Slablike ion temperature gradient driven mode in reversed shear tokamaks

The ion temperature gradient driven (ITG) mode in reversed shear tokamaks is analysed using a gyrokinetic toroidal particle code. It is found that the ITG mode in the reversed shear configuration shows a coupled mode structure between the slab and toroidal ITG modes. Especially in the qmin-region, a slablike feature due to the reversed shear slab ITG mode (Idomura Y, Tokuda S and Wakatani M 1999 Phys. Plasmas 6 4658) becomes strong. This coupled eigenmode structure is changed from a slab mode to a toroidal mode depending on ηi = Ln/Lti and Lti. Results show that in reversed shear tokamaks the ITG mode is determined from a competition between the slab and toroidal ITG modes.