Current initiation in low-density foam z-pinch plasmas

Low density agar and aerogel foams were tested as z-pinch loads on the Saturn accelerator to study current flow initiation. In these first experiments, we studied the initial plasma conditions by measuring the visible emission at early times with a framing camera and a streaked one-dimensional imaging system. Later, near the stagnation when the plasma is hotter, x-ray imaging and spectral diagnostics were used to characterize the plasma. Filamentation and arcing at the current contacts were observed. Bright implosion features were also observed. Increasing the early time conductivity, by coating the target with a high-z layer and by providing a low-current prepulse, is the most important factor in obtaining good coupling to the machine. None of the pinches were uniform along the z axis. The prime causes of these problems are believed to be the electrode contacts and the current return configuration. Solutions are discussed.