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Modelling of near LH effects on the SOL, in view of extrapolation to ITER

Modelling of near LH effects on the SOL, in view of extrapolation to ITER V. Petrzilka 1 , G. Corrigan 2 , P. Belo 3 , A. Ekedahl 4 , K. Erents 2 , M. Goniche 4 , P. Jacquet 2 , K. Kirov 2 , J. Mailloux 2 , V. Parail 2 , K. Rantamäki 5 , J. Spence 2 , S. Wiesen 2

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Modelling of near LH effects on the SOL, in view of extrapolation to ITER

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  1. Modelling of near LH effects on the SOL, in view of extrapolation to ITER V. Petrzilka1, G. Corrigan2, P. Belo3, A. Ekedahl4, K. Erents2, M. Goniche4, P. Jacquet2, K. Kirov2, J. Mailloux2, V. Parail2, K. Rantamäki5, J. Spence2, S. Wiesen2 1Association EURATOM-IPP.CR, Za Slovankou 3, 182 21 Praha 8, Czech Republic 2 Assoc. EURATOM-UKAEA, Culham Science Centre, Abingdon, OXON OX14 3DB, UK 3Association Euratom-IST, Centro de Fusao Nuclear, Lisboa, Portugal 34CEA, IRFM, 13108 Saint Paul-lez-Durance, France 5 Association Euratom - Tekes, VTT, P.O.Box 1000, FI-02044 VTT, Finland

  2. Outline 1. EDGE2D modelling of gas puff and heating by LH in the SOL 2. Treating the private space in front of the grill 3. Comparison with JET experimental data 4. Preliminary modelling exercise for ITER case 5. Additional LH features: flows due to the fast electron acceleration, ponderomotive effect 6. Needs for development of the modelling

  3. EDGE2D modelling of gas puffing and LH ionization in JET • Difficult to model since it is a 3D problem: LH launcher, first wall components and gas pipe have finite shape. However, a 2D model can provide useful insights. • Modelling with EDGE2D is ongoing, with the following features: • Code modified to extend SOL up to 10 cm, or more. • Simple model added to take into account the effect of LH. A fraction of LH power (a few %) is lost in the SOL  increases Te,SOL enhances ionization in the SOL. • The private space in front of the grill is taken into account by introducing limiter-like features. The poloidal limiters are modeled as spatially localized sinks, where the recombination is artificially strongly enhanced. • Modelling of SOL parameters for comparison with experimental results. ne,SOL, Jsat and Da

  4. Fast electron generation in front of the LH launcher TS: J. Gunn et al., J. Nuc. Mater. (2009) Hot spots on bumpers RFA measurements of fast electron beam Hot spots on magnetically components are observed during LH (JET, TS, TdeV…) The electrons beam generated by LH has a radial depht of a ~ 2-3 cm.

  5. EDGE2D - Effect of LH heating in the SOL V. Petrzilka et al., 33rd EPS Conf., Rome (2006) The gas puff enhances the ionization source near the separatrix. Gas puffing and heating together broaden the ionization source profile into the far SOL mid-plane, which results in a density increase.

  6. 2D modelling of the private space in front of the launcher V. Petrzilka et al., 34th EPS Conf., Warsaw (2007) 2D representation 3D picture The poloidal limiters are modeled as spatially localized sinks, where the recombination is artificially strongly enhanced.

  7. Comparison with experimental data M. Goniche et al., PPCF, 51 (2009) FD2, injected = 8.5x1021 el/s (from GIM6) Assume that the experimental increase of particle flux occurs on the flux tubes connected to the gas pipe (L ~ 1m) on a radial penetration DR ~ 0.05m (see plot) DJsat ~ 1.5x104 A/m2 ~ 1023 el/s/m2 DR ~ 0.05m & L ~ 1m DFSOL ~ 5x1021el/s ~ FD2, injected H-mode Assuming enhanced recycling during LH is negligible :  all gas is ionized in the far SOL.  only connected flux tubes are affected by ionization. Consistent with the assumption of a local effect of gas injection.

  8. ITER shot 90010 – LH ionization with TOP and OMP (outer mid plane) puff Initial Pdis profile [a.u.] OMP TOP puff 14*1022 el/s, heating 0; OMP puff 14*1022 el/s, heating 0; TOP puff 14*1022 el/s, heating Pdis ~ 750 kW OMP puff 14*1022 el/s, heating Pdis ~ 750 kW Electron density (m-3) Initial Pdis profile [a.u.] Distance from separatrix (m) • Preliminary modelling exercise for ITER case suggests that SOL density increase • can be obtained, assuming heating in the SOL by LH. • OMP puff more efficient than TOP puff. • However, for the ITER equilibrium available, the SOL width could not be enlarged, as the code failed when the 2nd X-point appeared in the modelling.

  9. Additional effects of LH that can be included in EDGE2D V. Petrzilka et al., 30th EPS Conf., St Petersburg (2003) The fast electron generation causes outflow of particles in front of the grill. In some cases, increase of reflection coefficient with power is observed  possibly ponderomotive effect.

  10. Development needed for LH modelling • A 3D model is needed to take into account the geometry (magnetic connections). • Wide SOL is needed for a realistic modelling, especially for ITER cases. The width can not be enlarged further, when the 2nd X point (the upper one) appears in the modelling region. • Better understanding of the whole process of the LH parasitic absorption (e.g. measurements of the fast electron beam), which would allow a more accurate description of the ionization process by LH in EDGE2D. • It would be needed to include effects of the flows, probably induced by fast particles in front of the LH grill, on the whole SOL. • Inclusion of nonlinear effects in EDGE2D – LH modelling, like ponderomotive force effects.

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