IMPURITY PRODUCTION MECHANISMS AND BEHAVIOUR DURING ADDITIONAL HEATING IN JET
Impurities in JET are investigated by spectroscopic and plasma edge diagnostics. Impurity influxes are measured by visible spectroscopy allowing identification of impurity sources and conclusions on production mechanisms. Metals and carbon in JET plasmas originate mainly from the limiters; physical sputtering is the release mechanism. Oxygen originates from the walls, presumably by photon or neutral particle desorption. During ICRH, antenna screen material is released by a process not yet understood. Transport studies yield D approximately equal 1 m**2/s for impurities. Ohmic and neutral beam heated plasmas are dominated by light impurities (C, O), in particular by oxygen at high n-e. Moderate metal levels (0.1 n-e) during ICRH are responsible for radiation losses of approximately equal 20% P-tot. These can be prevented temporarily by carbonization. Radiative power losses are 30-60 % P-tot for NBI and 40-70 % P-tot for ICRH. Z-eff ranges between 3.5 at low n-e and 2.5 at higher n-e. During magnetic separatrix operation, a reduction of metals and carbon is observed. The bulk plasma radiation drops compared to limiter discharges, but there is an additional contribution from the X-point regions. To date, no accumulation has been observed during NB counter injection.
Bibliographic Reference: 11TH INTERNATIONAL CONFERENCE ON PLASMA PHYSICS AND CONTROLLED NUCLEAR FUSION RESEARCH, KYOTO (JAPAN), NOV. 13-20, 1986 WRITE TO THE PUBLICATIONS OFFICER, JET JOINT UNDERTAKING, ABINGDON, OXON OX14 3EA (UK), MENTIONING REPORT JET-P(86)44, 1986
Record Number: 1989125077500 / Last updated on: 1987-12-01
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