Nonlinear Simulations of Deformation and Destruction of Magnetic Surfaces in Helical Devices

Stability of a shallow vacuum well case of H-1 Heliac is investigated by linear analyses and nonlinear simulations. The linear analysis predicts an appearance of two regions, where property of modes is different to each other. Nonlinear simulations are successfully executed in three dimensional geometry. Mode structures in nonlinear evolution of the pressure profile is consistent with the linear prediction.