1. Istituto di Fisica del Plasma “P.Caldirola”, Consiglio Nazionale delle RicercheEuratom-ENEA-CNR Association, Via R. Cozzi 53, 20125, Milan, Italy 2. Associa??o EURATOM/IST, Centro de Fus?o Nuclear, 1096, Lisbon Codex, Portugal
Abstract:
A major limit to steady state and advanced high operation of tokamaks of reactor class is due to the onset of tearing modes that develop magnetic and may cause loss of energy confinement or a major disruption. Here the structure of a classical problem
about the effects of external control helical fields is analysed and it is shown to offer a general paradigm of response of
low order classical and neoclassical tearing modes to a wide class of external perturbations. New results of principle on
the structural stability of the response model are obtained, leading to a clear interpretation of the role of “seed islands"
in the onset of neo-classical tearing modes and the role of finite ion larmor radius corrections to Ohm's law.
Received 12 November 2001 and Received in final form 4 January 2002