V. Gurovich

Parameters of the plasma produced at the surface of a ferroelectric cathode by different driving pulses

Spectroscopic investigations of the properties of a plasma produced by a ferroelectric-plasma source are presented. The electron plasma density, the electron and ion temperature, and the density of desorbed neutrals near the ferroelectric surface are determined from spectral line intensities and profiles. Three different methods of surface plasma formation are analyzed using a simplified model for the plasma production. The model predicts the total amount of charge in the plasma to be proportional to the dielectric constant of the ferroelectric material. Also, the model shows a strong dependence of the plasma parameters on the resistivity of the plasma transition layer. A maximal plasma density of ∼1015cm−3 is achieved when the electrons that were attached by the driving field to the ferroelectric surface are released from the surface owing to driving pulse sharp decay and ionized heavy atoms desorbed from the ferroelectric.

Time-resolved investigation of nanosecond discharge in dense gas sustained by short and long high-voltage pulse

The results of experimental and numerical studies of the generation of runaway electrons (RAE) in a pressurized air-filled diode under the application of 20 ns, 5 ns and 1 ns duration high-voltage pulses with an amplitude up to 160 kV are presented. It is shown that with a 1 ns pulse, RAE with energy ≥20 keV reach the anode prior to the formation of the plasma channel between the cathode and anode. Conversely, with 20 ns or 5 ns pulses, RAE with energy ≥20 keV were obtained at the anode only after the formation of the plasma channel. In addition, the high- and low-impedance stages of the development of the discharge were found. Finally, a comparison between experimental and numerical simulation results is presented.

Plasma window characterization

Parameters of an arc Ar plasma discharge used as a plasma window with a discharge current of ∼50A and a voltage of ∼58V are presented. It is shown that this arc discharge allows one to decrease the pressure at the low pressure end of the plasma window almost 380 times using relatively low pumping at the low pressure end of the plasma window. Calculations of the plasma parameters and their spatial distribution using a simple wall-stabilized arc model showed a satisfactory agreement with the experimentally obtained data. It is shown that a significant decrease in gas flow through the plasma window occurs due to the increase in plasma viscosity. An improvement of the plasma window ignition and some of its design aspects are described as well.

Simulation of Plasma Parameters During Hollow Cathodes Operation

b0 = impact parameter for coulomb collisions with a large scattering angle, m cv = specific heat capacity at constant volume for xenon gas, J= kg K ctotal = specific heat capacity at constant volume per unit of volume for xenon plasma, J= m kg K Di, Da = ion and ambipolar diffusion coefficient, m =s e = electron charge, C F = mass flow rate, kg=s Ie = electron current, A I i , I loss i = ion production and loss rates, A J i , J B i = radially averaged axial ion current densities at the orifice input and output, A=m J i = ion current to the wall, A=m 2 kB = Boltzmann constant, J= K L = orifice length, m M = xenon atom mass, kg m = electron mass, kg mXe = xenon gas molar mass, kg=mol n, n = plasma density and average plasma density, m 3 n0 , n B 0 = neutral gas density at the input and exit of the orifice, m 3 n0 = average neutral gas density, m 3 P 0 = neutral gas pressure at the orifice input/exit (superscript A=B) of the orifice, Pa Qei, Qen, Qtotal = electron—ion, electron—neutral, and total density of energy exchange rate, J= m s ~ R, R = ideal gas universal constant, J= Kmol , and resistance of the plasma within the orifice, r = orifice radius, m Te, Ti, T0 = electron, ion, and neutral gas temperature, eV T e = average electron temperature in the insert region Tr = reduced temperature Uion, Uexcit = mean electron energy loss due to an ionization/ excitation event, eV u0 = axial neutral gas velocity, m=s ue, u d e = electron thermal and drift velocity, m=s u i = radially averaged axial ion velocity at the input/ exit of the orifice, m=s = ratio between neutral gas density (orifice outlet)/ (orifice inlet) = plasma resistivity, Vm=A CEX, D = mean free path for charge exchange and debye length, m i, e = ion and electron mobility. ei, en, in = electron—ion, electron—neutral, and ion— neutral collision frequencies, s 1 = neutral gas viscosity, Pa s CEX, ion,

Energetic Particles and Radiation Intense Emission During Ferroelectric Surface Discharge

In this paper, the operation of ferroelectric plasma sources (FPSs) under the application of driving pulses with different amplitudes (4-40 kV) was studied. It was found that, in addition to the electron/ion flows studied in earlier research, the dense plasma formation during the fast fall (a few tens of nanoseconds) of the driving pulse is accompanied by the generation of a highly diverging ~180deg neutral flow with velocity of ~7ldr107 cm/s as well as by charged microparticles and intense extreme ultraviolet radiation. It was shown that the velocity and intensity of the generated neutral flow remained the same for different parameters of the driving pulse. A model for the neutrals and microparticles emission based on Coulomb microexplosions of ferroelectric ceramics is suggested. The application of the FPS as a promising micro thruster is also discussed.

Quasi-isentropic compression using compressed water flow generated by underwater electrical explosion of a wire array

A major experimental research area in material equation-of-state today involves the use of off-Hugoniot measurements rather than shock experiments that give only Hugoniot data. There is a wide range of applications using quasi-isentropic compression of matter including the direct measurement of the complete isentrope of materials in a single experiment and minimizing the heating of flyer plates for high-velocity shock measurements. We propose a novel approach to generating quasi-isentropic compression of matter. Using analytical modeling and hydrodynamic simulations, we show that a working fluid composed of compressed water, generated by an underwater electrical explosion of a planar wire array, might be used to efficiently drive the quasi-isentropic compression of a copper target to pressures ∼2 × 1011 Pa without any complex target designs.

Generation of fast cumulative water jets by underwater electrical explosion of conical wire arrays

The results of experiments with underwater electrical explosion of conical arrays of copper wires are presented. A pulsed generator producing a 300 kA-amplitude current with a 1.2 μs rise time was used in the explosion of the arrays. As a result of the explosion, fast-moving water jets, with velocities of up to 1200 m/s, were observed being ejected from the surface of the water covering the wire array. The position of the water jets was measured by multiple-exposure fast framing imaging. The apex angle of the array or the thickness of the water layer above the arrays was altered from shot to shot, which changed the resulting velocities and shapes of the emitted jets. A numerical model, based on the models of cumulation and penetration of a jet through material of similar density, is suggested. The velocities of jets obtained by this model, agree well with the experimentally observed jet velocities.

Underwater spherical shock wave

Summary form only given. The results of experimental and numerical studies of spherical implosion of converging spherical strong shock waves (SSW) generated using underwater electrical explosion of spherical Cu wire arrays are reported. In the experiment, a ~ 4 kJ pulse generator with discharged current amplitude -300 kA, and a rise time of ~ 1 μs was used for wire array explosion. Spherical wire arrays with radii of 10 mm, 12.5 mm, 15 mm and 20 mm were tested. Number of wires was varied in the range 20-40 for different wire diameters in the range 0.1-0.2 mm. A largest shock wave velocity, pressure, water temperature and density in the vicinity of the implosion origin were achieved for the array with radius of 10 mm. The emission from the plasma formed by SSW near the origin of implosion was collected by optical fibers and detected by photomultipliers. The time of the water self-emission appearance together with the data of energy delivered to the wire array were used for determination of the SSW and water parameters in the vicinity of the implosion center using hydrodynamic simulations coupled with SESAME data base for water.

Parameters of the Plasma Produced at the Surface of a Ferroelectric Cathode by Different Driving Pulses

Summary form only given. Spectroscopic investigations of the properties of the plasma produced by a ferroelectric plasma source are presented. The plasma electron density and electron and ion temperature near the ferroelectric surface were determined from spectral line intensities and broadenings. The density of neutrals in the vicinity of the FPS surface, determined by analyses of neutral atom emission lines accounting opacity effect, was found to be ~1016 cm-3 . It was shown that the plasma electron density depends on the method of driving pulses application. The latter determines the gas and plasma ambience and the direction of the electron flow with respect to the plasma. Three different methods of the plasma formation were tested and results are compared. It was shown that the plasma electron density depends on the method of driving pulses application. Maximal plasma density up to 1015 cm-3 is achieved when the electrons attached to the ferroelectric surface by the driving electric field are released from the surface owing to driving pulse sharp decay and ionize heavy atoms desorbed from the ceramic. A mechanism controlling the density of the surface plasma is suggested. This mechanism relates to the surface density of bounded polarization charges which in it turn depends on the driving electric field and the ferroelectric sample properties. It was found that the product of the average plasma density ne and the thickness of the plasma layer h in an incomplete surface discharge relates to the bound polarization charge surface density as sigma = ehne. This relation was verified by the data obtained in the experiments

High-frequency electron beam generation by ferroelectric cathode with anomalous plasma resistance caused by ion-acoustic instability

Summary form only given. We report results of spectroscopic research of high-frequency oscillations in the plasma produced on the surface of a ferroelectric ceramic sample which serves as a cathode. These oscillations appear when the accelerating pulse is applied to the sample and they are accompanied by emission of a high-frequency modulated electron beam. The plasma electron density and temperature were determined by comparison of the experimental results with the results of collision-radiative modeling. During the high-frequency oscillations a stationary pattern of spatial variation of the plasma density was obtained. An anisotropic electric field of amplitude /spl sim/1 kV/cm was found in the plasma by polarization spectroscopy of hydrogen lines. The obtained data are explained by excitation of nonlinear ion-acoustic waves in the plasma. These waves are excited at the vicinity of the cathode output grid and propagate towards the cathode. These waves turn into standing waves at the location where the wave velocity becomes equal to the velocity of the plasma propagating outward the ceramic surface. The measured electric field is explained by anomalous plasma resistance which is developed by interaction between the current carrying electrons and the ion sound waves. The high-frequency modulated electron emission is explained by the fast plasma potential variations at the vicinity of the output cathode grid. These fast potential variations are in resonance with the self-frequency of the external circuit.