Abstract
The ASDEX Upgrade electron cyclotron resonance heating operates at 105 GHz and 140 GHz with flexible launching geometry and polarization. In 2016 four Gyrotrons with 10 sec pulse length and output power close to 1 MW per unit were available. The system is presently being extended to eight similar units in total. High heating power and high plasma density operation will be a part of the future ASDEX Upgrade experiment program. For the electron cyclotron resonance heating, an O-2 mode scheme is proposed, which is compatible with the expected high plasma densities. It may, however, suffer from incomplete single-pass absorption. The situation can be improved significantly by installing holographic mirrors on the inner column, which allow for a second pass of the unabsorbed fraction of the millimetre wave beam. Since the beam path in the plasma is subject to refraction, the beam position on the holographic mirror has to be controlled. Thermocouples built into the mirror surface are used for this purpose. As a protective measure, the tiles of the heat shield on the inner column were modified in order to increase the shielding against unabsorbed millimetre wave power.
Highlights
Progress has been made at the ASDEX Upgrade tokamak in controlling high power (Pheat 20 MW) discharges, where the power normalized to the major radius (R0=1.65 m) is approaching ITER relevant values [1]
The ASDEX Upgrade electron cyclotron resonance heating operates at 105 GHz and 140 GHz with flexible launching geometry and polarization
High heating power and high plasma density operation will be a part of the future ASDEX Upgrade experiment program
Summary
Progress has been made at the ASDEX Upgrade tokamak in controlling high power (Pheat 20 MW) discharges, where the power normalized to the major radius (R0=1.65 m) is approaching ITER relevant values [1]. At ASDEX Upgrade (AUG) the electron cyclotron resonance heating (ECRH) can serve for this purpose This system routinely operates at 105 and 140 GHz [5] and it is used for various wave heating schemes and current drive. With respect to high density and high heating power operation, an O-2 mode scheme at 140 GHz has been developed [6]. This scheme extends the range of accessible plasma densities above the X-2 cut-off, it may suffer from reduced single pass absorption of the order of 60-75% [7].
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