Generation of High-Voltage Subnanosecond Pulses with a Peak Power of 700 MW and Repetition Frequency of Up to 3.5 kHz

Test results of a combined subnanosecond modulator with an output impedance of 45 , which incorporates an all-solid-state high-voltage nanosecond charging device (with an inductive energy storage and a semiconductor opening switch) and a pulse sharpener with gas-filled gaps, are presented. The sharpening and cutting spark gaps filled with hydrogen at a pressure of 100 atm ensured the formation of stable pulses with amplitudes of –(180–200) kV and durations of (400–700) ps at a repetition frequency of up to 3.5 kHz. An average output power of 1.4 kW was achieved for the modulator's burst-mode operation with a number of pulses in a packet of 10⁴at a maximum pulse repetition rate.     

A Source of Reference Light Pulses for Stabilization of the Energy Scale of Fast Multichannel Scintillation Detectors

Energy-scale monitoring systems for scintillation detectors with various sources of standard light pulses are considered. A LED-based light-pulse generator with active quenching of afterglow, which can reduce the light-pulse duration by half, is described. The number of photons per pulse may amount to 10⁹or more, the pulse duration being 10 ns. A long-term (a few weeks) instability of the light-flash intensity is ± 0.1%.     

A Subnanosecond Voltage Divider on Coupled Lines

The divider consists of two electrically and magnetically coupled coaxial lines inserted one into the other and having a single common outer conductor. One is an oil-filled line transmitting the main high-voltage pulse, and the other is a low-impedance measuring line, whose input is connected through a cable to the input of an oscilloscope. The experiment has confirmed the calculated division factor of 300 and a reproduction of the shape of the recorded pulse by the divider without distortions. The divider was used for recording bipolar pulses with ±120-kV amplitudes, a duration of 0.8 ns, and a rise time of 0.2 ns.     

High-Voltage Spark Gaps for Technological Purposes

High-power untriggered spark gaps intended for operation at a voltage of up to 150 kV and a current of 10 kA have a service life of up to 10¹¹pulses. The spark gaps ensure switching to a load for 5–20 ns with a pulse repetition rate of up to 400 Hz. They operate under atmospheric pressure without blowing-through in an installation for decontaminating processing of products with high-voltage pulses.     

A Facility with Resonant Pulse Compression for Generating High-Power Ku-Band Microwave Pulses

A generator of high-power Ku-band microwave pulses with resonant pulse compression is described. It allows thestepped control of output-pulse durations from 1 ns to 1.5 s at a pulse repetition rate of 0.2–1.5 kHz and a peak power of 58 kW to 10 MW. This source can be used for investigating the interaction of electromagnetic radiation with various objects.     

Method for increasing quality of the cathode surface of a vacuum gap

A method for controlled processing of the cathode surface in vacuum has been developed. The control is effected in a steady-state regime by monitoring the amplification factor of the electric-field strength at cathode microinhomogeneities. High-voltage pulses of nanosecond durations with amplitudes ensuring a breakdown delay time equal to the duration of the applied pulse, t_d = t_p, are used to affect the surface. This method allows the surface quality to be substantially improved after application of a minimum number of pulses. The application of five pulses at t_p = 10 ns with amplitudes ensuring the condition t_d = t_p to stainless-steel electrodes results in a decrease in the field-amplification factor by a factor exceeding 5 (from 136 to 26) and in an increase in the emission area by more than four orders of magnitude (from 4.6 × 10^?19 to 10^?14 m²).     

A Multichannel Automatized System for Measuring Current Pulses in the LIA-30 Electron Accelerator

In the LIA-30 high-power linear pulsed induction electron accelerator (40 MeV, 100 kA, 25 ns), the energy is stored, and pulses of the accelerating voltage are shaped by 288 water-insulated radial lines arranged in succession along a common air-free acceleration channel. The lines are simultaneously charged up to 500 kV from 72 shielded Marx generators. To measure the parameters (amplitude, pulse shape, pulse rise time, pulse fall time, and pulse duration) of the synchronized pulses of the charging current with amplitudes as high as 60 kA and duration of 0.85 s in each of the 72 charging circuits, an automatized measuring system is used. The current pulse is sensed at the output of each generator by a self-integrating Rogovsky coil galvanically isolated from the generator. The signal from the coil is transmitted over a cable to an analog-to-digital converter, sampled with a period of 50 ns, and recorded in memory. Upon operating the accelerator, the signals are reproduced in succession or selectively on the display screen, and their shapes are compared to the shape of a standard pulse.     

Formation of High-Power Pulses of Nanosecond Duration by Generators on Reverse Switch-on Dynistors with Sharpening Circuits Based on Diode Opening Switches

The basic principles of constructing generators of nanosecond pulses on reverse switch-on dynistors with sharpening output circuits based on diode opening switches are considered. The results of an experimental study of a high-power generator incorporating such a dynistor; a step-up pulse transformer; and a high-voltage diode opening switch, which is an assembly of drift step-recovery diodes connected in series, are presented. The output voltage pulses of the generator with an amplitude of 45 kV, a duration of 50 ns, a rise time of 10 ns, and a repetition rate of 1 kHz are applied to a load resistance of 25 .     

A General-Purpose Discharge Module for Pumping Solid-State Lasers

A module for pumping solid-state lasers makes it possible to form rectangular pulses which are independently adjustable in amplitude (75–300 A), duration (50–500 s), and repetition rate (up to 60 Hz). The module has small overall dimensions, and its efficiency exceeds >98 %; it uses a comparatively low voltage (400–800 V); and its pulse energy can be increased up to 1000 J and more.     

Formation of Short Pulses with a Subnanosecond Rise Time and a Peak Power of Up to 1 GW by a Semiconductor Avalanche Sharpener

The results of experiments on the formation of high-power pulses with a rise time of <1 ns and a duration of 1–2 ns by a solid-state semiconductor sharpener operating in the mode of delayed impact ionization wave are presented. A peak power of 1 GW in a single-pulse operation mode and 750 MW at a pulse repetition rate of 3.5 kHz was obtained across a 50- load. Experiments on the pulse transformation using a forming line with a variable wave impedance and generation of bipolar voltage pulses are described.     

A method for measuring spectral and time characteristics of mixed pulsed gamma-neutron fields with scintillation and Cherenkov detectors with nanosecond time resolution

A method for measuring spectral and time characteristics of pulsed mixed (n, γ) fields is described. The essence of this method is that a sequence of signals from individual (n, γ) particles registered by (n, γ) detectors is written in a computer with the subsequent amplitude-time analysis of the signal parameters. Fast scintillation and Cherenkov detectors with FWHM of pulses of ～1.5 and 2.5 ns, respectively, are used as (n, γ) detectors. A TDS-3054 broadband digital oscilloscope records signals and transmits them to the computer through a GPIB-USB interface. The equipment used ensures efficient detection of (n, γ) particles at detector counting rates of up to ～2 × 10⁸ pulses/s. The efficiency of this method has been tested in measurements of characteristics of (n, γ) radiation fields from an ИНГ-031 pulsed neutron generator and from a copper target irradiated with a beam of carbon nuclei with an energy of 200 MeV/amu from the TVN-ITEF acceleration-storage complex.     

Modernization of the Duoplasmatron of the И-2 Linear Accelerator

A modified ion source of the duoplasmatron type used in the -2 linear accelerator for generating a proton beam is described. Improving the designs of the electrodes, the magnetic circuit, the gas-supply channel, and the electromagnetic valve has made it possible to considerably increase the service life of the source (up to 10⁷ pulses), to reduce the consumption of hydrogen (up to 10 cm³/h at a pulse repetition rate of 1 Hz), and to increase the stability and reliability of the source operation in the regime of everyday service of the linear accelerator in applied research as an injector of the ITEP U-10 proton synchrotron.     

Multichannel Spark Gaps with Control Bar Electrodes: Their Development and Application (A Review)

Multichannel low-inductance (1 nH) gas-filled spark gaps (MSGs)¹ with several tens of channels each, bar control electrodes designed for an operating voltage of 100 kV, and a switched current of up to 400 kA are reviewed. The control electrodes, made in the form of narrow thin plates, have an intermediate potential, are positioned in the gap between two common main electrodes (high-voltage and low-voltage (grounded)), and are oriented uniformly along their length. Upon a near-simultaneous change in the bars' potential in a time of <15 ns, applying a signal through trigger circuits disturbs the electric-field distribution in the gas volume. The field strength sharply increases at the electrode surfaces and especially at the edges of the bars, from which breakdowns develop synchronously from one electrode to another or simultaneously to both main electrodes. When the discharge formation is completed, the main electrodes of the MSGs are short-circuited by discharges through parallel channels (whose number is equal to the number of bars). These switches ensure the nanosecond accuracy of the operation delay relative to the trigger pulse at a breakdown-strength margin of up to 100%, determined by the pressure (>0.1 MPa) of the MSG-filling gas. Electrical circuits for initiating the discharge development in the MSGs, the transients in such circuits, and the factors affecting the parameters of processes and the gap-breakdown delay and rate are considered. Particular MSG designs, multicable systems for parallel triggering of a large number of MSGs, and the use of 48 four-channel 50-kV MSGs in the first iron-free LIA-2 linear electron accelerator (2 MeV, 25 kA, and 60 ns) created in 1967 are described. The successful operation of MSGs stimulated further studies and the development of efficient trigatrons for operating voltages of 100 and 500 kV. Up to 3000 MSGs of this type are used in new high-power linear electron accelerators. A low-impedance (0.45 ) generator of high-voltage pulses (50–200 kV) with a multicable output has been developed to synchronously trigger such large numbers of trigatrons as these.     

A Triggered Gas-Filled Metal–Ceramic Spark Gap with a High Current Rise Rate and Stable Operation

A triggered gas-filled three-electrode metal–ceramic -01 spark gap with a field distortion is described. This device is intended for use as a nanosecond switch. Spark gaps operating within voltage ranges of 15–30 and 30–60 kV have been developed, manufactured, and tested. The operation delay with respect to the trigger pulse is 60 × 10 ns. Life tests at a pulse repetition rate of 1.1 Hz have shown that the parameters of spark gaps do not deteriorate after the total number of operations of up to 3 × 10⁶, which corresponds to a total charge of 4.5 × 10⁴ C. The probability of a breakdown during life tests was 10^–4. A batch of 20 spark gaps has been manufactured for the operation in a pulse voltage generator for supplying the discharge in a large-volume pulsed CO₂ laser. The test results confirm the stability of the parameters of the devices in the batch.     

A facility for metal surface treatment with an electron beam

A design for a facility for the surface treatment of metal samples is described, and the results from investigating the source of a high-current low-energy electron beam are presented. The electron beam, which has a current as high as 300 A, a pulse duration of 30 µs, and a pulse repetition rate of up to 10 Hz, is formed in a plasma-cathode gas-filled diode at an accelerating voltage of 20 kV. The space-charge compensated electron beam is transported a distance of 20 cm in a longitudinal magnetic field to the region of its interaction with a solid body. At a current density as high as 100 A/cm², the power density produced by the beam is sufficient for the metal surface to be melted in the duration of one or several pulses. Samples can be replaced in the facility without breaking the vacuum.Translated from Pribory i Tekhnika Eksperimenta, No. 1, 2005, pp. 135–140.Original Russian Text Copyright © 2004 by Koval, Shchanin, Devyatkov, Tolkachev, Vintizenko.     

An Optical-Fiber Setup for Inert Particle Concentration Measurements

An optical-fiber setup employing laser light designed to measure concentrations of 50-to 500-m particles moving with a speed of up to 10 m/s is described. The time resolution, the measurement time, and the counting of pulses reflected from the particles are programmed. The setup has the following basic parameters: time resolution is 10 s, spatial resolution is 50 m, sample size is up to 32 × 10³, and particle counting error is within 1%. The setup was applied to measurement of the solid-phase concentration in a two-phase flow in a volum concentration range of up to 30%.     

A 128-Channel Simultaneously Sampling Data Acquisition System for the Diagnostic Complex of Experimental Plasma Facilities

The simultaneously sampling data acquisition system contains 16 eight-channel modules, which record the shapes of single pulse signals, and the controller module of the system bus of the Eurocrate, which interacts with the basic computer of the diagnostic complex via an Ethernet-FX communication line supported by TCP/IP protocols. The recording modules are based on 12-bit analog-to-digital converters (ADC). The ADC samples are fixed in buffer storage units with a capacity of up to 1 Mword/channel. The current amplitudes of the input signals are measured simultaneously in all recording channels with a time jitter of 3 ns. The maximum sampling frequency is below 4 MHz.     

Efficiency of Pulsed Regimes for Enhancing the Breakdown Strength of Vacuum Insulation

Processing the experimental data on breakdown delay time in a vacuum was used to obtain the function K (t _p) of the relative change in the field gain factor at microscopic inhomogeneities of the cathode surface resulting from the realization of optimum pulse conditioning regimes. It is shown that over the range of pulse durations 10^–8 t _p 10^–6 s, the relative change in the state of the cathode surface corresponds to the relative changes in the breakdown strength of all-metal electrodes and to the voltage of the appearance of local flashes in a system of evaporated electrodes—a microchannel plate and the screen of an image intensifier. Applying optimum regimes for conditioning the surface with pulses of durations t _p < 10^–8 s makes it possible to achieve the limiting breakdown strength determined by the cathode mechanism of breakdown initiation.     

A Low-Voltage Spark Pulse Sharpener

A spark air pulse sharpener that generates 0.2- to 1.8-kV pulses is described. The sharpener operates stably at a primary-pulse amplitude of above 1 kV and at a 1- to 2.5-kHz pulse repetition rate. An attenuator with a set of replaceable resistors, which also corrects the leading edge, is used to produce pulses with a smaller amplitude. The pulses with a rise time of about 0.3-ns and a top unevenness of 5–7% are derived from the primary pulses with an 3- to 4-ns rise time. The instability of the instant of the spark-gap breakdown is 0.1 ns, and the amplitude instability is no higher than 1%.     

A Switch Based on Reverse Switch-on Dynistors with a Diode Sharpener of Switched Current Pulses

A principle of constructing a combined semiconductor switch based on a diode assembly and an assembly of reverse switch-on dynistors (RSDs) is considered. The diode assembly serves as a sharpener of current pulses switched by the RSD assembly. The results of tests of a combined switch, which forms 3.5-kV voltage pulses with a duration of 1 s and a rise time of 10 ns at a load of 10 , are presented. Ways of enhancing the switching capabilities of RSD switches with diode sharpeners are presented.