Comparison of Round and Knife-Edge-Like Cathodes on Gas-Puff Single-Liner Implosions

Preionization is believed to play an important role on the implosion of gas-puff Z-pinches. Some experiments have used an external preionization source, e.g., UV light or electron beam. In contrast, other experiments rely completely on overvoltage breakdown by the own generator’s voltage pulse. But the problem with this approach is that it might not produce reliable results because self-breakdown is mainly a stochastic process. In order to study reproducibility, we performed systematic studies on self-breakdown using two different cathode geometries: i) a smooth, round cathode to provide a homogenous electric field ii) a sharp, knife-edge-like geometry to enhance the electric field locally and eventually electron emission. The experiments were carried out on the Llampudken current generator, which provides a current pulse of ~400kA amplitude and 200ns rise time (10%-90%). We implemented gated XUV imaging, laser probing, filtered diodes and time-integrated X-ray imaging to obtain information about the implosion as well as the stagnation phase for the two cathode geometries. Preliminary analysis shows that erosion of the knife-edge cathode may be a serious problem, and on the contrary, the round cathode may have far more reliable results. Data is currently analyzed and further details will be shown and discussed.