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Synchrotron radiation leveling at future circular hadron colliders

Frank Zimmermann

Abstract

Luminosity leveling to limit the event pile up is a key ingredient of the LHC luminosity upgrade, the High-Luminosity LHC (HL-LHC). For a future circular hadron collider, such as the FCC-hh, operating at a centre-of-mass energy of 70-90 TeV, synchrotron radiation becomes significant, with radiation damping times of the order of one or a few hours. The rapid shrinkage of the emittance may call for a leveling of the beam-beam tune shift or of the event pile up, as previously explored. However, the strong synchrotron radiation emitted inside the cold superconducting magnets also represents a significant heat load and is likely to limit the total beam current. In this article, we discuss a new approach, namely synchrotron radiation power leveling, where the beam energy is adjusted during a physics store, either continually or in a few discrete steps, while the beam current decreases, so as to keep the synchrotron radiation power at or below a certain limiting value. In this way, both peak and integrated luminosity of the FCC-hh are increased, compared with operation at a fixed beam energy. The FCC-hh detectors, and in particular the physics event analysis, need to be prepared for this novel mode of operation. This article presents two example running scenarios for synchrotron radiation leveling at the FCC-hh. While not greatly reducing the integrated luminosity at highest collision energy, synchrotron-radiation leveling can significantly increase the number of events for key processes already occurring at lower energy. As an example, we show that it raises the number of di-Higgs production events by 60% or more.

Synchrotron radiation leveling at future circular hadron colliders

Abstract

Luminosity leveling to limit the event pile up is a key ingredient of the LHC luminosity upgrade, the High-Luminosity LHC (HL-LHC). For a future circular hadron collider, such as the FCC-hh, operating at a centre-of-mass energy of 70-90 TeV, synchrotron radiation becomes significant, with radiation damping times of the order of one or a few hours. The rapid shrinkage of the emittance may call for a leveling of the beam-beam tune shift or of the event pile up, as previously explored. However, the strong synchrotron radiation emitted inside the cold superconducting magnets also represents a significant heat load and is likely to limit the total beam current. In this article, we discuss a new approach, namely synchrotron radiation power leveling, where the beam energy is adjusted during a physics store, either continually or in a few discrete steps, while the beam current decreases, so as to keep the synchrotron radiation power at or below a certain limiting value. In this way, both peak and integrated luminosity of the FCC-hh are increased, compared with operation at a fixed beam energy. The FCC-hh detectors, and in particular the physics event analysis, need to be prepared for this novel mode of operation. This article presents two example running scenarios for synchrotron radiation leveling at the FCC-hh. While not greatly reducing the integrated luminosity at highest collision energy, synchrotron-radiation leveling can significantly increase the number of events for key processes already occurring at lower energy. As an example, we show that it raises the number of di-Higgs production events by 60% or more.
Paper Structure (12 sections, 82 equations, 12 figures, 2 tables)

This paper contains 12 sections, 82 equations, 12 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Constant energy dynamics
  3. Performance at fixed energy
  4. One-step leveling dynamics
  5. One-step leveling example
  6. Continuous leveling
  7. Continuous leveling example
  8. Discussion
  9. Detector & Physics Considerations
  10. Conclusions
  11. Two-step leveling with step at the beam-beam limit
  12. Continuous leveling below the beam-beam limit

Figures (12)

  • Figure 1: Ideal instantaneous luminosity during 24 h for fixed energy running in scenarios FCC-hh-12 (12 T field) and FCC-hh-14 (14 T dipole field).
  • Figure 2: Ideal integrated luminosity during 24 h for fixed energy running in scenarios FCC-hh-12 (12 T field) and FCC-hh-14 (14 T dipole field).
  • Figure 3: Beam energy in collision during 24 h with one-step leveling, where the dipole field increases from 12 and 14 T about 2.0 h into each physics fill, starting with the parameters of FCC-hh-12.
  • Figure 4: Ideal instantaneous luminosity during 24 h with one-step leveling increasing the dipole field from 12 and 14 T about 2.0 h into each physics fill, starting with the parameters of FCC-hh-12.
  • Figure 5: Ideal integrated luminosity during 24 h with one-step leveling increasing the dipole field from 12 and 14 T about 2.0 h into each physics fill, starting with the parameters of FCC-hh-12..
  • ...and 7 more figures