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Title: Radially scanning magnetic probes to study local helicity injection dynamics

Abstract

Two new magnetic probes have been deployed on the Pegasus spherical tokamak to study the dynamics of local helicity injection non-solenoidal plasma start-up and current drive. The magnetic radial array probe consists of 15 pickup coils (~5 × 8 mm each) that measure z(R) over a 15 cm linear extent. The coils consist of traces embedded in a printed circuit board. Three coil designs are utilized to balance frequency response and coil sensitivity. Helmholtz coil measurements are used to measure coil and full assembly bandwidths (~2 MHz and ~200 kHz, respectively) and sensitivities (0.18/0.35/0.96 mV T -1 s). The magnetic radial scanning probe is an array of Hall effect sensors that measure field strength ( |B|177 mT) and direction at 8 spatial points (ΔR = 1.5 cm), supporting the studies of equilibrium field structure and low-frequency (≤5 kHz) current dynamics. It uses commercial surface-mount Hall effect sensors with chip-integrated amplifiers and compensators that are mounted in a 3-D printed frame. Helmholtz coil measurements indicate negligible cross-field gain nonlinearity and provide absolute calibration of the diagnostic. Both probes are constructed as an electrostatically shielded insertable air-side assembly that mounts within a radially translatable ultrahigh vacuum assembly from an existing probe.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics
Publication Date:
Research Org.:
Univ. of Wisconsin, Madison, WI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1461755
Alternate Identifier(s):
OSTI ID: 1460027
Grant/Contract Number:  
FG02-96ER54375
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 89; Journal Issue: 10; Related Information: N.J. Richner, M.W. Bongard, R.J. Fonck, J.A. Reusch, and C.E. Schaefer, "Public Data Set: Radially Scanning Magnetic Probes to Study Local Helicity Injection Dynamics," DOI: 10.18138/1432455; Journal ID: ISSN 0034-6748
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; magnetic probe; helicity injection; local helicity injection; spherical tokamak; tokamak startup; electromagnetic interactions; plasma confinement; data acquisition; coils; electrical circuits; semiconductor devices; carbon based materials

Citation Formats

Richner, Nathan J., Bongard, Michael W., Fonck, Raymond J., Reusch, Joshua A., and Schaefer, Carolyn E. Radially scanning magnetic probes to study local helicity injection dynamics. United States: N. p., 2018. Web. doi:10.1063/1.5036527.
Richner, Nathan J., Bongard, Michael W., Fonck, Raymond J., Reusch, Joshua A., & Schaefer, Carolyn E. Radially scanning magnetic probes to study local helicity injection dynamics. United States. doi:10.1063/1.5036527.
Richner, Nathan J., Bongard, Michael W., Fonck, Raymond J., Reusch, Joshua A., and Schaefer, Carolyn E. Thu . "Radially scanning magnetic probes to study local helicity injection dynamics". United States. doi:10.1063/1.5036527.
@article{osti_1461755,
title = {Radially scanning magnetic probes to study local helicity injection dynamics},
author = {Richner, Nathan J. and Bongard, Michael W. and Fonck, Raymond J. and Reusch, Joshua A. and Schaefer, Carolyn E.},
abstractNote = {Two new magnetic probes have been deployed on the Pegasus spherical tokamak to study the dynamics of local helicity injection non-solenoidal plasma start-up and current drive. The magnetic radial array probe consists of 15 pickup coils (~5 × 8 mm each) that measure Ḃz(R) over a 15 cm linear extent. The coils consist of traces embedded in a printed circuit board. Three coil designs are utilized to balance frequency response and coil sensitivity. Helmholtz coil measurements are used to measure coil and full assembly bandwidths (~2 MHz and ~200 kHz, respectively) and sensitivities (0.18/0.35/0.96 mV T-1 s). The magnetic radial scanning probe is an array of Hall effect sensors that measure field strength (|B|177 mT) and direction at 8 spatial points (ΔR = 1.5 cm), supporting the studies of equilibrium field structure and low-frequency (≤5 kHz) current dynamics. It uses commercial surface-mount Hall effect sensors with chip-integrated amplifiers and compensators that are mounted in a 3-D printed frame. Helmholtz coil measurements indicate negligible cross-field gain nonlinearity and provide absolute calibration of the diagnostic. Both probes are constructed as an electrostatically shielded insertable air-side assembly that mounts within a radially translatable ultrahigh vacuum assembly from an existing probe.},
doi = {10.1063/1.5036527},
journal = {Review of Scientific Instruments},
number = 10,
volume = 89,
place = {United States},
year = {Thu Jul 12 00:00:00 EDT 2018},
month = {Thu Jul 12 00:00:00 EDT 2018}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on July 12, 2019
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