Observations from a Long Duration X-Ray Source for Laboratory Astrophysics

We discuss the characterization of a long-duration, broadband x-ray flux source forlaboratory astrophysics experiments. The experiments were done at the OMEGA EP high-power laser facility. This is a four-beam laser system that can deliver up to 4.4 kJ of UV laser energy in pulses of 10 ns duration. By driving sequentially in time an arrangement of three copper hohlraums, i.e. one hohlraum at a time, we can produce and sustain a 90 eV radiation temperature x-ray flux at the source for 30 ns. We call this concept the “Gatling-Gun” x-ray source. It is important to characterize and monitor the performance of the Gatling-Gun source since it is the x-ray flux that actually drives the laboratory astrophysics experiments, not the laser beams. To this end, we have field three diagnostics, namely VISAR, SOP and a gated grating spectrometer. The VISAR (velocity interferometry system for any reflector) is an optical laser interferometry diagnostic that measures the speed of a shock launched by the Gatling-Gun x-ray flux in an ablator; in turn, the shock speed relates to the radiation temperature which is an important characteristic of the x-ray flux. The SOP is a Streaked Optical Pyrometer that can be used to extract the brightness temperature of the shock front. The gated grating spectrometer records the spectral distribution of the broadband x-ray flux over a photon energy interval of almost 2 keV; this spectral information is important for understanding the experiment driven by the x-ray flux, it shows the thermalization of the x-ray field in the hohlraum, and provides yet another method to determine the radiation temperature. These diagnostics require advanced data processing, modeling and interpretation. This MS thesis presents the series of OMEGA EP experiments in which the diagnostics were fielded, the data recorded, and the results obtained for the characterization and performance of the Gatling-Gun x-ray source