Fusion Science and Technology / Volume 55 / Number 1 / January 2009 / Pages 94-107
Technical Paper / Electron Cyclotron Emission and Electron Cyclotron Resonance Heating
The development of electron cyclotron resonance heating (ECRH)-electron cyclotron current drive (ECCD) as a tool for suppression of plasma instabilities requires that the millimeter-wave beams used for testing magnetohydrodynamic (MHD) stabilization schemes for ITER be able to follow magnetic island position in real time. In the FTU tokamak, the design of a new ECRH fast-steerable launcher will enable a fast-controlled deposition at a precise poloidal location and the inclusion of the mirror motion in a feedback loop aimed at MHD stabilization. Two of the four existing transmission lines will be switched to the new launcher located in a different equatorial port. It will launch two independent beams with radius in the plasma changeable between 17 and 28 mm, in order to control the deposited power density. Real-time control of the poloidal steering requires high acceleration, speed, and positioning precision of the last mirror. Additionally, oblique toroidal injection at precise angles will allow current profile shaping through controlled ECCD and heating of overdense plasmas (ne > 2.4 × 1020 m-3) using electron Bernstein waves. For optimal O-X conversion, the required toroidal angle, estimated with dedicated beam-tracing calculations, is close to ±38.5 deg, near the upper limit in the toroidal steering angle. The launch requirements and their impact on the launcher design phase are presented in the paper.