Optimizing UNU/ICTP PFF Plasma Focus for Neon Soft X-ray Operation

The United Nations University/International Centre for Theoretical Physics Plasma Focus Facility (UNU/ICTP PFF), a 3.3-kJ plasma focus, was designed for operation in deuterium with a speed factor S such that the axial run-down time matches the current rise time at an end axial speed of nearly 10 cm/mus. For operation in neon, we first consider that a focus pinch temperature between 200 and 500 eV may be suitable for a good yield of neon soft X-rays, which corresponds to an end axial speed of 6-7 cm/mus. On this basis, for operation in neon, the standard UNU/ICTP PFF needs to have its anode length z₀ reduced by some 30%-40% to maintain the time matching. Numerical experiments using the Lee model code are carried out to determine the optimum configuration of the electrodes for the UNU/ICTP PFF capacitor system. The results show that an even more drastic shortening of anode length z₀ is required, from the original 16 to 7 cm, at the same time, increasing the anode radius ldquoardquo from 0.95 to 1.2 cm, to obtain an optimum yield of Y _sxr = 9.5 J. This represents a two- to threefold increase in the Y _sxr from that computed for the standard UNU/ICTP PFF.