Effect of nonaxisymmetric magnetic perturbations on divertor heat and particle flux profiles in National Spherical Torus Experiment

J. W. Ahn, R. Maingi, J. M. Canik, A. G. McLean, J. D. Lore, J. K. Park, V. A. Soukhanovskii, T. K. Gray, A. L. Roquemore

Research output: Contribution to journalArticlepeer-review

20 Scopus citations

Abstract

Small, nonaxisymmetric magnetic perturbations generated by external coils have been found to break the axisymmetry of heat and particle flux deposition pattern in the divertor area in the National Spherical Torus Experiment (NSTX). This breaking by the applied 3-D field causes strike point splitting that is represented as local peaks and valleys in the divertor profiles. In case of n 3 fields application, the broken toroidal symmetry of the divertor profile shows 120 of spatial periodicity while data for n 1 fields provide a fully nonaxisymmetric heat and particle deposition. Field line tracing showed good agreement with the measured heat and particle flux profiles. Higher toroidal mode number (n 3) of the applied perturbation produced more and finer striations in the divertor profiles than in the lower mode number (n 1) case. Following the previous result of the intrinsic strike point splitting by the n 3 error fields Nucl. Fusion 50, 045010 (2010); J. Nucl. Mater. (2011), doi:10.1016/j.jnucmat.2011.01.115, result of the connection length profile from field line tracing identifies intrinsic error field as a possible source of the intrinsic splitting. In determining the strike point splitting pattern, q 95 is found to play an important role; higher q95 produces finer striations and induces higher fraction of heat flux to flow through the split strike point channels. Higher pedestal electron collisionality also made the striations in the D profile more pronounced in the given range of collisionality variation. The radial location of local peaks in the profiles during the triggered edge localized modes (ELMs) by the applied n 3 fields stays similar before and after the application. This shows that the heat flux from the triggered ELMs follows the mode number of the applied perturbation. The external magnetic perturbation can reattach detached divertor plasma, but this can be overcome by detaching the plasma with additional divertor gas puffing.

Original languageEnglish
Article number056108
JournalPhysics of Plasmas
Volume18
Issue number5
DOIs
StatePublished - May 2011

Fingerprint

Dive into the research topics of 'Effect of nonaxisymmetric magnetic perturbations on divertor heat and particle flux profiles in National Spherical Torus Experiment'. Together they form a unique fingerprint.

Cite this