Diagnosing Magnetic Reconnection in Tokamak Scrape-off Layer Simulations

Magnetic reconnection in the scrape-off layer (SOL) may have several impacts on the operation of a tokamak, such as increased plasma flows and changes to the magnetic topology. In this work, we analyze data from the Gkeyll electromagnetic gyrokinetic code, using simulations that model the SOL of the National Spherical Torus Experiment at high beta parameters. These simulations exhibit magnetic fluctuations δB_⊥/B ∼ 1%, making this an interesting regime to look for indicators and effects of magnetic reconnection. Among these indicators is a locally large current, which allows the frozen flux constraint of ideal magnetohydrodynamics to be broken. Similarly, we look for regions of β_kin ∼ 1, where β_kin is the ratio between the kinetic energy of E×B flows in the plasma and the energy stored in B_⊥ fluctuations. If reconnection does happen at these sites, this would indicate a large energetic impact. Finally, we look for saddle points in the parallel magnetic vector potential A_∥, which correspond to the characteristic X-point magnetic topology in the perpendicular plane. Reassuringly, many of these indicator conditions highlight similar regions and times which will allow automated detection of reconnection in the SOL. This is also the first step in assessing the role of reconnection in SOL turbulence and transport.