IMPURITY STUDIES AND TRANSPORT CODE MODELLING OF JET PLASMAS
Impurities in JET are studied by visible and VUV spectroscopy, and from bolometer and soft X-ray signals. The measurements provide information on impurity influxes and densities in the plasma. These showed that light impurities could be controlled well initially, but were subsequently increasing. A relatively high level of metal impurities (about 0.2%) is mainly responsible for high radiative power losses (about 70% P-OMEGA). A wall material deposit on the graphite limiters is the primary cause of metal contamination. Molybdenum was present on the carbon surfaces as a result of the manufacturing process. Chlorine is an abundant impurity, probably introduced when washing the torus. Extensive transport code calculations have provided acceptably consistent models for present JET plasmas, taking account of transport, radiation and q<= 1 activity. With the high levels of impurities present, it has been necessary to reduce the magnitude of several of the commonly used transport coefficients. In addition, the relation between the global confinement time and the assumed local transport coefficients was destroyed by both the q<= 1 activity and impurity radiation. Control of metallic impurities should lead to improved performance.
Bibliographic Reference: 10TH INTERNATIONAL CONFERENCE ON PLASMA PHYSICS AND CONTROLLED NUCLEAR FUSION RESEARCH, LONDON (UK), SEPT. 12- 18, 1984 PUBLISHED BY IAEA, WIEN (AUSTRIA), 1985 VOL. 1, PP. 291-300
Record Number: 1989124029100 / Last updated on: 1987-01-01
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