45thInternational Conference on Plasma Physics and CF, April 2 – 6, 2018, Zvenigorod

Framework for verication of gyrokinetic codes: models and numerical implementations

Natalia Tronko1,2

1Max-Planck Institute for Plasma Physics, 85748, Garching, Germany,
2TU Munich, Mathematics Center, 85747, Garching, Germany

In fusion plasmas the strong magneticeld allows the fast gyro motion to be systematicallyremoved from the description of the dynamics, resulting in a considerable model simplicationand gain of computational time. Nowadays, the gyrokinetic (GK) codes play a major role in theunderstanding of the development and the saturation of turbulence and in the prediction of theconsequent transport.

Specicgyrokinetic results can impact our predictions of the plasma behaviour in ITER andin a reactor, and particularly involve sophisticated electromagnetic eects. Condence in thesepredictions requires a rigorous and systematic very cation, which should be regarded as an in-dispensable step before any validation against experiments can be considered meaningful.

We present a new and generic theoretical framework and specic numerical applications to testthe validity and the domain of applicability of existing GK codes. For a sound very cationprocess, the underlying theoretical GK model and the numerical scheme must be considered atthe same time, which makes this approach pioneering. At the analytical level, the main noveltyconsists in using advanced mathematical tools such as variational formulation of dynamics forsystematization of basic GK code's equations to access the limits of their applicability. Theindirect very cation of numerical scheme is proposed via the Benchmark process.

In this work, specic examples of code very cation are presented for two GK codes: the multi-species electromagnetic ORB5 (PIC), and the radially global version of GENE (Eulerian). Theproposed methodology can be applied to any existing GK code. We establish a hierarchy ofreduced GK Vlasov-Maxwell equations using the generic variational formulation. Then, wederive and include the models implemented in ORB5 [1] and GENE [2] inside this hierarchy.

At the computational level, detailed very cation of global electromagnetic test cases based onthe CYCLONE are considered, including a parametric -scan covering the transition betweenthe ITG to KBM and the spectral properties at the nominal value [3]. In addition to that,a hierarchy of the test cases for the gradient driven nonlinear global simulations, allowing tocompare transport properties is also considered.

References

[1].N. Tronko, A. Bottino, and E. Sonnendrucker. Second order gyrokinetic theory for Particle-In-Cell codes.Physics of Plasmas, 23:082505, 2016.

[2].N. Tronko, T. Bottino, A. Goerler, E. Sonnendrucker, D. Told, and L. Villard. Verication of gyrokineticcodes: theoretical background and applications. Physics of Plasmas, 24:056115, 2017.

[3].T. Goerler, N. Tronko, W. A. Hornsby, A. Bottino, R. Kleiber, C. Norcini, V. Grandgirard, F. Jenko, andE. Sonnendrucker. Intercode comparison of gyrokinetic global electromagnetic modes. Physics of Plasmas, 23:072503, 2016.

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