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The Cornell-BNL ERL Test Accelerator (CBETA) developed several energy-saving measures: multi-turn energy recovery, low-loss superconducting radiofrequency (SRF) cavities, and permanent magnets. With green technology becoming imperative for new high-power accelerators, the lessons learned will be important for projects like the FCC-ee or new light sources, where spinoffs and lessons learned from CBETA are already considered for modern designs., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The Cornell-Brookhaven CBETA machine is a four pass Energy Recovery Linac (ERL) with a Non-scaling Fixed-Field Alternating gradient (NS-FFA) arc. For online modeling of single particle dynamics in CBETA, a customized version of the Tao program, which is based upon the Bmad toolkit, has been developed. This online program, called CBETA-V, is interfaced to CBETA’s EPICS control system. This paper describes the online modeling system and initial experience during machine running., Proceedings of the 13th Int. Computational Accelerator Physics Conf., ICAP2018, Key West, FL, USA

CBETA, the Cornell-BNL ERL Test Accelerator, is an SRF multi-turn ERL which has been commissioned in the one-turn configuration from March to July 2019. During this time, the project has demonstrated an energy acceptance of 1.5 in the FFA arc, high-transmission energy recovery performance, and increased the CBETA energy-recovered maximum average current., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

We are successfully commissioning a unique Cornell University and Brookhaven National Laboratory Electron Recovery Linac (ERL) Test Accelerator ’CBETA’ [1]. The ERL has four accelerating passes through the supercon-ducting linac with a single Fixed Field Alternating Linear Gradient (FFA-LG) return beam line built of the Halbach type permanent magnets. CBETA ERL accelerates elec-trons from 42 MeV to 150 MeV, with the 6 MeV injec-tor. The novelties are that four electron beams, with ener-gies of 42, 78, 114, and 150 MeV, are merged by spreader beam lines into a single arc FFA-LG beam line. The elec-tron beams from the Main Linac Cryomodule (MLC) pass through the FFA-LG arc and are adiabatically merged into a single straight line. From the straight section the beams are brought back to the MLC the same way. This is the first 4 pass superconducting ERL and the first single permanent magnet return line., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The Cornell BNL ERL Test Accelerator (CBETA) employs a superconducting Main Linac Cryomodule in order to perform multi-turn energy recovery operation. Optimizing the field stability of the low bandwidth SRF cavities in the presence of microphonics with limited available RF power is a challenging task. Despite of this, the Main Linac Cryomodule has been successfully used in CBETA to impart a maximum energy gain of 54 MeV, well above the energy gain requirement of CBETA. In this paper, we present an overview of our RF commissioning procedure including automatic coarse tuning, measurement of DAC and phase offsets. We further detail our microphonics measurements from our most recent run period., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

The Cornell-BNL ERL Test Accelerator (CBETA) is a new multi-turn energy recovery linac currently being commissioned at Cornell University. It uses a superconducting main linac to accelerate electrons by 36 MeV and recover their energy. The energy recovery process is sensitive to fluctuations in the accelerating field of all cavities. In this paper, we outline our semi-automated RF commissioning procedure, which starts from automatic coarse tuning of the cavity all the way to adjusting the field control loops. We show some results of using these tools and describe the recent performance of the RF system during our ongoing commissioning phase., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

CBETA, a 4-pass electron Energy Recovery Linac (ERL) is presently under construction at Cornell University and is a collaboration between Brookhaven National Laboratory (BNL) and Cornell University. Beam commissioning began in March 2019 with a single pass ERL configuration. Commissioning of the complete 4-pass machine is scheduled to begin in fall 2019. The fixed field alternating gradient (FFA) return loop for CBETA uses Halbach permanent magnets with a common beam pipe for seven different energy beams (4 accelerating energies and 3 decelerating energies). One of the most challenging requirements for the CBETA BPM system is to independently measure the position of each of these beams. The overall design of the CBETA BPM system and the techniques planned to measure the position of each energy beam will be presented., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The Cornell-Brookhaven Energy-recovery Linac Test Accelerator is a four-pass, 150-MeV electron accelerator with a six-cell 1.3 GHz superconducting-RF linear accelerator and a fixed-field alternating-gradient (FFAG) return loop made up of Halbach-style quadrupole magnets. The optics matching between the linear accelerator and the return loop is achieved with a conventional magnet system comprised of 50 dipole magnets and 64 quadrupole magnets in four beamlines at each end of the linac. The 42-, 78-, 114- and 150-MeV electron beams are separated into independent vacuum chambers in order to allow for the path-length adjustment required by energy recovery. We report on the first beam tests of the initial installation of the splitter/combiner section at the exit of the linac. The vacuum system of the 42-MeV S1 line was installed during the first week of April. Nine dipole and four quadrupole magnets were installed and surveyed into position the following week, and the water cooling system was commissioned. A 6-MeV beam passed through the line on April~11 with no need for adjusting pre-set magnet excitation currents. One week later, time-of-flight measurements were used to calibrate and phase the individual superconducting RF cavities. The S1 magnet settings were then scaled up to achieve 5-cavity, 42-MeV operation through the first nine FFAG permanent-magnet quadrupoles. This initial Fractional Arc Test will conclude on May 18, when the installation of the remaining seven splitter/combiner lines and the return loop will begin. CBETA operations are scheduled to begin in early 2019., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The Cornell-BNL ERL Test Accelerator (CBETA) is a new multi-turn energy recovery linac currently under construction at Cornell University. It uses two superconducting linacs, both of which are susceptible to microphonics detuning. The high-current injector accelerates electrons to 6 MeV and the main linac accelerates and decelerates electrons by 36 MeV. In this paper, we discuss various measures taken to reduce vibrations caused by instabilities and flow transients in the cryogenic system of the main linac cryomodule. We further describe the use of a Least Mean Square algorithm in establishing a stable Active Microphonics Compensation system for operation of the main linac cavities., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The Main Linac Cryomodule (MLC) prototype is a key component of the Cornell-BNL ERL Test Accelerator (CBETA) project, which is a 4-turn FFAG ERL currently under construction at Cornell University. This novel cryomodule is the first SRF module ever to be fully optimized simultaneously for high efficient SRF cavity operation and for supporting very high CW beam currents. After a successful initial MLC testing, the MLC has now been moved into its final location for the CBETA ring. For a first beam test of the MLC and CBETA, the Cornell ERL high voltage DC gun and SRF injector cryomodule were connected to MLC via an entry beam line; a beam stop assembly was also installed at the exit line. In this paper, we summarize the performance of this novel ERL cryomodule including the results of the first beam test and the additional tests focused on RF field stability and cavity microphonics., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

A collaboration between Cornell University and Brookhaven National Laboratory has designed and is constructing CBETA, the Cornell-BNL ERL Test Accelerator on the Cornell campus. The ERL technology that has been prototyped at Cornell for many years is being used for this new accelerator, including a DC electron source and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current linac cryomodule optimized for ERLs, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams. BNL has designed multi-turn ERLs for several purpose, dominantly for the electron beam of eRHIC, its Electron Ion Collider (EIC) project and for the associated fast electron cooling system. Also in JLEIC, the EIC designed at JLAB, an ERL is envisioned to be used for electron cooling. The number of transport lines in an ERL is minimized by using return arcs that are comprised of a Fixed Field Alternating-gradient (FFA) design. This technique will be tested in CBETA, which has a single return for the 4-beam energies with strongly-focusing permanent magnets of Halbach type. The high-brightness beam with 150~MeV and up to 40~mA will have applications beyond accelerator research, in industry, in nuclear physics, and in X-ray science. Low current electron beam has already been sent through the most relevant parts of CBETA, from the DC gun through both cryomodules, through one of the 8 similar separator lines, and through one of the 27 similar FFA structures. Further construction is envisioned to lead to a commissioning start for the full system early in 2019., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

Cornell University has prototyped technology essential for any high brightness electron ERL. This includes a DC gun and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current CW cryomodule, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams, e.g. slid measurements for 6-D phase-space densities, a fast wire scanner for beam profiles, and beam loos diagnostics. All these are now available to equip a one-cryomodule ERL, and laboratory space has been cleared out and is radiation shielded to install this ERL at Cornell. BNL has designed a multi-turn ERL for eRHIC, where beam is transported more than 20 times around the RHIC tunnel. The number of transport lines is minimized by using two non-scaling (NS) FFAG arcs. A collaboration between BNL and Cornell has been formed to investigate the new NS-FFAG optics and the multi-turn eRHIC ERL design by building a 4-turn, one-cryomodule ERL at Cornell. It has a NS-FFAG return loop built with permanent magnets and is meant to accelerate 40mA beam to 200MeV., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA

The main linac prototype cryomodule (MLC) is a key component for the Cornell-BNL ERL Test Accelerator (CBETA), which is a 4-turn FFAG ERL under construction at Cornell University. The MLC has been designed for high current and efficient continuous wave (CW) SRF cavity operation, and houses six high Q0 7-cell SRF cavities with individual beamline higher order-modes (HOMs) absorbers for strong HOM suppression in high beam current operation. Cavities have achieved specification values of 16.2MV/m with high Q0 of 2.0·10¹⁰ at 1.8K in CW operation after cooldown optimizations and RF processing. Damping of the HOMs has been measured in detail, indicating that the loaded quality-factors of all critical modes are low enough to avoid BBU in high current, multi-turn ERL operation. Microphonics measurements have been carried out as well, and vibration sources have been determined and eliminated. Here we report on these cryomodule performance studies., Proceedings of the North American Particle Accelerator Conf., NAPAC2016, Chicago, IL, USA

The main linac cryomodule (MLC) prototype is a key component for the Cornell-BNL ERL Test Accelerator (CBETA) project, which is a 4-turn FFAG ERL under construction at Cornell University. This novel cryomodule is the first SRF module ever to be fully optimized simul-taneously for high efficient SRF cavity operation and for supporting very high CW beam currents. Initial MLC testing has demonstrated that cavity performance and HOMs damping meet specification values. Recent, addi-tional tests have focused on RF field stability, and cavity microphonics. In this paper, we summarize the perfor-mance of this novel ERL cryomodule and evaluate its beam capabilities based on the measured performance., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The Cornell BNL ERL Test Accelerator (CBETA) incorporates two SRF linacs; one for its injector and another for the energy recovery loop. Microphonics in both the cryomodules play a crucial role in determining the energy stability of the electron beam in high current operation. We have measured vibrations and frequency detuning of the SRF cavities and determined that the cryogenic system is the major source of microphonics in both cryomodules. In this paper we discuss these measurements and demonstrate an Active Microphonics Compensation system implemented using fast piezo-electric tuners which we incorporated in our Low Level RF control system to be used in routine operation., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

Cornell's Lab of Accelerator-based Sciences and Education (CLASSE) and the Collider Accelerator Department (BNL-CAD) are developing the first SRF multi-turn energy recovery linac with Non-Scaling Fixed Field Alternating Gradient (NS-FFAG) racetrack. The existing injector and superconducting linac at Cornell University are installed together with a single NS-FFAG arcs and straight section at the opposite side of the the linac to form an Electron Energy Recovery (ERL) system. Electron beam from the 6 MeV injector is injected into the 36 MeV superconducting linac, and accelerated by four successive passes: from 42 MeV up to 150 MeV using the same NS-FFAG structure made of permanent magnets. After the maximum energy of 150 MeV is reached, the electron beam is brought back to the linac with opposite Radio Frequency (RF) phase. Energy is recovered and reduced to the initial value of 6 MeV with 4 additional passes. There are many novelties: a single NS-FFAG structure, made of permanent magnets, brings electrons with four different energies back to the linac. A new adiabatic NS-FFAG arc-to-straight section merges 4 separated orbits into a single orbit in the straight section., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

We propose a novel use of Fixed Field Altrenating Gradient beam line (FFAG) to replace multiple beam lines in existing ERL’s (4-pass at Novosibirsk, ERL of CEBAF, ERL at KEK, etc.) with a single FFAG beam line connected with spreaders and combiners to the linac. We present two designs for the Electron Ion Colliders one at CERN LHeC and one at Brookhaven National Laboratory to be placed in the tunnel of the existing Relativistic Heavy Ion Collider (RHIC) called eRHIC. The proof of principle electron accelerator with the FFAG arc is to be built at Cornell University Wilson Hall where there are already available injector, superconducting linac accelerator and the dump. There are very new developments in the FFAG design never accomplished before: arc-to straight adiabatic matching with merged multiple orbits into one, permanent magnet design for the arc and straights with ability of four times in energy, etc., Proceedings of the 21st Int. Conf. on Cyclotrons and their Applications, Cyclotrons2016, Zurich, Switzerland

The main linac cryomodule (MLC) for the future energy-recovery linac (ERL) based X-ray light source at Cornell has been designed, fabricated, and tested. It houses six 7-cell SRF cavities with individual higher order-modes (HOMs) absorbers, cavity frequency tuners, and one magnet/BPM section. Cavities have achieved the specification values of 16.2MV/m with high-Q of 2.0·10¹⁰ in 1.8K in continuous wave (CW) mode. During initial MLC cavity testing, we encountered some field emission, reducing Q and lowering quench field. To overcome field emission and find optimal cool-down parameters, RF processing and thermal cycles with different cool-down conditions has been done. Here we report on these studies and present final results from the MLC cavity performance., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA

Electron beams ionize rest gas particles which then accumulate around them, disturbing beam dynamics and causing background radiation. While this effect has been predicted in the past, linacs have hitherto not suffered from it because of their rather small beam current. The effect of ions increases with larger currents and smaller cross sections of the beam, and it has clearly been observed in Cornell's high-brightness ERL injector for the first time. This presentation will show experimental evidence for ions, demonstrate strategies for their elimination, and will compare the experimental data to theories of beam-ion interactions., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA

The Cornell Main Linac cryomodule (MLC) is a key component in the CBETA project. The SRF cavities with high loaded-Q in the MLC are very sensitive to microphonics from mechanical vibrations. Poor frequency stability of the cavities would dramatically increase the input RF power required to maintain stable accelerating fields in the SRF cavities. In this paper, we present detailed results from microphonics measurement for the cavities in the MLC, discuss dominant vibration sources, and show vibration damping results. The current microphonics level meets the CBETA requirement of a 36MeV energy gain without applying fast tuner compensation., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA

The Cornell high intensity photoinjector reaches a new regime of linac beam parameters where high continuous-wave electron beam currents lead to ion trapping. Above 10 mA, we have observed beam trips that limit stable machine operation to approximately 10⁻¹⁵ minutes. By applying known ion clearing methods, the machine lifetime increases to at least 24 hours of continuous operation, suggesting that trapped ions are the most likely cause of the trips. In this paper we share some of our observations ion trapping in the photoinjector, as well as experimental tests of three common ion mitigation methods: clearing electrodes, beam shaking and bunch gaps., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

Cornell has designed, fabricated, and tested a high current (100 mA) CW SRF prototype cryomodule for the future energy-recovery linac (ERL) based synchrotron-light facility at Cornell . It houses six 7-cell SRF cavities with individual HOM absorbers and one magnet/ BPM section. Cavities are targeted to operate with high Qo of 2.0·10¹⁰ at 16.2 MV/m, 1.8 K in continuous wave (CW) mode. We will report the RF test results of 7-cell cavities in this cryomodule after initial cooldown and several thermal cycles with different cooldown method., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

We present our first measurements of trapped ions in the Cornell energy recovery linac (ERL) photoinjector. During high intensity operation, ions become trapped inside of the electric potential generated by the electron beam and oscillate transversely with a characteristic frequency. At high beam currents, electron beam-ion interactions result in excessive radiation, primarily due to beam losses and bremsstrahlung. However, by shaking the beam at the trapped ion's oscillation frequency, we are able to drive a resonance that severely reduces or eliminates this radiation. This both confirms the viability of beam shaking as an ion mitigation strategy inside high intensity injectors, and allows us to measure the trapped ion oscillation frequencies indirectly. Experimental data for a beam energy of 5 MeV, a bunch repetition rate of 1.3 GHz, and beam currents up to 20 mA, as well as simulations to describe our data and the beam shaking principle are presented., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

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Commissioning of the high brightness photoinjector for the Energy Recovery Linac at Cornell University continues. To aid in this process we have developed a ¿Virtual Accelerator¿ application, which provides the beam physicist with an online high-level physics description of the machine. This application combines a linear optics model called Numerical Transfer Matrix (NTMAT), developed at Cornell, and EPICS-DDS, a middle-layer software based on the Experimental Physics and Industrial Control System (EPICS) toolkit and the Data Distribution Service (DDS) data-centric publish/subscribe model. We present the initial results of implementing this new software tool and its deployment in the Cornell ERL injector control room., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan