Energy Recovery Linac Designs and Studies for Electron Cooling of Hadron Beams

The Electron-Ion Collider (EIC), currently being designed by scientists at Brookhaven National Lab (BNL) and Thomas Jefferson Laboratory (JLab), will be a next-generation particle accelerator that collides electrons with protons and nuclei to enable discovery on the forefront of knowledge about the fundamental building blocks of the universe.

The EIC will leverage the existing hadron infrastructure of the Relativistic Heavy Ion Collider (RHIC) at BNL, along with a new electron accelerator complex, to deliver high luminosity polarized electron and proton beams for precision nucleon studies. One particular challenge of this machine is the preservation of hadron beam quality during long experimental runs, with effects such as intra-beam scattering and the beam-beam effect causing beam degradation over time. One approach to address this challenge is to cool the hadron beams using electron beams provided by a separate accelerating system.

In this project, Xelera Research LLC, in collaboration with BNL and JLab scientists, designed and studied an energy-recovery linac (ERL) system capable of cooling EIC hadrons. A complete, closed optics design from cathode to beam stop was created for the high energy operation mode of the ERL (cooling 275 GeV protons). The design comprises a complete beamline, including the injector, merger, main linac, cooling section, return line, and beam stop. The layout geometry is shown here with section labels: Injector (IN), Merger (MG), ERL Linac (LA), Hadron Merge (HM), Cooling sections (C1 – C7), Hadron Demerge (HD), Turnaround A (TA), Return line (R1 – R4), Turnaround B (TB), Merge High Energy (MH), and Dump (DU):

These sections were designed using comprehensive modeling and global numerical optimization to achieve the desired beam parameters while suppressing the detrimental effects of coherent synchrotron radiation (CSR) and space charge (SC). Studies performed include start-to-end simulations which demonstrate emittance preservation through energy-recovery, beam breakup (BBU) simulations showing a threshold current well above the target operating current, and extensive tolerance studies. Here are the corresponding lattice beam functions, dispersion functions, and beam energy through the full machine:

In addition to forming the physics solution, the lattice was used to create a 3D model of the system and place it in the RHIC tunnel. EIC scientists provided not only the ERL specifications required for hadron cooling, but also 3D CAD layouts of the existing RHIC infrastructure. Incorporating this information has allowed the Xelera team to design an ERL solution that satisfied both the EIC cooling requirements as well as the realistic geometric constraints of the existing and/or planned facilities. This video shows a fly-through rendering of the 3D model in the tunnel:

This work was supported by DOE SBIR grant number DE-SC0020514.

References

E. Wang, et al., “The Accelerator Design Progress for EIC Strong Hadron Cooling”, in Proc. IPAC’21, Campinas, SP, Brazil, May 2021, pp. 1424–1427. doi:10.18429/JACoW-IPAC2021-TUPAB036

E. Wang, et al., “Electron Ion Collider Strong Hadron Cooling Injector and ERL”, in Proc. LINAC’22, Liverpool, UK, Aug.-Sep. 2022, pp. 7–12. doi:10.18429/JACoW-LINAC2022-MO2AA04

C. Gulliford, et al., “Design and optimization of an ERL for cooling EIC hadron beams”, in Proc. IPAC’23, Venice, Italy, May 2023, pp. 73-76. doi:10.18429/JACoW-IPAC2023-MOPA016