Design Studies for the Proof-of-Principle of a Gamma Factory

An exciting new project recently submitted to the European Strategy for Particle Physics is the prospect of a Gamma Factory (GF) at CERN, as part of the Beyond Colliders Programme. The GF is a new technique to generate ultra-intense and highly energetic beams of photons by making use of the existing accelerator infrastructure CERN. Instead of circulating protons in the LHC, partially-stripped ion beams are accelerated and made to interact with photons from an intense laser beam. The excited ultra-relativistic ions subsequently decay and emit photons that are relativistically boosted and thus generate highly collimated, high-intensity photon beams, with an unprecedented photon energies compared to existing light sources. Such photon beams are useful for myriad studies and applications, and can be scattered from a target to produce secondary beams of polarised electrons, polarised positrons, polarised muons, neutrinos, neutrons and radioactive ions. These beams offer a variety of new research opportunities at CERN in a wide area of fundamental as well as applied physics.

An initial Proof-of-Principle experiment at the CERN Super-Proton Synchrotron is being developed by a pioneering international GF collaboration of 62 scientists, 5 of whom are based at RHUL. The work proposed here, seeks to build on initial studies using software tools created by the RHUL group. These tools will be developed to enable a holistic approach to seamlessly simulate the passage of partially-stripped ions in the accelerator, their interaction with the photons, excitation and subsequent decay, using an extension of Geant4. We will apply these new tools to study and optimise the efficiency of the photon-ion interaction and determine the resulting distribution at the detector. In this was the design of a Proof-of-Principle experiment at the CERN SPS can be studied and optimised.

The Gamma Factory (GF) initiative proposes to create novel research tools at CERN by producing, accelerating and storing highly relativistic partially stripped ion beams in the LHC rings and by exciting their atomic degrees of freedom by lasers, to produce high-energy photon beams. Their intensity would be several orders of magnitude higher than those of the presently operating light sources in the particularly interesting gamma-ray energy domain reaching up to 400 MeV. In this energy domain, the high-intensity photon beams can be used to produce secondary beams of polarised electrons, polarised positrons, polarised muons, neutrinos, neutrons and radioactive ions. Given the available range of ion species, synchrotron energies, laser frequencies, interaction processes and secondary beams, this application range is potentially very wide. In short, the GF initiative is multi-disciplinary in nature and of interest for the following scientific communities:
- the accelerator physics community;
- the particle physics community;
- the atomic, molecular and optical physics community;
- the nuclear physics community;
- the applied physics community.

Example applications include:
Atomic Beams: for molecular and optical physics research; isoscalar ion beams for precision electroweak physics at LHC; electron beam for ep operation
of LHC; driver beams for plasma wakefield acceleration;

Photon beams: as FEL-like gamma ray sources exceeding the energy reach of FELS by four order of magnitude; high-intensity and high-brilliance photon collision schemes;

Gamma ray driven secondary beams: Polarised electron, positron and muon beams; High-purity neutrino beams; Neutron and radioactive-ion beams.