Hannover 2016 – scientific programme

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P: Fachverband Plasmaphysik

P 5: Poster Session- Helmholtz Graduate School for Plasma Physics

P 5.16: Poster

Monday, February 29, 2016, 16:30–19:00, Empore Lichthof

Critical beta of kinetic ballooning modes in simple geometry — •Ksenia Aleynikova, Alessandro Zocco, and Per Helander — Max-Planck-Institut für Plasmaphysik, Greifswald, Germany

In a fusion reactor, high density and plasma temperature are necessary to achieve favorable reaction conditions. This requires high plasma betas (the ratio of kinetic to magnetic pressure). However, at high betas, electromagnetic micro-turbulence due to the kinetic ballooning mode (KBM) instability can arise and generate anomalous losses of heat and particles. It is known that fluid magnetohydrodynamic (MHD) ballooning modes become linearly unstable when beta reaches a certain critical value (threshold). The same is expected for their kinetic counterparts - KBMs. Numerical simulations show that the critical beta for KBMs instability can be either higher or lower than the corresponding critical beta for MHD ballooning modes. Such discrepancy has not yet been understood. We consider the KBM as the electromagnetic correction of the ion temperature gradient (ITG) driven instability. An electromagnetic theory of ITG modes was developed in [A. Zocco et. al. P.P.C.F., 57(8), 2015] and the critical beta for their electromagnetic stabilization was derived, but kinetic ballooning modes were completely suppressed by diamagnetic effects. In this work, we first derive a new beta ordering for the electromagnetic theory of ITGs that accommodates KBMs. Then, we derive a new analytical expression for the critical beta of KBMs and numerically verify our predictions with the gyrokinetic code GS2 [http://gs2.sourceforge.net]. Our theoretical results and numerical calculations are in a good agreement.