Contributions from ion-atom charge exchange collisions to the CVI Lyman intensities in the JET tokamakFunded under: FP1-FUSION 9C
In a multi-keV temperature deuterium plasma such as JET, CVI emission arises from collision processes which, in the absence of neutral deuterium beam heating, occur near the plasma boundary. Distortions to the CVI Lyman decrement, such as the Ly beta/gamma/delta ratio and enhancement of the high quantum states (n about 12) are observed. These are correlated to the D(alpha) intensity and consequently to the influx of D(0) atoms at the plasma boundary. The intensities of the Lyman spectra are interpreted in terms of low energy electron transfer from thermal D(0) atoms to C(+6) ions, as well as electronic excitation of C(+5) ions in their ground state. The line-of-sight emission is modelled using an impurity ion transport code with input data on the electron and D(0) profiles. Electron transfer from excited states of D(0) as well as the ground state have to be included to give satisfactory agreement with the CVI Lyman spectra when the D(0) influx is high. The cross-sections for charge-transfer from excited states have been estimated using a simple Landau-Zenner model. Comparison of the relative intensities of the CVI Lyman series with the model calculations allows plausible corrections to be made to the effective charge transfer cross-section as a function of principal quantum number. The observations offer a potential method of measuring local D(0) concentrations near the boundary of high temperature, high D(0) recycling plasmas, but limited at present by the uncertainties of low energy charge transfer cross-sections.
Bibliographic Reference: Report: JET-P(88)68 EN (1988)
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 198910751 / Last updated on: 1994-12-01
Original language: en
Available languages: en