Modelling and Control of the HL-LHC Nested Magnet Circuits at CERN

In the scope of the High Luminosity - Large Hadron Collider project at CERN, six new superconducting quadrupole electromagnets are required for the final focusing of the beam before proton-to-proton collisions. To optimize the powering scheme, the quadrupoles will be powered in series by one high-current two-quadrant converter. Three four-quadrant power converters are electrically connected to different electromagnets in order to introduce current and magnetic field variations in different magnets for beam optic purposes. The interconnection of the different branches leads to a fourth order multi-input multi-output system where a variation in one power converter leads to a variation of the currents in the different sub-circuits. Nevertheless, the circuit currents are required to be precisely controlled both in transient and in steady states to ensure a proper beam stability. This paper presents the model and the proposed powering scheme of the nested magnet circuits. A digital control strategy to decouple the four systems and to achieve a high precision control is proposed and discussed.