CERN, Geneva, Switzerland
Fermilab, Batavia, USA
The performance of the Tevatron collider demonstrated continuous growth over the course of Run II, with the peak luminosity reaching 4·1032 cm-2 s-1 and the weekly integration rate exceeding 70 pb-1. This report presents a review of the most important advances that contributed to this performance improvement, including beam dynamics modeling, precision optics measurements and stability control, implementation of collimation during low-beta squeeze. Algorithms employed for optimization of the luminosity integration are presented and the lessons learned from high-luminosity operation are discussed. Studies of novel accelerator physics concepts at the Tevatron are described, such as the collimation techniques using crystal collimator and hollow electron beam, and compensation of beam-beam effects.
BNL, Upton, Long Island, New York, USA
CERN, Geneva, Switzerland
CINVESTAV, Mérida, Mexico
A major concern for the implementation of crab crossing in a future high-luminosity LHC (HL-LHC) is machine protection in an event of a fast crab-cavity failure. Certain types of abrupt crab-cavity phase and amplitude changes are simulated to characterize the effect of failures on the beam and the resulting particle-loss signatures. The time-dependent beam loss distributions around the ring and particle trajectories obtained from the simulations allow for a first assessment of the resulting beam impact on LHC collimators and on sensitive components around the ring. The simulation results are used to derive tolerances on the maximum rate of change in crab-cavity phase and amplitude which can be allowed with regard to machine safety.
Fermilab, Batavia, USA
Muon Collider (MC) is a promising candidate for the next energy frontier machine. However, in order to obtain peak luminosity in the 1034cm-2s-1 range the collider lattice design must satisfy a number of stringent requirements. In particular the expected large momentum spread of the muon beam and the very small β* call for a careful correction of the chromatic effects. Here we present a particular solution for the interaction region (IR) optics whose distinctive feature is a three-sextupole local chromatic correction scheme. The scheme may be applied to other future machines where chromatic effects are expected to be large.
MPI-P, München, Germany
UCR, Riverside, California, USA
The Muon Ionization Cooling Experiment (MICE) is being built at the ISIS proton synchrotron at Rutherford Appleton Laboratory (RAL) to test ionization cooling of a muon beam. Production of particles in the MICE beamline begins with a titanium target dipping into the ISIS proton beam. The resulting pions are captured, momentum-selected, and fed into a 5T superconducting solenoid. This magnet contains the pions and their decay muons which are then sent through the rest of the MICE beamline toward the cooling channel. During recent data-taking, it was determined that there is a significant background contamination of neutral particles populating the MICE muon beam. This contamination creates unwanted triggers in MICE, thus reducing the percentage of useful data taken during running. This paper describes the analysis done with time-of-flight detectors, used to identify particle type, in order to understand the level of contamination in both positive and negative polarity muon beams.
Fermilab, Batavia, USA
Magnetically confined hollow electron beams for controlled halo removal in high-energy colliders such as the Tevatron or the LHC may extend traditional collimation systems beyond the intensity limits imposed by tolerable material damage. They may also improve collimation performance by suppressing loss spikes due to beam jitter and by increasing capture efficiency. A hollow electron gun was designed and tested at Fermilab for this purpose. It was installed in one of the Tevatron electron lenses in the summer of 2010. We present the results of the first tests of the hollow-beam collimation concept on individual 980-GeV antiproton bunches in the Tevatron.
LBNL, Berkeley, California, USA
BNL, Upton, Long Island, New York, USA
Heidelberg University, Heidelberg, Germany
We have constructed two pairs of fast ionization chambers (BRAN) for measurement and optimization of luminosity at IR1 and IR5 of the LHC. These devices are capable of monitoring the performance of the LHC at low luminosity 1028 cm-2s−1 during beam commissioning all the way up to the expected full luminosity of 1034 cm-2s−1 at 7.0 TeV. The ionization chambers measure the intensity of hadronic/electromagnetic showers produced by the forward neutral particles of LHC collisions. To predict and improve the understanding of the BRAN performance, we created a detailed FLUKA model of the detector and its surroundings. In this paper, we describe the model and the results of our simulations including the detector’s estimated response to pp collisions at beam energies of 3.5, 5.0, and 7.0 TeV per beam. In addition, these simulations show the sensitivity of the BRAN to the crossing angle of the two LHC beams. It is shown that the BRAN sensitivity to crossing angle is proportional to the measurement of crossing angle by the LHC beam position monitors.
BNL, Upton, Long Island, New York, USA
Vibrations of the cryogenic triplet magnets at the Relativistic Heavy Ion Collider (RHIC) are suspected to be causing the beam perturbations observed at frequencies around 10 Hz. Several solutions to counteract the effect have been considered in the past, including reinforcing the magnet base support assembly, a mechanical servo feedback system, and a local beam feedback system at each of the two experimental areas. However, implementation of the mechanical solutions would be expensive, and the local feedback system was insufficient since perturbation amplitudes outside the experimental areas were still problematic. A global 10 Hz orbit feedback system is currently under development at RHIC consisting of 36 beam position monitors (BPMs) and 12 small dedicated dipole corrector magnets in each of the two counter-rotating rings. A subset of the system consisting of 8 BPMs and 4 corrector magnets in each ring was installed and successfully tested during the RHIC 2010 run; and the complete system is being installed for the 2011 run. A description of the overall system architecture and results with beam will be discussed.
BNL, Upton, Long Island, New York, USA
The RHIC LLRF upgrade is a flexible, modular system. Output signals are generated by a custom designed XMC card with 4 high speed digital to analog converters interfaced to a high performance field programmable gate array (FPGA). This paper discusses the hardware details of the XMC DAC board as well as the implementation of a low noise rf synthesizer with digital IQ modulation. This synthesizer also provides injection phase cogging and frequency hop rebucketing capabilities.
SLAC, Menlo Park, California, USA
LPSC, Grenoble, France
CERN, Geneva, Switzerland
INFN/LNF, Frascati (Roma), Italy
BINP SB RAS, Novosibirsk, Russia
IN2P3-LAPP, Annecy-le-Vieux, France
CEA, Gif-sur-Yvette, France
INFN Genova, Genova, Italy
University of Pisa and INFN, Pisa, Italy
BINP, Novosibirsk, Russia
LAL, Orsay, France
The SuperB international team continues to optimize the design of an electron-positron collider, which will allow the enhanced study of the origins of flavor physics. The project combines the best features of a linear collider (high single-collision luminosity) and a storage-ring collider (high repetition rate), bringing together all accelerator physics aspects to make a very high luminosity of 1036 cm-2 s-1. This asymmetric-energy collider with a polarized electron beam will produce hundreds of millions of B-mesons at the Y(4S) resonance. The present design is based on extremely low emittance beams colliding at a large Piwinski angle to allow very low ßy* without the need for ultra short bunches. Use of crab-waist sextupoles will enhance the luminosity, suppressing dangerous resonances and allowing for a higher beam-beam parameter. The project has flexible beam parameters, improved dynamic aperture, and spin-rotators in the Low Energy Ring for longitudinal polarization of the electron beam at the Interaction Point. Optimized for best colliding-beam performance, the facility may also provide high-brightness photon beams for synchrotron-radiation applications.
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
Kink instability presents one of the limiting factors from achieving higher luminosity in ERL based electron ion collider (EIC). However, we can take advantage of the flexibility of the linac and design a feedback system to cure the instability. This scheme raises the threshold of kink instability dramatically and provides for higher luminosity. We studied the effectiveness of this system and its dependence on the amplitude and phase of the feedback. In this paper we present results of theses studies of this scheme and describe its theoretical and practical limitations.
BNL, Upton, Long Island, New York, USA
Fermilab, Batavia, USA
LBNL, Berkeley, California, USA
An alternate structure for the 120mm Nb3Sn quadrupole magnet is presently under development for use in the upgrade for LHC at CERN. The design aims to build on existing technology developed in LARP with the LQ and HQ magnets and to further optimize the features required for operation in the accelerator. The structure includes features for maintaining mechanical alignment of the coils to achieve the required field quality. It also includes a helium containment vessel and provisions for cooling with 1.9k helium. The development effort includes the assembly of a six inch model to verify required coil load is achieved. Status of the R&D effort and an update on the magnet design, including its incorporation into the design of a complete one meter long cold mass is presented.
LBNL, Berkeley, California, USA
Fermilab, Batavia, USA
BNL, Upton, Long Island, New York, USA
Particle Beam Lasers, Inc., Northridge, California, USA
BNL, Upton, Long Island, New York, USA
UCLA, Los Angeles, California, USA
For a muon collider with copious decay particles in the plane of the storage ring, open-midplane dipoles (OMD) may be preferable to tungsten-shielded cosine-theta dipoles of large aperture. The OMD should have its midplane completely free of material, so as to dodge the radiation from decaying muons. Analysis funded by a Phase I SBIR suggests that a field of 10-20 T should be feasible, with homogeneity of 1x10-4 and energy deposition low enough for conduction cooling to 4.2 K helium. If funded, a Phase II SBIR would refine the analysis and build and test a proof-of-principle magnet.
BNL, Upton, Long Island, New York, USA
CERN, Geneva, Switzerland
LBNL, Berkeley, California, USA
The Luminosity Monitors for the high luminosity regions in the LHC have been operating to monitor and optimize the luminosity since the beginning of the 2009 run. The device is a gas ionization chamber, which has the ability to resolve bunch-by-bunch luminosity as well as survive the extreme levels of radiation at nominal high intensity LHC operations. The chambers are installed at the zero degree collision angle inside the neutral absorbers 140 m from the interaction point and monitor showers produced by high energy neutral particles from the collisions. A second device, a photo-multiplier based system (PMT) located directly behind the gas ionization chamber, has been also used at low luminosities. We will present operational results for the ionization chambers for both pp and Pb-Pb collisions. These measurements include signal, noise and background studies, and correlation between the gas ionization detector and the PMT. Also, comparison with ongoing modeling efforts will be included.
LBNL, Berkeley, California, USA
BNL, Upton, Long Island, New York, USA
To increase luminosity in the Relativistic Heavy Ion Collider’s (RHIC’s) polarized proton 250 GeV operations, we are considering reducing beta* to 0.65 m at the interaction points (IPs), and increasing bunch intensity. The new working point near the 2/3 integer will used on the ramp to preserve polarization. In addition, we plan to adjust the betatron-phase advances between IP6 and IP8 to (k+1/2)*PI so to lower the dynamic beta-beat from the beam-beam interaction. The effects of all these changes will impact the dynamic aperture, and hence, it must be evaluated carefully. In this article, we present the results of tracking the dynamic aperture with the proposed lattices.
LBNL, Berkeley, California, USA
Beam-beam effects limit luminosity in high energy colliders. Parallel beam-beam simulation codes were developed to study those beam-beam effects and to help the collider design. In this paper, we will present a parallel optimization algorithm integrating together with the parallel beam-beam simulation to optimize the luminosity of the colliding beams. This algorithm is based on a differential evolutionary global optimization method and takes advantage of the two-level parallelization in both parallel search and parallel objective function evaluation. This significantly increases the scalability of the simulation on peta-scale supercomputers and reduces the time for finding the optimal working point.
JLAB, Newport News, Virginia, USA
Macalester, St. Paul, Minnesota, USA
UCB, Berkeley, California, USA
The Medium-energy Electron Ion Collider (MEIC), a proposed medium-energy ring-ring electron-ion collider based on CEBAF at Jefferson Lab. The collider luminosity and stability are sensitive to the choice of a working point – the betatron and synchrotron tunes of the two colliding beams. Therefore, a careful selection of the working point is essential for stable operation of the collider, as well as for achieving high luminosity. Here we describe a novel approach for locating an optimal working point based on evolutionary algorithm techniques.
BNL, Upton, Long Island, New York, USA
As part of the search for a phase transition or critical point on the QCD phase diagram, an energy scan including 5 different energy settings was performed during the 2010 RHIC heavy ion run. While the top beam energy for heavy ions is at 100 GeV/n and the lowest achieved energy setpoint was significantly below RHICs injection energy of approximately 10 GeV/n, we also provided beams for data taking in a medium energy range above injection energy and below top beam energy. This paper reviews RHIC experience and challenges for RHIC medium energy operations that produced full experimental data sets at beam energies of 31.2 GeV/n and 19.5 GeV/n.
BNL, Upton, Long Island, New York, USA
RHIC operated at energies below the nominal ion injection energy of E=9.8 GeV/u in 2010. Earlier test runs and magnet measurements indicated that all defocusing sextupole unipolar power supplies should be reversed to provide the proper sign of chromaticity. However, vertical chromaticity at E=3.85 GeV/u with this power supply configuration was still not optimal. This uncertainty inspired a new machine configuration where only half of the defocusing sextupole power supplies were reversed, taking advantage of the flexibility of the RHIC nonlinear chromaticity correction system to mimic bipolar sextupoles. This configuration resulted in a 30 percent luminosity gain and eliminated the need for further polarity changes for later 2010 low energy physics operations. Here we describe the background to this problem, operational experience, and RHIC online model changes to implement this solution.
SLAC, Menlo Park, California, USA
IN2P3-LAPP, Annecy-le-Vieux, France
INFN/LNF, Frascati (Roma), Italy
We present a vibration budget for the SuperB accelerator. This includes ground motion data, motion sensitivity of machine components, and beam feedback system requirements.
BNL, Upton, Long Island, New York, USA
The low-energy physics program at the Relativistic Heavy Ion Collider (RHIC), motivated by a search for the QCD phase transition critical point, requires operation at low energies. At these energies, large nonlinear magnetic field errors and large beam sizes produce low beam lifetimes. A variety of beam dynamics effects such as Intrabeam Scattering (IBS), space charge and beam-beam forces also contribute. All these effects are important to understand beam lifetime limitations in RHIC at low energies. During the low-energy RHIC physics run in May-June 2010 at beam γ=6.1 and γ=4.1, gold beam lifetimes were measured for various values of space-charge tune shifts, transverse acceptance limitation by collimators, synchrotron tunes and RF voltage. This paper summarizes our observations and initial findings.
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.
JLAB, Newport News, Virginia, USA
Northern Illinois University, DeKalb, Illinois, USA
Cockcroft Institute, Warrington, Cheshire, United Kingdom
GOO Zaryad, Novosibirsk, Russia
ANL, Argonne, USA
ODU, Norfolk, Virginia, USA
SLAC, Menlo Park, California, USA
An electron-ion collider (MEIC) is envisioned as the primary future of the JLab nuclear science program beyond the 12 GeV upgraded CEBAF. The present MEIC design selects a ring-ring collider option and covers a CM energy range up to 51 GeV for both polarized light ions and un-polarized heavy ions, while higher CM energies could be reached by a future upgrade. The MEIC stored colliding ion beams, which will be generated, accumulated and accelerated in a green field ion complex, are designed to match the stored electron beam injected at full energy from the CEBAF in terms of emittance, bunch length, charge and repetition frequency. This design strategy ensures a high luminosity above 1034 s−1cm-2. A unique figure-8 shape collider ring is adopted for advantages of preserving ion polarization during acceleration and accommodation of a polarized deuteron beam for collisions. Our recent effort has been focused on completing this conceptual design as well as design optimization of major components. Significant progress has also been made in accelerator R&D including chromatic correction and dynamical aperture, beam-beam, high energy electron cooling and polarization tracking.