BNL, Upton, Long Island, New York
In this paper, we analyzed the linac optics design requirement for a multi-pass energy recovery linac (ERL) with one or more linacs. A set of general formula of constrains for the 2-D transverse matrix is derived to ensure design optics acceptance matching throughout the entire accelerating and decelerating process. Meanwhile, the rest free parameters can be adjusted for fulfilling other requirements or optimization purpose. As an example, we design the linac optics for the future MeRHIC (Medium Energy eRHIC) project and the optimization for enlarging the BBU threshold.
BNL, Upton, Long Island, New York
AES, Medford, NY
PKU/IHIP, Beijing
RF electron guns with strained super lattice GaAs cathodes can produce higher brightness and lower emittance polarized electron beams, due to the higher field gradient at the cathode surface compared with DC guns. The vacuum in the gun must be better than 10-11 torr to obtain a sufficient cathode life time with high quantum efficiency (QE). Such high vacuum cannot be obtained easily in a normal conducting RF gun. We report on an experiment with a superconducting RF (SRF) gun, which can maintain a vacuum of nearly 10-12 torr because of cryo-pumping at the temperature of 4.2K . The GaAs cathode was activated by Cs'O treatment with a QE of 3% and exhibits a long lifetime in a preparation chamber. This cathode will be used in a 1.3 GHz - cell SRF gun to measure the destruction of the QE by ion and electron back-bombardment.
BNL, Upton, Long Island, New York
AES, Medford, NY
PKU/IHIP, Beijing
Superconducting RF (SRF) electron guns deliver higher brightness beams than DC guns because the field gradient at the cathode is higher. SRF guns with metal cathodes have been successfully tested. For the production of polarized electrons a Gallium-Arsenide (GaAs) cathode must be used, and an experiment to test this type of cathode is under way at BNL. Since the cathode will be normal conducting, the primary concern is cathode-driven heat load. We present measurements of the electric resistance of GaAs at cryogenic temperatures, a prediction of the heat load, and verification by measuring the quality factor of the gun with and without the cathode.
BNL, Upton, Long Island, New York
We present our studies on various aspects of the beam dynamics in 'racetrack' design of the first stage electron-ion collider at RHIC (eRHIC), including transverse beam break up instabilities, electron beam emittance growth and energy loss due to synchrotron radiation, electron beam losses due to Touschek effects and residue gas scattering, beam-beam effects at the interaction region and emittance growth of ion beam due to electron bunch to bunch noises. For all effects considered above, no showstopper has been found.
BNL, Upton, Long Island, New York
A prototype ampere-class superconducting energy recovery linac (ERL) is under advanced construction at BNL. The ERL facility is comprised of a five-cell SC Linac plus a half-cell SC photo-injector RF electron gun, both operating at 703.75 MHz. The facility is designed for either a high-current mode of operation up to 0.5 A at 703.75 MHz or a high-bunch-charge mode of 5 nC at 10 MHz bunch frequency. The R&D facility serves a test bed for an envisioned electron-hadron collider, eRHIC. The high-current, high-charge operating parameters make effective higher-order-mode (HOM) damping mandatory, and requires to determination of HOM tolerances for a cavity upgrade. The niobium cavity has been tested at superconducting temperatures and has provided measured dipole shunt impedances for the estimate of a beam breakup instability. The facility will be assembled with a highly flexible lattice covering a vast operational parameter space for verification of the estimates and to serve as a test bed for the concepts directed at future projects.
BNL, Upton, Long Island, New York
During the second half of Run-9, the Relativistic Heavy Ion Collider (RHIC) provided polarized proton collisions at two interaction points with both longitudinal and vertical spin direction. Despite an increase in the peak luminosity by up to 40%, the average store luminosity did not increase compared to previous runs. We discuss the luminosity limitations and polarization performance during Run-9.