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Author(s):
S.-I. Itoh and K. Itoh
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Title:
Modelling of Improved Confinements - Peaked Profile Modes and H-Mode -
Date of publication:
Sep. 1990
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Key words:
peaked profile modes, H-mode
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Abstract:
Theoretical models on improved confinement with peaked density profile and on H-mode are discussed. A model theory of inward pinch and peaked density profile of ohmic discharges in tokamak is presented. Ion anomalous viscosity in the presence of sheared toroidal rotation causes the drift across the magnetic field. The ratio of viscosity to diffusion coefficient, Prandtl number, determines structures of E_gamma and density profile in a stationary state. In viscous plasmas, peaked profiles of both density and rotation velocity are possible without central particle/momentum sources. Resultant rotation of the core relative to the edge is in the counter direction to plasma current. Reduction of edge neutrals can induce further density peaking. H-mode transition model is further developed. The radial derivative of E_gamma, E_gamma', changes ion losscone loss through squeezing poloidal gyroradius and electron loss by affecting micro-instabilities. Charge neutrality condition predicts cusp type catastroph in the relation between the gradient and flux at edge. At the transition, E_gamma' jumps to negative and fluctuations and anomalous fluxes reduce simultaneously. Combined model predicts that the core density profile is flattened during H-phase.
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