Establish high-betaP scenario with large-radius ITB using KSTAR-like constraints, and integrating X-point radiator

2024 Research Campaign, Task Force: Integrated High beta-p Scenario

Purpose of Experiment

The purpose of this experiment is to 1) investigate for the first time the access of high-βP plasmas with internal transport barrier (ITB) with KSTAR-like constraints, 2) study He exhaust in high-βP plasma with large radius ITB and high dissipative divertor conditions, and 3) integrate X-point radiator/compact radiative divertor with high-β core. The experience and lesson learned from this experiment will directly contribute to the KSTAR FY24 joint high-βP experiment. The successful establishment of such a scenario in KSTAR will provide reference to future development of long pulse high-βP plasma with large radius ITB in a metal wall environment. The demonstration of a steady state high performance scenario is highly desired (and proposed) by many attractive fusion pilot plant (FPP) designs.

Experimental Approach

The primary limitations to develop KSTAR-similar shape high-βP scenario is the KSTAR operational constraints, including KSTAR plasma current ramp-up rate <0.5 MA/s, timing limitations for the transition to diverted shape, no NBI feedback control, F-coil operation constraints, etc. To explore the high-βP scenario within the above constraints, the following elements/approaches will be deployed to realize the goals: KSTAR-like shape development: the new KSTAR reference shape will be used as target, and we will work with the DIII-D/KSTAR task force to share the effort on this development. In KSTAR, the transition to diverted shape happens after 0.5 s, which is significantly later than in DIII-D. KSTAR-like power injection: KSTAR is equipped with 4-5 MW NBI power and 1-2 MW ECH power. Because the KSTAR volume is about half of the SVR DIII-D volume, the Paux/Vplasma is similar in both devices. We will use maximized scaled-up KSTAR-similar shape with scaled-up maximized allowed power. No OANBCD is available in KSTAR. Off-axis ECCD is available for ρ<0.8. Auxiliary power cannot be added < 0.3 s in KSTAR. No βN feedback control on NBI power in KSTAR. Here are the details of the NBI system: • 2 sets of NBIs (NB1=4~5MW, NB2=4MW) with 3 ion sources (named A, B, C) respectively • Among them, 2 ion sources (NB2-B and NB2-C < 2MW) are Off-Axis Other KSTAR-like constraints: gas injection; F-coil operation [dIPF1/dt < 10kA/sec (Limit on dIP/dt), dIPF6/dt < 5.5 kA/sec (Limit on radial control)] The experimental strategy is to start with DIII-D high q95 high-βp reference shot (e.g. #154406, Ip = 0.6 MA, Bt = 2.05 T, q95~11), with small shape modifications to adapt to new stage 1 divertor. This reference shot already meets the requirement of KSTAR-like Ip ramp-up rate. Gradually add KSTAR-like constraints into the following discharges, starting from plasma shape, late shaping transition, then gas injection, F-coil operation, maximum allowed power, late power injection, and finally removing βN feedback control on NBI power. If time allows: 1) Explore lower q95 with higher target Ip or a second Ip ramp-up and without clamped E-coil; 2) Explore ECH+NBI to reduce NBI power used in the experiment.

See more details, including project leads, at U.S. Department of Energy, Office of Scientific and Technical Information (OSTI).