Peculiarities of detecting pulses of runaway electrons and X-rays generated by high-voltage nanosecond discharges in ope
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Peculiarities of Detecting Pulses of Runaway Electrons and Xrays Generated by HighVoltage Nanosecond Discharges in Open Atmosphere L. P. Babich and T. V. Loiko Russian Federal Nuclear Center, AllRussia Research Institute of Experimental Physics, Sarov, Nizhni Novgorod oblast, 607188 Russia Received March 6, 2009; in final form, June 5, 2009
Abstract—Peculiarities of detecting pulses of highenergy runaway electrons and the accompanying Xrays generated by highvoltage nanosecond discharges at high overvoltages in dense gases are discussed. Methods for overcoming difficulties encountered in such measurements are demonstrated. Different techniques for detecting runaway electrons and Xrays generated by discharges in open atmosphere are described, and typ ical errors that may be done when interpreting measurement results are considered. Experiments with the use of a smallsize generator of nanosecond pulses with the idlerunning voltage of 250–270 kV and stored energy of ~0.5 J have been carried out. It is shown that, in measuring runaway electron pulses by using an experimen tal configuration with a grid anode, a major portion of the recorded signal is attributed to electromagnetic dis turbances. It is found that Xrays are mainly generated due to the deceleration of runaway electrons in the anode, rather than in gas. The number of runaway electrons with energies ~300 keV does not exceed 109 per shot, and the Xray dose is 60–200 µR/shot, depending on the anode material. DOI: 10.1134/S1063780X10030086
1. INTRODUCTION In the late 1960s and early 1970s, pioneer studies of highvoltage nanosecond discharges developing in dense gases in the runaway electron (RE) regime were carried out at the AllUnion Research Institute of Experimental Physics [1, 2]. Experimental and theo retical studies of such discharges were then carried out in the Soviet Union and United States (see, e.g., [3– 16] and references in [11, 14]) and are now being stud ied in Russia (see, e.g., [17–30]). In our experiments [4, 5, 10, 11, 13–16], the high voltage unit of a Belkin–Tsukerman smallsize gener ator of nanosecond Xray pulses was used as a source of nanosecond highvoltage pulses [31, 32]. Its main elements are a pulsed stepup transformer and pulse shaping switch (usually, it is an R43 switch with a breakdown voltage of Usw = 140–150 kV and front duration shorter than 1 ns). The cases of the generator and switch form a highvoltage capacitor with a capac itance of С0 ≈ 50 pF, the device inductance being L0 ≈ 80 nH. In the idlerunning mode, the device generated a voltage pulse with an amplitude of Uidle ≈ 1.8Usw. Discharges in open atmosphere (i.e., in atmo sphericpressure air) have been studied most thor oughly. It was found that such discharges possess spe cific features atypical of classical gas discharges devel oping in the electron drift mode. Among these features, there are diffusive forms of discharges devel oping without gap preionization, generation of high
energy REs penetrating through a window
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