title: Global gyrokinetic stability of pressure-gradient-driven electromagnetic modes in tokamaks with regions of low shear.
abstract: Tokamaks with large pressure gradients (alpha(max)) formed in regions of weak magnetic shear are shown to be susceptible to novel, low-n, global, kinetic, electromagnetic modes with a toroidal mode number n in the range 2</=n</=12. For a weakly varying monotonic safety factor profile q with its minimum q(min)>1 on the magnetic axis and alpha(max) near q(min), new, global kinetic infernal modes with a strong mode rotation omega(r) and a finite growth rate gamma<|omega(r)| are found. For equilibria with reverse shear where q(min) is off axis and alpha(max) near q(min), the existence of an unstable low-n global branch of Alfve n ion temperature gradient modes is revealed with an oscillatory gamma as a function of n. The addition of trapped electron dynamics is shown to be further destabilizing.
authors.affiliation: CRPP, Association EURATOM - Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Ganesh
authors.forename: J
authors.initials: J
authors.lastname: Vaclavik