Chapter 2: Plasma confinement and transport

Abstract

Physics knowledge in plasma confinement and transport relevant to design of a reactor-scale tokamak is reviewed and methodologies for projecting confinement properties to ITER are provided. Theoretical approaches to describing a turbulent plasma transport in a tokamak are outlined and phenomenology of major energy confinement regimes observed in tokamaks, including those with edge and internal transport barriers, is described. The chapter is focused on the energy confinement in the high confinement regime (H-mode) with the edge localized MHD modes, the basic operational regime of ITER. Three approaches are being pursued: (i) derivation of empirical global scaling laws; (ii) non-dimensionally similar studies; and (iii) one dimensional transport modelling codes, with the first approach recommended as the most robust at the present time. Special attention is paid to analysis of uncertainties in confinement predictions. Empirical scaling relations for projecting the L-mode to H-mode power threshold based on regression analysis of an extensive database are discussed. Particle and toroidal momentum confinement and their relation to energy confinement are reviewed.

Progress toward fully noninductive discharge operation in DIII-D using off-axis neutral beam injection

“…The calculated ideal low-n stability limit to b N is found to be the largest in discharges with the broadest pressure profiles. Confinement of the thermal component of the plasma, when compared to the IPB98(y,2) scaling, 9 is as expected for H-mode. However, global confinement with q min > 2 is below what is typically associated with H-mode, as determined by a comparison to the ITER-89P scaling.…”

“…The figure shows the ratio of the thermal energy confinement time (s Eth ) to s 98 , the confinement time predicted by the IPB98(y,2) energy confinement scaling. 9 This value is referred to here as H 98 , the H-mode confinement scaling factor, although here the thermal energy confinement time is determined from the measured thermal pressure profile integrated over the plasma volume (W th ). The value of H 98 is usually determined for DIII-D by subtracting an estimate of the fast ion stored energy from the total stored energy obtained from an equilibrium reconstruction using the EFIT 27 code (W MHD ).…”

“…The database contains discharges with a range of parameters (e.g., q min ; q 95 , b N ; f BS ; f NI ) sufficiently broad that the model is well validated and the extrapolations necessary to study steady-state solutions are of reasonable range. The plasma pressure is found by using the IPB98(y,2) global confinement scaling 9 to determine the thermal plasma pressure, and the fast ion pressure is obtained from a model that uses as input the neutral beam power and estimates of n e and T e . The noninductive current fractions are determined from theorybased analytic models with coefficients that are determined from fits to the experimental database.…”

Determination of the non-ideal response of a high temperature tokamak plasma to a static external magnetic perturbation via asymptotic matching

“…1,12 Shielding currents are excited by plasma rotation 1 or by a combination of pressure gradients and the characteristic favorable average magnetic field-line curvature present in tokamak plasmas. 13 The latter mechanism for exciting shielding currents is of particular significance for ITER, 14 because of the low intrinsic plasma rotation expected in this device. In addition to shielding currents at rational surfaces, an external magnetic perturbation excites currents that are distributed throughout the bulk of the plasma.…”

Overview of the JET results

“…H-mode and hybrid plasmas were obtained with energy confinement enhancement factors (H 98 ) in the range of 0.9-1.2 [53] when compared with IPB98(y,2) scaling law [54]. It was previously reported that stationary H-modes could be re-established with the ILW by avoiding W accumulation through the production of frequent ELM regimes by gas puffing [12].…”