MESS: a new Magnetic Energy Storage Scheme for improving the power handling in fusion experiments, a conceptual study

The plasma breakdown and ramp up in fusion experiments require high peaks of power, increasing with the size of the machines and plasma current value. In ITER, the power peak reaches 600 MW and in DEMO the present estimation gives values higher than 1 GW, far beyond the limits generally Mxed by the power grid operators, even for special plants. Experience from existing fusion experiments, fed by weak grids, reports about the use of local Nywheel generators to store the majority of the energy necessary to provide the required pulsed power for the plasma formation, so as to reduce the demand from the grid. In this paper, a new inductive energy storage scheme is studied: it can be applied both to tokamak or RFP experiments and can efficiently support the operation of the Central Solenoid (CS), without the need for resistive switching networks, thus with the advantage of energy dissipation avoidance The principle is applied to the case of a Fusion-Fission Hybrid Reactor, based on Reversed Field Pinch conMguration operated exploiting the Nux double swing. The basic idea is to provide a SMES (Superconducting Magnetic Energy Storage) Coil (SC), precharged along with the CS one to the same current value. Then, for the ramp up of the plasma, the initial CS Nux decrease is performed through the control of the voltage applied to the CS and recovering the magnetic energy on the SC, whose current increases. After CS zero crossing, the energy stored in the SC is transferred back to CS in such a way to provide the voltage for plasma sustainment during the Nat top phase. The paper will describe the concept and the scheme operation, which could be also considered for applications outside the fusion Meld; then, a conceptual design for the selected case is proposed.