RESUMEN
The use of an electron beam to pump an excimer laser has the advantage of being readily scalable to higher laser energies at high efficiency. Typically, a pulsed power driver generates the electron beam in a vacuum diode that consists of an electron emitter and a thin anode foil that holds the vacuum against the atmospheric-pressure laser gas. Even a miniscule leak in the anode foil can lead to an electrical breakdown in the vacuum diode, resulting in the destruction of the foil and evidence of the failure mechanism. The problem is even more onerous at the high voltage, high current, and pulse repetition frequencies needed for the large-area diodes used in excimer lasers for fusion research. Electra is one such laser used at the Naval Research Laboratory to develop excimer laser technologies for inertial fusion energy. To achieve longevity on Electra, it was necessary to instantly detect an incipient foil failure and halt the pulsed power drivers so the physical cause(s) could be studied. This rapid detection was accomplished using an optically filtered photodiode that senses the presence of argon emission from a Penning discharge vessel attached to the vacuum diodes. Details of this "Spectral Penning Leak Detector" device and its operation are presented. The diagnostics allowed the identification of a recurrent pinhole leak in the anode foil induced by cathode spots, which were created by electron emission from the foil during post-pulse voltage reversals. Eliminating the voltage reversals increased the continuous operation of the Electra laser from hundreds of shots to over 90 000 shots.
RESUMEN
An electrical feedthrough, operating at 10(-6) Torr, for use in vacuum systems utilizing Swagelock or Wilson-type seals is described. It features a pair of center conductors with a coaxial shield and can be used with a variety of detachable probes.
RESUMEN
A Thomson scattering system has been designed and constructed for probing a relativistic electron beam heated plasma. Ruby laser light scattered through 90 degrees is resolved by a polychromator and detected by one of six photomultipliers. The system is capable of resolving electron temperatures of 150 eV at densities of n(e)<10(13) cm(-3) with a 4-J ruby laser and an f/9 throughput collection system. Scaling to a 10-J, f/5 system would allow resolving densities of approximately 10(12) cm(-3). System design, calibration, alignment, and data reduction are discussed. At elevated temperatures (T(e) approximately 600 eV) evidence of the relativistic blue shift was observed.