Development and Testing of a Three-Dimensional Canonical Vorticity Probe*

To examine momentum redistribution processes and study generalized helicities during plasma relaxation in MST RFP plasma, a new 3D canonical vorticity probe is being tested to measure plasma ion flow and magnetic field vectors at four spatial locations arranged in a tetrahedral shape. These measurements permit the calculation of ∇×B and ∇×V via the finite difference method. The vorticity probe consists of four probe heads arranged in a tetrahedral pattern, with an overall probe diameter of 3.2 cm. The probe head diameter is 1.0 cm which is of the order of the ion Larmor radius, ~ 0.9 cm. Each head has four moly electrodes, also arranged in tetrahedral geometry, that are biased relative to a common return electrode, using four power supplies, to measure the local ion flow. All 17 measured ion saturation currents are connected to a 150 kHz-isolation amplifier. Additionally, each head has three orthogonal magnetic coils within to measure equilibrium and fluctuating magnetic fields. The equilibrium magnetic field will be used to orient the four heads in MST lab frame. The measured magnetic signals are integrated with a 250 kHz bandwidth and an RC constant equal to 0.1 ms. All signals are digitized at 1MHz. Preliminary results, calibrations, drawings, and photos will be presented.