Gyrokinetic investigation of ion temperature gradient instability in helical RFPs

Micro-instabilities in the RFP, like the Ion Temperature Gradient (ITG) mode, have been investigated in the last years from several viewpoints and with various numerical tools. The strongest underlying assumption for all of these approaches is that the magnetic equilibrium does not deviate significantly from axisymmetry. Contrary to this, in RFX-mod, the physical conditions more favorable for the onset of electrostatic/electromagnetic turbulence emerge when magnetic surfaces are helical, i.e., during the single helicity states of the RFP (see e.g. [1]). In general, we wish to systematically revisit the existing gyrokinetic studies of microturbulence focusing on the novel 3D feature. The RFP equilibria will be derived using the VMEC code and subsequently applied to the nonlinear gyrokinetic code GENE [2] with the aid of the GIST interface code [3]. The physical problem we address here is the occurrence of ITG instability in single helicity plasmas, and its distinct properties compared to the axisymmetric geometry. In this context, a selective benchmarking with results obtained with the gyrokinetic code GS2 [4] will also be presented. References [1] S. Guo, Phys. Plasmas 15, 122510 (2008); I. Predebon et al., Phys. Plasmas 17, 012304 (2010) [2] http://www.ipp.mpg.de/~fsj/gene/ [3] http://www.ipp.mpg.de/~pax/ [4] http://gs2.sourceforge.net/