Enhancement of electromagnetic effects on core micro-turbulence by fast ion
pressure gradients
J. Garcia1, J. Citrin1,2, T. Goerler3, F. Jenko3, P. Maget1, P. Mantica4, M.J. Pueschel5, D. Told3, C.
Bourdelle1, R. Dumont1, G. Giruzzi1, J.W. Haverkort2,6, G.M.D. Hogeweij2, T. Johnson7 and JETEFDA contributors∗
JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB, UK
1
CEA, IRFM, F-13108 Saint Paul Lez Durance, France
FOM Institute DIFFER – Dutch Institute for Fundamental Energy Research - Association EURATOM-FOM,
Nieuwegein, The Netherlands
3
Max Planck Institute for Plasma Physics, EURATOM Association, Boltzmannstr. 2, 85748 Garching,
Germany
4
Istituto di Fisica del Plasma “P. Caldirola”, Associazione Euratom-ENEA-CNR,Milano, Italy
5
University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
6
Centrum Wiskunde & Informatica (CWI), PO Box 94079, Amsterdam, The Netherlands
7
Euratom-VR Association, EES, KTH, Stockholm, Sweden
*
See the Appendix of F. Romanelli et al., Proceedings of the 24th IAEA Fusion Energy Conference 2012, San
Diego, USA
2
Extensive linear and non-linear gyrokinetic simulations, including kinetic electrons,
collisions, flow shear, realistic geometry, electromagnetic effects, impurities as well as
perpendicular and parallel magnetic fluctuations performed with the GENE [1] code, have
shown for the first time that the large population of fast ions found in the plasma core under
particular heating conditions has a strong impact on core microturbulence. In particular,
nonlinear electromagnetic stabilization of Ion Temperature Gradient (ITG) turbulence can be
very much enhanced by fast ion pressure gradients [2]. These results can explain the improved
ion energy confinement regime observed in L-mode ion heat transport studies at the JET
tokamak which manifests itself as a reduction of the ion temperature stiffness and which, until
now had not been reproduced by nonlinear gyrokinetic simulations [3].
The same effect has been shown to be important in high beta hybrid scenarios from JET with
a large population of fast ions, about 10% of the electron density. Electromagnetic effects are
shown to be essential in order to obtain an agreement between simulation and experiment.
When the fast ions are included, R/LTi increases by 25% for the same ion heat flux [4] This
can explain the high core ion temperature gradients obtained in these regimes as the flow
shear is found to play a much weaker role. The calculated ion heat flux is found to be in the
direct vicinity of the boundary between ITG and electromagnetic modes which strongly
increase both thermal and fast ion transport and lead to ion heat fluxes much beyond the
experimental one.
Another key point is that fast ions increase core pressure without increasing thermal
turbulence leading to a Shafranov-shift unachievable by simple thermal pressure, which is
limited by microturbulence. This feature has been seen to favorably impact edge transport.
The Shafranov-shift increases by 4cm, leading to a pedestal pressure which can increase by
10% when the extra core pressure is taken into account as shown by the Peeling-Ballooning
analyses performed with the MISHKA [5] code.
This work was supported by EURATOM and carried out within the framework of the
European Fusion Development Agreement. The views and opinions expressed herein do not
necessarily reflect those of the European Commission.
[1] F. Jenko, W. Dorland, M. Kotschenreuther, and B.N. Rogers, Phys. Plasmas 7, 1904 (2000); see http://gene.rzg.mpg.de
for code details and access.
[2] J. Citrin et al., Phys. Rev. Lett. 111, 155001 (2013)
[3] P. Mantica et al., Phys. Rev. Lett. 102, 175002 (2009)
[4] J. Garcia et al.,to be submitted to Phys. Rev. Lett.
[5] G.T.A. Huysmans et al., Plasma Phys. Control. Fusion 8, 4292 (2001).