Soft X-ray yield measurement in a small plasma focus operated in neon

Abstract

The United Nations University/International Center for Theoretical Physics Plasma Focus Facility (UNU/ICTP PFF), a small plasma focus, has proven very useful as a training device for research initiation and as a test bed for applications. In this work, its performance in terms of a soft X-ray (SXR) source is examined. The total SXR yield when operated in neon is measured using low-cost detectors, including a calorimeter and a five-channel filtered PIN system. For a charging voltage of 14 kV with 2.9 kJ stored energy, the optimum operating pressure in neon is found to be in the range of 2.7-3.3 torr, resulting in a total SXR yield of 6J/shot into 4/spl pi/ steradians measured by the calorimeter in agreement with the PIN detectors. Spectral data shows that 64% of the total SXR yield is contributed by the Ly-/spl alpha/ and He-/spl alpha/ lines and 36% by the rest, mainly the radiative recombination. The low total SXR yield (0.2 % of stored energy) is consistent with numerical computations of focus dynamics, which reveals that 3% of stored energy is converted into plasma energy. This low conversion rate into plasma energy is due to the large inductance of 110 nH of this simple single-capacitor device. Thus, for development as a SXR source, reduction of inductance is necessary.