Research Milestones

FY26 Research Milestones

R(26-1):  Commission operational tools that enable high-performance discharges in NSTX-U

Description:  NSTX-U is designed to develop the physics and technical basis required for stationary, long pulse, high non-inductive fraction operation in a low-aspect-ratio tokamak. A major research goal during the FY26 commissioning campaign on NSTX-U is to develop high-performance H-mode scenarios that simultaneously exceed the current (Ip > 1.4 MA) and magnetic field strength (BT > 0.55) achieved on NSTX. A critical component of these scenarios is maximizing the achievable elongation at low internal inductance (li). This effort will build on the ramp-up simulation development that identifies ramp-up scenarios that optimize the achievable elongation. Dedicated experiments will quantify the vertical and MHD stability limits in the ramp-up phase in order to compare to the simulation results and identify avenues for potential expansion of these limits through new scenario or control tools. Building upon the results of the FY16 NSTX-U run campaign and the FY17-18 milestones on error field identification and correction, a re-assessment of low-n error fields, mode-locking, and optimal error field correction will be made. Further, RWM control and dynamic error field correction algorithms using both proportional and state-space n ≥ 1 feedback schemes will be implemented taking advantage of the spectrum flexibility provided by the 2nd SPA power supply. This effort will enable access to large 𝛃N/li, which is critical for high-current H-mode scenarios. 

R(26-1):  Assess H-mode energy confinement and pedestal characteristics with higher field, plasma current, and NBI heating power (Provisional)

Description: Future ST devices such as ST-FNSF will operate at higher toroidal field, plasma current and heating power than NSTX. To establish the physics basis for future STs, which are generally expected to operate in lower collisionality regimes, it is important to characterize confinement and pedestal structure over an expanded range of engineering parameters.  H-mode studies in NSTX and MAST have shown that the global energy confinement exhibits a more favorable scaling with collisionality (BτE ~ 1/ν*e) than that from ITER98y,2. In addition, the H-mode pedestal pressure increases with ~IP2.  With higher BT, IP, and NBI power with beams at different tangency radii, NSTX-U and MAST-U provide an excellent opportunity to assess the core and boundary characteristics in regimes more relevant to future STs and to explore the accessibility to lower collisionality. Specifically, the relation between H-mode energy confinement and pedestal structure with increasing IP, BT and PNBI will be determined and compared with previous NSTX and MAST results, including emphasis on the collisionality dependence of confinement and beta dependence of pedestal width. Coupled with low-k turbulence diagnostics and gyrokinetic simulations, the experiments will provide further evidence for the mechanisms underlying the observed confinement scaling and pedestal structure.  During FY2023-24, significant effort will be put toward profile and turbulence diagnostic commissioning for these experiments on NSTX-U.