Critical gradient formula for toroidal electron temperature gradient modes

Under certain conditions, the electron heat transport induced by electron temperature gradient (ETG) streamers is sufficiently large and sensitive with respect to the normalized electron temperature gradient to represent a possible cause for electron temperature profile consistency (stiffness). Here, linear gyrokinetic simulations of toroidal ETG modes in tokamak core and edge plasmas are presented. An algebraic formula for the threshold of the linear instability is derived from the numerical solutions of the linear gyrokinetic equations which recovers previous analytical results in the appropriate limits. (C) 2001 American Institute of Physics.