Numerical Investigation Of A New ICRF Heating Scenario In Three-ion Species Plasma On CFETR

For a fusion device,plasma pre-heating is required before the self-sustaining burning-state reactions of deuterium(D)and tritium(T)commence.As an important auxiliary heating method of the current magnetic confinement fusion devices,plasma heating with waves in ion-cyclotron range of frequencies(ICRF)is effective in tokamaks.There are advantages of prior bulk ion heating include an improved energy confinement,a higher Q-value,and an increased thermal fusion yield.A new three-ion ICRF heating scheme for plasmas in the Chinese Fusion Engineering Test Reactor(CFETR)that require an increase in the bulk ion temperature via heating the lithium(beryllium)impurities in the D–T plasmas,was studied numerically using the 2-D full-wave codes.The main simulation results are as follows:(1)The on-axis heating can be realized in the(~7Li)-D-T and(~9Be)-D–T scheme when the wave frequency f=37 MHz and f=38 MHz;The radio-frequency wave power is strongly absorbed by very few ~7Li and ~9Be ions with the concentration of 0.01%–0.2%in a suitable mixture of D–T plasma(X_T≈48%-56%and X_T≈58%-65%,respectively).Due to the presence of the third minority ions,a two mode conversion layers is formed in the D-T plasma.And the fundamental resonance layers of third minority ions are very close to the two mode conversion layers,which leads a double-pass absorption.Hence,the minority ion heating is enhanced.An oscillatory behaviour of the ~7Li and ~9Be absorption efficiency arising from interference by adjusting the mixtures over a wide range;By varying the toroidal mode number,it is found that absorption becomes more effective of these new three-ion heating scenarios under a low mode number;Moreover,it is found that most of the minority ions tail energy is transferred to background ions via collisions in the estimate of the ~7Li and ~9Be ions tail energy.This is because the tail energy of ~7Li and ~9Be ions is lower than their critical energy,which is beneficial to heating the background D-T ions.When the concentration of beryllium ion is reduced to 0.1%,almost 1 Me V energetic ions can be generated in the(~9Be)-D–T scheme.In addition,the effect of background ion temperature on the heating of minority ions is also studied.(2)In contrast to the(~3He)-D–T scheme,(~7Li)-D–T and(~9Be)-D–T scheme can absorb RF power more effectively and provide greater bulk ion heating for the CFETR.By solving the steady-state Fokker–Planck equations,it is found that over 90%collisional power in the(~7Li)-D–T scheme is transferred to the majority species,while more than80%of collisional power in the(~9Be)-D–T scheme is transferred to the background ions,both of which are better than that of the(~3He)-D–T scheme.Also,the(~7Li)-D–T and(~9Be)-D–T scheme are the ICRF heating method that creates minimal plasma dilution.