Sub-nanosecond High Voltage Pulses Research Articles

Development of a High-Power Burst Pulse Generator Based on the Sequential Operation of Magnetic Switches

Nanosecond and subnanosecond high-voltage pulses have used in new biological applications, such as cancer treatment using an ultrashort pulsed high electric field. For this treatment, the use of high-power pulsed electromagnetic wave has been proposed to obtain the required high electric field. This paper focuses on the design of a compact high-power pulsed electromagnetic wave generator using a nanosecond pulsed power generator for cancer treatment. We developed a pulsed power generator that continuously outputs multiple pulses via a nonlinear transmission line (NLTL) using magnetic switches. The NLTL comprises a ladder of capacitors and saturable inductors. The NLTL generates a pulse train by delaying the propagation of the pulse using the magnetic switch of each ladder. The frequency of repetition of the burst pulse is 13.8 MHz. The peak output voltage is 7 kV at the maximum input voltage of 28 kV. The number of pulses in the pulse train can be varied by the number of units of the magnetic switch.

Experimental Observation of Delayed Impact-Ionization Avalanche Breakdown in Semiconductor Structures without p–n Junctions

We have experimentally studied the dynamics of impact-ionization switching in semiconductor structures without p–n junctions when subnanosecond high-voltage pulses are applied. Silicon n+–n–n+ type structures and volume ZnSe samples with planar ohmic contacts exhibit reversible avalanche switching to the conducting state within about 200 ps, which resembles the well-known phenomenon of delayed avalanche breakdown in reverse-biased p+–n–n+ diode structures. Experimental data are compared to the results of numerical simulations.

Экспериментальное наблюдение задержанного ударно-ионизационного пробоя полупроводниковых структур без p-n-переходов

AbstractWe have experimentally studied the dynamics of impact-ionization switching in semiconductor structures without p – n junctions when subnanosecond high-voltage pulses are applied. Silicon n ^+– n – n ^+ type structures and volume ZnSe samples with planar ohmic contacts exhibit reversible avalanche switching to the conducting state within about 200 ps, which resembles the well-known phenomenon of delayed avalanche breakdown in reverse-biased p ^+– n – n ^+ diode structures. Experimental data are compared to the results of numerical simulations.

The Driving Conditions for Obtaining Subnanosecond High-Voltage Pulses From a Silicon-Avalanche-Shaper Diode

Silicon-avalanche-shaper (SAS) diodes are fast-closing switches capable of producing high-voltage pulses with a rise time of ~100 ps. The SAS can be driven by a positive, nanosecond scale, high-voltage pulse applied to its cathode where the magnitude of the driving pulse is correlated to the magnitude of the pulse at the SAS anode (output). Drift-step-recovery diodes (DSRDs) are fast-opening switches capable of producing high-voltage pulses with a rise time of the order of 1 ns. Thus, DSRDs are good candidates for driving SAS diodes. In this paper, the SAS output is studied with respect to its driving conditions. First, the SAS output is examined with respect to the magnitude and rise time of the driving pulse, utilizing three DSRDs to produce pulses with various rise times from 0.5 to 5 ns. In addition, the effect of the driving pulse repetition frequency (PRF) on the SAS output is studied. An experimental demonstration using a 1.5-kV SAS fabricated at the Ioffe Physical Technical Institute shows the advantage of driving the SAS with the short, 0.5 ns, pulses, and the degradation of performance due to high PRF, up to 10 MHz.

Radiation from a semiconductor target excited by an electron beam in a gas diode

Radiation from a semiconductor target excited by an electron beam in a gas-filled diode was investigated at different gas (air) pressures. Subnanosecond high-voltage pulses (up to 200 kV) were applied to the pointed cathode of the diode. The targets in the form of a 15 — 20-μm-thick single-crystal CdS film with reflecting coatings forming an optical cavity and 0.7 — 1-mm-thick ZnSe plates were used. As the air pressure increased from 0.1 to 5 Torr, a decrease in the amplitude and duration of laser radiation pulses from the targets was observed. Lasing (λ = 520 nm) of CdS targets terminated at pressures greater than 2.2 Torr. The laser pulse duration varied from 125 to 20 ps. The study of the dynamics of radiation from ZnSe targets (λ = 460 nm) at atmospheric pressure showed that when the gap between the target and the electrodes was 0.2 — 1 mm thick, an intense near-surface glow was observed that consisted of a few pulses with the duration from 20 to 100 ps, caused by runaway electrons. Investigations showed that the runaway electrons may play an essential role in the excitation of semiconductors by subnanosecond high-voltage pulses.

亚纳秒脉冲高电压测量探头

亚纳秒脉冲高电压测量探头

Intensity of electric field radiating from high-power pulsed electromagnetic wave generator for use in biological applications

Cancer treatment is one of several new applications which use nanosecond and subnanosecond high-voltage pulses. This study focuses on the design of a compact highpower pulsed electromagnetic wave generator using a nanosecond pulsed power generator to apply a high-intensity electric field for the treatment of cancer; the pulses cause apoptosis in cancer cells. We applied an L-C inversion circuit to the pulsed power generator to obtain a voltage waveform with a single frequency, which is applied to an antenna. A water gap switch and water capacitors were used in the L-C inversion circuit to obtain a pulsed voltage with a frequency element of 250 MHz. In this experiment, an electromagnetic wave was radiated underwater by a loop antenna. A measuring double loop antenna placed 0.15 m and 0.3 m from the radiating antenna detected electric field intensities of 112 kV/m and 49 kV/m, respectively. A focusing bowl was attached to the radiating antenna to obtain a higher electric field. The electric field intensity of the radiating antenna with the focusing bowl, 300 kV/m, was 6 times higher than that without the focusing bowl. The intensity distribution of the electric field focused by the focusing bowl was measured. A measuring small loop antenna detected peak electric field intensity of 11.3 kV/cm at a focal point. Areas with electric field intensity greater than 10.8 kV/cm were approximately 5 mm square and 3 mm wide in the x-z plane and y-axis, respectively.

A compact subnanosecond high-voltage bipolar pulse generator with spark gaps

Two modifications of the compact subnanosecond high-voltage bipolar pulse generator with an active unit based on a high-impedance charging line, forming line, and two uncontrolled nitrogen spark gaps without gas purging are studied. In both cases, the forming lines are charged with compression of the energies of incident pulses with a ∼160-kV amplitude, a ∼4-ns duration, and a ∼1.5-ns leading edge. The difference of operation modes of the circuits and their efficiency are specified by a point of connecting the load. In conditions of nanosecond prebreakdown overvoltage at a 100-Hz repetition rate, the spark gaps were energized with a relative scatter of ±(100–170) ps, thus specifying the stability of the shape of output bipolar pulses with a voltage difference up to 250 kV.

10.1007/s11455-008-2025-3

It is experimentally demonstrated that, upon the application of a subnanosecond high-voltage pulse to the gap of a diode filled with air at atmospheric pressure, a bunch of runaway electrons is formed in a sharply inhomogeneous electric field near the cathode. The bunch duration does not exceed 50 ps, which is shorter than the electron flight time through the interelectrode gap in the continuous acceleration regime. This duration remained unchanged when the gap width was varied between 6 and 26 mm. The electron energy in the picosecond electron beam, as determined from the time-of-flight measurements in the drift channel behind the anode foil of the diode, agree with the results of numerical calculations of the electron acceleration dynamics in the vacuum diode approximation.

Lasing in zinc selenide single crystals pumped by high-voltage subnanosecond pulses

The action of subnanosecond high-voltage pulses (U = 50–200 kV, tp = 100–500 ps) on 1–2-mm-thick plane–parallel ZnSe plates is studied. A sample was placed between a cathode and a circular anode. A discharge propagated along the lines of force of the electric field. Lasing at 480 nm appeared at the discharge front and opposite to the cathode. The average propagation velocity of the discharge achieved 5×108 cm s-1, the pulse power was 600 W, and the radiation divergence did not exceed 2–3°. No streamer discharges oriented along crystallographic directions were observed.

Electron source and acceleration regime of a picosecond electron beam in a gas-filled diode with inhomogeneous field

It is experimentally demonstrated that, upon the application of a subnanosecond high-voltage pulse to the gap of a diode filled with air at atmospheric pressure, a bunch of runaway electrons is formed in a sharply inhomogeneous electric field near the cathode. The bunch duration does not exceed 50 ps, which is shorter than the electron flight time through the interelectrode gap in the continuous acceleration regime. This duration remained unchanged when the gap width was varied between 6 and 26 mm. The electron energy in the picosecond electron beam, as determined from the time-of-flight measurements in the drift channel behind the anode foil of the diode, agree with the results of numerical calculations of the electron acceleration dynamics in the vacuum diode approximation.

Nanosecond High Voltage Pulse Generator Using Water Gap Switch for Compact High Power Pulsed Microwave Generator

Nanosecond and sub-nanosecond high voltage pulses can provide new applications. A cancer treatment by an ultra-short pulse high electric field is one of them. High power pulsed microwave has been proposed to apply the high electric field for that treatment. This work focuses on the design of a compact high power pulsed microwave generator using a nanosecond pulse power generator for the cancer treatment. To obtain fast rise time of voltage and current for nanosecond pulses, a switch has to have low inductance. Water gap switches have this property. Since water has a dielectric strength exceeding 1 MV/cm, gap distances for switching can be reduced to several hundreds of micrometers, and still allow switching of tens of kV. The narrow gaps allow us to reduce the switch inductance. In this study, the water gap switch was built in a Blumlein pulse forming line. The Blumlein line was designed to provide a pulse of 1 ns and to match an impedance to 16 Omega of an antenna. By using the water gap switch in the Blumlein line, the voltage rise time obtained approximately 750 ps at 13 kV of a peak pulse voltage. An electromagnetic wave was radiated underwater by the loop antenna. A measuring antenna at 0.15 m and 0.4 m from the radiating antenna caught electric field intensities of 116 kV/m and 32 kV/m, respectively. A frequency element of 250 MHz had higher intensity.

Initial stages of subnanosecond electric pulse breakdown in high-pressure gas discharge gaps

The prebreakdown and initial stages of discharge in high-pressure gas filled gaps under the action of subnanosecond high-voltage pulses have been experimentally and theoretically studied. The breakdown appears as a bright flash almost homogeneously filling the interelectrode gap within a period of time on the order of 100 ps. The observed phenomena are theoretically interpreted using a model that takes into account the heating of electrons due to collisions with gas molecules and the electron-impact ionization of these molecules. Calculations show that gas ionization is performed by “hot” electrons and has either a step-or flashlike character, in agreement with experimental observations. The characteristic time of ionization is 10–20 ps. The results lead to the conclusion that, using high-pressure gas discharge switches, it is possible to obtain voltage pulses with front widths on the order of several dozen picoseconds.

Gas-discharge gap passage by injected high-energy electrons driven by a high-voltage pulse

The motion of high-energy electrons in a gas-discharge gap filled by nitrogen at atmospheric pressure has been simulated. Electrons were driven by a subnanosecond high-voltage pulse with an amplitude of 150 kV. It is established that the injected electrons can reach the anode only for a very high initial energy, which cannot be provided by means of explosive emission. Therefore, under usual experimental conditions, electron emission from the cathode cannot account for the main fraction of electrons generated in a gas-filled diode at atmospheric pressure.

Generation of subnanosecond high-voltage pulses with a peak power of up to 300 MW and a repetition rate of 2 kHz

We report on the results of testing a hybrid subnanosecond modulator with an input resistance of 50 Ω based on an all-solid-state high-voltage nanosecond-pulse charging source with an inductive energy accumulator, a semiconductor current switch, and a pulse shaper with gas-discharge gaps. Use of the sharpening and cutting discharge gaps filled with hydrogen at a pressure of 100 atm ensured the stable formation of pulses with a peak amplitude of up to 140 kV and a pulse width of ∼500 ps at a repetition rate of up to 2 kHz.

An experimental system for studying the dynamics of the pulsed subnanosecond electric breakdown of gas gaps

In order to study pulsed gas breakdown initiation dynamics, a subnanosecond voltage pulse with a width of 0.2–4 ns and a height of 20–150 kV is applied to a gas-discharge gap. The voltage rise rate ranges from 6×1013 to 7.5×1014 V/s. The amplitude and duration of subnanosecond high-voltage pulses are adjusted continuously, as well as the magnitude and profile of the discharge current. The glow accompanying prebreakdown and breakdown processes in the gap is registered by a high-speed electron-optical camera.

A transistorized Marx bank circuit providing sub-nanosecond high-voltage pulses

An improved version of a Marx bank circuit has been developed using 2N5551/2N5550 transistors as switching elements in avalanche mode which provides a negative pulse of about 4 kV amplitude and <or=ns rise time. The circuit has about 14 ns delay and <or=ns jitter.