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Title: High- β equilibrium and ballooning stability of the low aspect ratio CNT stellarator

Abstract

In the paper, the existence and ballooning-stability of low aspect ratio stellarator equilibria is predicted for the Columbia Neutral Torus (CNT) with the aid of 3D numerical tools. In addition to having a low aspect ratio, CNT is characterized by a low magnetic field and small plasma volume. Also, highly overdense plasmas were recently heated in CNT by means of microwaves. These characteristics suggest that CNT might attain relatively high values of plasma beta and thus be of use in the experimental study of stellarator stability to high-beta instabilities such as ballooning modes. As a first step in that direction, here the ballooning stability limit is found numerically. Depending on the particular magnetic configuration we expect volume-averaged β limits in the range 0.9%–3.0%, and possibly higher, and observe indications of a second region of ballooning stability. As the aspect ratio is reduced, stability is found to increase in some configurations and decrease in others. Energy-balance estimates using stellarator scaling laws indicate that the lower β limit may be attainable with overdense heating at powers of 40 to 100 kW. The present study serves the additional purpose of testing VMEC and other stellarator codes at high values of β and atmore » low aspect ratios. For this reason, the study was carried out both for free boundary, for maximum fidelity to experiment, as well as with a fixed boundary, as a numerical test.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [1]
  1. Columbia Univ., New York, NY (United States)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1358669
Report Number(s):
PPPL-5382
Journal ID: ISSN 1070-664X
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 4; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; energy confinement; density limit; modes; plasmas; instabilities; w7-as

Citation Formats

Hammond, K. C., Lazerson, S. A., and Volpe, F. A. High-β equilibrium and ballooning stability of the low aspect ratio CNT stellarator. United States: N. p., 2017. Web. doi:10.1063/1.4979284.
Hammond, K. C., Lazerson, S. A., & Volpe, F. A. High-β equilibrium and ballooning stability of the low aspect ratio CNT stellarator. United States. doi:10.1063/1.4979284.
Hammond, K. C., Lazerson, S. A., and Volpe, F. A. Fri . "High-β equilibrium and ballooning stability of the low aspect ratio CNT stellarator". United States. doi:10.1063/1.4979284. https://www.osti.gov/servlets/purl/1358669.
@article{osti_1358669,
title = {High-β equilibrium and ballooning stability of the low aspect ratio CNT stellarator},
author = {Hammond, K. C. and Lazerson, S. A. and Volpe, F. A.},
abstractNote = {In the paper, the existence and ballooning-stability of low aspect ratio stellarator equilibria is predicted for the Columbia Neutral Torus (CNT) with the aid of 3D numerical tools. In addition to having a low aspect ratio, CNT is characterized by a low magnetic field and small plasma volume. Also, highly overdense plasmas were recently heated in CNT by means of microwaves. These characteristics suggest that CNT might attain relatively high values of plasma beta and thus be of use in the experimental study of stellarator stability to high-beta instabilities such as ballooning modes. As a first step in that direction, here the ballooning stability limit is found numerically. Depending on the particular magnetic configuration we expect volume-averaged β limits in the range 0.9%–3.0%, and possibly higher, and observe indications of a second region of ballooning stability. As the aspect ratio is reduced, stability is found to increase in some configurations and decrease in others. Energy-balance estimates using stellarator scaling laws indicate that the lower β limit may be attainable with overdense heating at powers of 40 to 100 kW. The present study serves the additional purpose of testing VMEC and other stellarator codes at high values of β and at low aspect ratios. For this reason, the study was carried out both for free boundary, for maximum fidelity to experiment, as well as with a fixed boundary, as a numerical test.},
doi = {10.1063/1.4979284},
journal = {Physics of Plasmas},
number = 4,
volume = 24,
place = {United States},
year = {Fri Apr 07 00:00:00 EDT 2017},
month = {Fri Apr 07 00:00:00 EDT 2017}
}

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