2025 – Steady-state hybrid scenario with Tungsten radiation and control strategies for KSTAR long pulse operation

Steady-state hybrid scenario with Tungsten radiation and control strategies for KSTAR long pulse operation

2025 Research Campaign, Task Force: W Compatible Steady State Scenarios

Purpose of Experiment

The purpose of this experiment is to bring the steady-state hybrid scenario as close as possible to the required ITER metrics of projected fusion power and fusion gain Q, with increased electron heating, lower q95 and optimized density. Increased core radiation to address the new ITER W wall will be included, by comparing LBO-W and W-equivalent radiators such as Kr and Xe. Absolute and normalized metrics can be used in D3D to increase the values of projected metrics for the ITER goals. More specifically, a series of physics issues in the present scenario need to be addressed.

Experimental Approach

D3D has recently acquired new tools and new understanding that can be applied most efficiently: – Port the scenario to the correct ITER shape and reactor-relevant q95 values (~5): an old LSN shape was used in previous experiments for this scenario, and it is known that shaping has a significant impact on the confinement, pedestal regime and MHD stability of a plasma. This experiment will use the progress made in the 2024 campaign where the ITER shape was applied to a higher density version of this scenario, which however suffered from various issues (addressed in the next paragraphs). Higher NB and EC current drive will be needed to lower the q95 range and optimize the resulting pedestal. Smaller volume and higher aspect ratio require increased power and optimization of the kinetic profiles to address the poorer n=1 MHD stability and the differences in higher order modes that are needed to provide the flux pumping mechanism – Optimization of the ECCD magnitude, location and deposition shape is needed to maximise the CD, reduce the injected torque, and avoid sawteeth. Small sawteeth were present in the 2024 first attempt at this work, where no tailoring of the current profile, density nor the heating was possible. The tradeoffs between higher density (better MHD stability, higher bootstrap current, more impurity dilution) and externally driven current (which maximises at low density) will be studied, to find the optimum operational space that maximises stability and performance. – Finally, W and W-equivalent radiators will be injected during to the flattop of the new scenario, to simulate the W source in the divertor and first wall of ITER and most FPP designs. The goal is to compare “real” W and W-equivalent radiators to bracket the resulting concentration (ie transport) and radiation (ie loss rates and profiles) and assess the modifications needed to the scenario to offset the added radiation and the impact on the kinetic profiles that were once stationary and fully-NI. The fidelity to ITER conditions will also be increased by the use of higher ECH power (only 2.8 MW were available in early 2024) and lower voltage beams which decreases the overall injected torque and ion heating for a lower rotation, higher Te/Ti solution (given that counterIp beams can only be used sparingly in steady-state scenarios, due to their driving counter-Ip plasma current and reducing the non-inductive fraction). This experiment directly addresses the goal of the ITER Integrated Scenarios area on providing solutions for the steady-state ITER mission, with a scenario that has demonstrated fully noninductive conditions in several experiments. Reaching higher betaN, higher confinement and ITER relevant core radiation at lower q95 is one crucial goal of all scenarios geared toward fusion reactors, and this experiment will be able to assess the requirements in H&CD, transport and stability for all of these metrics.

Interested in a behind-the-scenes look at DIII-D? Join us for a virtual tour during Fusion Energy Week (tour times: May 7 at 10am PDT, May 8 at 4pm PDT)! Sign up for a tour here.

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