THOMSON SCATTERING DIAGNOSTIC FOR THE TDEV TOKAMAK

The Thomson scattering diagnostic system on the TdeV tokamak (R/a=87/27 cm, BT=1.5 T, Ip<300 kA) routinely monitors electron temperature (Te) and density (ne). The scattered light from a vertically oriented Nd:YAG laser beam (E=0.8 J, f=50 Hz, Δt=30 ns) is analyzed by six polychromators looking at different vertical positions. Each polychromator splits the light into three spectral bands by means of bandpass interference filters. Avalanche photodiode detectors are used to measure the scattered radiation. These detectors also measure the plasma radiation (including bremsstrahlung) between laser pulses. Two polychromators are optimized for edge temperature measurements (50<Te<400 eV), while the four others look at the main plasma (0.3<Te<4 keV). Sawtooth-correlated variations of Te(t) and ne(t) are measured by creating a time base locked-in on the sawtooth crash time of soft x-ray signals, so that we can remove the aliasing effect of undersampling T e. Most of the observed temperature fluctuations (20%) at the plasma center are sawtooth induced. © 1995 American Institute of Physics.