Upgrades to the 4-strap ICRF Antenna in Alcator C-Mod
Authors: G. Schilling, J.C. Hosea, J.R. Wilson, W. Beck, R.L. Boivin, P.T. Bonoli, D. Gwinn, W.D. Lee, E. Nelson-Melby, M. Porkolab, R. Vieira, S.J. Wukitch, and J.A. Goetz
Date of PPPL Report: June 2001
Presented at: the 14th Topical Conference on Applications of Radio Frequency Powers in Plasmas in Oxnard, CA, May 7-9, 2001. Proceedings to be published by the American Institute of Physics (AIP).
A 4-strap ICRF antenna suitable for plasma heating and current drive has been designed and fabricated for the Alcator C-Mod tokamak. Initial operation in plasma was limited by high metallic impurity injection resulting from front surface arcing between protection tiles and from current straps to Faraday shields. Antenna modifications were made in 2/2000, resulting in impurity reduction, but low heating efficiency was observed when the antenna was operated in its 4-strap rather than a 2-strap configuration. Further modifications were made in 7/2000, with the installation of BN plasma-facing tiles and radiofrequency bypassing of the antenna backplane edges and ends to reduce potential leakage coupling to plasma surface modes. Good heating efficiency was now observed in both heating configurations, but coupled power was limited to 2.5 MW in H-mode, 3 MW in L-mode, by plasma-wall interactions. Additional modifications were started in 2/2001 and will be completed by this meeting. All the above upgrades and their effect on antenna performance will be presented.