Ion pressure gradient effects on Kelvin-Helmholtz and interchange instabilities

In the flow-free state, radial force-balance implies that the poloidal components of the ExB and ion diamagnetic drifts, \textasciitilde grad(Pi) / n, are mirrored : vE $+$ vdi $=$ 0. Analysis [1] of the linearized fluid equations shows that the mirrored state is stable in the absence of the interchange drive, \textasciitilde grad(Pe$+$Pi) / n, i.e., the K-H instability is absent. With the interchange drive present, the mirrored-state growth rate passes through a global \textit{minimum} value with \textit{increasing} ion pressure gradient, due to sheared ExB flow and diamagnetic suppression, admitting a stability interval in a neighborhood of the minimum if other damping mechanisms are present. The K-H instability is recovered, absent the interchange drive, if force-balance is generalized to include neoclassical poloidal flows (vE $+$ vdi $+$ vnc $=$ 0, vnc \textasciitilde grad(Ti)) [2], so that mirroring is lost. Implications for achieving a quiescent H-mode are discussed, and SOLT simulations, which include nonlinear ion pressure effects, are compared with the linear picture. [1] J.R. Myra et al., J. Plasma Phys. \textbf{82}, 905820210 (2016). [2] L. Ch\^{o}n\'{e} et al., Phys. Plasmas \textbf{21}, 070702 (2014).