Technique for inferring angle change as a function of time for high-current electron beams using a dose-rate monitor array.

Intense electron beams striking a high-atomic number target produce high-output pulsed photon fluxes for flash x-ray experiments. Without an external guide field, such beams are subject to the dynamics of high-current electron beam propagation, including changes to electron trajectories either from self-fields or from development of beam instabilities. The bremsstrahlung output (dose-rate) scales approximately as IVx, where I is the beam current, V the electron energy, and x is in the range 2.0-2.65 and depends upon the electron angle on the converter. Using experimental beam data (dose-rate, I and V), this equation can be solved for x, a process known as "inverting the radiographer's equation." Inversion methods that rely on thermoluminescent dosimeters, which are time-integrated, yield no information about evolution of the electron beam angle in time. We propose here an inversion method that uses several dose-rate monitors at different angles with respect to the beam axis. By measuring dose-rates at different angles, one can infer the time-dependent beam voltage and angle. This method compares well with estimates of corrected voltage and results in a self-consistent picture of beam dynamics. Techniques are demonstrated using data from self-magnetic pinch experiments at the RITS-6 facility at Sandia National Laboratories.