Characterizing the photon spectrum in the DARHT Axis-I diode

Abstract

An array of photon diagnostics have been deployed on a high power relativistic electron beam diode. Surface flashover of a carbon fiber velvet cathode generates a discharge from which electrons are accelerated through a 17.8 cm diode. This discharge is assumed to be a hydrocarbon mixture. A small portion of the off energy electrons (1-3 MeV) accelerated during the rise and fall of the 80 ns FWHM pulse impact the beam pipe and generate a Bremsstrahlung spectrum of 0.1-3 MeV photons. The principal objective of these experiments is to quantify the dynamics of the hard X-ray and -ray flux generated in the diode region, in addition to quantifying dynamics of the visible photons generated, and the ion species of the surface discharge on the velvet cathode. A qualitative comparison of different diagnostic results are presented, which include time resolved measurements with X-ray PIN diodes, a PMT, and CCD images. In addition initial visible spectroscopy measurements will also be presented.

Beam Dynamics for ARIA

“…In Axis-I the diode current is essentially zero until the voltage reaches ~ 1.5 MV. Moreover, the earliest part of the leading edge, with energy less than ~3-MeV, begins to be scraped off on the beam pipe before reaching the first cell [37]. Thus, for a 3. , which is so much less than the injected KE δ that it can be neglected.…”