MEASUREMENT OF FAST-ION DYNAMICS IN A HIGH-TEMPERATURE PLASMA

Measurement of fast changes and fluctuations in ion flow and/or temper ature 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: measuremen ts from two different chordal views of the plasma can be made simultan eously. All 32 spectral channels on the exit plane of the duo-spectrom eter are read out and digitized at 1 MHz in parallel to achieve high t ime resolution. We have obtained these key results: (1)The toroidal ve locity fluctuations of the plasma are coherent with the large-scale ma gnetic tearing modes; during a sawtooth event the scalar product of (v ) over tilde(phi) and (B) over tilde(r), is similar to that expected f or the MHD dynamo electromotive force. (2) Toroidal plasma flow closel y tracks the toroidal rotation of the magnetic tearing modes, includin g the fast changes that occur during sawtooth and locking events.