7 Design and Principles of Linear Accelerators and Colliders
329
ERL transports a short electron bunch with a high repetition frequency of 1.3 GHz.
Coherent, high-intensity THz radiation from such short electron bunches has many
unique applications in material science.
7.8.5 bERLinPro
As of 2019, the Helmholtz-Zentrum Berlin is constructing the Energy-Recovery
Linac Prototype bERLinPro, an SRF-based demonstration facility for the science
and technology of ERLs for future high power, high brilliance electron beam
applications [149]. bERLinPro is designed to accelerate a high current (100 mA,
50 MeV), high brilliance (normalized emittances below 1 mm·mrad) CW electron
beam. The ERL as a prototype to demonstrate low normalized beam emittance of
1 mm·mrad at 100 mA and short pulses of about 2 ps. The high-brilliance beam
will originate from a gun configured with (1.4 λ)/2 cell SRF cavity with a normalconducting, high quantum efficiency. This injector is planned to support 6 mA beam
current and up to 3.5 MeV beam kinetic energy.
7.8.6 CBETA
Cornell-BNL-ERL-Test-Accelerator (CBETA) is a test ERL [150], featuring four
accelerating passes through the superconducting linac with a single Fixed Field
Alternating Linear Gradient (FFA-LG) return beamline built of the Halbach-type
permanent magnets. The CBETA ERL accelerates electrons from 42 to 150 MeV,
with a 6 MeV injector. The novelty is that four electron beams, with energies
of 42, 78, 114, and 150 MeV, are merged by spreader beamlines into singlearc FFA-LG beamlines. The electron beams from the main linac cryomodule
pass through the FFA-LG arc and are adiabatically merged into a single straight
line. This is the first 4-pass superconducting ERL and the first single permanent
magnet return line. It promises to deliver unprecedentedly high beam current with
simultaneously small emittance. A collaboration between Cornell and Brookhaven
National Laboratory has constructed the CBETA facility on the Cornell campus
[151], and commissioning is ongoing as of the summer of 2019. A DC photoemitter electron source, a high-power SRF injector linac, a high-current SRF linac
for energy recovery, and a permanent-magnet return loop have been assembled to
the 4-turn SRF ERL. CBETA provides essential R&D for the EIC. Furthermore, the
high-brightness beam with 150 MeV and up to 40 mA will have applications beyond
EIC cooling and basic accelerator research, for industry, nuclear physics, and X-ray
science.
329
ERL transports a short electron bunch with a high repetition frequency of 1.3 GHz.
Coherent, high-intensity THz radiation from such short electron bunches has many
unique applications in material science.
7.8.5 bERLinPro
As of 2019, the Helmholtz-Zentrum Berlin is constructing the Energy-Recovery
Linac Prototype bERLinPro, an SRF-based demonstration facility for the science
and technology of ERLs for future high power, high brilliance electron beam
applications [149]. bERLinPro is designed to accelerate a high current (100 mA,
50 MeV), high brilliance (normalized emittances below 1 mm·mrad) CW electron
beam. The ERL as a prototype to demonstrate low normalized beam emittance of
1 mm·mrad at 100 mA and short pulses of about 2 ps. The high-brilliance beam
will originate from a gun configured with (1.4 λ)/2 cell SRF cavity with a normalconducting, high quantum efficiency. This injector is planned to support 6 mA beam
current and up to 3.5 MeV beam kinetic energy.
7.8.6 CBETA
Cornell-BNL-ERL-Test-Accelerator (CBETA) is a test ERL [150], featuring four
accelerating passes through the superconducting linac with a single Fixed Field
Alternating Linear Gradient (FFA-LG) return beamline built of the Halbach-type
permanent magnets. The CBETA ERL accelerates electrons from 42 to 150 MeV,
with a 6 MeV injector. The novelty is that four electron beams, with energies
of 42, 78, 114, and 150 MeV, are merged by spreader beamlines into singlearc FFA-LG beamlines. The electron beams from the main linac cryomodule
pass through the FFA-LG arc and are adiabatically merged into a single straight
line. This is the first 4-pass superconducting ERL and the first single permanent
magnet return line. It promises to deliver unprecedentedly high beam current with
simultaneously small emittance. A collaboration between Cornell and Brookhaven
National Laboratory has constructed the CBETA facility on the Cornell campus
[151], and commissioning is ongoing as of the summer of 2019. A DC photoemitter electron source, a high-power SRF injector linac, a high-current SRF linac
for energy recovery, and a permanent-magnet return loop have been assembled to
the 4-turn SRF ERL. CBETA provides essential R&D for the EIC. Furthermore, the
high-brightness beam with 150 MeV and up to 40 mA will have applications beyond
EIC cooling and basic accelerator research, for industry, nuclear physics, and X-ray
science.