Recombination kinetics of impurities during a major disruption in tokamak plasmas

The investigations of major disruptions in the TVD and DAMAVAND tokamaks showed that, in the rapid phase of disruption, accelerated ({approx}1 keV) ions and charge-exchange neutrals are generated near the rational magnetic surfaces; this is accompanied by the bursts of line emission from light impur...

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Bibliographic Details
Published in:Plasma physics reports 2005-06, Vol.31 (6), p.439-451
Main Authors: Shurygin, V. A., Brevnov, N. N., Gott, Yu. V.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BOUNDARY LAYERS
CARBON IONS
CHARGE EXCHANGE
CHARGE STATES
COMPUTERIZED SIMULATION
ELECTRIC CURRENTS
ELECTRIC DISCHARGES
EMISSION
KEV RANGE
MAGNETIC SURFACES
PLASMA
PLASMA CONFINEMENT
PLASMA DIAGNOSTICS
PLASMA IMPURITIES
PLASMA INSTABILITY
PLASMA SIMULATION
REACTION KINETICS
RECOMBINATION
TOKAMAK DEVICES
TRIPLETS
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Summary:The investigations of major disruptions in the TVD and DAMAVAND tokamaks showed that, in the rapid phase of disruption, accelerated ({approx}1 keV) ions and charge-exchange neutrals are generated near the rational magnetic surfaces; this is accompanied by the bursts of line emission from light impurities (C, O). In the present paper, an analysis is made of the bursts of the CV triplet emission (2271-2278 A) observed over all of the viewing chords in high-current discharges and also of a decrease in the spectral line emission below its initial (predisruption) level both in the plasma core and at the plasma edge in low-current discharges. The data from measurements of the spatial and temporal parameters of the CV line emission from the central and peripheral plasma regions in the rapid phase of disruption in the DAMAVAND tokamak are compared to the results from model calculations of the kinetics of the charge-state distribution of carbon impurity ions (during the disruption, their kinetics is governed by the increase in the effective recombination rate). A key result of the kinetic model is an increase in the effective rate of charge exchange of impurity ions by two orders of magnitude. Numerical simulations show that the dispersion of the charge-state distribution increases substantially; this is attributed to the rapid phase of disruption being dominated by the recombination of impurity ions through charge exchange with neutrals rather than by the anomalous transport. In this case, carbon impurities in the plasma are transported to the region of increased radiative losses on a time scale of 50 {mu}s.
ISSN:1063-780X
1562-6938
DOI:10.1134/1.1947329