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.
A localized force-free current is proposed as a model for the observed coronal loops. An upper limit for the growth rate of kink instabilities in this model is found by solving numerically, in cylinder symmetry, the MHD equation of motion, with the boundary condition/3 = 0 outside the loop.For various current densities a spectrum of kinks is found. These instabilities will disrupt the loops that are long or strongly twisted, on a time scale of a few seconds.
The low-/3coronal loop model of Sillen and Kattenberg (1980) is extended to include a surrounding current-free plasma. We calculated the dispersion curves of kink modes by solving the linearized MHDequations of motion.We found a strong stabilizing influence on the growth rates of kink instabilities due to the surrounding plasma.In loops that are thick, have small current densities and that have a high density and a low magnetic field strength the growth times for kinks become of the order of days.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.