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内容記述 |
The parameter R_D = P_rad/P_cond, which measures the ratio of radiated power to conductive heat flux at downstream Scrape-Off-Layer (SOL), is proposed as a robust and practically useful figure of merit for divertor detachment control. The simulations performed using the SOLEDGE3X-EIRENE code predict that the instant where R_D passes through unity (that is, when P_rad ? P_cond) coincides with the detachment of the radiation front from the divertor target. Furthermore, as a function of R_D, there is a decrease in target temperature and an increase in the distance at which the radiation front detaches from the target. These simulations cover scenarios in WEST and TCV with different levels of confinement, divertor closure, impurity concentration, and input power. The physical rationale underlying the above definition of R_D is that when the divertor radiated power is comparable to the conductive heat flux, there will be a lack of energy reaching the target. Consequently, the radiation front detaches some distance from the divertor target. R_D can thus be a good indicator for transitions to and from the detachment state. By monitoring R_D, it becomes easier to maintain the heat flux deposition at the target at a manageable level. The evaluation of R_D requires diagnostic measurement of downstream radiation and upstream temperature which is feasible in tokamak devices. The robustness of this figure of merit is evaluated through realistic time-dependent numerical simulations for the WEST tokamak, as well as experimental data from WEST, TCV, and JT-60U cases. The results show that R_D is capable of capturing the evolution of divertor plasma states, despite the different discharges and machines, suggesting that R_D can serve as a valuable control variable for real-time experimental divertor detachment control. |
