The science
To work successfully, ITER and future fusion energy reactors cannot allow the walls of the divertor plates to melt, which extract excess heat from the plasma in a reactor. These walls are particularly vulnerable to melting when tight areas are exposed to heat. Based on current experiments on ITER and future reactors, scientists have predicted a dangerously narrow heat load range if reactors generate 500 megawatts of power from 50 megawatts of input energy. This risk is partly due to the fact that ITER is much larger and has far stronger magnetic fields than existing experiments. This means that the width of the ITER heat load may differ from today’s tokamaks. However, extreme computer analysis shows that turbulence reduces this risk. The analysis predicts that turbulence in the reactor plasma will distribute the heat load to an area more than six times wider than predicted by today’s tokamaks. The scientists obtained these results using a machine learning program based on the results of the ITER simulation at full power. The result is a simple analytical formula that predicts both the existing tokamak results and the ITER results.
The impact
The wider distribution of the thermal load on the divertor walls due to turbulence enables scientists to operate ITER more cost-effectively. This will help ITER achieve its goal of generating fusion power. A predictive formula based on first principles simulations can enable scientists to design more reliable and efficient future fusion reactors. These constructions had to take into account the limits imposed by the exhaust heat load range. The discovery in the present study will open new theoretical and experimental research on turbulence in boundary plasmas in current and future tokamak reactors. The results are an important step in fusion science and technology needed for future fusion power.
Summary
Extreme-scale simulations using the particle-in-cell tokamak code XGC on the Titan and Summit supercomputers at Oak Ridge National Laboratory reproduce tight heat stress results from existing tokamaks. However, the same code predicts that the thermal load width for a full power ITER plasma will be more than six times wider than the dangerously narrow values extrapolated from today’s tokamaks. A machine learning program found a hidden kinetic parameter that was missing in the previous experimental extrapolation parameter set and suggests a new formula for heat load width that works for both today’s tokamaks and full-power ITERs. The new formula will be verified using three new high-fidelity ITER simulations on the Summit and Theta supercomputers of the Department of Energy. The analysis of the physical data from the simulations shows that the widening of the heat load in the ITER at full power is due to the turbulent heat distribution through kinetic turbulence, which cannot be seen at the edge of today’s tokamaks. New experiments in existing tokamaks will validate the new prediction formula and ITER-compatible turbulence physics. This step will make today’s experiments more relevant to ITER and find the most successful operational pathway and design for efficient future fusion reactors.
financing
Funding for this research was provided by the Department of Energy Office of Science, Fusion Energy Sciences, and Advanced Scientific Computing Research programs through the SciDAC Program Partnership Center for High-Fidelity Boundary Plasma Simulation.
Comments are closed.