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Simulations of the H to L transition in JET plasmas

Simulations of the H to L transition in JET plasmas. P. Belo 1 , V. Parail 2 , I. Nunes 1 , G. Corrigan 2 , J. Lonnroth 3 , C. Maggi 4 , D. C. McDonald 2 A. Salmi 3 and JET EFDA contributors b

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Simulations of the H to L transition in JET plasmas

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  1. Simulations of the H to L transition in JET plasmas P. Belo1 , V. Parail2, I. Nunes1, G. Corrigan2, J. Lonnroth3, C. Maggi4, D. C. McDonald2 A. Salmi3 and JET EFDA contributors b 1EURATOM/IST Fusion Association, Centro de Fusão Nuclear, Av. Rovisco Pais 1049-001 Lisboa Portugal 2EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB, UK; 3Association EURATOM-Tekes, Aalto University, P.O. Box 14100, 00076 Aalto, Finland 4MPI für Plasmaphysik EURATOM Association, Boltzmannstr.2, D-85748 Garching, Germany bSee the Appendix of F. Romanelli et al., Proceedings of the 23rd IAEA Fusion Energy Conference 2010, Daejeon, Korea ISM meeting

  2. Simulations of the H to L transition in JET plasmas • Motivation • In ITER PF coils are set behind the cryostat and so the position control system has a relatively slow (~2 s) reaction to a sudden change in plasma parameters like a rapid H-L transition. In ITER this can happen when the fusion power stops at the current flat top. • There are some pulses at JET where the NBI is switched off during the current flattop. • Simulations with JETTO for example low triangularity pulse #72207 • Full predictive runs • Runs including the ASCOT code for the NBI fast particles • Summary

  3. Shot # 72207 IPLA • #72207 is a low triangularity pulse without any external gas puff. • The NBI auxiliary heating was switched off during the current flat top NBI Wdia LID4 Da

  4. JETTO simulations Experimental Type I H-mode Type III H-mode L-mode • All simulations with JETTO the Bohm/GyroBohm empirical transport model was used. • NBI phase: the transport coefficients within the ETB region were reduced to Ion neoclassical level, and the ELMs were triggered when ac reached ac=1.3. • At the switch off of the NBI three different types of transport was used: • Continuous ELM model with ac=1.0 (type I H-mode) • Continuous ELM model with ac=0.4 (type III H-mode) • L-mode, without any transport barrier IP NBI Wdia D

  5. JETTO simulations, NBI phase: Experimental Simulated NBI phase: • The temperature and density are measured from the LIDR and Ti from CX • There is a small over estimation of the density and temperature • It is difficult from this measurements to know the real values for the boundary conditions. • Bohm/GyroBhom coefficients for the H-mode are dependent on the temperatures at the boundry. ne Te Ti R (m)

  6. JETTO simulations, Intermediate phase: Experimental Type I H-mode Type III H-mode L-mode • Although the energy content follows the type III ELMs, is the L-mode case that has the closest values to the experimental profiles • Again the boundary conditions are unknown ne Te R (m)

  7. JETTO/ASCOT runs for fast particles H-mode Experimental Interpretative L-mode • In the JETTO/ASCOT simulations we used: • Bohm/GyroBohm • Density and temperature interpretative • Density and temperature predictive • H-mode • L-mode • The slowing down of the fast NBI particles is not the full answer. The slowing down time is 2 to 4 times faster then the intermediate phase that is in ~200 ms. NBI

  8. EDGE2D simulations: profiles • The simulated profiles are within the error bar of the experiments. • The perpendicular transport coefficients, the input power and the core source were give by the JETTO runs • At t=53.3 se the plasma is assumed to be in type I ELMy H-mode and at t=53.6 s at type III ELMy H-mode Experimental Simulated T= 53.3 s T= 53.6 s ne ne Te Te Ti

  9. EDGE2D simulations: LCFS • To take into account the changes in core particle source and power crossing the separatrix the duration of each EDGE2D was 50 ms. Type I ELMy H-mode Type III ELMy H-mode

  10. EDGE2D simulations: Targets • Temperature time traces at the divertor target plates Type I ELMy H-mode Type III ELMy H-mode

  11. Summary 722107272674396 NBI • Initial simulations with JETTO shown that the H-L transition occurs ~200 ms after the NBI switch off. • The slowing down of the fast particles is ~ 50 ms • This result is good news for ITER the confinement time is ~2 s, the same order of the reaction of the controller Wdia Da Da Da

  12. Future work • A more self consistent model will be done using the power flux level crossing the LCFS • A more self consistent boundary conditions for core and edge will be done using JINTRAC • Similar study will be done to plasmas closer to the ITER like configuration

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