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Compact toroid formation, dynamics and lifetime in collisional plasmas generated at high fill pressures

Published online by Cambridge University Press:  13 March 2009

J. C. Dooling ,
T. M. York ,
M. Niimura ,
F. Aghamir ,
F. B. Mead  and
D. R. Shieh
J. C. Dooling
Affiliation:
The Pennsylvania State University, University Park, Pennsylvania, U.S.A.
T. M. York
Affiliation:
The Pennsylvania State University, University Park, Pennsylvania, U.S.A.
M. Niimura
Affiliation:
The Pennsylvania State University, University Park, Pennsylvania, U.S.A.
F. Aghamir
Affiliation:
The Pennsylvania State University, University Park, Pennsylvania, U.S.A.
F. B. Mead
Affiliation:
The Pennsylvania State University, University Park, Pennsylvania, U.S.A.
D. R. Shieh
Affiliation:
The Pennsylvania State University, University Park, Pennsylvania, U.S.A.
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Abstract

A 0·50 m long compact-toroid transport experiment (CTTX) has been studied with a number of diagnostics, including Thomson scattering, to determine local plasma properties and gradients indicative of transport processes. The CTTX bias and main field strengths were –0·09 and 0·35 T. Compact toroid formation and lifetime were studied at static fill pressures of 20, 100 and 150 mTorr deuterium, between 3 and 30μs after firing of the main bank. Thomson-scattering diagnosis was carried out using a Q-switched Nd: glass laser operated at both fundamental (1053 nm) and second-harmonic wavelengths (527 nm). For each pressure, scattering tests were conducted at radii r of 0·1, 1·0, 1·85 and 2·60 cm and axial positions z of 6·7, 13·0 and 19·0 cm (1054 nm); supplementary data were obtained at r = 0·1, 1·35 and 2·10 cm at z = 6·7 cm (527 nm). Electron densities and temperatures were in the ranges 1021–1022 m-3 and 2–20 eV. Thomson-scattering results are compared with diamagnetic loop, inter-ferometry, luminosity and piezoelectric pressure-probe data. Axial behaviour of the formation CT plasma varies significantly with initial fill pressure: continuous axial contraction occurs at ISOmTorr; whereas the 20 mTorr plasma appears first to contract then expand. Particle loss times are found to decrease from 70 μs at 20 mTorr to 24 μs at 100 mTorr and 12 μs at 150 mTorr. Energy decay times are 6, 7 and 5 μs for 20, 100 and 150 mTorr respectively. Flux-decay times are approximately 20 μs for 20 mTorr, 12 μs for 100 mTorr and 20 μs for 150 mTorr fill pressure. These values are two to four times longer than would be expected from theory using classical transport. In order to explain the sustained magnetic flux, the role of electric fields within the compact toroid is considered.

Type
Research Article
Information
Journal of Plasma Physics , Volume 43 , Issue 3 , June 1990 , pp. 419 - 449
Copyright
Copyright © Cambridge University Press 1990

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