IMPURITY AND RADIATION STUDIES DURING THE JET OHMIC HEATING PHASE
Impurities have been studied by visible and VUV spectroscopy, and from bolometer and soft X-ray signals. Plasma dimensions and parameters were a=1.1 m, b=1.3-1.5 m R=3 m, I-p <-- 3.7 MA, n-e <-- 3.3 x 10**19 m**-3. Oxygen, carbon, wall material (Ni,Cr,Fe), molybdenum and chlorine have been identified as the main impurities. The metal impurities came mainly from the carbon limiter surfaces; their densities increased with plasma current and decreased with electron density. Light impurities depended more on the state of the vacuum vessel and size and elongation of the plasma. In two main plasma cleaning campaigns: a period of 12000 PDC pulses and repetitive carbonization of the vessel walls, some reduction of oxygen and chlorine, a decrease of the molybdenum fraction in the plasma were observed, and, in the second case, a reduction of the metal content by about a factor of five with gradual decrease of oxygen and chlorine, and the radiated power low. High electron densities led to higher radiated power, but reduced Z-eff. The impurity levels of high density pulses after carbonization were as low as 2.5% C, 1% O, 0.05% Cl and 0.015% metals, resulting in Z-eff approximately equal 2.6 and a fraction of deuterons of about 75%.
Bibliographic Reference: WRITE TO THE PUBLICATIONS OFFICER, JET JOINT UNDERTAKING, ABINGDON, OXON OX14 3EA (UK), MENTIONING REPORT JET-P(85)08, 1985
Record Number: 1989124078400 / Last updated on: 1987-01-01
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