Development and implementation of a 3D 6-tip mach probe arranged in an octahedral geometry on WiPPL device*

Measurements and simulations show that plasma relaxation processes in the RFP drive and radially redistribute both current and momentum. To examine the momentum redistribution processes better, a new prototype Mach probe has been designed and tested to measure the 3D plasma flow. The probe consists of 6 molybdenum tips that are arranged on the flattened vertices of an octahedron made of BN. The probe has three coils wound on a BN bobbin to measure the equilibrium and fluctuating magnetic field. Multipole return electrodes at various distances from the tips will determine the optimum location for the return current so that plasma perturbation is minimized. The return electrodes will act as the floating reference for tip biasing. A new 6 channel power supply has been constructed to measure current collected by each tip and the return electrode with a set of voltage dividers. All 7 currents are connected to a 100 kHz isolation amplifier. The magnetic signals are integrated with a 250 kHz bandwidth. All signals are digitized at 1 MHz. Preliminary results, calibration, drawings and photos will be presented.

*Work supported by DoE.

*LLNL-ABS-824175 is supported by Wisconsin Plasma Physics Laboratory (WiPPL) DE-SC0018266, LLNL DE-AC52-07NA27344 and the Alexander von Humboldt Foundation.