A. A. Zherlitsyn

Decimeter-band frequency-tunable sources of high-power microwave pulses

This article describes S-band sources of high-power microwave (HPM) pulses: a resonant backward wave oscillator (BWO) producing ∼5-GW, 100-J pulses, based on the SINUS-7 electron accelerator, and a double-section vircator with a peak power of ∼1 GW and a pulse width of 20-50 ns, powered from either the SINUS-7 accelerator or the MARINA inductive-store pulse driver with a fuse opening switch.

S-band vircator with electron beam premodulation based on compact pulse driver with inductive energy storage

This paper describes an S-band vircator system with electron beam premodulation, built on the base of the MARINA compact high-voltage pulser with inductive energy storage. The peak microwave output was /spl sim/1 GW with /spl sim/5% power efficiency and 50-ns full-width at half-maximum. The microwave frequency was constant during the pulse as determined by the resonator. Substantial spontaneous shortening of the microwave pulse was observed. Possible mechanisms for this phenomenon are discussed and supported by three-dimensional KARAT simulations.

S-Band Coaxial Vircator With Electron Beam Premodulation Based on Compact Linear Transformer Driver

A two-section coaxial vircator with radial electron beam injection and electrodynamic feedback was developed. The use of electron beam premodulation in the vircator allows an increase in efficiency and ensures single-mode oscillation. The vircator operates with no external magnetic field, features a comparatively low operating impedance of the vacuum diode (10-15 Ω), and makes feasible wide-band frequency tuning through varying the resonator parameters. The vircator was simulated using the PIC-code KARAT. It is shown that, in a wide range of electron beam power (10-25 GW), the oscillation efficiency is 12%-15% and the frequency tuning bandwidth is 15 %. In the experiments on a compact linear transformer driver at a cathode voltage of 300 kV, diode current of 20 kA, and driving pulse duration of 250 ns, the single H11 mode oscillation at 2.2 GHz with a 300-MW microwave peak power and 130-ns pulse duration at half the power level was realized.

Capacitor units with air insulation for linear transformers

The design of two capacitor units intended for use in high-power pulsed generators is described and the results of their tests are presented. Each unit is an assembly consisting of a multichannel spark gap and two capacitors with a total capacitance of 80 or 16 nF and a charging voltage of up to 100 kV. The use of air at atmospheric pressure as the insulating and working medium of the spark gap is a feature of the capacitor units. The following parameters of the output pulses were obtained at a resistive load for the 80- and 16-nF units: currents of ∼48 and ∼20 kA, voltages of ∼55 and ∼52 kV, and times of energy deposition into the load of ∼140 and ∼60 ns, respectively. A model for numerical calculation of the transient discharge process in the capacitor units is presented and the influence of the capacitance of the capacitors and the number of spark channels in the spark gap on the parameters of the generated pulse is analyzed.

Capacitor blocks for linear transformer driver stages.

In the Linear Transformer Driver (LTD) technology, the low inductance energy storage components and switches are directly incorporated into the individual cavities (named stages) to generate a fast output voltage pulse, which is added along a vacuum coaxial line like in an inductive voltage adder. LTD stages with air insulation were recently developed, where air is used both as insulation in a primary side of the stages and as working gas in the LTD spark gap switches. A custom designed unit, referred to as a capacitor block, was developed for use as a main structural element of the transformer stages. The capacitor block incorporates two capacitors GA 35426 (40 nF, 100 kV) and multichannel multigap gas switch. Several modifications of the capacitor blocks were developed and tested on the life time and self breakdown probability. Blocks were tested both as separate units and in an assembly of capacitive module, consisting of five capacitor blocks. This paper presents detailed design of capacitor blocks, description of operation regimes, numerical simulation of electric field in the switches, and test results.

A Vacuum Feedthrough Insulator at a Voltage of ∼1 MV

The design and results of tests of a vacuum feedthrough insulator for a pulsed electron accelerator with a voltage of ∼1 MV, a current of ∼20 kA, and a half-height voltage-pulse duration of ≥ 400 ns are presented. A method for distributing the voltage over the sections of the insulator due to an electron emission from specially created surfaces is proposed.

Analysis of propagation of a high-current electron beam from a sectioned plasma-filled diode

We report on the results of analysis of propagation of an electron beam from a plasma-filled diode in the absence of the metal anode between the regions of beam generation and transportation. The diode parameters are 160 kA, 400 kV, and 50 GW. At a distance exceeding 10 cm behind the generation region, a beam current of 100 kA to the target and an energy density of 20 J/cm2 are attained for the beam cross-sectional area of about 200 cm2. The possibility of varying the beam current and energy density by changing the distance to the target is demonstrated.

Plasma-filled diode based on the coaxial gun

The paper presents the results of studies of a coaxial gun for a plasma-filled electron diode. Effects of the discharge channel diameter and gun current on characteristics of the plasma and pulse generated in the diode were investigated. The electron beam with maximum energy of ≥1 MeV at the current of ≈100 kA was obtained in the experiments with a plasma-filled diode. The energy of ≈5 kJ with the peak power of ≥100 GW dissipated in the diode.

Application of a cylindrical diode as a load with vacuum insulation in high-voltage generators

Results of experimental tests of the possibility of using cylindrical diodes in the self-magnetic insulation mode as an equivalent load with a stable impedance of about units of ohms at voltages below 450 kV are given. The diode with a radial size of ∼10 cm and an interelectrode gap of ∼1.5 cm demonstrated a stable resistance of ∼3 Ω within ∼200 ns. The analyzed results show that the current of the self-magnetic insulation in the diode is determined by the limiting current.

Power Increase of the Electron Source Based on the Plasma-Filled Diode

The technique of a linear transformer driver (LTD) now allows building the generators of high-power nanosecond pulses with the current rise time of ~100 ns without intermediate power compression stages. This technique is being examined for use in high-current high-voltage electron sources based on plasma-filled diodes. The power of a plasma-filled diode is determined by the driving circuit parameters and the transition diode resistance. The problem of power rise can be solved by increasing the stored energy in the circuit inductance provided that the diode resistance rise rate is constant. In experiments on the LTD (53 nF, 480 kV), the possibility has been checked out for such increase in the stored energy. A current increase from 50 to 180 kA was obtained by increasing the current rise rate from 0.4 to 1.9 kA/ns. Stored energy has been increased, respectively, from 0.2 to 3.6 kJ. The time of energy transfer into the circuit inductance was about 120-140 ns. Maintaining the diode resistance rise rate at 0.5 Q/ns has been shown. Diode power has been increased up to 170 GW. Further increase in power of the plasma-filled diode has been obtained using simulation circuit of the Megavolt (MV) range LTD. To simulate such a linear transformer, the driver circuit was made as Marx generator with coaxial water line (5.3 Ω, 56 ns, and 1.5 MV), providing a current input of 160 kA into the 550-nil inductance in 120 ns. Stored energy in the inductance was about 7 kJ. The following diode parameters were obtained: 150 kA, 1.9 MV, and 250 GW at a resistance rise rate more than 0.5 Q/ns. The experiments prove that the resistance rise rate of the plasma-filled diode is constant on increasing the stored energy in the inductance up to 7 kJ. It allows scaling the power of an electron source based on the plasma-filled diode.