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ERL Particle Colliders

Integrating ERL technologies directly in the design of new particle colliders enables to unlock unprecedented performance in an energy sustainable way. Especially in the realm of H and HH Factories, ep/eA colliders, and potentially muon colliders, ERL can be a paradigm shifting technology to enhance particle physics research. 



The LHeC is a high energy electron-ion collider using the HL-LHC ring for the ions and an ERL for the electrons to provide a center of mass collision energy of 1.2 TeV. It consists of a racetrack configuration tangential to the LHC ring with collisions foreseen at IP2. This arrangement transforms the LHC into a 3-beam facility with simultaneous pp and ep operation at different IPs, as the electron beam has little impact on the proton beams. This means that the electron-hadron programme would not impact the integrated luminosity of the main hh programme. The electron beam energy is 50 GeV, bringing the total LHeC cost (without detector) about 1 billion CHF. The three-turn LHeC configuration has two oppositely positioned electron linacs and three arcs housed in the same tunnel. The two linacs are about 0.8 km length and the arcs have a 0.55 km radius leading to an ERL circumference of 5.4 km, or 1/5 of the LHC length (i.e. smaller than the SPS). The luminosity is expected to reach 1034 cm-2 s-1.


The FCC-eh is a similar concept to the LHeC with a significantly higher center of mass collision energy of 3.5 TeV, based on a 60 GeV ERL energy colliding with one of the hadron beams of the FCC-hh machine. The preferred interaction point for such electron-hadron collisions at the FCC complex is the “L” interaction point close to the main CERN site. The ERL linacs are about 1 km length and with a 1 km arc radius, resulting in the ERL circumference of about 9 km, or 1/11 of the FCC length. The FCC-eh collider would open up new horizons for the physics of deep inelastic scattering and be both a high-precision Higgs factory and a powerful microscope that could discover new particles, study quark/gluon interactions, and examine possible further substructure of matter in the world.


The Circular Energy Recovery Collider (CERC) is an alternative approach to current designs for high-energy electron-positron colliders either based on two storage rings with 100 km circumference of two large linear accelerators. Using energy-recovery linacs located in the same-size 100 km tunnel would allow a large reduction of the beam energy losses, and therefore a reduction of the power consumption, while providing higher luminosity. It also opens a path for extending the center-of-mass (CM) energy to 500 GeV, which would enable double-Higgs production, and event to 600 GeV for ttH production and measurements of the top Yukawa coupling. Furthermore, this approach would allow recycling not only the energy but also the particles. This feature opens the possibility for colliding fully polarized electron and positron beams.


A twin-axis linear collider with energy recovery and multiple use of beams has been proposed, which could increase the luminosity by four orders of magnitude. In the twin linear collider, the beams are accelerated and then decelerated down to 𝐸 ≈ 5 GeV in separate parallel linacs with coupled RF systems. The RF power is always divided equally among the linacs with RF energy being transferred to the accelerating beam from the decelerated beam with a small addition from an external RF source. The linacs can be either two separate SC linacs connected by RF couplers at the ends of multi-cell cavities (9-cell TESLA cavity) or one linac consisting of twin (dual) cavities with axes for two beams. The collider is assumed to operate at an energy of 2𝐸≈ 250 GeV (with a possible increase up to 500 GeV) in semi-continuous mode with a gated duty cycle (2 seconds on, four seconds off. The performance claimed with current SC Nb technology and a power of 𝑃 100 MW, is a luminosity of~0.33 × 1036 cmsa center-of-mass energy of 250 GeV. 


ReLiC is an extrapolation of the ERLC concept which does involve twin axis cavities. he concept is based on segmenting two superconducting (SRF) linear accelerators into sections divided by separators, where used (decelerating) beams are separated from colliding with accelerating beams by a combination of DC electric and magnetic fields. This design provides for undisturbed straight trajectories of the accelerating beams and on-axis beam propagating both accelerated and decelerated beams in the SRF structures of the linac. In contrast with circular e+ecolliders, ReLiC would collide beams only once with a disruption parameter typical for linear colliders to boost the luminosity. The ReLiC design minimizes synchrotron radiation losses, which limit average beam currents in circular e+ecolliders. These novel features would allow operation at center-of-mass energies from 100 GeV to 3 TeV range, and at a claimed luminosity level between 1036 cm-2 sec-1 to 1037 cm-2 sec-1

  • V.N. Litvinenko et al., “The ReLiC: Recycling Linear e+e- Collider,” arXiv:2203.06476, 2022.