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Title: Tandem mirror thermal barrier experimental program plan

Abstract

This report describes an experimental plan for the development of the Tandem Mirror Thermal Barrier. Included is: (1) a description of thermal barrier related physics experiments; (2) thermal barrier related experiments in the existing TMX and Phaedrus experiments; (3) a thermal barrier TMX upgrade; and (4) initiation of investigations of axisymmetric magnetic geometry. Experimental studies of the first two items are presently underway. Results are expected from the TMX upgrade by the close of 1981 and from axisymmetric tandem mirror experiments at the end of 1983. Plans for Phaedrus upgrades are developing for the same period.

Authors:
; ;
Publication Date:
Research Org.:
California Univ., Livermore (USA). Lawrence Livermore Lab.
OSTI Identifier:
5723689
Report Number(s):
UCID-18505
TRN: 80-004864
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; TMX DEVICES; PLASMA CONFINEMENT; ELECTRON TEMPERATURE; MAGNET COILS; PLUGGING; TEMPERATURE GRADIENTS; CONFINEMENT; ELECTRIC COILS; ELECTRICAL EQUIPMENT; EQUIPMENT; MAGNETIC MIRRORS; OPEN PLASMA DEVICES; THERMONUCLEAR DEVICES; 700101* - Fusion Energy- Plasma Research- Confinement, Heating, & Production; 700202 - Fusion Power Plant Technology- Magnet Coils & Fields

Citation Formats

Coensgen, F.H., Drake, R.P., and Simonen, T.C.. Tandem mirror thermal barrier experimental program plan. United States: N. p., 1980. Web. doi:10.2172/5723689.
Coensgen, F.H., Drake, R.P., & Simonen, T.C.. Tandem mirror thermal barrier experimental program plan. United States. doi:10.2172/5723689.
Coensgen, F.H., Drake, R.P., and Simonen, T.C.. 1980. "Tandem mirror thermal barrier experimental program plan". United States. doi:10.2172/5723689. https://www.osti.gov/servlets/purl/5723689.
@article{osti_5723689,
title = {Tandem mirror thermal barrier experimental program plan},
author = {Coensgen, F.H. and Drake, R.P. and Simonen, T.C.},
abstractNote = {This report describes an experimental plan for the development of the Tandem Mirror Thermal Barrier. Included is: (1) a description of thermal barrier related physics experiments; (2) thermal barrier related experiments in the existing TMX and Phaedrus experiments; (3) a thermal barrier TMX upgrade; and (4) initiation of investigations of axisymmetric magnetic geometry. Experimental studies of the first two items are presently underway. Results are expected from the TMX upgrade by the close of 1981 and from axisymmetric tandem mirror experiments at the end of 1983. Plans for Phaedrus upgrades are developing for the same period.},
doi = {10.2172/5723689},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1980,
month = 1
}

Technical Report:

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  • The collisional fluxes of trapped electrons escaping from the plug and the center cell electrons passing over the thermal barrier and becoming trapped are evaluated for a simple thermal barrier model appropriate to present tandem mirror experiments.
  • An analytic expression for the trapping current in the thermal barrier cell of a tandem mirror due to pitch-angle scattering has been obtained. The overall system is assumed to be maintained in steady state by particle injection in the central cell and charge exchange pumping is assumed in the barrier cell. Trapping of ions in the thermal barrier due to Coulomb interactions sets an irreducible minimum against which any pumping mechanism must compete. A series of boundary value problems in the various regions of phase space is obtained based on the smallness of the bounce time with respect to themore » collision time. A high barrier mirror ratio, long central cell and deep barrier electrostatic potential are implicit in the analysis. For conditions of interest a Lorentz collision operator describes reasonably well the kinetic problem which we have solved using a square-well approximation. Analytic results agree with numerical results within expected limits on the order of the inverse of the barrier mirror ratio (approx. 10 to 20%). A boundary layer mechanism has been proposed which limits the trapping current value as the pumping rate is increased.« less
  • An axisymmetric pumping scheme is proposed to pump the particles that trap in a thermal barrier without invoking the neutral beam or geodesic curvature. In this scheme a magnetic scraper is moved uni-directionally on the barrier peak to push the barely trapped particles into the central cell. We utilize a potential jump that forms at the peak field for sufficiently strong pumping. The non-collisional catching effect has to be limited by setting an upper limit on the scraping frequency of the magnetic bump. On the other hand, the dynamic stability of the pumping scheme sets a lower limit on themore » scraping frequency. Using the variational method, we are able to estimate the window between these two limits, which seems feasible for the Tara reactor parameter set. A primary calculation shows that the magnetic bump, ..delta..B/B is about 10/sup -4/ and the scraping frequency, nu/sub sc/, is about 10/sup +5/sec/sup -1/, which are similar to the parameters required for those for drift pumping.« less
  • In order to assess the possible benefit of applying electron cyclotron resonance heating (ECRH) in the thermal barrier region of a tandem mirror a simple thermal barrier model is considered. The collisional fluxes of the hot,barrier electrons diffusing into the central cell and plug, the warm electrons escaping from the plug, and the cooler, central cell electrons passing over the thermal barrier and becoming trapped, are evaluated.
  • It is shown that in general the stability of a hot electron symmetric tandem mirror is the same as the stability of its barrier-plug cell alone, plus an additional limitation on the center cell length such that the center cell Alfven frequency is higher than the average barrier-plug E x B drift and the hot electron precession frequency. Stability of the hot electron barrier-plug cell is studied extensively.