Aleksei S. Stepchenko

Relativistic X-band BWO with 3-GW output power

Results from a study of a relativistic X-band backward-wave oscillator (RBWO) with 3-GW output microwave power are presented. The RBWO was driven by the high-current electron accelerator SINUS-7. The dependence of radiated microwave pulse duration on microwave power was obtained. Pulse shortening occurring at the higher power levels is probably attributable to explosive electron emission from the slow wave structure (SWS). An increase in the cross section of the electrodynamic structure seems to be a way to increase the microwave pulse duration. Experimental results from a moderately oversized X-band RBWO using a resonance reflector are described. This tube can be operated with a low external magnetic field.

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.

Compact 1000 pps high-voltage nanosecond pulse generator

A compact high-voltage nanosecond generator is described with pulse repetition rate of up to 1000 pps. The generator includes a 30-/spl Omega/ coaxial forming line charged by a built-in Tesla transformer with high coupling coefficient, and a high voltage (N/sub 2/) gas gap switch with gas circulating between the electrodes. The maximum forming line charge voltage is 450 kV, the pulse duration is /spl sim/4 ns, and its amplitude for a matched load is up to 200 kV. The generator has been applied to create powerful sources of ultrawide-band electromagnetic radiation and nanosecond microwave pulses.

A high-power periodic nanosecond pulse source of coherent 8-cm electromagnetic radiation

The generation of short electromagnetic pulses excited in an extended slow-wave system (SWS) of a relativistic backward wave tube (BWT) operating in the so-called superradiance regime with a carrier frequency of 3.7 GHz has been simulated and experimentally studied. At a decreased magnetic field (about 0.2 T) in the SWS, the BWT generated 2.5-ns microwave pulses with a power of up to 800 MW. At a pulse repetition rate of 100 Hz, the working life of the system was limited by the lifetime of an explosive emission cathode (106 pulses). The possibility of phase synchronization of the high-frequency field of the relativistic microwave oscillator with respect to the voltage pulse front is demonstrated for the first time.

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.

Periodically pulsed high voltage generator based on Tesla transformer and spiral forming line

Summary form only given, as follows. Well known are nanosecond HV periodically pulsed generators based on high-coupling Tesla transformers and long coaxial forming lines with oil insulation. Combining Tesla transformer with long forming line allowed substantial increase in its charging efficiency and resulted in production of relatively compact HV generators and high-current electron accelerators with the average power in the range of several hundreds kilowatts. These accelerators are widely applied for HPM pulse production at high pulse repetition rates. Increasing the pulse width of the HV generators requires using longer forming lines. In the case of relatively high-ohmic loads, the problem may be used, alternatively, by utilizing spiral forming lines. This allows an increase in the generator impedance and pulse width, keeping the same stored energy, and with no substantial increase in the generator size. 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., 100-ns, 600-kV pulses were produced in a /spl sim/100-Ohm load.

Stable pulse-periodic source of GW-level nanosecond microwave pulses

Recent studies of the generation of GW-level nanosecond microwave pulses in extended BWO-type slow-wave structures have been showed an opportunity for stabilization of the RF field phase. Decline in the dependence of the output microwave power on the electron energy in this operation mode allows reaching radiation peak power spread not exceeding voltage variation on a vacuum diode. Superradiative microwave generators can produce high peak power with moderate beam energy and have good efficiency. This paper discusses the possible application of such systems.

650-kJ power supply for one-second highly-stable magnetic field source

Summary form only given, as follows. Producing HPM emission at high pulse repetition rates requires strong magnetic fields, which commonly employs superconductive systems. Realizing batch high rep-rate regimes allows utilization of quasi steady-state magnetic fields using capacitive energy stores. Molecular capacitors storing as much as /spl sim/3.8 J/cm/sup 3/ are most suitable for this purpose. The paper presents a fully controllable power source for a one-second solenoid storing 650 kJ. The store consists of 12 molecular capacitors connected serially in four stages. The total store capacity is 3.45 F and its output voltage is 600 V. The bank charge is made by four independent 10-A DC sources and it takes less than four minutes. When forming the magnetic field pulse, the solenoid is switched onto the energy store via a pulsed stabilizer of a current based on isolated gate bipolar transistors (IGBTs). Controlling the transistors from a PWM-controller with solenoid current feedback allows a decrease in the magnetic field less than 5% while the capacitor bank voltage drops from 600 to 300 V. The maximum current of the solenoid is 1.2 kA. Thus, using the pulsed current stabilizer allows useful consumption of up to 75% of the capacitor bank stored energy.

A power supply for one-second source of highly-stable magnetic field

Generation of high-power microwave (HPM) pulses at high pulse rates requires strong magnetic fields, which are commonly produced in superconductive cryomagnets. Batch operation of HPM sources allows the use of quasi-stable magnetic field produced in a solenoid powered from a bank of capacitors. Modern capacitors (such as molecular ones) possess energy storing density /spl sim/3.8 J/cm/sup 3/. This paper presents a fully controlled power source for a one-second solenoid. The energy store consists of 32 molecular capacitors connected in series in four stages. The total capacity of the store is 9.2 F, the output voltage is 600 V, and the stored energy is 1.6 MJ. The capacitive store is charged from four independent 20-Ampere DC sources. The charging takes less than 5 min. To produce the magnetic field, the solenoid is switched onto the capacitive store via switching current regulator assembled from isolated-gate bipolar transistors (IGBTs). Controlling the transistor switch with PWM-controller allows a decrease in the solenoid current less than 5% while the voltage across the capacitive store drops from 600 to 300 V. The solenoid maximum current is 1.2 kA.