Electron cyclotron emission measurements on T-10 with a grating polychromator

Abstract

Measurements of second-harmonic electron cyclotron emission (ECE) were performed on T-10 with a new six-channel grating polychromator, based on the conical diffraction principle. From these measurements, highly time-resolved (25–200 μs) and space-resolved (Δx = 4 cm) direct information on the relative electron temperature was obtained. The temperature scale was calibrated by Thomson scattering and soft-X-ray measurements. Third-harmonic measurements confirmed the second-harmonic Te-profiles and from these measurements an effective wall reflection coefficient r = 0.85 for ECE radiation was deduced. Sawtooth activity gave direct information on the inversion radius, which is related to the q = 1 surface. The location of the q = 1 surface was also independently calculated from Te-profiles, using Spitzer's resistivity. The agreement between the two approaches is good, if one assumes proximity of the inversion layer and the q = 1 surface. The change of the temperature profile observed during the fast relaxation of a sawtooth excludes the evolution to a flat profile in T-10 as predicted by Kadomtsev's full reconnection model. For correlation between the central electron density ne(0), the plasma current I, and the sawtooth period ∇τsaw, the experimental scaling law ∇τsaw = (0.8 ± 0.1) × 10−36 /I was found for plasmas with Te(0) ≈ 1.2 keV. An analysis of the propagation of the heat pulse generated by internal disruptions gave an electron heat conductivity profile i n agreement with profiles deduced from power balance calculations. The absolute magnitude of the electron heat conductivity corresponds to 0.6 times the Alcator-INTOR value. The evolution of the electron temperature profile during first-harmonic ordinary-mode electron cyclotron resonance heating (ECRH) is also given. It was observed for the first time that the sawteeth are stabilized during heating outside the q = 1 radius. Furthermore, it is concluded that not only does high-intensity ECRH heat the bulk of the resonant electrons, but additionally a small (⪅0.35%) population of suprathermal trapped electrons (Tst > 6 keV) is created. The effect of pellet injection on the temperature profile is also shown.