BNL, Upton, Long Island, New York, USA
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
Laser acceleration of ion beams is normally realized via irradiating thin-foil targets with near-IR solid-state lasers with up to petawatt (PW) peak power. Despite demonstration of significant achievements, further progress towards practical application of such beam sources is hindered by the challenges inherent in constructing still more intense and higher-contrast lasers. Our recent studies of the radiation pressure acceleration indicate that the combination of a 10-μm CO2 laser with a gas jet target offers a unique opportunity for a breakthrough in the field. Strong power scaling of this regime holds the promise of achieving the hundreds of MeV proton beams with just sub-PW CO2 laser pulses. Generation of such pulses is a challenging task. We discuss a strategy of the CO2 laser upgrade aimed to providing a more compact and economical hadron source for cancer therapy. This include optimization of the method of the 10μm short-pulse generation, higher amplification in the CO2 gas under combined isotopic and power broadening effects, and the pulse shortening to a few laser cycles (150-200 fs) via self-chirping in the laser-produced plasma and the consecutive dispersive compression.
PKU/IHIP, Beijing, People's Republic of China
BNL, Upton, Long Island, New York, USA
Stony Brook University, Stony Brook, USA
Two years ago, we obtained an emission gain of 40 from the Diamond Amplifier Cathode (DAC) in our test system. In our current systematic study of hydrogenation, the highest gain we registered in emission scanning was 178. We proved that our treatments for improving the diamond amplifiers are reproducible. Upcoming tests planned include testing DAC in a RF cavity. Already, we have designed a system for these tests using our 112 MHz superconducting cavity, wherein we will measure DAC parameters, such as the limit, if any, on emission current density, the bunch charge, and the bunch length.
AES, Princeton, New Jersey, USA
BNL, Upton, Long Island, New York, USA
A polarized SRF photocathode gun is being considered as a high-brightness electron injector for the International Linear Collider (ILC). The conceptual engineering analysis and design of this injector, which is required to deliver a large emittance ratio, is presented. The delivered beam parameters we predict are compared to the required performance after the ILC damping ring. The analysis indicates that it may be possible to save cost by eliminating the damping ring though higher values of the emittance ratio are still to be demonstrated.
BNL, Upton, Long Island, New York, USA
AES, Medford, NY, USA
RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode’s surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1⁄2 cell SRF gun, the vacuum can be maintained at nearly 10-12 Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun.
BNL, Upton, Long Island, New York, USA
FRIB, East Lansing, Michigan, USA
MIT, Middleton, Massachusetts, USA
We present the design of future high-energy high-luminosity electron-hadron collider at RHIC called eRHIC. We plan on adding 20 (potentially 30) GeV energy recovery linacs to accelerate and to collide polarized and unpolarized electrons with hadrons in RHIC. The center-of-mass energy of eRHIC will range from 30 to 200 GeV. The luminosity exceeding 1034 cm-2 s-1 can be achieved in eRHIC using the low-beta interaction region with a 10 mrad crab crossing. We report on the progress of important eRHIC R&D such as the high-current polarized electron source, the coherent electron cooling and the compact magnets for recirculating passes. A natural staging scenario of step-by-step increases of the electron beam energy by builiding-up of eRHIC's SRF linacs and a potential of adding polarized positrons are also presented.
BNL, Upton, Long Island, New York, USA
Niowave, Inc., Lansing, Michigan, USA
Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Niowave is supported by the U.S. DOE under SBIR contract No. DE-FG02-07ER84861
BNL, Upton, Long Island, New York, USA
A 56 MHz Superconducting RF Cavity operating at 4.4K is being constructed for the RHIC collider. This cavity is a quarter wave resonator with beam transmission along the centreline. This cavity will increase collision luminosity by providing a large longitudinal bucket for stored bunches of RHIC ion beam. The major components of this assembly are the niobium cavity with the mechanical tuner, its titanium helium vessel and vacuum cryostat, the support system, and the ports for HOM and fundamental dampers. The cavity and its helium vessel must meet the ASME pressure vessel code and it must not be sensitive to frequency shift due to pressure fluctuations from the helium supply system. Frequency tuning achieved by a two stage mechanical tuner is required to meet performance parameters. This tuner mechanism pushes and pulls the tuning plate in the gap of niobium cavity. The tuner mechanism has two separate drive systems to provide both coarse and fine tuning capabilities. This paper discusses the design detail and how the design requirements are met.
BNL, Upton, Long Island, New York, USA
JLAB, Newport News, Virginia, USA
AES, Medford, NY, USA
The Brookhaven National Laboratory (BNL) 5-cell, 703 MHz superconducting RF accelerating cavity has been installed in the high-current energy recovery linac (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 1010. Here we will present its performance in the horizontal tests, and discuss technical issues involved in its implementation in the ERL.
BNL, Upton, Long Island, New York, USA
A fundamental power coupler (FPC) is designed to obtain the ability of fast tuning the 56MHz SRF cavity in RHIC. The FPC will be inserted from one of the chemical cleaning ports at the rear end of the cavity with magnetic coupling to the RF field. The size and the location of the FPC are decided based on the required operational external Q of the cavity. The FPC is designed with variable coupling that would cover a range of power levels, and it is thermally isolated from the base temperature of the cavity, which is 4.2K. A 1kW power amplifier will also be used to close an amplitude control feedback loop. In this paper, we discuss the coupling factor of the FPC with the carefully chosen design, as well as the thermal issues.
BNL, Upton, Long Island, New York, USA
At each injection and extraction period of RHIC operation, the beam frequency will be sweeping across a wide range, and some of the harmonics will cross the frequency of the 56MHz SRF cavity. To avoid cavity excitation during these periods, a fundamental damper was designed for the quarter-wave resonator to heavily detune the cavity. The power extracted by the fundamental damper should be compliant with the cooling ability of the system at all stages. In this paper, we discussed the power output from the fundamental damper when it is fully extracted, inserted, and during its movement.
BNL, Upton, Long Island, New York, USA
AES, Medford, NY, USA
The 703 MHz superconducting gun for BNL ERL prototype was tested at JLab with and without choke-joint and cathode stalk. Without choke-joint and cathode stalk, the gradient reached 25MV/m with Q0~6·109. The gun cathode insertion port is equipped with a choke joint with triangular grooves for multipacting suppression. We carried out tests with choke-joint and cathode stalk. The test results show that there are at least two barriers at about 5MV/m and 3.5 MV/m. We considered several possibilities and finally found that the limitation was because the triangular grooves were rounded after BCP, which caused strong multipacting in the choke-joint. This paper presents the primary test result of test results of the gun and discusses the multipacting analysis in the choke-joint. It also suggests possible solutions for the gun and multipacting suppressing for a similar structure.
BNL, Upton, Long Island, New York, USA
Damping higher order modes (HOMs) significantly to avoid beam instability is a challenge for the high current Energy Recovery Linac-based eRHIC at BNL. To avoid the overheating effect and high tuning sensitivity, current, a new band-stop HOM coupler is being designed at BNL. The new HOM coupler has a bandwidth of tens of MHz to reject the fundamental mode, which will avoid overheating due to fundamental frequency shifting because of cooling down. In addition, the S21 parameter of the band-pass filter is nearly flat from first higher order mode to 5 times the fundamental frequency. The simulation results showed that the new couplers effectively damp HOMs for the eRHIC cavity with enlarged beam tube diameter and two 120° HOM couplers at each side of cavity. This paper presents the design of HOM coupler, HOM damping capacity for eRHIC cavity and prototype test results.
BNL, Upton, Long Island, New York, USA
AES, Medford, NY, USA
The 703MHz superconducting gun will have 2 fundamental power couplers (FPCs). Each FPC will deliver up to 500kW of RF power. In order to prepare the couplers for high power RF service and process multipacting, the FPCs should be conditioned before they are installed in the gun. A conditioning cart based test stand, which includes a vacuum pumping system, controllable bake-out system, diagnostics, interlocks and data log system has been designed, constructed and commissioned by collaboration of BNL and AES. This paper presents FPC conditioning cart systems and summarizes the conditioning process and results.
BNL, Upton, Long Island, New York, USA
PKU/IHIP, Beijing, People's Republic of China
Stony Brook University, Stony Brook, USA
BNL, Upton, Long Island, New York, USA
AES, Medford, NY, USA
An innovative feature of the proposed Energy Recovery Linac (ERL) at Brookhaven National Laboratory (BNL) is the use of a solenoid made with High Temperature Superconductor (HTS) with the Superconducting RF cavity. The use of HTS in the solenoid offers many advantages. The solenoid is located in the transition region (4 K to room temperature) where the temperature is too high for a conventional low temperature superconductor and the heat load on the cryogenic system too high for copper coils. Proximity to the cavity provides early focusing and thus a reduction in the emittance of the electron beam. In addition, taking full advantage of the high critical temperature of HTS, the solenoid has been designed to reach the required field at ~77 K, which can be obtained with liquid nitrogen. This significantly reduces the cost of testing and allows a variety of critical pre‐tests (e.g. measurements of the axial and fringe fields) which would have been very expensive at 4 K in liquid helium because of the additional requirements for a cryostat and associated facilities. This paper will present the design, construction, test results and current status of this HTS solenoid.
BNL, Upton, Long Island, New York, USA
A vertical facility has been constructed to test SRF cavities and can be utilized for other use. The liquid helium volume for the large vertical dewar is approximate 84 inches tall by 40 inches diameter with a working clear inner diameter of 38 inch with the inner cold magnetic shield system installed. For radiation enclosure, the test dewar is situated inside a concrete block structure. The structure is above ground and is accessible from the top, and has a retractable concrete roof. A second radiation concrete facility, with ground level access via a labyrinth is also available for testing of smaller cavities in 2 smaller dewars.
AES, Medford, NY, USA
BNL, Upton, Long Island, New York, USA
JLAB, Newport News, Virginia, USA
Tech-X, Boulder, Colorado, USA
BNL, Upton, Long Island, New York, USA
Emission of electrons from a diamond-amplified cathode was recently demonstrated*. This experiment was based on a promising new concept** for generation of high-current, high-brightness, and low thermal emittance electron beams. The measurements from transmission and emission experiments have shown the potential to realize the diamond-amplified cathode concept. However, the results indicate that the involved physical properties should be understood in greater detail to build diamond cathodes with optical properties. We have already made progress in understanding the secondary electron generation and charge transport in diamond with the models we implemented in the VORPAL computational framework. We have been implementing models for electron emission from diamond and will present results from 3D VORPAL simulations with the integrated capabilities on generating electrons and holes, initiated by energetic primary electrons, propagation of the charge clouds, and then the emission of electrons into diamond. We will discuss simulation results on the dependence of the electron emission on diamond surface properties.
* X. Chang et al., Electron Beam Emission from a Diamond-Amplified Cathodes, to appear in Phys. Rev. Lett. (2010).
** I. Ben-Zvi et al., Secondary emission enhanced photoinjector, Rep. C-A/AP/149, BNL (2004).
Tech-X, Boulder, Colorado, USA
BNL, Upton, Long Island, New York, USA
Stony Brook University, Stony Brook, USA
Beamlines at new light sources, such as the National Synchrotron Light Source II will operate at flux levels beyond the saturation level of existing diagnostics, necessitating the development of new devices. Currently, there is no detector which can span the entire flux range that is possible even in a second generation light source and will become crucial for next generation light sources. One new approach* is a diamond-based detector that will be able to monitor beam position, flux and timing to much better resolution. Furthermore, this detector also has linear response to flux over 11 orders of magnitude. However, the successful development of the detector requires thorough understanding and optimization of the physical processes involved. We will discuss the new modeling capabilities we have been implementing in the VORPAL 3D code to investigate the effects of charge generation due to absorption of x-ray photons, transport, and charge trapping. We will report results from VORPAL simulations on charge collection and how it depends on applied field, charge trapping, and the energy of absorbed photons.
*J. W. Keister, J. Smedley, D. A. Dimitrov, and R. Busby, Charge Collection and Propagation in Diamond X-ray Detectors, IEEE Transactions on Nuclear Science, 57, 2400 (2010).
BNL, Upton, Long Island, New York, USA
PKU/IHIP, Beijing, People's Republic of China
Stony Brook University, Stony Brook, USA
The future electron-ion collider eRHIC requires a high average current (~50 mA), short bunch (~3 mm), low emittance (~20 μm) polarized electron source. The maximum average current of a polarized electron source so far is more than 1 mA, but much less than 50 mA, from a GaAs:Cs cathode [1]. One possible approach to overcome the average current limit and to achieve the required 50 mA beam for eRHIC, is to combine beamlets from multiple cathodes to one beam. In this paper, we present the feasibility studies of this technique.
BNL, Upton, Long Island, New York, USA
Tech-X, Boulder, Colorado, USA
JLAB, Newport News, Virginia, USA
Coherent electron cooling (CEC) has a potential to significantly boost luminosity of high-energy, high-intensity hadron-hadron and electron-hadron colliders*. In a CEC system, a hadron beam interacts with a cooling electron beam. A perturbation of the electron density caused by ions is amplified and fed back to the ions to reduce the energy spread and the emittance of the ion beam. To demonstrate the feasibility of CEC we propose a proof-of-principle experiment at RHIC using one of JLab’s SRF cryo-modules. In this paper, we describe the experimental setup for CeC installed into one of RHIC's interaction regions. We present results of analytical estimates and results of initial simulations of cooling a gold-ion beam at 40 GeV/u energy via CeC.
* Vladimir N. Litvinenko, Yaroslav S. Derbenev, Physical Review Letters 102, 114801
BNL, Upton, Long Island, New York, USA
BNL, Upton, Long Island, New York, USA
* V.N. Litvinenko, I. Ben-Zvi, Proceedings of FEL'2004, http://jacow.org/f04/papers/WEBOS04/
PKU/IHIP, Beijing, People's Republic of China
BNL, Upton, Long Island, New York, USA
CST of America, Wellesley Hills, Massachusetts, USA
We characterized a BNL 1.3GHz half-cell SRF gun is tested for GaAs photocathode. The gun already was simulated several years ago via two-dimensional (2D) numerical codes (i.e., Superfish and Parmela) with and without the beam. In this paper, we discuss our investigation of its characteristics using a three dimensional (3D) full-wave code (CST STUDIO SUITE™).The input/pickup couplers are sited symmetrically on the same side of the gun at an angle of 180⁰. In particular, the inner conductor of the pickup coupler is considerably shorter than that of the input coupler. We evaluated the cross-talk between the beam (trajectory) and the signal on the input coupler compared our findings with published results based on analytical models. The CST STUDIO SUITE™ also was used to predict the field within the cavity; particularly, a combination of transient/eigenmode solvers was employed to accurately construct the RF field for the particles, which also includes the effects of the couplers. Finally, we explored the beam’s dynamics with a particle in cell (PIC) simulation, validated the results and compare them with 2D code result.
BNL, Upton, Long Island, New York, USA
Fermilab, Batavia, USA
Electron cooling was proposed to increase the luminosity of RHIC operation for heavy ion beam energies below 10 GeV/nucleon. The electron cooling system needed should be able to deliver an electron beam of adequate quality in a wide range of electron beam energies (0.9-5 MeV). An option of using an electrostatic accelerator for cooling heavy ions in RHIC was studied in detail. In this paper, we describe the requirements and options to be considered in the design of such a cooler for RHIC, as well as the associated challenges. The expected luminosity improvement and limitations with such electron cooling system are also discussed.
BNL, Upton, Long Island, New York, USA
In order to meet the requirements of high average current accelerators, such as the Superconducting Proton Linac (SPL) at CERN and the electron–ion collider (eRHIC) at BNL, a high current 5-cell SRF cavity, called BNL3 cavity, was designed. The optimization process aimed at maximizing the R/Q of the fundamental mode and the geometry factor G under an acceptable RF field level of Bpeak/Eacc or Epeak/Eacc. In addition, a pivotal consideration for the high current accelerators is efficient damping of dangerous higher-order modes (HOM) to avoid inducing emittance degradation, cryogenic loading or beam-breakup (BBU). To transport the HOMs out of the cavity, the BNL3 cavity employs a larger beam pipe, allowing the propagation of HOMs but not the fundamental mode. Moreover, concerning the BBU effect, the BNL3 cavity is aimed at low (R/Q)Qext for dangerous modes, including dipole modes and quadrupole modes. This paper presents the design of the BNL3 cavity, including the optimization for the fundamental mode, and the BBU limitation for dipole and quadrupole modes. The BBU simulation results show that the designed cavity is qualified for high-current, multi-pass machines such as eRHIC.
AES, Medford, NY, USA
Stony Brook University, Stony Brook, USA
BNL, Upton, Long Island, New York, USA
Advanced Energy Systems, Inc. is under contract to Stony Brook University to design and build a 704 MHz, high current, Superconducting RF (SRF) five cell cavity to be tested at Brookhaven National Laboratory. This cavity is being designed to the requirements of the SPL at CERN while also considering operation with electrons for a potential RHIC upgrade at Brookhaven. The β=1 cavity shape, developed by Brookhaven, is designed to accelerate 40 mA of protons at an accelerating field of 25 MV/m with a Q0 > 8·109 at 2K while providing excellent HOM damping for potential electron applications. 10-CFR-851 states that all pressurized vessels on DOE sites must conform to applicable national consensus codes or, if they do not apply, provide an equivalent level of safety and protection. This paper presents how the 2007 ASME Boiler and Pressure Vessel Code Section VIII, Division 2 requirements can be used to satisfy the DOE pressure safety requirements for a non-code specified material (niobium) pressure vessel.