Author/Authors :
Bobkov، نويسنده , , Vl. and Braun، نويسنده , , F. and Dux، نويسنده , , R. and Giannone، نويسنده , , L. and Herrmann، نويسنده , , A. and Kallenbach، نويسنده , , A. and Müller، نويسنده , , H.W. and Neu، نويسنده , , R. and Noterdaeme، نويسنده , , J.-M. and Pütterich، نويسنده , , Th. and Rohde، نويسنده , , V.، نويسنده ,
Abstract :
In the 2007 and early part of 2008 experimental campaigns, ASDEX Upgrade operated with full tungsten (W) wall without boronization. Use of ICRF power results in a significant increase of W source. Low temperature conditions at the plasma facing components, achieved by a large clearance between the separatrix and the antenna (>6 cm) and by elevated gas puff rates ( > 5 × 10 21 s - 1 ) help to lower W sputtering yield during ICRF. Operation of neighboring ICRF antennas at the phase difference close to −90° can lead to a reduction in the W source. However, a reduction of parallel near-fields by antenna design is needed to further minimize the W source. A relation has been established between the HFSS code calculations predicting a dominant role of box currents in the formation of parallel antenna near-fields and the experiment. The shapes of the measured vertical profile of effective sputtering yields and the calculated sheath driving voltages show a qualitative agreement. This confirms that the existing tools are a good basis to design an improved antenna.
