advanced gyrotron collector sweeping

with smooth power distribution



V. Erckmann1, M. Schmid2, H.P. Laqua1, G. Dammertz2, S. Illy2, H. Braune1, F. Hollmann1,

W. Kasparek3, G. Michel1, F. Noke1, F. Purps1,
ECRH groups at IPP Greifswald1, FZK Karlsruhe2, and IPF Stuttgart1.



1Max-Planck-Institut für Plasmaphysik (IPP), EURATOM-Association, D-17491 Greifswald, Germany

2Forschungszentrum Karlsruhe, Association EURATOM-FZK, IHM, D-76021 Karlsruhe, Germany

3Institut für Plasmaforschung, Universität Stuttgart, Pfaffenwaldring 31, D-70569 Stuttgart, Germany



Present day high power cw gyrotrons operate with an rf-power of typically 1 MW and efficiencies of 35-50 % [1,2], thus typically 1-2 MW power remains in the spent electron-beam and must be dumped in the gyrotron-collector. Vertical magnetic Field Sweeping (VFS) is a well established method and commonly used to bring the local collector power density down to acceptable values. A less established method is ‘Transverse Field Sweeping’ (TFS), which was invented in Russia [3] and further investigated at FZK [4].  TFS proved to have a power capability comparable to VFS. The electron beam power distribution obtained with either method, however, shows pronounced maxima and the collectors operate at the technical limits. As these maxima determine the overall collector capability, we have investigated a new collector sweeping method, which generates a homogenous power deposition profile thus enhancing the total heat load capability of state of the art collectors significantly. The experiments were performed using a commercial THALES Gyrotron TH 1507 (140 GHz, 1 MW, cw), the results are reported. The application of the new sweeping method may be attractive for existing tubes, because they can be operated with higher safety margin (higher lifetime), as well as for future ITER gyrotrons with higher rf-power (towards 2 MW), because existing collector designs may already satisfy the additional power demands.



[1]     G. Dammertz, S. Alberti, A. Arnold, E. Borie, et al., IEEE Trans. Plasma Science 30 (2002) 808-818

[2]     K. Felch, M. Blank, P. Borchard, P. Cahalan, S. Cauffman, T.S. Chu and H. Jory,

         Journal of Physics:  Conference Series 25 (2005) pp. 13-23.

[3]     private communication

[4]     M. Schmid, S. Illy, G. Dammertz, V. Erckmann, M. Thumm:
Transverse Field Collector Sweep System for high power CW Gyrotrons,

to be published in Fusion Science and Technology