Photodiodes with x-ray sensitive photocathodes are commonly used as broadband x-ray detectors in fusion plasma diagnostics. We have measured the photocathode quantum efficiency between 1–500 Å of common photocathode materials including aluminum, copper, nickel, gold, three forms of carbon, chromium, and cesium iodide. We have also studied the effects of the experimental environment and long-term cathode aging on the measured quantum efficiencies. In addition, we have measured the x-ray mass-absorption coefficients of x-ray filter windows of Kimfoil, aluminum, polypropylene, and Formvar in energy regions where data were previously unavailable. Measurements between 1–50 Å were performed at the Los Alamos Scientific Laboratory’s low-energy x-ray calibration facility, while the measurements between 50–500 Å were performed at the National Bureau of Standard’s synchrotron ultraviolet radiation facility.

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The dynamics and energy flow in Au plasmas produced by a 0.35-/xm laser have been studied with layered targets with 6-and 24-beam spherical illumination from the Omega laser, to understand the processes leading to subkiloelectronvolt x-ray emission. A significant enhancement in x-ray conversion at low intensities is observed for the 24-beam irradiations with higher energy, greater uniformity, and larger targets. Results are interpreted by comparison with hydrodynamics-code calculations. The depth of energy penetration and x-ray emission in the plasma appears to be well understood, but some details of the x-ray time signature and spectra are not.

Photodiodes with x-ray sensitive photocathodes are commonly used as broadband x-ray detectors in fusion plasma diagnostics. We have measured the risetime of the detector system and have measured the quantum efficiency between 1-500 A of numerous photocathode materials of practical interest. The materials studied include aluminum, copper, nickel, gold, three forms of carbon, chromium, and cesium iodide. The results of the measurements are compared with Henk«*'s semiempirical model of photoyieid. We have studied the effects of long-term cathode aging and use as a plasma diagnostic on cathode quantum efficiency. In addition, we have measured the x-ray mass-absorption coefficient of several ultrasoft x-ray windows in energy regions where data were unavailable. Windows studied were made of aluminum, Formvar, polypropylene, and Kimfoil. Measurements between 1-50 A were performed with the Los Aiamos Scientific Laboratory's low-energy x-ray calibration facility, and the measurements between 50-550 A were performed at the National Bureau of Standard's synchrotron ultraviolet radiation facility.