Perspectives of Fusion-Fission Hybrid Systems with the Reversed Field Pinch as a neutron source

Fusion-Fission Hybrid Reactor (FFHR), neutron-producing fusion core surrounded by a fission blanket, benefits from a renovated interest because of (i) its potentiality to address energy production before the availability of pure fusion reactors, (ii) its capability of fission fuel fertilization and (iii) waste management. The core fusion reactor of a FFHR requires less stringent performances respect to DEMO or the fusion power plants: it has to produce less than a hundred of MW of fusion power with Q = 1-5 and comes with a reduced fast neutron wall load, sustainable by the available nuclear material. While the Reversed Field Pinch (RFP) has yet an energy confinement too low for a high Q reactor, it is an alternative configuration to tokamak and stellarator for this application. Its disruption-free configuration, the need of a much weaker toroidal magnetic field coils and the capability of reaching thermonuclear temperatures without additional heating, but only by ohmic heating (due to no intrinsic plasma current limit and the strong winding of current lines due to the low q values), are significant advantages. New studies are in progress in order to revisit the status and the potentiality of the RFP as a fusion core in FFHR, taking into account the recent progress and expected improvement in RFP physics brought by the results of the RFX-mod experiment (R=2, a=0.46, Ip=2MA) and its underway upgrade. Scaling from the obtained experimental results opens the possibility, with increased machine size and plasma current, to realize a more robust and simple fusion neutron source respect to the other considered solutions; starting from these result, the possibility to realize a preliminary pilot experiment with a RFP (R=4m, a=0.8m, Ip=12-14MA) as a simplified neutron fusion source is in progress.