R. Connolly

High Current Energy Recovery Linac at BNL

We present the design and parameters of an energy recovery linac (ERL) facility, which is under construction in the Collider-Accelerator Department at BNL. This R&D facility has the goal of demonstrating CW operation of an ERL with an average beam current in the range of 0.1 - 1 ampere and with very high efficiency of energy recovery. The possibility of a future upgrade to a two-pass ERL is also being considered. The heart of the facility is a 5-cell 703.75 MHz super-conducting RF linac with strong Higher Order Mode (HOM) damping. The flexible lattice of the ERL provides a test-bed for exploring issues of transverse and longitudinal instabilities and diagnostics of intense CW electron beams. This ERL is also perfectly suited for a far-IR FEL. We present the status and plans for construction and commissioning of this facility.

Electron Cooling of RHIC

We report progress on the R&D program for electron-cooling of the Relativistic Heavy Ion Collider (RHIC). This electron cooler is designed to cool 100 GeV/nucleon at storage energy using 54 MeV electrons. The electron source will be a superconducting RF photocathode gun. The accelerator will be a superconducting energy recovery linac. The frequency of the accelerator is set at 703.75 MHz. The maximum electron bunch frequency is 9.38 MHz, with bunch charge of 20 nC. The R&D program has the following components: The photoinjector and its photocathode, the superconducting linac cavity, start-to-end beam dynamics with magnetized electrons, electron cooling calculations including benchmarking experiments and development of a large superconducting solenoid. The photoinjector and linac cavity are being incorporated into an energy recovery linac aimed at demonstrating ampere class current at about 20 MeV.

Extremely High Current, High-Brightness Energy Recovery Linac

Next generation light-sources, electron coolers, high-power FELs, Compton X-ray sources and many other accelerators were made possible by the emerging technology of high-power, high-brightness electron beams. In order to get the anticipated performance level of ampere-class currents, many technological barriers are yet to be broken. BNL’s Collider-Accelerator Department is pursuing some of these technologies for its electron cooling of RHIC application, as well as a possible future electron-hadron collider. We will describe work on CW, high-current and high-brightness electron beams. This will include a description of a superconducting, laser-photocathode RF gun and an accelerator cavity capable of producing low emittance (about 1 micron rms normalized) one nano-Coulomb bunches at currents of the order of one ampere average.

Tune feedback at RHIC

Preliminary phase-locked loop betatron tune measurement results were obtained during RHIC 2000 with a resonant Beam Position Monitor. These results suggested the possibility of incorporating PLL tune measurement into a tune feedback system for RHIC 2001. Tune feedback is useful in a superconducting accelerator, where the machine cycle time is long and inefficient acceleration due to resonance crossing is not comfortably tolerated. This is particularly true with the higher beam intensities planned for RHIC 2001. We present descriptions of a PLL tune measurement system implemented in the DSP/FPGA environment of a RHIC BPM electronics module and the feedback system into which the measurement is incorporated to regulate tune. In addition, we present results from the commissioning of this system during RHIC 2001.

A prototype ionization profile monitor for RHIC

Transverse beam profiles in the Relativistic Heavy-Ion Collider (RHIC) will be measured with ionization profile monitors (IPMs). Each IPM collects and measures the distribution of electrons in the beamline resulting from residual gas ionization during bunch passage. The electrons are swept transversely from the beamline and collected on strip anodes oriented parallel to the beam axis. At each bunch passage the charge pulses are amplified, integrated, and digitized for display as a profile histogram. A prototype detector was tested in the injection line during the RHIC Sextant Test. This paper describes the detector and gives results from the beam tests.

RHIC beam instrumentation

AbstractRHICinstrumentationsystemsmustaccuratelycharacterizediversebeamsofupto110bunchesineachofthetwocolliderrings,rangingfrom10 11 protons/bunchat250GeVto10 9 Au þ79 ions/bunchat100GeV=nucleon; aswellaslower-intensitycommissioningandpilotbunches.Thecolliderinstrumentationincludes:667beampositionmonitor(BPM)channels,363beamlossmonitor(BLM)channels,wallcurrentmonitors,DCcurrenttransformers,ionizationprofilemonitors,tunemeasurementdevices,andresonantSchottkymonitors.ColliderinstrumentationisalsousedintheAGS-to-RHICtransferline,including52BPMchannels,56BLMchannels,5fastintegratingcurrenttransformers,and12videobeamprofilemonitors(RHICDesignManual,April1998;Proceedingsofthe’98BeamInstrumentationWorkshop,1998).PublishedbyElsevierScienceB.V. PACS: 29.20.Lq;29.27. a;07.05.HdKeywords: Accelerator;RHIC;Instrumentation;Positionmonitor;Lossmonitor;Currentmonitor;Luminositymonitor 1. Beampositionmonitors1.1. BPM assemblies and cablesThebeampositionmonitor(BPM)electrodeassembliesforthecolliderringandtheAGS-to-RHIC(AtR)lineshareacommonmechanicaldesign[1].AllAtRassembliesoperateatroomtemperature;mostcolliderassembliesoperateat4:2K: Eachassemblycontains23cmlong,3cmwide shorted striplines with a controlled 50Oimpedance.Largestriplinescoupleenoughpowertoallowaccuratemeasurementoflow-intensitypilotbunches.Theshorteddesignrequireselectro-nicswithlowreturnlosstolimitimpedance,butthestaticcryogenicthermalloadisreducedbyafactoroftwoovermoreexpensiveback-termi-nateddesigns.Mostoftheassembliescontaintwoopposingstriplines,andmeasureeitherhorizontalorverticalbeampositionatalocationwithcorrespondinglarge optical beta function. These single-planemonitorsaredesignatedType1ðID¼ 8cmÞ; acutawayviewofoneisshowninFig.1.Incriticalareasaroundtheinteractionregions,assemblieswithfourstriplinesareinstalled,allowingsimulta-neousmeasurementofbothhorizontalandver-ticalpositions.Tomatchexpectedbeamsizeand

Beam profile measurements and transverse phase-space reconstruction on the relativistic heavy-ion collider

Abstract The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab was commissioned during the summer of 1999. Transverse beam profiles on RHIC are measured with ionization profile monitors (IPMs). An IPM measures beam profiles by collecting the electrons liberated by residual gas ionization by the beam. The detector is placed in the gap of a dipole magnet to force the electrons to travel in straight lines from the beamline center to the collector. One IPM was tested and it measured the profiles of a single gold bunch containing 108 ions on consecutive turns. We show an example of one of these profiles giving transverse emittance. Several profiles are assembled into a mountain-range plot which shows betatron oscillations at injection. Finally, we use tomographic techniques to reconstruct the beam transverse phase space at two times in the early beam store.

Operations and Performance of RHIC as a Cu-Cu Collider

The 5thyear of RHIC operations, started in November 2004 and expected to last till June 2005, consists of a physics run with Cu-Cu collisions at 100 GeV/u followed by one with polarized protons (pp) at 100 GeV [1]. We will address here the overall performance of the RHIC complex used for the first time as a Cu-Cu collider, and compare it with previous operational experience with Au, PP and asymmetric d-Au collisions. We will also discuss operational improvements, such as a squeeze to 85cm in the high luminosity interaction regions from the design value of 1m, system improvements, machine performance and limitations, and address reliability and uptime issues.

Laser profile measurements of an H/sup -/ beam

A non-intercepting beam profile monitor for H/sup -/ beams is being developed at Brookhaven National Lab. An H/sup -/ ion has a first ionization potential of 0.75eV. Electrons can be removed from an H/sup -/ beam by passing light from a near infrared laser through it. Experiments have been performed on the BNL linac to measure the transverse profile of a 750keV beam by using a Nd:YAG laser to photoneutralize narrow slices of the beam. The laser beam is scanned across the ion beam neutralizing the portion of the beam struck by the laser. The electrons are removed from the ion beam and the beam current notch is measured.

Beam lifetime and emittance growth measurements of gold beams in RHIC at storage

During stores of gold beams, longitudinal and transverse beam sizes were recorded., Longitudinal profiles were obtained with a wall current monitor. Transverse profiles were reconstructed from gold-gold collision rates at various relative transverse beam positions. The total beam lifetime was measured with a beam current transformer, the bunched beam lifetime with the wall current monitor. Diffusion rates in the beam halo were determined from the change in the loss rate when a scraper is retracted. The measurements are used to determine the lifetime limiting effects. Beam growth measurements are compared with computations of beam-growth times from intra-beam scattering.