Conical microducts and minithrottles can be used to accelerate micropellets of fusionable fuel up to very high speeds (∼108 cm/s). The central collision of two pellets flying in opposite directions can produce a hot plasma where fusion reactions are triggered. The main drawback of this scheme is the short confinement time provided by the external guide tube (throttle). To obtain high yield, an extra force of confinement is advisable. In this paper, the performance of fuel implosions within conical targets and the effect of ultrashort magnetic fields and pinch forces are analyzed. Although very high currents are needed to stretch the confinement time, modern technologies based on pulse-power machines and fast discharges induced by ultrashort lasers can provide a solution to this problem.