Operation Experience with the ASDEX Upgrade ECRH System

Abstract In 1989 the planning for a 140-GHz, 2-MW, 2-s electron cyclotron resonance heating system for ASDEX Upgrade started. These plans were finally approved in 1993. The system comprises four gyrotrons with four separate transmission lines and launchers. Although a 0.5-s test gyrotron was already installed in autumn 1994, it was only in summer 1997 when the first gyrotron of the final system was ready for use in the experiments, and in spring 2000 the system was completed with all four gyrotrons. This paper reviews the experience gained in construction and operation of this system. In particular, we describe how we solved problems with external magnetic fields affecting gyrotron operation. These fields originate both from the tokamak and from the cryomagnet of adjacent gyrotrons. We also report about the gyrotron performance, our techniques for the alignment of the transmission lines, the calibration of the polarizer mirrors, and the power calibration.

[1]  W. Kasparek,et al.  Microwave reflection properties of grooved metallic mirrors , 1992 .

[2]  H. P. Laqua,et al.  20 years of ECRH at W7-A and W7-AS , 2003 .

[3]  A. Manini,et al.  Density response to central electron heating: theoretical investigations and experimental observations in ASDEX Upgrade , 2004 .

[4]  J. Stober,et al.  Influence of the heating profile on impurity transport in ASDEX Upgrade , 2003 .

[5]  A. Manini,et al.  Role of Te/Ti and ∇vtor in ion heat transport of ASDEX Upgrade H-mode plasmas , 2006 .

[6]  F. Leuterer,et al.  Enhancement of the stabilization efficiency of a neoclassical magnetic island by modulated electron cyclotron current drive in the ASDEX upgrade tokamak. , 2007, Physical review letters.

[7]  F. Imbeaux,et al.  Modelling of ECH Modulation Experiments in ASDEX Upgrade with an Empirical Critical Temperature Gradient Length Transport Model , 2001 .

[8]  G. Gantenbein,et al.  Millimetre-Wave Technology and Performance of the 2 MW, 140 Ghz ECRH System on the Stellarator W7-AS , 1995 .

[9]  G. Gantenbein,et al.  Neoclassical tearing modes and their stabilization by electron cyclotron current drive in ASDEX Upgrade , 2001 .

[10]  Julien Fuchs,et al.  Impurity behaviour in the ASDEX Upgrade divertor tokamak with large area tungsten walls , 2002 .

[11]  F. Leuterer,et al.  The ECRH system of ASDEX Upgrade , 2001 .

[12]  F. Leuterer,et al.  Electron heat transport in ASDEX Upgrade: experiment and modelling , 2003 .

[13]  J. Stober,et al.  Experimental evidence for gradient length-driven electron transport in tokamaks. , 2001, Physical review letters.

[14]  Manfred Thumm,et al.  Recent advanced technology in electron cyclotron heating systems , 1995 .

[15]  F. Leuterer,et al.  Experimental characterization of the electron heat transport in low-density ASDEX upgrade plasmas. , 2001, Physical review letters.

[16]  F. Leuterer,et al.  Broadband Polarizers for High-Power Multi-Frequency ECRH Systems , 2005 .

[17]  F. Leuterer,et al.  Modulated ECRH power deposition in ASDEX Upgrade , 2003 .

[18]  G. Gantenbein,et al.  Status of the new multi-frequency ECRH system for ASDEX Upgrade , 2007, 2007 IEEE 34th International Conference on Plasma Science (ICOPS).

[19]  F. Leuterer,et al.  Response of internal transport barriers to central electron heating and current drive on ASDEX Upgrade , 1999 .

[20]  Gunter,et al.  Complete suppression of neoclassical tearing modes with current drive at the electron-cyclotron-resonance frequency in ASDEX upgrade tokamak , 2000, Physical review letters.

[21]  F. Leuterer,et al.  Experimental study of trapped-electron-mode properties in tokamaks: threshold and stabilization by collisions. , 2005, Physical review letters.

[22]  G. G. Denisov,et al.  3D wavebeam field reconstruction from intensity measurements in a few cross sections , 1995 .

[23]  Gunter,et al.  Simultaneous attainment of high electron and ion temperatures in discharges with internal transport barriers in ASDEX upgrade , 2000, Physical review letters.

[24]  W. Suttrop,et al.  ECRH power disposition studies in ASDEX Upgrade , 2002 .

[25]  Gerd Gantenbein,et al.  The New Multifrequency Electron Cyclotron Resonance Heating System for ASDEX Upgrade , 2007 .

[26]  G. Gantenbein,et al.  Experience with the ECRH System of ASDEX Upgrade , 2001 .

[27]  N. Gallagher,et al.  Relative phases of electromagnetic waves diffracted by a perfectly conducting rectangular-grooved grating. , 1988, Journal of the Optical Society of America. A, Optics and image science.

[28]  J. Stober,et al.  Present Status of the New Multifrequency ECRH System for ASDEX Upgrade , 2008, IEEE Transactions on Plasma Science.

[29]  Manfred Thumm,et al.  Passive high-power microwave components , 2002 .