Electron temperature measurements during electron cyclotron heating on pdx using a ten-channel grating polychromator

First-harmonic electron cyclotron heating (ECH) experiments (P_RF≈ 80 kW, f ≅ 60 GHz) have been conducted on the Princeton Divertor Experiment (PDX) (R =137 cm, a ≈ 40 cm). Off-axis (≈ 4 cm) location of the resonance zone resulted in heating without sawtooth or m = 1 activity. However, heating with the resonance zone at the plasma centre caused very-large-amplitude sawteeth accompanied by strong m = 1 activity: ΔT/TMAX ≈ 0.41, sawtooth period ≈ 4 ms, m = 1 period ≅ 90 μs (11 kHz). This is the first time such intense MHD activity driven by low power (PRF/POH ^ 0.35) ECH has been observed. (For both cases, there was no sawtooth activity in the Ohmic phase of the discharge before ECH) At very low densities, there is a clear indication that a superthermal electron population is created during ECH. - The electron temperature evolution was monitored using a grating polychromator which measured second-harmonic electron cyclotron emission from the low field side of the tokamak. Interference from the high-power heating pulse on the broadband detectors in the grating instrument was eliminated by using a waveguide filter in the transmission line which brought the emission signal to the grating instrument.