Continuous-wave photoinjectors operating at high accelerating gradients promise to revolutionize many areas of science and applications. They can establish the basis for a new generation of monochromatic x-ray free electron lasers, high-brightness hadron beams, or a new generation of microchip production. In this Letter we report on the record-performing superconducting rf electron gun with CsK_{2}Sb photocathode. The gun is generating high charge electron bunches (up to 10  nC/bunch) and low transverse emittances, while operating for months with a single photocathode. This achievement opens a new era in generating high-power beams with a very high average brightness.

The BNL CA-D controls environment has recently been adopting modern programming languages such as Python. A new framework has been created to instantiate setting and measurement parameters in Python as an alternative to C++ and Java process-variable-like objects. With the help of automated testing tools such as pyTest and Coverage, a test suite is generated and executed before the release of Python-based accelerator device objects (ADO) to assure quality as well as compatibility. This suite allows developers to add custom tests, repeat failed tests, create random inputs, and log failures.

The Low Energy RHIC electron Cooling (LEReC) project at Brookhaven National Laboratory recently demonstrated for the first time cooling of hadron bunches with radio-frequency (rf) accelerated electron bunches. LEReC uses a high-voltage photoemission electron gun with stringent requirements for beam current, beam quality, and stability. The electron gun has a photocathode with a high-power fiber laser, and a novel cathode production, transport, and exchange system. It has been demonstrated that the high-voltage photoemission gun can continually produce a high-current electron beam with a beam quality suitable for electron cooling. We describe the operational experience with the LEReC dc photoemission gun in RHIC and discuss the important aspects needed to achieve the required beam current, beam quality, and stability.

A high-current high-brightness electron accelerator for low-energy RHIC electron cooling (LEReC) was successfully commissioned at Brookhaven National Laboratory. The LEReC accelerator includes a dc photoemission gun, a laser system, a photocathode delivery system, magnets, beam diagnostics, a superconducting rf booster cavity, and a set of normal conducting rf cavities to provide enough flexibility to tune the beam in the longitudinal phase space. Cooling with nonmagnetized rf accelerated electron beams requires longitudinal corrections to obtain a small momentum spread while preserving the transverse emittances. Electron beams with kinetic energies of 1.6 and 2.0 MeV with a beam quality suitable for cooling were successfully propagated through 100 m of beam lines, including dispersion sections, maintained through both cooling sections in RHIC and used for cooling ions in both RHIC rings simultaneously. The beam quality suitable for cooling RHIC beams was achieved in 2018, which led to the first experimental demonstration of bunched beam electron cooling of hadron beams in 2019.

Cooling of beams of gold ions using electron bunches accelerated with radio-frequency systems was recently experimentally demonstrated in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. Such an approach is new and opens the possibility of using this technique at higher energies than possible with electrostatic acceleration of electron beams. The challenges of this approach include generation of electron beams suitable for cooling, delivery of electron bunches of the required quality to the cooling sections without degradation of beam angular divergence and energy spread, achieving the required small angles between electron and ion trajectories in the cooling sections, precise velocity matching between the two beams, high-current operation of the electron accelerator, as well as several physics effects related to bunched-beam cooling. Here we report on the first demonstration of cooling hadron beams using this new approach.

CW photoinjectors operating at high accelerating gradients promise to revolutionize many areas of science and applications. They can establish the basis for a new generation of monochromatic X-ray free electron lasers, high brightness hadron beams, or a new generation of microchip production. In this letter we report on the record-performing superconducting RF electron gun with $\textrm{CsK}_{2}\textrm{Sb}$ photocathode. The gun is generating high charge electron bunches (up to 10 nC/bunch) and low transverse emittances, while operating for months with a single photocathode. This achievement opens a new era in generating high-power beams with a very high average brightness.

The fast extraction kicker system at AGS to RHIC transport line uses Stanford Research DG535 delay generators to time, synchronize, and trigger charging power supplies and high-level thyratron trigger pulse generators. This timing system has been upgraded to use an SRS DG645 instrument due to reliability issues with the aforementioned model and slow response time of GPIB buses. The new model provides the relative timing of the separate kicker modules of the assembly from a synchronized external trigger with the RF system. Specifications of the timing scheme, an algorithm to load settings synchronized with RHIC real-time events, and performance analysis of the software will be presented in the paper.

The Low Energy RHIC electron Cooler (LEReC) was recently commissioned at BNL. The LEReC is the first electron cooler based on 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 the required small angles between electrons and ions in the cooling sections, precise velocity 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 the cooling process. Here we report on the first demonstration of Au ion cooling in RHIC using this new approach.

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 must come from Tandem and EBIS source, respectively. To reduce systematic errors in the detector, the luminosity for the two species 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 injector chain with these ions are reviewed.

Non-magnetized bunched electron cooling of low energy RHIC requires electron beam energy in range of 1.6-2.6 MeV, with average current up to 45 mA, very small energy spread, and low emittance [1]. A 400 kV DC gun equipped with photocathode and laser delivery system will serve as a source of high quality electron beam. Acceleration will be achieved by an SRF 704 MHz booster cavity and other RF components that are scheduled to be operational in early 2018. The DC gun testing in its installed location in RHIC will start in early 2017. During this stage we plan to test the critical equipment in close to operation conditions: laser beam delivery system, cathode QE lifetime, DC gun, beam instrumentation, high power beam dump system, and controls. In this paper we describe the gun test set up, major components, and parameters to be achieved and measured during the gun beam test.

are in doubt. This level also provides for the smooth transition back and forth between high power operation and the benign diagnostic pilot bunch operation. The pilot bunch parameters in the main linac are estimated on the basis of the expected stress in the accelerator structure copper. Beam tests have been done at the SLAC linac to examine the behavior of the copper at the damage stress threshold. Typical pilot beam parameters (compared with nominal) are: 10 times reduced intensity, 10 times increased horizontal emittance and 1000 times increased vertical emittance, resulting in a reduction in charge density of 10{sup 5}. The second level is the primary protection against a single aberrant pulse. Its goal is to reduce the possibility that a substantial transverse field changes the trajectory of the high power beam from one pulse to the next. All devices that could produce such a field are (1) monitored by a fast response network and where possible have (2) deliberately slowed response times. A ''maximum allowable interpulse difference'' is evaluated for each such device as well as the beam trajectory monitors in each interpulse period.

A beam energy scan of deuteron-gold collision, with center-of-mass energy at 19.6, 39, 62.4 and 200.7 GeV/n, was performed at the Relativistic Heavy Ion Collider in 2016 to study the threshold for quark-gluon plasma (QGP) production. The lattice, RF, stochastic cooling and other subsystems were in different configurations for the various energies. The operational challenges changed with every new energy. The operational experience at each energy, the operation performance, highlights and lessons of the beam energy scan are reviewed in this report.

A half-cell superconducting rf electron gun is designed to provide 0.5 A, 2 MeV beam for the Brookhaven National Laboratory R&D Energy Recovery Linac. Total rf power of 1 MW must be delivered to beam to meet the beam current and energy specifications, resulting in very strong coupling. Two opposing fundamental power couplers (FPCs) are employed to minimize the transverse kick to beam traversing the structure and to halve the power through the coupler. A single-window coaxial coupler has been designed to meet the average power and rf coupling requirements. The coupler features a planar beryllia rf window for better handling high thermal stresses and a "pringle"-shaped tip of the antenna for enhancing rf coupling. Two FPCs have been fabricated and tested in preparation for the gun cryomodule assembly. A room-temperature test stand was used for conditioning couplers in full reflection regime with variable phase of the reflecting wave. The couplers were tested up to 250 kW in pulse mode and 125 kW in cw mode at different settings of the reflecting wave phase to expose all rf surfaces along the couplers to high fields. Several multipacting barriers were encountered and successfully processed away. The rf power levels, at which multipacting was found, match well those found in computer simulations.

The BNL 5-cell, 703 MHz superconducting accelerating cavity has been installed in the high-current ERL experiment. This experiment will function as a proving ground for the development of high-current machines in general and is particularly targeted at beam development for an electron-ion collider (eRHIC). The cavity performed well in vertical tests, demonstrating gradients of 20 MV/m and a Q0 of 1e10. Here we will present its performance in the horizontal tests, and discuss technical issues involved in its implementation in the ERL.

This paper examines the equipment and software from which the controls system interface for the Energy Recovery Linac (ERL) will be implemented at the Brookhaven National Laboratory.1 Magnet/Power Supplies (electron beam steering and focusing) Steering and focusing of the electron beam will be performed using magnets and power supplies that are controlled through several different DC power supply interfaces, each supporting 16 bit sampling of setpoints and readbacks and monitoring of power supply statuses.

Brookhaven's AGS Booster has been modified to deliver slow extracted beam to a new beam line, the NASA Space Radiation Laboratory (NSRL). This facility was constructed in collaboration with NASA for the purpose of performing radiation effect studies for the NASA space program. The design of the resonant extraction system has been described. A more detailed description, which includes predictions of the slow extracted beam time structure has been described. In this report we present results of the system commissioning and performance.