Effects of complex symmetry-breakings on alpha particle power loads on first wall structures and equilibrium in ITER

Abstract

Abstract. Within the ITPA Topical Group on Energetic Particles, we have investigated the impact that various mechanisms breaking the tokamak axisymmetry can have on the fusion alpha particle confinement in ITER as well as on the wall power loads due to these alphas. In addition to the well known TF ripple, the 3D effect due to ferromagnetic materials (in ferritic inserts, FI, and test blanket modules, TBM) and ELM mitigation coils are included in these mechanisms. ITER Scenario-4 was chosen since, due to its lower plasma current, it is more vulnerable for various off-normal features. First, the validity of using a 2D equilibrium was investigated: a 3D equilibrium was reconstructed using the VMEC code, and it was verified that no 3D equilibrium reconstruction is needed but it is sufficient to add the vacuum field perturbations onto an axisymmetric equilibrium. Then the alpha particle confinement was studied using three independent codes, ASCOT, DELTA5D, and F3D OFMC, all of which assume MHD quiescent background plasma and no anomalous diffusion. All the codes gave a loss power fraction of about 0.2% . The distribution of the peak power load was found to depend on the first wall shape. We also made the first attempt to accommodate the effect of fast ion related MHD on the wall loads in ITER using the HMGC and ASCOT codes. The power flux to the wall was found to increase due to the redistribution of fast ion by the MHD activity. Furthermore, the effect of the ELM mitigation field on the fast ion confinement was addressed by simulating NBI ions with the F3D OFMC code. The loss power fraction of NBI ions was found to increase from 0.3 % without the ELM mitigation field to 4-5% with the ELM mitigation field.

High field side launch of RF waves: A new approach to reactor actuators

“…The majority of fast ions (ICRF minority heating and/or fusion-α's) exit on LFS, and runaway electrons also shift their orbits to the LFS. Simulations of ITER lost ion heat loads show peaked heat loads on the LFS with essentially no heat load on the HFS wall [23].…”

A Scoping Study for High-Field-Side Launch of Lower Hybrid Waves on ADX MIT

“…The generation and accumulation of high-Z impurities in the presence of high-power RF actuators is a major hurdle, and the improved impurity screening on the HFS will lessen the impact of high-Z wall materials on tokamak performance. The HFS wall also has lower energetic particle loading [15] and neutron loading [16], [17] than the LFS wall. Damage due to unconfined fast particles (trapped ion banana orbits and runaway electron orbits) observed on existing experiments is concentrated near the LFS midplane.…”

Using neutral beams as a light ion beam probe (invited)

“…In fact, simulations show that ELM mitigation coils (referred to as ELM-coil in this paper) can induce up to 5% loss of beam ions in ITER. 18 The LIBP technique has been used to investigate the effects of applied 3D fields on DIII-D. 19 The experiments are carried out in MHD-quiescent L-mode plasmas with externally applied n = 2 field from ELM-coils. A counter-NBI (with respect to the plasma current direction) and a co-NBI are utilized as the LIBP source beam successively.…”