Development of Systematic, Self-consistent Algorithm for the K-DEMO Steady-state Operation Scenario

Abstract

Korean Fusion Demonstration Reactor (K-DEMO) project is aiming to realize a net electricity generation, a self-sustained tritium, but also to be used as a component test facility. Recent progress of superconducting materials and manufacturing experiences in KSTAR magnet leads a distinct design feature of K-DEMO which is high central magnetic field at the plasma center of more than 7 T. A burning plasma is a kind of self-organized plasma that most heating is from the alpha particle and most plasma current is sustained by self-driven current different from the present experimental device. To analyze such a complex phenomenon with a computational method, an integrated numerical package is strongly required but also a systematic and self-consistent algorithm is essential. Based on magnet coil and its surroundings, geometrical parameters such as major/minor radius are determined. To estimate overall plasma performance, 0-D plasma operation contour analysis code is first developed and determined a range of domain which satisfies the target fusion power in density/temperature space. Within this calculation regime, a new algorithm for K-DEMO is developed to address a steady-state pressure and current profile under ideal magnetohydrodynamic (MHD) stability and technological level. To consider profile effect carefully which regulate plasma confinement and bootstrap current, the main variables of object function is set to be pressure and current density profile subject to the largest fusion gain. Target pressure profiles with different pedestal structures are investigated by scanning their broadness, pedestal height, and width. Formation of stable equilibria is evaluated by solving Grad-Shafranov equation and checking linear MHD stability. For the case of potentially stable equilibrium, required external heating distribution is calculated by considering both power balance and external current drive alignment to reproduce the pressure profile of the stable equilibrium. The equilibrium and corresponding external heating configuration with the highest fusion gain above target fusion power are chosen for designing an optimal scenario. As a final step, electron/ion temperature and poloidal flux evolutions are solved with the derived heating configuration to find a steady-state scenario and achieve self-consistent plasma profiles. To implement the developed algorithm, integrated numerical package is organized with existing codes connecting with the standard data model. This code package is benchmarked with KSTAR discharge. An economic K-DEMO steady-state target operation scenario has been studied through the designed algorithm considering self-consistency with equilibrium, stability, confinement, and heating/current drive. Steady-state solution shows a viable power plant demonstration but also produces key features of K-DEMO discharges. K-DEMO is targeting phased approach starting from the first phase of 2000 MW and the second phase of 3000 MW. Extrapolating operation regime of ITER to a high magnetic field, 2000 MW stable pressure and current profiles are derived. Additionally, assuming enhanced density limit and pedestal pressure, ultimate 3000 MW case is shown. In conclusion, a systematic, self-consistent algorithm to find a burning plasma operation scenario has been developed for the steady-state pressure and current profile maximizing the fusion gain and applied to K-DEMO. An efficient and stable burning plasma operation in K-DEMO seems to have a good prospect in terms of current physics/engineering level.