Observation of the avalanche of runaway electrons in air in a strong electric field

Emission Features and Structure of an Electron Beam versus Gas Pressure and Magnetic Field in a Cold-Cathode Coaxial Diode

The structure of the emission surface of a cold tubular cathode and electron beam was investigated as a function of the magnetic field in the coaxial diode of the high-current accelerator. The runaway mode of magnetized electrons in atmospheric air enabled registering the instantaneous structure of activated field-emission centers at the cathode edge. The region of air pressure (about 3 Torr) was determined experimentally and via analysis, where the explosive emission mechanism of the appearance of fast electrons with energies above 100 keV is replaced by the runaway electrons in a gas.

Pulsed power technology based on semiconductor opening switches: A review

This paper presents a systematized review of the research on the production of nanosecond high-power pulses using solid-state generators based on an inductive energy store and a semiconductor opening switch that have been performed in the past 25 years. This research has been underway since 1992-1993 when the nanosecond cutoff of ultrahigh-density currents in semiconductor diodes was discovered and named the SOS (Semiconductor Opening Switch) effect. The discovery of the SOS effect provided a breakthrough in the development of semiconductor generators, as their most important characteristics, such as pulse power and output voltage, were increased tens and hundreds of times compared with previously known semiconductor generators. In particular, in the nanosecond semiconductor technology, megavolt voltages combined with gigawatt peak powers have been achieved. This review considers the main physical processes that determine the mechanism of operation of a SOS based on the SOS effect. The principle of operation, design, and characteristics of SOS diodes and SOS generators is described, and prospects for their further development are discussed. Examples are given of using SOS generators in various pulsed power applications such as electron accelerators, X-ray pulse devices, high-power microwave electronics, pumping of gas lasers, and ignition of electrical discharges.

Semiconductor sharpeners providing a subnanosecond voltage rise time of GW-range pulses

The article describes semiconductor sharpeners providing a subnanosecond voltage rise time of GW-range pulses. The sharpeners are made as stacks of series-connected dynistor structures built into an oil-filled coaxial line with 48 Ω wave impedance at the place of an inner conductor. Two sequential sections of pulse sharpening are used. An input voltage pulse has the amplitude of 540 kV with the rise time of ∼1.2 ns at 0.2-0.9 level from the amplitude and voltage rise rate of ∼0.3 MV/ns. After pulse propagation through the sharpening sections, its rise time is reduced down to 360 ps, and the voltage rise rate is increased up to ∼0.95 MV/ns. Peak power of the sharpened pulse is within the range of 4.5-5.5 GW. The sharpeners are tested at a pulse repetition frequency of up to 1 kHz. Sharpener operation is studied by numerical simulation methods. Experimental waveforms of output pulses and the corresponding calculated voltage-time dependences are in statistical agreement.

Energy compression of nanosecond high-voltage pulses based on two-stage hybrid scheme

Test results of high-voltage subnanosecond pulse generator with a hybrid, two-stage energy compression scheme are presented. After the first compression section with a gas discharger, a ferrite-filled gyromagnetic nonlinear transmitting line is used. The offered technical solution makes it possible to increase the voltage pulse amplitude from -185 kV to -325 kV, with a 2-ns pulse rise time minimized down to ∼180 ps. For the small output voltage amplitude of -240 kV, the shortest pulse front of ∼85 ps was obtained. The generator with maximum amplitude was utilized to form an ultra-short flow of runaway electrons in air-filled discharge gap with particles' energy approaching to 700 keV.

Electric field in a plasma channel in a high-pressure nanosecond discharge in hydrogen: a coherent anti-stokes Raman scattering study

Experimental results of a study of the electric field in a plasma channel produced during nanosecond discharge at a H2 gas pressure of (2-3)×10(5)  Pa by the coherent anti-Stokes scattering method are reported. The discharge was ignited by applying a voltage pulse with an amplitude of ∼100  kV and a duration of ∼5  ns to a blade cathode placed at a distance of 10 and 20 mm from the anode. It was shown that this type of gas discharge is characterized by the presence of an electric field in the plasma channel with root-mean-square intensities of up to 30  kV/cm. Using polarization measurements, it was found that the direction of the electric field is along the cathode-anode axis.

Spectroscopic study of plasma evolution in runaway nanosecond atmospheric-pressure He discharges

Time- and space-resolved visible-emission spectroscopy measurements are applied to study plasma parameters in nanosecond electrical discharges in He gas at pressure of 10(5) Pa, using a 150 kV, 5 ns duration high-voltage pulse. The plasma evolution during the discharge is investigated by applying line-shape analysis of several He I spectral transitions, with the Stark and opacity effects accounted for. The analysis shows that the discharge plasma is not in equilibrium and that significant electric fields of several kV/cm are present in the plasma during the discharge. Regions of plasma with significantly different electron densities are identified and a qualitative model of the plasma formation and evolution is proposed.

Time-domain reflectometry of high-voltage nonlinear loads with picosecond resolution

The construction and characterization of a measuring module for high voltage time-domain reflectometry with picosecond resolution is presented. The device provides registration of low-distortion reflections from the load at conditions of irregular shape and pronounced instability of an incident probing pulse with amplitude of hundreds of kilovolts and a width/front up to ~2 ns. This is achieved with registration of differential reflecting signals by using two voltage probes, whose original signals are shifted in time and have a calibrated delay. Specially designed voltage dividers based on coaxial coupled lines with equalized dielectric constant of insulation meet the requirements of voltage probes identity. Reflectometry allows one to study dynamic changes of the loads for a specific time range of ~10(-10) s and faster. An example of reflectometry-based analysis for variations in breakdown development rate of atmospheric discharge gap supplied with the pulses of ~100-kV amplitude and a front slope of ~4 × 10(14) V/s is presented.