Conceptual Design of the FCC-hh Dipole Circuits With Integrated CLIQ Protection System

Abstract

The Future Circular Collider (FCC-hh) project is a conceptual study whose goal is to design the successor of the Large Hadron Collider, increasing the collision energy from 14 to 100 TeV. The energy stored in the 16-T superconducting dipole magnets and the length of the sectors composing the 100-km FCC tunnel are considerably larger than those in present accelerators. This means that the energy stored in the FCC-hh dipole circuit is likely to be much higher than that in existing superconducting circuits. In the case of magnet quenches or faults, the circuit needs to be protected, i.e., its energy needs to be rapidly dissipated without inducing excessive voltages in the magnet chain. This article proposes a conceptual design for the FCC-hh dipole circuit, which satisfies the constraint of the maximum allowable voltage-to-ground and fulfills additional requirements related to the FCC-hh operation and tunnel layout. A compromise among the considered requirements leads to a relatively simple circuit layout and a large number of circuits for the entire machine. The behavior of the proposed circuit during the critical fast power abort phase is simulated through a numerical model, which covers the electrical circuit domain and the electrothermal magnet domain. Each FCC-hh dipole magnet is protected by means of the coupling-loss-induced quench (CLIQ) protection system, which also acts at the circuit level. The simulations predict severe voltage oscillations in the FCC-hh dipole circuits that may pose a problem for the quench detection system. The simulations also show that the severity of the oscillations is not due to the presence of CLIQ. This protection system can be integrated into the proposed circuit layout and represents an effective protection system for the entire string of FCC-hh dipole magnets.

The CLIQ Quench Protection System Applied to the 16 T FCC-hh Dipole Magnets

“…Considering the results reported in the companion paper [8], which show that CLIQ can be employed to protect a string of 16 T magnets, the article makes the CLIQ system a strong candidate for the protection of the FCC-hh main dipole magnets.…”

“…Since the electrical circuit contains a large number of dipole magnets, the maximum voltage-to-ground depends on the adopted circuit layout. This aspect is discussed in the companion paper [8]. In this article, another feedback loop of Fig.…”

“…For an exhaustive study, one must also consider the possible implications of the CLIQ protection system on the other two domains. The potential issues introduced by CLIQ at the circuital level are discussed in the companion paper [8], which shows that CLIQ is not adding complexity to the circuit design. The potential issues introduced by CLIQ at the mechanical level, in terms of additional mechanical stress with respect to the one predicted by the standard mechanical analysis, need to be carefully evaluated.…”

“…The fourth aspect considered is the study of the layout of the circuit containing the FCC magnets and it is also centralized. This last aspect is discussed in the companion paper [8].…”

Nb3Sn Accelerator Dipole Magnet Needs for a Future Circular Collider

“…Concerning the integration of the magnet in a circuit string, a strong limitation comes from the maximum voltage to ground that one is ready to accept in case of a quench. A study performed for the FCC (Prioli et al 2019) has shown that, if a single magnet can be protected, a string of magnets can also be protected within given constraints (in particular voltage withstand levels and the time constant of the circuit) by a proper subdivision of a powering sector in multiple circuits.…”