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An approach to rapid plasma shape diagnostics in tokamaks

Published online by Cambridge University Press:  13 March 2009

D. K. Lee  and
Y. K. M. Peng
D. K. Lee
Affiliation:
Fusion Energy Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, U.S.A.
Y. K. M. Peng
Affiliation:
Fusion Energy Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, U.S.A.
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Abstract

A study is made of a diagnostic procedure which allows one to estimate the plasma boundary shape and location in a tokamak by using numerical values of the poloidal magnetic flux function ψ in the vicinity of the plasma. In the case of the Impurity Study Experiment (ISX-B) tokamak, the magnetic sensor coils located around the periphery of the vacuum chamber provide information on ∂BR/∂t and ∂Bz/∂t, which can be processed to obtain data on ψ (and ∂ψ/∂n) through the relation BR = - R-1∂ψ/∂Z and Bz = R-1∂ψ/∂R. This leads to a Cauchy boundary condition for the Grad-Shafranov equation Δ*ψ = 0 in the region between the contour of the sensor coil locations and the plasma boundary flux surface. Numerical equilibria calculated for the ISX-B with different shapes are used to simulate ψ data along the coil locations. Random errors are added to the data to test the efficacy of two different approaches: global fitting and local fitting. Reasonably accurate results are obtained by the method of global fitting of the boundary values, which is based on the expansion of ψ in terms of eigenfunctions of Δ*ψ = 0 in a toroidal ring co-ordinate system. This approach is found to permit a relatively large random error in poloidal B field values at the sensor coils and appears to have the potential of rapidly displaying the plasma shape and location.

Type
Research Article
Information
Journal of Plasma Physics , Volume 25 , Issue 1 , February 1981 , pp. 161 - 173
Copyright
Copyright © Cambridge University Press 1981

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