Speaker
Description
See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1084.pdf
Clear evidences that, due to a strong outward impurity convection, impurity core penetration is prevented have been found in the RFX-mod RFP device. A comparable convection of the main gas has not been observed [1] so that a favorable situation with peaked or flat density profiles and hollow impurity profiles is produced. Analysis of impurity transport relies on best reconstruction of impurity emission pattern with a 1-dim Collisional-Radiative code in which the radial impurity flux is schematized as a sum of a convective and a diffusive term [2,3]. The diffusion coefficient D and the velocity V, which are input to the simulation are varied until the experimental emission is reproduced. While the steady-state impurity profile is determined by the ratio V/D (peaking factor), the discrimination between D and V requires transient perturbative experiments. The experimental evidence of impurity outward convection in RFX-mod helical regimes occurring at high plasma current (I>1.2 MA) has been found in Li and C solid room temperature pellets experiments [4], Ne doped D2 cryogenic pellet injection, Ne gas puffing and Ni LBO experiments [5] (W LBO didn't show accumulation effects too). Similar D and V have been found for all the considered impurity species, without strong dependence on mass/charge. RFX-mod is now being upgraded to RFX-mod2, aiming at reducing secondary tearing mode amplitude which affects the duration of the improved confinement Single Helicity states [6]. In order to perform more detailed analysis of the impurity transport inside the outward convection barrier, the impurity source should be further inside the plasma. With this aim, Ni-tracer encapsulated solid pellet (Ni-TESPEL) experiments are foreseen in the new device [7]. The available 1-dimensional, time dependent Ni Collisional Radiative code, used to reconstruct experimental Ni emissions in RFX-mod [ 4] has been upgraded in preparation of such experiments in RFX-mod2 including the possibility of a Ni source (boundary condition) inside the plasma, placed in a time dependent position. The solid pellet injector already used in RFX-mod to inject C and Li solid pellets, will be adapted to inject TESPEL in RFX-mod2 (0.7/0.9 mm polystyrene ball with Ni powder inside, injection velocity up to 200 m/s can be reached). In this contribution, the solid pellet injector will be described, simulations of the pellet ablation [8] for different scenarios of RFX-mod2 plasma will be presented, Ni ion density, line and continuum emission profiles predicted by the code will be described and discussed.
[1] F.Auriemma et al Nucl. Fusion 55 (2015) 043010
[2] L.Carraro et al. Nucl. Fusion 36(1996) 1623
[3]M.Mattioli et al Plasma Phys. Control. Fusion 44 (2002)33 [4]T.Barbui et al. Plasma Phys. Control.Fusion 57 (2015) 025006 [5]S.Menmuir et al.PlasmaPhys.Control.Fusion 52 (2010) 095001
[6]L.Marrelli This conference
[7]N.Tamura "Versatility and Flexibility of the TracerEncapsulated Solid Pellet as a Diagnostic Tool in Magnetic Fusion Plasmas", 3rd ECPD, May 2019, Lisbon, Portugal
[8] K.V.Khlopenkov,S.Sudo Review of Scientific Instruments 69,9 (1998)3194
