Operation of the Z accelerator in a long-pulse mode

Summary form only given. Recently there has been considerable interest in operating the Z accelerator in a long-pulse mode for isentropic compression experiments (ICE), and for long-pulse Z-pinch implosions. In normal Z operation the current rises to a peak in about 80 ns with experiments or implosions occurring at 100 to 120 ns. By shorting self-break water switches in the pulse-forming lines (PFL) of Z, it is possible to slow the rise-time of the current so that the peak current occurs at about 180 ns. Experiments and circuit-code calculations show that it is possible to get even longer rise-times by adding inductors to where the line-1 water switches are located. A series of single-line tests were done on Z to confirm this effect, and nine-line and full-machine tests were done as a demonstration. In general, the machine shots done at full voltage did not match the circuit-code predictions. The measured pulse lengths and peak amplitudes were shorter and lower than predicted. When the shots were repeated at lower charge voltages, the match was much better. The discrepancy between the measurement and circuit code was thus discovered to be related to a breakdown to ground at the water-switch location. Results of experiments and simulations will be shown, and recommendations for fixes to allow reliable operation in the long-pulse mode will be presented.