LOW POWER MODE EXCITATION FOR THE COLD TEST
OF NEXT GENERATION FUSION GYROTRONS
D. Wagner
Max-Planck-Institut für
Plasmaphysik, EURATOM Association,
85740 Garching, Germany
A. Arnold2), T.
Rzesnicki1), M. Thumm1,2)
1) Forschungszentrum
Karlsruhe, Association EURATOM-FZK,
Institut für Hochleistungsimpuls- und Mikrowellentechnik
76021 Karlsruhe, Germany
2) Universität Karlsruhe, Institut für
Höchstfrequenztechnik und Elektronik
76128 Karlsruhe, Germany
Next generation gyrotrons
for nuclear fusion plasma heating will employ coaxial cavities with an output
power in the range of 2 MW. To test the performance of their quasi-optical mode
converter, the gyrotron mode has to be excited at low power. Since the mode
spectrum in such cavities is very dense, a pure single-mode excitation by
direct coupling of a gaussian beam onto the mode specific caustic through the
translucent wall of a coaxial cavity would require a very high cavity quality
factor. Another possibility is to generate a different, well separated mode in
a cavity with much lower Q and the use of a second mode converter for
conversion to the gyrotron mode. Both principles are currently under test for
the rotating TE34,19 mode at 170 GHz. In this case the intermediate
mode is the degenerate whispering gallery mode TE93,2.