Arcing and rf signal generation during target irradiation by a high-energy, pulsed neutral particle beam

Abstract

We present a theory describing the dynamics of arc discharges In bulk dielectric materials on board space-based vehicles. Such "punch-through" arcs can occur In target satellites irradiated by high-energy (250 MeV), pulsed (100 mA x 10 ms) neutral particle beams. We treat the arc as a capacitively limited avalanche current in the target dielectric material, and we find expressions for the arc duration, charge transport, current, and discharge energy. These quantities are adjusted to be consistent with known scaling laws for the area of charge depleted by the arc. After a brief account of the statistical distribution of voltages at which the arc starts and stops, we calculate the signal strength and frequency spectrum of the electromagnetic radiation broadcast by the arc. We find that arcs from thick (~1 cm) targets can generate rf signals detectable up to 1000 km from the target, by a radio receiver operating at frequency 80 MHz, bandwidth 100 kHz, and detection threshold-105 dBm. These thicktarget arc signals are 10 to 20 dB above ambient noise at the receiver, and they provide target hit assessment if the signal spectrum can be sampled at several frequencies In the nominal range 30-200 MHz. Thin-target (~1 mm) arc signals are much weaker, but when they are detectable in conjunction with thick-target signals, target discrimination is possible by comparing the signal frequency spectra. appears to be less important in determining when the arc starts and stops than the probability of ionizing collisions which maintain the arc. We analyze the distribution of arcs over various arc start and stop voltages, and we conclude that "typical" arcs from target dielectrics (~1 cm thick) may show peak currents ~500 A and may have durations as long as 0.5 ps. In Sec. III-E, we calculate the fields and energy radiated by bulk discharge arcs terminating at an anode which ls-in effect-a metal surface. We do not treat radiation from the stripped NPB nuclei or from arcs that pass charge through the anode surface. We estimate arc broadcast fields and signal strengths observable at a remote rf receiver and show that a nominal thicktarget arc signal is detectable at target-observer distances up to 1000 km, by a receiver operating at frequency ~80 MHz, bandwidth ~100 kHz, and tnreshold sensitivity (-)105 dBm. The arc signal here is ~15 dB above ambient thermal and background noise. In Sec. III-F, we compare the frequency 3pectra of signals from arcs in "thick" and "thin" targets. Over a frequency range 0-1 GHz, spectral outputs from thick targets decrease with frequency, while they increase for thin targets. This difference can be used to discriminate between arc signals emanating from thick and thin targets, i£ the observer's rf receiver can be scanned over a nominal frequency range 30-200 MHz. We close this report, in Sec. III-G, with comments on how various aspects of the present calculation might be extended or improved. Our overall conclusion is that both hit assessment and thick-vs thintarget discrimination by analysis of AGEMPs (...