Local Physics Basis of Confinement Degradation in JET ELMy H-Mode Plasmas and Implications for Tokamak Reactors
Authors: R.V. Budny, B. Alper, D.N. Borba, J.G. Cordey, D.R. Ernst, C. Giraud, C.W. Gowers, K. Gunther, T.S. Hahm, G.W. Hammett, N.C. Hawkes, L.D. Horton, G. Saibene, R. Sartori, E.J. Synakowski, M.G. von Hellermann, and K.-D. Zastrow
Date of PPPL Report: February 2001
Published in: Nucl. Fusion 42 (January 2002) 66-75.
First results of gyrokinetic analysis of JET [Joint European Torus] ELMy H-mode [edge localized modes, high-confinement] plasmas are presented. ELMy H-mode plasmas form the basis of conservative performance predictions for tokamak reactors of the size of ITER [International Thermonuclear Experimental Reactor]. Relatively high performance for long duration has been achieved and the scaling appears to be favorable. It will be necessary to sustain low Zeff and high density for high fusion yield. This paper studies the degradation in confinement and increase in the anomalous heat transport observed in two JET plasmas: one with an intense gas puff and the other with a spontaneous transition between Type I to III ELMs at the heating power threshold. Linear gyrokinetic analysis gives the growth rate, glin of the fastest growing modes. The flow-shearing rate wExB and glin are large near the top of the pedestal. Their ratio decreases approximately when the confinement degrades and the transport increases. This suggests that tokamak reactors may require intense toroidal or poloidal torque input to maintain sufficiently high |wExB|/glinnear the top of the pedestal for high confinement.