Density measurements in flash board plasmas for a magnetically confined plasma opening switch

Summary form only given, as follows. Fiber optic interferometer (FOI) plasma density measurements were performed on flashboard (FB) generated plasmas for a magnetically confined plasm a opening switch (MCPOS) under development at the Centre d Etudes de Gramat, France. For the MCPOS to function correctly a fill-plasma of /spl sim/4e14/cc is required in the A-K gap. Earlier measurements had shown that the fill-plasma density is at least an order of magnitude lower than this and thus, the flashboards should be reconfigured for better operation. To motivate better FB reconfiguration, a testbed was designed to study the dependence of FB plasma on the drive circuit and the slow coil magnetic field. For these tests, a single FB was used to represent one out of 144 actual FBs in the real MCPOS. The slow coil magnetic field in turn, was represented by a simple axial magnetic field of up to 0.5 T, normal to the FB surface. Density measurements taken with a 4-beam, fiber optic interferometer show that the plasma emitted by the FB moves at /spl sim/10 cm/5s in a direction at /spl sim/45 deg to the normal, for an axial field of /spl sim/0.5 T. This J/spl times/B cross-field motion might explain the anomalously low densities measured in the MCPOS earlier. These measurements motivated new FB and slow coil configurations from which further measurements were made of the fill density in the A-K gap region of the MCPOS at CEG. In addition to the density measurements, the various FB configurations were simulated by a circuit code. The predictions of the code were compared to current measurements in the FB drive circuit. These comparisons allowed evaluation of the dependence of FB current on key circuit parameters such as the peaking capacitor, drive voltage etc. The benchtop and MCPOS A-K gap measurements and circuit simulations are presented and discussed.