Search NASA⌕ Search

SEARCH · Search NASA

Results for “PLASMA PRODUCTION”

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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Picosecond runaway electron beams in air

Experimental data on the generation of picosecond runaway electron beams in an air gap with an inhomogeneous electric field at a cathode voltage of up to 500 kV are presented. The methods and equipment developed for these experiments made it possible to measure the beam characteristics with a time resolution of better than 10{sup -11} s, determine the voltage range and the beam formation time in the breakdown delay stage, and demonstrate the influence of the state of the cathode surface on the stability of runaway electron generation. It is demonstrated that the critical electron runaway field in air agrees with the classical concepts and that the accelerated beam can be compressed to {approx}20 ps. It is unlikely that, under these conditions, the beam duration is limited due to the transition of field emission from the cathode to a microexplosion of inhomogeneities. The maximum energy acquired by runaway electrons in the course of acceleration does not exceed the value corresponding to the electrode voltage.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Expansion of the cathode spot and generation of shock waves in the plasma of a volume discharge in atmospheric-pressure helium

The expansion of the cathode spot and the generation of shock waves during the formation and development of a pulsed volume discharge in atmospheric-pressure helium were studied by analyzing the emission spectra of the cathode plasma and the spatiotemporal behavior of the plasma glow. The transition of a diffuse volume discharge in a centimeter-long gap into a high-current diffuse mode when the gas pressure increased from 1 to 5 atm and the applied voltage rose from the statistical breakdown voltage to a 100% overvoltage was investigated. Analytical expressions for the radius of the cathode spot and its expansion velocity obtained in the framework of a spherically symmetric model agree satisfactorily with the experimental data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Electromagnetic radiation from a plasma slab during the development of Weibel instability

Electromagnetic radiation from an anisotropic plasma slab formed by ionization of matter in the field of a high-power femtosecond pulse is studied. It is shown that the growth of initial field perturbations in the course of Weibel instability is accompanied by the generation of nonmonochromatic radiation with a characteristic frequency on the order of the instability growth rate. It is found that perturbations with characteristic scale lengths less than or on the order of the ratio of the speed of light to the Langmuir frequency are excited and radiated most efficiently, provided that the slab is thicker than this ratio.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Beam discharge excited by distributed virtual cathode

A new type of beam discharge, i.e., beam discharge with a distributed virtual cathode (VC) is proposed and considered by numerical simulation. The discharge is established during counter motion of high-current electron beams in a gas-filled equipotential cavity and is characterized by a state of hot dense electron plasma of primary electrons. The discharge temporal dynamics is studied. It is shown that the VC lifetime depends linearly from this sum in a wide range of the sum of beam currents, from the boundary current of two-beam instability to the critical current of Pierce instability. Generation of nonlinear electrostatic structures shaped as phase bubbles in the discharge is detected, and their dynamics is studied. The parameters are determined, at which the multiple coexistence of phase bubbles and their coalescence during collisions is observed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Experimental study of the spatial structure of high-energy ion sources in micropinch

Images of ion sources in the plasma of a micropinch discharge were recorded. The most intense ion source was found to be a Greater-Than-Or-Slanted-Equal-To 1-mm-diameter 3-mm-long anode region. The main contribution to the images is made by single-charged ions of the plasma-forming element with energies of 10-50 keV.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Compression zone of a magnetoplasma compressor as a source of extreme UV radiation

Results from experimental studies of extreme UV (EUV) radiation from the compression zone of a magnetoplasma compressor (MPC) operating with xenon are presented. Two MPC operating modes that differ in the method of xenon injection into the discharge were studied. It is shown that EUV radiation in the wavelength range of 5-80 nm is emitted from the compression zone. In the MPC operating mode with local xenon injection directly into the compression zone surrounded by helium plasma, the radiation power reaches it peak value of 16-18 kW in the wavelength range of 12.2-15.8 nm.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Millimeter-wave spectral line radiation from a powerful explosion

Millimeter-wave spectral line radiation from a powerful air explosion accompanied by neutron, X-ray, and gamma emission is considered. It is shown that the main contribution to the line radiation in the frequency window of air near the wavelength of 2.3 mm is made by nitric oxide molecules. The set of kinetic equations for a partially ionized plasma near the explosion is solved by the Runge-Kutta method. It is shown that the density of nitrogen oxide molecules increases in time to a certain steady-state level. The spectral power of radiation in the NO lines is estimated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Study of the core gaps formed accidentally during wire explosion

During wire explosion, along with striations (a regular structure with alternating lower and higher density bands), low-density regions the characteristic axial size of which differs substantially from that of striations and can reach 1-2 mm are also observed in the discharge channel. Such irregular structures came to be known as 'gaps' (D. B. Sinars et al., Phys. Plasmas 8, 216 (2001)). In the present study, the mechanism of the formation of core gaps during explosions of 25- and 50-{mu}m-diameter copper and nickel wires in air is investigated. It is shown that the specific energy deposited in the gap region substantially exceeds the average specific energy deposited in the wire material.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Three-dimensional simulations of anomalous absorption of laser radiation by plasma with supercritical density

A three-dimensional (3D) model of the interaction of laser radiation with plasma in the framework of Maxwell-Vlasov equations has been used to calculate the anomalous optical absorption in plasma of supercritical density. The results of calculations confirmed the development of anomalous absorption that was previously revealed by 2D models, which were insufficient for comparison to the experiment. Calculations were performed for a system containing about 10{sup 6} macroparticles that allowed the absorption coefficient and other characteristics of anomalous absorption in plasma with an inhomogeneous surface to be determined as functions of various parameters of the incident radiation and plasma target. Results are analyzed and estimations are obtained for the contributions of ionization processes and pair collisions of electrons, which show that these factors were quite reasonably ignored in the model. All quantitative results are obtained for the third harmonic of neodymium laser ({lambda} = 0.351 {mu}m) at a tenfold excess of the substance density over a critical value for this radiation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Beams of fast neutral atoms and molecules in low-pressure gas-discharge plasma

Fast neutral atom and molecule beams have been studied, the beams being produced in a vacuum chamber at nitrogen, argon, or helium pressure of 0.1-10 Pa due to charge-exchange collisions of ions accelerated in the sheath between the glow discharge plasma and a negative grid immersed therein. From a flat grid, two broad beams of molecules with continuous distribution of their energy from zero up to e(U + U{sub c}) (where U is voltage between the grid and the vacuum chamber and U{sub c} is cathode fall of the discharge) are propagating in opposite directions. The beam propagating from the concave surface of a 0.2-m-diameter grid is focused within a 10-mm-diameter spot on the target surface. When a 0.2-m-diameter 0.2-m-high cylindrical grid covered by end disks and composed of parallel 1.5-mm-diameter knitting needles spaced by 4.5 mm is immersed in the plasma, the accelerated ions pass through the gaps between the needles, turn inside the grid into fast atoms or molecules, and escape from the grid through the gaps on its opposite side. The Doppler shift of spectral lines allows for measuring the fast atom energy, which corresponds to the potential difference between the plasma inside the chamber and the plasma produced as a result of charge-exchange collisions inside the cylindrical grid.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Study of the implosion characteristics of quasi-spherical wire arrays on the Angara-5-1 facility at currents of up to 4 MA

Results are presented from experimental studies of the spatial distribution of the density of matter in the central part of the discharge gap and the formation of the temporal profile of the X-ray power in the course of implosion of quasi-spherical wire arrays at discharge currents of up to 4 MA. The spatial distribution of the X-ray intensity in the central part of the discharge gap and the temporal profile of the X-ray power are used as implosion characteristics of quasi-spherical wire arrays. The quasi-spherical arrays were formed by the radial stretching of unstrained wires of initially cylindrical and conical wire arrays under the action of the electrostatic field. The temporal profile of the output X-ray pulse in the photon energy range of 0.1-1 keV is shown to depend on both the geometrical parameters of the quasi-spherical array and the longitudinal distribution of its mass. It is found that a 40% increase in the wire mass due to deposition of an additional mass in the equatorial region of a quasi-spherical array leads to a 15% increase in the average current radius of the pinch and a 30% decrease in the X-ray yield. Experiments with quasi-spherical arrays made of kapron fibers with deposited Al and Bi conducting layers were also carried out. It is demonstrated that application of such arrays makes it possible to control the profile and duration of the generated X-ray pulse by varying the mass, material, and location of the deposited layer. It is found that deposition of an additional mass in the form of a thin Bi stripe on tungsten wires near the cathode end of the array allows one to mitigate the influence of the cathode zipper effect on the pinch compression and formation of the X-ray pulse in tungsten arrays.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Study of the contributions of the electrode materials to the plasma of a high-current vacuum spark

The contribution of the electrode material to the formation of the plasma of a low-inductive high-current vacuum spark and its influence on the process of discharge micropinching were studied using X-ray spectroscopy and laser diagnostics. Electrode system configurations are determined in which the contributions of the materials of both electrodes to the plasma emitting X-rays are comparable and in which the contribution of one electrode is dominating. It is found that discharge pinching occurs primarily in the vapor of the pointed electrode independently of its polarity. The experimental results indicate the formation of a suprathermal electron beam in the micropinch region.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

On the spectrum of Z-pinch plasma neutrons

Generation of neutrons from Z-pinch discharges in a deuterated gas medium has been studied. It is shown that a power-law energy dependence of the number of high-energy deuterons in Z-pinch plasma explains the observed broadening of the neutron spectrum in these systems. It is established that, at an average ion energy below 3 keV in Z-pinch plasma, neutrons are mostly generated due to the interaction of high-energy ({approx}100-keV) deuterons with the main plasma components.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Hybrid X-pinches

Results from experimental studies of a hybrid X-pinch with an initial configuration in the form of a high-current diode with conical tungsten electrodes spaced by 1-2 mm and connected to one another with 20- to 100-{mu}m-diameter wires are presented. The experiments were carried out at four facilities with a current amplitude from 200 to 1000 kA and front duration from 45 to 200 ns. It is shown that, in spite of their simpler configuration, hybrid X-pinches with a short rise time of the current pulse (50-100 ns) are highly competitive with standard X-pinches in the generated soft X-ray power and the formation of a single hot spot in them is much more stable, while hard X-ray emission is almost absent. The possibility of using hybrid X-pinches as soft X-ray sources for point projection X-ray imaging of plasma objects is considered.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Pulsed submicrosecond multichannel sliding discharges of opposite polarities: Filling of the discharge gap with spark channels

Results are presented from measurements of the discharge current and the factor of the discharge gap filling with spark channels during pulsed sliding discharges of opposite polarities in Ne, Ar, and Xe on an aluminum oxide ceramic surface. The measurements were performed in the regime of single pulses of submi-crosecond duration at discharge voltages of 0-12 kV with two discharge chambers with different thicknesses of the ceramic plate (0.4 and 0.17 cm) and different electrode gap lengths (4 and 10.3 cm) at gas pressures of 30 and 100 kPa. The results obtained for discharges of opposite polarities are compared with one another, and common features of discharges in three gases are revealed. It is shown that the filling of the discharge gap with spark channels in the gases under study is more efficient in the case of the positive polarity of the discharge voltage, except Xe at a pressure of 100 kPa in the electrode gap of length 10.3 cm. The quasi-homogeneous regime of discharge in each of the three gases is attained easier at lower gas pressures. Comparison of the data on the filling factors of the discharge gap and the peak currents of opposite-polarity discharges for each gas at a given pressure indicates that the higher the discharge current, the more densely the discharge gap is filled with spark channels.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Noninductive plasma generation and current drive in the Globus-M spherical tokamak

Experimental results on the generation and maintenance of the toroidal current in the Globus-M spherical tokamak by using waves in the lower hybrid frequency range without applying an inductive vortex electric field are presented. For this purpose, the original ridge guide antennas forming a field distribution similar to that produced by multiwaveguide grills were used. The high-frequency field (900 MHz) was used for both plasma generation and current drive. The magnitude of the generated current reached 21 kA, and its direction depended on the direction of the vertical magnetic field. Analysis of the experimental results indicates that the major fraction of the current is carried by the suprathermal electron beam.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

X-pinch. Part I

Results of experimental studies of the X-pinch since its invention and implementation in 1982 at the Lebedev Physical Institute are presented. The concept of the X-pinch arose in the course of innovative experiments on studying the generation of hot dense plasma in nanosecond Z-pinches. The main idea was to localize the region occupied by the plasma and stabilize the moment of its formation. This was achieved by using a load in the form of crossed wires. The resulting plasma object turned out to be so interesting that a new scientific direction appeared in plasma physics. At present, studies in this direction are being performed in many laboratories worldwide. The term X-pinch became conventional, and sections devoted to its study are always present at plasma conferences. X-pinch is not only a very interesting scientific object, but also a unique source of X-ray emission with extreme parameters. The use of X-pinches for point-projection X-ray radiography of high-energy-density objects provided many new experimental results. In some cases, the concepts of the processes occurring in matter upon fast energy deposition changed dramatically. The review consists of two parts. The first part briefly outlines the history of creation and studies of X-pinches, describes the diagnostic techniques and devices developed during these studies, and presents the main results obtained in studying the physical processes occurring in the X-pinch. The second part is devoted to the results of detailed studies of the X-pinch hot spot—the region where the highest plasma parameters are achieved and which is a source of X-ray emission with extreme parameters. Some results of X-pinch simulations are also presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

A Plasma Generator with Magnetic Vortex Stabilization and Possibilities of Its Use

A design of a plasma generator, the parameters of the resulting plasma, and the possibilities of its use for the synthesis of nanosized powders and optical emission spectroscopy are described. The device operation is based on the arc discharge of alternating current (66 kHz) in an argon jet between water-cooled metal electrodes. The discharge is stabilized by a flow of isolating gas (helium, nitrogen, air) and an axial magnetic field. The gas flow is fed tangentially to the discharge axis. The plasma between the electrodes has the shape of a cylinder remote from the chamber walls. The temperature and electron concentration in the cross section of the plasma cylinder vary along the radius and take the maximum and minimum values.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗