Comprehensive 3-D simulation and performance of ITER plasma facing and nearby components during transient events—Serious design issues

Abstract

A key obstacle to a successful magnetic fusion energy production in Tokamak reactors is performance during abnormal events. Abnormal events include plasma disruptions, edge-localized modes (ELMs), vertical displacement events, and runaway electrons. While tremendous efforts are being made to find ways to mitigate such events, a credible reactor design must be able to tolerate a few of these transient events. We have recently enhanced our comprehensive HEIGHTS (High Energy Interaction with General Heterogeneous Target Systems) simulation package to enable detailed 3-D investigation of the overall aspects of plasma-material interaction processes during all the transient events. Advanced models and numerical tools were developed to efficiently couple major key processes during the transient events, and in particular disruptions and giant ELMs. These include dynamic interaction, deposition, and scattering of the escaping core plasma particles with the evolving and propagating secondary divertor vapor/plasma in the strong magnetic field. These details are critical for assessing the damage to all interior components, including the hidden structure and the first wall which were not directly exposed to these transient events and never thought to be affected as a result. Despite developing numerous efficient numerical techniques and solution methods, such calculations take several months on current supercomputers to complete. Our present results show, for the first time, that unmitigated transient events could cause significant melting and vaporization damage to most interior and hidden components, including the first wall that were not directly exposed to these events. The current ITER divertor design may not work properly and need to be significantly modified or redesigned to prevent this damage. Published by AIP Publishing. https://doi.

Potential design problems for ITER fusion device

“…These methods include new three-dimensional Monte Carlo (MC) kinetic model to simulate the spatial distribution of ion and electron energy depositions of the incident core particles on the inner and outer ITER divertor plates. These advanced numerical methods were extensively verified and benchmarked in current tokamak devices 6 , 8 . The simulations also include detail implementation of the complex magnetic field structure and the exact geometry of various ITER internal components.…”

“…When the tokamak power is increased to cause significant erosion of the divertor plates during transient events at normal and abnormal operations, the plates will melt and vaporize the divertor material soon after the start of the transient events. Further heating from the escaping plasma particles will continue to heat the vaporized material and form a secondary divertor plasma that expands following the magnetic field lines into the scrape-off layer and continue to interacts with the incoming DT plasma 6 . Assuming the damage from the transient events to only affect the divertor plate which claimed to be easily repaired or replaced is no longer the case due to the involvement of the secondary plasma formed from vaporized divertor materials 13 .…”

“…Simulation of such events requires integrating various interaction processes including particle and photon energy deposition, material thermal evolution, phase transformation, melting, vaporization, atomic physics models, ionization, plasma formation, MHD evolution, plasma opacity, and photon transport in strong magnetic and electric fields environment and in full 3D real reactor design. Recently, we significantly enhanced our comprehensive HEIGHTS simulation package to efficiently integrate various models of different interaction processes implemented for the exact current ITER design 6 . Figure 1 illustrates the simulation domain of ITER internal plasma facing components using the adaptive mesh refinement (AMR) to map details of the design from submicron to tens of meters scale.…”

“…The detailed simulation of the core particles motion into the SOL (Fig. 1 a) is used in our comprehensive model as an input power source to activate the magnetohydrodynamic models in HEIGHTS package 6 . Each time step simulation requires at least ~ 10 3 particles to achieve reasonable compromise between accuracy of calculation and simulation time.…”

“…This work carefully predicts and simulates the evolution and propagation of the secondary plasma generated from the divertor plate material, its interactions with various reactor components following a disruption or an ELM event initially incident on both the inner and outer divertor plates. This secondary divertor plasma has completely different physics and hydrodynamic evolution compared to the core DT plasma 6 . While disruptions and ELMs are much different in energy content, they both have serious consequences to the performance of the current divertor designs in the tokamak concept for ITER and beyond.…”