Akash Shukla, UT-Austin

"Gyrokinetic Simulations of the SOL in the Low Recycling Regime"

Abstract: Improving energy confinement in tokamak reactors is essential for reducing reactor cost and moving towards commercially viable fusion reactors. Maintaining good confinement is difficult because the large temperature gradients typically required to achieve fusion temperatures cause heat loss, degrading confinement. Reducing these temperature gradients while maintaining high temperatures is possible if the temperature of the edge of the reactor is raised. Studying heat exhaust which occurs in the scrape-off layer (SOL) of the tokamak is essential for being able to determine the edge temperature. The low-recycling regime is a method by which the SOL and edge temperature can be raised and energy confinement can be improved. However, raising the edge temperature comes with challenges such as impurity sputtering.

Simulating the low-recycling regime is essential to finding ways to overcome these challenges, but fluid simulations typically used to simulate the SOL are not valid in the low recycling regime where the plasma is not collisional and kinetic effects are important. In fact, kinetic effects such as mirror force are crucial to overcoming challenges associated with low-recycling. Here, we use the Gkeyll code to conduct gyrokinetic simulations of the Spherical Tokamak for Energy Production (STEP) SOL that demonstrate that we can address impurity sputtering using special magnetic configurations. We also present preliminary gyrokinetic simulations of the Lithium Tokamak Experiment (LTX), a tokamak designed to study low-recycling, which will be used to provide SOL data to the experimental team in the future.