M. Minty

Status of head-on beam-beam compensation in RHIC

In polarized proton operation, the performance of the Relativistic Heavy Ion Collider (RHIC) is limited by the head-on beam-beam effect. To overcome this limitation, two electron lenses are under commissioning. We give an overview of head-on beam-beam compensation in general and in the specific design for RHIC, which is based on electron lenses. The status of installation and commissioning are presented along with plans for the future.

Generation of 180 W average green power from a frequency-doubled picosecond rod fiber amplifier

We report on the generation of 180 W average green power from a frequency-doubled picosecond rod fiber amplifier. In an Yb-doped fiber master-oscillator-power-amplifier system, 2.3-ps 704 MHz pulses are first amplified in small-core fibers and then in large-mode-area rod fibers to produce 270 W average infrared power with a high polarization extinction ratio and diffraction-limited beam quality. By carrying out frequency doubling in a lithium triborate (LBO) crystal, 180 W average green power is generated. To the best of our knowledge, this is the highest average green power achieved in fiber-based laser systems.

Proposed BPM-Based Bunch Crabbing Angle Monitor

A tilted (i.e. with different transverse displacements of the bunch head and tail) bunch traversing a button beam profile monitor will produce signals on opposite pickup electrodes that will have different degrees of distortion depending on the tilt angle. In particular, the zero-crossing time difference between the two signals will be approximately proportional to the tilt angle. We perform simulations to study this effect as a possible diagnostic tool for measuring the crabbing angles in a future electron-ion collider.

ER@CEBAF, a 7 GeV, 5-Pass, Energy Recovery Experiment

A multiple-pass, high-energy ERL experiment at the JLab CEBAF will be instrumental in providing necessary information and technology testing for a number of possible future applications and facilities such as Linac-Ring based colliders, which have been designed at BNL (eRHIC) and CERN (LHeC), and also drivers for high-energy FELs and 4th GLS. ER@CEBAF is aimed at investigating 6D optics and beam dynamics issues in ERLs, such as synchrotron radiation effects, emittance preservation, stability, beam losses, multiple-pass orbit control/correction, multiple-pass beam dynamics in the presence of cavity HOMs, BBU and other halo studies, handling of large (SR induced) momentum spread bunches, and development of multiple-beam diagnostics instrumentation. Figure 1: 12 GeV CEBAF recirculating linac. Location of chicane and dump line for ER@CEBAF. Since it was launched 2+ years ago, the project has progressed in defining the necessary modifications to CEBAF (Fig. 1, Tab. 1, 2), including a 4-dipole phase chicane in recirculation Arc A, beam extraction and a dump line at the end of the south linac, and additional dedicated multiplebeam diagnostics. This equipment can remain in place to Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy, † and by Jefferson Science Associates, LLC under Contract No. DEAC05-06OR23177 with the U.S. Department of Energy. ‡ Spokesperson. fmeot@bnl.gov; satogata@jlab.org Table 1: Machine/Lattice Parameters of ER@CEBAF fRF 1497 MHz RF frequency Elinac 700 MeV Gain per linac (baseline) Einj 79 MeV = Elinac × 123/1090 φFODO 60 deg Per cell, at first NL pass and last SL pass M56 <90 cm Compression, Arc A Extraction 8 deg Angle to dump line

RHIC Performance with Stochastic Cooling for Ions and Head-on Beam-beam Compensation for Protons

The Relativistic Heavy Ion Collider (RHIC) has two main operating modes with heavy ions and polarized protons respectively. In addition to a continuous increase in the bunch intensity in all modes, two major new systems were completed recently mitigating the main luminosity limit and leading to significant performance improvements. For heavy ion operation stochastic cooling mitigates the effects of intrabeam scattering, and for polarized proton operation head-on beam-beam compensation mitigates the beam-beam effect. We present the performance increases with these upgrades to date, as well as an overview of all operating modes past and planned.

Record Performance of SRF Gun with CsK2Sb Photocathode

High-gradient CW photo-injectors 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, nuclearwaste transmutation or a new generation of microchip production. In this paper we report on our operation of a superconducting RF electron gun with a record-high accelerating gradient at the CsK2Sb photocathode (i.e. ~ 20 MV/m) generating a record-high bunch charge (i.e., 2 nC). We briefly describe the system and then detail our experimental results. INTRODUCTION The coherent electron cooling experiment (CeC PoP) [1, 2] is expected to demonstrate cooling of a single hadron bunch in RHIC. A superconducting RF gun operating at 112 MHz frequencies generates the electron beam. 500MHz normal conducting cavities provide energy chirp for ballistic compression of the beam. 704-MHz superconducting cavity will accelerate beam to the final energy. The electron beam merges with the hadron beam and after cooling process is steered to a dump. The FEL-like structure enhances the electron-hadron interaction. The electron beam parameters are shown in the Table 1. Table 1: Parameters of the Electron Beam

Observation of snake resonances at Relativistic Heavy Ion Collider

The Siberian snakes are powerful tools in preserving polarization in high energy accelerators has been demonstrated at the Brookhaven Relativistic Heavy Ion Collider (RHIC). Equipped with two full Siberian snakes in each ring, polarization is preserved during acceleration from injection to 100 GeV. However, the Siberian snakes also introduce a new set of depolarization resonances, i.e. snake resonances as first discoverd by Lee and Tepikian [1]. The intrinsic spin resonances above 100 GeV are about a factor of two stronger than those below 100 GeV which raises the challenge to preserve the polarization up to 250 GeV. In 2009, polarized protons collided for the first time at the RHIC design store energy of 250 GeV. This paper presents the experimental measurements of snake resonances at RHIC. The plan for avoiding these resonanances is also presented.