An Impurity Powder Dropper for the SMART Tokamak

This work presents the design and performance characterization of an impurity powder dropper (IPD) developed for the Small Aspect Ratio Tokamak (SMART) at the University of Seville, Spain. SMART studies positive and negative triangularity plasmas within the low aspect ratio range of 1.4 < R/a < 3, with a major radius (R) of 0.40–0.60 m and a minor radius (a) of 0.20–0.33 m. The IPD gravitationally delivers boron (B) powder into the plasma, which ablates and transports the injected material. The B species coat SMART’s stainless steel vacuum vessel walls and this boronization process reduces the influx of intrinsic wall impurities, such as oxygen, carbon, nitrogen, and iron, which radiate power and cool the plasma. It also reduces gas fueling/recycling from the wall. Mounted on the top of the vessel, the IPD drops controlled amounts of powder by a piezoelectric blade driven by a signal generator to vibrate at a set frequency. We calibrated the drop rate for 1–10 mg/s, enabling controlled B coating while achieving efficient powder ablation. The coatings produced by the IPD will be evaluated using post-exposure material analysis and optical emission spectroscopy with a broad-range spectrometer.

We acknowledge US DOE no. DE-AC02-09CH11466.