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Title: Novel design methods for magnetic flux loops in the National Compact Stellarator Experiment

Abstract

Magnetic pickup loops on the vacuum vessel (VV) can provide an abundance of equilibrium information for stellarators. A substantial effort has gone into designing flux loops for the National Compact Stellarator Experiment (NCSX) [Zarnstorff et al., Plasma Phys. Controlled Fusion 43, A237 (2001)], a three-field period quasi-axisymmetric stellarator under construction at the Princeton Plasma Physics Laboratory. The design philosophy, to measure all of the magnetic field distributions normal to the VV that can be measured, has necessitated the development of singular value decomposition algorithms for identifying efficient loop locations. Fields are expected to be predominantly stellarator symmetric (SS)--the symmetry of the machine design--with toroidal mode numbers per torus (n) equal to a multiple of 3 and possessing reflection symmetry in a period. However, plasma instabilities and coil imperfections will generate non-SS fields that must also be diagnosed. The measured symmetric fields will yield important information on the plasma current and pressure profile as well as on the plasma shape. All fields that obey the design symmetries could be measured by placing flux loops in a single half-period of the VV, but accurate resolution of nonsymmetric modes, quantified by the condition number of a matrix, requires repositioning loops to equivalent locationsmore » on the full torus. A subarray of loops located along the inside wall of the vertically elongated cross section was designed to detect n=3, m=5 or 6 resonant field perturbations that can cause important islands. Additional subarrays included are continuous in the toroidal and poloidal directions. Loops are also placed at symmetry points of the VV to obtain maximal sensitivity to asymmetric perturbations. Combining results from various calculations which have made extensive use of a database of 2500 free-boundary VMEC equilibria, has led to the choice of 225 flux loops for NCSX, of which 151 have distinct shapes.« less

Authors:
; ; ; ;  [1];  [2];  [2];  [2];  [2]
  1. Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20975042
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 5; Other Information: DOI: 10.1063/1.2472368; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ALGORITHMS; ASYMMETRY; AXIAL SYMMETRY; DESIGN; DISTURBANCES; ELECTRIC CURRENTS; EQUILIBRIUM; INFORMATION; MAGNETIC FIELDS; MAGNETIC FLUX; PLASMA; PLASMA CONFINEMENT; PLASMA DIAGNOSTICS; PLASMA INSTABILITY; PLASMA PRESSURE; STELLARATORS

Citation Formats

Pomphrey, N., Lazarus, E., Zarnstorff, M., Boozer, A., Brooks, A., Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543, Columbia University, New York, New York 10027, and Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543. Novel design methods for magnetic flux loops in the National Compact Stellarator Experiment. United States: N. p., 2007. Web. doi:10.1063/1.2472368.
Pomphrey, N., Lazarus, E., Zarnstorff, M., Boozer, A., Brooks, A., Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543, Columbia University, New York, New York 10027, & Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543. Novel design methods for magnetic flux loops in the National Compact Stellarator Experiment. United States. doi:10.1063/1.2472368.
Pomphrey, N., Lazarus, E., Zarnstorff, M., Boozer, A., Brooks, A., Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543, Columbia University, New York, New York 10027, and Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543. Tue . "Novel design methods for magnetic flux loops in the National Compact Stellarator Experiment". United States. doi:10.1063/1.2472368.
@article{osti_20975042,
title = {Novel design methods for magnetic flux loops in the National Compact Stellarator Experiment},
author = {Pomphrey, N. and Lazarus, E. and Zarnstorff, M. and Boozer, A. and Brooks, A. and Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 and Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543 and Columbia University, New York, New York 10027 and Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543},
abstractNote = {Magnetic pickup loops on the vacuum vessel (VV) can provide an abundance of equilibrium information for stellarators. A substantial effort has gone into designing flux loops for the National Compact Stellarator Experiment (NCSX) [Zarnstorff et al., Plasma Phys. Controlled Fusion 43, A237 (2001)], a three-field period quasi-axisymmetric stellarator under construction at the Princeton Plasma Physics Laboratory. The design philosophy, to measure all of the magnetic field distributions normal to the VV that can be measured, has necessitated the development of singular value decomposition algorithms for identifying efficient loop locations. Fields are expected to be predominantly stellarator symmetric (SS)--the symmetry of the machine design--with toroidal mode numbers per torus (n) equal to a multiple of 3 and possessing reflection symmetry in a period. However, plasma instabilities and coil imperfections will generate non-SS fields that must also be diagnosed. The measured symmetric fields will yield important information on the plasma current and pressure profile as well as on the plasma shape. All fields that obey the design symmetries could be measured by placing flux loops in a single half-period of the VV, but accurate resolution of nonsymmetric modes, quantified by the condition number of a matrix, requires repositioning loops to equivalent locations on the full torus. A subarray of loops located along the inside wall of the vertically elongated cross section was designed to detect n=3, m=5 or 6 resonant field perturbations that can cause important islands. Additional subarrays included are continuous in the toroidal and poloidal directions. Loops are also placed at symmetry points of the VV to obtain maximal sensitivity to asymmetric perturbations. Combining results from various calculations which have made extensive use of a database of 2500 free-boundary VMEC equilibria, has led to the choice of 225 flux loops for NCSX, of which 151 have distinct shapes.},
doi = {10.1063/1.2472368},
journal = {Physics of Plasmas},
number = 5,
volume = 14,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}