Search NASA⌕ Search

SEARCH · Search NASA

Results for “Large Plasma Device”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Design of the Lanthanum hexaboride based plasma source for the large plasma device at UCLA

The Large Plasma Device (LAPD) at UCLA (University of California, Los Angeles) produces an 18 m long, magnetized, quiescent, and uniform plasma at a high repetition rate to enable studies of fundamental plasma physics. Here, we report on a major upgrade to the LAPD plasma source that allows for more robust operation and significant expansion of achievable plasma parameters. The original plasma source made use of a heated barium oxide (BaO) coated nickel sheet as an electron emitter. This source had a number of drawbacks, including a limited range of plasma density (≲4.0 × 10 12 cm −3 ), a limited discharge duration (∼10 ms), and susceptibility to poisoning following oxygen exposure. Further, the new plasma source utilizes a 38 cm diameter lanthanum hexaboride (LaB 6 ) cathode, which has a significantly higher emissivity, allowing for a much larger discharge power density, and is robust to exposure to air. Peak plasma density of up to 3.0 × 10 13 cm −33 in helium gas has been achieved. The typical operating pressure is ∼10 −5 Torr, while dynamic pressure can be achieved through the gas-puffing technique. Discharges as long as 70 ms have been produced, enabling a variety of long-time-scale studies of processes, such as turbulent particle transport. The new source has been in continuous operation for 14 months, having survived air leaks, power outages that led to rapid temperature changes on the cathode and heater, and planned machine openings. We describe the design, construction, and initial operation of this novel new large-area LaB6 plasma source.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Plasma potential shaping using end-electrodes in the Large Plasma Device

We perform experiments in the Large Plasma Device at the University of California, Los Angeles, studying how different end-electrode biasing schemes modify the radial potential profile in the machine. We impose biasing profiles of different polarities and gradient signs on a set of five concentric electrodes placed 12 m downstream from the plasma source. We find that imposing concave-down profiles (negative potential radial gradient) on the electrodes creates radial potential profiles halfway up the plasma column that are comparable to those imposed on the electrodes and a few electron temperature in height, regardless of the biasing polarity. On the other hand, imposing concave-up profiles (positive potential radial gradient) leads to non-monotonic radial potential profiles. This observation can be explained by the current drawn through the electrodes and the parallel plasma resistivity, highlighting their important role in controlling the rotation of plasma. Concave-down plasma potential profiles, obtained by drawing electrons on the axis, are predicted to drive azimuthal drift velocities that can approach significant fractions of the ion sound speed in the central region of the plasma column.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Electromagnetic Inhomogeneous-Energy-Density-Driven Instability in the UCLA Large Plasma Device (EM-IEDDI in LAPD) (Final Technical Report)

Using the Large Plasma Device (LAPD), the electromagnetic signatures associated with the inhomogeneous-energy-density-driven (IEDD) instability were targeted for documentation in a lab experiment. Exploitable features of LAPD are the extreme-length, high-beta, low-collisionality, and excellent reproducibility. The signatures of interest were mode amplitude, mode structure, frequency spectrum, phase velocity, and excitation threshold. The abrupt inhomogeneity at the interface between two coaxial plasma columns, that have disparate space potential values, were expected to generate a strong, localized, transverse, dc electric field and form a strong ExB-flow inhomogeneity that was expected to trigger broadband, intermediate-frequency waves that propagate many gyroradii beyond the interfacial source region. WVU was unable to destabilize the IEDDI mode in LAPD. Experimental limitation of three different parameters conspire to prevent IEDDI-favorable conditions even though Alfven-favorable conditions are met. Electron-neutral collision frequency is too high, Structuring of the radial profile of the radial electric field is negligible and the control of that structure is minimal, and the Magnetic field is too large for some purposes and too small for other purposes. WVU designed a new antenna and relied on externally-driving the IEDDI (instead of spontaneous destabilization). The antenna operation failed for unforeseen reasons and lack of electrician time and availability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Impact of the electron density and temperature gradient on drift-wave turbulence in the Large Plasma Device

In this paper we present an experimental study of edge turbulence in the Large Plasma Device at UCLA. We utilize a scan of discharge power and prefill pressure (neutral density) to show experimentally that turbulent density fluctuations decrease with decreasing density gradient, as predicted for resistive drift-wave turbulence (RDWT). As expected for RDWT, we observe that the cross-phase between the density and potential fluctuations is close to 0. Moreover, the addition of an electron temperature gradient leads to a reduction in the amplitude of the density fluctuations, as expected for RDWT. However, counter to theoretical expectations, we find that the potential fluctuations do not follow the same trends as the density fluctuations for changes either in density gradients or the addition of a temperature gradient. The disconnect between the density and potential fluctuations is connected to changes in the parallel flows as a result of differences in the prefill pressure, i.e. neutral density. Further analysis of the density and potential fluctuation spectra show that the electron temperature gradient reduces the low frequency fluctuations up to $10 \,{\rm kHz}$ and the introduction of a temperature gradient leads to an unexpected ${\sim }{\rm \pi}$ shift of the density–potential cross-phase at ${\sim }10\,{\rm kHz}$ , while maintaining the typical resistive drift-wave cross-phase at lower frequencies. These experiments partly confirm existing knowledge on resistive drift-wave turbulence, but also introduce new observations that indicate a need for dedicated nonlinear three-dimensional turbulence simulations that include neutrals.

Physics↗
DOE OSTI2022

First Results from the Thomson Scattering Diagnostic on the Large Plasma Device

We present the first Thomson scattering measurements of electron density and temperature in the Large Plasma Device (LAPD), a 22 m long magnetized linear plasma device at the University of California Los Angeles (UCLA). The diagnostic spectrally resolves the Doppler shift imparted on light from a frequency-doubled Nd:YAG laser when scattered by plasma electrons. A fiber array coupled to a triple-grating spectrometer is used to obtain high stray light rejection and discriminate the faint scattering signal from a much larger background. In the center of the plasma column, the measured electron density and temperature are about ne≈1.5×1013 cm−3 and Te≈ 3 eV, respectively, depending on the discharge parameters and in good agreement with Langmuir probe data. Optical design considerations to maximize photon count while minimizing alignment sensitivity are discussed in detail and compared to numerical calculations. Raman scattering off of a quartz crystal probe is used for an absolute irradiance calibration of the system.

Kaloyan, Marietta (ORCID:0000000182593038)↗
DOE OSTI2022

Thomson scattering on the large plasma device

We have developed a non-collective Thomson scattering diagnostic for measurements of electron density and temperature on the Large Plasma Device. A triple grating spectrometer with a tunable notch filter is used to discriminate the faint scattering signal from the stray light. In this paper, we describe the diagnostic and its calibration via Raman scattering and present the first measurements performed with the fully commissioned system. Depending on the discharge conditions, the measured densities and temperatures range from 4.0 × 10 12 to 2.8 × 10 13 cm -3 and from 1.2 to 6.8 eV, respectively. The variation of the measurement error with plasma parameters and discharges averaged is also discussed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Turbulence and transport in mirror geometries in the Large Plasma Device

Thanks to advances in plasma science and enabling technology, mirror machines are being reconsidered for fusion power plants and as possible fusion volumetric neutron sources. However, cross-field transport and turbulence in mirrors remains relatively understudied compared with toroidal devices. Turbulence and transport in mirror configurations were studied utilizing the flexible magnetic geometry of the Large Plasma Device (LAPD). Multiple mirror ratios from $M=1$ to $M=2.68$ and three mirror-cell lengths from $L=3.51$ to $L=10.86$ m were examined. Langmuir and magnetic probes were used to measure profiles of density, temperature, potential and magnetic field. The electric field-fluctuation-driven ${\tilde {\boldsymbol{E}}} \times {\boldsymbol{B}}$ particle flux, where $\boldsymbol{B}$ is the background field, was calculated from these quantities. Two probe correlation techniques were used to infer wavenumbers and two-dimensional structure. Cross-field particle flux and density fluctuation power decreased with increased mirror ratio. Core density and temperatures remain similar with mirror ratio, but radial line-integrated density increased. The physical expansion of the plasma in the mirror cell by using a higher field in the source region may have led to reduced density fluctuation power through the increased gradient scale length. This increased scale length reduced the growth rate and saturation level of rotational interchange and drift-like instabilities. Despite the introduction of magnetic curvature, no evidence of mirror-driven instabilities – interchange, velocity space or otherwise – were observed. For curvature-induced interchange, many possible stabilization mechanisms were present, suppressing the visibility of the instability.

Travis, Phil (ORCID:0000000343170432)↗
DOE OSTI2025

Physics of beam-driven ion cyclotron emission in the large plasma device

Abstract Ion cyclotron emission (ICE) is widely observed from spatially localised minority energetic ion populations in toroidal magnetically confined fusion (MCF) plasmas, both tokamaks and stellarators. Its spectral structure is typically regular with narrow suprathermal peaks, whose frequency separation matches a local energetic ion cyclotron frequency. Here we report the first computational (fully nonlinear self-consistent kinetic particle-in-cell code) and analytical (linear magnetoacoustic cyclotron instability (MCI)) studies of ICE observations from cylindrical plasmas contained in the Large Plasma Device (LAPD). Because LAPD is cylindrical, the plasma physics giving rise to the observed ICE spectrum necessarily excludes toroidal effects. Our approach, previously successful for toroidal plasma ICE, assumes slab geometry and hence is well adapted to LAPD. ICE from LAPD is strongly electrostatic, as distinct from electromagnetic, and is driven by 15 keV beam ions for which the ratio of perpendicular speed to the local Alfven speed, v ⊥ / v A , is 0.15, lower than in MCF plasmas from which beam-driven ICE has previously been observed. Our results are in good agreement with these observations. There is congruence between simulated ICE spectra, obtained in the saturated nonlinear regime of our computations, and observed ICE spectra; the underlying physics is essentially the same as in toroidal plasmas; and there is alignment with linear analytical theory where appropriate. The present work establishes a mapping from the cylindrical LAPD ICE observations to toroidal MCF ICE observations. The LAPD spectra are instances of beam-driven MCI-type ICE in its sub-Alfvenic, predominantly electrostatic manifestation, which has precedents in MCF stretching back to the 1990s. An interesting corollary is that, for many purposes, ICE in toroidal MCF plasmas ‘might as well’ be occurring in a cylinder.

Samant, O. (ORCID:0000000226055363)↗
DOE OSTI2021

Electromagnetic turbulence in increased β plasmas in the Large Plasma Device

The variation of pressure-gradient-driven turbulence with plasma $\beta$ (up to $\beta \approx 15\,\%$ ) is investigated in linear, magnetized plasma. The magnitude of magnetic fluctuations is observed to increase substantially with increasing $\beta$ . More importantly, parallel magnetic fluctuations are observed to dominate at higher $\beta$ values, with $\delta B_\parallel / \delta B_\perp \approx 2$ and $\delta B / B_0 \approx 1\,\%$ . Parallel magnetic fluctuations are strongly correlated with density fluctuations and the two are observed to be out of phase. The relative magnitude of and cross-phase between density and parallel magnetic field fluctuations are consistent with the dynamic pressure balance ( $P+{B_{0}^2}/{2\mu _0} = \textrm {constant}$ ). A local slab model theory for electromagnetic, modified drift Alfvén waves, including parallel magnetic fluctuations, shows partial agreement with experimental observations.

Physics↗
DOE OSTI2022

Reduction in RF sheath rectification with insulating antenna enclosure walls

Abstract Radiofrequency (RF) sheath rectification is one of the most prominent deleterious effects associated with ion cyclotron range of frequencies (ICRF) heating in fusion plasmas. RF sheaths and associated effects, such as impurity generation and convective cell generation, need to be mitigated to ensure that ICRF is a viable option for heating in future fusion devices. Experiments were performed on the Large Plasma Device (LAPD) at UCLA to explore the effects of using electrically-insulating antenna enclosures on RF rectified sheaths. Three different enclosure side-wall materials were used, including copper, MACOR (electrically insulating), and MACOR over copper. In the case of the MACOR–copper side walls, the non-conductive MACOR material was exposed to the bulk plasma but a layer of copper was added below to allow for image currents to flow. All three of the experiments had similar plasma density, temperature, and background magnetic field. In the case of the copper enclosure, RF rectified potentials, many times the local electron temperature, and associated formation of convective cells were observed and reported Martin M. et al (2017 Phys. Rev. Lett. 119 205002). In the experiments with MACOR and MACOR–copper enclosures, RF rectification was significantly reduced. Additionally, these latter two experiments showed no evidence of convective cell formation. Although the results from the MACOR experiment are reminiscent of the results obtained in ASDEX-U with a three-strap antenna optimized to reduce image currents on the antenna limiters Bobkov V. et al (2016 Nucl. Fusion 56 084001), the MACOR–copper experiment seems to suggest that insulating plasma facing materials have at least an equally strong impact on reducing potential rectification.

Physics↗
DOE OSTI2021

The geometry of the ICRF-induced wave–SOL interaction. A multi-machine experimental review in view of the ITER operation

As a part of ITPA-Integrated Operational Scenario activities, this contribution reviews recent experimental characterizations of radio-frequency (RF)-induced scrape-off layer (SOL) modifications of various tokamaks worldwide and of the LArge Plasma Device at UCLA. The phenomenology, as observed using a large variety of measurement techniques, is consistent with expectations from RF sheath rectification. Emphasis is then put on the complex three-dimensional (3D) spatial patterns of the RF–SOL interaction, in relation to the magnetic topology and the spatial distribution of RF currents over the metallic structures surrounding the RF wave launchers. Dependence on the local plasma parameters in the antenna vicinity is also briefly addressed. The final part discusses implications for future devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Final CRADA Report – NFE-21-08693

TAE Technologies is developing a magnetic fusion energy concept known as the beam-driven field-reversed configuration (FRC) with the ultimate goal of developing a reactor for commercial electricity production capable of burning aneutronic pB11 fuel. To achieve the high plasma temperatures this requires, auxiliary radiofrequency (RF) heating will likely be needed. High Harmonic Fast Wave (HHFW) heating has been identified as a candidate RF heating scheme to overcome the unique challenges posed to RF heating by the FRC, including the large distance from the plasma edge to the last closed flux surface and a magnetic field profile with strength decreasing from edge to core and reversing sign at a null point inside the plasma. The purpose of this project was to develop the experimental capabilities to test HHFW on TAE’s C-2W device through the design of a phased array antenna and accompanying matching network. The design was performed by ORNL and informed by experiments with a prototype four-strap phased antenna-array that was manufactured and installed on the LArge Plasma Device (LAPD) at UCLA and simulations conducted with the Petra-M code under the purview of a previous INFUSE grant. The ORNL team completed the conceptual design of the antenna and matching network which was then handed off to the TAE Mechanical Design team. The design was then iterated on to ensure changes to the mechanical design did not interfere with the RF performance. This process is now complete, and, with mechanical design in hand, TAE is proceeding with plans for final integration.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Continuum electromagnetic gyrokinetic simulations of turbulence in the tokamak scrape-off layer and laboratory devices

Here, we present algorithms and results from Gkeyll, a full-f continuum, electromagnetic gyrokinetic code, designed to study turbulence in the edge region of fusion devices. The edge is computationally very challenging, requiring robust algorithms that can handle large-amplitude fluctuations and stable interactions with plasma sheaths. We present an energy-conserving high-order discontinuous Galerkin scheme that solves gyrokinetic equations in Hamiltonian form. Efficiency is improved by a careful choice of basis functions and automatically generated computation kernels. Previous verification tests were performed in the straight-field-line large plasma device [Shi et al., J. Plasma Phys. 83, 905830304 (2017)] and the Texas Helimak, a simple magnetized torus [Bernard et al., Phys. Plasmas 26, 042301 (2019)], including the effect of end-plate biasing on turbulence. Results for the scrape-off layer for NSTX parameters with a model helical magnetic geometry with bad curvature have been obtained [Shi et al., Phys. Plasmas 26, 012307 (2019)]. In this paper, we present algorithms for the two formulations of electromagnetic gyrokinetics: the Hamiltonian and the symplectic. We describe each formulation and show results of benchmark tests. Although our scheme works for the Hamiltonian formulation, the presence of spurious numerical modes for high-β and large $k^2_⊥ρ^2_s$ regimes shows that the symplectic formulation is more robust. We then review our recent algorithm for the symplectic formulation [Mandell et al., J. Plasma Phys. 86, 905860109 (2020)], along with example application of this new capability. Maintaining positivity of the distribution function can be challenging, and we describe a new and novel exponential recovery based algorithm to address this.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Development of an Ultrahigh-bandwidth Phase Contrast Imaging System for detection of electron scale turbulence and Gigahertz Radio-Frequency Waves

The study of waves and turbulence is vital to the development of future reactor-grade plasma devices developed in the quest for fusion energy. These fluctuations are responsible for moving heat and particles across the magnetic field, and a predictive understanding of them is needed to achieve the density and temperature required to sustain a plasma fusion reaction. While many techniques have been developed for measuring waves and fluctuations, every measurement method has limitations. There are relatively few techniques for measuring very high frequency fluctuations, such as radio frequency waves injected to heat the plasma, unstable waves driven by suprathermal particles, or short wavelength electrostatic waves driven by electron temperature or density gradients. The present project builds upon the proven phase contrast imaging (PCI) technique to extend the response of the diagnostic by orders of magnitude in frequency and almost a factor of ten in spatial resolution. PCI provides a measurement of electron density based on small angle scattering of a CO-2 laser beam by using optical techniques to render a phase shift as an intensity change on a detector. Due to the telecommunications revolution, technological development by manufacturers has focused on components in the near -infrared, so that high- quality lasers and detectors at 1.55 µm are readily available. Shifting PCI design to a new, shorter wavelength has numerous advantages and challenges. Similar detector performance is available with room-temperature arrays with GHz bandwidth, while the detector arrays for 10.6 µm required liquid nitrogen cooling and were therefore limited to a bandwidth of about 1 MHz. Shifting to a shorter wavelength reduces the angle at which the laser beam scatters off of plasma waves, allowing more such scattered components to pass through the aperture of the vacuum vessel port and be collected by the PCI, which increases the spatial resolution. Concomitant with these benefits, various questions of performance arise. At shorter laser wave- length, the sensitivity to mirror and lens quality is increased, the contribution of the laser to the overall system noise is increased, and the sensitivity to vibrations is increased. The custom optical components at the heart of the PCI technique were required to be properly scaled for the shorter wavelength, so fabrication technologies needed to be explored. This project was designed to show that a low noise, high response PCI system at 1.55 µm could be constructed and operated, and then to quantify potential issues to allow extrapolation to a full-size production system providing physics measurements on a large plasma device. The first stage, producing the custom optical component called a Phase Plate, was successfully achieved using two methods. First, an easily reproduced masking and coating technique was able to produce good phase plates with the required parameters. Second, a nanofabrication technique was found to produce extremely high quality phase plates at a competitive price. The PCI constructed with the new phase plates and 1.55 µm laser was found to provide excellent wavelength measurements with the theoretically expected response. The sensitivity to optical surface quality was found to be in line with previous measurements at 10.6 µm. The observed signal-to-noise ratio was similar to the theoretically expected value. The effect of vibrations on PCI was studied with the first measurement of the effect of beam motion on PCI response and comparison to theory, allowing for a quantitative prediction of the effect of vibrations on a production PCI system and the requirements for improved beam stabilization. PCI is an extremely cost-effective method to provide a low noise, absolutely calibrated measurement of plasma fluctuations across a wide spatial scale. This project has shown that a 1.55 µm PCI using modern techniques and components is less expensive than the 10.6 µm PCI of a few years ago, with the largest savings in phase plate fabrication and the infrared detector array.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

RF-transpond: A 1D coupled cold plasma wave and plasma transport model for ponderomotive force driven density modification parallel to B

The RF-Transpond code couples a fluid plasma transport solver with a frequency domain cold plasma RF wave solver in a 1D domain parallel to a strong background magnetic field. A ponderomotive force term proportional to parallel gradients in the electric field strength is included in the transport model in order to describe ponderomotive effects in the scrape-off layer (SOL) of fusion plasmas. The transport and wave codes are verified independently and a coupled case corresponding to experimental parameters from the LArge Plasma Device (LAPD) is presented. The density perturbation ratio R n , calculated to describe ponderomotive force driven modifications, is up to 20% for the simulation inputs used.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Laser-produced plasmas as drivers of laboratory collisionless quasi-parallel shocks

The creation of a repeatable collisionless quasi-parallel shock in the laboratory would provide a valuable platform for experimental studies of space and astrophysical shocks. However, conducting such an experiment presents substantial challenges. Scaling the results of hybrid simulations of quasi-parallel shock formation to the laboratory highlights the experimentally demanding combination of dense, fast, and magnetized background and driver plasmas required. One possible driver for such experiments is high-energy laser-produced plasmas (LPPs). Preliminary experiments at the University of California, Los Angeles, have explored LPPs as drivers of quasi-parallel shocks by combining the Phoenix Laser Laboratory [Niemann et al., J. Instrum. 7, P03010 (2012)] with a large plasma device [Gekelman et al., Rev. Sci. Instrum. 87, 025105 (2016)]. Beam instabilities and waves characteristic of the early stages of shock formation are observed, but spatial dispersion of the laser-produced plasma prematurely terminates the process. This result is illustrated by experimental measurements and Monte Carlo calculations of LPP density dispersion. The experimentally validated Monte Carlo model is then applied to evaluate several possible approaches to mitigating LPP dispersion in future experiments.

Heuer, P. V. (ORCID:0000000150506606)↗
DOE OSTI2020

Scaling arguments for a plasma experiment relevant to an interplanetary coronal mass ejection

We present the design of a plasma experiment scaled to be relevant to an interplanetary coronal mass ejection (ICME) traveling from the Sun to the Earth. The experiment would launch a compact torus of plasma (the scaled analog of the coronal mass ejected by the Sun) into a magnetized background plasma (the scaled analog of the interplanetary medium, the diffuse magnetized plasma that fills the Solar System). We present the complete process of scaling the ICME system to a laboratory experiment: beginning with the ICME features that we aim to replicate with a laboratory experiment, explaining how these desired features are translated into specific design constraints, and presenting a set of experimental parameters that meet those constraints. We find that the experiment would be possible with plasma conditions typically achieved in large-scale facilities such as the Big Red Ball at the University of Wisconsin or the LArge Plasma Device at the University of California, Los Angeles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗