Presentation Extension of the operating space of high-βN fully non-inductive scenarios on TCV using Neutral Beam Injection

Piron, C.  ,  Garcia, J.  ,  Goodman, T.  ,  Agostini, M.  ,  Fontana, M.  ,  Giruzzi, G.  ,  Gobbin, M.  ,  Karpushov, A.  ,  Kong, M.  ,  Merle, A.  ,  Morales, J.  ,  Orsitto, F.  ,  Nowak, S.  ,  Pigatto, L.  ,  Sauter, O.  ,  Testa, D.  ,  M.Vallar  ,  吉田, 麻衣子

The fully non-inductive sustainment (Vloop~0) of high normalized beta (βN) plasmas is a crucial challenge for the steady-state operation of a tokamak reactor. In order to assess the difficulties found on such scenarios, steady-state regimes have been explored at TCV using the newly available 1MW Neutral Beam Injection (NBI) system. Compared to the past, higher current (Ip=[130, 150]kA) and density have been explored with co-Ip NBI in low single-null plasmas (Bt0=1.4T). The exploration of the operating space has been carried out by carefully scanning the total auxiliary power Paux=PEC+PNB, the NB power fraction (PNB/Paux) and the NB and EC heating and current drive radial deposition. βN values up to 1.4 and 1.7 at Vloop~0 have been reached in L-mode and H-mode plasmas, respectively. Fully non-inductive operation could not be achieved with NB only, whose injection could even increase Vloop in presence of EC waves. Internal Transport Barriers, which are expected to maximize the boostrap current fraction, were not formed either in the electron and the ion channel in the plasmas explored up to date, despite the significant increasing of the toroidal rotation and Fast Ion (FI) fraction with NBI, which are known to reduce turbulence [4]. The possibility that these plasmas are Trapped Electron Mode (TEM) turbulence dominated is being analysed in dedicated transport analyses. A strong contribution of bulk and FIs to the total plasma pressure has been experimentally evidenced and confirmed by modelling (ASTRA, NUBEAM). Interpretative simulations predict also that FI charge-exchange reactions are the main loss channel for NB heating efficiency. Similar results were also obtained in inductive L-mode plasmas in circular limiter configuration at TCV. Nonetheless, NBCD efficiency is observed to be lower in the low single-null plasmas investigated in this work, despite the expected reduced neutral penetration from the edge. Interpretative transport analyses with TRANSP coupled to NUBEAM are carried out to quantify the role on the NBCD efficiency of NBI losses and of the anisotropy in the FI velocity space distribution. A complete understanding of this evidence is crucial for advancing the development of fully non-inductive scenarios.
The 27th IAEA Fusion Energy Conference

Number of accesses :  

Other information