First fast Z-pinch current scaling experiments suggest faster radiated power dependence

Abstract

Summary form only given. In previous current-scaling experiments performed by William A. Stygar, the load masses were 5.8 mg for 90 kV charging of the Marx generators and 2.7 mg for 60 kV charging, resulting in implosion times of the order of 95 ns. The observed average peak radiated powers and energies were respectively 132TW and 1.625MJ for the 90-kV shots and 82.3TW and 0.841MJ for the 60-kV shots. The peak radiated X-ray power was proportional to the 1.24th power of the load current (P/spl prop/I/sup 1.24/), and the total radiated X-ray energy was proportional to the 1.73rd power of the load current (E/spl prop/I/sup 1.73/). In the present current scaling experiments the purpose is to look at current scaling of X-ray energy and power at shorter implosion times. The wire number (300), the array diameter (20 mm) and the height (1 cm) were the same as in previous studies. However the load masses were half the previous ones and equal to 2.5 and 1.25 mgr. This caused the arrays to pinch faster: /spl sim/80 ns into the current pulse. The power output at full charging of the Marx's (90 kV) and the standard 100 ns current drive of Z driver was quite high for a single 20-mm diameter W wire array and equal to 170TW. The total radiated energy was equal to 1.14MJ. We fired one shot at full 90 kV charge (Z/spl I.bar/1142) and a second one at 60 kV (Z/spl I.bar/1143). The pinches were of very high quality as witnessed by the output X-ray pulses and framing cameras. The FWHM of both shots were 3.9 ns and the rise times 2.5 and 3.1 ns. The peak load currents were respectively 16.45 and 11.09MA. The radiated power ratio is equal to the current ratio to the 1.88th power (P/spl prop/I/sup 1.88/) while the ratio of the total radiated energy is almost the same and equal to the 1.90th power of the current ratio (E/spl prop/I/sup 1.90/). Despite the fact that fast pinches do not use all the available Z driver energy and consequently deliver less total radiated X-ray energy, they however yield more radiated power and tighter stagnations than the slower, higher mass pinches. This may be most important for ICF loads. More shots are planned to further validate and confirm these scoping results.