Strike Point Splitting by non-axisymmetric fields in tokamaks

Abstract

Ideal plasma shielding and amplification of resonant magnetic perturbations in non-axisymmetric tokamak is presented by field line tracing simulation with full ideal plasma response, compared to vacuum field model and measurements of divertor lobe structures. Field line tracing simulations in NSTX with toroidal nonaxisymmetry indicate the ideal plasma response can significantly shield/amplify and phase shift the vacuum resonant magnetic perturbations. Ideal plasma shielding is found to prevent magnetic islands from opening and modify the degree of stochasticity. The overall helical lobe structures of the vacuum field are not changed by the ideal plasma response for high toroidal mode n=3. On the other hand, strong amplification of vacuum fields by the ideal plasma response is predicted for low toroidal mode n=1, better reproducing measurements of strong striation of the field lines on the divertor plate.