APACHE: A low-background hard x-ray spectrometer for 10. 6-. mu. m laser fusion experiments

Journal Article · Sun Aug 01 00:00:00 EDT 1982 · Rev. Sci. Instrum.; (United States)

DOI:https://doi.org/10.1063/1.1137134· OSTI ID:5090324

Priedhorsky, W; Lier, D

We describe a ten-channel hard x-ray spectrometer, named APACHE, which is used to diagnose target x-ray spectra at the HELIOS 10.6-..mu..m laser fusion facility. Each channel consists of a filter, scintillator, and photodiode detector. Spectral bands are defined by filtration, and the choice of scintillator type and thickness. This scheme of channel definition gives broad spectral response channels, but it also yields large signals at the detector. This allows the use of insensitive photodiodes as detectors, reducing the effect of penetrating background. The two scintillators used, cesium fluoride and a lead-loaded plastic scintillator (NE142), have time responses of a few nanoseconds. The system is thus unable to resolve the 1-ns laser pulse, but is useful in isolating the target signal from laser electron beam, and possible target neutron, backgrounds. Cesium fluoride has a low scintillation response for h..nu..< or =100 keV, and is used for higher-energy channels; NE142, which is self-absorbing in thick sections, is used for low-energy channels. Both scintillators have been shown to be stable over a time scale of months. Because of the broad spectral response functions, the channel signals are fit to an exponential spectrum. Very good fits are obtained by this method. The APACHE results are corroborated by an independent thermoluminescent dosimeter system. A fast detector is used to provide approx.400 ps time resolution in a separated broad high-energy channel (named CYCLOPS). The agreement of the fast signal with that predicted from the APACHE spectrum demonstrates that APACHE measures the prompt hard x-ray signal. A linear relation is found between fastest ion velocity and APACHE kT/sub H/, providing an additional check of APACHE results. The APACHE system has proved convenient to field and free of background, and is a standard diagnostic at the HELIOS facility. We routinely measure hard x-ray yields of tens of joules from laser shots on high-Z targets.

• Research Organization: Los Alamos National Laboratory, P.O. Box 1663 MS-410, Los Alamos, New Mexico 87545
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 5090324
• Journal Information: Rev. Sci. Instrum.; (United States), Vol. 53:8
• Country of Publication: United States
• Language: English

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