Subnanosecond front, high-voltage generator based on a combined pulsed forming line

Abstract

Nonsymnnetric pulsed double forming line is proposed to shorten the high voltage pulse rise time of the nanosecond generator up to <1 ns. The rate of rise twofold increasinlg has been obtained by the short DFL energy store, mounted in single line output of nanosecond driver without any additional peaking spark gap.High volta e pulse modulators are the basic elements of coherent microwave pulse generators and RF-band ultra wide band videopulse sources2. These devices form the accelerating vollage pulses on the cathodes of high current electron accelerators or transmit the energy as TEM-wave directly to the radiating aerial. In both cases, special requirements are imposed iupon the pulse of the high volta e generator, namely, its form, duration, rise time. The problem of transient time reduction is essential to the high power electron autooscillators, particularly at nanosecond pulse duration. One of the methods of solving this problem is to increase the spectrum power density of initial perturbation over the operating frequency band. This is provided by front sharpening of electron beam current pulse, all other factors being equal, and, consequently, by the rate of rise increase of accelerating voltage /dV/dt) by which vacuum diode of the high current accelerator is fed. The initial perturbation power can be additionally amplified by specific form of nanosecond pulse, namely, with a short subnanosecond burst preceding the flat of pulse (Fig.l), applied to the accelerator cathode. Spectrum of ultra wide band videopulse is determined by the same parameter of high voltage [pulse (dV/dt) and radiating aerial frequency characteristic in total. By this means the further progress of simple and effective forming techniques of high voltage pulses with subnanosecond band front is considered to be important.High voltage coaxial forming lines (FL) connected to the load by untriggered high pressure gas commutator are practised on a large scale for the forming of nanosecond pulses with the high rate of riise. It should be stressed that there is the pulse rate of rise limiting. This limitation is connected with the probable exciting of the higher mode in coaxial line. The minimum rise time therewith is defined by the lowest cutoff frequency of the TE mode: (t),,=l5(D+d)1, ps, where the outer (D) and inner (d) diameters of the coaxial line conductors are expressed in terms of cm. For instance, at D=10 cm and FL wave resistance p=40 Ohm, we derive (t ), i , = 200 ps. Thus, small cross section lines, in fact, can form and transmit the pulses with rise time significantly less than 1 ns, without any distortions.Under these conditions switching characteristic of the gap switch is the crucial factor for obtaining load pulse rise time, which is considerably shorter than 1 ns. If the FL is charged by pulse transformer within microsecond interval4, the high pressure commutator usual1 provides pulse rise time at the level of 1 ns and over4, . Therefore, there is a need to use the additional stages of the energy compression6" Fig.1. The 'sh...

Ultrafast gas breakdown at pressures below one atmosphere

“…A RADAN 303A high voltage pulser [12] with pulse slicer SN4 providing pulse amplitudes between 20 and 150 kV into matched load, minimum risetime 150 ps, pulse durations 250 -1500 ps, nominal impedance 45 Ω , is connected to a spark gap in a vacuum chamber (pressure between 10 -5 and 600 torr) via a 2 m oil-filled coaxial 45-Ω-line, see Fig. 1.…”

Subnanosecond Breakdown of Insulating Media

“…The recent availability of high-voltage pulsers reaching into the several 100 kV regime with risetimes of less than 300 ps [13,14], and of transient digitizers with risetimes down to 100 ps enables exploration of breakdown at higher voltages and shorter pulse risetimes than several years ago. A crucial element is the application of a high voltage pulse to a test gap, with the goal to minimize risetime limitations due to capacitance and changes in geometry.…”