Divertor Study on DEMO Reactor

Abstract

Huge power handling in the SOL/divertor region is one of the crucial issues for a tokamak fusion reactor. Divertor design study of a DEMO reactor with fusion power of 3 GW and ITER size plasma has progressed using the integrated divertor code SONIC. Recently, to improve conversion of the solution for the DEMO divertor plasma simulation, SONIC code has been improved. The calculation time is significantly reduced by (i) the backflow model for the simplified impurity exhaust process and (ii) optimization on HELIOS at BA-IFERC. In the SONIC simulation, the partial detached divertor plasma was obtained by the Ar impurity seeding. Although the plasma heat load at the outer target was reduced by the partial detachment, the contribution of the impurity radiation and the surface recombination of the fuel ions to the target heat load became large. As a result, the peak of the total target heat load was estimated to be 16 MW/m 2 . In order to reduce the total heat load, control of the impurity radiation profile by kind of seeding impurity species and the divertor geometry has been studied. They can decrease the target heat load, but the peak heat load is still larger than the heat removal capability of the present divertor target concept. Further design study including change of the machine specifications is necessary.

Mode Structure Analysis of Detached Plasmas with 2D Images

“…(1), (2). Here, m = 0, 1, and 2 modes correspond to circular, decentered, and elliptical components, respectively.…”

“…To keep the heat load to the divertor plate less than the safety limit, neutralization of plasmas via radiation from impurity and volumetric plasma recombination processes, so called plasma detachment [1], is thought to be inevitable, and control of plasma detachment is an important issues in next fusion devices. However, there are still issues with the modeling of the plasma detachment; a discrepancy between the experimental results and the numerical simulation regarding the particle flux reduction [2] suggested unknown features in the atomic and molecular processes and/or cross-field transports.…”

The influence of the radial particle transport on the divertor plasma detachment

“…Recently, in order to improve the accuracy of simulation of the DEMO divertor [11], the code suite has been improved to include: (1) contribution from the impurities to the electron density, (2) the ion heat flux limiter, (3) smoothing source terms near the target to reduce the Monte-Carlo noise/perturbation, (4) time averaging of the impurity Monte-Carlo result to reduce the large oscillation, and (5) correcting thermal force term for long mean-free-path. Fig.…”

Kinetic Modelling of the Plasma Recombination

“…Typically, plasma detachment is reached at sufficiently high upstream SOL densities, leading to electron cooling in front of the divertor plates and to so called roll over of the divertor ion flux [2]. Physics of the plasma detachment is not yet well understood and there exist number of experimental observations, which cannot be reproduced by SOL simulating large fluid codes [3][4][5][6][7]. One of the possible explanations is the influence of kinetic effects, which might play dominant role in the detachment [8,9].…”