Improved reconstruction of neutral distribution in C-2W

Balmer-α emission measured with filtered high-speed cameras along with neutral density measurements near the wall using a suite of inverse magnetron gauges have been used to constrain DEGAS2 neutral particle modeling in C-2W[1].

The C-2W device uses eight neutral beams to inject large-orbit fast ions which sustain field-reversed configuration plasmas in steady-state. These fast ions carry current which maintains the magnetic configuration and collisionally heats the thermal plasma. Fast ions are lost via charge-exchange with neutral gas originating from plasma wall recycling, particle fueling, cold gas bleed from the beam injectors, beam dump recycling, and warm neutrals from beam capture.

These non-axisymmetric sources make reconstruction of the resulting neutral distribution challenging, so dedicated experiments have been performed to isolate individual source magnitudes. Titanium gettering and cleaning discharges are shown to decrease wall recycling which decreases the neutral density and the resulting charge-exchange loss.

[1] Gota et al., Nucl.  Fusion 61,106039 (2021)