Electron cyclotron resonance heating (ECRH) is a mature technology that has
progressed constantly over a period of forty years, particularly as a tool in
magnetic confinement fusion. As with other heating methods, this technique has
seen a steady increase in the sophistication of its applications, from bulk heating
through profile tailoring and finally to distribution function engineering. By
comparison with other techniques, ECRH presents the significant advantages
of good coupling, localized power deposition, easy launching and precise
directionality. This paper reviews some recent applications related to third
harmonic ECRH and highlights the role of the relaxation dynamics of
suprathermal electrons, both in real space and in velocity space, in regulating the
overall effect of ECRH on fusion plasmas. A technique for direct visualization
of these relaxation phenomena, using modulated ECRH, is described and
demonstrated. |