STATUS OF THE NEW MULTI-FREQUENCY ECRH SYSTEM

AT ASDEX UPGRADE

D. Wagner, T. Franke, F. Leuterer, F. Monaco, M. Münich, H. Schütz,

J. Stober, F. Volpe, H Zohm

Max-Plank-Institut für Plasmaphysik, EURATOM-IPP, Boltzmannstr.2, D-85748 Garching, Germany

¹M. Thumm, ²R. Heidinger, ²A. Meier, ¹G. Gantenbein, ¹J. Flamm

Forschungszentrum Karlsruhe, EURATOM-FZK,

¹Institut für Hochleistungsimpuls- und Mikrowellentechnik,

²Institut für Materialforschung,

PO Box 3640, D-76021 Karlsruhe, Germany

W. Kasparek, C. Lechte

Institut für Plasmaforschung, Universität Stuttgart, D-70569 Stuttgart, Germany

A.G. Litvak, G.G. Denisov, A. Cirkov

Institute of Applied Physics, 46 Ulyanov St., Nizhny Novgorod, 603950, Russia

E.M. Tai, L.G. Popov, V.O. Nichiporenko, V.E. Myasnikov, E.A. Solyanova, SA. Malygin

GYCOM Ltd, 46 Ulyanov St., Nizhny Novgorod, 603155, Russia

Abstract

The two-frequency gyrotron Odissey-2 is in routine operation in the new multi-frequency ECRH system at ASDEX Upgrade. It works at 105 and 140 GHz respectively. The two frequencies correspond to the resonances of a single disc CVD diamond window with a thickness of 1.8 mm. A further extension of the system is underway. In its final stage the system will consist of 4 gyrotrons with a total power up to 4 MW and a pulse length of 10 s. The next two gyrotrons Elisey-1 and Elisey-2 will also work at 105 and 140 GHz. A fourth gyrotron (Odissey-1) is planned to be a multi-frequency gyrotron with two additional frequencies between 105 and 140 GHz. It requires therefore broadband vacuum windows both at the gyrotron and at the torus. Since the gyrotron emits a linearly polarized beam a Brewster window can be applied. At the torus a double disc window was installed which is also transparent for elliptically polarized beams. In an in-situ measurement its reflectivity was successfully tested.

The transmission line consists mainly of non-evacuated oversized corrugated waveguides (I.D. 87mm). Each gyrotron is connected to a Matching Optic Units (MOU) containing an individual pair of phase correcting mirrors for each frequency. The following quasi-optical components, a pair of polarizers as well as focusing mirrors, work at all frequencies and couple the beam either to the waveguides or to short pulse calorimetric or to long-pulse loads. The measured transmission loss is below 10 % and in good agreement with theory. Occasional arcing problems exist mainly on polarizers and in a mirror box at the torus where dust particles can be collected on the mirror surfaces.

The system includes also fast steerable launchers in the torus. They use a fast spindle drive with magnetic vacuum feed throughs. The launchers were successfully tested during regular operating conditions. A fast feedback control for the suppression of Neoclassical Tearing Modes (NTM) is under development. It will enable to suppress NTMs on a time scale faster than their growth time (~100 ms at ASDEX Upgrade). The control of the launcher movement by the fast control system of ASDEX Upgrade was successfully tested. The system is also a crucial tool to avoid the accumulation of tungsten in the plasma center since ASDEX Upgrade is operated with a fully tungsten-covered inner wall. At 105 GHz the gyrotron is used as a source for a Collective Thomson Scattering (CTS) diagnostic. Here the second transmission line is used to receive the scattered signal. Plasma startup using ECRH both at 105 and 140 GHz has also been demonstrated.