Jena 2013 – wissenschaftliches Programm
P 17.2: Poster
Donnerstag, 28. Februar 2013, 14:00–16:00, Poster EG
Electron Bernstein wave heating at the stellarator TJ-K — •Alf Köhn, Udo Höfel, Eberhard Holzhauer, Fabian Olbrich, Stefan Wolf, and Mirko Ramisch — Institut für Plasmaforschung, Universität Stuttgart
If the plasma density exceeds the cutoff density of the injected microwaves it becomes inaccessible to them and the waves are reflected. Conventional O- or X-mode heating at the electron cyclotron resonance frequency (ECRF) can no longer take place. Electron Bernstein waves (EBWs) can be used to overcome this limitation: no high-density cutoff exists for these waves and they are very well absorbed at the ECRF and its harmonics. Since this applies to high- and low-temperature plasmas, there exists a wide range of possible applications for them. Due to their electrostatic nature, however, they need to be coupled to injected electromagnetic waves.
In the stellarator TJ-K, overdense plasmas are routinely created by microwave heating at 8 GHz. Appropriate shaping of the injected microwave beam allows to efficiently excite EBWs provided that the fundamental ECRF is located inside the confinement region. As soon as the EBW heating sets in, a sudden increase in the plasma density is observed illustrating the efficiency of this heating mechanism. During a discharge, the background magnetic field can be ramped down by almost a factor of 5 and EBW heating at high harmonics of the ECRF can be investigated. With decreasing magnetic field a reduction in the turbulence level of the plasma density is observed.