title: Nonlinear Stability and Saturation of Ballooning Modes in Tokamaks.
abstract: The theory of tokamak stability to nonlinear "ballooning" displacements of elliptical magnetic flux tubes is presented. Above a critical pressure profile the energy stored in the plasma may be lowered by finite (but not infinitesimal) displacements of such tubes (metastability). Above a higher pressure profile, the linear stability boundary, such tubes are linearly and nonlinearly unstable. The predicted saturated flux tube displacement can be of the order of the pressure gradient scale length. Plasma transport from these displaced flux tubes may explain the rapid loss of confinement in some experiments.
authors.affiliation: CCFE, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, United Kingdom.
authors.forename: C J
authors.initials: CJ
authors.lastname: Ham
authors.affiliation: CCFE, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, United Kingdom.
authors.forename: S C
authors.initials: SC
authors.lastname: Cowley
authors.affiliation: CCFE, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Brochard
authors.affiliation: York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom.
authors.forename: H R
authors.initials: HR
authors.lastname: Wilson