very small, but for stronger driving, the mean field of the state has field line safety factor q0(r) just above the pitch of the electrodes m∕n = 1 except near the edge, where q0 increases monotonically. This state is characterized as a single helicity Ohmic equilibrium with the helical symmetry of the applied field. The plasma appears to be close to force-free in the interior, but current density crosses the magnetic flux surfaces near the edge, where current must enter and exit through the helical electrodes. This perpendicular current density drives large helical plasma flows. The sensitivity of this state to flow boundary conditions, plasma resistivity profile, the strength of electrostatic driving, and parameters such as the loop voltage and the Lundquist number is explored. The magnetic helicity is calculated for both the transient period and time-asymptotic state. Possible applications to current drive in toroidal confinement devices and to electrical transformers are discussed.

Akçay, Cihan↗
DOE OSTI2022

Plasma-based edge terminations for gallium nitride power devices

A p-n diode includes a first electrode, a n-GaN layer on the first electrode, a p-GaN layer on the n-GaN layer, and a second electrode on a first portion of the p-GaN layer. A region of the p-GaN layer surrounding the electrode is a passivated region. Treating a GaN power device having a p-GaN layer includes covering a portion of the p-GaN layer with a metal layer, exposing the p-GaN layer to a hydrogen plasma, and thermally annealing the p-GaN layer, thereby passivating a region of the p-GaN layer proximate the metal layer.

Zhao, Yuji↗