Misalignment of magnetic field in DIII-D assessed by post-mortem analysis of divertor targets

Nuclear Fushion

article

R. Masline¹  I. Bykov²  R.A. Moyer¹  A. Wingen³  J. Guterl²  D. Rudakov¹  W.R. Wampler⁴  H.Q. Wang²  J.G. Watkins⁴  D.M. Orlov¹ 

[1] University of California San Diego;General Atomics;Oak Ridge National Laboratory;Sandia National Laboratories

关键词: DIII-D;    tokamak;    divertor;    magnetic field;    misalignment;   

DOI  :  10.1088/1741-4326/ac9cf1

来源: Institute of Physics Publishing Ltd.

【 摘 要 】

We assess the toroidal magnetic fieldB _t asymmetry in DIII-D due to a misalignment of the toroidal field coils with respect to the poloidal magnetic field coils and vacuum vessel. The peak-to-peak variation of the divertor strike point (SP) radius is measured to be 1 cm, with ann= 1 toroidal pattern. We use the centre of a narrow carbon deposition band on tungsten-coated divertor tiles just inside the outer strike point (OSP) as a proxy for the divertor SP location. The band occurred in a series of reverseB _t discharges with the OSP positioned on the divertor inserts due to strongE × Bdrift transport of C from the inner to the outer SP through the private flux region. The variation in band radius (and hence the magnetic SP) is a (4.89 ± 0.31) mm shift toward (310 ± 4)° toroidal direction. These measurements agree well with previous measurements of the 3D magnetic field distribution (Luxon 2003Nucl. Fusion431813), simulations performed by themafotfield line integration code, and recent Langmuir probe measurements in the small-angle-slot (SAS) divertor (Watkinset al2019Nucl. Mater. Energy1846). Comparison of these measurements in the SAS divertor also indicates that there is the possibility of a tilt (in conjunction with the shift) of theB _t coil field of (0.04 ± 0.07)° towards the toroidal angle of (215 ± 25)°. Previous measurements suggested a field misalignment of (4.6 ± 0.3) mm in the 270° toroidal direction, and a tilt of (0.06 ± 0.02)° toward the 114° toroidal direction, which is similar to the results reported here. These studies will be important for better understanding the radial variation of the toroidal strike line in DIII-D, for designing the new generation of SAS divertor, and for developing an understanding of the impact of error fields on tokamaks with tightly baffled slot divertors.

【 授权许可】

Unknown