Alexander V. Gunin

Repetitively pulsed high-current accelerators with transformer charging of forming lines

This article describes the principles of operation and the parameters of the SINUS setups designed at the Institute of High-Current Electronics, Siberian Division, Russian Academy of Science, over the period from 1990 to 2002. A characteristic feature of accelerators of the SINUS type is the use of coaxial forming lines (in particular, with a spiral central conductor) which are charged by a built-in Tesla transformer to produce the accelerating high-voltage pulses. This ensures a reasonable compactness and long lifetime of the setups. The range of parameters of the SINUS setups is as follows: ○ Voltage amplitude at the cathode: 200-2000 kV ○ Electron beam current: 2-20 kA ○ Equivalent load impedance: 30-180 Ω ○ Accelerating pulse duration: 4-130 ns ○ Pulse repetition rate: up to 400 Hz ○ Pulse amplitude instability (RMS): 0.7-2.5% A number of setups of this type use a three-electrode controllable gas gap switch. This has made possible on-line electronic control (from pulse to pulse) of the output voltage pulse amplitude. The control band width δ = ΔU/U max was up to 75%. Studies have been performed on the lifetime of explosive-emission cathodes. At current densities of 25-30 A/cm 2 , a pulse duration of ∼20 ns, and a pulse repetition rate of 100 Hz, the metal-dielectric cathode in a planar geometry retained its emissivity within 10 8 pulses. The SINUS accelerators are traditionally employed for producing high-power microwave radiation in various systems with a coaxial electron beam in a longitudinal magnetic field. For this purpose, magnetic systems with a solenoid powered from the bank of molecular capacitors have been designed. The duration of a quasistationary magnetic field was 1 s at a maximum solenoid power of 365 kW. The possibility has been shown to exist for a self-contained power supply of the accelerator from the bank of molecular capacitors in the batch mode. With an average power consumption of about 120 kW, the setup produces pulses in a batch of duration 2.5 s at a pulse repetition rate of 200 Hz.

Repetitive sub-gigawatt rf source based on gyromagnetic nonlinear transmission line

We demonstrate a high power repetitive rf source using gyromagnetic nonlinear transmission line to produce rf oscillations. Saturated NiZn ferrites act as active nonlinear medium first sharpening the pumping high voltage nanosecond pulse and then radiating at central frequency of about 1 GHz: shock rise time excites gyromagnetic precession in ferrites forming damping rf oscillations. The optimal length of nonlinear transmission line was found to be of about 1 m. SINUS-200 high voltage driver with Tesla transformer incorporated into pulse forming line has been designed and fabricated to produce bursts of 1000 pulses with 200 Hz repetition rate. A band-pass filter and mode-converter have been designed to extract rf pulse from low-frequency component and to form TE(11) mode of circular waveguide with linear polarization. A wide-band horn antenna has been fabricated to form Gaussian distribution of radiation pattern. The peak value of electric field strength of a radiated pulse at the distance of 3.5 m away from antenna is measured to be 160 kV/m. The corresponding rf peak power of 260 MW was achieved.

Repetitive nanosecond high-voltage generator based on spiral forming line

This paper presents a nanosecond periodically-pulsed generator based on a spiral line charged by means of a high-coupling Tesla transformer. At repetition rate of 100 p.p.s., 130 ns, 500-700 kV pulses were produced in a 100-150 /spl Omega/ load.

Long-lived explosive-emission cathode for high-power microwave radiation generators

The operation of cold explosive-emission cathodes having a current density of ∼104 A/cm2, fabricated using various materials, was investigated under a large number of switching cycles. The cathode voltage was ∼500 kV, the maximum current ∼5 kA, and the pulse duration ∼20 ns. It is shown that when the number of switchings is small (⩽103 pulses), cathodes having similar geometry exhibit similar emission properties. For most of the materials studied, as the number of switching cycles increases (⩾103 pulses), the current rise time increases (as far as the pulse duration) and the maximum vacuum diode current decreases. When a graphite cathode was used, the maximum current remained unchanged up to 108 switching cycles. The mass removed from the cathode was determined for various materials. The results were used to achieve continuous operation of a relativistic 3 cm backward-wave tube having an output power of 350–400MW and an almost constant power level during 108 pulses at a repetition frequency of 100–150 Hz.

Effective transformation of the energy of high-voltage pulses into high-frequency oscillations using a saturated-ferrite-loaded transmission line

A new method of converting a high-voltage video pulse into high-frequency oscillations using a nonlinear transmission line with temporal dispersion has been studied. The dispersion was provided by pulsed magnetization reversal in a ferrite, which was initially magnetized to saturation in an external magnetic field. For a 9-ns pulse, an average energy conversion efficiency of about 10% was achieved. It is demonstrated that oscillations at frequencies within 600 MHz-1.1 GHz with a spectral width of about 15% (at a −3 dB level) can be excited using voltage pulses with an amplitude of 110–290 kV. The optimum bias magnetization fields are within 20–40 kA/m.

High power microwave beam steering based on gyromagnetic nonlinear transmission lines

We demonstrate electronically controlled beam steering by high power RF pulses produced by two gyromagnetic nonlinear transmission lines (NLTLs) connected to a one high voltage driver. Each NLTL is capable of producing several ns RF pulses with peak power from 50 to 700 MW (6% standard deviation) at frequencies from 0.5 to 1.7 GHz (1% standard deviation) with 100 Hz repetition rate. Using a helix antenna allows irradiating of RF pulses with almost circular polarization and 350 MW maximum peak power, which corresponds to 350 kV effective potential of radiation. At the installation of two identical channels, we demonstrate the possibility of beam steering within ±15° in the horizontal plane by coherent RF pulses with circular polarization at 1.0 GHz center frequency. Fourfold increase in the power flux density for in-phase irradiation of RF pulses is confirmed by comparison with one-channel operation.

X-Band Relativistic BWO-RR With Controlled Microwave Pulse Duration

The effective 1-s batch of 100-Hz pulse repetition rate mode of an X-band relativistic backward-wave oscillator with a resonance reflector (RBWO-RR) was realized using the “SINUS” pulse-periodic nanosecond accelerator allowing mechanically installed high voltage pulse length of 13 and 42 ns. Magnetic held about of 2 T was produced by two-section solenoid to transport the electron beam along RBWO-RR electrodynamic system. T M01 to T E11 mode converter connected to the oscillator output allowed Gaussian radiation pattern. The microwave oscillator allowed producing the microwave pulse length of 4.7 and 29 ns. The energy of the microwave pulse measured by the X-band aperture calorimeter was 1.4 or 6.3 J corresponding to the mentioned above microwave pulse length of 4.7 or 29 ns, respectively. That allowed estimations of the microwave peak power as high as 280 ± 30 MW and 210 ± 20 MW related to the pulse lengths. The efficiency of the oscillator was 23-25%. A possibility of the microwave pulse length fine tuning within 25 to 34 ns range in the “long pulse mode” by changing the solenoid magnetic held conhguration was shown.

Effective irradiation of high-power RF pulses from gyromagnetic nonlinear transmission lines

Summary form only given. Development of HPM sources based on gyromagnetic nonlinear transmission lines (NLTLs) includes the appropriate filtration of the high voltage video pulse and the irradiation antenna. We present experimental results of testing of band-pass filters designed for NLTLs. The influence of a band-pass filter bandwidth on the irradiated RF peak power is discussed. Two antenna systems have been developed to irradiate RF pulses with peak power up to 1.4 G W. To increase the directivity of the irradiation the 4 channel splitter into four 50 Ohm loads (antenna array) has been designed and tested. The coherent parallel excitation of several NLTLs is discovered to be possible due to the low jitter - about 5% of the period of oscillations. The possibility of the elongation of the RF pulses produced in the gyromagnetic NLTLs using coupled coaxial lines with spatial dispersion is discussed.

Operating features of a high-voltage spark gap switch with gas blow normal to the breakdown path in a repetitively pulsed mode

The results of studies of a high-voltage two-electrode spark gap switch (SGS) with forced gas blow at an operation voltage of up to 1.2 MV are presented. An SGS filled with nitrogen as the working gas at a pressure of up to 16 atm operated as the high-voltage switch of a high-current nanosecond electron accelerator. The gas flow was directed normally to the breakdown path. The SGS switched a 50-Ω forming line with an electrical length of 10 ns to a matched load. The voltage rise time across the electrodes before breakdown was ∼25µs. A stable repetitively pulsed mode is realized at operating voltages of 100–680 kV and pulse repetition rates of up to 270 Hz with a standard deviation of the pulse breakdown voltage of ≤1%. The physical mechanisms that determine unstable operation of the device during self-breakdown are analyzed.

A Nanosecond High-Voltage Periodically Pulsed Generator Based on a Helix Forming Line

A nanosecond high-voltage periodically pulsed generator based on a helix forming line is described. The line is charged from a high-coupling Tesla transformer. Compared with a conventional coaxial line, the helix line provides a fourfold increase in the generator impedance and pulse width without a significant increase in the generator dimensions, with the energy stored remaining the same.