Power exhaust concepts and divertor designs for Japanese and European DEMO fusion reactors

Abstract

Concepts of the power exhaust and divertor design have been developed, with a high priority in the pre-conceptual design phase of the Japan–Europe broader approach DEMO design activity (BA DDA). Common critical issues are the large power exhaust and its fraction in the main plasma and divertor by the radiative cooling (P rad tot/P heat ⩾ 0.8). Different exhaust concepts in the main plasma and divertor have been developed for Japanese (JA) and European (EU) DEMOs. JA proposed a conventional closed divertor geometry to challenge large P sep/R p handling of 30–35 MW m−1 in order to maintain the radiation fraction in the main plasma at the ITER-level (f rad main = P rad main/P heat ∼ 0.4) and higher plasma performance. EU challenged both increasing f rad main to ∼0.65 and handling the ITER-level P sep/R p in the open divertor geometry. Power exhaust simulations have been performed by SONIC (JA) and SOLPS5.1 (EU) with corresponding P sep = 250–300 MW and 150–200 MW, respectively. Both results showed that large divertor radiation fraction (P rad div/P sep ⩾ 0.8) was required to reduce both peak q target (⩽10 MW m−2) and T e,i div. In addition, the JA divertor performance with EU-reference P sep of 150 MW showed benefit of the closed geometry to reduce the peak q target and T e,i div near the separatrix, and to produce the partial detachment. Integrated designs of the water cooled divertor target, cassette and coolant pipe routing have been developed in both EU and JA, based on the tungsten (W) monoblock concept with Cu-alloy pipe. For year-long operation, DEMO-specific risks such as radiation embrittlement of Cu-interlayers and Cu-alloy cooling pipe were recognized, and both foresee higher water temperature (130 °C–200 °C) compared to that for ITER. At the same time, several improved technologies of high heat flux components have been developed in EU, and different heat sink design, i.e. Cu-alloy cooling pipes for targets and RAFM steel ones for the baffle, dome and cassette, was proposed in JA. The two approaches provide important case-studies of the DEMO divertor, and will significantly contribute to both DEMO designs.

Effect of elastic scattering between ions and neutral particles on ion transport perpendicular to magnetic fields in divertor plasmas

“…The anomalous diffusion coefficient $$$ {D}_{\mathrm{a}} $$$ is 0.3 m 2 s −1 with reference to other previous works. [ 24–26 ] On the other hand, in case B, although the velocity is calculated from Equations (1) and (2), the movement of guiding center in the direction perpendicular to magnetic fields is ignored. In other words, Equation (3) is not used.…”

“…The background plasma parameters, including plasma density $$$ {n}_{\mathrm{i}} $$$, ion temperature $$$ {T}_{\mathrm{i}} $$$, and electron temperature $$$ {T}_{\mathrm{e}} $$$, are fixed at 1 × 10 20 m −3 , 50 eV, and 50 eV, respectively, based on the SONIC simulation results. [ 25,26 ] These are the values at the divertor plate of JA DEMO reactor near a peak of heat load. Temperature and density plateaued in a width of about a few cm; hence, the background values are chosen as representative conditions.…”

“…Enhancement of the radial transport by the large-angle elastic scattering may improve the result and also may affect design study of JA DEMO reactor. [25,26] In the SOLPS code, the large-angle elastic scattering is taken into account. However, how the elastic scattering affects the plasma transport in the direction perpendicular to magnetic field lines, especially in the detachment, has not been investigated in detail.…”

Physics design of 14 MeV neutron generator facility at the Institute for Plasma Research

“…It will be operated on a maximum fusion power of 500 MW [1,2]. Further demonstration reactors for power plants are under design [3][4][5][6][7]. Various design and material irradiation experiments are required to perform to support nuclear fusion power plants.…”

SOLPS-ITER modeling of EU-DEMO Ar-seeded cases with drifts and kinetic neutrals

“…This can help to decrease the power flux density and electron temperature on divertor targets and prevent tungsten sputtering. Several publications, such as [2][3][4], explore possible impurity seeding and deuterium puffing rates to achieve conditions with electron temperatures and power flux density below 5 eV and 5 MW m −2 , respectively. However, until now, such modeling for EU-DEMO was performed without drifts or without kinetic neutrals.…”