Upgrading DIII-D to Close the Gaps to Future Fusion Reactors*

The DIII-D program is pursuing an ambitious plan to rapidly close critical design gaps to a Fusion Pilot Plant (FPP), including integrating performance and exhaust solutions, addressing plasma interacting material and technology issues through an expanded R&D effort, and resolving a high fusion gain path to ITER and a pulsed/steady-state FPP. Key to the DIII-D approach is major facility upgrades to access reactor-relevant physics regimes with increased flexibilities. A staged divertor program will allow for more plasma shaping, and higher current and density, to enable more reactor-relevant core-edge integration. The electron cyclotron heating (ECH) will be increased to 10 gyrotrons, with an extension to 20 gyrotrons by 2028, to furnish low-torque electron heating and profile control, while new reactor-relevant solutions for efficient off-axis current drive will be pioneered by high-field-side lower hybrid current drive, helicon waves and top launch ECH to enable FPP steady-state scenarios. Additional proposed facility upgrades include an expanded set of 3D coils, and disruption mitigation and materials testing capabilities. An exciting option for a negative triangularity path is being assessed.

Together these elements will enable reactor solutions to be pioneered and projected with confidence.