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Title: Tearing mode dynamics and locking in the presence of external magnetic perturbations

In normal operation, Madison Symmetric Torus (MST) [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch plasmas exhibit several rotating tearing modes (TMs). Application of a resonant magnetic perturbation (RMP) results in braking of mode rotation and, if the perturbation amplitude is sufficiently high, in a wall-locked state. The coils that produce the magnetic perturbation in MST give rise to RMPs with several toroidal harmonics. As a result, simultaneous deceleration of all modes is observed. In this paper, the measured TM dynamics is shown to be in qualitative agreement with a magnetohydrodynamical model of the RMP interaction with the TM [R. Fitzpatrick, Nucl. Fusion 33, 1049 (1993)] adapted to MST. To correctly model the TM dynamics, the electromagnetic torque acting on several TMs is included. Quantitative agreement of the TM slowing-down time was obtained for a kinematic viscosity in the order of ν k i n 10 20 m 2/s. Analysis of discharges with different plasma densities shows an increase of the locking threshold with increasing density. Modeling results show good agreement with the experimental trend, assuming a density-independent kinematic viscosity. Finally, comparison of the viscosity estimates in this paper to those made previously with other techniques in MST plasmas suggests the possibility that the RMP technique may allow for estimates of the viscosity over a broad range of plasmas in MST and other devices.
Authors:
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [1] ;  [2]
  1. KTH Royal Inst. of Technology, Stockholm (Sweden). Dept. of Fusion Plasma Physics. School of Electrical Engineering
  2. Univ. of Wisconsin, Madison, WI (United States). Dept. of Physics
Publication Date:
Grant/Contract Number:
FC02-05ER54814
Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 6; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
Univ. of Wisconsin, Madison, WI (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; isotopes; plasma confinement; plasma density; magnetic ordering; tokamaks; plasma devices; wave mechanics; viscosity; plasma interactions; torque
OSTI Identifier:
1471533
Alternate Identifier(s):
OSTI ID: 1256537

Fridström, R., Munaretto, S., Frassinetti, L., Chapman, B. E., Brunsell, P. R., and Sarff, J. S.. Tearing mode dynamics and locking in the presence of external magnetic perturbations. United States: N. p., Web. doi:10.1063/1.4953438.
Fridström, R., Munaretto, S., Frassinetti, L., Chapman, B. E., Brunsell, P. R., & Sarff, J. S.. Tearing mode dynamics and locking in the presence of external magnetic perturbations. United States. doi:10.1063/1.4953438.
Fridström, R., Munaretto, S., Frassinetti, L., Chapman, B. E., Brunsell, P. R., and Sarff, J. S.. 2016. "Tearing mode dynamics and locking in the presence of external magnetic perturbations". United States. doi:10.1063/1.4953438. https://www.osti.gov/servlets/purl/1471533.
@article{osti_1471533,
title = {Tearing mode dynamics and locking in the presence of external magnetic perturbations},
author = {Fridström, R. and Munaretto, S. and Frassinetti, L. and Chapman, B. E. and Brunsell, P. R. and Sarff, J. S.},
abstractNote = {In normal operation, Madison Symmetric Torus (MST) [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch plasmas exhibit several rotating tearing modes (TMs). Application of a resonant magnetic perturbation (RMP) results in braking of mode rotation and, if the perturbation amplitude is sufficiently high, in a wall-locked state. The coils that produce the magnetic perturbation in MST give rise to RMPs with several toroidal harmonics. As a result, simultaneous deceleration of all modes is observed. In this paper, the measured TM dynamics is shown to be in qualitative agreement with a magnetohydrodynamical model of the RMP interaction with the TM [R. Fitzpatrick, Nucl. Fusion 33, 1049 (1993)] adapted to MST. To correctly model the TM dynamics, the electromagnetic torque acting on several TMs is included. Quantitative agreement of the TM slowing-down time was obtained for a kinematic viscosity in the order of νkin≈10–20 m2/s. Analysis of discharges with different plasma densities shows an increase of the locking threshold with increasing density. Modeling results show good agreement with the experimental trend, assuming a density-independent kinematic viscosity. Finally, comparison of the viscosity estimates in this paper to those made previously with other techniques in MST plasmas suggests the possibility that the RMP technique may allow for estimates of the viscosity over a broad range of plasmas in MST and other devices.},
doi = {10.1063/1.4953438},
journal = {Physics of Plasmas},
number = 6,
volume = 23,
place = {United States},
year = {2016},
month = {6}
}