1 / 22

Development of a synthetic diagnostic for the non-linear MHD-code JOREK

Development of a synthetic diagnostic for the non-linear MHD-code JOREK. R. Wenninger , H. Zohm and the ASDEX Upgrade Team. Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstr. 2, 85748 Garching, Germany. Many thanks to

candra
Download Presentation

Development of a synthetic diagnostic for the non-linear MHD-code JOREK

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Development of a synthetic diagnostic for the non-linear MHD-code JOREK R. Wenninger, H. Zohm and the ASDEX Upgrade Team Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstr. 2, 85748 Garching, Germany Many thanks to G. Huysmans, V. Igochine, S. Günter, W. C. Müller, M. Maraschek, O. Maj PhD Network – Advanced Course, Garching 05.10.2009

  2. Objective Comparison Topic: Plasma edge phenomena (e.g. ELMs) Theory (JOREK) Experiment (AUG) Method: Synthetic Diagnostic R. Wenninger

  3. Outline • Motivation: Edge Localised Modes • JOREK: A non-linear MHD Code • Synthetic diagnostics • Example: Synthetic Magnetics • Further diagnostics considered to synthesis R. Wenninger

  4. Motivation: Edge Localised Modes I • “Edge Localised Modes” (ELMs): Cyclic MHD instabilities destabilised by pressure gradient in the H-mode edge pedestal • Losses of up to 10% plasma energy in several 100 s • One of the main concerns for operation of ITER and later devices • Control technology is essential  physics understanding required R. Wenninger

  5. Motivation: Edge Localised Modes II Peeling-Ballooning model: • Evaluates linear ideal MHD stability boundary • Type I ELMs: Intermediate-n MHD boundary agrees with experiment at ELM-onset for various machines • Other scenarios (Type III, RMP ELM mitigated,…) operate below this boundary • Comments: • ELM crash is non-linear [Wilson 04]  Special code needed to account for this • Modelling of edge current? Snyder [NF 2009] R. Wenninger

  6. Motivation: Edge Localised Modes III • Still considerable lack of basic understanding towards the ELM crash mechanism Some open questions: • What is the mechanism for the detachment of the filaments associated with ELMs? • What is the mechanism for the ELM energy loss? • Is current ejected during an ELM: what mechanism, and how fast? • What determines the size (energy / particle losses) of an ELM? • What are the mechanisms for ELM suppression (QH, RMP) and active/passive mitigation (RMP, Pellets, Vert. Kicks) R. Wenninger

  7. JOREK: Code features I • JOREK has been developed with the specific aim to simulate ELMs by G. Huysmans (CEA) • It evolves MHD equations non-linearly • Reduced MHD  5 instead 8 evolved variables: • Density • Temperature • Electric potential (perp. Velocity) • Parallel velocity • Poloidal flux • Resistivity, viscosity and particle and temperature sources implemented • Time stepping fully implicit R. Wenninger

  8. JOREK: Code features II • Geometric features: • X-point geometry: Closed and open field lines are included • Generalised finite elements in 3D (flux aligned) • Boundary of domain in the SOL (initially a flux surface) – treated as an ideal wall R. Wenninger

  9. JOREK: Qualitative agreement with experimental results I • Edge density and temperature perturbations periodic in poloidal and toroidal direction > • Detaching of density-filament-like structures observed  Density Temperature Seen with fast visible cameras [Kirk 2006] R. Wenninger

  10. JOREK: Qualitative agreement with experimental results II Good agreement of profile evolution • measured by Thompson Scattering • modeled by JOREK (midplane profiles): Density: Shows a minimum + erodes Temperature: Stays monotonic but erodes EXP.: MAST THEO.: JOREK 480A 700 A 1170 A R. Wenninger

  11. Comparison Recon- struction Code Theo. Plasma Quantities Exp. Plasma Quantities Measured Signal Comparison Synthetic Diagnostic Code Theo. Plasma Quantities Synthetic Signal Measured Signal Synthetic diagnostics: Introduction A synthetic diagnostics models to a reasonable precision, what a corresponding real diagnostics would measure, if the plasma would be in the state as described by a modelling code. • Standard approach for Theory-Exp.-Comparison: • Approach with synthetic diagnostic: R. Wenninger

  12. Comparison Recon- struction Code Theo. Plasma Quantities Exp. Plasma Quantities Measured Signal Comparison Synthetic Diagnostic Code Theo. Plasma Quantities Synthetic Signal Measured Signal Advantages of a synthetic diagnostics • For many measurements it is not possible to reconstruct associated local plasma quantities (e.g. magnetics) • Various diagnostics signals are functions of more than one plasma quantity • In general: Description in plasma quantities by codes is often higher dimensional than description in measurements  Synthetic diagnostic in contrary to calibration relation tends to be an injective transformation more often R. Wenninger

  13. Synthetic Magnetics: Introduction • Objective • Simulate Bpol in the part of the AUG vessel containing the pickup coils for every time step • Extract from that synthetic signals for the real AUG coils • Guide lines • JOREK can only provide information on toroidal currents • Reduced MHD model currently does not account for plasma rotation, which significantly impacts coil signals  Add rotation (In first step non-differential) R. Wenninger

  14. Synthetic Magnetics: Adjust JOREK to AUG • JOREK Boundary JOREK: • Boundary condition: =const. • AUG: Conducting structures • Vessel wall AUG and attached components • Passive Stabilization Loop (PSL) • All can be regarded as ideal conducting • Special treatment for PSL? JOREK AUG PSL R. Wenninger

  15. Synthetic Magn.: Effects of conducting structures • Changing magnetic Field  Induced Voltage  Induced Current in conducting structures • Artificial distinction between effects of these currents in conducting structures: • T1: Induce eddy currents  B,IND=B,ORG • T2: Currents induced in macroscopic loops (e.g. PSL). (Can an ELM related current perturbation induce a significant macroscopic current?) • Dealing with T1: • Set =0 on AUG B=1/R(t)=0 • Additional dealing with T2: • INH (j  0, PSL = 0): Contribution from the plasma currents. PSL is modelled as an ideal conductor free of macroscopic currents. • HOM (j = 0, PSL = 1): Flux component from a macroscopic PSL current only. • The final solution:  = C HOM + INH R. Wenninger

  16. Synthetic Magnetics: Obtaining  on AUG Solution 1: Disadvantage: The partial differential equation is solved on an area, which is much larger than the one we are interested in.  Efficiency can be improved • Solve on AUG • Get j from JOREK R. Wenninger

  17. Synthetic Magnetics: Obtaining  on AUG\ JOREK Solution 2: • Extend JOREK Solution: • The solution on JOREK and further out is corresponding to a virtual ideal wall at JOREK  How can we get rid of it? • Decompose solution: JOREK JE Situation without plasma current but virtual ideal wall  Surface current on JOREK Situation with plasma current but without virtual ideal wall JE,I JE,H R. Wenninger

  18. Synthetic Magnetics: Obtaining  on AUG\ JOREK • Calculate JE,H: Homogeneous PDE: Derivative at JOREK: Values at AUG:  Well posed problem • Calculate JE = c - JE,H R. Wenninger

  19. Further diagnostics considered to synthesis • General Criteria: • Diagnostics for quantities calculated by JOREK • Measured in high temporal and spatial resolution in optimum dimensionality • Some candidates: • Electron Cyclotron Emission: • Now at AUG in 2D • Generic tool to synthesis any kind of line integrated diagnostics (e.g. Interferometry, Spectroscopy) • Thompson Scattering • Langmuir probe • … R. Wenninger

  20. Summary • Gaining further understanding in Edge Localised Modes is vital for the development of tokamaks • JOREK is a non-linear MHD code that reproduces a number of ELM-features experimentally observed • A synthetic diagnostic offers a basis for an advanced theory-experiment-comparison • An accurate and efficient approach to synthesis magnetic signals for AUG has been developed R. Wenninger

  21. R. Wenninger

  22. Poloidal flux Parallel momentum Poloidal momentum Temperature Density JOREK: Equations Formulation using electric and magnetic potentials:  Reduction from 8 to 5 variables R. Wenninger

More Related