The definitions and correlations existing between different terms used by physicists and engineers are clarified in order to deal with the assessment of the poloidal flux requirement in a fusion experiment. The theoretical formulation of both the Faraday and the Poynting methods, for the internal flux evaluation, is briefly reviewed. Heuristic expressions that allow estimates of internal flux consumption are reported for the specific case of an ignition experiment represented by the Ignitor configuration. The analytical and heuristic results for both internal and external poloidal flux requirements are checked against numerical evaluations carried out by using the TSC transport and magnetohydrodynamics code and the TEQ equilibrium code. A fairly good agreement between the different estimates is found. This suggests that simple heuristic expressions can be used to evaluate the poloidal flux requirement of future experiments, even if a detailed simulation of the plasma current penetration process is strongly recommended to correctly assess and optimize the resistive poloidal flux consumption. Finally, the poloidal flux requirement for different plasma scenarios in the Ignitor experiment is compared with the magnetic flux variation that can be delivered by the poloidal field system.
