Integrated Predictive Modelling at JET: Progress and Prospects V. Parail 1

1. 1) Integrated Predictive Modelling at JET: Progress and Prospects V. Parail1 With contributions from: P. Belo, G. Corrigan, W. Fundamenski, W. Houlberg, G. Huysmans, X. Garbet, F. Imbeaux, X. Litaudon. A. Loarte, J. Lonnroth, P. Monier-Garbet, T. Onjun, G. Saibene, T. Tala, H. Wilson and EFDA-JET collaborators

2. Outlook • What is integrated modelling? • Why do we need it; • Modelling codes, available at JET; • Recent examples of integrated modelling of JET plasmas: • Optimised shear plasma with ITBs; • ELMy H-mode, role of gas puffing; • Impurity accumulation and radiative collapse of ELMy H-mode; • Modelling of the Scrape Off Layer • Problems and prospects.

3. What is integratedmodelling (1) • Traditionally, plasma in tokamak is divided into two regions: CORE and SOL; • Indeed they have disparate time and space scales: • Plasma behaviour is controlled by different processes in CORE and SOL FIRST WALL CORE SOL

4. What is integratedmodelling (2) • Closer look reveals, however that these regions influence each other in many ways: • atomic physics penetrates into plasma core with neutrals and impurities; • profile stiffness makes core plasma dependant on the edge; • Edge transport barrier (which serves to separate core from SOL) is controlled by both; • MHD stability of ETB is influenced by the SOL; FIRST WALL CORE SOL

5. What is integratedmodelling (3) SAWTEETH MHD NEUTRALS IMPURITIES HEAT and PARTICLE FLUX GRADIENT REGION FIRST WALL ETB SOL ITB(s) PROFILE STIFFNESS STIFF PROFILES

6. Why do we need Integrated Modelling (1) • Profile stiffness in probably one of the best examples of a strong link between core and edge; • In case of a strong stiffness: confinement is controlled by the edge only; Stiff region

7. Why do we need Integrated Modelling (2) • Dynamical interaction of ITB(s) and ETB:

8. Why do we need Integrated Modelling (3) • Dynamical interaction of ITB(s) and ETB: • If enough power is applied, ITB expands toward the edge and triggers L-H transition; • Emerging ETB and subsequent strong ELMs can erode ITB , sometimes leading to its complete collapse;

9. Why do we need Integrated Modelling (4) • ELMy H-mode provides a classical example of the interplay between core and edge transport as well as between transport and MHD stability;

10. Why do we need Integrated Modelling (5) • Role of gas puffing in ELM dynamics: • Medium gas puffing reduces ELM frequency and amplitude without significant degradation in confinement; • Strong gas puffing leads to serious degradation in confinement and transition to type-III ELMs.

11. Why do we need Integrated Modelling (6) • Impurity accumulation in the plasma core: • The main gas puffing plays a decisive role in impurity accumulation and thermal collapse of plasma; Main gas puff drops below critical level

12. Modelling codes, available at JET(1) • JET has a suite of transport codes, which are linked with JET and ITER Profile Databases and are available to remote users. This suite includes: • 1.5D core transport code JETTO, which solves equations for electron and ion temperature, two hydrogenic ion densities, cold neutrals density and current density; • 1D core transport code SANCO, which solves continuity equations for all ionisation states of up to 2 impurity species. The code is linked with JETTO; • 2D SOL transport code EDGE2D/NIMBUS, which solves 2D transport equations for electron and ion temperature, two main hydrogenic ions and impurity densities as well as cold neutrals distribution in the SOL;

13. Modelling codes, available at JET(2) • A coupling between core (JETTO and SANCO) and edge (EDGE2D/NIMBUS) codes: COCONUT; • We have a link (a unidirectional one, no feedback loop) between transport code JETTO and linear MHD stability codes IDBALL, HELENA, MISHKA and ELITE; • MISHKA and ELITE do a linear stability analysis of low to medium-n ballooning and kink/peeling modes, including effect of finite Larmor radius; • All our codes are available for all EFDA-JET collaborators, including remote users; • The list of active remote users includes EU Associations, some US Universities, Kurchatov Institute (Moscow), ITER Central Team; • We provide training for new users (more than 30 users have been trained so far)

14. Modelling codes, available at JET(3) Present limitations in the modelling of core plasma: • ICRH heating is not included into JETTO due to big disparity in computation time (JETTO~1min CPU, PION~1hour CPU); • No feedback from MHD stability codes; • Linear MHD stability analysis only no reliable model for ELM; • Limited choice of theory-based transport models, particularly concerning ITB;

15. Modelling codes, available at JET(4) Present limitations in the modelling of SOL plasma: • Fluid approximation for SOL plasma (though flux limiters and some drifts are introduced); • Very limited package for plasma-wall interaction (such as description of chemical sputtering, wall and target plate recycling, kinetic model for sheath); • Lack of theory-based models for anomalous transport in the SOL both between and during ELMs

16. Modelling codes, available at JET(4) Problem of the multiplicity of transport and MHD stability codes: • Three 1.5D core transport codes are presently used at JET (JETTO, ASTRA, CRONOS); • These codes use different format for both input and output parameters and different numerical schemes; • They also use different graphic packages and file storing facilities; • Two 2D SOL codes (EDGE2D/NIMBUS and B2/EIRENA) with the same problems, which were mentioned above;

17. Recent examples of integrated modelling (1) Optimised shear plasma with ITBs • There can be more than one ITB in the same shot; • ITB can change its radial position; • ITB dynamically interacts with ETB; • There is more than one mechanism of the ITB formation • Strong shear flow; • negative magnetic shear; • Zero magnetic shear; • Low order rational magnetic surfaces; • Strong density gradient;

18. Recent examples of integrated modelling (2) • We manage to reproduce both double-ITB structure and an expansion of the outer ITB and its interaction with the ETB; • Bohm/gyroBohm empirical modes has been used in the simulation with:

19. Recent examples of integrated modelling (3) • It was not really an integrated modelling, we simulate ETB by imposing a proper boundary conditions. Modelling of ELMy H-mode, role of gas puffing. • To simulate H-mode plasma, we assume that all transport coefficients are reduced to the level of ion neo-classical within the barrier; • width of the ETB is prescribed by the formula(s); • COCONUT is used so that SOL physics is included (which controls penetration of neutrals)

20. Recent examples of integrated modelling (4) • MHD stability reveals very interesting dependence of edge stability on the level of gas puffing: Low/no puffing Medium puffing Strong puffing

21. Recent examples of integrated modelling (5) • This integrated approach allows us to reproduce experimentally observed transition from pure type-I ELMs to a mixture of type-I-II and then to type-III with an increase in the level of gas puffing;

22. Recent examples of integrated modelling (6) • Instead of using ad hoc assumption about ELM duration and amplitude, Johnny Lonnroth starts using theory-based models for peeling and ballooning mode evolution, coupled with transport equations:

23. Recent examples of integrated modelling (7) • One of the most interesting outcome of this modelling that even pure ballooning model reproduces discrete repetitive ELMs; • Combination of peeling and ballooning reproduce “composite” ELM, which is triggered by ballooning mode and then taken over by peeling J. Lonnroth, 2003

24. Recent examples of integrated modelling (8) P. Snyder, H. Wilson

25. Recent examples of integrated modelling (9) Impurity accumulation and radiative collapse of H-mode • Our experience in modelling of an ELMy H-mode shows that most of all gas puffing influences plasma parameters in the SOL and within the ETB; Main gas puff drops below critical level

26. Recent examples of integrated modelling (10) • ETB is of a particular interest for our study since anomalous transport there is suppressed between ELMs and penetration of impurities is controlled by the neo-classical diffusion and pinch: • here K is always positive and H is negative for the banana regime and positive for the PS regime;

27. Two sets of boundary conditions were used: the blue one corresponds to a constant level of gas puff and the red one- to its decrease • There is a change in the radiated power and in ELM behaviour at the time of the change in the boundary; P. Belo, 2003

28. Modelling of the SOL (1) • Modelling of the SOL raises an ultimate challenge because of: • 2D transport with disparate scales: • This includes modelling of very short MHD phenomena like ELM (with the duration ~100sec); • Kinetic effects are important in longitudinal transport: • Cold neutrals are 3D, as a rule; • Plasma-wall interaction involves processes, which are far from being common in plasma physics (chemical sputtering, blistering,…); • Link with the core transport codes is crucial;

29. Modelling of the SOL (2) • Dynamics of the ELM penetration into SOL and it’s expansion towards target is simulated with COCONUT Ti Te T=t0+2 t=t0+ =4sec t=t0 (before ELM) J. Lonnroth, 2003

30. 2,0 1,5 1,0 0,5 z (m) 0,0 -0,5 -1,0 -1,5 x B B D 2,0 2,5 3,0 3,5 4,0 R (m) Modelling of the SOL (3) • Accelerated Simulation of Charged Particle Orbits in a Tokamak • Guiding-centre orbit following • 3-D Monte Carlo code • All neo-classical effects (drifts) • Ion-ion and ion-neutral collisions • Self-consistent radial electric fields • Real tokamak background data • Parallelized using the MPI standard W. Fundamenski, 2003

31. Modelling of the SOL (4) EFIT  GRID2D  OSM2  EIRENE  ASCOT W. Fundamenski, 2003

32. Integration of transport and MHD codes in JET (1) • The main motivation behind the Project is the multiplicity of available codes in JET: 1.5D core transport (ASTRA, CRONOS, JETTO), MHD stability codes (MISHKA, ELITE, CHEESE, HELENA), 2D SOL codes (B2/EIRENA, EDGE2D/NIMBUS) and some turbulence simulation codes (KINEZERO, GS2, CUTIE); • The second drive comes from the recognition that we are dealing with more and more complex phenomena, which require integrated approach;

33. Integration of transport and MHD codes in JET (2) • We decide that the first step towards unification and integration would be to bring all codes under the same shell so that similar codes can share the same input/output files; • They will be all linked with JET and ITER Profile databases and will all share the same input/output files; • This would allow users to use any code in a similar way and to compare the codes in a very easy way; • Eventually I hope we will be able to choose the best combination of codes (or modules) and to make this option a preferential one on JET;

34. Integration of transport and MHD codes in JET (3)

35. Integration of transport and MHD codes in JET (4) • We will try to modularise transport codes and share as many components, as possible (and practical): • common impurity solver (SANCO); • equilibrium solver (and interface with MHD stability codes); • transport models; • Heating and current drive solvers (TRANSP Monte-Carlo package for NBI, PION for ICRH); • postprocessing tools (synthetic diagnostics); • feedback control module;

36. Problems and Prospects (1) • The accuracy of our predictions is inversely proportional to the complexity of plasma scenario (L-H-ITB); • The main scientific challenge comes from the fact that predictive modelling requires integration of processes having different dimensionalities as well as problems of disparate time or space scales; • Predictive modelling requires specialists with a deep knowledge of plasma theory, experiment and applied mathematics, which are very difficult to bring up;

37. Problems and Prospects (2) • Last years saw a very fast integration of theoretical, experimental and modelling activities in plasma physics; • ITER will be a logical next step in this integration since it will require internationally approved integrated modelling codes.