📝 SummarXiv

Abstract

Issues of tokamak power plants, such as maximum possible length of a pulse of fusion power and the evolution of the current profile towards disruptive states, are tightly constrained by the evolution equation for the magnetic field. This equation follows from Faraday's Law and the purely mathematical relation between the magnetic and the electric fields. The validity of detailed simulations is tested by consistency with Faraday's Law, not the other way around. The high sensitivity of tokamaks to variations in the radial profile of the loop voltage make them disruption prone on a shorter timescale than the time that they can be maintained by a solenoid. The frequency of disruptions and the temporal decay of $n\tau_ET$ in high performance tokamak experiments show the importance of careful profile control. Feasible computational simulations from startup to shutdown for prototype plasmas could greatly clarify these constraints and the feasibility of their avoidance. Clarification could also be obtained by operating existing experiments in a way that simulates power-plant constraints. This paper has two purposes: (1) Illustrate issues on which research should be focused for the credibility tokamak power plants. (2) Encourage thought on the allocation of resources among the various fusion concepts to minimize the time and the cost to the achievement of practical fusion power.