Kink instabilities in long ion layers immersed in a dense background plasma are studied. A numerical extension of the analytic model of Lovelace indicates that these instabilities will occur for values of the self‐magnetic field index below those predicted previously. A quasineutral hybrid simulation code has been used to verify these lower thresholds. The simulations also show that the end of exponential growth occurs due to a nonlinear shift in the betatron frequency at large amplitude, producing an increase in layer thickness and a layer which has many non‐axis‐encircling ions.