Extreme Conditions for Plasma-Facing Components in Tokamak Fusion Devices

Abstract

Abstract-Safe and reliable operation is still one of the major challenges in the development of fusion energy. In magnetic fusion devices, perfect plasma confinement is difficult to achieve. During transient loss of plasma confinement, high plasma power and particle beams (power densities up to hundreds of gigawatts per square meter in time duration on the order of milliseconds) strike the reactor walls, particularly the divertor plate, and can significantly damage the exposed surfaces and also indirectly damage nearby components. To predict the resulting damage of the direct plasma impact on the divertor plate, comprehensive multiphysics multiphase models are developed, integrated, and implemented in the High Energy Interaction with General Heterogeneous Target Systems computer simulation package. The evolution of the divertor material, resulting vaporization, heating and ionization of vapor plasma to higher temperatures, and, consequently, the resulting photon radiation, transport, and deposition around the divertor area are calculated for typical instability parameters of the edge-localized modes and disruption for an ITER-like geometry. Index Terms-Computer simulation, plasma density, plasma temperature, radiation effects, reactor design, Tokamak devices. W E SIMULATED the evolution of an edge-localized mode (ELM) plasma impact onto the divertor surface of an ITER-like geometry with strong and inclined magnetic field configuration using the High Energy Interaction with General Heterogeneous Target Systems (HEIGHTS) computer simulation package with extensive integrated models [1]- We studied the effect of ELMs on the divertor plate with different durations of 1, 0.5, and 0.1 ms. The ELM durations of 0.5 and 1 ms correspond to deposition powers of 0.92 MW/cm 2 and 0.46 MW/cm 2 , respectively. The shorter ELM initiates intense surface vaporization. The produced plasma cloud has a high temperature (up to 60 eV) and is very effective in forming a stable vapor/plasma shielding for the ELM incoming particles because of the insufficient time for vapor MHD motion and expansion/transport. The plasma shielding layer acts as an absorption layer for the rest of the ELM impact near the strike point location. The ELM particles decelerate, scatter, and deviate from the initial impinging direction in the plasma cloud that results in a significant decrease in erosion depth directly at the strike point and to a broadening of the whole erosion area. Because the plasma cloud is located near the strike point and relatively in confined position, the processes of plasma radiation and transport are evolved in this confined area around the divertor strike point but relatively far from nearby components. The impact ELM energy is consumed mostly for vaporization because of insufficient time for thermal relaxation and heat conduction inside the divertor plate. The MHD role and the expansion of the evolved vapor plasma increase appreciably with ELM impact duration. The plasma cloud has sufficient time for motion and expansion in the dome area [see We calculated the incident photon fluxes along the dump and dome surfaces using our Monte Carlo radiation transport model implemented in HEIGHTS. For the same impact of total ELM energy of 12.6 MJ, higher radiation deposition was predicted for the longer impact duration of 1.0 ms. The maximum energy deposited reaches values up to 40 J/cm 2 . These values are 0093-3813/$26.0