K. N. Tarasyan

Transport model of canonical profiles for electron and ion temperatures in tokamaks

A set of transport equations using canonical ion and electron temperature profiles is proposed. Simulations of electron cyclotron resonance heating on T-10 and of the L-mode in TFTR, JET and ASDEX have been performed. From an analysis of the results of the calculations it is possible to construct universal expressions for heat fluxes without free parameters. On the basis of the developed model, several predictions are made for the International Thermonuclear Experimental Reactor (ITER).

Improved confinement regimes within the transport model of canonical profiles

The canonical profiles transport model is extended to describe various modes with improved confinement in tokamaks. A generalized profile consistency principle is proposed and a corresponding mathematical formalism is formulated. This formalism is used for the modelling of various regimes, such as H modes in DIII-D, JET and ASDEX, the hot ion mode and enhanced performance after pellet injection (PEP mode) in JET. This modelling, together with a known global scaling law, allowed the dependence of the internal model parameters on the plasma geometry and other physical variables to be established. This makes the model predictive. The approximate analytical criteria for the L to H and L to hot ion mode transitions are also obtained

Simulation of START shots with the canonical profile transport model

The canonical profile transport model, which has been benchmarked previously for tokamaks with a conventional aspect ratio, is applied to simulations of the spherical tokamak START. A set of Ohmic shots is used to modify the model so that it is appropriate for the specific conditions of the spherical tokamak plasma. The application of the model as a tool to analyze neutral beam-heated START shots allows the estimation of the neutral beam-injection power absorbed by the plasma, PNBabs, which is experimentally uncertain. The modeling shows that both PNBabs and the energy confinement time increase with increasing the average density. Finally, the modified model is used to simulate the performance of the new megaampere spherical tokamak MAST at Culham.

Non-local plasma response within the canonical profiles transport model

The experiments on some tokamaks are simulated, where a fast response near the plasma centre was observed after cooling (by impurity ablation) or heating (by current rampup) at the edge. The canonical profiles transport model (CPTM) is modified for the simulations. The existing equations describing a slow relaxation of the real profile to the canonical profile are complemented by equations describing a fast evolution of the canonical profile. The problem of the canonical profile determination is linked to the transport set through the boundary conditions. Ohms law and one of the Maxwell equations at the edge are used as boundary conditions for the canonical profile of μc (μ = 1/q, q is the safety factor). Therefore, a change of Te(r) profile near the edge leads to a redistribution of the μc(r) profile and to a jump in the electron and ion heat diffusivities over the whole plasma cross-section. The sign of the response (heating or cooling) is very sensitive to details of Te(r) and the evolution of its gradient at the edge. The model reasonably describes both the core heating in TFTR and TEXT, and the core cooling in JET.

Ion energy balance in T-10

The authors report the results of ion temperature measurements in the T-10 tokamak, with allowance for corrections due to the effect of kinetic transport of ions to the energy spectrum of atoms. On the basis of the experimental data they analyse the ion energy balance in the Ohmic heating and ECRH regimes over a broad range of plasma parameters.

Investigation of the H-mode during ECRH in the T-10 tokamak

An improved confinement regime with an external transport barrier (H-mode) is obtained during electron-cyclotron resonance heating of a plasma in the T-10 tokamak. A characteristic feature of this regime is a spontaneous density growth accompanied by a drop in the intensity of Dα line and an increase in βp by a factor of ∼1.6. The threshold power for the L-H transition is close to that predicted by the ITER scaling. The best characteristics of the H-mode are achieved with decreasing qL to 2.2. It is shown that the external transport barrier arises for electrons, whereas the heat transport barrier insignificantly contributes to improved confinement.

Test of canonical profiles and semi-empirical transport models with JT-60U plasmas

A canonical profiles transport model and a semi-empirical transport model are tested against JT-60U plasmas. The simulations were carried out with the 1.5-D transport code ASTRA, comprising the particle transport, and the electron and ion heat transport.