Parameter study of L–H transition for plasma operation scenario development in JA DEMO

We have investigated the L–H transition in JA DEMO, a design concept of the steady-state tokamak fusion demonstration reactor. We develop an L–H transition model, which determines the minimum pedestal growth time such that a power ratio, the net plasma loss power across the separatrix over the L–H threshold power, is maintained at a constant value during pedestal growth for a given external heating power. We conduct parameter studies using an integrated modeling code, considering impurity transport. The dependence of the heating power and time required for the L–H transition on the plasma density, temperature, threshold power, impurity density fraction, and impurity transport coefficients is clarified. We evaluate the appropriate impurity density fraction for the L–H transition and the divertor heat load reduction. The fraction depends on the impurity transport coefficients and external heating power. The obtained results are necessary to confirm the L–H transition feasibility and to develop the plasma operation scenario consistent with the various engineering constraints in a design-stage reactor. The heating power required for the L–H transition turns out to be lower than the power supposed to be installable in the current design activities of JA DEMO.