The understanding and predictive capability of transport physics and plasma confinement is reviewed from the perspective of achieving reactor-scale burning plasmas in the ITER tokamak, for both core and edge plasma regions. Very considerable progress has been made in understanding, controlling and predicting tokamak transport across a wide variety of plasma conditions and regimes since the publication of the ITER Physics Basis (IPB) document (1999 Nucl. Fusion 39 2137–2664). Major areas of progress considered here follow. (1) Substantial improvement in the physics content, capability and reliability of transport simulation and modelling codes, leading to much increased theory/experiment interaction as these codes are increasingly used to interpret and predict experiment. (2) Remarkable progress has been made in developing and understanding regimes of improved core confinement. Internal transport barriers and other forms of reduced core transport are now routinely obtained in all the leading tokamak devices worldwide. (3) The importance of controlling the H-mode edge pedestal is now generally recognized. Substantial progress has been made in extending high confinement H-mode operation to the Greenwald density, the demonstration of Type I ELM mitigation and control techniques and systematic explanation of Type I ELM stability. Theory-based predictive capability has also shown progress by integrating the plasma and neutral transport with MHD stability. (4) Transport projections to ITER are now made using three complementary approaches: empirical or global scaling, theory-based transport modelling and dimensionless parameter scaling (previously, empirical scaling was the dominant approach). For the ITER base case or the reference scenario of conventional ELMy H-mode operation, all three techniques predict that ITER will have sufficient confinement to meet its design target of Q = 10 operation, within similar uncertainties.
Analysis of experiments with electron cyclotron resonance heating (ECRH) requires a good knowledge of the ECRH power profile. This profile is reconstructed by analysis of the transient process after on-axis ECRH switching on in special experiments with suppressed sawtooth oscillations in the T-10 tokamak. The calculations show that the absorbed ECRH power, P T EC , determined by the change in time derivative of the electron temperature at the region of ECRH power input, and the absorbed ECRH power, P β EC , determined by the magnetic measurements, are several times different. Depending on the plasma density and plasma current, their relation, γ EC = P T EC /P β EC , changes from 0.2 to 0.4. Analysis of different explanations for this effect shows that adequate description of the transient process demands introduction of a ballistic jump in the total heat flux just after on-axis ECRH switching on. The effective heat diffusivity increases up to values of 10-15 m 2 s −1 in the first 100-200 µs and decreases down to values of 1.5-2.0 m 2 s −1 during the following 1-2 ms. Note that such a non-monotone dependence of the effective heat diffusivity cannot be described by the modern critical gradient models. It seems that plasma reacts directly to the deposited power but not to the corresponding consequences (the increase in temperature or gradients). Different physical mechanisms could be proposed for this process (partial destruction of magnetic surfaces, fast transition of information through the turbulent cell connections), but each of them needs further confirmation.
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