Measurements of Soft-X-Ray Spectra in Ecr-Heated Tokamak Plasmas and a Comparison with Fokker-Planck Simulations

Soft x-ray spectra have been measured in the RTP tokamak both during the ohmic phase for densities 2 X 10(19) less-than-or-equal-to n(e)(0) less-than-or-equal-to 7 X 10(19) m-3, and during the ECRH phase at a density n(e)(0) = 2 X 10(19) m-3 for several power levels. Large deformations of the soft x-ray spectra have been observed down to energies as low as hv almost-equal-to 4 keV making the determination of the electron temperature difficult. The soft x-ray spectrum of the Ohmic phase has an almost flat tail, while the spectrum during ECRH shows a strong deformation at energies several times thermal and has a moderate tail. Simulations of the experimental data have been performed using a (2 + 1)-dimensional bounce-average Fokker-Planck code and good agreement has been found. Using the simulated electron velocity distribution, some important quantities like the energy of the suprathermal population and the change in conductivity with respect to the neoclassical value have been determined