Effect of 3 T magnetic field on RF plasma sputtering in an ITER-relevant first mirror unit

Nuclear Fushion

article

Kunal Soni¹  Santhosh Iyyakkunnel²  Roland Steiner¹  Rodrigo Antunes¹  Lucas Moser¹  Oliver Bieri²  Laurent Marot¹  Ernst Meyer¹ 

[1] Department of Physics, University of Basel;Division of Radiological Physics, Department of Radiology, University Hospital Basel;Department of Biomedical Engineering, University of Basel;ITER Organization

关键词: RF plasma;    magnetic field;    first mirror;    notch filter;    ITER;   

DOI  :  10.1088/1741-4326/ac8b20

来源: Institute of Physics Publishing Ltd.

【 摘 要 】

The first mirror (FM) cleaning operations in ITER are expected to be executed in the presence of a sim 3T magnetic field. In the RF plasma cleaning configuration, this would have a significant influence on the plasma properties, ion energy, angle of incidence as well as flux spatial distribution. To this end, RF discharges were excited in an ITER-sized mock-up of a first mirror unit (FMU) consisting of a powered first mirror M1 and a grounded second mirror M2 placed in a homogeneous 3 T magnetic field. The plasma discharge was confined in a beam extending in the direction of the magnetic field, consequently wetting a limited portion of the FMU walls. In the DC-decoupled scheme (withoutλ /4 filter), this considerably influenced the self-bias voltageV _DC that develops on M1. Changing the angleαbetween M1 normal and magnetic field, modified the plasma wetted wall areaA _g and the resultingV _DC varied by over two orders of magnitude. Plasma exposure experiments were also done in the DC-coupled scheme (withλ /4 filter), wherein the angle and wetted surface determined the area of wall sputtered. Increasingαled to an increase in the sputtered wall areaA _g, and consequently the wall deposition on grounded M2. However, in all the cases M1 was entirely clean with the exception of edge deposits in some. In contrast, both M1 and M2 are coated with wall deposits in the absence of a magnetic field and a similar plasma exposure. The results show that plasma cleaning withλ /4 filter in a 3 T magnetic field at ITER could potentially prevent the parasitic wall deposition on FMs. The results also highlight the importance of FM orientation in the magnetic field and the wetted area in the plasma cleaning in both the DC-coupled and decoupled schemes within the ITER diagnostic systems.

【 授权许可】

Unknown