ENERGY-BALANCE IN THE CSSU DEVICE

An analysis of the energy balance in the Coaxial Slow Source Upgrade ( CSSU) device is reported. The CSSU consists of two concentric coils ca rrying pulsed azimuthal currents only, which form an elongated plasma (an 'annular field reversed configuration (FRC)') in the space between the coils. The plasma contains no toroidal field, and is confined by poloidal fields only, resulting in a very high average beta. The CSSU, which operates at loop voltages of 2 kV or less and with risetimes of the order of 70 mu s, was developed to provide a low voltage, slow fo rmation alternative to conventional FRC generation techniques that are based on fast theta pinch technology. It is found that the CSSU devic e does form annular FRCs, which persist for the duration of the induct ive current drive, apparently free of MHD instability. Temperatures ar e low, however, and the transport is correspondingly poor. To analyse the energy balance, the power input to the plasma is calculated direct ly from external and internal magnetic field measurements. No assumpti ons about the resistivity profile have been made. A triple Langmuir pr obe located at the device end region was used to calculate the energy lost due to escaping particles. Electron temperature measurements from Thomson scattering and impurity estimates from doping studies are use d in a time dependent corona model calculation to show that the CSSU p lasma is impurity line radiation dominated. Time dependent coronal cal culations imply that, with operation over much longer formation times (> 100 to 200 mu s) at lower density (10(14) cm(-3)), it may be possib le to burn through the carbon and oxygen impurity radiation barriers a nd attain plasma conditions closer to those produced in conventional F RCs.