Generation and heating of toroidally confined overdense plasmas with 2.45 GHz microwaves

A. Köhn, G. Birkenmeier, E. Holzhauer, M. Ramisch, U. Stroth

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Abstract

In the stellarator TJ-K, overdense low-temperature plasmas are created by means of microwaves at 2.45 GHz. Extensive studies have been carried out to understand the heating process. The plasma breakdown at the cyclotron resonance layer has been directly observed with a multiple Langmuir probe array. Profile measurements indicate power deposition at the plasma boundary, where the upper hybrid resonance (UHR) is located. This result is confirmed by full-wave simulations which emphasize the importance of the vacuum vessel to increase the absorbed microwave power due to multiple reflections. Further indications for heating at the UHR layer are found by measurements of the wave electric field of the incident microwave and by power-modulation experiments. In contrast to similar experiments, no indication for heating by electron Bernstein waves was found.

Original languageEnglish
Article number035003
JournalPlasma Physics and Controlled Fusion
Volume52
Issue number3
DOIs
StatePublished - 2010
Externally publishedYes

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