  The onset and characteristics of Micro-Tearing Modes (MTM) in the core of
spherical (NSTX) and conventional tokamaks (ASDEX-UG and JET) are studied
through local linear gyrokinetic simulations with gyro [J. Candy and E. Belli,
General Atomics Report GA-A26818 (2011)]. For experimentally relevant core
plasma parameters in the NSTX and ASDEX-UG tokamaks, in agreement with previous
works, we find MTMs as the dominant linear instability. Also, for JET-like core
parameters considered in our study an MTM is found as the most unstable mode.
In all these plasmas, finite collisionality is needed for MTMs to become
unstable and the electron temperature gradient is found to be the fundamental
drive. However, a significant difference is observed in the dependence of
linear growth rate of MTMs on electron temperature gradient. While it varies
weakly and non-monotonically in JET and ASDEX-UG plasmas, in NSTX it increases
with the electron temperature gradient.
