CERN, Geneva
The LHC hardware and beam commissioning and initial operation will be reviewed both in terms of beam and hardware performance. The implemented machine protection measures and their impact on LHC operation will be presented.
Muons, Inc, Batavia
Fermilab, Batavia
We study electron-positron in-flight annihilation as a potential source of quasi-monoenergetic photon (or gamma-ray) beams. A high-intensity tunable-energy (1.5 MeV to 15 MeV) gamma source has many potential uses in medical, industrial and security applications. Several electron-positron collision geometries are considered: a) head-on; b) collinear; and c) positron beam incident on a fixed electron target. We analyze advantages of each of the geometries in order to optimize parameters of the generated gamma-ray beams.
KEK, Ibaraki
The KEKB is a high luminosity accelerator which achieved the highest luminosity record of 2.1x1034. It requires the precise and stable beam control to keep its high luminosity continually. Slight change of the magnetic field may easily deteriorate the performance of the collisions of the very small and thin beams. The field measurement accuracy better than 10-4 has been already achieved. The resolution of the measurement has reached to a few 10-5. But it is known by the beam studies that the field change less than 10-4 may cause deterioration of the luminosity. The requirement on the stability of magnetic field will be stricter for future nano beam colliders. We have studied the effects of the following conditions on the magnetic field by using some KEKB magnets: changes of the magnetic field due to air or cooling water temperature, changes due to initialization conditions, field coupling between the adjacent magnets, effect of excitation of the adjacent magnet and behavior of the magnetic field under polarity change have been measured. These studies are not only useful for the existing KEKB but also important for future nano beam accelerators.
KEK, Ibaraki
To supply the electrical power for the superconducting correctors in the interaction region of the proposed SuperKEKB, a kind of vapor cooled current leads is designed, which consists of 8 brass leads and can transport currents to 4 correctors simultaneously. The design current of the leads is about 50 A. The thermal and electrical behaviors have studied by the finite elements method and the cryogenic experiment is also planed to validate the performance. In this paper the design will be presented and the finite element model will be compared with the experimental data.
Fermilab, Batavia
Magnetic and mechanical designs of a superconducting quadrupole magnet with 120-mm aperture suitable for interaction regions of hadron colliders are presented. The magnet is based on a two-layer shell-type coil and a cold iron yoke. Special spacers made of a low-Z material are implemented in the coil midplanes to reduce the level of radiation heat deposition in the coil. The quadrupole mechanical structure is based on a thick aluminum collar supported by the iron yoke and stainless steel skin. Magnet parameters including maximum field gradient, field quality and temperature margin for NbTi or Nb3Sn coils at the operating temperatures of 1.9 K and 4.5 K are reported. The level and distribution of radiation heat deposition in the coil and other magnet components are discussed.
LBNL, Berkeley, California
Fermilab, Batavia
BNL, Upton, Long Island, New York
Advanced superconductors such as Nb3Sn are being considered for future magnet upgrades of the Large Hadron Collider (LHC) at CERN. The US LHC Accelerator Research Program (LARP) has developed a large bore (120mm) Nb3Sn IR quadrupole (HQ) capable of reaching 15 T at its conductor and a gradients of 199T/m at 4.4K and 219T/m at 1.9K. HQ is addressing coil alignment and accelerator field quality in a shell-based mechanical structure. In this paper we summarize the fabrication, assembly and initial test results of the 1 m long two-layer magnet.
SLAC, Menlo Park, California
LBNL, Berkeley, California
CERN, Geneva
CEA, Gif-sur-Yvette
Lancaster University, Lancaster
We present results from the measurement of the 3-D luminosity distribution with the ATLAS Inner Detector during early running. The spatial distribution of pp interactions is reconstructed by a dedicated algorithm in the High-Level Trigger that fits tracks and primary event vertices in real time, and by an offline algorithm that takes full advantage of the high tracking efficiency and resolution. The number of vertices provides online monitoring of the instantaneous luminosity, while luminous-centroid motion mirrors IP-orbit and RF-phase drifts. The x, y and z luminous widths reflect the evolution of the transverse and longitudinal emittances. The length scales of the IP orbit bumps, which directly impact the accuracy of the transverse convolved beam sizes measured during van der Meer scans, are calibrated offline against the measured displacement of the luminous centroid; this significantly improves the accuracy of the absolute luminosity calibration. The simultaneous determination, during such scans, of the transverse convolved beam sizes (from the luminosity variation) and of the corresponding luminous sizes can be used to disentangle the transverse IP sizes of the two beams.
BNL, Upton, Long Island, New York
CERN, Geneva
Using the vernier scan or Van der Meer scan technique, where one beam is swept stepwise across the other while measuring the collision rate as a function of beam displacement, the transverse beam profiles, the luminosity and the effective cross section of the detector in question can be measured. This report briefly recalls the vernier scan method and presents results from the first RHIC polarized proton run at 250 GeV/beam in 2009.
CERN, Geneva
Once circulating beams have been established in the LHC the first step towards collisions is to remove the physical separation used to avoid collisions during injection and ramp. A residual separation can remain after the collapsing of the separation bumps. The so-called Van Der Meer method allows for a minimization of this unwanted separation by transversally scanning one beam through the other. The beam sizes at the IP can also be determined by this method and used to give an absolute measurement of the luminosity. We report on how this measurement was implemented and performed in the LHC to optimize and calibrate luminosity.
Fermilab, Batavia
Synchro-betatron resonances can lead to emittance growth and the loss of luminosity. We consider the detailed dynamics of a bunch near such a low order resonance driven by crossing angles at the collision points. We characterize the nature of diffusion and find that it is anomalous and sub-diffusive. This affects both the shape of the beam distribution and the time scales for growth. Predictions of a simplified anomalous diffusion model are compared with direct simulations.
Heidelberg University, Heidelberg
LBNL, Berkeley, California
BNL, Upton, Long Island, New York
CERN, Geneva
The LHC BRAN luminosity detector monitors the high luminosity interaction regions (Atlas and CMS). This chamber, which is an Argon gas ionization detector measures the forward neutral particles from collisions the interaction region. To predict and improve the understanding of the detector's performance, we produced a detailed model of the detector and its surroundings in FLUKA. In this paper, we present the model and results of our simulations including the detector's estimated response to interactions for beam energies of 3.5, 5.0, and 7.0 TeV.
LBNL, Berkeley, California
CERN, Geneva
BNL, Upton, Long Island, New York
The Luminosity Monitor for the LHC is ready for operation during the planned 2009-2010 run. The device designed for the high luminosity regions is a gas ionization chamber, that is designed with the ability to resolve bunch by bunch luminosity as well as survive extreme levels of radiation. The devices are installed at the zero degree collision angle in the TAN absorbers ±140m from the IP and monitor showers produced by high energy neutrons from the IP. They are used in real time as a collider operations tool for optimizing the luminosity at ATLAS and CMS. A photo-multiplier based system is used at low luminosities and also available. We will present early test results, noise and background studies and correlation between the gas ionization and the PMT. Comparison with ongoing modeling efforts will be included.
BNL, Upton, Long Island, New York
Since the last successful RHIC Au+Au run in 2007 (Run7), the RHIC experiments have made numerous detector improvements and upgrades. In order to benefit from the enhanced detector capabilities and to increase the yield of rare events in the acquired heavy ion data a significant increase in luminosity is essential. In Run7 RHIC achieved an average store luminosity of <L>=12x1026 cm-2 s-1 by operating with 103 bunches (out of 110 possible), and by squeezing to β*=0.8 m. Our goal for this year's run, Run10, was to achieve an average of <L>=27x1026 cm-2 s-1. The measures taken were decreasing β* to 0.6 m, and reducing longitudinal and transverse emittances by means of bunched-beam stochastic cooling. In addition we introduced a lattice to suppress intra-beam scattering (IBS) in both RHIC rings, upgraded the RF system, and separated transition crossings in both rings while ramping. We present an overview of the changes and the results in terms of Run10 increased instantaneous luminosity, luminosity lifetime, and integrated luminosity.
BNL, Upton, Long Island, New York
In this report we present recent experimental data from the Relativistic Heavy ion Collider (RHIC) illustrating effects resulting from of ~ 10 Hz vibrations of the triplet quadrupole magnets in the interactions regions and evaluate the impact of these vibrations on RHIC collider performance. Measurements revealed modulation of the betatron tunes of appreciable magnitude relative to the beam-beam parameter. Comparison of the discrete frequencies in the spectra of the measured beam positions and betatron tunes confirmed a common source. The tune modulations were shown to result from feed-down in the sextupole magnets in the interaction regions. In addition we show that the distortions to the closed orbit of the two counter-rotating beams produced a modulated crossing angle at the interaction point(s).
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.
BNL, Upton, Long Island, New York
University of Tuebingen, Tuebingen
Installation of electron lenses for the purpose of head-on beam-beam compensation is foreseen at RHIC. To optimize the relative alignment of the electron lens beam with the circulating proton (or ion) beam, photon detectors will be installed to measure the bremsstrahlung generated by momentum transfer from protons to electrons. We present the detector layout and simulations of the bremsstrahlung signal as function of beam offset and crossing angle.
BNL, Upton, Long Island, New York
CERN, Geneva
IR4 is a potential candidate for the installation of crab cavities in the CERN Large Hadron Collider. In this paper we present several operational scenarios in which the effect of the kick imparted by the cavity is enhanced by performing a dynamic unsqueeze of the beta function at collision energy. Linear optics, power supply requirements, beam aperture and finally potential luminosity increase studies will be discussed in order to rank and assess the feasibility of the various options.
KEK, Ibaraki
Crab cavities were installed in the KEKB rings in order to increase the luminosity. We measured the tilt of the bunches in the x-z plane using streak cameras. In a previous report*, the measured tilt in the HER was 2 times smaller than the expected crabbing angle, while the LER measurement was consistent with that expected. After the streak camera's vertical sweep speed was calibrated, the results were consistent with the expected crabbing angle in both rings.
* H. Ikeda et al., PAC07, 4018.
BNL, Upton, Long Island, New York
The Relativistic Heavy Ion Collider (RHIC) operates with either ions or polarized protons. After increasing the heavy ion luminosity by two orders of magnitude since its commissioning in 2000, the current luminosity upgrade program aims for an increase by another factor of 4 by means of 3D stochastic cooling and a new 56 MHz SRF system. An Electron Beam Ion Source is being commissioned that will allow the use of uranium beams. Electron cooling is considered for collider operation below the current injection energy. For the polarized proton operation both luminosity and polarization are important. In addition to ongoing improvements in the AGS injector, the development of a new high-intensity polarized source has started. In RHIC a number of upgrades are under way to increase the intensity and polarization transmission to 250 GeV beam energy. Electron lenses will be installed to partially compensate the head-on beam-beam effect.
BNL, Upton, Long Island, New York
CERN, Geneva
The 3rd LHC Crab Cavity workshop (LHC-CC09) took place at CERN in October 2009. It reviewed the current status and identified a clear strategy towards a future crab-cavity implementation. Following the success of crab cavities in KEK-B and the strong potential for luminosity gain and leveling, CERN will pursue crab crossing for the LHC upgrade. We present the summaries of the various workshop sessions which have led to the LHC crab-cavity strategy, covering topics like layout, cryomodule design, construction, integration, validation, and planning.
IN2P3-LAPP, Annecy-le-Vieux
INFN/LNF, Frascati (Roma)
Following previous measurements, more detailed preliminary ground motion measurements have been performed at the LNF site for the Super B project site characterization. First, results of vertical ground motion measurements done during 18 hours are shown in order to get an idea of the evolution of the ground motion amplitude with time. Secondly, measurements of ground motion (in the 3 directions of space) were performed at different locations on surface in order to evaluate and to compare the influence of various vibration sources. Then, results of ground motion coherence measured for different distances at two locations close to each other but with soft and rigid floor are compared. These measurements are also compared to the ones done in the ATF2 beam line where a special floor was built for stability. By this way, the results reveal that the LNF is a good site to use ground motion coherence properties for stability like it has been done for ATF2.
INFN/LNF, Frascati (Roma)
LPSC, Grenoble
SLAC, Menlo Park, California
CERN, Geneva
IN2P3-LAPP, Annecy-le-Vieux
LAL, Orsay
INFN-Pisa, Pisa
CEA, Gif-sur-Yvette
IN2P3 IPNL, Villeurbanne
BINP SB RAS, Novosibirsk
University of Pisa and INFN, Pisa
The SuperB project is an international effort aiming at building in Italy a very high luminosity e+e- (1036 cm-2 sec-1) asymmetric collider at the B mesons cm energy. The accelerator design has been extensively studied and changed during the past year. The present design, - based on the new collision scheme, with large Piwinski angle and the use of 'crab' sextupoles, which has been successfully tested at the DAPHNE Phi-Factory at LNF Frascati, - provides larger flexibility, better dynamic aperture and in the Low Energy Ring spin manipulation sections, needed for having longitudinal polarization of the electron beam at the Interaction Point. The Interaction Region has been further optimized in terms of apertures and reduced backgrounds in the detector. The injector complex design has been also updated. A summary of the design status, including details on lattice and spin manipulation will be presented in this paper.
INFN/LNF, Frascati (Roma)
An innovatory interaction region has been recently conceived and realized on the Frascati DAΦNE lepton collider. The concept of tight focusing and small crossing angle adopted until now to achieve high luminosity in multibunch collisions has evolved towards enhanced beam focusing at the interaction point with large horizontal crossing angle, thanks to a new compensation mechanism for the beam-beam resonances. The novel configuration has been tested with a small detector without solenoidal field yielding a remarkable improvement in term of peak as well as integrated luminosity. The high luminosity interaction region has now been modified to host a large detector with a strong solenoidal field integral which significantly perturbs the beam optics introducing new design challenges in terms of interaction region optics design, beam transverse coupling control and beam stay clear requirements.
INFN/LNF, Frascati (Roma)
CERN, Geneva
BINP SB RAS, Novosibirsk
Recently the peak luminosity achieved on the DAΦNE collider has been improved by almost a factor 3 by implementing a novel collision scheme based on large Piwinski angle and Crab-Waist. This encouraging result opened new perspectives for physics research and a new run with the KLOE-2 detector has been scheduled to start by spring 2010. The KLOE-2 installation is a complex operation requiring a careful design effort and a several months long shutdown. The high luminosity interaction region has been deeply revised in order to take into account the effect on the beam caused by the solenoidal field of the experimental detector and to ensure background rejection. The shutdown has been also used to implement several other modifications aimed at improving beam dynamics: the wiggler poles have been displaced from the magnet axis in order to cancel high order terms in the field, the feedback systems have been equipped with stronger power supplies and more efficient kickers and electrodes have been inserted inside the wiggler and the dipole vacuum chambers, in the positron ring, to avoid the e-cloud formation. A low level RF feedback has been added to the cavity control in both rings.
KEK, Ibaraki
A new set of magnets, skew sextupole magnets, were designed, manufactured, measured and installed during the winter shutdown of 2009. Twenty magnets were installed in the HER and eight magnets were installed in the LER. It was a challenging job for the magnet group to design, manufacture, measure the magnetic field and install them in the tunnel in just three months. Much effort to finish the installation in time and reduce the production cost was made at every step of the entire process. With these newly installed skew sextupole magnets, a significant luminosity boost was achieved. The production and installation of the skew sextupole magnets are described in this report.
KEK, Ibaraki
Eight superconducting accelerating cavities have been stably operated in the KEKB with sufficiently low trip rates. Two superconducting crab cavities were installed in 2007 and soon the crab crossing operation started. Recently the KEKB luminosity reached the world record of 2.1 x 1034 cm-1s-1. Stable operations of the accelerating cavities contributed for the luminosity increase. For the future Super-KEKB, we are developing a high power coupler for an input power of 600 kW and a HOM damper for RF power absorption more than 30 kW. The Super-KEKB requires RF operations with the high beam loading and the low RF voltage than the present KEKB operation. To suppress klystron output powers the external Q value has to be reduced. A new operation was proposed for superconducting cavities. In order to keep high RF voltages in each cavity, some cavities reverse its synchronous beam phase while the total RF voltage is kept as low as the required one. Beam studies were successfully carried out with one cavity reversed its synchronous beam phase.
KEK, Ibaraki
Optics parameters at the interaction point, beta, x-y coupling, dispersion and their chromatic aberrations, seriously affect the beam-beam performance as is shown in experiments and simulations. The control of the optics parameters is essential to maintain the high luminosity in KEKB. They drift day by day, or before and after the beam abort. They were often monitored at intervals of the operation with taking the study time. They are recently measured during the physics run using a pilot bunch without collision. We show the measured the optics parameters and their variations and discuss the relation to the luminosity.
KEK, Ibaraki
Super B factories are designed with very low emittance and very low beta function at the interaction point. The two beams collide with a large crossing angle, thus the overlap area of the beams is limited at a small part of their length. Simulation of the beam-beam effects is hard because of the longitudinal slice of the beam is the order of 100. We discuss two methods for the simulation. One is a simplified method, which is mixture of the particle in cell and Gaussian approximation. The other is fully strong-strong simulation using the particle in cell. The shifted Green function is used to calculate the beam-beam force for less overlap of the beam distribution. Luminosity and its degradation due to IP optics errors in Super B factories are discussed.
KEK, Ibaraki
Using a weak-strong beam-beam code, in which the symplectic maps for the linear coupling and chromatic aberrations were implemented, the luminosity degradation caused by the linear and chromatic X-Y couplings at the interaction point (IP) were evaluated for the SuperKEKB project under design. The linear and chromatic X-Y couplings were estimated through modeling the machine errors using random seeds, based on a baseline design of the SuperKEKB rings. It was found that the linear and chromatic X-Y couplings can potentially degrade the luminosity performance.
IHEP Beijing, Beijing
IHEP Beiing, Beijing
As a tau-charm factory like collider, the upgrade project of the Beijing Electron Positron Collider (BEPCII), has reached its first design value of luminosity. During the commissioning of its luminosity, beam optics recovery, machine parameters measurement, detector solenoid compensation, and instability cure are main problems we met. Besides commissioning the machine, beams were delivered to the users from high energy physics and synchrotron radiation. This paper summarizes the accelerator physics issues in the BEPCII luminosity commissioning.
Supported by National Natural Sciences Foundation of China (10725525)
Fermilab, Batavia
JINR, Dubna, Moscow Region
Design of a muon collider interaction region (IR) presents a number of challenges arising from low beta* < 1 cm, correspondingly large beta-function values and beam sizes at IR magnets, as well as the necessity to protect superconducting magnets and collider detectors from muon decay products. As a consequence, the designs of the IR optics, magnets and machine-detector interface are strongly interlaced and iterative. A consistent solution for the 1.5 TeV c.o.m. muon collider IR is presented. It can provide an average luminosity of 1034/cm2/s with an adequate protection of magnet and detector components.
SLAC, Menlo Park, California
We present a conceptual design for a polarimeter based on Compton scattering of laser light on the electron beam for the Super-B accelerator proposed for Frascati, Italy. The accelerator design has polarized electrons in the low-energy ring (4.18 GeV). We want to measure the polarization of every bunch every few seconds using a laser with 119 Mhz repetition rate. The spin rotator section has a second point between the solenoids and interaction point where the polarization is nearly longitudinal with helicity opposite to that found at the interaction point. We plan to use this point to measure the polarization as the possible location near the interaction point has too much background from the collision. We show the area in the accelerator where the polarimeter would be installed and describe the laser as well as the detectors for the Compton scattered electrons and photons.
SLAC, Menlo Park, California
Cockcroft Institute, Warrington, Cheshire
INFN/LNF, Frascati (Roma)
BINP SB RAS, Novosibirsk
The availability of longitudinally polarized electrons is an important aspect of the design of the proposed SuperB project at LNF Frascati. Spin rotators are an integral part of the design of the Interaction Region (IR). We have chosen a solenoid-dipole design; at the 4.18 GeV nominal energy this is more compact that a design purely based on dipole magnets. Integration with the local chromaticity correction of the ultra-low beta* IR has been achieved. The spin rotators are symmetric about the Interaction Point, this design saves a significant amount of length as the dipoles become a part of the overall 360 deg. bend. The layout leaves limited opportunity to setup the optics for minimum depolarization; this is acceptable since beam life time in SuperB at high luminosity is only about 5 min and up-to 90% polarized electrons will be injected continuously. In this way an average beam polarization of about 70% is maintained. Simulations and analytic estimates with the DESY code SLICKTRACK and other codes indicate such operation is feasible from a spin-dynamics point of view. The paper will discuss the overall spin-rotator design as well as the spin dynamics in the ring.
MPI-P, München
IHEP Beijing, Beijing
Muon colliders would open new frontiers of investigation in high energy particle physics, allowing precision measurements to be made at the TeV energy frontier. One of the greatest challenges to constructing a muon collider is the cooling of a beam of muons on a timescale comparable to the lifetime of the muon. Frictional cooling holds promise for use in a muon collider scheme. By balancing energy loss to a gas with energy gain from an electric field, a beam of muons is brought to an equilibrium energy in 100s of nanoseconds. A frictional cooling scheme for producing high-luminosity beams for a muon collider is presented.
CERN, Geneva
UMAN, Manchester
Cockcroft Institute, Warrington, Cheshire
The University of Liverpool, Liverpool
DESY, Hamburg
DESY Zeuthen, Zeuthen
INFN-Bologna, Bologna
The LHeC aims at colliding hadron-lepton beams with center of mass energies in the TeV scale. For this purpose the existing LHC storage ring is extended by a high energy electron accelerator in the energy range of 60 to 140 GeV. The electron beam will be accelerated and stored in a LEP like storage ring in the LHC tunnel. In this paper we present the layout of the interaction region which has to deliver at the same time well matched beam optics and an efficient separation of the electron and proton beams. In general the large momentum difference of the two colliding beams provides a very elegant way to solve this problem: A focusing scheme that leads to the required beam sizes of the electrons and protons is combined with an early but gentle beam separation to avoid parasitic beam encounters and still keep the synchrotron radiation level in the IR within reasonable limits. We present in this paper two versions of this concept: A high luminosity layout where the mini beta magnets are embedded into the detector design as well as an IR design that is optimised for maximum acceptance of the particle detector.
CERN, Geneva
SLAC, Menlo Park, California
BNL, Upton, Long Island, New York
Cockcroft Institute, Warrington, Cheshire
The University of Liverpool, Liverpool
LPNHE, Paris
We consider three different scenarios for the recirculating electron linear accelerator (RLA) of a linac-ring type electron-proton collider based on the LHC (LHeC): i) a basic version consisting of a 60 GeV pulsed, 1.5 km long linac, ii) a higher luminosity configuration with a 60 GeV 4 km long cw energy-recovery linac (ERL), and iii) a high energy option using a 140 GeV pulsed linac of 4 km active length. This paper describes the footprint, optics of linac and return arcs, emittance growth from chromaticity and synchrotron radiation, a set of parameters, and the performance reach for the three scenarios.
BNL, Upton, Long Island, New York
Beam-beam effects in eRHIC have a number of unique features, which distinguish them from both hadron and lepton colliders. Due to beam-beam interaction, both electron and hadron beams would suffer quality degradation or beam loss from without proper treatments. Those features need novel study and dedicate countermeasures. We study the beam dynamics and resulting luminosity of the characteristics, including mismatch, disruption and pinch effects on electron beam, in additional to their consequences on the opposing beam as a wake field and other incoherent effects of hadron beam. We also carry out countermeasures to prevent beam quality degrade and coherent instability.
BNL, Upton, Long Island, New York
The luminosity of a ring-ring electron-ion collider is limited by the beam-beam effect on the electrons. Simulation studies have shown that for short ion bunches this limit can be significantly increased by head-on beam-beam compensation via an electron lens. However, due to the large beam-beam parameter experienced by the electrons, together with an ion bunch length comparable to the beta-function at the IP, electrons perform a sizeable fraction of a betatron oscillation period inside both the long ion bunches and the electron lens. Recent results of our simulation studies of this effect will be presented.
IHEP Beijing, Beijing
Optics correction is an important issue at BEPCII. Due to the errors in all kinds of components of a storage ring, the real optics of a storage ring is different from the design one. This paper introduces some developments of optics calibration at BEPCII storage ring. We use the method that fit the measured response matrix to the model response matrix to get the fudge factor of the quadrupole field and the sextupole field. On the other hand, in considering fringing fields of quadrupole magnet and interaction of quadrupole magnet iron core and sextupole magnet iron core, the model is calibrated.
CERN, Geneva
Background and loss rates vary when beams are brought into collisions in the LHC and when the beam separation is varied during luminosity scans. We report on the first observations in the early LHC operation. The observed effects are analyzed and compared with models and simulation.
JAI, Oxford
CERN, Geneva
Fermilab, Batavia
We present the current status of the beam tracking simulations of the Compact Linear Collider (CLIC) from the exit of the damping ring to the interaction point, including the ring to main linac (RTML) section, main linac, beam delivery system (BDS) and beam-beam interactions. This model introduces realistic alignment survey errors, dynamic imperfections and also the possibility to study collective effects in the main linac and the BDS. Special emphasis is put on low emittance transport and beam stabilization studies, applying beam based alignment methods and feedback systems. The aim is to perform realistic integrated simulations to obtain reliable luminosity predictions.
CASA, newport news
JLAB, Newport News, Virginia
One key limiting factor to a collider luminosity is bean-beam interactions which usually can cause serious emittance growth of colliding beams and fast reduction of luminosity. Such nonlinear collective beam effect can be a very serious design challenge when the machine parameters are pushed into a new regime. In this paper, we present simulation studies of the beam-beam effect for a medium energy ring-ring electron-ion collider based on CEBAF.
KEK, Ibaraki
KEKB, an asymmetric electron/positron double-ring collider, utilizes the crab cavity to perform the head-on collision at the interaction point. We observed peculiar phenomena at the transition from the collision to non-collision, where the bunch length slightly changed, even though the beam current and the RF related parameters were almost constant. We also observed that the transverse beam size of both beams changed at the transition. An experimental study was carried out to investigate whether the bunch length would change or not, when the vertical beam size was intentionally changed. The bunch length was measured using a monitor based on the beam spectrum with a resolution of 0.01 mm. We found that the bunch length slightly changed together with the vertical beam size under non-colliding condition. We expect that the change in the bunch length is not caused by the colliding effects, but is related to the longitudinal space charge transformed from the transverse plane. Since the longitudinal space charge effect is negligible for the relativistic beams, some tilting effect of a bunch is suspected.
KEK, Ibaraki
As part of the design works of the interaction region (IR) of SuperKEKB (the upgrade of KEKB B-factory (KEKB)), the loss factor and impedance of beam ducts for the interaction point (IP duct) were calculated by GdfiedL. The IP duct is round and connected to beam ducts for electron and positron beams with a diameter of 20 mm via Y-shaped crotch ducts at both ends. The lengths of the straight section and crotch section are about 200 mm, respectively. The beam crossing angle is 83 mrad. Calculations for two types of IP duct were performed. Both ducts are almost same in design except for the diameter of the straight section (20 mm and 30 mm). The loss factors were about 0.001 V/pC in both cases when the bunch length was 6 mm. The longitudinal impedances showed that there were no modes trapped longitudinally in IP duct. However, from the results of the transverse impedance and eigenmode calculation, it was found that many TE modes can be trapped at the crotch section if the beam is off-center of the beam duct. For comparison, the loss factor and impedance of the IR beam duct of KEKB are also being calculated now. Full details of the calculation results will be provided in this report.
Fermilab, Batavia
Electron lenses are proposed as a way to mitigate head-on beam-beam effects for the LHC upgrade. An extensive effort was put together within the US LARP in order to develop numerical simulations of beam-beam effects in the presence of electron lenses. In this report the results of beam-beam simulations for RHIC and LHC are presented. The effect of electron lenses is demonstrated and sensitivity of beam-beam compensation to imperfections is discussed.
IHEP Beijing, Beijing
BEPCII is the upgrade project of the Beijing Electron Positron Collider (BEPC) with its design luminosity of 1x1033cm-2s-1 @1.89 GeV. The construction of BEPCII was completed in May 2008. The collider has been operated for high energy physics experiments since February 2009 with 1/5 of design luminosity at psi(3680). The luminosity has been steadily increased during the operation. Status and updated performance of BEPCII will be reported.
BNL, Upton, Long Island, New York
Future projects for electron-hadron colliders will be reviewed. Existing designs will be presented and, when possible, compared. The challenges and required R&D program will be discussed.
KEK, Ibaraki
KEKB is an e-/e+ collider for the study of B physics and is also used for machine studies for future machines. The peak luminosity of KEKB, which is the world-highest value, has been still increasing. This report summarizes recent progress at KEKB.
INFN/LNF, Frascati (Roma)
SLAC, Menlo Park, California
Rome University La Sapienza, Roma
The SuperB project has the goal to build in the Frascati or Tor Vergata area, an asymmetric e+/e- Super Flavor Factory to achieve a peak luminosity > 1036 cm-2 s-1. The SuperB design is based on collisions with extremely low vertical emittance beams. A source of emittance growth comes from the bunch by bunch feedback systems producing high power correction signals to damp the beams. To limit any undesirable effect, a large R&D program is in progress, partially funded by the INFN Fifth National Scientific Committee through the SFEED (SuperB feedback) project approved within the 2010 budget. One of the first steps of the R&D program consists in the upgrade and test of new 12-bit feedback systems in the vertical plane of the DAΦNE main rings. The systems are the direct evolution of the previous 8-bit system design by a KEK/SLAC/LNF collaboration, yielding a good compatibility with the powerful diagnostics and analysis programs developed in the past. Studies on their effects in the longitudinal plane are also in progress.
INFN/LNF, Frascati (Roma)
CERN, Geneva
In the two beam acceleration scheme the Main Beam must be precisely synchronized with respect to the RF power produced by the Drive Beam. Timing errors would have an impact on the collider performances. The Drive Beam phase errors should be controlled, by means of a feed forward system, within 0.1° (23fs @ 12GHz) to avoid a luminosity reduction larger than 2%. A beam phase arrival monitor is an essential component of the system. Its design has been based on the following main requirements: resolution of the order of 20fs, very low coupling impedance due to the very high beam current and integrated filtering elements to reject RF noise and weak fields in the beam pipe that could otherwise affect the measurements.
JAI, Oxford
The design luminosity of the future linear colliders requires transverse beam size at the nanometre level at the interaction point (IP), as well as stabilisation of the beams at the sub-nanometre level. Different imperfections, for example ground motion, can generate relative vertical offsets of the two colliding beams at the IP which significantly degrade the luminosity. In principle, a beam-based intra-train feedback system in the interaction region can correct the relative beam-beam offset and steer the beams back into collision. In addition, this feedback system might considerably help to relax the required tight stability tolerances of the final doublet magnets. For CLIC, with bunch separations of 0.5 ns and train length of 156 ns intra-train feedback corrections are specially challenging. In this paper we describe the design and simulation of an intra-train feedback system for CLIC. Results of luminosity performance simulation are presented and discussed.
JAI, Oxford
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
CERN, Geneva
SLAC, Menlo Park, California
Important efforts have recently been dedicated to the improvement of the design of the baseline collimation system of the Compact Linear Collider (CLIC). Different aspects of the design have been optimized: the transverse collimation depths have been recalculated in order to reduce the collimator wakefield effects while maintaining a good efficiency in cleaning the undesired beam halo; the geometric design of the spoilers have also been reviewed to minimize wakefields; in addition, the optics design have been polished to improve the collimation efficiency. This paper describes the current status of the CLIC collimation system after this optimization.
Cockcroft Institute, Lancaster University, Lancaster
JLAB, Newport News, Virginia
The planned luminosity upgrade to LHC is likely to necessitate a large crossing angle and a local crab crossing scheme. For this scheme crab cavities align bunches prior to collision. The scheme requires at least four such cavities, a pair on each beam line either side of the interaction point (IP). Upstream cavities initiate rotation and downstream cavities cancel rotation. Cancellation is usually done at a location where the optics has re-aligned the bunch. The beam line separation near the IP necessitates a more compact design than is possible with elliptical cavities such as those used at KEK. The reduction in size must be achieved without an increase in the operational frequency to maintain compatibility with the long bunch length of the LHC. This paper proposes a suitable superconducting variant of a four rod coaxial deflecting cavity (to be phased as a crab cavity), and presents analytical models and simulations of suitable designs.
CEA, Gif-sur-Yvette
The International Linear Collider reference design is based on a collision scheme with a 14 mrad crossing angle. Consequently, the detector solenoid and the machine axis do not coincide. It provokes a position offset of the beam at the Interaction Point in addition to a beam size growth. These effects are modified by the insertion of the anti-DID (Detector Integrated Dipole) aiming at reducing background in the detector. Furthermore a crab cavity is necessary to restore a 'head on' like collision, leading to higher luminosity. This introduces new beam distortions. In this paper, optics studies and simulations of beam transport in the Interaction Region taking these elements into account are presented. Correction schemes of the beam offset and beam size growth are exposed and their associated tolerances are evaluated.
CERN, Geneva
UMAN, Manchester
Uppsala University, Uppsala
The 1.5TeV CLIC beams, with a total power of 14MW per beam, are disrupted at the interaction point due to the very strong beam-beam effect. As a result, some 3.5MW reach the main dump in form of beamstrahlung photons. About 0.5MW of e+e- pairs with a very broad energy spectrum need to be disposed along the post-collision line. The conceptual design of this beam line will be presented. Emphasis will be on the optimization studies of the CLIC post-collision line design with respect to the energy deposition in windows, dumps and scrapers, on the design of the luminosity monitoring for a fast feedback to the beam steering and on the background conditions for the luminosity monitoring equipment.
CERN, Geneva
University of Oslo, Oslo
The physics experiments at CLIC will require that the machine scans lower than nominal centre-of-mass energy. We present different options to achieve this and discuss the implications for luminosity and the machine design.
CERN, Geneva
The Compact Linear Collider (CLIC) accelerator has strong precision requirements on the position of the beam. The beam position will be sensitive to external dynamic magnetic fields (stray fields) in the nanotesla regime. The impact of these fields on the CLIC main beam has been studied by performing simulations on the lattices and tolerances have been determined. Several mitigation techniques will be discussed.
CERN, Geneva
Beam-Beam background is one of the main issues of the CLIC MDI at 3 TeV CM. The background level have a significant impact on the interaction region design. This paper presents a study of the background expected rates versus luminosity according to different beam parameters and considering different machine conditions, using an integrated simulation of the Main LINAC and BDS sub-systems.
CERN, Geneva
Cockcroft Institute, Warrington, Cheshire
Fermilab, Batavia
JAI, Oxford
The CLIC BDS tuning, alignment and feedbacks studies have been typically performed independently and only over particular sections of the BDS. An effort is being put to integrate all these procedures to realistically evaluate the luminosity performance.
CERN, Geneva
The main detector solenoid and associated magnets can have an important impact on the CLIC luminosity. These effects are discussed for different solenoid designs. In particular, the luminosity loss due to incoherent synchrotron radiation in the experiment solenoid and QD0 overlap is evaluated. The impact of the AntiDiD (Anti Detector integrated Dipole) on luminosity and compensated techniques on beam optic distortion are also discussed.
CERN, Geneva
Cockcroft Institute, Warrington, Cheshire
JAI, Oxford
SLAC, Menlo Park, California
The CLIC Conceptual Design Report must be ready by 2010. This paper aims at addressing all the critical points of the CLIC BDS to be later implemented in the CDR. This includes risk evaluation and possible solutions to a number of selected points. The smooth and practical transition between the 500 GeV CLIC and the design energy of 3 TeV is also studied.
INFN/LNF, Frascati (Roma)
To achieve luminosities significantly higher than in existing machines, future storage-ring based colliders will need to operate in novel parameter regimes combining ultra-low emittance, large Piwinski angle and high bunch charge; implementation of techniques such as a "crab waist" will add further challenges. Understanding the beam-beam interaction in these situations will be essential for the design of future very high luminosity colliders. Recent developments in modeling tools for studying beam-beam effects, capable of investigating the relevant regimes, will be discussed and examples, including tests with crab waist collisions in DAΦNE, will be presented.
CERN, Geneva
I will briefly describe CERN's colliders starting with the ISR, going through LEP, and finishing with the LHC. The common threads will be discussed in terms of people and techniques. I will start by describing the incredible impact on accelerator physics of the almost forgotten, first ever hadron collider, the ISR. I will then present the construction and 12 years of operation of LEP. Finally I will also provide the first results of beam operation in the LHC as well as the plans for the near and far future.
KEK, Ibaraki
Hitachi Technologies and Services Co., Ltd., Kandatsu, Tsuchiura
Two superconducting crab cavities were successfully installed into the KEKB accelerator in January 2007. Since then the crab cavities have been in stable operation for 3 years up to now, thanks to reliable operation of the cryogenic system of the KEKB including a large-scale helium refrigerator. This means that the cryostat for the crab cavities was well designed and constructed properly, although there are some technical complexities in the cryostat, such as two helium vessels in a cryostat, a movable coaxial coupler which is cooled with liquid helium and so on. The KEKB cryogenic system was also appropriately modified to operate the two crab cavity cryostats stably. This cryogenic system is described in this presentation. A calorimetric method to measure the Q-factors of the crab cavities is suggested, which employs an electric compensation heater in the cryostat, instead of the conventional method, which measures the descending rate of liquid helium level. Measurement results of the Q-factors of crab cavities after being assembled in the cryostat and after being installed into the KEKB accelerator are compared with the vertical test results.
INFN-Ferrara, Ferrara
UNIFE, Ferrara
Univ. degli Studi di Padova, Padova
INFN/LNL, Legnaro (PD)
JINR, Dubna, Moscow Region
Channeling in bent crystals is a technique with high potential to steer charged-particle beams for several applications in accelerators physics. Revisited methods of silicon micromachining techniques allowed one to realize a new generation of crystals. Characterizations using x-ray diffraction, atomic force microscopy, high resolution transmission electron microscopy and ion beam analysis techniques, showed high quality of the crystals. A specifically designed holder allowed to mechanically bend a crystal at given curvature and remove unwanted torsion. Characterization of such crystals with 400 GeV at CERN H8 external line highlighted 85% single-pass efficiency. A selected crystal has been installed inside the SPS ring in the environment of the CERN experiment UA9 and successfully employed for collimation of the circulating beam.
On behalf of UA9 collaboration
CERN, Geneva
The Phase I Luminosity Upgrade of LHC (SLHC) will be based on a new Nb-Ti inner triplet for the high luminosity region ATLAS and CMS. The new proposed layout aims at pushing beta* down to 30 cm replacing the current LHC inner triplet, with longer ones operating at lower gradient (123 T/m) and therefore offering enough aperture for the beam to reduce beta* to its prescribed value. As a consequence of this new longer interaction region, the number of parasitic encounters will increase from 15 to 21 before the separation dipole D1, with an impact on the dynamic aperture of the machine. In this paper the effect of the beam-beam interaction is evaluated for the SLHC layout and optics, at injection and in collision, evaluating the possible impact of a few additional parasitic collisions inside and beyond the D1 separation dipole till the two beams do no longer occupy the same vacuum chamber. Whenever needed, a comparison with the nominal LHC will be given. Then a possible backup collision optics will be discussed for the SLHC, offering a much wider crossing angle at an intermediate beta* of 40 cm in order to reach a target dynamic aperture of 7.5 σ.
CERN, Geneva
During the first years of operation of the LHC unknown field errors or misalignments could lead to unmatched optics and discrepancies with respect to the model. This could affect some critical parameters such as the luminosity or the lifetime. It is therefore desirable to implement tools which allow for fine tuning of the IP optics and could be used during the commissioning phase of the LHC. In this paper we report on the implementation the performances and the limitations of these commissioning tools.
BINP SB RAS, Novosibirsk
We applied Frequency Map Analysis (FMA) - a method that is widely used to explore dynamics of Hamiltonian systems - to beam-beam effects study. The method turned out to be rather informative and illustrative in case of a novel Crab Waist collision approach, when "crab" focusing of colliding beams results in significant suppression of betatron coupling resonances. Application of FMA provides visible information about all the working resonances, their widths and locations in the planes of betatron tunes and betatron amplitudes, so the process of resonances suppression due to the beams crabbing is clearly seen.
BNL, Upton, Long Island, New York
SBU, Stony Brook, New York
The RHIC beam lifetime in polarized proton operation is dominated by the beam-beam effect, parameter modulations, and nonlinear magnet errors in the interaction region magnets. Sextupole and skew sextupole errors have been corrected deterministically for a number of years based on tune shift measurements with orbit bumps in the triplets. During the most recent polarized proton run 10- and 12-pole correctors were set through an iterative procedure, and used for the first time operationally in one of the beams. We report on the procedure to set these high-order multipole correctors and estimate their effect on the integrated luminosity.
KEK, Ibaraki
The KEKB and PEP-II B factories have achieved world record luminosities while doubling or tripling their original design luminosities. The demand now from the physics community is for Super B Factories with orders of magnitude higher luminosities than those achieved by the present generation of machines. This talk will discuss the next-generation B factories, which aim to push back the luminosity frontier in the search for physics beyond the Standard Model.
CERN, Geneva
The CLIC study is a site independent study exploring technological developments to extend linear colliders into the Multi-TeV colliding beam energy range at reasonable cost and power consumption. A conceptual design report (CDR) of an electron-positron Compact LInear Collider (CLIC) with a 3 TeV center-of-mass collision energy is presently being prepared including results of 25 years of R&D to address the feasibility of its novel and promising technology, especially in an ambitious Test Facility, CTF3. The R&D is performed by a multi-lateral CLIC/CTF3 collaboration strong of 37 volunteer institutes from 19 countries from which the outstanding work and results are reported.