Disentangle transport degradation from reduced fueling efficiency

Determine whether resonant magnetic perturbation-induced plasma pump-out at MAST results from a reduction in the average particle confinement time, representing enhanced transport, or from a reduction in neutral fueling efficiency.

Background

The single-reservoir particle-balance analysis initially attributes the density reduction caused by resonant magnetic perturbations to a shorter average particle confinement time, while the multi-reservoir model introduces a fueling-efficiency parameter for the fraction of ionizations that supply the confined plasma. The paper shows that reducing the confinement time or reducing the fueling efficiency can produce identical model time traces, so the available global measurements do not distinguish the two mechanisms.

Resolving this ambiguity is important because the mechanisms have different physical implications: a reduction in $\tau_p$ would indicate increased particle transport or exhaust, whereas a reduction in fueling efficiency would indicate that ionizations increasingly occur on field lines connected to divertor targets and therefore fail to fuel the confined plasma.