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Title: High-resolution disruption halo current measurements using Langmuir probes in Alcator C-Mod

Journal Article · · Nuclear Fusion
ORCiD logo [1];  [1];  [2];  [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Massachusetts Institute of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
  2. Research Science Institute, McLean, VA (United States)
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We report halo currents generated during disruptions on Alcator C-Mod have been measured with Langmuir 'rail' probes. These rail probes are embedded in a lower outboard divertor module in a closely-spaced vertical (poloidal) array. The dense array provides detailed resolution of the spatial dependence (~1 cm spacing) of the halo current distribution in the plasma scrape-off region with high time resolution (400 kHz digitization rate). As the plasma limits on the outboard divertor plate, the contact point is clearly discernible in the halo current data (as an inversion of current) and moves vertically down the divertor plate on many disruptions. These data are consistent with filament reconstructions of the plasma boundary, from which the edge safety factor of the disrupting plasma can be calculated. Additionally, the halo current 'footprint' on the divertor plate is obtained and related to the halo flux width. The voltage driving halo current and the effective resistance of the plasma region through which the halo current flows to reach the probes are also investigated. Estimations of the sheath resistance and halo region resistivity and temperature are given. This information could prove useful for modeling halo current dynamics.

Research Organization:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Grant/Contract Number:
FC02-99ER54512
OSTI ID:
1540530
Report Number(s):
NF-102019.R1
Journal Information:
Nuclear Fusion, Vol. 58, Issue 1; ISSN 0029-5515
Publisher:
IOP ScienceCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 7 works
Citation information provided by
Web of Science

References (9)

Disruptions and halo currents in Alcator C-Mod journal May 1996
The Plasma Boundary of Magnetic Fusion Devices book January 2000
Reconstruction of current profile parameters and plasma shapes in tokamaks journal November 1985
TSC plasma halo simulation of a DIII-D vertical displacement episode journal July 1993
Progress in understanding halo current at JET journal April 2009
Determination of T e from a Langmuir probe in a magnetic field by directly measuring the probe's sheath drop using a pin-plate probe journal November 1995
Effect of Halo Current and Its Toroidal Asymmetry During Disruptions in JT-60U journal November 1995
Edge safety factor at the onset of plasma disruption during VDEs in JT-60U journal September 2004
Observation of poloidal current flow to the vacuum vessel wall during vertical instabilities in the DIII-D tokamak journal March 1991

Cited By (1)

Simulating the nonlinear interaction of relativistic electrons and tokamak plasma instabilities: Implementation and validation of a fluid model journal June 2019

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Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
halo current
vertical displacement event
Langmuir probe
disruption