Effects of Relativistic and Absorption on ECE Spectra in High Temperature Tokamak Plasma

Abstract

Using the extended Trubnikov's expression for the fully relativistic Maxwellian in the case of oblique propagation to the magnetic field (Bt), electron cyclotron emission (ECE) spectra are calculated in a high temperature (Te) tokamak plasma. We investigate the ECE by changing the angles between the sight line and the equatorial plane or Bt direction. Feature of ECE spectra can be interpreted from the viewpoints of relativistic, Doppler and absorption effects. The downshift frequency variation due to the relativistic effect in the high field side (HFS) observation is bigger than that in the low field side observation. Absorption at the HFS plasma results in the deep dip at the HFS of fundamental, second and third harmonics in the ECE spectra. For the vertical observation, in the case of optically thin case, ECE spectra are similar to the emissivity profile, and when electron density (ne) is higher, ECE spectra are modified due to the absorption in plasma. Since the Bt, ne, Te increase in the case of the SlimCS DEMO reactor, the ECE spectra expands to high frequency emission (∼2000 GHz). So, ECE detector in the case of Fourier transform spectrometer system should be modified from present liquid He cooled InSb detector because of the detection of high frequency emission.