INVESTIGATION OF THE LOW-INDUCTANCE VACUUM SPARK AS A SOURCE OF SOFT-X-RAY ATOMIC QUASI-CONTINUA FOR OPTICAL-PUMPING

A simplified radiative collapse model has been applied to a high-Z (Ce ) low-inductance vacuum spark plasma, in order to assess the possibili ty of using this simple discharge to generate N-shell atomic quasi-con tinua for optical pumping of soft x-ray lasers. The radiative losses o f the complex Ce ions are computed using statistical methods developed for unresolved transition arrays, and atomic data from the average io n model. The calculations predict that at sufficiently high current, a radiative collapse followed by micropinching takes place at the openi ng of the M-shell, in good agreement with experimental observations. T he model predicts that the radiative losses associated with the quasi- continuum emission allow the plasma to be compressed to relatively hig h density prior to the micropinch. Nevertheless, despite this 'mild' r adiative collapse, the average quasi-continuum brightness is below tha t required for optical pumping. Scaling the results to discharge curre nts shows this limitation to be intrinsic to Z-pinch type discharges.