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High fusion power experiments using D-T mixtures in ELM-free H-mode and optimized shear regimes in JET are reported. A fusion power of 16.1 MW has been produced in as ELM-free H-mode at 4.2 MA/3.6T. The transient value of the fusion amplification factor was 0.95+0.17, consistent with the high value of nDT(0) tEdia Ti(0)=8.7x10(20)m(-3)s keV+20%, and maintained for about half an energy confinement time until excessive edge pressure gradients resulted in discharge termination by MHD instabilities. The ratio of D-D and D-T fusion powers (from separate but otherwise similar discharges) showed the expected factor of 210, validating D-D projections of D-T performance for similar pressure profiles and good plasma mixture control which was achieved by loading the vessel walls with the appropriate D-T mix. Magnetic fluctuation spectra showed no evidence of Alfvenic instabilities driven by alpha particles, in agreement with theoretical model calculations. Alpha particle heating has been unambiguously observed, its effect being separated successfully from possible isotope effects on energy confinement by varying the tritium concentration in otherwise similar discharges. The scan showed that there was no or at most a very weak isotope effect on the energy confinement time. The highest electron temperature was clearly correlated with the maximum alpha particle heating power and the optimum D-T mixture; the maximum increase was 1.3+0.23 ke V with 1.3 MW of alpha particle heating power, consistent with classical expectations for alpha particle confinement and heating. In the optimized shear regime, clear internal transport barriers were established for the first in D-T, with a power similar to that required in D-D. The ion thermal conductivity in the plasma core approached neoclassical levels. Real time power control maintained the plasma core close to limits set by pressure gradient driven MHD instabilities, allowing 8.2 MW of D-T fusion power with nDT(0) TediaTi(0) =10(21) m(-3

Additional information

Authors: KEILHACKER M, JET Joint Undertaking, Abingdon, Oxfordshire (GB)
Bibliographic Reference: Article: High Fusion Performance from Deuterium-Tritium Plasmas in JET, JET-P (1998) 36
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