Measurement of Fast Ion Dynamics in a High Temperature Plasma

Measurement of fast changes and fluctuations in ion flow and/or temperature is critical to understanding a diversity of plasma phenomena. We have developed a high-resolution spectrometer to measure impurity ion temperatures and flow velocities in high-temperature plasmas with 250 kHz bandwidth. This device is actually a duo-spectrometer: measurements from two different chordal views of the plasma can be made simultaneously. All 32 spectral channels on the exit plane of the duo-spectrometer are read out and digitized at 1 MHz in parallel to achieve high time resolution. We have obtained these key results: (1) The toroidal velocity fluctuations of the plasma are coherent with the large-scale magnetic tearing modes; during a sawtooth event the scalar product of ṽ_φ and B̃_r is similar to that expected for the MHD dynamo electromotive force. (2) Toroidal plasma flow closely tracks the toroidal rotation of the magnetic tearing modes, including the fast changes that occur during sawtooth and locking events.