Формирование двух импульсов тока пучка убегающих электронов

The conditions for the formation of two current pulses of runaway electron beams during the breakdown of a point-to-plane and tube-to-plane gaps in high-pressure air, nitrogen, and helium are studied. It has been shown experimentally that, depending on a pressure and kind of gas, a rise time of voltage pulse with an amplitude of tens of kilovolts, three modes of generation of runaway electron beams are observed. In the first mode, a single current pulse of runaway electron beam is observed at the maximum voltage across the gap, when a streamer appears in the vicinity of the pointed electrode (cathode). Its duration is ≈100 ps. In the second mode, two current pulses of runaway electron beams are observed at a lower pressure. The first pulse is generated as in the first mode. The second pulse is generated after the gap is bridged by the streamer (the first ionization wave). The electron energy in the second pulse is significantly less than in the first one, but the duration and amplitude of second current pulse under optimal conditions are greater. The third mode is implemented at lower pressures than in the second one. The generation of runaway electrons continues after the first pulse without a pause in the quasi-stationary stage. The total current pulse duration is hundreds of picoseconds.

Energy Model of Neuron Activation

On the basis of the neurophysiological strength-duration (amplitude-duration) curve of neuron activation (which relates the threshold amplitude of a rectangular current pulse of neuron activation to the pulse duration), as well as with the use of activation energy constraint (the threshold curve corresponds to the energy threshold of neuron activation by a rectangular current pulse), an energy model of neuron activation by a single current pulse has been constructed. The constructed model of activation, which determines its spectral properties, is a bandpass filter. Under the condition of minimum-phase feature of the neuron activation model, on the basis of Hilbert transform, the possibilities of phase-frequency response calculation from its amplitude-frequency response have been considered. Approximation to the amplitude-frequency response by the response of the Butterworth filter of the first order, as well as obtaining the pulse response corresponding to this approximation, give us the possibility of analyzing the efficiency of activating current pulses of various shapes, including analysis in accordance with the energy constraint.

Silicon Carbide Junction Transistors and Schottky Rectifiers optimized for 250°C operation

ABSTRACTElectrical performance and reliability of SiC Junction Transistors (SJTs) and Schottky rectifiers are presented. The 650 V/50 A-rated SiC SJTs feature current gains (β) up to 110 at room-temperature, 70 at 250°C, and stable breakdown characteristics. Single current pulse measurements indicate an almost invariant β up to 800 A/cm2 at 175°C – a measure of the SOA boundary for pulsed current SJT operation. Lower than 5 mA/cm2 leakage currents are measured on the SJTs at the rated blocking voltage and at 250°C. 1200 V Schottky rectifiers designed for high-temperature operation display < 3 mA/cm2 leakage currents up to 250°C. A 10x reduction in leakage current and 23% reduction in junction capacitance are observed when compared to the nearest competitor. The high-temperature Schottky rectifiers and SJTs display stable breakdown voltages and on-state characteristics after long-term HTRB stressing. A significant improvement in current gain stability is achieved by fine-tuning the fabrication process.