Speaker
Description
The PPPL Impurity Powder Dropper (IPD) represents a novel capability for simultaneously controlling main ion recycling, modifying edge plasma conditions, and managing material surfaces in reactor-relevant environments. Coordinated experimental campaigns across multiple plasma confinement devices over a range of magnetic configurations have demonstrated that controlled low-Z particulate injection enables real-time wall conditioning while also providing substantial performance enhancements through modification of edge and core plasma profiles.
In tokamaks, powder injection acts as an in-situ boronization tool capable of reducing impurity sources in real-time during plasma operation. For example, ASDEX-Upgrade results show cumulative injection of only a few hundred milligrams of B produces substantial reductions in O and W emission, suppresses inter-ELM W influx, and supports recovery of low-ν* RMP ELM suppression, with post-mortem material analysis confirming micron-scale boron deposition across the divertor and limiter surfaces. Similarly, KSTAR results demonstrate parallel PSI benefits as BN injection reduces Dα emission by 30–40%, mitigates or suppresses ELMs, and lowers global recycling.
Stellarators exhibit complementary performance pathways. Short-pulse B₄C injections on W7-X produce rapid edge ablation leading to field aligned transport providing toroidal equilibration of ablated material and divertor deposition consistent with EMC3-EIRENE/DIS modeling. Material assimilation undergoes a characteristic two-stage confinement response whereby a transient stored-energy loss due to the particulate ablation is followed by a profile shift leading to a recovery of 20–40% higher ion temperatures and total stored energy. This response correlates with steepened edge ion-temperature gradients while spectroscopic and profile measurements indicate transitions toward ion-root confinement driven by edge density modification and Er restructuring. Comparably, on the Large Helical Device (LHD), B and BN powder injections have produced measurable main ion density control through generation of a low recycling wall and reduced intrinsic impurity sources. These injections have also steepened edge Te/Ti gradients with a broadband reduction in turbulence thus enabling the transition to a higher confinement ITG-suppressed state.
Cross-configuration analysis indicates that, despite differences in magnetic geometry and parallel transport paths, the performance gains observed on both tokamaks and stellarators share common underlying mechanisms through dynamic modification of edge impurity sources, redistribution of radiative power, and subsequent modification of temperature and density profiles. These results underscore the versatility of impurity powder injection across confinement concepts and highlights the emerging role of IPD systems as multifunctional tools for real-time wall conditioning, and as dynamic actuators for turbulence regulation, impurity control, and profile shaping.