Diagnostics of plasma channel for HIF transport

An alternate technique for heavy ion final transport, from the driver to th e target, is by the use of the self-standing Z-pinched plasma channel. Expe riments conducted at the Lawrence Berkeley National Laboratory have produce d 40 cm long stable plasma channels with a peak discharge current of 55 kA in a 7Torr nitrogen gas fill. These channels are produced using a double pu lse discharge scheme, namely, a pre-pulse discharge and a main capacitor ba nk discharge. It is postulated that the channel's insensitivity to MHD inst abilities within the time scale relevant to beam transport is due to the wa ll effect the pre-pulse discharge creates. This is accomplished by leaving a gas density depression on the channel's axis after hydrodynamic expansion . Since the pre-pulse discharge creates the initial conditions for the main bank Z-pinch, it is critical to understand how to control and engineer the pre-pulse. Here we present some of the results of ongoing experiments gear ed to understand the underlying physics of the LBNL 2-pinch plasma channel. Schlieren and phase contrast measurements show the radial propagation of a shock wave during the pre-pulse discharge and suggest indirectly the evide nce of the on axis gas density depression, that is believed to be <1/10 of the original gas fill pressure. For the main bank Z-pinch, interferometry s how an integrated electron line density of 1.6 x 10(17) cm(-2) for a 15 kV discharge on axis. These measurements coupled with Faraday rotation measure ments will indicate ultimately the current density distribution in the chan nel. This data will be used to benchmark simulation codes. (C) 2001 Elsevie r Science B.V. All rights reserved.