Exploration of Non-Resonant Divertor Features on the Compact Toroidal Hybrid

• Main Authors: Garcia, K. A, Bader, A, Frerichs, H, Hartwell, G. J, Schmitt, J. C, Allen, N, Schmitz, O
• Format: Journal Article
• Language: English
• Published: 24-08-2023
• Subjects: Physics - Plasma Physics
• DOI: 10.48550/arxiv.2307.10971

Non-resonant divertors (NRDs) separate the confined plasma from the
surrounding plasma facing components (PFCs). The resulting striking field line
intersection pattern on these PFCs is insensitive to plasma equilibrium
effects. However, a complex scrape-off layer (SOL), created by chaotic magnetic
topology in the plasma edge, connects the core plasma to the PFCs through
varying magnetic flux tubes. The Compact Toroidal Hybrid (CTH) serves as a
test-bed to study this by scanning across its inductive current. Simulations
observe a significant change of the chaotic edge structure and an effective
distance between the confined plasma and the instrumented wall targets. The
intersection pattern is observed to be a narrow helical band, which we claim is
a resilient strike line pattern. However, signatures of finger-like structures,
defined as heteroclinic tangles in chaotic domains, within the plasma edge
connect the island chains to this resilient pattern. The dominant connection
length field lines intersecting the targets are observed via heat flux
modelling with EMC3-EIRENE. At low inductive current levels, the excursion of
the field lines resembles a limited plasma wall scenario. At high currents, a
private flux region is created in the area where the helical strike line
pattern splits into two bands. These bands are divertor legs with distinct SOL
parallel particle flow channels. The results demonstrate the NRD strike line
pattern resiliency within CTH, but also show the underlying chaotic edge
structure determining if the configuration is diverted or limited. This work
supports future design efforts for a mechanical structure for the NRD.