The Cornell-BNL ERL test accelerator (CBETA): experiences, spinoffs, and lessons learned
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IJCLab
As accelerators become larger and their beams require more power, efficiency becomes an important paradigm. Energy Recovery Linacs (ERLs), the use of superconducting cavities (SRF), and permanent magnets address this concern. A collaboration between Cornell University and Brookhaven National Laboratory has designed, constructed, and commissioned CBETA, the Cornell-BNL ERL Test Accelerator at Cornell University, culminating in 4-turn ERL operation at Christmas of 2019. As first multi-turn ERL that recovers energy into SRF cavities, CBETA returns the beam 4 times through the same linac to add energy each time; it then returns the beam 4 more times at the decelerating phase of the same linac to recover the beam energy into the E&M field of the SRF cavities. Another first is the large energy-acceptance return loop that simultaneously transports 7 beams of different energy through a Fixed Field Alternating-gradient (FFA) lattice, which is comprised of permanent magnets. Successfully establishing 4-turn energy recovery at CBETA is especially relevant in the light of the increasing importance that ERLs have obtained: ERLs are part of the hadron coolers for the EIC, they are part of the LHeC plans, they are an integral component of ee Higgs Factory design options, they can be drivers for low energy nuclear physics experiments, they have been investigated as drivers for compact Compton-x-ray sources, and they have become strong contenders as new EUV sources for microchip lithography. The permanent-magnet FFA technology pioneered at CBETA has another promising spin off: it is the basis of an energy-doubling upgrade option for CEBAF.
Luc Perrot, Julien Michaud
