V. Ts. Gurovich

Characterization of the plasma on dielectric fiber (velvet) cathodes

An investigation of the properties of the plasma and the electron beam produced by velvet cathodes in a diode powered by a ∼200kV, ∼300ns pulse is presented. Spectroscopic measurements demonstrated that the source of the electrons is surface plasma with electron density and temperature of ∼4×1014cm−3 and ∼7eV, respectively, for an electron current density of ∼50A∕cm2. At the beginning of the accelerating pulse, the plasma expands at a velocity of ∼106cm∕s towards the anode for a few millimeters, where its stoppage occurs. It was shown by optical and x-ray diagnostics that in spite of the individual character and nonuniform cross-sectional distribution of the cathode plasma sources, the uniformity of the extracted electron beam is satisfactory. A mechanism controlling the electron current-density cross-sectional uniformity is suggested. This mechanism is based on a fast radial plasma expansion towards the center due to a magnetic-field radial gradient. Finally, it was shown that the interaction of the elec...

Analysis of shock wave measurements in water by a piezoelectric pressure probe

Investigation of underwater electrical wire explosions occurring in the time scale of few microseconds requires a measurement of pressure waves with nanosecond rise time and microsecond fall time. Various types of pressure gauges are used for this purpose, however, none of them seems to be suitable for the task since the frequency range of the pressure waves lies between 107 and 109 Hz, whereas all types of mechanical gauges have a bandwidth below 107 Hz. Therefore, a mathematical processing of measurements is required for reconstruction of the actual pressure wave forms. In this article, a signal processing algorithm, based on energy conservation requirements and Fourier analysis, for reconstruction of the wave form of the pressure wave generated under water by electrical explosion of wires is proposed. The gauge used in the experiments is a PCB 119A12 type pressure gauge with a bandwidth below 1 MHz produced by Piezo-Electronics, Inc. Pressure waves were produced by underwater electrical explosion of a ...

Grid-controlled electron emission from a hollow-anode electron source

We describe the operation of a hollow-anode electron source with a biased output grid in a diode powered by a 200 kV 400 ns pulse. The hollow anode had a ferroelectric plasma source incorporated in it. Three electrical schemes for the hollow-anode output grid bias were tested and compared. It is shown that the use of an autobias grid allows electron-beam generation with a current amplitude up to 1.2 kA in a plasma emission-limited mode and with insignificant plasma prefilling of the accelerating gap. The use of an externally biased output grid (either with a positive or negative potential) showed the possibility to control the emission properties of the hollow-anode plasma without changing the amplitude of the discharge current. Electron beams with an amplitude up to 2 kA and insignificant plasma prefilling of the accelerating gap were obtained. It was found that the application of the accelerating pulse leads to a drastic increase in the potential of the plasma up to several kV. It is shown that, in spit...

High-frequency electron beam modulation by a ferroelectric cathode with anomalous plasma resistance

Spectroscopic measurements are reported of the plasma formed inside a cathode having a ferroelectric source incorporated in it. These measurements were performed during the generation of a high-frequency modulated electron beam in a planar diode with the above cathode. It was found that there is a spatially periodic structure in the plasma density, electric field, and electron energy in the plasma in the longitudinal direction from the ferroelectric surface. The plasma density, electric field, and electron energy vary in the range of 5×1013–5×1014 cm−3, 0–1 kV/cm, and 2–30 eV, respectively. Also, it was found that the plasma electron temperature is ∼8 eV in the vicinity of the ferroelectric surface and ∼2 eV in the bulk of the plasma. To explain the obtained experimental data a qualitative model is suggested. The model is based on fast periodic appearance of anomalous plasma resistance due to generation of ion-acoustic instability. The latter is controlled by the ratio between the velocities of the curren...

Landau-Stanyukovich rule and the similarity parameter for converging shocks

The similarity parameter α of a self-similarity problem of the second kind is determined numerically in the course of solving the basic equations. The Landau-Stanyukovich rule gives an approximate value of α close to the true one. This estimate should be refined in further numerical calculations. The determination of the status of the Landau-Stanyukovich rule and the development of this approach make it possible to find the upper and lower bounds for α(γ) for a given adiabatic index γ. The narrowness of the interval between these values makes it possible to find the value of α different from the true one by 0.01–0.02. In this case, the self-similarity problem of the second kind is actually reduced to a self-similarity problem of the first kind in which the value of α follows from the dimension analysis of the key physical parameters of the problem and does not require solving the equations.

Multicapillary and carbon fiber cathodes for high-current electron beam generation

We report results of investigation of a high-current electron diode with multicapillary cordierite and glass cathodes assisted by velvet-type and ferroelectric plasma source igniters, and carbon fiber cathodes. Parameters of the plasma inside the capillary channels and in the vicinity of the cathode surface were studied during the accelerating pulse in a diode powered by a ∼200kV, ∼300ns pulse. The nature of uniformity in emission current density distribution and possibility of electron beam control duration for multicapillary cathode will also be presented. For carbon fiber cathodes it was found that application of the accelerating pulse leads to generation of the surface plasma in a form of several mm size plasma spots. The cathode plasma density and temperature were measured using non-disturbing spectroscopic methods.

Low-pressure hollow-anode plasma sources

The operation of hollow anodes (HAs) with either multi-arc or magnetron-like or ferroelectric plasma source (FPS) ignition is described. These HA sources produce in the vicinity of the HA output grid a plasma with a density n ≈ 5 × 1012 cm−3 and this plasma acquires a positive potential of several tens of volts. HAs with an incorporated FPS have demonstrated the best operation characteristics and smallest dimensions. Also, the FPS allows us to achieve an HA discharge with a current amplitude I d ≤ 1.2 kA at a gas pressure of about 10−5 Torr. These HA modifications were used as a cathode in a diode powered by a 200 kV, 400 ns pulse. The parameters of the electron beam with an amplitude of 1.5 kA or less are presented. The accelerating pulse causes an increase in the HA plasma potential of up to 6 kV. A model that explains the electron emission from the positively charged plasma is proposed.

Quantum creation of the universe with a minimum scalar-field energy

The quantum creation of a closed Friedmann universe is studied on the basis of a Wheeler-DeWitt equation with two arguments — a scale factor and a scalar-field potential. In the quasiclassical approximation the wave function of the universe (WF) starts to evolve at a zero scalar field. A near-Planckian energy density of the field arises as a result of tunneling through a potential barrier. In our opinion, this variant of the scenario most closely resembles creation ex nihilo. The only parameter controlling quantum evolution is the mass of a quantum of the scalar field. In the paper by Khalatnikov and Schiller [JETP Lett. 57,1 (1993)], tunneling through the classically inaccessible region of the superpotential U(a,φ) is calculated by the instanton method. However, this method requires that the potential U(a,φ) satisfy special conditions in the space (a,φ). For this reason, in the present paper the tunneling calculation is performed by the method of characteristics for the quasiclassical approximation of the Wheeler-DeWitt equation under the barrier. The WKB theory, which has been well-developed for one-dimensional problems, is employed along each characteristic. It is shown that the corresponding turning points are also points where U(a, φ)=0. The total barrier penetrability is obtained by averaging over a bundle of characteristics.

A Low-Pressure Hollow Anode Plasma Source for Generation of High-Current Electron Beams

Summary form only given. We report results on a high-current hollow anode plasma source triggered by a ferroelectric surface discharge. This plasma source was used for generation of high-current electron beams in a diode under acceleration voltage of 300 kV and ~400 ns pulse duration. For the ferroelectric sample we used a BaTi solid solution with a large dielectric constant (epsiap1600). The studied hollow anode design allows reliable ignition and sustaining of the discharge with current amplitude of up to 1.2 kA and pulse duration of up to 20 mus. Parameters of the hollow anode plasma and generated electron beam were studied by the use of different time and space resolved electrical, optical, X-ray and spectroscopic diagnostics. Generation of high-current electron beams with current amplitude up to 1 kA was demonstrated. Models explaining electron emission from positively charged hollow anode plasma and the existence of an optimal resistor which supplies an auto-bias potential to the hollow-anode output grid are suggested