Electron Cyclotron Heating Applied to the JT-60U Tokamak

The application of the electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) to the JT-60U tokamak started in 1999. Because the power deposition by the electron cyclotron wave is very localized and controllable, the application of ECH/ECCD has been very attractive for the following recent studies in the JT-60U: (a) the extension of plasma performance toward high normalized beta (_N), (b) high bootstrap current fraction, and (c) long-pulse operation (65 s). Plasma produced in the studies aiming at advanced steady tokamak is considered to be in a kind of "self-organized state" with external input power by joule heating plus additional heating. The internal transport barrier that develops by the additional heating enhances the local bootstrap current by steep pressure gradient, and then the modified plasma current profile establishes a different confining poloidal magnetic field configuration from the initial configuration. In such experimental research in the JT-60U, the ECH contributes as an active tool for the plasma control to study the physical mechanisms of high- magnetohydrodynamic instability, internal transport barrier, current hole, and so on. Results of the ECH/ECCD applications in the JT-60U are briefly reviewed.