skip to main content

DOE PAGESDOE PAGES

Title: Error field detection in DIII-D by magnetic steering of locked modes

Optimal correction coil currents for the n = 1 intrinsic error field of the DIII-D tokamak are inferred by applying a rotating external magnetic perturbation to steer the phase of a saturated locked mode with poloidal/toroidal mode number m/n = 2/1. The error field is detected non-disruptively in a single discharge, based on the toroidal torque balance of the resonant surface, which is assumed to be dominated by the balance of resonant electromagnetic torques. This is equivalent to the island being locked at all times to the resonant 2/1 component of the total of the applied and intrinsic error fields, such that the deviation of the locked mode phase from the applied field phase depends on the existing error field. The optimal set of correction coil currents is determined to be those currents which best cancels the torque from the error field, based on fitting of the torque balance model. The toroidal electromagnetic torques are calculated from experimental data using a simplified approach incorporating realistic DIII-D geometry, and including the effect of the plasma response on island torque balance based on the ideal plasma response to external fields. This method of error field detection is demonstrated in DIII-D discharges, andmore » the results are compared with those based on the onset of low-density locked modes in ohmic plasmas. Furthermore, this magnetic steering technique presents an efficient approach to error field detection and is a promising method for ITER, particularly during initial operation when the lack of auxiliary heating systems makes established techniques based on rotation or plasma amplification unsuitable.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [1]
  1. Columbia Univ., New York, NY (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Grant/Contract Number:
FC02-04ER54698
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 54; Journal Issue: 3; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
tokamak; error field; locked mode
OSTI Identifier:
1352308

Shiraki, Daisuke, La Haye, Robert J., Logan, Nikolas C., Strait, Edward J., and Volpe, Francesco A.. Error field detection in DIII-D by magnetic steering of locked modes. United States: N. p., Web. doi:10.1088/0029-5515/54/3/033006.
Shiraki, Daisuke, La Haye, Robert J., Logan, Nikolas C., Strait, Edward J., & Volpe, Francesco A.. Error field detection in DIII-D by magnetic steering of locked modes. United States. doi:10.1088/0029-5515/54/3/033006.
Shiraki, Daisuke, La Haye, Robert J., Logan, Nikolas C., Strait, Edward J., and Volpe, Francesco A.. 2014. "Error field detection in DIII-D by magnetic steering of locked modes". United States. doi:10.1088/0029-5515/54/3/033006. https://www.osti.gov/servlets/purl/1352308.
@article{osti_1352308,
title = {Error field detection in DIII-D by magnetic steering of locked modes},
author = {Shiraki, Daisuke and La Haye, Robert J. and Logan, Nikolas C. and Strait, Edward J. and Volpe, Francesco A.},
abstractNote = {Optimal correction coil currents for the n = 1 intrinsic error field of the DIII-D tokamak are inferred by applying a rotating external magnetic perturbation to steer the phase of a saturated locked mode with poloidal/toroidal mode number m/n = 2/1. The error field is detected non-disruptively in a single discharge, based on the toroidal torque balance of the resonant surface, which is assumed to be dominated by the balance of resonant electromagnetic torques. This is equivalent to the island being locked at all times to the resonant 2/1 component of the total of the applied and intrinsic error fields, such that the deviation of the locked mode phase from the applied field phase depends on the existing error field. The optimal set of correction coil currents is determined to be those currents which best cancels the torque from the error field, based on fitting of the torque balance model. The toroidal electromagnetic torques are calculated from experimental data using a simplified approach incorporating realistic DIII-D geometry, and including the effect of the plasma response on island torque balance based on the ideal plasma response to external fields. This method of error field detection is demonstrated in DIII-D discharges, and the results are compared with those based on the onset of low-density locked modes in ohmic plasmas. Furthermore, this magnetic steering technique presents an efficient approach to error field detection and is a promising method for ITER, particularly during initial operation when the lack of auxiliary heating systems makes established techniques based on rotation or plasma amplification unsuitable.},
doi = {10.1088/0029-5515/54/3/033006},
journal = {Nuclear Fusion},
number = 3,
volume = 54,
place = {United States},
year = {2014},
month = {2}
}