X-ray diodes for laser fusion plasma diagnostics

Abstract

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.

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