Poloidal variation of high-Z impurity density due to hydrogen minority ion cyclotron resonance heating on Alcator C-Mod

• Main Authors: Reinke, Matthew Logan (Contributor), Rice, John E. (Contributor), Howard, Nathaniel Thomas (Contributor), Bader, Andrew (Contributor), Wukitch, Stephen James (Contributor), Lin, Yijun (Contributor), Pace, David C. (Contributor), Podpaly, Yuri (Contributor), Hutchinson, Ian Horner (Author), Hubbard, Amanda E (Author), Hughes Jr, Jerry (Author)
• Other Authors: Massachusetts Institute of Technology. Department of Nuclear Science and Engineering (Contributor), Massachusetts Institute of Technology. Plasma Science and Fusion Center (Contributor), Koch Institute for Integrative Cancer Research at MIT (Contributor), Hutchinson, Ian (Contributor), Hutchinson, Ian H. (Contributor), Hubbard, Amanda E. (Contributor), Hughes, Jerry W. (Contributor)
• Format: Article
• Language: English
• Published: IOP Publishing, 2014-01-17T15:25:28Z.
• Subjects: Article
• Online Access: Get fulltext

In the Alcator C-Mod tokamak, strong, steady-state variations of molybdenum density within a flux surface are routinely observed in plasmas using hydrogen minority ion cyclotron resonant heating. In/out asymmetries, up to a factor of 2, occur with either inboard or outboard accumulation depending on the major radius of the minority resonance layer. These poloidal variations can be attributed to the impurity's high charge and large mass in the neoclassical parallel force balance. The large mass enhances the centrifugal force, causing outboard accumulation while the high charge enhances ion-impurity friction and makes impurities sensitive to small poloidal variations in the plasma potential. Quantitative comparisons between existing parallel high-Z impurity transport theories and experimental results for r/a < 0.7 show good agreement when the resonance layer is on the high-field side of the tokamak but disagree substantially for low-field side heating. Ion-impurity friction is insufficient to explain the experimental results, and the accumulation of impurity density on the inboard side of flux surface is shown to be driven by a poloidal potential variation due to magnetic trapping of non-thermal, cyclotron heated minority ions. Parallel impurity transport theory is extended to account for cyclotron effects and shown to agree with experimentally measured impurity density asymmetries.
United States. Dept. of Energy (Agreement DE-FC02-99ER54512)
United States. Dept. of Energy. Office of Fusion Energy Sciences (Postdoctoral Research Program)