S. N. Rukin

Production of short microwave pulses with a peak power exceeding the driving electron beam power

This article presents results of theoretical and experimental studies on the production of ultrashort ~a few RF cycles duration! microwave pulses of gigawatt peak powers based on superradiance from high-current electron beams. With the Cherenkov backward-wave‐electron-beam interaction in a low-dispersion slow-wave structure, microwave pulses with a peak power greater than the peak power of the driving electron beam have been produced for the first time. In an experiment using the SINUS-150 compact high-current electron accelerator, with a 2.6-kA injected beam current and a 330-kV electron energy, microwave pulses of 1.2 GW peak power and;0.5 ns duration ~FWHM! were generated in the X-band. Production of superradiance pulses in a repetitive regime ~3500 Hz! in the Ka-band has been demonstrated using a compact hybrid SOS-modulator. The effect of spatial accumulation of microwave energy in extended slow-wave structures with substantially nonuniform coupling has been demonstrated. In an experiment using the SINUS-200 compact accelerator, X-band pulses of ;3 GW peak power and 0.6‐0.7 ns width~FWHM! were produced with a power conversion efficiency of 150‐180% and an energy efficiency of ;15%.

A NOVEL NANOSECOND SEMICONDUCTOR OPENING SWITCH FOR MEGAVOLT REPETITIVE PULSED POWER TECHNOLOGY: EXP

A novel nanosecond semiconductor opening switch (SOS) has been developed which has a pulsed power of the GW range and voltage levels of up to a few 100s of kV. The SOS is based on high-voltage solid state rectifiers and is designed for pulsed power generators with inductive energy storage. A 30 115 opening phase duration. a 45 k A interrupted current. and a 450 kV opened SOS voltage have been attained with the use of a three-stage, 2 kJ. 150 kV open circuit Marx generator as the SOS driver. On the basis of the experimental results obtained, we have developed and tested repetitive high-current generators and accelerators with a 0.5 MV output voltage and a 15 to 100 ns pulse width. The ideology is presented of constructing high-power megavolt pulsed generators with an all-solid-state switching system. A description is provided of the setups developed on this principle. We discuss features peculiar to the setups developed and prospects of developing these further .

Novel nanosecond semiconductor opening switch for megavolt repetitive pulsed power technology: experiment and applications

A novel nanosecond semiconductor opening switch (SOS) has been developed which has a pulsed power of the GW range and voltage levels of up to a few 100s of kV. The SOS is based on high-voltage solid state rectifiers and is designed for pulsed power generators with inductive energy storage. A 30 ns opening phase duration, a 45 kA interrupted current, and a 450 kV opened SOS voltage have been attained with the use of a three-stage, 2 kJ, 150 kV open circuit Marx generator as the SOS driver. On the basis of the experimental results obtained, we have developed and tested repetitive high-current generators and accelerators with a 0.5 MV output voltage and a 15 to 100 ns pulse width. The ideology is presented of constructing high-power megavolt pulsed generators with an all-solid- state switching system. A description is provided of the setups developed on this principle. We discuss features peculiar to the setups developed and prospects of developing these further.

Degradation and Recovery of the Emission From a Graphite Cathode in Relation to the Repetition Frequency of Nanosecond Accelerating Pulses

A study has been performed on the emissive characteristics of a cold graphite cathode in a magnetically insulated coaxial diode under the action of nanosecond accelerating pulses at a pulse repetition frequency (PRF) of up to 3.5 kHz. Emission was observed to degrade at PRF < 1 kHz and recover at PRF ~3.5 kHz. Estimates of the temperature conditions in the region of an explosive electron emission (EEE) center have shown that the pulse interval t~1 ms suffices for this region to cool down to 300 K. The cooling occurs predominantly by heat conduction. For t~0.3 ms, the residual heat is substantial. It has been proposed that there exists a frequency limit for the cathode microrelief polishing effect. The results of an experiment on the study of the mechanism of cathode emission recovery with increasing PRF are presented. Micrographs of the cathode taken after aging, photographs of the cathode in operation, and analyses of the fractional composition of the material removed from the cathode suggest that heating of some regions of the cathode emitting edge to the melting point of graphite plays an important role in the recovery of emission. This counts in favor of the hypothesized dominant contribution of thermoelectronic emission to the initiation of EEE due to the residual heat remaining in regions that have not cooled off during the pulse interval

Repetitive nanosecond all-solid-state pulsers based on SOS diodes

The paper describes design and technical specifications of nanosecond high-voltage pulsed generators that have an all-solid-state switching system. As a final power amplifier the semiconductor opening switch (SOS) and an inductive store are used. The devices present desktop hand-carried units that are capable of delivering to a load pulses with the following parameters: voltage 110 to 450 kV; current 0.4 to 1.5 kA; pulse width 20 to 40 ns; continuous pulse repetition rate 100 to 1000 pps; and burst mode up to 5000 pps.

Generation of gigawatt 10-GHz pulses with stable phase

The generation of microwave pulses in a 10-GHz range has been studied in a nonstationary relativistic backward wave oscillator (BWO) operating at a pulse train repetition rate of up to 300 Hz. Regimes with a stabilized phase of the high-frequency filling of pulses with respect to the accelerating voltage pulse front have been observed at a BWO peak output power of ∼1 and 3 GW. In pulse trains with a length of 10–100 s, the average output microwave power reached ∼1 kW.

High-power subnanosecond 38 GHz microwave pulses generated at a repetition rate of up to 3.5 kHz

An original relativistic backward tube (BWT) for a 38 GHz range is developed and tested. The BWT is capable of generating stable pulses of ∼250 ps duration and a peak power of ∼250 MW in trains with a length of up to 1 s at a repetition rate of 1–3.5 kHz. The BWT design implements an inhomogeneous slow-wave structure of increased cross section with a band reflector. A pulsed electron beam (∼270 keV, ∼2 kA, 0.9 ns) was injected by a high-current accelerator based on a high-voltage generator with an inductive energy store, a semiconductor current interrupter, and a pulse-shaping hydrogen-filled discharge gap. A focusing magnetic field of 2 T was generated by a cooled pulsed solenoid power-supplied from a special stabilized current source.

High peak power and high average power subnanosecond modulator operating at a repetition frequency of 3.5 kHz

This paper presents results of tests of a hybrid subnanosecond modulator with an output resistance of 45 /spl Omega/. The modulator comprises an all-solid-state nanosecond charger, which is equipped with an inductive energy store and a semiconductor opening switch, and a pulse peaker with hydrogen spark gaps. The modulator generates stable pulses-(180 to 200) kV in amplitude and 400 to 700 ps long at a pulse repetition rate of up to 3.5 kHz. An average output power of 1.5 kW was achieved under the pulse burst mode.

Semiconductor opening switch research at IEP

This paper describes the physical principles of operation of semiconductor opening switches (SOS). The SOS effect occurs at a current density of up to 60 kA/cm/sup 2/ in silicon p/sup +/-p-n-n/sup +/ structures filled with residual electron-hole plasma with the concentration between 10/sup 16/ and 10/sup 17/ cm/sup -3/. On the basis of a theoretical model developed for plasma dynamic calculation the mechanism by which the current passes through the structure at the stage of high conduction and the processes that occur at the stage of current interruption have been investigated. Dynamics of the electron-hole plasma were calculated with allowance for real distribution of impurity doping in the structures. Experimentally obtained current density-time, and current density-interruption time dependencies of semiconductor opening switches are discussed. Applications of the SOS effect in pulsed power is also be demonstrated.

Ultrafast current switching using the tunneling-assisted impact ionization front in a silicon semiconductor closing switch

Ultrafast current switching in semiconductors, based on the mechanism of tunneling-assisted impact ionization front, has been experimentally implemented and theoretically studied. A voltage pulse with an amplitude of 220 kV and a front duration of 1 ns was applied to a semiconductor device containing 20 serially connected silicon diode structures. After switching, 150-to 160-kV pulses with a power of 500 MW, a pulse duration of 1.4 ns, and a front duration of 200–250 ps were obtained in a 50-Ω transmission line. The maximum current and voltage buildup rates amounted to 10 kA/ns and 500 kV/ns, respectively, at a switched current density of 13 kA/cm2. The results of numerical simulation are presented, which show that the current switching is initiated at a threshold field strength of about 1 MV/cm in the vicinity of the p-n junction, where the tunneling-assisted impact ionization begins.