Real-time wall conditioning experiments utilizing the impurity powder dropper on LHD *

Controlled injections of B and BN from the PPPL designed Impurity Powder Dropper into LHD have demonstrated positive effects on the wall conditions in both an intra and inter-shot basis.  Reactions to particulate injection depend upon discharge length which governs the effective time for plasma and vessel response to the added material.  In 4s long plasmas, a reduction in both wall recycling and native impurity content is noted over the course of several discharges.  For plasmas greater than 10s in length, improvements are observed in real time as a consequence of extended injection times. For multi-minute plasmas, repeated sets of 3 x 10s boron injection pulses every 3 minutes resulted in prompt reduction of plasma density presumably through ion co-deposition with the main ion species at the first wall surfaces and gettering by the newly applied boron layer.   This ability to demonstrate active control in steady state scenarios is an important initial step in the development of this technique as a real time boronization alternative.  Powder assimilation efficiency is also studied with modelling from coupled EMC3-EIRENE and DUSTT simulations supporting observed results and further indicating scenarios which could lead to promising long pulse real time boronization applications.