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Abstract

Characteristics of the operation of the DITE tokamak with the Mk-II bundle divertor and neutral beam heating are described. In these experiments the divertor was pumped by a liquid helium cooled cryopump, and fuelling was by gas input into the tokamak vacuum vessel. Generally a fuelling RATE OF 1-2X10**21 ATOMS IS REQUIRED TO SUSTAIN A constant density with the divertor operating, and about 50 % of the gas input flows into the divertor. Global power balances have been carried out using instrumentation distributed around the tokamak and in the divertor. It is found that the wall loading exhibits substantial toroidal and poloidal asymmetries, with a high loading near the gas feed when the divertor is operating. The percentage power exhaust to the divertor is highest, up to 70 % on ohmic discharges with the gas feed turned off and the density falling. With 1.4 MW of the neutral beam heating, about 24 % of the power is seen at the divertor plates. Typically, between 70 % and 80 % of the input power can be counted for. Measurements in the scrape-off plasma show that the density is about 1 x 10**19 m -3- at 30 to 40 mm outside the separatrix, when the line average density in the tokamak is 2-2.5 x 10**19 m**-3. However there is less than 10 % re-ionization of recycled neutrals in the divertor, as determined from H-alpha measurements. In addition, the strong coupling observed between the particle and power flow to the divertor suggests that the exhaust is convective, and this may be a consequence of the strong mirror field characteristic of the bundle divertor magnetic geometry.

Additional information

Authors: JOHNSON P C, CULHAM LABORATORY, ABINGDON, OXON. (UK);AXON K B, CULHAM LABORATORY, ABINGDON, OXON. (UK);BRADLEY J E, CULHAM LABORATORY, ABINGDON, OXON. (UK);BURT J, CULHAM LABORATORY, ABINGDON, OXON. (UK);CLARK W H M, CULHAM LABORATORY, ABINGDON, OXON. (UK);ERENTS S K, CULHAM LABORATORY, ABINGDON, OXON. (UK);FIELDING S J, CULHAM LABORATORY, ABINGDON, OXON. (UK);GOODALL D H J, CULHAM LABORATORY, ABINGDON, OXON. (UK);HARBOUR P J CULHAM LABORATORY, ABINGDON, OXON. (UK), CULHAM LABORATORY, ABINGDON, OXON. (UK)
Bibliographic Reference: JOURNAL OF NUCLEAR MATERIALS, VOL. 121 (1984), PP. 210-221
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