Power Exhaust Characteristics and Dissipation limits in the SVR Divertor on DIII-D

Measurements in the Shape Volume Rise (SVR) divertor using both flush and recessed Surface Eroding Thermocouples (SETCs) reveal that over 60% of surface heating near the outer strike point (OSP) during detachment is due to radiation. The SVR geometry in DIII-D, characterized by expanded plasma volume and increased upper triangularity, significantly enhances edge pressure and pedestal performance. In upper single-null plasmas, diagnostics indicate strong in–out divertor asymmetry, with peak heat flux at the OSP nearly twice that at the inner divertor. At 60% of the Greenwald limit and with B × ∇B drift directed into the divertor, a broad, flat heat flux profile is observed extending from the OSP well into the far scrape-off layer (SOL). Initial nitrogen seeding experiments, limited to moderate injection levels, reduced the OSP heat flux by ~80%, while heat flux in the far SOL remained high—consistent with partial detachment localized near the OSP. Full detachment is anticipated with higher seeding levels. Neon seeding suppressed heat flux to below 1 MW/m² across the entire outer divertor, producing a flat profile; far-SOL heat flux is expected to decrease further under more complete detachment conditions. These initial results demonstrate strong local power dissipation with limited far-SOL spreading. Ongoing experiments will explore full divertor detachment and broader dissipation strategies without compromising core confinement.

Work supported by the Department of Energy under Award Number(s) DE-FC02-04ER54698, DE-SC0023378, DE-AC05-00OR22725 and DE-NA0003525.