Volt-second consumption in tokamaks with sawtooth activity

Abstract

The effects of sawtooth activity on the poloidal magnetic flux and energy balances in tokamak plasmas on a diffusive time-scale are evaluated through the application of conservation principles to Maxwell's equations. Poloidal magnetic flux (volt-second) consumption can be partitioned into internal and dissipative components by two methods: the ‘axial method’ based on a magnetic flux balance and the ‘Poynting method’ based on a magnetic energy balance. Both methods require additional terms that specifically account for the poloidal flux and magnetic energy changes during magnetic reconnection derived from analysis on a magnetohydrodynamic time-scale. In experimental analyses these terms are absorbed in the inferred resistive dissipation, while in predictive analyses they must be evaluated directly. The dissipation of poloidal flux by sawtooth activity can exceed the normal resistive dissipation when the axial method of accounting is used.