Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation

WEST is an MA class superconducting, actively cooled, full tungsten (W) tokamak, designed to operate in long pulses up to 1000 s. In support of ITER operation and DEMO conceptual activities, key missions of WEST are: (i) qualification of high heat flux plasma-facing components in integrating both technological and physics aspects in relevant heat and particle exhaust conditions, particularly for the tungsten monoblocks foreseen in ITER divertor; (ii) integrated steady-state operation at high confinement, with a focus on power exhaust issues. During the phase 1 of operation (2017–2020), a set of actively cooled ITER-grade plasma facing unit prototypes was integrated into the inertially cooled W coated startup lower divertor. Up to 8.8 MW of RF power has been coupled to the plasma and divertor heat flux of up to 6 MW m−2 were reached. Long pulse operation was started, using the upper actively cooled divertor, with a discharge of about 1 min achieved. This paper gives an overview of the results achieved in phase 1. Perspectives for phase 2, operating with the full capability of the device with the complete ITER-grade actively cooled lower divertor, are also described

Magnetohydrodynamics modelling of H-mode plasma response to external resonant magnetic perturbations

The response of an H-mode plasma to Resonant Magnetic Perturbations (RMPs) generated by so-called I-coils in DIII-D experiments on type I edge localized modes suppression is modelled using the nonlinear reduced magnetohydrodynamics (with zero-β, i.e. zero plasma temperature, in the version used here) code JOREK in X-point geometry. JOREK self-consistently advances in time the magnetic flux, vorticity, and plasma density in the presence of the RMPs. Without any toroidal rotation, the magnetic response from the plasma does not significantly modify the islands widths. A radial convective E⃗×B⃗ plasma transport is observed to occur in the presence of the RMPs. The possibility that this mechanism could explain the enhanced density transport observed experimentally in DIII-D is discussed. Simulations with a rigid-body-like rotation at a fixed velocity shows evidence of a screening of the RMPs. The extension of our results to realistic parameters is discussed

Quasi-linear MHD modelling of H-mode plasma response to resonant magnetic perturbations

The plasma response to externally imposed resonant magnetic perturbations (RMPs) is investigated through quasi-linear MHD modelling in the case where the resonant surfaces are located in the pedestal of an H-mode plasma. The pedestal is a particular region regarding the question of plasma response to RMPs because of its strong E × B and electron diamagnetic rotations. It is found that a strong rotational screening takes place in most of the pedestal. The RMPs may, however, penetrate in a narrow layer at the very edge, where the plasma is cold and resistive. The possibility that one harmonic of the RMPs may also penetrate if its resonant surface is at a particular location, close to the top of the pedestal, where the E × B and electron diamagnetic rotations compensate each other, is discussed. Finally, the RMPs are found to produce some additional transport, even though they do not penetrate

The optimization of resonant magnetic perturbation spectra for the COMPASS tokamak

The COMPASS tokamak, recently transferred from UKAEA Culham to IPP Prague, is equipped with a set of saddle coils for producing controlled resonant magnetic perturbations (RMPs). In the future experimental programme of COMPASS we plan to focus on studies of RMPs, especially in view of their application as an ELM control mechanism and their considered use in ITER. In the present contribution we describe the preparatory calculations for the planned experiments. We computed the spectra of perturbations for several different equilibria predicted by MHD simulations and determined the positions and sizes of the resulting islands. It is shown how the saddle coils of COMPASS can be adapted to our equilibria to obtain good island overlap at the edge, which is believed to be a key component in the ELM mitigation effect. The techniques used for adapting the coils to achieve this result are described. Those are fairly general and could be used in the design of RMP coils on other machines