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Results for “plasma switch”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

XUV-driven plasma switch for THz: new spatio-temporal overlap tool for XUV–THz pump–probe experiments at FELs

A simple and robust tool for spatio-temporal overlap of THz and XUV pulses in in-vacuum pump–probe experiments is presented. The technique exploits ultrafast changes of the optical properties in semiconductors (i.e. silicon) driven by ultrashort XUV pulses that are probed by THz pulses. This work demonstrates that this tool can be used for a large range of XUV fluences that are significantly lower than when probing by visible and near-infrared pulses. This tool is mainly targeted at emerging X-ray free-electron laser facilities, but can be utilized also at table-top high-harmonics sources.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Establishing criteria for the transition from kinetic to fluid modeling in hollow cathode analysis

Hollow cathodes for plasma switch applications are investigated via 2D3V particle-in-cell simulations of the channel and plume region. The kinetic nature of the plasma within the channel is dependent on the thermalization rate of electrons, emitted from the insert. When Coulomb collisions occur at a much greater rate than ionization or excitation collisions, the electron energy distribution function rapidly relaxes to a Maxwellian and the plasma within the channel can be described accurately via a fluid model. In contrast, if inelastic processes are much faster than Coulomb collisions, then the electron energy distribution function in the channel exhibits a notable high-energy tail, and a kinetic treatment is required. This criterion is applied to hollow cathodes from the literature, revealing that a fluid approach is suitable for most electric propulsion applications, whereas a kinetic treatment can be more critical to accurate modeling of plasma switches.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Electron-beam–controlled deflection of near-infrared laser in semiconductor plasma

A timing method for experiments on the interaction of a near-infrared laser and an ultra-relativistic electron beam via a semiconductor plasma switch is experimentally validated. As an intermediate medium, a thin Si plate is excited by the energetic, intense electron beam to produce a semiconductor plasma, which in turn deflects counter-colliding laser light having 1 μm wavelength. An electron beam of sub-nC charge sufficiently induces the needed electron number density gradient of 1×10 20 cm -3 per tens of μm length at the interaction point. Demonstration during an inverse Compton scattering experiment by a counter-colliding electron beam of 300 pC and 70 MeV with an Nd: YAG laser at a wavelength of 1 μm is reported here.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Experimental determination of the thermal, turbulent, and rotational ion motion and magnetic field profiles in imploding plasmas

A tutorial is presented on advances in spectroscopic diagnostic methods developed for measuring key plasma properties in pulsed-power systems such as Z-pinches, magnetized-plasma compression devices, ion and electron diodes, and plasma switches. The parameters measured include the true ion temperature in Z-pinch implosions, which led to a discovery that much of the ion kinetic energy at stagnation is stored in hydrodynamic rather than in thermal motion. This observation contributed a new important insight into the understanding of the ion thermalization at stagnation and stimulated further investigations of turbulence at stagnation, discussed here too. The second part of this tutorial is devoted to the development of measurements for magnetic-field distributions in Z-pinches and in other pulsed-power systems, as well as their use in studying the plasma dynamics, resistivity, and pressure and energy balance. The latter study raises intriguing questions on the implosion process. In particular, in Z-pinches, the current during stagnation was found to largely flow at relatively large radii, outside the stagnation region. The magnetic-field measurements also enable investigations into the compression of a pre-magnetized cylindrical plasma that uncover striking phenomena related to the current flow, where the current was found to redistribute toward the outer regions during the implosion. Observation of the rotation of the magnetized plasma is also discussed. Lastly, experimental and theoretical investigations of a non-diffusive fast penetration of magnetic field into a low-density plasma, including its effect on the plasma dynamics, are described

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Controlling the charge of dust particles in a plasma afterglow by timed switching of an electrode voltage

Abstract A method is demonstrated for controlling the charge of a dust particle in a plasma afterglow, allowing a wider range of outcomes than an earlier method. As in the earlier method, the dust particles are located near an electrode that has a DC voltage during the afterglow. Here, that DC voltage is switched to a positive value at a specified delay time, instead of maintaining a constant negative voltage as in the earlier method. Adjusting the timing of this switching allows one to control the residual charge gradually over a wide range that includes both negative and positive values of charge. For comparison, only positive residual charges were attained in the earlier method. We were able to adjust the residual charge from about −2000 e to +10 000 e , for our experimental parameters (8.35 µ m particles, 8 mTorr argon pressure, and a DC voltage that was switched from −150 V to +125 V within the first two milliseconds of the afterglow). The plasma conditions near the dust particles changed from ion-rich to electron-rich, when the electrode was switched from cathodic to anodic. Making this change at a specified time, as the electrons and ions decay in the afterglow, provides this control capability. These results also give insight into the time development of a dust particle’s charge in the afterglow, on a sub-millisecond time scale.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Positive charging of grains in an afterglow plasma is enhanced by ions drifting in an electric field

In a plasma, the polarity of a dust grain's charge is typically negative, but it can reverse and become positive in an afterglow, when the power sustaining the plasma is switched off. This positive charging, which occurs in the afterglow's first few milliseconds, is studied for grains much larger than a few nm. It is hypothesized that the positive charging is enhanced by the presence of a dc electric field, which causes ions to drift through the neutral gas. A larger value of the reduced electric field E/N leads to a larger ion kinetic energy and thus a greater collection of positive charge on a grain. The maximum possible positive charge is attained if the grain's surface potential rises to match the ion kinetic energy, at a time before ions have departed and the grain's charge becomes frozen. Thereafter, when vacuum conditions prevail, the grain will retain its positive residual charge. In an experiment, dust grains were electrically levitated in a capacitively coupled plasma until the power was abruptly turned off. In the afterglow, grains fell faster than expected due to gravity alone, indicating a downward electric force, in the presence of a remaining dc electric field. Acceleration measurements yielded repeatable results for the residual charge's value, which was of the order +10 4 e and increased with E/N, supporting the hypothesis.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Modeling the Low-Pressure High-Voltage Branch of the Paschen Curve for Hydrogen and Deuterium

A physical and numerical model of the Townsend discharge in molecular hydrogen and deuterium has been developed to meet the needs of designing a plasma-based switching device for power grid applications. Here, the model allows to predict the low-pressure branch of the Paschen curve for applied voltage in the range of several hundred kilovolts. In the regime of interest, electrons are in a runaway state and ionization by ions and fast neutrals sustains the discharge. It was essential to correctly account for both gas-phase and surface interactions (electron emission and electron backscattering), especially in terms of their dependence on particle energy. The model yields results consistent with prior data obtained for lower voltage. The three-species (electrons, ions, and fast neutrals) model successfully captures the essential physics of the process.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Collective Thomson scattering measurement of plasma evolution during the current pulse in a laser-triggered switch

High-voltage laser-triggered switches (HV-LTSs) are used in pulsed-power applications where low jitter and precise timing are required. The switches allow operation in the megaampere, megavolt regime while maintaining low insertion losses. Currently, there is a lack of detailed plasma measurements in these switches, yet such measurements are needed to elucidate the detailed physics, which include a range of processes such as laser breakdown, streamer formation and growth, current flow, plasma evolution, and cooling. Detailed spatially- and temporally resolved measurements of plasma properties within the switches could contribute to validating and advancing numeric models of these systems. This contribution presents laser Thomson scattering measurements of the electron number density and temperature evolution in a HV-LTS. The switch was operated at 6 kV with current flow for a duration of 145 ns and a peak current density of 0.2 MA/cm2 into a matched load. The Thomson scattering diagnostic system uses a 532 nm probe from an Nd:YAG laser allowing a temporal resolution of ∼10 ns. We find that during the switch current pulse, the plasma electron temperature rose from a starting value of 8.1 ± 1.6 eV (due to cooling of the earlier trigger laser plasma) to a peak value of 26 ± 5 eV with an associated increase in the electron density from 8.6 ± 1.7 × 1017 to 3.1 ± 0.6 × 1018 cm−3.

Gottfried, Jacob A. (ORCID:0000000290058841)↗
DOE OSTI2023

A mid-scale plasma-electrode Pockels cell for the FLUX laser

A mid-scale (270 x 270-mm aperture) plasma-electrode Pockels cell (PEPC) has been developed for the pump laser system in FLUX (the fourth-generation laser for ultrabroadband experiments). The FLUX mid-scale PEPC is adapted from the PEPC used in the OMEGA EP beamlines (410 x 410-mm aperture), with certain dimensions scaled to reduce capacitance while maintaining key plasma characteristics. After experimental optimization of operating parameters, particularly the plasma current, <70-ns switching time with excellent (>1000:1) contrast has been demonstrated. Dependence of optical switching performance on operating conditions is explained by a plasma model.

AMICA↗
DOE OSTI2020

Uncovering a membrane-distal conformation of KRAS available to recruit RAF to the plasma membrane

The small GTPase KRAS is localized at the plasma membrane where it functions as a molecular switch, coupling extracellular growth factor stimulation to intracellular signaling networks. In this process, KRAS recruits effectors, such as RAF kinase, to the plasma membrane where they are activated by a series of complex molecular steps. Defining the membrane-bound state of KRAS is fundamental to understanding the activation of RAF kinase and in evaluating novel therapeutic opportunities for the inhibition of oncogenic KRAS-mediated signaling. We combined multiple biophysical measurements and computational methodologies to generate a consensus model for authentically processed, membrane-anchored KRAS. In contrast to the two membrane-proximal conformations previously reported, we identify a third significantly populated state using a combination of neutron reflectivity, fast photochemical oxidation of proteins (FPOP), and NMR. In this highly populated state, which we refer to as “membrane-distal” and estimate to comprise ~90% of the ensemble, the G-domain does not directly contact the membrane but is tethered via its C-terminal hypervariable region and carboxymethylated farnesyl moiety, as shown by FPOP. Subsequent interaction of the RAF1 RAS binding domain with KRAS does not significantly change G-domain configurations on the membrane but affects their relative populations. Overall, our results are consistent with a directional fly-casting mechanism for KRAS, in which the membrane-distal state of the G-domain can effectively recruit RAF kinase from the cytoplasm for activation at the membrane.

KRAS↗
DOE OSTI2021

Underwater plasma breakdown characteristics with respect to highly pressurized drilling applications

Deep earth drilling is a key technique to extract oil, gas, and geothermal heat from the earth. Many complex energy focusing methods have been explored as an alternative approach to reach these resources but most of them require high energy. However, by utilizing short time span liquid plasma discharges, energy focusing can be achieved within traditional drilling systems. These discharges induce a rapid expansion process and a resulting shockwave. It is believed that this focused energy will lower the required cutting force to progress through the rock. Lowering the required cutting force will allow for lower drill bit wear, quicker rate of penetration, and an overall cost savings of the project. Plasma breakdown characteristics at drilling relevant pressures, ranging from 1 to 350 atm, were studied. A resistance–capacitance circuit with an air gapped spark switch was utilized to generate pulsed plasma between the pressurized electrodes. It was found that the required breakdown voltage increases as the pressure increases. It was also found that a plasma channel formation and an associated breakdown may or may not occur between the electrodes at different pressures due to variation in required breakdown voltages. Breakdown time-lag in the dielectric medium (tap water, 780 μS cm –1 ) increased as the pressure was increased, which indicated a higher voltage drop at higher pressures (>100 atm). The plasma generated cavitation bubble with an associated shockwave occurred as pressures were increased. However, the bubble radius and the bubble duration decreased as the pressure was increased. The plasma generated shockwave speeds fall within the expected speed of sound in water. Lastly, preliminary rock cracking tests were performed on granite at high pressures (340 and 272 atm) and it was found that plasma is able to create cracks in the rock.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Coulomb expansion of a thin dust cloud observed experimentally under afterglow plasma conditions

The Coulomb expansion of a thin cloud of charged dust particles was observed experimentally, in a plasma afterglow. This expansion occurs due to mutual repulsion among positively charged dust particles, after electrons and ions have escaped the chamber volume. In the experiment, a two-dimensional cloud of dust particles was initially levitated in a glow-discharge plasma. The power was then switched off to produce afterglow conditions. The subsequent fall of the dust cloud was slowed by reversing the electric force, to an upward direction, allowing an extended observation. At early time, measurements of the Coulomb expansion in the horizontal direction are found to be accurately modeled by the equation of state for a uniformly charged thin disk. Finally, bouncing from the lower electrode was found to be avoided by lowering the impact velocity <100 mm/s.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Plasma Emission, Wave Speeds, and Temperatures of Laser-Supported Plasmas in Air

A study of the generation and subsequent expansion of plasmas using a single beam (532 nm) from the second harmonic generator of a Q-switched Nd:YAG laser is described. The plasmas in air are studied using an intensified charge-coupled device camera over periods of 1000 ns following the laser pulses. The plasma experimental results are interpreted in terms of wave speeds and plasma temperatures. Energy balance equations are considered to estimate the plasma temperatures and the laser-supported radiation (LSR) and the laser-supported detonation (LSD) wave speeds. Within 1000 ns observation time, the circular spectral images turn elliptical because of plasma expansion toward the laser beam. The plasma expansion increases with increasing laser irradiance. A laser irradiance range of [Formula: see text] yields LSR wave speeds between 45 and 170 km/s and LSD wave speeds of 90–130 km/s. The measured wave speeds are compared with the LSR and the LSR wave speed models. The plasma temperatures are between 90,000 and 120,000 K at 15 ns after the laser pulse based on measured emission spectra and are between 640,000 and 760,000 K at 3 ns based on the LSR model.

Engineering↗
DOE OSTI2024

Temperature Distribution Within an Ignition Kernel Initiated by a Laser-Induced Plasma

The sizes of, and temperature distributions within, ignition kernels initiated by a Q-switched neodymium-doped yttrium aluminum garnet laser-induced plasma in an unconfined lean premixed hydrogen-air upward jet flow are investigated. The experiments involved a range of jet velocities and a range of deposited laser energies at a fixed height above the exit along the axis of a burner. The growth of, and the temperature distributions within, the ignition kernels, as affected by the size and the energy distribution of the laser-induced plasma, are monitored with an infrared camera. The initial ignition kernels’ areas are larger with higher laser pulse energies and remain unchanged up to [Formula: see text] and then increase by factors of up to 3 at [Formula: see text]. The change in the kernel area caused by the jet velocities is less than 1.5%. An increase of the bulk velocity by 190% decreases the ignition kernel temperature by 6%. This reduction in the ignition kernel temperatures is because of an increase in energy losses by a factor of 2 and decreases in heat releases by 2% at [Formula: see text] and by 11% at [Formula: see text]. The present contributions are: measurements of and insights into temperature distributions and kernel development rates during the laser-induced plasma ignition process at different deposited energies and flow velocities.

Engineering↗