STFC/RAL/ISIS, Chilton, Didcot, Oxon
Imperial College of Science and Technology, Department of Physics, London
STFC/RAL/ISIS, Chilton, Didcot, Oxon
STFC/RAL, Chilton, Didcot, Oxon
ANL, Argonne, Illinois
Northern Illinois University, DeKalb, Illinois
A multi-charge-state injector for high-intensity heavy-ion LINAC is being developed at ANL. The injector consists of an all-permanent magnet ECR ion source, a 100 kV platform and a Low Energy Beam Transport (LEBT). The latter comprises two 60-degree bending magnets, electrostatic triplets and beam diagnostics stations. The first results of beam measurements in the LEBT will be presented.
ANL, Argonne, Illinois
The Advanced Exotic Beam Laboratory (AEBL) being developed at ANL consists of an 833 MV heavy-ion driver linac capable of producing uranium ions up to 200 MeV/u and protons to 580 MeV with 400 kW beam power. We have designed all accelerator components including a two charge state LEBT, an RFQ, a MEBT, a superconducting linac, a stripper section and beam switchyard. We present the results of an optimized linac design and end-to-end simulations which include possible machine errors.
ANL, Argonne, Illinois
The Office of Science of the Department of Energy is currently considering options for an advanced radioactive beam facility in the U. S. The U. S. facility will complement capabilities both existing and planned elsewhere. As envisioned at ANL, the facility, called the Advanced Exotic Beam Laboratory (AEBL), would consist of a heavy-ion driver linac, a post-accelerator and experimental areas. The proposed design of the AEBL driver linac is a cw, fully superconducting, 833 MV linac capable of accelerating uranium ions up to 200 MeV/u and protons to 580 MeV with 400 kW beam power. An extensive research and development effort has resolved many technical issues related to the construction of the driver linac and other systems required for AEBL. This paper presents the status of planning, some options for such a facility, as well as, progress in related R&D.
ANL, Argonne, Illinois
The Intense Pulsed Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS) accelerates 3.2x 1012 protons from 50 MeV to 450 MeV at 30 Hz. During the 14.2 ms acceleration period, the RF frequency varies from 2.21 MHz to 5.14 MHz. In order to improve capture efficiency, we varied the injection timing and the early RF voltage profiles. The experimental results are compared with similar studies at ISIS and calculation done with the 1-D tracking code, Capture-SPC. This allowed us to optimize injection time and the RF voltage profile for better capture efficiency. An optimized injection time and RF voltage profile was found that resulted in raising the capture efficiency from 85.1% to 88.6%. These studies have now also been expanded to included 2nd harmonic RF during the capture and initial acceleration cycle in the RCS.
Fermilab, Batavia, Illinois
High intensity operation of the Fermilab Main Injector has resulted in increased activation of machine components. Efforts to permit operation at high power include creation of collimation systems to localize losses away from locations which require maintenance. As a first step, a collimation system to remove halo from the incoming beam was installed in the Spring 2006 Facility Shutdown*. We report on commissioning studies and operational experience including observations of Booster beam properties, effects on Main Injector loss and activation, and operational results.
* B. C. Brown, et al., "Collimation System for the Fermilab Booster to Main Injector Transfer Line", this conference.
Fermilab, Batavia, Illinois
A collimation system has been created for removing proton beam halo in the 8 GeV transfer line from the Fermilab Booster to Main Injector. A pair of 1.14 meter collimators with 5.08 cm rectangular apertures are installed in a 5 meter straight section. Horizontal and vertical motion systems allow them to be positioned such that halo can be scraped from four sides. An additional pair of collimators, placed one cell (90 degrees) downstream scrape halo which is of opposite phase. Each collimator pair can scrape about 600 Watts of beam power, limited by long term activation of materials outside of the beam line tunnel. Personnel exposure is reduced by surrounding the iron absorber with a layer of marble. Design features,radiation calculations and instrumentation considerations will be described.
Fermilab, Batavia, Illinois
NSCL, East Lansing, Michigan
Fermilab, Batavia, Illinois
LANL, Los Alamos, New Mexico
Rochester University, Rochester, New York
Carbon foils are widely used in charge-exchange injection in high intensity hadron accelerators. There are a variety of physics issues associated with the use of carbon foils, including stripping efficiency, energy deposition, foil lifetime (temperature rise, mechanical stress and buckling), multiple Coulomb scattering, large angle single Coulomb scattering, energy straggling and radiation activation. This paper will give a brief discussion of these issues based on the study of the Proton Driver and experience of the Fermilab Booster. Details can be found in Ref*.
* W. Chou et al., "Transport and Injection of 8 GeV H- Ions," Fermilab-TM-2285 (2007).
Fermilab, Batavia, Illinois
Two barrier rf systems were fabricated, tested and installed in the Fermilab Main Injector.* Each can provide 8-10 kV rectangular pulses (the rf barriers) at 90 kHz. When a stationary barrier is combined with a moving barrier, injected beams from the Booster can be continuously deflected, folded and stacked in the Main Injector (MI), which leads to doubling of the beam intensity. This paper gives a report on the beam experiment using this novel technology.
* W. Chou, D. Wildman and A. Takagi, "Induction Barrier RF and Applications in Main Injector," Fermilab-Conf-06-227 (2006).
Fermilab, Batavia, Illinois
A two-year Large Aperture Quadrupole (WQB) Project was completed in the summer of 2006 at Fermilab.* Nine WQBs were designed, fabricated and bench-tested by the Technical Division. Seven of them were installed in the Main Injector and the other two for spares. They perform well. The aperture increase meets the design goal and the perturbation to the lattice is minimal. The machine acceptance in the injection and extraction regions is increased from 40π to 60π mm-mrad. This paper gives a brief report of the operation and performance of these magnets. Details can be found in Ref**.
* D. Harding et al, "A Wide Aperture Quadrupole for the Fermilab Main Injector," this conference.
** W. Chou, Fermilab Beams-doc-#2479, http://beamdocs.fnal.gov/AD-public/DocDB/DocumentDatabase
Fermilab, Batavia, Illinois
KEK, Ibaraki
Measurements of the tune on the front porch of the Tevatron* showed a drift of the tune which tracked the time dependence of the sextupole moment in the dipoles. Calculations using survey data to calculate the closed orbit failed to reproduce the observed tune shifts. The feed down of these sextupole moments generates a quadrupole field at the ends of the dipoles. It is suggested, based on calculations, that the change in the sextupole moment of the dipoles also produces a change in the strength of the strength of the zero length quadrupole incorporated in the end of the dipoles and that this change can account for the observed tune drifts.
*Tevatron Chromaticity and Tune Drift and Snapshot Studies Report, G. Annala, P. Bauer, M. Martens, D. Still, G. Velev, Beams-doc-1236 (Jan. 5,2005)
Fermilab, Batavia, Illinois
A 8 GeV H- superconducting linac has been proposed as an alternative injector for the Main Injector to support a 2 MW Neutrino program. An injection absorber is required to accept protons generated after the secondary stripping foil which will intercept the un-stripped H- and H0 particles after the MI primary foil injection point. The motivations underlying the choice of a compact internal absorber over an external absorber will be discussed. We show that using a high-Z material (tungsten) for the inner shielding allows the construction a compact absorber that can take a very intense beam and fits within the existing enclosure. The absorber requirements and a shielding design and the results of energy deposition calculations are presented.
BNL, Upton, Long Island, New York
The technique for H- charge exchange for multi-turn injection utilizing stripping foils in the energy range of a few hundred MeV has been used at many labs for decades and most recently up to 1 GeV at the SNS. Utilization the beam from the proposed Proton Driver* would permit the extension of this technique up to 8 GeV. The injection layout and required accelerator modifications are discussed. Results from transverse and longitudinal simulations are presented.
* W. G. Foster and J. A. MacLachlan, "A Multi-mission 8 GeV Injector Linac as a Fermilab Booster Replacement", Proc. Of LINAC-2002, Gyeongju, Korea, p.86.
Fermilab, Batavia, Illinois
BINP SB RAS, Novosibirsk
Fermilab, Batavia, Illinois
Fermilab, Batavia, Illinois
The operation and performance of the new, 15 Hz, H- charge exchange injection system for the FNAL Booster is described. The new system installed in 2006 was necessary to allow injection into the Booster at up to 15 Hz. It was built using radiation hardened materials which will allow the Booster to reliably meet the high intensity and repetition rate requirements of the Fermilab's HEP program. The new design uses three orbit bump magnets (Orbmps) rather than the usual four and permits injection into the Booster without a septum magnet. Injection beam line modification and compensation for the quadrupole gradients of the Orbmp magnets is discussed.
Fermilab, Batavia, Illinois
The NuMI beamline at Fermilab has been operational since the spring of 2005 delivering high-intensity neutrino beams to the MINOS experiment. A beam power on target of 310 kW has been achieved and a total of more than 2·1020 protons have been delivered to the NuMI target. Upgrades to NuMI are planned in preparation for the future MINERvA and NOvA neutrino experiments increasing the NuMI beam power capability from 400 kW to 700 kW and then as much as 1.2 MW. An overview of the future upgrade to NuMI is presented.
Fermilab, Batavia, Illinois
A 0.1 A, 4.3 MeV DC electron beam is routinely used to cool 8 GeV antiprotons in Fermilab's Recycler storage ring. While the primary function of the electron cooler is to increase the longitudinal phase-space density of the antiprotons, significant transverse cooling rates have been observed as well. Numerical characterization of electron cooling is done by two types of measurements: friction force measurements by the voltage jump method and diffusion/cooling rates measurements. The paper will present the recent measurement results and will compare them to a non-magnetized model.
Fermilab, Batavia, Illinois
Fermilab, Batavia, Illinois
CERN, Geneva
Fermilab, Batavia, Illinois
Upon the termination of the Fermilab Collider program, the current Recycler anti-proton storage ring will be converted to a proton pre-injector for the Main Injector synchrotron. This is scheduled to increase the beam power for the 120 GeV Neutrino program to upwards of 700KW. A transport line that can provide direct injection from the Booster to the Recycler while preserving direct injection from the Booster into the Main Injector and the 8 GeV Booster Neutrino program will be discussed,and its concept design will be presented.
Fermilab, Batavia, Illinois
Upon the termination of the Fermilab Collider program, the current Recycler anti-proton storage ring will be converted to a proton pre-injector for the Main Injector synchrotron. This is scheduled to increase the beam power for the 120 GeV Neutrino program to upwards of 700KW. Due to momentum aperture restriction, a new transport line that extracts the beam from the Recycler at a dispersion free region to the main injector will be discussed, and its concept design will be presented.
Fermilab, Batavia, Illinois
Fermilab, Batavia, Illinois
Fermilab, Batavia, Illinois
LBNL, Berkeley, California
LBNL, Berkeley, California
An over-dense microwave driven ion source capable of producing deuterium (or hydrogen) beams at 100-200 mA/cm2 with an atomic fraction > 90% was designed as a part of an Accelerator Driven Neutron Source (ADNS). The ion source was tested with an electrostatic low energy beam transport section (LEBT) and measured emittance data was compared to PBGUNS simulations. In our design a 40 mA D+ beam is produced from a 6 mm diameter aperture using a 60 kV extraction voltage. The LEBT section consists of 5 electrodes arranged to form 2 Einzel lenses that focus the beam into the RFQ entrance. To create the ECR condition, 2 induction coils are used to generate a ~875 Gauss magnetic field on axis inside the source chamber. To prevent HV breakdown in the LEBT, a magnetic field clamp is necessary to minimize the field in this region. The microwave power is matched to the plasma by an autotuner. A significant improvement in the atomic fracion of the beam was achieved by installing a boron nitride liner inside the ion source
IUCF, Bloomington, Indiana
The Low Energy Neutron Source (LENS) at Indiana University is producing neutrons by using a 7 MeV proton beam incident on a Beryllium target. The Proton Delivery System is currently being upgraded. A new DTL section will be added to increase proton beam energy from 7 to 13 MeV. A 3 MeV RFQ and 13 MeV DTL will be powered by 1 MW klystrons. The goal of this upgrade is a 13 MeV, 20 mA proton beam with duty factor more than 1%. At this power level it becomes increasingly important to make a proton beam that is uniformly distributed to prevent excessive thermal stress at the surface of the Be target. To achieve this goal two octupole magnets are being implemented in the LENS beam transport line. In this paper we discuss the experimental results of the beam intensity redistribution as well as some features inherent in tuning of the nonlinear beamline and our operational experience.
UMD, College Park, Maryland
The University of Maryland Electron Ring (UMER) is a low energy, high current recirculator for beam physics research. The electron beam current is adjustable from 0.7 mA, an emittance dominated beam, to 100 mA, a strongly space charge dominated beam. UMER is addressing issues in beam physics relevant to many applications that require intense beams of high quality such as advanced concept accelerators, free electron lasers, spallation neutron sources, and future heavy-ion drivers for inertial fusion. The primary focus of this presentation is experimental results and improvements in multi-turn operation of the electron ring. Transport of a low current beam over 100 turns (3600 full lattice periods) has been achieved. Results of high current, space charge dominated multi-turn transport will also be presented.
UMD, College Park, Maryland
The University of Maryland Electron Ring (UMER) is a low energy, high current recirculator for beam physics research. The electron storage ring has been closed and recent operations have been focused on achieving multi-turn transport. An entire suite of terminal diagnostics is available for time-resolved phase space measurements of the beam. These diagnostics have been mounted and tested at several points on the ring before it was closed. UMER utilizes a unique injection scheme which uses the fringe fields of an offset quadrupole to assist a pulsed dipole in bending the beam into the ring. Similar concepts, along with more traditional electrostatic methods, are being considered for beam extraction. This presentation will focus on the recent efforts to design and deploy these major subsystems required for beam extraction.
Texas A&M University, College Station, Texas
A conceptual design is presented for the 50 Tesla superconducting solenoids that are required for an optimized fast cooling ring in current designs for multi-TeV muon colliders. The solenoid utilizes high-performance multi-filament Bi-2212/Ag round strand. The conductor is a cable-in-conduit consisting of six such strands cabled around a thin-wall spring tube then drawn within an outer sheath. The spring tube and the sheath are made from high-strength superalloy Inconel. The solenoid coil comprises 5 concentric shells supported independently in the conventional manner. Each shell consists of a winding of the structured cable, impregnated in the voids between cables but empty inside so that the spring tubes decouple stress so that it cannot strain-degrade the fragile strands, and a high-modulus overband. An expansion bladder is located between the winding and the overband, and is pressurized and then frozen to provide hydraulic compressive preload to each shell. This approach makes it possible to accommodate ~10 T field contribution from each shell without degradation, and provides distributed refrigeration so that heat is removed throughout the windings.
ORNL, Oak Ridge, Tennessee
NSCL, East Lansing, Michigan
In supporting pre-conceptual research and development of the Rare-Isotope Accelerator facility or similar next-generation exotic beam facilities, one critical focus area is to estimate the level of activation and radiation in the linear accelerator second stripping region and to determine if remote handling is necessary in this area. A basic geometric layout of the second stripping region having beamline magnets, beam pipes and boxes, a stripper foil, beam slits, and surrounding concrete shielding was constructed for Monte Carlo simulations. Beam characteristics were provided within the stripping region based on this layout. Radiation fields, radioactive inventories, levels of activation, heat loads on surrounding components, and prompt and delayed radiation dose rates were simulated using Monte-Carlo radiation transport code PHITS. Preliminary results from simulations using a simplified geometry show that remote handling of foils and slits will be necessary. Simulations using a realistic geometry are underway and the results will be presented.
NSCL, East Lansing, Michigan
To support pre-conceptual research and development for rare isotope beam production via projectile fragmentation at the Rare-Isotope Accelerator facility or similar next-generation exotic beam facilities, the interactions between primary beams and beryllium and liquid-lithium production targets in the fragment pre-separator area were simulated using the Monte-Carlo radiation transport code PHITS. The purpose of this simulation is to determine the magnitude of the radiation fields in the pre-separator area so that levels of hadron flux and energy deposition can be obtained. It was of particular interest to estimate the maximum radiation doses to magnet coils and other components such as the electromagnetic pump for a liquid-lithium loop, and to estimate component lifetimes. We will show a detailed geometry of the pre-separator area developed for these simulations. We will provide verification that trajectories of beams and fragments when transported in the PHITS simulations agree with results from standard ion-optics calculations. We will present estimates of radiation doses to pre-separator components and give estimates for component lifetimes.
LLNL, Livermore, California
NSCL, East Lansing, Michigan
ORNL, Oak Ridge, Tennessee
LANL, Los Alamos, New Mexico
NSCL, East Lansing, Michigan
Rare Isotope Beams (RIBs) are created at the National Superconducting Cyclotron Laboratory (NSCL) by the in-flight particle fragmentation method. A novel system is proposed to stop the RIBS in a helium filled gas system followed by reacceleration that will provide opportunities for an experimental program ranging from low-energy Coulomb excitation to transfer reaction studies of astrophysical reactions. The beam from the gas stopper will first be brought into a Electron Beam Ion Trap (EBIT) charge breeder on a high voltage platform to increase its charge state and then accelerated initially up to about 3 MeV/u by a system consisting of an external multi-harmonic buncher and a radio frequency quadrupole (RFQ) followed a superconducting linac. The superconducting linac will use quarter-wave resonators with bopt of 0.047 and 0.085 for acceleration and superconducting solenoid magnets for transverse focusing. The paper will discuss the accelerator system design and present the end-to-end beam dynamics simulations.
NSCL, East Lansing, Michigan
NSCL, East Lansing, Michigan
CESR-LEPP, Ithaca, New York
Following two decades of operation at 5 GeV beam energy for studies of bottom quark bound states, the Cornell Electron Storage Ring (CESR) converted to 2 GeV operation in 2001 for the purpose of investigating bound states of charm quarks. This reduction of beam energy resulted in increased relative contributions of the beam-beam force. The beam-beam interaction has been found to have considerable consequences for the optics and for the injection aperture. We describe recent developments in our modelling of the beam-beam interaction, experimental validation techniques, and investigations into compensation strategies.
LLNL, Livermore, California
A compact Dielectric Wall Accelerator (DWA), with field gradient up to 100 MV/m, is being developed to accelerate proton bunches for use in cancer therapy treatment. The injector first generates a few nanosecond long and 40 pQ proton bunch, which is then compressed in the compression section at the end of the injector. Finally the bunch is accelerated in the high-gradient DWA accelerator to energy up to 70 - 250 MeV. The Particle-In-Cell (PIC) code LSP is used to model several aspects of this design. First, we use LSP to determine the needed voltage waveform in the A-K gap that will produce a proton bunch with the requisite charge. We then model pulse compression and shaping in the section between the A-K gap and the DWA. We finally use LSP to model the beam transport through the DWA.
LLNL, Livermore, California
Proton accelerator structures for medical applications using Dielectric Wall Accelerator (DWA) technology allows for the utilization of high field gradients on the order of 100 MV/m to accelerate the proton bunch. Medical applications involving cancer therapy treatment usually desire short bunch lengths on the order of hundreds of picoseconds in order to limit the extent of the energy deposited in the tumor site (in 3D space, time, and deposited proton charge). Electromagnetic simulations of the DWA structure, in combination with injections of proton bunches, have been performed using 3D finite difference codes in combination with particle pushing codes. Electromagnetic simulations of DWA structures includes these effects and also includes the details of the switch configuration and how that switch time affects the electric field pulse which accelerates the particle beam. Design trade-offs include the driving switch effects, layer-to-layer coupling analysis and its affect on the pulse rise time.
LLNL, Livermore, California
An investigation is being made into the feasibility of making a compact proton accelerator for medical radiation treatment. The accelerator is based on high gradient insulation (HGI) technology. The beam energy should be tunable between 70 and 250 MeV to allow the Bragg peak to address tumors at different depths in the patient. The desired radiation dose is consistent with a beam charge of 40 pico-coulombs. The particle source is a small 2 mm plasma device from which a several nano-second pulse can be extracted. The beam current is selectable by the potential of the extraction electrode and is adjustable in the range of 10-100 milli-Amperes. This beam is then accelerated and focused by the next three electrodes forming a Accel-Deaccel-Accel (ADA) structure leading to the DWA accelerator block. The spot size is adjustable over 2 to 10 mm. A transparent grid terminates the injector section and prevents the very high gradient of the HGI structure from influencing the overall focusing of the system. The beam energy is determined by the length of the DWA structure that is charged. This give independent selection of beam dose, size and energy.
LLNL, Livermore, California
The dielectric wall accelerator (DWA) is a compact induction accelerator structure that incorporates the accelerating mechanism, pulse forming structure, and switch structure into an integrated module. The DWA consists of stacked stripline Blumlein assemblies, which can provide accelerating gradients in excess of 100 MeV/meter. Blumleins are switched sequentially according to a prescribed acceleration schedule to maintain synchronism with the proton bunch as it accelerates. A finite difference time domain code (FDTD) is used to determine the applied acceleration field to the proton bunch. Particle simulations are used to model the injector as well as the accelerator stack to determine the proton bunch energy distribution, both longitudinal and transverse dynamic focusing, and emittance associated with various DWA configurations.
LLNL, Livermore, California
A compact proton accelerator for medical applications is being developed at Lawrence Livermore National Laboratory. The accelerator architecture is based on the dielectric wall accelerator (DWA) concept. One critical area to consider is the switch region. Electromagnetic field simulations and thermal calculations of the switch area were performed to help determine the operating limits of the SiC switches. Different geometries were considered for the field simulation including the shape of the thin indium solder meniscus between the electrodes and SiC, and possible misalignment of electrodes and SiC during manufacturing. Electromagnetic field simulations were also utilized to demonstrate how the field stress could be reduced. Both transient and steady-state thermal simulations were analyzed to find the average power capability of the switches.
LANL, Los Alamos, New Mexico
At the core of the Los Alamos Neutron Science Center (LANSCE) accelerator lies an 800-MeV proton linac that drives user facilities for isotope production, proton radiography, ultra-cold neutrons, weapons neutron research and for various sciences using neutron scattering. LANSCE is in the planning phase of a refurbishment project that will sustain reliable facility operations well into the next decade. The general goals for LANSCE-R are to (1) preserve dependable operation of the linac and (2) increase the cost effectiveness of operations. Requirements can be met for overall beam intensity, availability, and reliability with long-term sustainability and minimal disruption to scheduled user programs. The baseline refurbishment project consists of replacing the 201 MHz RF systems, upgrading a substantial fraction of the 805 MHz RF systems, updating the control system, and replacing or improving a variety of diagnostics and accelerator subsystems. The plans for the various LANSCE-R improvements will be presented and the preliminary cost and schedule estimates will be discussed.
LANL, Los Alamos, New Mexico
The LANSCE linac simultaneously provides both H+ and H- beams to several user facilities. The Weapons Neutron Research (WNR) user facility is configured to accept the H- beam with a typical pulse pattern of one linac micro-pulse every 1.8 microseconds. To produce this pulse spacing a slow-wave chopper located in the 750 keV injector beam transport is employed to intensity modulate the beam. The beam is subsequently bunched at both 16.77 MHz and 201.25 MHz prior to entering the 100 MeV drift tube linac. One downside of the chopping process is that the majority of the beam produced by the ion source during the WNR macro-pulses is discarded. By applying a longitudinal bunching action immediately following the ion source, simulations have shown that some of this discarded beam can be used to increase the charge in these micro-pulses. Recently, we began an effort to develop this buncher by superimposing 16.77 MHz RF voltage on one of the HVDC electrodes in the 80 kV column located inside H- Cockcroft-Walton dome. This paper describes the beam dynamics simulations, design and implementation of the rf hardware and the results of tests performed with the system.
LANL, Los Alamos, New Mexico
The aim of the helicon plasma generator-assisted negative ion source development at Los Alamos Neutron Science Center (LANSCE) is to use high-density helicon plasmas for producing intense beams of H- ions. Our work consists of two development paths, construction of a hybrid ion source and replacement of the LANSCE surface converter ion source filaments by helicon plasma generators. The hybrid ion source is a combination of a long-life plasma cathode, sustained by a helicon plasma generator, with a stationary, pulsed main discharge (multi-cusp H- production chamber) directly coupled to each other. The electrons are transferred from the helicon plasma to the cusp-chamber by thermal flow process to ignite and sustain the main discharge. Replacing the filaments of the surface converter source by two helicon plasma generators is a low-cost solution, building upon the well-proven converter-type ion sources. Both development paths are aimed at meeting the beam production goals of the LANSCE 800 MeV linear accelerator refurbishment project. The design and status of both ion source types is discussed.
INFN/LNF, Frascati (Roma)
SLAC, Menlo Park, California
We present a preliminary design of an interaction region for a Super-B Factory with luminosity of 1x1036 cm2/s. The collision has a ± 17 mrad crossing angle and the first magnetic element starts 30 cm from the collision point. We show that synchrotron radiation backgrounds are controlled and are at least as good as the backgrounds calculated for the PEP-II accelerator. How the beams get into and out of a shared beam pipe is illustrated along with the control of relatively high synchrotron radiation power from the outgoing beams. The high luminosity makes radiative bhabha backgrounds significantly higher than that of the present B-Factories and this must be addresed in the initial design.
CERN, Geneva
The ILC positron damping ring comprises hundreds of meters of wiggler sections, where many more photons than in the arcs are emitted, and with the smallest beam-pipe aperture of the ring. A significant electron-cloud density can therefore be accumulated via photo-emission and via beam-induced multipacting. In field-free regions the electron-cloud build up may be suppressed by adding weak solenoid fields, but the electron cloud remaining in the wigglers as well as in the arc dipole magnets can still drive single-bunch and multi-bunch beam instabilities. This paper studies the electron-cloud formation in an ILC wiggler section for various scenarios, as well as its character, and possible mitigation schemes.
SLAC, Menlo Park, California
During Run 5, PEP-II has been plagued by beam instabilities causing beam aborts due to radiation in the BaBar detector or due to fast beam loss triggering the dI/dt interlock. The latest of such instabilities occurred in the High Energy Ring (HER), severely curtailing the maximum beam current achievable during physics running. Techniques used in tracking down this instability included fast monitoring of background radiation, temperatures and vacuum pressure. In this way, the origin of the instability was localized and inspection of the vacuum system revealed several damaged bellows shields. Replacing these units significantly reduced the incident rate but did not eliminate it fully. After the end of the run, a number of damaged rf seals were found, possibly having caused the remaining incidents of instability. In this paper we will outline the steps taken to diagnose and remedy the issue and also compare the different signatures of vacuum-induced instabilities we have seen in both rings of PEP-II during the run.
SLAC, Menlo Park, California
INFN/LNF, Frascati (Roma)
ORNL, Oak Ridge, Tennessee
The chopper system for the Spallation Neutron Source (SNS) provides a gap in the beam for clean extraction from the accumulator ring. It consists of a pre-chopper in the low energy beam transport and a faster chopper in the medium energy beam transport (MEBT). The original "meander line" design of the MEBT chopper deflector was successfully tested with low power beam during the SNS linac commissioning but turned out to be unsuitable for high power beam operation due to poor cooling of the copper strip line through the dielectric substrate. We developed a new deflecting structure, with higher deflection efficiency and with rise and fall time easily customizable to match the available high voltage pulse generator. In this paper we describe design, implementation and beam tests results of the new MEBT chopper deflector.
ORNL, Oak Ridge, Tennessee
The Spallation Neutron Source accelerator systems will deliver a 1.0 GeV, 1.4 MW proton beam to a liquid mercury target for neutron scattering research. The accelerator complex consists of an H- injector, capable of producing one-ms-long pulses at 60 Hz repetition rate with 38 mA peak current, a 1 GeV linear accelerator, an accumulator ring and associated transport lines. The 2.5 MeV beam from the Front End is accelerated to 86 MeV in the Drift Tube Linac, then to 185 MeV in a Coupled-Cavity Linac and finally to 1 GeV in the Superconducting Linac. With the completion of beam commissioning, the accelerator complex began operation in June 2006 and beam power is being gradually ramped up toward the design goal. Operational experience with the injector and linac will be presented including chopper performance, transverse emittance evolution along the linac, and the results of a beam loss study.
ORNL, Oak Ridge, Tennessee
Beam envelope calculations show that a solenoid-drift-(singlet quad)-(sector dipole)-(singlet quad)-drift-solenoid LEBT allows for transporting 65-kV, high-current H- beams with smaller beam radii than the initially-explored (doublet quad)-drift-(double-focusing dipole)-drift-solenoid configuration. In addition, it appears that the new configuration is more robust because it allows for perfect matching of the final beam parameters for broad ranges of the parameters describing the lattice and the input beam. Such a LEBT with a dipole (switching-) magnet is required to assure meeting the 99% ion source availability requirement after upgrading the power of the Spallation Neutron Source. The SNS power upgrade will roughly double the neutron flux by increasing the proton beam energy from 1 to 1.3 GeV and by increasing the LINAC beam peak current from 38 to 59 mA. Because the RFQ losses increase with beam current and emittance, the RFQ input current needs to be increased from 41 to 67 mA if the normalized emittance can be maintained at 0.2 mm-mrad, or to 95 mA if the emittance increases to 0.35 mm-mrad.
Far-Tech, Inc., San Diego, California
Electron cyclotron resonance ion sources (ECRIS) that generate multiply charged ions reduce the cost to produce radioactive ion beams by reducing the accelerating voltage needed to achieve the desired beam energy. FAR-TECH, Inc. is developing an integrated suite of numerical codes to simulate ECRIS ion capture, charge breeding, and ion extraction. Ion extraction is modeled with a particle in cell (PIC) code. Since the ion dynamics are strongly dependent on the behavior of the plasma sheath at the boundary between the ECRIS plasma and the ion optics, the PIC code uses an adaptive Poisson solver to accurately resolve the potential drop in the sheath. Results of the integrated ECRIS model will be presented, including calculations of extraction efficiency with multiple ion species.
Far-Tech, Inc., San Diego, California
ANL, Argonne, Illinois
UW-Madison/PD, Madison, Wisconsin
The electron cyclotron-resonance ion source (ECRIS) is one of the most efficient ways to provide high-quality, high-charge-state ion beam for research and development of particle accelerators and atomic physics experiments. For ECR ion source performance optimization, FAR-TECH Inc. is developing an integrated suite of computer codes: the Generalized ECRIS plasma Modeling code (GEM), the MCBC (Monte Carlo Beam Capture) module, to study beam capture and charge-breeding processes in ECRIS, and the extraction section code. Our recent progress includes the following: algorithm update of Coulomb collision in MCBC for more accurate calculations of the beam capture efficiency, which depends on beam energy and the background plasma, 2D extension of GEM by adding the radial dimension, and the ion extraction section modeling using an adaptive technique.
Far-Tech, Inc., San Diego, California
To model ECRIS, GEM is being extended to 2D by adding radial dimension. The electron distribution function (EDF) is calculated on each magnetic flux surface using a bounce-averaged Fokker-Planck code with 2D ECR heating (ECRH) modeling. The ion fluid model is also being extended to 2D by adding collisional radial transport terms. All species in ECRIS are balanced by keeping the neutrality in each cell and the plasma potential is calculated by maintaining the ambipolarity globally. The graphical user interface (GUI) and parallel computing ability of GEM make it an easy-to-use tool for ECRIS research. Numerical results and comparisons with experimental data will be presented.
Linac Systems, Albuquerque, New Mexico
JP Accelerator Works, Los Alamos, New Mexico
* J. D. Sherman, these conference proceedings.
BNL, Upton, Long Island, New York
A part of a new EBIS-based heavy ion preinjector, the low energy beam transport (LEBT) section between the high current EBIS and the RFQ is a challenging design, because it must serve many functions. In addition to the requirement to provide an efficient matching between the EBIS and the RFQ, this line must serve as a fast switchyard, allowing singly charged ions from external sources to be transported into the EBIS trap region, and extracted, highly charged ions to be deflected to off-axis diagnostics (time-of-flight, or emittance). The space charge of the 5-10 mA extracted heavy ion beam is a major consideration in the design, and the space charge force varies for different ion beams having Q/m from 1-0.16. The line includes electrostatic lenses, spherical and parallel-plate deflectors, magnetic solenoid, and diagnostics for measuring current, charge state distributions, emittance, and profile. A prototype of this beamline has been built, and results of tests will be presented.
BNL, Upton, Long Island, New York
Full spin flip in the presence of full Siberian snake has been achieved by using an rf dipole or solenoid as spin flipper at IUCF and COSY. This technique requires one to change the snake configuration to move the spin tune away from half integer. However, this is not practical for an operational high energy polarized proton collider like RHIC where beam lifetime is sensitive to small betatron tune change. An new technique of achieving full spin flip with the spin tune staying at half integer is proposed. This paper presents the design of RHIC spin flipper along with simulation results.
BNL, Upton, Long Island, New York
Snake depolarizing resonances due to the imperfect cancellation of the accumulated perturbations on the spin precession between snakes were observed at the Relativistic Heavy Ion Collider~(RHIC). During the RHIC 2005 and 2006 polarized proton runs, we mapped out the spectrum of odd order snake resonance at Qy=7/10. Here, Qy is the beam vertical betatron tune. We also studied the beam polarization after crossing the 7/10th resonance as a function of resonance crossing rate. This paper reports the measured resonance spectrum as well as the results of resonance crossing.
The work was performed under the US Department of Energy Contract No. DE-AC02-98CH1-886, and with support of RIKEN(Japan) and RenaissanceTechnologies C orp.(USA)
KEK, Ibaraki
CERN, Geneva
A small angle (< 1mrad) crab scheme is an attractive option for the LHC luminosity upgrade to recover the geometric luminosity loss from the finite crossing angle, which steeply increases to unacceptable levels as the IP beta function is reduced below its nominal value. The crab compensation in the LHC can be accomplished using only two sets of deflecting rf cavities, placed in collision-free straight sections of LHC to nullify the crossing angles at IP1 & IP5. We present IR optics configurations with low-angle crab crossing, study the beam-beam performance and proton-beam emittance growth in the presence of crab compensation, lattice errors, crab RF noise sources. We also explore a 400MHz superconducting cavity design and discuss the pertinent RF challenges.
BNL, Upton, Long Island, New York
CERN, Geneva
We use transverse beam transfer functions to measure tune distributions of colliding beams in RHIC. The tune has a distribution due to the beam-beam interaction, nonlinear magnetic fields – particularly in the interaction region magnets, and non-zero chromaticity in conjunction with momentum spread. The measured tune distributions are compared with calculations.
BNL, Upton, Long Island, New York
CERN, Geneva
SLAC, Menlo Park, California
Fermilab, Batavia, Illinois
LBNL, Berkeley, California
A DC wire has been installed in RHIC to explore the long-range beam-beam effect, and test its compensation. We report on experiments that measure the effect of the wire's electro-magnetic field on the beam's lifetime and tune distribution, and accompanying simulations.
BNL, Upton, Long Island, New York
Gold ions for the 2007 run of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) are accelerated in the Tandem, Booster and AGS prior to injection into RHIC. The setup and performance of this chain of accelerators will be reviewed with a focus on improvements in the quality of beam delivered to RHIC. In particular, more uniform stripping foils between Booster and AGS, and a new bunch merging scheme in AGS promise to provide beam bunches with reduced longitudinal emittance for RHIC.
BNL, Upton, Long Island, New York
Beam-beam effects present one of major factors limiting the luminosity of colliders. In the linac-ring option of eRHIC design, an electron beam accelerated in a superconducting energy recovery linac collides with a proton beam circulating in the RHIC ring. There are some features of beam-beam effects which require careful examination in linac-ring configuration. First, the beam-beam interaction can induce specific head-tail type instability of the proton beam referred to as kink instability. Thus, beam stability conditions should be established to avoid proton beam loss. Also, the electron beam transverse disruption by collisions has to be evaluated to ensure beam quality is good enough for the energy recovery pass. In addition, fluctuations of electron beam current and/or electron beam size, as well as transverse offset, can cause proton beam emittance growth. The tolerances for those factors should be determined and possible countermeasures should be developed to mitigate the emittance growth. In this paper, a soft Gaussian strong-strong simulation is used to study all of mentioned beam-beam interaction features and possible techniques to reduce the emittance growth.
BNL, Upton, Long Island, New York
A beam-based method was proposed and applied to check the polarities of the arc sextupoles in the Relativistic Heavy Ion Collider (RHIC) with repetitive local horizontal bumps. Wrong sextupole polarities can be easily identified from mismatched signs and amplitudes of the horizontal and vertical tune shifts from bump to bump and/or from arc to arc. This check takes less than 2 hours for both RHIC Blue and Yellow rings. Tune shifts in both planes during this study were tracked with a high-resolution baseband tunemeter (BBQ) system. This method was successfully used to the sextupole polarity check in the RHIC run06.
BNL, Upton, Long Island, New York
To achieve the RHIC polarized proton enhanced luminosity goal of 150*1030 cm-2 sec-1 on average in stores at 250 GeV, the luminosity needs to be increased by a factor of 3 compared to what was achieved in 2006. Since the number of bunches is already at its maximum of 111, limited by the injection kickers and the experiments' time resolution, the luminosity can only be increased by either increasing the bunch intensity and/or reducing the beam emittance. This leads to a larger beam-beam tuneshift parameter. Operation during 2006 has shown that the beam-beam interaction is already dominating the luminosity lifetime. To overcome this limitation, a near-integer working point is under study. We will present recent results of these studies.
BNL, Upton, Long Island, New York
IAP, Frankfurt am Main
The EBIS (Electron Beam Ion Source) Project at Brookhaven National Laboratory is in the second year of a four-year project. It will replace the Tandem Van de Graaff accelerators with an EBIS, an RFQ, and one IH Linac cavity as the heavy ion preinjector for the Relativistic Heavy Ion Collider (RHIC), and for the NASA Space Radiation Laboratory (NSRL). The preinjector will provide all ions species, He to U, (Q/m>0.16) at 2 MeV/amu at a repetition rate of 5 Hz, pulse length of 10–40 μs, and intensities of ~2.0 mA. End-to-end simulations (from EBIS to the Booster injection) as well as error sensitivity studies will be presented and physics issues will be discussed.
#Raparia@bnl.gov
BNL, Upton, Long Island, New York
There is significant interest in RHIC heavy ion collisions at c.m. energies of 5-50 GeV/u, motivated by a search for the QCD phase transition critical point. The low end of this energy range is well below the nominal RHIC injection c.m. energy of 19.6 GeV/u. There are several challenges that face RHIC operations in this regime, including longitudinal acceptance, magnet field quality, lattice control, and luminosity monitoring. We report on the status of work to address these challenges and include results from beam tests of low-energy RHIC operations with protons and gold.
BNL, Upton, Long Island, New York
We explore the possibility of using two non-scaling FFAG with a smaller number of distributed RF cavities for a high power heavy ion driver. The pulsed heavy ion source would consist of an Electron Beam Ion Source (EBIS), fed continuously from a high charge state Electron Cyclotron Resonance (ECR) source. The Radio Frequency Quadrupole (RFQ) and a short 10 MeV/u linac would follow the ion source. Microseconds long heavy ion beam bunches from the EBIS would be injected in a single turn into a multi-pass small aperture non-scaling Fixed Field Alternating Gradient (FFAG) accelerator. The heavy ion maximum kinetic energy is assumed to be 400 MeV/u with a total of 400 kW power for uranium ion beams. Partially stripped heavy ions would be accelerated from 10 MeV/u to 67 MeV/u with a first non-scaling FFAG, while, after further stripping, a second non-scaling FFAG would accelerate from 67 to 400 MeV/u.
BNL, Upton, Long Island, New York
There are three main sources of the experimental background at RHIC. The beam-gas induced background is associated with the vacuum pressure, the beam-chamber-interaction induced background can be improved by collimations, and the beam-beam induced background is somewhat inherent, and probably harmless for the experimental data taking. The zero degree calorimeter (ZDC) is an essential luminosity detector for heavy ion operations in RHIC. It is shown that, however, the ratio of ZDC singles (background) and coincident rate is also useful in proton runs for background evaluations. In this article, the experimental background problem in RHIC polarized proton runs is reported.
BNL, Upton, Long Island, New York
The beam emittance growth in RHIC polarized proton runs has a dependence on the dynamic pressure rise, which is caused by the electron cloud and peaked at the end of the beam injection and the early energy acceleration. This emittance growth is usually presented without beam instability, and it is slower than the ones above the instability threshold. The effect on the machine luminosity, nevertheless, is significant, and it is currently a limiting factor in machine performance. The electron cloud is substantially reduced at the store, the emittance growth there has no dependence on the bunch spacing and instead it has a clear dependence on the beam-beam parameter. The results of the machine operation and beam studies will be reported.