Integrated Tokamak Modelling

1 - Introduction

 

In parallel to the construction of ITER, many initiatives are needed to address complementary technological issues relevant to a fusion reactor, as well as many remaining scientific issues. One of the next decade’s scientific challenges consists of merging the scientific knowledge accumulated during the past 40 years into a reliable set of validated simulation tools, accessible and useful for ITER prediction and interpretation activity, as well as for the conceptual design of DEMO and future reactors. Obviously such simulators involve a high degree of “integration” in several respects: integration of multi-space, multi-scale (time and space) physics, integration of physics and technology models, inter-discipline integration etc. This very distinctive feature, in the framework of a rather long term and world-wide activity, constrains strongly the choices to be made at all levels of developments. A European Task Force on Integrated Tokamak Modelling (EU-ITM-TF) has been created with the long-term aim of providing the EU with a set of codes necessary for preparing and analysing future ITER discharges, with the highest degree of flexibility and reliability.

The task force was initiated in late 2003 with a long term work plan along the following lines:

  • structure the EU modelling effort for both the existing devices and ITER;
  • address the modelling issues which require a high degree of integration (physics integration, code integration, discipline integration);
  • identify the theory and modelling development needs;
  • strengthen the collaborative modelling activity between EU and other ITER partners and promote EU modelling activity at ITER level;
  • provide EU modellers with a code platform structure, which enables easy coupling between codes and models, provides access to device geometries and databases, strengthens systematic code comparisons and confrontations with data;
  • implement a systematic verification and experimental validation procedure for the task force modelling activities, as well as documentation and reporting.

The task force is structured under five Integrated Modelling Projects addressing integrated physics issues

  • IMP1: Equilibrium and Linear MHD Stability;
  • IMP2: Non-linear MHD and Disruptions;
  • IMP3: Transport Code and Discharge Evolution (incl. core-edge coupling issues);
  • IMP4: Transport Processes and Micro-stability;
  • IMP5: Heating, Current Drive and Fast Particles

and two Support Projects

  • CPP: Code Platform Project, responsible for developing, maintaining and operating the code platform structure;
  • DCP: Data Coordination Project, supporting IMPs and CPP for Verification and Validation aspects and standardisation of data interfaces and access). The seven projects are working in close collaboration with each other, establishing the foundations of the simulators.

 

2 - IMP1: Equilibrium and Linear MHD Stability

IMP1 has now identified a full list of equilibrium codes (free and fixed boundary, low and high resolution) as well as a list of linear MHD codes and flux surface reconstruction tools. The contributed codes are standardised to avoid any internal information on machine or diagnostic data. All geometry/diagnostic data come from external databases. As consequence of the adaptation of the codes to be machine independent, the same version of the code can be applied to all machines from which a machine description is available. For example, a new version of EFIT has been applied to Tore Supra, JET and ITER equilibria.

3 - IMP2: Non-linear MHD and Disruptions

 

IMP2 identified four physics problems where relevant integration work could be undertaken:

  • Predicting the behaviour of Sawtooth Oscillations;
  • Predicting the destabilization of Resistive Wall Modes;
  • Impact of Edge Localized Modes on tokamak performance;
  • Possible improvements on the modelling of Neoclassical Tearing Modes.


4 - IMP3: Transport Code and Discharge Evolution

 

IMP3 is actively preparing the integration of the four major transport codes operated in Europe (ASTRA, CRONOS, JETTO and RITM) in the task force framework, as well as their validation and verification. A core transport code benchmarking will be initiated in November by IMP3. This long term activity is developed in close collaboration with the JET Integration of Transport Codes Project and is utilizing JAMS, the code management and launch system used at JET for transport and MHD codes. Significant benchmarking of existing edge codes has also occurred within the ITM, EFDA-JET, ITPA and European Laboratories frameworks. Results from early stages have already been reported by D. Coster at the 2004 PSI conference. Together with the JET code improvement effort, a new coupling of the edge plasma code EDGE2D with the Monte-Carlo code EIRENE has been successfully performed (as an addition to the long standing EDGE2D-NIMBUS option). Finally, an initial version of possible interfaces for various edge code interactions has been created and placed on the EFDA-TF-ITM website.

5 - IMP4: Transport Processes and Micro-stability

 

The first instalment of Transport Processes and Micro-Stability code catalogue is available on the IMP4 website. It covers the turbulence simulation codes, whether fluid or kinetic, in three spatial dimensions. A total of eleven codes from seven Associations are currently listed. Three codes are gyrokinetic and the rest are fluid (whether gyro-fluid with Landau closures or based on the Braginskii equations). Most codes are specialised to simulate either the core or the edge plasma, but certain codes in the catalogue can treat both situations. The cross verification of codes within each of the main categories (micro-stability, micro-turbulence, and neoclassical transport) has started. Reference test cases have been defined. Specifications are inspired by the US Cyclone project (1997-2000). Three cases were identified, one being the original Cyclone test case, for turbulence in the tokamak core. The second is a small device test based on FT-2 parameters, for cases with reduced scale separation. The third is an L-mode ASDEX-Upgrade test case, for edge turbulence codes.

6 - IMP5: Heating, Current Drive and Fast Particles

 

Finally, the work carried out within the framework of IMP5 is concentrated on developing a package of codes for prediction and interpretation of heating, current drive and fast particles instabilities. Twelve different tasks have been initiated in these domains, and IMP5 is presently working closely with DCP to include in the phase 4 data structure the schemas related to heating, current drive and fast particles issues.