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.

Tokamak heat transport – a study of heat pulse propagation in JET

“…The potential of heat pulse analysis to derive values of Xe nc , and hence T E nc , allows us to examine various T E scaling laws more critically than is possible on the basis of power balance analysis. We consider the family of scaling laws: T E = const-P" 7 where the constant may contain global plasma parameters. The value of 7 is usually around 7 = 0.5 (e.g.…”

“…Generally, the value for x e as derived from heat pulse analysis, x" P » is found to exceed the value x°L 0 as derived from a global power balance analysis. This discrepancy ranges from a factor of 1 to 4 (T-10, FT, ISX-B, JET, Refs [3][4][5][6][7]) to up to a factor of 20 (TFTR, Ref. [8]).…”

Electron Cyclotron Waves

“…Most tokamaks equipped with ECRH report a lengthening of the sawtooth period or complete sawtooth stabilization by ECRH near the sawtooth inversion radius (see, e.g. the early experiments on T-10 [32] or the more recent and more detailed results from TCV [33] and ASDEX Upgrade [34]). The sawtooth crash is triggered when the m=1, n=1 internal kink mode is destabilized [35].…”

The effects of kinetic instabilities on the electron cyclotron emission from runaway electrons

“…Unlike the forward method used in previous codes like HORACE [19], in our model we use a backward method to calculate the ECE power based on the reciprocal theorem [20], an innovative approach which separates the wave emission and absorption by introducing an artificial wave propagating against the radiation direction along the same ray path. The reflection loss and the polarization scrambling [21][22][23] of the waves are included in the reciprocal calculations. The RE distribution function is calculated using a newly-developed kinetic simulation model, coupled to a kinetic instability calculation framework using the quasilinear diffusion model [24].…”