Speaker
Description
We present three-dimensional EMC3-EIRENE modeling of an MPEX-like linear plasma configuration, showing that access to a high-recycling regime can be maintained even at significantly oblique target angles via utilization of near-target neutral baffles. MPEX (Materials Plasma Exposure eXperiment) plans to expose candidate material targets to extreme plasma fluences in tokamak divertor-relevant unbiased sheath regimes. Tilting the targets relative to the plasma column leads to the formation of a more reactor-relevant Chodura sheath, but also reduces the ion flux to the target due to both geometric expansion of the plasma footprint and a reduction in ionization of recycled neutrals.
Simulations in the geometry of Proto-Lite (a helicon-only prototype of MPEX) show that in a high-density upstream plasma regime, tilting the target to 85 degrees relative to surface normal decreases the recycling-driven target ion flux by over a factor of 2 relative to a standard 0 degree to normal target. However, simulations show that the inclusion of neutral baffling around the target sample holder reflects recycled neutrals into the plasma column, bringing the target back into the high-recycling regime and recovering up to 80% of the lost ion flux.
Comparisons are shown to early experiments in Proto-Lite, which has been upgraded to allow both tilted and standard target holder configurations. D-alpha emission trends at the target confirm the escape of recycled neutrals from the plasma column at significant target tilt. Experiments with baffle plates opposite the tilted target (in a geometry reminiscent of a tokamak slot divertor) exhibit enhanced D-alpha emission, indicating improved ion flux to the target. Implications for initial experiments in MPEX – which only includes a standard target configuration in its baseline project scope – are discussed.
This work is supported by the DOE Office of Science, Office of Fusion Energy Science, under contract number DE-AC05-00OR22725.