Keith Cartwright

The graphite-differential absorption spectrometer (G-DAS) is a diagnostic sensor being developed to characterize the high-energy x-ray spectrum emitted by pulsed power machines, enhancing our understanding of the radiation environment and source dynamics. Using an inverse model, G-DAS employs a beam transmission analysis technique where the spectrum is unfolded from transmission signals acquired after the photon beam passes through a segmented graphite stack of six attenuating graphite disks, each 4 cm thick. Each gap (2 cm) between disks has two CaF2 thermoluminescence detectors for measuring the deposited energies. Drawing parallels to methods used to specify photon spectra of clinical linacs, the G-DAS analysis assumes that the spectra from pulsed power machines follow a parameterized functional form based on bremsstrahlung physics. Each spectrum can then be fully characterized by a unique set of those parameters, reducing the task to only determining the free parameters for the spectrum in question. The performance of the implemented method is evaluated using experimental and Monte Carlo simulated transmission data as well as synthetic spectra.

Magnetic insulation of electrons prevents losses and can be applied to generating radiation or electron sources for high current and high power applications. Ion emission from the anode may degrade magnetic insulation. We develop equilibrium theory, self-consistently coupling magnetically insulated electron flow with free-flowing injected ions. Generally, ion injection is self-limiting from space charge; however, once insulation strength drops below about 1.2x the magnetic insulation threshold, ion space-charge limits vanish. The gap effectively short-circuits and the electron flow layer asymptotically approaches the anode. In this regime a quasineutral, nonthermal plasma manifests, effectively reducing gap distance and suggesting quasiequilibrium gap closure evolution.