A New Launcher for Real-Time ECRH Experiments on FTU

Abstract 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.

[1]  H. Laqua,et al.  Electron Bernstein wave heating and diagnostic , 2007 .

[2]  L. Rosenhead.  Conduction of Heat in Solids , 1947, Nature.

[3]  A. Popov,et al.  Conversion of normal waves in the electron-cyclotron frequency range at the critical surface in a cold anisotropic plasma inhomogeneous in two dimensions , 2007 .

[4]  A. Popov.  On O–X mode conversion in spherical tokamaks , 2007 .

[5]  G. G. Denisov,et al.  RF Analysis of ITER Remote Steering Antenna for Electron-Cyclotron Plasma Heating , 2001 .

[6]  S. Nowak,et al.  Three-dimensional propagation and absorption of high frequency Gaussian beams in magnetoactive plasmas , 1994 .

[7]  G. Giruzzi,et al.  Impact of bulk non-Maxwellian electrons on electron temperature measurements (invited) , 2003 .

[8]  G. Granucci,et al.  Short-pulse Calorimetric Load for High Power Millimeter-wave Beams , 2004, Infrared and Millimeter Waves, Conference Digest of the 2004 Joint 29th International Conference on 2004 and 12th International Conference on Terahertz Electronics, 2004..

[9]  F. Volpe,et al.  Critical issues highlighted by collective Thomson scattering below electron cyclotron resonance in FTU , 2006 .

[10]  S. Kaye,et al.  Oblique electron cyclotron emission for electron distribution studies (invited) , 1997 .

[11]  J. Preinhaelter,et al.  Penetration of high-frequency waves into a weakly inhomogeneous magnetized plasma at oblique incidence and their transformation to Bernstein modes , 1973, Journal of Plasma Physics.

[12]  G. Gantenbein,et al.  Performance of a remote steering antenna for ECRH/ECCD applications in ITER using a four-wall corrugated square waveguide , 2003 .

[13]  É. Suvorov,et al.  On the influence of 2D inhomogeneity on electromagnetic mode conversion near the cut-off surfaces in magnetized plasmas , 2006, 2007 International Kharkov Symposium Physics and Engrg. of Millimeter and Sub-Millimeter Waves (MSMW).

[14]  C. Sozzi,et al.  ECRH antenna at 140 GHz on FTU Tokamak , 2001 .

[15]  B. Cockeram,et al.  The development and testing of emissivity enhancement coatings for themophotovoltaic (TPV) radiator applications , 1999 .

[16]  V. Erckmann,et al.  A fast switch, combiner and narrow-band filter for high-power millimetre wave beams , 2008 .

[17]  D. Ćirić,et al.  Development and tests of B4C-covered heat shields for TJ-II , 2001 .

[18]  Howard Martin Stainer.  Waves in a Plasma in a Magnetic Field. , 1966 .

[19]  C. P. Moeller,et al.  A METHOD OF REMOTELY STEERING A MICROWAVE BEAM LAUNCHED FROM A HIGHLY OVERMODED CORRUGATED WAVEGUIDE , 1998 .

[20]  R. Neu,et al.  Evaluation of vacuum plasma-sprayed boron carbide protection for the stainless steel first wall of WENDELSTEIN 7-X , 2004 .

[21]  Alessandro Bruschi,et al.  Chapter 11: The Heating and Current Drive Systems of the FTU , 2004 .

[22]  William Bin,et al.  High-Power Millimeter-Wave Calorimetric Beam Absorbers , 2008 .

[23]  E. Mjølhus,et al.  Coupling to Z mode near critical angle , 1984, Journal of Plasma Physics.

[24]  J. R. Martin-Solis,et al.  Disruption avoidance in the Frascati Tokamak Upgrade by means of magnetohydrodynamic mode stabilization using electron-cyclotron-resonance heating. , 2008, Physical review letters.

[25]  É. Suvorov,et al.  Effects of Two-Dimensional Inhomogeneity in O-X Mode Conversion in Tokamak Plasmas , 2008 .

[26]  A. Bruschi,et al.  Beam Combination and Routing at High Power with a Ring-Type Waveguide Millimeter-Wave Resonator , 2008 .

[27]  S. Cirant.  Overview of Electron Cyclotron Heating and Electron Cyclotron Current Drive Launcher Development in Magnetic Fusion Devices , 2008 .

[28]  G. Granucci,et al.  ECH/ECCD Applications for MHD Studies and Automatic Control in FTU Tokamak , 2008 .