The deduction of low-Z ion temperature and densities in the JET tokamak using charge exchange recombination spectroscopy

Abstract

A charge exchange recombination spectroscopy (CXRS) diagnostic has been established on JET to study fully stripped low-Z species. Ion temperature in the plasma centre is measured from visible lines of helium, carbon and oxygen excited by charge exchange with heating neutral beam particles. Coincident cold components produced at the plasma edge are apparent on helium and carbon spectra and inost spectra are subject to accidental blending from other species' edge plasma emission. The charge exchange feature can be isolated from the various composite lines and all three impurities agree on the same temperature within experimental error. Observed column emissivities are converted into absolute impurity densities using a neutral beam attenuation code and charge exchange effective rate coefficients. Comprehensive new calculations have been performed to obtain the effective rate coefficients. The models take detailed account of cascading and the influence of the plasma environment in causing I-mixing, and allow the n-dependence of the rate coefficients to be addressed experimentally. The effective ion charge reconstructed from simultaneous measurements of the densities of dominant impurities shows good agreement with the value inferred from visible Bremsstrahlung. Some illustrative results are shown for helium (helium discharge or minority r.f. heating), carbon and oxygen concentrations monitored during characteristic operating regimes.

Charge exchange in Be4+–H(n= 1, 2) collisions studied systematically by atomic-orbital close-coupling calculations

“…The high principal numbers of the active electron support this analysis. (Isler 1994, Boileau et al 1989 We start with a short description of the used theoretical approach, then continue with the description of employed basis sets and close with a detailed analysis of the calculated cross sections. Atomic units are used unless otherwise stated.…”

“…The ratio of the 6 → 5 line and the 8 → 6 line are compared for a single collision environment (red), a multi-collisional environment (green). The experimental value from JET by Boileau et al (Boileau et al 1989) is marked with a cross and the one from Summers et al (Summers et al 1992) with an x (a) for an H(1s) donor atom. (b) for an H(n = 2) donor atom.…”

“…C q+ ) in the plasma and injected fast neutral atoms, like e.g. H, He, or Li, to measure ion densities (von Hellermann et al 1990, Schorn et al 1991, Mandl et al 1993, temperatures (von Hellermann et al 1990, Schorn et al 1992, Mandl et al 1993, velocities of plasma rotation, and Z eff , the effective charge of the plasma (Isler 1994, Wolfrum et al 1993, Boileau et al 1989.…”

Charge transfer in collisions of Beq+(q=2-4) and Bq+(q=3-5) ions with H

“…Charge transfer processes in atom -multi-charged ion collisions play an important role in magnetic fusion plasmas investigation and the radiation following the charge transfer processes has been widely used as a plasma diagnostic tool, namely the charge-exchange-recombination spectroscopy (CXRS) diagnostics [1]. The electron capture processes of multiply charged impurity ions in magnetic fusion plasma with the neutral hydrogen species are also important in the studies of impurity transport in the edge and divertor plasma regions [2].…”

DIII-D Diagnostic Systems

“…Since then, it has become the basis for one of the standard ion diagnostic techniques on magnetic fusion devices equipped with neutral beam injection [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Exploiting Doppler broadening and Doppler shift of excited spectral lines, CER spectroscopy gives the ion temperature T i , toroidal rotation speed V " , and poloidal rotation speed V " of the ion species being measured.…”