Modelling Third Field Operation in the ITER Prefusion Power Operation Phase

Full text: The ITER low activation phase consists of H and He plasmas, split into prefusion power operation phases 1 and 2 (PFPO-1 and PFPO-2). The PFPO-1 phase will include 20 MW of electron cyclotron resonance heating (ECRH) and possibly 10 MW of ion cyclotron radio frequency heating (ICRH), while the PFPO-2 phase will include the full heating and current drive (H&CD) capabilities, i.e., 73MWof H&CD power. The L-H power threshold displays a density optimum for ITER q₉₅ = 3 operation at n/nG ∼ 0.4 , where n_G is the Greenwald density. At half field for n/n_G ∼ 0.4 in PFPO-1, H-mode access is predicted to be unlikely in PFPO-1 in H and marginal in He. Accessing H-mode allows the determination of the heating power required to operate ITER in H-mode and to commission/demonstrate ELM control schemes, both of which are key to the research plan. Hence, operating 5 MA/1.8 T (q₉₅ = 3) plasmas is foreseen, since it makes the H-mode access more likely in PFPO-1. Scenarios have been developed for both PFPO-1 and PFPO-2 phases. H-mode scenarios at 1.8 T and low density are developed according to the limited power installed in PFPO-1, providing the density upper limit, and to the fact that low density and dominant ECRH can lead to low edge ion power flow preventing H-mode access. Hence it is important to qualify which key elements can be addressed in such plasmas to determine whether the required resources to implement the 1.8 T research programme are worthwhile. Integrated simulations of ITER 5 MA/1.8 T plasmas have been carried out with various 1.5D transport integrated modelling suites of codes by the ITPA topical group on integrated operation scenarios (ITPA-IOS) in collaboration with the IO and with support from the ITPA Transport and Confinement and Energetic Particles groups. The present contribution reports the results of self-consistent transport and H&CD analyses to assess the efficiency of EC and IC heating in 5 MA/1.8 T plasmas in L and H-modes. With a view to study H-modes at 1.8 T in PFPO-2, the possibility to heat these plasmas with NBI has been assessed as well. These issues are assessed by the application of a range of integrated modelling suites, used in association with either simplified H&CD models or more sophisticated codes for ECRH, ICRH and NBI modelling. (author)