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The Electron Ion Collider (EIC) under construction at Brookhaven National Laboratory is a high luminosity collider as the next major research facility for the nuclear physics community. Among the numerous RF subsystems in the EIC, the electron storage ring (ESR) fundamental RF cavities system is one of the most challenging. This system will handle a high beam current of up to 2.5 A and replenish up to 10 MW of beam power losses from synchrotron radiation and HOM. Variable coupling is required in the cavities due to the wide range of required total RF voltage and beam current combinations. In this paper, we will present the status of the design and future plans., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

An Accelerator Research facility is a unique science and engineering challenge in that the requirements for developing a robust, optimized science facility are limited by engineering and cost limitations. Each facility is planned to achieve some science goal within a given schedule and budget and is then expected to operate for three decades. In three decades, the mechanical systems and the industrial IO to control them is not likely to change. In that same time, electronics will go through some 4 generations of change. The software that integrates the systems and provides tools for operations, automation, data analysis and machine studies will have many new standards. To help understand the process of designing and planning such a facility, we explain the specifications and requirements for the Electron Ion Collider (EIC) from both a physics and engineering perspective., Proceedings of the 5th North American Particle Accelerator Conference, NAPAC2022, Albuquerque, NM, USA

The EIC is a major new project under construction at BNL in partnership with JLab. It relies upon a number of new SRF cavities at 197 MHz, 394 MHz, 591 MHz and 1773 MHz to pre-bunch, accelerate, cool and crab the stored beams. R is focusing on the 591 MHz elliptical cavity and 197 MHz crab cavity first as these are the most challenging. Preliminary designs of these cavities are presented along with an R status report. To avoid developing multiple different cryostats a modular approach is adopted using a high degree of commonality of parts and systems. This approach may be easily adapted to other frequencies and applications., Proceedings of the 65th ICFA Advanced Beam Dynamics Workshop on High Luminosity Circular e+e- Colliders, eeFACT2022, Frascati, Italy

In preparation for the 2023 RHIC sPHENIX experi-mental program the superconducting 56 MHz quarter-wave resonator cryomodule, used operationally for longitudinal bunch compression with up to 1 MV RF voltage, is being refit to accommodate an expected beam current of 418 mA per ring, an increase of ~1.5 relative to previous operation. The upgrades to the system include an improved fundamental mode damp-er, and dual function fundamental power and higher-order mode damper couplers. This paper will describe the preliminary testing, select subsystem changes and plans for testing the cryomodule prior to installation in the RHIC beam line in 2022., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

The future EIC Electron storage ring at BNL needs to compensate up to 10 MW synchrotron loss with RF systems. The RF system relies on 34 fundamental power couplers to deliver RF power from power sources at room temperature to 17 SRF cavities at 2 K. Each power coupler will operate with 400 kW forward power, with full reflection for ~10% of time. We are developing two 1 MW coaxial FPCs at BNL, one with a BeO window and the other with an Al₂O₃ window. This paper will briefly summarize test results of high power test on the BeO window FPC , and then describe the development status of the Al₂O₃ window FPC., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

The Electron Ion Collider aims to produce luminosities of 10³⁴ cm⁻²s⁻¹ . The machine will operate over a broad range of collision energies with highly polarized beams. The coexistence of highly radiative electrons and nonradiative ions produce a host of unique effects. Strong hadron cooling will be employed for the final factor of 3 luminosity boost., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The Electron-Ion Collider (EIC) is being designed for construction at Brookhaven National Laboratory. Activities have been focused on beam-beam simulations, polarization studies, and beam dynamics, as well as on maturing the layout and lattice design of the constituent accelerators and the interaction region. The latest design advances will be presented., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The design of the electron-ion collider EIC to be constructed at Brookhaven National Laboratory has been continuously evolving towards a realistic and robust design that meets all the requirements set forth by the nuclear physics community in the White Paper. Over the past year activities have been focused on maturing the design, and on developing alternatives to mitigate risk. These include improvements of the interaction region design as well as modifications of the hadron ring vacuum system to accommodate the high average and peak beam currents. Beam dynamics studies have been performed to determine and optimize the dynamic aperture in the two collider rings and the beam-beam performance. We will present the EIC design with a focus on recent developments., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The Low Energy RHIC electron Cooler (LEReC) is the first electron cooler based on rf acceleration of electron bunches. To further improve RHIC luminosity for heavy ion beam energies below 10 GeV/nucleon, a normal conducting RF cavity at 1.4 GHz was designed and fabricated for the LINAC that will provide longer electron bunches for the LEReC. It is a single-cell cavity with an effective cavity length shorter than half of the 1.4 GHz wavelength. This cavity was fabricated and tested on-site at BNL to verify RF properties, i.e. the resonance frequency, FPC coupling strength, tuner system performance, and high power tests. In this paper, we report the RF test results for this cavity., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

This paper presents an overview of the Interaction Region (IR) design for the planned Electron-Ion Collider (EIC) at Brookhaven National Laboratory. The IR is designed to meet the requirements of the nuclear physics community *. The IR design features a ±4.5 m free space for the detector; a forward spectrometer magnet is used for the detection of hadrons scattered under small angles. The hadrons are separated from the neutrons allowing detection of neutrons up to ±4 mrad. On the rear side, the electrons are separated from photons using a weak dipole magnet for the luminosity monitor and to detect scattered electrons (e-tagger). To avoid synchrotron radiation backgrounds in the detector no strong electron bending magnet is placed within 40 m upstream of the IP. The magnet apertures on the rear side are large enough to allow synchrotron radiation to pass through the magnets. The beam pipe has been optimized to reduce the impedance; the total power loss in the central vacuum chamber is expected to be less than 90 W. To reduce risk and cost the IR is designed to employ standard NbTi superconducting magnets, which are described in a separate paper., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The Electron Ion Collider (EIC) to be constructed at Brookhaven National Laboratory in the USA will be a complex system of accelerators providing high luminosity, high polarization, variable center of mass energy collisions between electrons and protons or ions. To achieve this a variety of RF systems are required. They must provide for capture, formation and storage of Ampere-class beams in the electron and hadron storage rings (ESR and HSR), fast acceleration of high-charge polarized electron bunches in the rapid cycling synchrotron (RCS), provision of cold high current electron bunches in the high-energy cooler ERL and precise high-gradient crabbing of electrons and hadrons either side of the interaction point. The challenges include strong HOM damping in the storage ring cavities and cooler ERL, very high fundamental mode power in the ESR and cooler injector, extremely stable low-noise operation of the crab cavities, mitigation of transient beam loading from gaps, and operating over a wide range of energies and beam currents. We describe the high-level system parameters and principal design choices made and progress on the R plan to develop these state of the art systems., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

A folded coaxial tuner without spring fingers was designed for the Low Energy RHIC electron Cooler (LEReC) 2.1 GHz warm cavity. During RHIC run 2019, this tuner was found to cause cavity trips via different failure modes. After analyzing these failure modes, a new straight coaxial tuner without spring fingers was proposed and was installed. We show the operational experience of the new tuner in this paper., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The electron-ion luminosity in EIC has a number of limits, including the ion intensity available from the injectors, the total ion beam current, the electron bunch intensity, the total electron current, the synchrotron radiation power, the beam-beam effect, the achievable beta functions at the interaction points (IPs), the maximum angular spreads at the IP, the ion emittances reachable with stochastic or strong cooling, the ratio of horizontal to vertical emittance, and space charge effects. We map the e-A luminosity over the center-of-mass energy range for some ions ranging from deuterons to uranium ions. For e-Au collisions the present design provides for electron-nucleon (e-Au) peak luminosities of 1.7x1033 cm⁻²s⁻¹ with stochastic cooling, and 4.7x1033 cm⁻²s⁻¹ with strong hadron cooling., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

We will present currents status of the CeC experiment at RHIC and discuss plans for future. Special focus will be given to unexpected experimental results obtained during RHIC Run 18 and discovery of a previously unknown type of microwave instability. We called this new phenomenon micro-bunching Plasma Cascade Instability (PCI). Our plan for future experiments includes suppressing this instability in the CeC accelerator and using it as a broad-band amplifier in the CeC system., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The design effort for the electron-ion collider eRHIC has concentrated on electron-proton collisions at the highest luminosities over the widest possible energy range. The present design also provides for electron-nucleon peak luminosities of up to 4.7·10³³ cm⁻²s^{−1} with strong hadron cooling, and up to 1.7·10³³ cm⁻²s^{−1} with stochastic cooling. Here we discuss the performance limitations and design choices for electron-ion collisions that are different from the electron-proton collisions. These include the ion bunch preparation in the injector chain, acceleration and intrabeam scattering in the hadron ring, path length adjustment and synchronization with the electron ring, stochastic cooling upgrades, machine protection upgrades, and operation with polarized electron beams colliding with either unpolarized ion beams or polarized He-3., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

Superconducting RF (SRF) photoinjectors are considered to be a potential breakthrough in the area of high brightness electron sources. However, there is always the very important question of the compatibility of SRF cavities and high quantum efficiency (QE) photocathodes. A deposition of active elements from high QE photocathodes on the surface of a cavity makes it more vulnerable to multipacting (MP) and could affect the operation of an SRF gun. On the other side, MP can significantly reduce the lifetime of a photocathode. It is well known in the SRF community that a strong coupling, high forward power and sufficient cleanliness of cavity walls are the key components to overcome a low-level MP zone. In this paper we present a theoretical model of passing a MP barrier which could help estimate the desirable conditions for successful operation of an SRF gun. We demonstrate our results for the 113 MHz SRF photo-injector for Coherent electron Cooling (CeC) alongside with the experimental observations and 3D simulations of the MP discharge in the cavity. The results of the theoretical model and simulations show good agreement with the experimental results, and demonstrate that, if approached carefully, MP zones can be easily passed without any harm to the photocathode., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

For the proposed electron-ion collider eRHIC, an electron storage ring will be installed in the existing RHIC tunnel. To reach the high luminosity of up to 10³⁴ cm⁻² sec⁻¹, beam currents up to 2.5A have to be stored. Besides high luminosity the physics program requires spin polarization levels of 70 percent, with both spin "up" and spin "down" orientations present in the fill. This is only feasible by using a full-energy spin polarized injector that replaces bunches faster than the depolarization rate. To limit the repetition rate of that injector to about one hertz, the polarization lifetime in the storage ring has to be maximized by proper spin matching and countermeasures for the machine misalignments. We will give an overview of the electron storage ring design., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The brand-new state of the art electron accelerator, LEReC, was built and commissioned at BNL. LEReC accelerator includes a photocathode DC gun, a laser system, a photocathode delivery system, magnets, beam diagnostics, a SRF booster cavity, and a set of Normal Conducting RF cavities to provide sufficient flexibility to tune the beam in the longitudinal phase space. Electron beam quality suitable for cooling in the Relativistic Heavy Ion Collider (RHIC) was achieved [1], which lead to the first demonstration of bunched beam electron cooling of hadron beams [2]. This presentation will discuss commissioning results, achieved beam parameters and performance of the LEReC systems., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

The Electron-Ion Collider (EIC) is being envisioned as the next facility to be constructed by the DOE Nuclear Physics program. Brookhaven National Laboratory is proposing eRHIC, a facility based on the existing RHIC complex as a cost effective realization of the EIC project with a peak luminosity of 10³⁴ cm⁻² sec⁻¹. An electron storage ring with an energy range from 5 to 18 GeV will be added in the existing RHIC tunnel. A spin-transparent rapid-cycling synchrotron (RCS) will serve as a full-energy polarized electron injector. Recent design improvements include reduction of the IR magnet strengths to avoid the necessity for Nb₃Sn magnets, and a novel hadron injection scheme to maximize the integrated luminosity. We will provide an overview of this proposed project and present the current design status., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

With the completion of the National Academies of Sciences Assessment of a US Electron-Ion Collider, the prospects for construction of such a facility have taken a step forward. This paper provides an overview of the two site-specific EIC designs: JLEIC (Jefferson Lab) and eRHIC (BNL) as well as brief overview of ongoing EIC R, Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

The Linac of Low Energy RHIC electron Cooler (LEReC) is designed to deliver a 1.6 MeV to 2.6 MeV electron beam, with peak-to-peak dp/p less than 7·10⁻⁴. The booster cavity is the major accelerating component in LEReC, which is a 0.4 cell cavity operating at 2 K, with a maximum energy gain of 2.2 MeV. It is modified from the Energy Recovery Linac (ERL) photocathode gun, with fundamental power coupler (FPC), pickup coupler (PU) and higher order mode (HOM) coupler close to each other. The direct coupling between FPC and PU induced crosstalk effect in this cavity. This effect is simulated and measured, and is further corrected using low level RF (LLRF) to meet the energy spread requirement., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

In this talk we will present the status of the Coherent electron Cooling demonstration experiment at BNL and our proposed step using plasma-cascade micro-bunching amplifier. We will present both the progress and the stumbling blocks with this challenging project. The presentation will also contain relevant theory and simulations. Finally, we will present the design of our next experiment and prediction for CeC cooling 26.5 GeV/u hadron beam in RHIC., Proceedings of the 12th Workshop on Beam Cooling and Related Topics, COOL2019, Novosibirsk, Russia

The future electron-ion collider (EIC) aims at an electron-proton luminosity of 10³³ to 10³⁴ cm⁻² sec⁻¹ and a center-of-mass energy range from 20 to 140 GeV. The eRHIC design has been continuously evolving over a couple of years and has reached a considerable level of maturity. The concept is generally conservative with very few risk items which are mitigated in various ways., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

The Low Energy RHIC electron Cooler (LEReC) was recently constructed and commissioned at BNL. The LEReC is the first electron cooler based on the RF acceleration of electron bunches (previous electron coolers all used DC beams). Bunched electron beams are necessary for cooling hadron beams at high energies. The challenges of such an approach include generation of electron beams suitable for cooling, delivery of electron beams of the required quality to the cooling sections without degradation of beam emittances and energy spread, achieving required small angles between electrons and ions in the cooling sections, precise energy matching between the two beams, high-current operation of the electron accelerator, as well as several physics effects related to bunched beam cooling. Following successful commissioning of the electron accelerator in 2018, the focus of the LEReC project in 2019 was on establishing electron-ion interactions and demonstration of cooling process using electron energy of 1.6MeV (ion energy of 3.85GeV/n), which is the lowest energy of interest. Here we report on the first demonstration of Au ion cooling in RHIC using this new approach., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

The brand new non-magnetized bunched beam electron cooler (LEReC) [1] has been built to provide luminosity improvement for Beam Energy Scan II (BES-II) physics program at the Relativistic Heavy Ion Collider (RHIC) BES-II [2]. The LEReC accelerator includes a photocathode DC gun, a laser system, a photocathode delivery system, magnets, beam diagnostics, a SRF booster cavity, and a set of Normal Conducting RF cavities to provide sufficient flexibility to tune the beam in the longitudinal phase space. This high-current high-power accelerator was successfully commissioned in period of March -September 2018. Beam quality suitable for cooling has been demonstrated. In this paper we discuss beam commissioning results and experience learned during commissioning., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

A 112 MHz SRF electron photoinjector (gun) was developed at Brookhaven National Laboratory to produce high-brightness and high-bunch-charge bunches for the coherent electron cooling proof-of-principle experiment. The gun is designed to deliver electrons with a kinetic energy of up to 2 MeV. Electrons are generated by illuminating a high quantum efficiency (QE) K2CsSb photoemission layer with a green laser operating at a wavelength of 532 nm. The gun was able to generating 3 nC bunches at 1.7 MeV. The design goals, fabrication, performance and operational experience are reported here., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

RHIC provided Au-Au collisions at beam energies of 9.8, 7.3, 4.59 and 3.85 GeV/nucleon during the first year of the Beam Energy Scan II in 2019. The physics goals at the first two higher beam energies were achieved. At the two lower beam energies, bunched electron beam cooling has been demonstrated successfully. The accelerator performance was improved compared to when RHIC was operated at these energies in earlier years. This article will introduce the challenges to operate RHIC at low energies and the corresponding countermeasures, and review the improvement of accelerator performance during the operation in 2019., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

RHIC operated in fixed target mode at beam energies 4.59, 7.3, and 31.2 GeV/nucleon in 2019 as a part of the Beam Energy Scan II program. To scrape beam halo effectively at the fixed target which is 2.05 m away from the center of the STAR detectors, lattice design with relative large beta function at STAR was implemented at the two lower energies. The kickers of the base-band tune (BBQ) measurement system were engaged to dilute the beam transversely to maintain the event rate except for 31.2 GeV/nucleon. In addition, beam orbit control, tune and chromaticity adjustments were used to level the event rate. This paper will review the operational experience of RHIC in fixed target mode at various energies., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

The low energy RHIC Electron Cooler (LEReC) will be operating with 1.6-2.6 MeV electron beams having up to 140 kW power. It was determined that under the worst case scenario the missteered electron beam can damage the vacuum chamber and in-vacuum components within 40 us. Hence, the LEReC requires a dedicated fast machine protection system (MPS). The LEReC MPS has been designed and built and currently is under commissioning. In this paper we describe the most recent developments with the LEReC MPS., Proceedings of the 7\textsuperscript{th} Int. Beam Instrumentation Conf., IBIC2018, Shanghai, China

In this talk we are presenting the most recent results from the commissioning of unique Coherent Electron Cooling system, which is using an FEL amplifier to facilitate cooling of hadrons by an electron beam. We present achieved results as well as changes we encountered in the process., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

The Linac of Low Energy RHIC electron Cooler (LEReC) is designed to deliver a 1.6 MeV to 2.6 MeV electron beam, with peak-to-peak dp/p less than 7·10⁻⁴. The booster cavity is the major accelerating component in LEReC, which is a 0.4 cell cavity operating at 2 K, with a maximum energy gain of 2.2 MeV. It is modified from the Energy Recovery Linac (ERL) photocathode gun, with fundamental power coupler, pickup coupler and HOM coupler close to each other. Crosstalk effect in this cavity is simulated and measured. Correction method is proposed to meet the energy spread requirement., Proceedings of the 29\textsuperscript{th} Linear Accelerator Conf., LINAC2018, Beijing, China

The Rapid Cycling Synchrotron (RCS) for the eRHIC Ring-Ring design will provide on energy injection (up to 18 GeV) of high charge, polarized electron bunches to the eRHIC electron storage ring. The RF system comprises a large number of 563MHz fundamental cavities, providing up to 45MV per turn. The cavities will operate in pulsed mode with, Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The electron-ion collider eRHIC aims at a luminosity around 10³⁴cm⁻²sec⁻¹, using strong cooling of the hadron beam. Since the required cooling techniques are not yet readily available, an initial version with a peak luminosity of 3*10³³cm⁻²sec⁻¹ is being developed that can later be outfitted with strong hadron cooling. We will report on the current design status and the envisioned path towards 10³⁴cm⁻²sec⁻¹ luminosity., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

704 MHz deflecting cavity was designed for the Low Energy RHIC electron Cooling (LEReC) project. The cavity will serve as a major component in diagnostic line. In LEReC project the requirement on the energy spread of the electron beam is extremely high (better than 10⁻⁴) and the diagnostic system has to to be designed accordingly. The 704 MHz transverse deflecting cavity provides the vertical kick to the beam after it passes through the dispersion dipole so that we can measure the energy spread of the core of the bunch. Traditional way of determining the electrical center of the cavity involves the needle pulling and integration of the signal which is prone to the cumulative error. We present the measurement result from a wire stretching system that is much more efficient and accurate compared to the bead/needle pulling method. Both simulation and experimental results are shown in this paper and the potential in further application is discussed at the end., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

We have refined the design for the Rapid Cycling Synchrotron (RCS) polarized electron injector for eRHIC. The newer design includes bypasses for the eRHIC detectors and definition of the lattice layout in the existing RHIC tunnel. Additionally, we provide more details on the RF, alignment and orbit control, and magnet specifications., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The coherent electron cooling proof-of-principle experiment is aimed to demonstrate new technique suitable for cooling of the high energy protons and is essential for a future electron-hadron collider. In this paper we present the current status of the equipment, achieved beam parameters, and progress of the experiment. Future plans are also discussed., Proceedings of the 11th Workshop on Beam Cooling and Related Topics, COOL2017, Bonn, Germany

A 5-cell 650 MHz SRF cavity was designed for eRHIC SRF linac. One Cu cavity was fabricated for HOM damping study, and one Nb cavity was fabricated for SRF studies. Through various post-processing recipes and vertical tests, the SRF study includes high Q-value study for ERL SRF linac and high gradient study for recirculating linac. This paper reports the HOM damping measurement on the Cu cavity and preliminary vertical test results., Proceedings of the 29\textsuperscript{th} Linear Accelerator Conf., LINAC2018, Beijing, China

To improve RHIC luminosity for heavy ion beam energies below 10 GeV/nucleon, the Low Energy RHIC electron Cooler (LEReC) is designed, and is currently under commissioning at BNL. The linac of LEReC consists of a DC photoemission gun, a 704 MHz superconducting radio frequency (SRF) booster cavity, a three-cell 2.1 GHz third harmonic cavity for RF curvature correction, a single-cell 704 MHz cavity for energy de-chirping and a 704 MHz deflecting cavity for diagnostic line. In this paper, we present the commissioning of three normal conducting cavities mentioned above., Proceedings of the 29\textsuperscript{th} Linear Accelerator Conf., LINAC2018, Beijing, China

To increase the real estate gradient in the eRHIC electron accelerator waveguide HOM couplers are being considered. These significantly reduce the length of individual cavities and address inter-cavity trapped modes, allowing for an increased number of cavities per cryomodule, which would increase the real estate gradient. The choice of waveguide went to a dual ridge waveguide due to a smaller size compared to rectangular waveguides. The waveguide termination, to convert the RF energy into thermal energy, is a custom designed load based on a silicon carbide dielectric that is already being used in beamline absorbers. Simulations of the RF properties of the load are presented as well as first measurements on a prototype., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

ERL-Ring eRHIC aims to build a new high current (50 mA), multi-pass (6 passes) ERL to provide 3-18 GeV electron beams to collide with proton beams from existing RHIC. One critical challenge for eRHIC is to damp HOMs. The average HOM power is up to 8 kW per cavity, and it will get worse when the electron beam spectrum overlaps with cavity HOM spectrum. A novel HOM damping scheme by employing ridge waveguides has been worked out at BNL, which is able to well damp both longitudinal and transversal modes. This paper will describe the design of the HOM damping scheme, including RF design, HOM damping results, progress of prototyping., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

In the design of eRHIC at BNL, HOM power plays a major role for the SRF installation. Depending on the final accelerator design and choice of cavity, up to 100kW of HOM power is estimated to be generated, presenting a big challenge for the HOM damping concept. Due to this high amount of HOM power, all current concepts for eRHIC would use room temperature beam line absorbers equipped with silicone-carbide dielectrics to absorb HOM power. Concepts, designs and simulations for these beam line absorbers will be presented., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

The FY18 RHIC physics program calls for Ru-Ru and Zr-Zr collisions at 100GeV using isobaric Ruthenium and Zirconium ions, each having 96 nucleons. In the injector chain, these two ions have to come from tandem and EBIS source, respectively. To reduce systematic errors in the detector, the luminosity between the two species combinations is matched as closely as possible, and the species are switched frequently. Several bunch merges are needed in the Booster and AGS to reach the desired bunch intensity for RHIC. The setup and performance of Booster and AGS with these ions are reviewed., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

One important component for LEReC project is a 704 MHz booster cavity, which was modified from the BNL ERL 704 MHz SRF gun cavity. The major modifications include converting the upstream cathode transportation to a proper beam pipe, adding a HOM coaxial line HOM damper to the downstream, retracting FPC insertions, and improvement of cryomodule layout. In the past one and half year, tremendous work was completed: the cavity was modified and tested vertically, FPC were conditioned, and HOM damper were designed and conditioned, cryomodule was re-assembled. The booster cavity cryomodule was successfully commissioned in mid October, and it was moved to LEReC location at RHIC tunnel 2 O'clock early November. This paper will report the configuration of the new cryomodule and its commissioning results., Proceedings of the 29\textsuperscript{th} Linear Accelerator Conf., LINAC2018, Beijing, China

A 15 MeV CW SRF accelerator had been commissioned at Brookhaven National Laboratory to test the coherent electron cooling concept. The accelerator consists of an SRF 113-MHz photoemission gun, two 500 MHz bunching cavities and a 704-MHz 5-cell SRF linac. In this paper we describe our experience with this system with focus on unusual phenomena, such as multipacting in the SRF gun. We also discuss issues of wakefields in the CeC accelerator., Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA

eRHIC ERL SRF requires 160 5-cell 650 MHz SRF cavities. The 650 MHz cavity has been designed and two prototypes have been fabricated, one Cu cavity for HOM study and one Nb cavity for cavity performance study. This paper will describe cavity design and the progress of prototyping., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

This report gives a detail design of a 1.3 GHz input coupler for second harmonic cavity for eRHIC project. This coupler is designed to transmit 200KW CW RF to the cavity to compensate the synchrotron radiation loss. This report include RF and thermal simulation for this design., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The eRHIC project will be a electron and proton collider proposed in BNL. These high repetition rates will require Super-Conducting Radio-Frequency cavities with fundamental frequency of 650MHZ for high current applications. Each with a string of two of those cavities. The strong electromagnetic fields in the SRF cavities will extract electrons from the cavity walls and will accelerate those. Most dark current will be deposited locally, although some electrons may reach several neighbour cyromodules, thereby gaining substantial energy before they hit a collimator or other aperture. Simulation of these effects is therefore crucial for the design of the machine. Track3P code was used to simulate field-emission electrons from different SRF cavities setup to optimize the field emission dark current characterizes., Proceedings of the North American Particle Accelerator Conf., NAPAC2016, Chicago, IL, USA

Coherent electron cooling is new cooling technique to be tested at BNL. Presently we are in the commissioning stage of the accelerator system. In this paper we present status of various systems and achieved beam parameters as well as operational experience. Near term future plans are also discussed., Proceedings of the North American Particle Accelerator Conf., NAPAC2016, Chicago, IL, USA

The Coherent Electron Cooling Proof-of-Principle (CeC PoP) experiment employs a high-gradient CW photo-injector based on the superconducting RF cavity. Such guns operating at high accelerating gradients promise to revolutionize many sciences and applications. They can establish the basis for super-bright monochromatic X-ray and gamma ray sources, high luminosity hadron colliders, nuclear waste transmutation or a new generation of microchip production. In this paper we report on our operation of a superconducting RF electron gun with a high accelerating gradient at the CsK2Sb photo-cathode (i.e. ~ 20 MV/m) generating a record-high bunch charge (above 4 nC). We give short description of the system and then detail our experimental results., Proceedings of the North American Particle Accelerator Conf., NAPAC2016, Chicago, IL, USA

BNL R&D ERL beam commissioning started in June 2014 [*]. The key components of R&D ERL are the highly damped 5-cell 704 MHz superconducting RF cavity and the high-current superconducting RF gun. The gun is equipped with a multi-alkaline photocathode insertion system. The first photocurrent from ERL SRF gun has been observed in November 2014. In June 2015 a high charge 0.5nC and 20 uA average current were demonstrated. In July 2015 gun to dump beam test started. The beam was successfully transported from the SRF gun through the injection system, then through the linac to the beam dump. All ERL components have been installed. In October 2015, SRF gun cavity has been found contaminated during severe cathode stalk RF conditioning. This cavity has been sent for repair and modification for later use in low-energy RHIC electron cooler (LEReC)[**]. LEReC scheduled to start commissioning in early of 2018. We present our results of BNL ERL beam commissioning, the measured beam properties, the operational status, and future prospects., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA