Nondimensional transport scaling in the Tokamak Fusion Test Reactor: Is tokamak transport Bohm or gyro-Bohm?

F. W. Perkins, Cris W. Barnes, D. W. Johnson, S. D. Scott, M. C. Zarnstorff, M. G. Bell, R. E. Bell, C. E. Bush, B. Grek, K. W. Hill, D. K. Mansfield, H. Park, A. T. Ramsey, J. Schivell, B. C. Stratton, E. Synakowski

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Abstract

General plasma physics principles state that power flow Q(r) through a magnetic surface in a tokamak should scale as Q(r) = {32π2Rr 3Te2c nea/[eB(a2-r 2)2]} F(ρ*,β,v*,r/a,q,s,r/R,...) where the arguments of F are local, nondimensional plasma parameters and nondimensional gradients. This paper reports an experimental determination of how F varies with normalized gyroradius ρ* ≡ (2T eMi)1/2c/eBa and collisionality v* ≡ (R/r)3/2qRve(me/ 2Te) 1/2 for discharges prepared so that other nondimensional parameters remain close to constant. Tokamak Fusion Test Reactor (TFTR) [D. M. Meade et al., in Plasma Physics and Controlled Nuclear Fusion Research, 1990, Proceedings of the 13th International Conference, Washington (International Atomic Energy Agency, Vienna, 1991), Vol. 1, p. 9] L-mode data show F to be independent of ρ* and numerically small, corresponding to Bohm scaling with a small multiplicative constant. By contrast, most theories predict gyro-Bohm scaling: F ∝ ρ*. Bohm scaling implies that the largest scale size for microinstability turbulence depends on machine size. Analysis of a collisionality scan finds Bohm-normalized power flow to be independent of collisionality. Implications for future theory, experiment, and reactor extrapolations are discussed.

Original languageEnglish
Pages (from-to)477-498
Number of pages22
JournalPhysics of Fluids B
Volume5
Issue number2
DOIs
StatePublished - 1993

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