Short wavelength ion temperature gradient mode and coupling with trapped electrons

The effect of trapped electrons on the ion temperature gradient (ITG) mode in a regime where its wavelength is shorter than the conventional ITG mode (k⊥ρLi≤1) has been studied. Such a mode propagates in the ion diamagnetic direction with a typical scale length k⊥ρLi⪢1 and is termed as the short wavelength ITG (SWITG) mode. The effect of the trapped electrons on this SWITG mode is investigated, for the first time, using a global and local linear gyrokinetic model. The trapped electrons are observed to destabilize the mode strongly. Comparison of the various parameter scans for the SWITG mode with and without the trapped electrons is presented. One important result obtained is that, while in the absence of the trapped electrons the mode was found to subside with increasing value of ϵn=Ln/R exhibiting the character of a slablike mode, the presence of the trapped electrons has been observed to enhance the ϵn=Ln/R window of the existence of the SWITG mode making the mode more toroidal like.