Heat flux width in DIII-D high-power-density experiments

Recent DIII-D experiments pushed peak parallel heat flux at the miplane to a projected-maximum value of q_||≈1.1 GW/m² with current heating capacity and parameters, in able to better understand how key divertor metrics scale to a fusion pilot plant (FPP). In particular, heat flux width and peak value scaling is crucial for designing future reactors as it determines divertor survivability, an outstanding problem and key boundary condition. A multi-machine regression[1] predicts narrow heat flux widths—and high peak flux—in reactors; however, recent work at DIII-D[2] and AUG[3] shows the potential for departure from this scaling, with divertor peak values saturating with increasing power. High q_|| experiments performed recently cover plasma current values from I_p=1.0-1.9 MA, and auxiliary power values from P_aux=5-17 MW. Discharges were lower single null, with the strike point on the lower (floor) level of the divertor to allow the higher triangularity necessary to run higher performance discharges; ∇B drift is into the divertor, with attached divertor conditions to allow for heat flux characterization. Primary divertor diagnostics include IR camera measurements of heat flux to the target, and an array of in-target Langmuir probes for divertor temperature density and ion saturation current profiles. At I_p=1.9 MW and P_inj=15.5 MW, we find a measured peak parallel heat flux to the target of approximately 675 MW/m².

[1] Eich et al., Nucl. Fusion 53 (2013) 093031

[2] Leonard et al., Nucl. Mat. Energy 25 (2020) 100869

[3] Eich et al., Nucl. Fusion 58 (2018)