Electrical Simulations of the SIS100 Superconducting Dipole and Quadrupole Circuits: Transients, Earthing and Failure Modes

The 100 Tm superconducting synchrotron SIS100 is the main accelerator of the international Facility for Antiproton and Ion Research (FAIR) currently under advanced construction in Darmstadt, Germany. The SIS100 dipole circuit which creates the magnetic field required to bend the beam, consists of 108 dipoles distributed over six arc sections of the ring. The magnetic field for the beam focusing is generated by three individual quadrupole circuits with total amount of 166 magnets located in both arc and straight sections of the ring. The dipole circuit is powered from two synchronized power converters and will be cycled up to 13.2 kA at 28 kA/s. The dipole magnet chain is not self-protecting. 12 energy extraction resistors are used to protect the superconducting coils and bus-bars against overheating and overvoltage in case of a quench. The largest quadrupole circuit consists of 83 magnets. The nominal current is 10.5 kA cycled up to 22 kA/s. Similarly to dipoles, the quadrupole circuit is not self-protecting. Four energy extraction units are used to discharge the circuit's energy in case of a quench or fast power abort. This work presents a customized Python software tool created to simulate electrical behavior of a superconducting magnet chain. The software is under development at GSI. However, certain modules strongly rely on the approach developed at CERN. The paper contains selected simulations of the SIS100 dipole and defocusing quadrupole circuits. Special attention is drawn to: transient effects during typical operation and during the fast power abort; the damping effect of vacuum chambers; voltage distribution in the circuits and basic failure modes.