skip to main content


Title: Impact of toroidal and poloidal mode spectra on the control of non-axisymmetric fields in tokamaks

In several tokamaks, non-axisymmetric magnetic field studies show that applied magnetic fields with a toroidal harmonic n = 2 can lead to disruptive n = 1 locked modes. In Ohmic plasmas, n = 2 magnetic reconnection thresholds in otherwise stable discharges are readily accessed at edge safety factors q ~ 3, low density, and low rotation. Similar to previous studies with n = 1 fields, the thresholds are correlated with the “overlap” field computed with the IPEC code. The overlap field quantifies the plasma-mediated coupling of the external field to the resonant field. Remarkably, the “critical overlap fields” at which magnetic islands form are similar for applied n =1 and 2 fields. The critical overlap field increases with plasma density and edge safety factor but is independent of the toroidal field. Poloidal harmonics m > nq dominate the drive for resonant fields while m < nq harmonics have a negligible impact. This contrasts with previous results in H-mode discharges at high plasma pressure in which the toroidal angular momentum is sensitive to low poloidal harmonics. Altogether, these results highlight unique requirements for n > 1 field control including the need for multiple rows of coils to control selected plasma parametersmore » for specific functions (e.g., rotation control or ELM suppression).« less
ORCiD logo [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [2] ;  [7] ; ORCiD logo [2] ;  [8] ;  [8] ;  [5] ;  [2] ;  [9] ;  [10] ;  [5] ;  [4] ;  [5]
  1. General Atomics, San Diego, CA (United States); U.S. Dept. of Energy, Washington, D.C. (United States)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  3. Univ. di Padova, Padova (Italy)
  4. Chinese Academy of Sciences, Hefei (People's Republic of China)
  5. General Atomics, San Diego, CA (United States)
  6. KTH Royal Institute of Technology, Stockholm (Sweden)
  7. Columbia Univ., New York, NY (United States)
  8. National Fusion Research Institute, Daejeon (South Korea)
  9. Consorzio RFX, EURATOM-ENEA Assoc., Padova (Italy)
  10. Univ. of California San Diego, La Jolla, CA (United States)
Publication Date:
Grant/Contract Number:
FC02-04ER54698; AC02-09CH11466; FG02-04ER54761; FG02-05ER54809
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 5; Journal ID: ISSN 1070-664X
American Institute of Physics (AIP)
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
Contributing Orgs:
JET Contributors
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1361859