| Paper | Title | Page |
|---|---|---|
| WEPP001 | Energy Loss of Coasting Gold Ions and Deutrons in RHIC | 2518 |
|
||
| The total energy loss of coasting gold ion beams was measured at RHIC at two energies, corresponding to a gamma of 75.2 and 107.4. We describe the experiment and observations and compare the measured total energy loss with expectations from ionization losses at the residual gas, the energy loss due to impedance and synchrotron radiation. We find that the measured energy losses are below what is expected from free space synchrotron radiation. We believe that this shows evidence for suppression of synchrotron radiation which is cut off at long wavelength by the presence of the conducting beam pipe. | ||
| WEPP002 | The Effect of Head-on Beam-beam Compensation on the Stochastic Boundaries and Particle Diffusion in RHIC | 2521 |
|
||
| To compensate the effects from the head-on beam-beam interactions in the polarized proton operation in the Relativistic Heavy Ion Collider (RHIC), an electron lens (e-lens) is proposed to collide head-on with the proton beam. We used an extended version of SixTrack for multiparticle beam-beam simulation in order to study the effect of the e-lens on the stochastic boundary and also on diffusion. The stochastic boundary was analyzed using Lypunov exponents and the diffusion was characterized as the average rms spread of the action after 104 turns. For both studies the simulations were performed with and without the e-lens and with full and partial compensation. | ||
| WEPP003 | Optics Flexibility in the LHC at Top Energy | 2524 |
|
||
| We report on studies of optics flexibility which allow for tune changes of the order of half a unit at top energy in the LHC. We describe how this could be done using one or several of the insertions IR2, IR4, IR8 or the main quadrupoles and discuss and compare the implications. This flexibility could be used to compensate for the loss in tune for high beta optics and may make it feasible to use the standard injection and ramp for these configurations. Potential further applications are also highlighted. | ||
| WEPP004 | Overall Optics Solutions for Very High Beta in Atlas | 2527 |
|
||
| An insertion optics with a beta-star of at least 2600 m has been requested by the ATLAS experiment at the LHC. This is very far from the standard LHC physics optics and implies a significant reduction in the phase advance from this insertion corresponding to about half a unit in tune. We describe several alternatives how this could be integrated in overall LHC optics solutions with the possibility to inject, ramp and un-squeeze to the required very high beta. | ||
| WEPP005 | Measurements and Effects of the Magnetic Hysteresis on the LHC Crossing Angle and Separation Bumps | 2530 |
|
||
| The superconducting orbit corrector magnets (MCBC and MCBY) in the Large Hadron Collider (LHC) at CERN will be used to generate parallel separation and crossing angles at the interaction points during the different phases that will bring the LHC beams into collision. However, the field errors generated by the inherent hysteresis in the operation region of the orbit correctors may lead to unwanted orbit perturbations that could have a critical effect on luminosity. This paper presents the results obtained from dedicated cryogenic measurements on the orbit correctors from the simulated results on the impact of the hysteresis on the LHC orbit. | ||
| WEPP006 | Effects of Ultraperipheral Nuclear Collisions in the LHC and their Alleviation | 2533 |
|
||
| Electromagnetic interactions between colliding heavy ions at the LHC are the sources of specific beam loss mechanisms that may quench superconducting magnets. We propose a simple yet efficient strategy to alleviate the effect of localized losses from bound-free pair production by spreading them out in several magnets by means of orbit bumps. We also consider the consequences of neutron emission by electromagnetic dissociation and show through simulations that ions modified by this process will be intercepted by the collimation system, without further modifications. | ||
| WEPP007 | Crab Compensation for LHC Beams | 2536 |
|
||
| An R&D program to establish a road map for the installation of crab cavities in the LHC is rapidly advancing. Both local and global crab schemes are under investigation to develop cavities that will be compatible with LHC optics and meet aperture requirements. The design of a prototype TM110 cavity and pertinent RF requirements including impedance estimates and damping are discussed. Some alternate cavity designs are also explored. The required optics modifications to accommodate the crab cavities and some particle stability studies are presented. | ||
| WEPP008 | Localizing Sources of Horizontal Orbit Oscillations at RHIC | 2539 |
|
||
| Horizontal oscillations of the closed orbit at frequencies around 10Hz are observed at RHIC. These oscillations lead to beam beam offsets at the collision point, resulting in emittance growth and reduced luminosity. An approach to localize the sources of these vibrations using a special mode of RHIC turn-by-turn BPM data is presented. Data from the 2005-06 are analyzed to spatially resolve the location of the dominant sources. | ||
| WEPP009 | Collimator Integration and Installation Example of One Object to be Installed in the LHC | 2542 |
|
||
| The collimation system is a vital part of the LHC project, protecting the accelerator against unavoidable regular and irregular beam loss. About 80 collimators will be installed in the machine before the first run. Two insertion regions are dedicated to collimation and these regions will be among the most radioactive in the LHC. The space available in the collimation regions is very restricted. It was therefore important to ensure that the 3-D integration of these areas of the LHC tunnel would allow straightforward installation of collimators and also exchange of collimators under the remote handling constraints imposed by high radiation levels. The paper describes the 3-D integration studies and verifications of the collimation regions combining the restricted space available, the dimensions of the different types of collimators and the space needed for transport and handling. The paper explains how installation has been planned and carried out taking into account the handling system and component availability. | ||
| WEPP010 | Scheduling the Powering Tests | 2545 |
|
||
| The Large Hadron Collider is now entering in its final phase before receiving beam, and the activities at CERN between 2007 and 2008 have shifted from installation work to the commissioning of the technical systems (“hardware commissioning”). Due to the unprecedented complexity of this machine, all the systems are or will be tested as far as possible before the cool-down starts. Systems are firstly tested individually before being globally tested together. The architecture of LHC, which is partitioned into eight cryogenically and electrically independent sectors, allows the commissioning on a sector by sector basis. When a sector reaches nominal cryogenic conditions, commissioning of the magnet powering system to nominal current for all magnets can be performed. This paper briefly describes the different activities to be performed during the powering tests of the superconducting magnet system and presents the scheduling issues raised by co-activities as well as the management of resources. | ||
| WEPP011 | Setup and Performance of RHIC for the 2008 Run with Deuteron and Gold Collisions | 2548 |
|
||
| This year deuterons and gold ions were collided in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) for the first time since 2003. The setup and performance of the collider for this run is reviewed with a focus on improvements that have led to an order of magnitude increase in luminosity since the 2003 run. | ||
| WEPP012 | Analysis of Optical Layouts for the Phase 1 Upgrade of the CERN Large Hadron Collider Insertion Regions | 2551 |
|
||
| In the framework of the studies for the upgrade of the insertions of the CERN Large Hadron Collider, four optical layouts were proposed with the aim of reducing the beta-function at the collision point down to 25 cm. The different candidate layouts are presented. Results from the studies performed on mechanical and dynamic aperture are summarized, together with the evaluation of beam-beam effects. Particular emphasis is given to the comparison of the optics performance, which led to retain two promising layouts for further investigation and development. | ||
| WEPP013 | Increasing the Integrated Luminosity of SLHC by Levelling via the Crossing Angle | 2554 |
|
||
| With an increase of luminosity by a factor of 10, the luminosity lifetime in an upgraded LHC would be limited to a few hours. Furthermore, schemes relying on stronger focusing and reduced beam current increase (which are intrisically less dangerous for machine protection) are penalized by a very short lifetime of around 2 hours. We show in this paper that the "early separation" scheme and/or crab cavities scheme lend themselves to a very efficient luminosity leveling scheme. It allows constant luminosity over many hours as well as a significant increase of integrated luminosity above the performance announced so far. This is achieved by adjusting the crossing angle rather than the beam size by means of a bump closed inside the experimental straight section, i.e. operationally simple. The initially large crossing angle reduces the beam-beam tune shift, allowing an increased beam current and higher performance for lower pile-up in the detector and lower energy deposition in the triplet. The impact of the required large Piwinski angle is investigated. | ||
| WEPP015 | Experience with IBS-suppression Lattice in RHIC | 2557 |
|
||
| An intra-beam scattering (IBS) is the limiting factor of the luminosity lifetime for RHIC operating with heavy ions. In order to suppress the IBS we designed and implemented new lattice with higher betatron tunes. This lattice had been developed during last three years and had been used for gold ions in yellow ring of the RHIC during d-Au part of the RHIC Run-8. The use of this lattice allowed both significant increases in the luminosity lifetime and the luminosity levels via reduction of beta-stars in the IPs. In this paper we report on the development, the tests and the performance of IBS-suppression lattice in RHIC, including the resulting increases in the peak and the average luminosity. We also report on our plans for future steps with the IBS suppression. | ||
| WEPP016 | FEL-based Coherent Electron Cooling for High-energy Hadron Colliders | 2560 |
|
||
|
Cooling intense high-energy hadron beams remains a major challenge in modern accelerator physics. Synchrotron radiation of such beams is too feeble and two common methods, stochastic and electron cooling, are not efficient in providing significant cooling for high energy hadron, especially proton, colliders. In this paper we discuss a practical scheme of Coherent Electron Cooling, which promises short cooling times (below one hour) for intense proton beams in RHIC at 250 GeV or in LHC at 7 TeV*. Coherent Electron Cooling was suggested early 1980s as a possibility for using various microwave instabilities in an electron beam to enhance its interaction with hadrons**. The capabilities of present-day accelerator technology, ERLs, and high-gain Free-Electron Lasers (FELs), finally caught up with the idea and provided the all necessary ingredients for realizing such a process at energies typical for modern high energy hadron colliders. In this paper, we discuss the principles, the main limitations of this scheme and present some predictions for Coherent Electron Cooling in RHIC and the LHC operating with ions or protons.
*V. N. Litvinenko, Y. S. Derbenev, Proc. 29th Int. FEL Conference, Novosibirsk, August, 2007. |
||
| WEPP018 | Operational Experience with a Near-integer Working Point at RHIC | 2563 |
|
||
| During the RHIC polarized proton run in FY 2006 it became evident that the luminosity performance is limited by the beam-beam effect. With a working point between 2/3 and 7/10, and the necessity to mirror the tunes of the two RHIC rings at the diagonal, the beam with a horizontal tune closest to 2/3 showed poor lifetime. To overcome this limitation, a near-integer working point has been proposed. Tracking studies performed at both working points showed a larger dynamic aperture near the integer tune than above 2/3. In Run-8, this new working point was commissioned in one ring of RHIC, while the other ring was operated at the same working point as in Run-6. In this paper we report the commissioning process and operational experience with this new working point. | ||
| WEPP019 | RHIC Polarized Proton Performance in Run-8 | 2566 |
|
||
| During Run-8, the Relativistic Heavy Ion Collider (RHIC) provided collisions of spin-polarized proton beams at two interaction regions. Helical spin rotators at these two interaction regions were used to control the spin orientation of both beams at the collision points. Physics data were taken with different orientations of the beam polarization. We present recent developments and improvements as well as the luminosity and polarization performance achieved during Run-8. | ||
| WEPP024 | Non-linear Correction Schemes for the Phase 1 LHC Insertion Region Upgrade and Dynamic Aperture Studies | 2569 |
|
||
| The Phase 1 LHC Interaction Region (IR) upgrade aims at increasing the machine luminosity essentially by reducing the beam size at the Interaction Point (IP). This requires a total redesign of the full IR. A large set of options have been proposed with conceptually different designs. This paper reports on a general approach for the compensation of the multipolar errors of the IR magnets in the design phase. The goal is to use the same correction approach for the different designs. The correction algorithm is based on the computation of the IR transfer map. Its performance is tested using the dynamic aperture as figure of merit. | ||
| WEPP025 | Optics Correction in the LHC | 2572 |
|
||
| Optics correction in the LHC is challenged by the tight aperture constrains and the demand of a highly performing BPM system. To guarantee that the LHC optics remains within a maximum allowable beta-beating of 20% several methods are being investigated through computer simulations and experiments at existing hadron machines. A software package to consolidate the implementation of the various techniques during LHC operation is underway (or nearing completion) | ||
| WEPP026 | Reliable Operation of the AC Dipole in the LHC | 2575 |
|
||
| The AC dipole in the LHC will not only provide transverse oscillations without emittance growth but also with a safety guarantee. These two features are due to the adiabaticity of the excitation. However chromaticity and non-linear fields spoil this adiabaticity. This paper assesses the margins of the relevant parameters for a reliable and safe operation of AC dipoles in the LHC. | ||
| WEPP028 | Flexible Momentum Compaction Return Arcs for RLAs | 2578 |
|
||
| Neutrino Factories and Muon Colliders require rapid acceleration of short-lived muons to multi-GeV and TeV energies. A Recirculating Linear Accelerator (RLA) that uses a single Linac and teardrop return arcs can provide exceptionally fast and economical acceleration to the extent that the focusing range of the RLA quadrupoles allows each muon to pass several times through each high-gradient cavity and the cost of the return arcs is appropriate. Flexible Momentum Compaction (FMC) lattice designs for the teardrop return arcs provide sufficient momentum acceptance to allow multiple passes of each sign of muon in one string of magnets to improve cost-effectiveness. | ||
| WEPP029 | Project of the Nuclotron-based Ion Collider Facility (NICA) at JINR | 2581 |
|
||
| The Nuclotron-based Ion Collider fAcility (NICA) is the new accelerator complex being constructed at JINR aimed to provide collider experiments with heavy ions up to uranium at maximum energy (center of mass) equal to 9 GeV/u. It includes new 6 Mev/u linac, 440 MeV/u booster, upgraded SC synchrotron Nuclotron and collider consisting of two SC rings, which provide average luminosity of 1027cm-2s-1. General goal of the project is to start in the coming 5-7 years experimental study of hot and dense strongly interacting QCD matter and search for possible manifestation of signs of the mixed phase and critical endpoint in heavy ion collisions. The NICA and the Multi Purpose Detector (MPD) are proposed for these purposes. Accelerator complex NICA is being built on the experience and technological developments at the Nuclotron facility and incorporates new technological concepts. The new facility will allow also an effective acceleration of light ions to the Nuclotron maximum energy and an increase of intensity of polarized deuteron beams up to the level above 1010 particles/cycle. The scheme of the facility, its operation scenario and beam dynamics are presented in the report. | ||
| WEPP030 | LHC Luminosity Upgrade: Protecting Insertion Region Magnets from Collision Debris | 2584 |
|
||
| The Large Hadron Collider built at CERN now enters a starting-up phase where with the present design luminosities up to 1034 cm-2 s-1 will be reached after the running in phase. A possible upgrading of the machine to luminosities up to 1035 cm-2 s-1 requires a completely new insertion region design, and will be implemented in essentially two phases. The energy from collision debris is deposited in the insertion regions and in particular in the superconducting magnet coils with a possible risk of quench. We describe here how to protect the interaction region magnets against this irradiation to keep the energy deposition below critical values estimated for safe operation. The constraint is to keep the absorber size as small as possible to leave most of the magnet aperture available for the beam. This can be done by choosing a suitable material and design minimizing the load on the cryogenic system. We will describe a proposal of a design for the phase I upgrade lay-out (i.e., luminosities up to 2.5 1034 cm-2 s-1). | ||
| WEPP031 | Energy Deposited in the High Luminosity Inner Triplets of the LHC by Collision Debris | 2587 |
|
||
| The 14 TeV center of mass proton-proton collisions in the LHC produce not only interesting events for physics but also debris ending up in the accelerator equipment, in particular in the superconducting magnet coils. Evaluations of the deposited heat, that has to be transferred to the cryogenic system, have been made to guarantee that the energy deposition in the superconducting magnets does not exceed limits for magnet quenching and the capacity of the cryogenic system. The models of the LHC baseline are detailed and include description of, for energy deposition, essential elements like beam-pipes and corrector magnets. The evaluations made using the Monte-Carlo code FLUKA are compared to previous studies using MARS. For the comparison and consolidation of the calculations, a dedicated study of a simplified model has been made, showing satisfactory agreement. | ||
| WEPP032 | Parametric Study of Energy Deposition in the LHC Inner Triplet for the Phase 1 Upgrade | 2590 |
|
||
| To be able to make a global parametric analysis and to have some basic understanding of the influence of critical parameters, scaling laws may be of help. For the design of the LHC collision insertion regions, one of the critical parameters is the energy deposited in the insertion superconducting magnet coils, to avoid magnet quench, too heavy load on the cryogenic system, and degradation of the superconductor due to radiation. The influence on energy deposition of some key parameters for magnet design, such as the magnet apertures, the magnet lengths and positions, has been studied for some specified optical beta-value at the collision point. | ||
| WEPP034 | Study of Beam-beam effect at various collision scheme in LHC | 2593 |
|
||
| LHC is designed as two major collision points with finite crossing angle of 140μrad (half). The Piwinski angle is 0.4 for the design. Upgrade plans have been studied to increase the luminosity 10 times. Large Piwinski angle scheme is one of the option for the upgrade. The one turn map with the two beam-beam interactions can be expanded by Taylor series. Analyzing the one turn map gives information of resonance behavior of the beam-beam interactions. We discuss the one turn map for the design LHC and upgrade scheme. | ||
| WEPP035 | Study of Beam-beam Issue for KEKB Crab Crossing | 2596 |
|
||
| A short lifetime at collision is one of the limits on luminosity performance at KEKB in crab crossing mode. The beam-beam halo was evaluated via simulation. The beam lifetime and profile were measured for various beam conditions, vertical emittances, tunes and collision offsets. We discuss why the lifetime is shortened by the beam-beam interaction. | ||
| WEPP036 | DAΦNE Setup and Operation with the Crab-Waist Collision Scheme | 2599 |
|
||
| In the second half of 2007 a major upgrade has been implemented on the Frascati DAΦNE collider in order to test the novel idea of Crab Waist collisions. New vacuum chambers and permanent quadrupole magnets have been designed, fabricated and installed to realize the new configuration. At the same time the performances of relevant hardware components, such as fast injection kickers and shielded bellows have been improved relying on new design concepts. The collider has been successfully commissioned in this new configuration. The paper describes the new layout as well as several experimental results about linear and non-linear optics setup and optimization, damping of beam instabilities and discusses the obtained luminosity performances. | ||
| WEPP037 | Independent Component Analysis of Tevatron Turn-by-turn BPM Measurements | 2602 |
|
||
| Transverse dipole coherent beam oscillations in the Tevatron were analyzed with different independent component analysis algorithms. This allowed to obtain the model-independent values of coupled beta-functions as well as betatron phase advance and dispersion along the ring from a single kick measurement. Using a 1-turn shift of turn-by-turn BPM readings for virtual doubling of the number of BPMs it is also possible to measure the fractional part of betatron tunes with high accuracy. Good agreement with the linear optical model of the Tevatron was observed. | ||
| WEPP039 | Design of a 1036 cm-2 s-1 Super-B Factory | 2605 |
|
||
| Submitted for the High Luminosity Study Group for an Asymmetric Super-B-Factory: Parameters are being studied for a high luminosity e+e- collider operating at the Upsilon 4S that would deliver a luminosity of 1 to 2 x 1036/cm2/s. This collider would use a novel combination of linear collider and storage ring techniques. In this scheme an electron beam and a positron beam are stored in low-emittance damping rings similar to those designed for a Linear Collider (LC) or the next generation light source. A LC style interaction region is included in the ring to produce sub-millimeter vertical beta functions at the collision point. A large crossing angle (±25 mrad) is used at the collision point to allow beam separation. A crab-waist scheme is used to reduce the hourglass effect and restore peak luminosity. Beam currents of about 1.8 A in 1400 bunches can produce a luminosity of 1036/cm2/s with upgrade possibilities. Design parameters and beam dynamics effects are discussed. | ||
| WEPP040 | New Low Emittance Lattices for the SuperB Accelerator Project | 2608 |
|
||
| New low emittance lattices (1.6 nm at 7 GeV, 2.8 nm at 4 GeV) have been designed for the asymmetric SuperB accelerator aiming at a luminosity of 1036 cm-2 s-1. Main optics features are two alternating arc cells with different horizontal phase advance, in order to decrease beam emittance and allow at the same time for easy chromaticity correction in the arcs. Emittance can be further reduced by a factor of two for luminosity upgrade. New beam parameters have been chosen to fulfill the transparency conditions for 4x7 GeV beams, different from the asymmetric currents used in operating B-Factories. Beam polarization schemes have been studied and will be implemented in the lattice. | ||
| WEPP041 | High-current Effects in the PEP-II Storage Rings | 2611 |
|
||
| High beam currents, 2A(HER) & 3A(LER), in PEP-II has been a challenge for the vacuum system. For the ~1 cm long bunches peak currents reach 50 A. Thus modest impedances can give rise to voltage spikes and discharges. A weakness was uncovered during Run 6: rf seals at the "flex flanges" that join the HER arc dipole and quadrupole chambers became a source of an increasing number of HER beam aborts. Vacuum activity was seen and thermal sensors on these flanges saw temperature spikes. Inspection of the seals found arcing and melting, prompting us to replace all of these seals with an improved design using Inconel instead of GlidCop fingers. We believe the GlidCop fingers do not maintain elasticity and hence can not follow chamber motion due to thermal effects. The Run 7 startup confirmed the success of this repair. However, high bunch current in the LER caused breakdown in a LER kicker. This limited the LER bunch current to about 1 mA. Inspection revealed damage to one of the recently added Macor pins that help support the electrodes. Failure analysis revealed heating of the pin & post-facto modeling shows high fields coming from a combination of HOM impedance and high peak currents. | ||
| WEPP042 | An Improved Design for a SuperB Interaction Region | 2614 |
|
||
| We present an improved design for a SuperB interaction region. The new design attempts to minimize the bending of the two colliding beams which results from shared magnetic elements near the Interaction Point (IP). The total crossing angle at the IP is increased from 34 mrad to 50 mrad and the distance from the IP to the first quadrupole is increased. Although the two beams still travel through this shared magnet, these changes allow for a new a new magnetic field design with a septum which gives the magnet two magnetic centers. This greatly reduces the beam bending from this shared quadrupole and thereby reduces the radiative bhabha background for the detector as well as any beam emittance growth from the bending. We decribe the new design for the interaction region. | ||
| WEPP044 | Commissioning the 90° Lattice for the PEP II High Energy Ring | 2617 |
|
||
| In order to benefit from further reduction of the vertical IP beta function of the PEP-II HER the bunch length should be reduced. This will be achieved by changing the phase advance from 60 deg to 90 deg in the four arcs not adjacent to the IR region, thus reducing momentum compaction by about 30% and reducing bunch length from a present 12 mm down to 8.5 mm at low beam current. In preparation to implement the 90 deg lattice the main HER quadrupole and sextupole strings and their power supplies have been reconfigured. Compared to the 60 deg lattice it was expected that dynamic aperture and injection will be more difficult. The synchrotron tune initially will be lower but can be brought back by raising the rf voltage. Beam emittance is held at 48 nmr by introducing a significant dispersion beat in the arcs. The lattice was successfully commissioned at currents up to 800mA in August 2007. In this paper we will compare the actual machine with the predicted behaviour, explain the correction strategies used and give an overall assessment of the operation and the benefit of the new lattice configuration. | ||
| WEPP045 | Suppression of Beam-beam Resonances in Crab Waist Collisions | 2620 |
|
||
| The recently proposed Crab Waist scheme of beam-beam collisions can substantially increase the collider luminosity since it combines several potentially advantageous ideas. One of the basic ingredients of the scheme is the use of dedicated sextupoles in the interaction region for the vertical beta function waist rotation at the interaction point. In this paper we show how this nonlinear focusing helps to suppress betatron and synchrobetatron resonances arising in beam-beam collisions due to particles’ vertical motion modulation by their horizontal oscillations. | ||
| WEPP046 | Final Focus for the Crab-waist Tau-charm Factory | 2623 |
|
||
| In the crab-waist colliders design of the final focus region is a matter of primary importance. The paper describes analysis of final focus quadrupole design and results of particles tracking through the quadrupoles. | ||
| WEPP047 | Optics Implications of Implementing Nb3Sn Magnets in the LHC Phase I Upgrade | 2626 |
|
||
| CERN has encouraged the US-LARP collaboration to participate in Phase I of the LHC luminosity upgrade by analyzing the benefits gained by using Nb3Sn technology to replace the functionality of select magnets CERN is commited to construct using NbTi magnets. Early studies have shown that the much higher gradients (shorter magnetic lengths) and energy load of Nb3Sn magnets compared to their NbTi counterpars is very favorable – allowing the insertion of additional absorbers between Q1 & Q2, for example. This paper discusses the relative merits of the NbTi and Nb3Sn options. | ||
| WEPP048 | Recirculating Linear Muon Accelerator with Ramped Quadrupoles | 2629 |
|
||
|
Neutrino Factories and Muon Colliders require rapid acceleration of short-lived muons to multi-GeV and TeV energies. A Recirculating Linear Accelerator (RLA) that uses a single Linac and teardrop return arcs can provide exceptionally fast and economical acceleration to the extent that the focusing range of the RLA quadrupoles allows each muon to pass several times through each high-gradient cavity. A new concept of rapidly changing the strength of the RLA focusing quadrupoles as the muons gain energy is being developed to increase the number of passes that each muon will make in the RF cavities, leading to greater cost effectiveness. We are developing the optics and technical requirements for RLA designs, using RF cavities capable of simultaneous acceleration of both μ+ and μ- species, with pulsed Linac quadrupoles to allow the maximum number of passes.
Supported in part by DOE STTR grant DE-FG02-05ER86253 |
||
| WEPP049 | Advances on ELIC Design Studies | 2632 |
|
||
| An electron-ion collider of a center-of-mass energy up to 90 GeV at luminosity up to 1035 cm-2s-1 with both beams highly polarized is essential for exploring the new QCD frontier of strong color fields in nuclear and precisely imaging the sea-quarks and gluons in the nucleon. A conceptual design of a ring-ring collider based on CEBAF (ELIC) with energies up to 9 GeV for electrons/positrons and up to 225 GeV for protons and 100 GeV/u for ions has been proposed to fulfill the science desire and to serve as the next step for CEBAF after the planned 12 GeV energy upgrade of the fixed target program. Here, we summarize recent design progress for the ELIC complex with four interaction points (IP); including interaction region optics with chromatic aberration compensation scheme and complete lattices for the Figure-8 collider rings. Further optimization of crab crossing angles at the IPs, simulations of beam-beam interactions and electron polarization in the Figure-8 ring and its matching at the IPs are also discussed. | ||
| WEPP051 | QCD Explorer Based eA and γA Colliders | 2635 |
|
||
| TeV scale lepton-hadron and photon-hadron colliders are necessary both to clarify fundamental aspects of strong interactions and for adequate interpretation of the LHC data. Today, there are two realistic proposals for the post-HERA era, namely, QCD Explorer (QCD-E) and Large Hadron electron Collider (LHeC). Both QCD-E and LHeC can operate as eA colliders, whereas γp and γA options are unique for QCD-E. Another advantage of QCD-E is the possibility to increase the center of mass energy by lengthening of electron linac. In this presentation main parameters of the QCD-E nucleus options are discussed. | ||
| WEPP052 | A Storage Ring Based Option for the LHeC | 2638 |
|
||
| The LHeC aims at the generation of Hadron-Lepton collisions with center of mass energies in the TeV scale and luminosities of the order of 1033 cm-2 sec-1 by taking advantage of the existing LHC 7 TeV proton ring and adding a high energy electron accelerator. This paper presents technical considerations and potential parameter choices for such a machine and outlines some of the challenges arising when an electron storage ring based option, constructed within the existing infrastructure of the LHC, is chosen. | ||
| WEPP053 | Beam Transport in Toroidal Magnetic field | 2641 |
|
||
| The concept of a storage ring with toroidal magnetic field was presented in the two previous EPAC conferences. Here we report the first results of experiments performed with beam transport in toroidal magnetic fields and details of the injection system. The beam transport experiments were carried out with 30 degree toroidal segments with an axial magnetic field of 0.6T. The space charge force and dynamics of a proton beam near the brillouin flow limit are presented here. The multiturn injection system relies on a specified injection coil together with an electric kicker system. The scaling law for the complete storage ring is discussed. The advantages and disadvantages for such a stellarator type storage ring on the 5T level will be reviewed. | ||
| WEPP056 | Aperture Restriction Localisation in the LHC Arcs using an RF Mole and the LHC Beam Position Measurement System | 2644 |
|
||
| Ensuring that the two 27km beam pipes of the LHC do not contain aperture restrictions is of utmost importance. Most of the ring is composed of continuous cryostats, so any intervention to remove aperture restrictions when the machine is at its operating temperature of 1.9K will require a substantial amount of time. On warming-up the first cooled sector, several of the sliding contacts which provide electrical continuity for the image current between successive sections of the vacuum chamber were found to have buckled into the beam pipe. This led to a search for a technique to verify the integrity of a complete LHC arc (~3km) before any subsequent cool-down. In this paper the successful results from using a polycarbonate ball fitted with a 40MHz RF transmitter will be presented. Propulsion of the ball is achieved by sucking filtered air through the entire arc, while its progress is traced every 54m via the LHC beam position measurement system which is auto-triggered by the RF transmitter on passage of the ball. Reflectometry at frequencies in the 4-8 GHz range can cover the gaps between beam position monitors and could therefore be used to localise a ball blocked by an obstacle. | ||
| WEPP057 | Fitting Algorithms for Optical and Beam Parameters in Transfer Lines with Application to the LHC Injection Line TI2 | 2647 |
|
||
| As part of the commissioning with beam of the transfer line TI2 from the SPS to the LHC, a series of optics measurements has been conducted. The paper presents the results in terms of Twiss parameters (including the dispersion), emittance and momentum spread obtained from the combination of trajectory and beam profile measurements. Profiting from the redundancy of monitors, there is a possibility of applying different fitting algorithms to retrieve beam parameters and to extract information on the optics of the line. The results from the different fit methods applied to the data will be compared with the expected values and cross-checked with independent measurements with a particular emphasis on the error analysis. | ||
| WEPP058 | Optics Measurements and Matching of TT2-TT10 Line for Injection of the LHC Beam in the SPS | 2650 |
|
||
| A well matched injection in the SPS is very important for preserving the emittance of the LHC beam. The paper presents the algorithms used for the analysis and the results of the optics measurements done in the transfer line TT2-TT10 and in the SPS. The dispersion is computed by varying the beam momentum and recording the offsets at the BPMs, while the Twiss parameters and emittance measurements in TT2-TT10 are performed with beam profile monitors equipped with OTR screens. These results are completed by those obtained with a matching monitor installed in the SPS as a prototype for the LHC. This device makes use of an OTR screen and a fast acquisition system, to get the turn by turn beam profiles right at injection in the ring, from which the beam mismatch is computed and compared with the results obtained in the line. Finally, on the basis of such measurments, a betatron and dispersion matching of TT2-TT10 for injection in the SPS has been performed and successfully put in operation. | ||
| WEPP059 | Automatic Post-operational Checks for the LHC Beam Dump System | 2653 |
|
||
| In order to ensure the required level of reliability of the LHC beam dump system a series of internal post-operational checks after each dump action must be performed. Several data handling and data analysis systems are required internally and at different levels of the LHC control system. This paper describes the data acquisition and analysis systems deployed for post-operational checks, and describes the experience from the commissioning of the equipment where these systems were used to analyse the dump kicker performance. | ||
| WEPP060 | Abort Gap Cleaning Using the Transverse Feedback System: Simulation and Measurements in the SPS for the LHC Beam Dump System | 2656 |
|
||
| The critical and delicate process of dumping the beams of the LHC requires very low particle densities within the 3 microseconds of the dump kicker rising edge. High beam population in this so-called 'abort gap' might cause magnet quenches or even damage. Constant refilling due to diffusion processes is expected which will be counter-acted by an active abort gap cleaning system employing the transverse feedback kickers. In order to assess the feasibility and performance of such an abort gap cleaning system, simulations and measurements with beam in the SPS have been performed. Here we report on the results of these studies. | ||
| WEPP061 | A Position Monitor for the Aborted Beam in KEKB | 2659 |
|
||
| The beams in the KEKB rings are aborted by abort kickers, Lambertson septums and dumps. First the beams are kicked by the abort kickers rapidly in the horizontal direction to outside the beam pipe and are bent slowly in the vertical direction. At the same time horizontal magnetic fields shake the beam to protect the abort window where the kicked beam passes and protect the window from heat by the high current beam. A beam position monitor is installed in front of the dump. We can get some informations of aborted beam by the monitor. In this paper a method for monitoring the beam in the high energy ring at KEKB is described. | ||
| WEPP063 | R-matrices of the Fast Beam Extraction Section of AGS | 2662 |
|
||
| The Fast Beam Extraction (FEB) system of the Alternating Gradient synchrotron (AGS) extracts the beam bunches from AGS into the AGS-to-RHIC (AtR) beam transfer line, and the extracted bunches are injected into the Relativistic Heavy Ion Collider (RHIC) synchrotron. In a particular section of the beam extraction line the beam bunches are transported through the fringe field region of three main AGS magnets. Optical characteristics of this section change with trajectory and momentum. Therefore the calculation of the R-matrices in this part of the extraction line requires special attention. To describe accurately the R-matrices, the magnetic field of the AGS main magnets was measured on the median plane of the AGS magnet in both, the circulating beam region and the fringe field region, where the extracted beam is transported. Using these magnetic field maps we describe the procedure we use to calculate the R-matrices at the beam extraction region. These R-matrices are used to calculate the beam parameters at the starting point of the AtR beam transfer line and the required quadrupole settings to match to RHIC’s acceptance. | ||
| WEPP064 | Apertures in the LHC Beam Dump System and Beam Losses during Beam Abort | 2665 |
|
||
| The LHC beam dump system is used to dispose accelerated protons and ions in a wide energy range from 450 GeV up to 7 TeV. An abort gap of 3 microseconds is foreseen to avoid sweeping particles through the ring aperture. This paper gives a brief overview of the critical apertures in the extraction region and the two beam dump lines, and presents MAD-X tracking studies made to investigate the impact of particles swept through the aperture due to extraction kicker failures or spurious particles within the abort gap. | ||
| WEPP065 | Beam Commissioning of the SPS-to-LHC Transfer Line TI 2 | 2668 |
|
||
| The transfer line for the LHC Ring 1 was successfully commissioned with beam in the autumn of 2007. After extraction from the SPS accelerator and about 2.7 km of new transfer line, the beam arrived at the temporarily installed beam dump, about 50 m before the start of the LHC tunnel, without the need of any beam threading. This paper gives an overview of the hardware commissioning period and the actual beam tests carried out. It summarises the results of the beam test optics measurements and the performance of the installed hardware. | ||
| WEPP066 | Results from the LHC Beam Dump Reliability Run | 2671 |
|
||
| The LHC Beam Dumping System is one of the vital elements of the LHC Machine Protection System and has to operate reliably every time a beam dump request is made. Detailed dependability calculations have been made, resulting in expected rates for the different system failure modes. A 'reliability run' of the system, installed in its final configuration in the LHC, has been made to discover infant mortality problems and to compare the occurrence of the measured failure modes with their calculations. | ||
| WEPP068 | Impact Distribution of the Beam Losses at the LHC Collimators in Case of Magnet Failures | 2674 |
|
||
| During LHC operation, magnet failures may affect the beam optics leading to proton losses in the collimators. These losses, with about 360MJ of stored energy per beam at nominal collision operation, are potentially dangerous for the accelerator equipment. The LHC Machine Protection Systems ensure that the beam is extracted safely before these losses can produce any damage. As a magnet failure develops, so does the distribution of the lost particles, longitudinally along the ring as well as transversally at each collimator. The transversal impact distributions of lost particles at the most affected collimators and their evolution with time have been studied for representative magnet failures in the LHC. It has been found that the impact distribution at a given collimator can be approximated by an exponential function with time-dependent parameters. The average impact parameter ranges from about 7 to 620 μm for the cases studied. | ||
| WEPP069 | Tracking Tools to Estimate the Quench Time Constants for Magnet Failures in LHC | 2677 |
|
||
| At LHC, beam losses, with about 360MJ of stored energy per beam at nominal collision operation, are potentially dangerous for the accelerator equipment and can also affect the operational efficiency by inducing quenches in superconducting magnets. Magnet failures may affect the beam leading to proton losses primarily in collimators and secondary in superconducting magnets due to scattering of protons from collimator jaws. The evolution of the beam during magnet failures has been simulated using MAD-X with a variable magnetic field. The impacts of particles in the collimators have been recorded as a function of time. A second program, CollTrack, has been used to determine the loss patterns of scattered particles from each collimator as a function of the initial impact parameter. The magnets that are likely to quench are identified and an estimation of the time between the beginning of a failure and a quench is obtained by combining the results from the simulations. The time to a start of a quench is a relevant parameter to determine the dump threshold of beam loss monitors in order to optimize protection redundancy and operation smoothness for LHC. | ||
| WEPP070 | High Efficiency Collimation with Bent Crystals | 2680 |
|
||
| A revolutionary collimation approach is being developed by the H8RD22 collaboration. The basic idea is to replace the amorphous jaws, which spread the beam halo in the whole solid angle, with bent crystals, which are able to deviate the halo particles in a given direction outside the beam core. Studies to investigate the bent crystal properties have been carried out over the past 3 years at the H8 beam line (CERN SPS) with a 400 GeV/c proton beam. The crucial result of these studies is the observation of the Volume Reflection effect, the coherent scattering of the beam on the crystalline plane which provides a small but very efficient (respectively, 14 μrad and 98% at 400 GeV/c) particle deflection. The high efficiency (which should increase at higher energy) combined with a large angular acceptance (~100 μrad) led to the development of multi-reflection systems to increase the deflection angle. Nowadays this system has reached the stage to be tested in a circular accelerator as a primary collimator to verify the effective collimation efficiency in a complex environment. The second phase of the LHC collimation could be the first application of this crystal based system. | ||
| WEPP071 | Preliminary Exploratory Study of Different Phase II Collimators | 2683 |
|
||
| The LHC collimation system is installed and commissioned in different phases, following the natural evolution of the LHC performance. To improve cleaning efficiency towards the end of the low beta squeeze at 7TeV, and in stable physics conditions, it is foreseen to complement the 30 highly robust Phase I secondary collimators with low impedance Phase II collimators. At this stage, their design is not yet finalized. Possible options include metallic collimators, graphite jaws with a movable metallic foil, or collimators with metallic rotating jaws. As part of the evaluation of the different designs, the FLUKA Monte Carlo code is extensively used for calculating energy deposition and studying material damage and activation. This report outlines the simulation approach and defines the critical quantities involved. | ||
| WEPP072 | Evaluation of Beam Losses and Energy Deposition for A Possible Phase II Design for LHC Collimation | 2686 |
|
||
| The LHC beams are designed to have high stability and to be stored for many hours. The nominal beam intensity lifetime is expected to be of the order of 20h. The Phase II collimation system has to be able to handle particle losses in stable physics conditions at 7 TeV in order to avoid beam aborts and to allow correction of parameters and restoration to nominal conditions. Monte Carlo simulations are needed in order to evaluate the behavior of metallic high-Z collimators during operation scenarios using a realistic distribution of losses, which is a mix of the three limiting halo cases. Moreover, the consequences in the IR7 insertion of the worst (case) abnormal beam loss are evaluated. The case refers to a spontaneous trigger of the horizontal extraction kicker at top energy, when Phase II collimators are used. These studies are an important input for engineering design of the collimation Phase II system and for the evaluation of their effect on adjacent components. The goal is to build collimators that can survive the expected conditions during LHC stable physics runs, in order to avoid quenches of the SC magnets and to protect other LHC equipments. | ||
| WEPP073 | Simulation Studies of Impact of SPS Beam with Collimator Materials | 2689 |
|
||
|
Over the past years detailed simulations were carried out to study the impact of the full LHC 7 TeV beam on a target to assess the damage caused to the equipment as a result of an accident, especially to collimators and beam absorbers, and to estimate the thickness of a sacrificial absorber that would be required to stop the beam. This study has shown that the target material will be strongly heated by the beam and transformed into plasma. It has been estimated that the beam would tunnel up to 30 m in solid copper and to about 10 m in solid carbon*. Another interesting outcome of this study was that the LHC beam could be used as a tool to study High-Energy-Density (HED) states in matter. Using the same tools, we recently studied the impact of the SPS 450 GeV proton beam on tungsten and copper targets**. It has been found that the material will be seriously damaged and some tunneling of the beam into the target is expected. It should be possible to validate the predictions with a test facility to deflect the high energy high intensity SPS beam on collimator and absorber materials that will become operational in the next years.
*N. A. Tahir et al. J. Appl. Phys. 97 (2005) 083532. |
||
| WEPP075 | Effects of the Cryogenic Operational Conditions on the Mechanical Stability of the FLASH Linear Accelerator Modules | 2692 |
|
||
| The Free electron LASer in Hamburg (FLASH) accelerating modules have been instrumented with vertical geophones on their corresponding quadrupoles and their vacuum vessels. The signals from these geophones are constantly monitored and the data are integrated into the control system of the accelerator. Therefore, vibration stability studies of a string of superconducting accelerating modules, in various cryogenic conditions, are now possible for the first time. The results of this experiment will be an important reference for both the European X-ray Free Electron Laser (XFEL) and the International Linear Collider (ILC) linear accelerators which are expected to take advantage from the separation between the feed lines of the 4.5 K shield and of the quadrupole, which will operate in a 2 K Helium-II bath. | ||
| WEPP077 | The XFEL Laser Heater | 2695 |
|
||
| The high-brilliance photo-cathode gun foreseen for the X-FEL will provide beams with extremely small momentum spread that will make the beam susceptible to micro-bunching instabilities which will spoil SASE operation. It is therefore desirable to increase the momentum spread to a level that prevents these instabilties but still is compatible with SASE operation. The laser heater will achive this by superimposing a transversely polarized laser and the electron beam in a properly tuned undulator, thereby producing a momentum modulation that is smeared out in a dogleg chicane to obtain the desired momentum spread increase. We present the initial design and layout of the laser heater system for the X-FEL in Hamburg. | ||
| WEPP078 | PHIL: a Test Beam line at LAL | 2698 |
|
||
| For 2004, in the framework of a European contract, LAL is in charge of the construction of one photo-injector for the drive beam linac of the CLIC Test Facility 3 at CERN. This contract together with national funds allowed LAL to build a test accelerator with the same photo-injector as for CTF3. The goal is to undergo experiments on advanced RF guns but a part of the beam time will be also shared with users of the electron beam. So far, the construction of this accelerator at LAL was very much delayed because of the legal obligation to upgrade the radiation shielding in agreement with the actual radiation safety thresholds. The required civil engineering is now finished and the installation of the components is under way. We will first present a design of the accelerator and few dynamic simulation results. Finally we will give a status of the accelerator construction up to date. | ||
| WEPP079 | Beam Dynamics Layout and Loss Studies for the FAIR P-Injector | 2701 |
|
||
| The development of coupled CH-DTL cavities represents a major achievement in the development of the 325 MHz, 70 MeV FAIR P-Injector. This coupled-cavity solution has important consequencies on the beam dynamics design which has to be adapted to this new kind of resonator. In combination with the KONUS beam dynamics, this solution allows to achieve all the requirements of the FAIR project in terms of beam intensity and quality reducing at the same time the number of focusing elements along the machine. A layout based on 6 CH coupled modules is presented and compared with a solution composed of three coupled modules up to 35 MeV followed by three long single resonators up to the energy of 70 MeV. A redesigned 35 MeV intertank section became necessary to avoid beam losses and emittance growth. Finally, the effect of random mistakes such as quadrupole misalignments and phase as well as voltage setting errors have been investigated to determine the tolerances of mechanical construction and rf controls during operation. | ||
| WEPP080 | Baseline Design of the ESS Bilbao Linac | 2704 |
|
||
The baseline design for the ESS-B accelerator adheres to suggestions made by ESS-I, and seeks to enter a design phase for a machine based upon a 150 mA +H proton beam. Such intensity was to be delivered, as stated in the 2003 Technical Report by a tandem of two proton ion sources of some 85 mA each funnelled after the two beams are accelerated up to about 20 MeV. Current activities developed during the last few years within the CARE and EUROTRANS efforts have resulted in significant advances in both ion source and low-energy acceleration technologies which will surely have a relevant impact on the proposed accelerator design. More into specifics, our current activities are being directed towards the exploration of:
|
||
| WEPP081 | Wake-fields and Beam Dynamics Simulations for ILC ACD Accelerating Cavities | 2707 |
|
||
| The ILC aims at colliding bunches of electrons and positrons at a centre of mass energy of 0.5 TeV and in a proposed upgrade to 1 TeV. These bunches of charged particle are accelerated in superconducting linacs. The baseline design for the ILC relies on the relatively mature TESLA-style cavities, with a proposed gradient of more than 30 MV/m and is known as the baseline configuration document (BCD). However, here we investigate electromagnetic fields in superconducting cavities, with the potential to reach accelerating gradients in excess of 50 MV/m, and these are the subject of the alternative configuration document (ACD). We analyse the band structure and necessary damping requirement of the wake-fields in two design configurations: Cornell's re-entrant cavity and KEK's Ichiro cavity. The emittance dilution arising from beams subjected to injection offsets and from cavity misalignments are studied in beam dynamics simulations. | ||
| WEPP082 | Recirculator SALO Project in NSC KIPT | 2710 |
|
||
| In NSC KIPT the electron recirculator project on energy up to 730 MeV is developing. The accelerator is designed first of all as a facility for basic research in the field of a nuclear physics. Superconducting accelerating structure TESLA on frequency of 1.3 GHz, developed in DESY, is used for a speed-up of electrons. Isochronous and achromatic system of injection and magneto-optical system recirculator arcs allow to gain good beam parameters on an exit of the accelerator. Channels of an extraction of particles on experimental stations are presented. Opportunities for use of recirculator beams for applied research are considered. | ||
| WEPP083 | Development of an X-band Hybrid Dielectric-iris-loaded Accelerator | 2713 |
|
||
| A compact x-band hybrid dielectric-iris-loaded travelling-wave linac with constant impendence structure has been designed. By adjusting the values of and the numbers of cells, the beam energy of 29 MeV, the capture efficiency about 50% and the energy spread about with the beam current being 70 mA and the electric gun voltage being 50KeV are obtained through longitudinal dynamics calculation. The length of accelerator tube is 1.12m . The maximum accelerating gradient is less than 45MV/m. By using electromagnetic code such as MAFIA, the attenuation per unit length of structure , the shunt impedance , the quality factor Q, the group velocity and the phase velocity are got by optimizing the dimensions of the cavities. | ||
| WEPP084 | Fabrication of a Quadrant-type Accelerator Structure for CLIC | 2716 |
|
||
| In order to heavily damp the higher order modes of an accelerator structure for CLIC, two kind of damping mechanisms are implemented in one of the designs. Here each cell is equipped with electrically coupled damping channels in addition to the magnetically coupled waveguides. This design requires an assembly of longitudinally cut four quadrants to form a structure and the parts are necessarily made with milling. Since KEK has developed a high-precision machining of X-band accelerator cells with milling and turning at the same time, the experience was extended to the milling of this quadrant. Firstly, the fabrication test of a short quadrant was performed with multiple vendors to taste the present-day engineering level of milling. Following this, a full-size quadrant is also made. In this course, some of the key features are addressed, such as flatness of the reference mating surfaces, alignment grooves, 3D profile shape of the cells, surface roughness and edge treatment. In this paper, these issues are discussed from both fabrication and evaluation point of views. | ||
| WEPP085 | RF Coupler Kicks and Wake-fields in SC Accelerating Cavities | 2719 |
|
||
| The main accelerating cavities of the ILC provide acceleration of both positron and electron beams to 250 GeV per beam and 500 GeV per beam in a proposed upgrade. The wake-field excited by each ultra-relativistic beam in the accelerating cavities can seriously dilute the emittance of the particles within the beams. Each cavity is supplied with both fundamental and higher order mode couplers. The geometrical configuration of these RF couplers results in an asymmetrical field and this gives rise to both an RF kick being applied to the beam and transverse wake-field. Detailed e.m. fields are simulated in the vicinity of the couplers in order to assess the impact on the beam dynamics. We investigate modified geometries with a view to alleviating the emittance dilution resulting from the e.m. field associated with the RF couplers. | ||
| WEPP087 | Observation and Mitigation of Multipass BBU in CEBAF | 2722 |
|
||
| The CEBAF recirculating accelerator at Jefferson Lab consists of two linacs carrying beam for up to five passes of acceleration. The Beam Break-Up (BBU) phenomenon was anticipated during design of the accelerator. The threshold beam current to induce BBU was calculated to be approximately 20 milliamperes, far above operational current. No sign of BBU was ever seen in more than a decade of operation. A specially designed acceleration cavity in a recently installed cryomodule was found to cause a BBU instability under special conditions with as low as 40 uA of injected beam current. This presented an opportunity to study BBU in a five-pass accelerator. In this paper we will discuss multipass BBU, show observational data, and discuss the ways we have developed to maintain the instability threshold current to values above those required for operation. | ||
| WEPP089 | Wake-field Suppression in the CLIC Main Linac | 2725 |
|
||
| The CLIC linear collider aims at accelerating multiple bunches of electrons and positrons and colliding at a centre of mass energy of 3 TeV. These bunches are accelerated through X-band linacs operating at an accelerating frequency of 12 GHz. Each beam readily excites wake-fields in the accelerating cavities of each linac. The transverse components of the wake-fields, if left unchecked, can dilute the beam emittance. The present CLIC design relies on heavy damping of these wake-fields in order to ameliorate the effects of the wake-field on the beam emittance. Here we present initial results on a modified design which combines both damping and detuning of the cell frequencies of each cavity structure in order to enhance the overall decay of the wake-field. Interleaving of cell frequencies is explored as a means to improve the damping. | ||
| WEPP090 | Accelerator Design for a 1/2 MW Electron Linac for Rare Isotope Beam Production | 2728 |
|
||
| TRIUMF, in collaboration with university partners, proposes to construct a megawatt-class electron linear accelerator (linac) as a photo-fission driver for radioactive ion beam production (RIB) for nuclear astrophysics studies and materials science. The design strategy, including upgrade path, for this cost-effective facility is elaborated. The 50 MeV, 10 mA, c.w. linac is based on TESLA/ILC super-conducting radio-frequency (SRF) technology at 1.3 GHz and 2K; and consists of an electron gun, buncher and capture sections, followed by 10 MeV and 40 MeV cryomodules containing one and four 9-cell cavities, respectively. Preliminary results from PARMELA beam dynamics simulations are presented. C. W. operation leads to challenges of large cryogenic heat load, input coupler power handling and beam loss mitigation similar to those encountered in ERL-based light sources. Unlike those sources there is no need for high beam brilliance, and a triode thermionic gun modulated at 1.3 GHz is employed; nor are short bunches required, and so the HOM excitation is modest. Many of the major sub-system components have been identified and where possible existing designs will be adopted. | ||
| WEPP091 | Injector Upgrade for the S-DALINAC | 2731 |
|
||
| Since 1991 the superconducting Darmstadt linear accelerator S-DALINAC provides an electron beam of up to 130 MeV for nuclear and astrophysical experiments. Currently its injector delivers beams of up to 10 MeV with a current of up to 60 μA. The upgrade aims to increase both parameters to 14 MeV and 150 μA in order to allow more demanding astrophysical experiments. Therefore, a modified cryostat module equipped with two new cavities is required. Due to an increase in RF power to 2 kW the old coaxial RF input couplers, being designed for a maximum power of 500 W, have to be replaced by new waveguide couplers. We review the design principles and report on the fabrication of the coupler and the whole module. | ||
| WEPP092 | Tuning of Waveguide to Cavity Coupling Coefficient Beta for a PWT Linac and a Photocathode Gun | 2734 |
|
||
| The waveguide to cavity coupling coefficient beta for two types of accelerating structures: a Plane Wave Transformer (PWT) linac and a 1.6 cell photocathode gun has been tuned to obtain critical coupling in both. Analytical calculation of the dimensions of slot required for critical coupling have been done using Gao’s formulation based on Bethe’s theory for hole coupling. While the PWT linac structure, with high inter-cell coupling, shows good agreement between measured and predicted slot dimensions for different values of beta, the agreement is not so good in the photocathode gun on account of poor inter-cell coupling. This paper discusses details of the analytical calculation of slot dimensions for the two structures, their comparison with experimentally measured results, and the procedure adopted for tuning the two structures to critical coupling. | ||
| WEPP093 | Prototype of Parallel Coupled Accelerating Structure | 2737 |
|
||
| The prototype of parallel coupled accelerating structure is developed. It consists of five accelerating cavities, common excitation cavity and RF power waveguide feeder. The excitation cavity is a segment of rectangular waveguide loaded by cupper pins. The excitation cavity operate mode is TE105. Connection between excitation cavity and accelerating cavities is performed by magnetic field. The expressions for coupled factor excitation cavity to accelerating cavities and coefficient of efficiency for RF power transmission from generator to accelerating cavities are obtained using coupled cavities theory. The parallel coupled accelerating structure electrodynamic characteristics are measured. | ||
| WEPP096 | Nextef: The 100MW X-band Test Facility in KEK | 2740 |
|
||
| Nextef is a new X-band test facility in KEK. By combining the power from two klystrons, 100MW-class X-band RF power will be available. The facility is for researches on future high gradient linear accelerators. The commissioning operation of the whole facility was started in November 2007. It is planed to conduct high power testing of X-band accelerator structures as well as the fundamental researches such as the RF breakdown experiment with specially designed waveguides. | ||
| WEPP097 | Simulation of Wakefield Effect in ILC IR Chamber | 2743 |
|
||
| To achieve super high luminosity, high current beams with very short bunch length are needed, which carry high intensity EM fields. For ILC, two bunch trains with bunch length of 300μm and bunch charge of 3.2nC are needed to collide at the IR to achieve the ILC luminosity goals. When the 300μm bunches pass through the IR chamber, wakefields will be excited, which will cause HOM power flowing through the IR chamber beam pipe to the final doublets due to the high frequency characteristic of the induced wakefields. Since superconducting technology is adopted for the final doublets of ILC BDS, whose operation stability might be affected by the HOM power produced at the IR chamber, quench might happen. In this paper, we did some analytical estimation and numerical simulation on the wakefield effects in ILC IR chamber. | ||
| WEPP098 | Efficient Traveling-wave Accelerating Structure for Linear Accelerators | 2746 |
|
||
| The shaped traveling-wave (STW) structure contains periodic structure of cavities with optimal shape and magnetic coupling operating in the forward traveling-wave mode. The structure combines the advantages of conventional standing-wave (SW) and traveling-wave (TW) structures. It ensures high efficiency of the use of radio-frequency (RF) power for the particle acceleration inherent in the SW structures. Also it gives a possibility to vary output energy of the particles by changing the beam loading and provides for good matching with RF generator without application of special matching devices that is inherent in the TW structures. The STW structure is well suited for compact variable-energy electron linear accelerators used for radiation technologies. | ||
| WEPP099 | Results from Atomic Layer Deposition and Tunneling Spectroscopy for Superconducting RF Cavities | 2749 |
|
||
| Atomic Layer Deposition is a process that synthesizes materials in successive monolayers, at rates on the order of 1 micron/hour. We have been using this technique at Argonne as a possible way to improve both superconducting rf (SCRF) and normal rf structure performance. Initial experiments have led to a new model of high field Q-slope and new ways of controlling SCRF surfaces, as well as suggesting ways to significantly improve the operating gradients of both superconducting and normal structures. We have also been testing this technique in superconducting structures. Initial measurements show significant improvement over “cavity-grade” Nb samples. | ||
| WEPP102 | Design of the ILC RTML Extraction Lines | 2752 |
|
||
| The Damping Ring to the Main Linac beamline (RTML) is equipped with three extraction lines (EL). Each EL can be used both for an emergency abort dumping of the beam and the tune-up continual train-by-train extraction. Two of the extraction lines are located downstream of the first and second stages of the RTML bunch compressor, and must accept both compressed and uncompressed beam with energy spread of 2.5 % and 0.15 % respectively. In this paper we report optical design that allowed us to minimize the length of the extraction lines while offsetting the beam dumps from the main line by the distance required for acceptable radiation level in the service tunnel. Proposed extraction lines can accommodate beams with different energy spreads at the same time providing the beam size suitable for the aluminum dump window. | ||
| WEPP105 | First Operation Results of the Superconducting Photoinjector at ELBE | 2755 |
|
||
| In November 2007 the first electron beam was generated from the superconducting RF photo electron gun installed at the ELBE linear accelerator facility. The injector together with a sophisticated laser system and a diagnostic beam line were developed and constructed within a collaboration of BESSY, DESY, MBI and FZD. Delivering a CW beam with up to 1 mA average current, a significant improvement of the beam quality like an increase of the bunch charge up to 1 nC and a reduced transverse emittance will be obtained. After the cool-down of the cryostat the RF properties of the 3½-cell niobium cavity like pass band mode frequencies, unloaded quality factor versus accelerating gradient, Lorentz force detuning, and He pressure influence were measured. The first beam was extracted of a Cu photo cathode using a 262 nm UV laser system with a repetition rate of 100 kHz and about 0.4 W laser power. Later, caesium telluride photo cathodes will be applied. The installed diagnostics allow beam current, energy, energy spread, transverse emittance and bunch length measurements of the beam. The results of these measurements and the operational experiences with the gun will be presented. | ||
| WEPP106 | High-gradient Experiments with Narrow Waveguides | 2758 |
|
||
| High-gradient RF breakdown studies are presently being conducted at Nextef. To study the characteristics of different materials on high-field RF breakdown, we have performed experiments by using a reduced cross-sectional waveguide that has a field of approximately 200MV/m at an RF power of 100MW. A description of the high-gradient testing of copper and stainless-steel waveguides is reported. | ||
| WEPP108 | The MICE Diffuser System | 2761 |
|
||
| The MICE experiment at RAL will measure the performance of a cooling channel in a variety of configurations of momentum and initial emittance. Coverage in phase space relies on the MICE diffuser, a system with five different thickness lead degraders, remotely operated in a high magnetic field. Technical issues and degrader optimisation for beam matching are discussed. | ||
| WEPP110 | Design and Operational Experience of the MICE Target | 2764 |
|
||
| The MICE experiment requires a beam of low energy muons to test muon cooling. This beam will be derived parasitically from the ISIS synchrotron. A novel target mechanism has been developed which allows the insertion of a small titanium target into the proton beam halo on demand. The target must remain outside of the beam envelope during acceleration, and then overtake the beam during the last 2ms before extraction. The technical specifications are demanding, and require large accelerations and precise and reproducible location of the target in each cycle. The mechanism must also operate in a high radiation environment, and the moving parts and materials must be compatible with the stringent requirements of operating in a working accelerator. The design, and the commissioning and operational experience using this system during the first operating periods in 2008 is described. | ||
| WEPP111 | Modeling Breakdown in RF Cavities Using Particle-in-cell (PIC) codes | 2767 |
|
||
A main limitation on future accelerator projects is breakdown of metallic structures. We have developed computer models of the process of breakdown using Particle-In-Cell (PIC) codes which include: Fowler-Nordheim field emission due to large surface electric fields, impact ionization of neutral gas, ion-induced secondary electron emission, ion-induced sputtering of neutrals, the effects of applied magnetic fields, plasma radiation effects, and surface heating. Two computational tools have been used to self-consistently model the breakdown. These are
|
||
| WEPP116 | Muon Decay Ring Study | 2770 |
|
||
|
Three different muon decay ring configurations are being considered for a neutrino factory. A racetrack design is the current ISS baseline (as it allows greater flexibility in the choice of detector sites) but triangular and bow-tie rings have advantages in neutrino production rates*. Using tracking code simulations, a study of the latter two designs is carried out. Since spin depolarisation measurements have been proposed for muon energy calibration**, spin tracking is included in this study. Dynamic aperture is important and is also calculated.
*International Scoping Study report, 2006. |
||
| WEPP119 | The International Design Study for a Neutrino Factory | 2773 |
|
||
| The International Design Study (IDS) is the successor to the International Scoping Study (ISS), which identified a baseline scenario for a Neutrino Factory. IDS was launched in August 2007, with the aim of developing the baseline to the point where a full, technical design report can be written. The accelerator complex starts with a 4 MW proton driver operating at 50 Hz producing three to five, 1-2 ns bunches per pulse. The proton beam impacts on a liquid mercury jet target; pions are generated and are captured in a solenoid channel; they decay to muons which are phase rotated and formed into trains of interleaved bunches alternating in sign. The muon bunches then undergo ionisation cooling so as to be accepted by a linac, two dogbone recirculating linacs and finally an FFAG for acceleration to 25GeV. The muons are transferred to purpose-built storage rings, with long production straights, where they decay to neutrinos which are directed to detectors at distances of about 3000 km and 7500 km. IDS will be developing this baseline design, identifying its strengths and weaknesses, and progressing the whole towards a self-consistent scenario for the final technical design report stage. | ||
| WEPP120 | G4Beamline Particle Tracking in Matter-dominated Beam Lines | 2776 |
|
||
| Most computer programs that calculate the trajectories of particles in accelerators assume that the particles travel in an evacuated chamber. The development of muon beams, which are needed for future facilities such as muon colliders and neutrino factories, is limited by the lack of user-friendly numerical simulation codes that accurately calculate scattering and energy loss in matter. Geant4 is an internationally supported tracking toolkit that was developed to simulate particle interactions in large detectors for high energy physics experiments, and includes most of what is known about the interactions of particles and matter. Geant4 has been partially adapted in a program called G4beamline to develop muon beam line designs. We are continuing the development of G4beamline to enhance its graphical user-interface and add other features to the program to facilitate its use by a larger set of beam line and accelerator developers. | ||
| WEPP121 | Recirculating Ring for an Ionization Cooling Channel | 2779 |
|
||
| In a muon acceleration facility such as a Neutrino Factory or Muon Collider, the muons created from pion decay occupy a large volume of phase space. For a good capture efficiency this phase space should be reduced and this is typically achieved using ionisation cooling channels. These are quite expensive but the cost can be reduced by recirculating muons through the cooling hardware. Recirculating a high emittance beam typical of a Neutrino Factory is very challenging if it is to be achieved without significant losses. I describe latest attempts to design a high acceptance recirculator for a muon front end. | ||
| WEPP122 | Commissioning Status of the MICE Muon Beamline | 2782 |
|
||
|
It is planned to install a Muon Ionisation Cooling Experiment (MICE) at the ISIS facility at Rutherford Appleton Laboratory. This experiment will be the first demonstration of ionisation cooling as a means to reduce the large transverse emittances expected in the early stages of a Neutrino Factory. A new muon beamline has been installed on ISIS, in order to supply muons of characteristic energy and emittance to the experiment. This paper gives an overview of the goals and design of the beamline, the detectors used to characterise the beam, and the techniques and results which have been obtained during its first operating periods in 2008.
K. Tilley on behalf of the MICE Collaboration. |
||
| WEPP123 | Isochronous Pion Decay Channel for Enhanced Muon Capture | 2785 |
|
||
| Intense muon beams have many potential applications, including neutrino factories and muon colliders. However, muons are produced in tertiary beams into a diffuse phase space. To make useful beams, the muons must be rapidly cooled before they decay. A promising new concept for the collection and cooling of muon beams is being investigated, namely, the use of a nearly Isochronous Helical Transport Channel (IHTC) to facilitate capture of muons into RF bunches. Such a distribution could be cooled quickly and coalesced into a single bunch to optimize the luminosity of a muon collider. We describe the IHTC and provide simulations demonstrating isochronicity, even in the absence of RF and absorber. | ||
| WEPP124 | The Status of Turkish Accelerator Complex Project | 2788 |
|
||
| The Turkish Accelerator Complex (TAC) is proposed as a regional facility for accelerator based fundamental and applied research in 1997 with support of Turkish State Planning Organization (DPT). The feasibility and conceptual design phases of TAC proposal were completed in 2001 and 2005, respectively. Again with support of DPT, the technical design phase of TAC was started at the beginning of 2006. The complex will include 1 GeV electron linac and 3.56 GeV positron ring for linac on ring type electron-positron collider as a charm factory and a few GeV proton linac. Besides the particle factory, it is also planned to produce SASE FEL from electron linac and synchrotron radiation from positron ring. It is planed that the TDR of TAC Project will be completed in 2011 and the construction will be performed during following ten years . | ||
| WEPP125 | Analysis of the Vertical Beam Instability in CTF3 Combiner Ring and New RF Deflector Design | 2791 |
|
||
| In the last CTF3 run (November 2007) a vertical beam instability has been found in the Combiner Ring during operation. Possible sources of the instability are the vertical deflecting modes excited by the beam in the RF deflectors. In the first part of the paper we illustrate the results of the beam dynamics analysis obtained by a dedicated tracking code that allows including the induced transverse wake field and the multi-bunch multi-passage effects. To reduce the effects of such vertical trapped modes, the RF deflectors have been modified and two new deflectors have been designed. They have been made in aluminium and have two more ports in the input and output coupler cells to absorb the beam induced field on the vertical modes. The design of the new deflectors and the RF measurements are then presented in the paper. | ||
| WEPP127 | ALaDyn: a High Accuracy Code for the Laser-plasma Interaction | 2794 |
|
||
| ALaDyn (Acceleration by LAser and DYNamics of charged particles) is a relativistic fully parallelized PIC code to investigate the interaction of a laser pulse with a plasma and/or an externally injected beam. The code is based on compact high order finite differences schemes ensuring higher spectral accuracy compared to standard Yee schemes. We present the main features and the performances of the code together with a set of validation tests obtained comparing the results with well-established analytical/numerical results. A preliminary benchmarking with the PIC code VORPAL is also presented. An application to a physically relevant case concerning the externally-injected configuration proposed for the CNR-INFN experiment PLASMONX will be analyzed. | ||
| WEPP129 | Digital Acceleration Scheme of the KEK All-ion Accelerator | 2797 |
|
||
|
R&D works to realize an all-ion accelerator (AIA)*-capable of accelerating all ions of any possible charge state, based on the induction synchrotron concept, which was demonstrated using the KEK 12 GeV-PS in 2006 **, is going on. In the induction synchrotron, unlike an RF synchrotron, operational performance is not limited due to the frequency band-width, since the switching power supply to energize the induction acceleration system is triggered by signals obtained from the bunch monitor. For a POP experiment of AIA, argon ions will be accelerated in the KEK-500 MeV booster ring, a Rapid Cycle Synchrotron (f=20 Hz) and the RCS requires a dynamic change in the acceleration voltage. Since the induction acceleration voltage per pulse is fixed, a novel technique combining the pulse density control and intermittent operation of multi-acceleration cells has been proposed. The acceleration scheme of the AIA fully employing this technique was verified by computer simulation and demonstrated at our test facility, where a new induction acceleration cell generating an acceleration voltage pulse of 2 μsec long was triggered by a beam simulator to mimic a circulating Ar beam in the KEK-AIA
* K. Takayama, Y. Arakida, T. Iwashita, Y. Shimosaki, T. Dixit, K. Torikai, J. of Appl. Phys. 101, 063304 (2007). |
||
| WEPP131 | RF-breakdown Experiments at the CTF3 Two-beam Test-stand | 2800 |
|
||
| The Two-beam Test-stand (TBTS) in the CLIC Test Facility CTF3 offers unique possibilities to conduct RF-breakdown related experiments on the accelerating structures and the power extraction and transfer structures with beam. We report on the set-up of two such experiments, one for the measurement of the transverse kick and the other for the measurement of positive ion currents. The purpose of the transverse kick measurements is to determine the effects of a RF-breakdown event on the beam. Five BPMs in the TBTS will be used to study the trajectory of a pulse train after a RF-breakdown event, with important implications for the operation of CLIC. Ion currents ejected from accelerating structures during RF-breakdown events have already been observed at the 30 GHz test stand at the present test facility. Results and their implications for RF-breakdown physics are presented, as well as plans for similar measurements at the TBTS. | ||
| WEPP132 | Efficiency Enhancement of Active High-Power Pulse Compressors | 2803 |
|
||
| High power microwaves needed to accelerate particles in multi-TeV colliders can be produced using active pulse compressors. An active compressor has a storage cavity whose Q-factor is modulated by means of RF switch. An efficiency of such compressor is limited due to diffraction losses at power accumulation regime and in conventional case does not exceed 81.4%. A new microwave pulse compressor operated with a superposition of quasi-degenerated modes is suggested. A proper choice of eigen frequencies and Q-factors of these modes allows essential enhancement of efficiency (asymptotically up to 100%). A 30 GHz project of multi-megawatt compressor based on dual-mode circular cross-section cavity is considered. | ||
| WEPP133 | High-gradient Multi-mode Two-beam Accelerating Structure | 2806 |
|
||
|
A new accelerating structure which is aimed to provide gradient >150 MV/m for next generation of multi-TeV linear colliders is suggested. The structure is based on periodic system of quasi-optical cavities*. Each of these cavities is excited in several equidistantly-spaced eigen modes by the drive beam in such a way that the RF fields reach peak values only during the short time intervals when an accelerating bunch is resident in the cavities, thus exposing the cavity surfaces to strong fields for only a small fraction of time. This feature is expected to raise the breakdown and pulse heating thresholds. The proposed structure embodies most of additional attractive properties: the cavity is an all metallic structure, no transfer or coupling structures are needed between the drive and acceleration channels, the cavity fields are symmetric around the axes of the drive beam and the accelerated beam, the cavity can exhibit high transformer ratio. Calculations of single quasi-optical rectangular cavity with parameters of drive and accelerating beams close to ones adopted for the CLIC project show that high gradient as well as high efficiency are achievable.
*S. V. Kuzikov et al. "Quasi-optical accelerating structure operated with a superposition of synchronized modes," Conf. Digest of Joint 32nd IRMMW Conf., Cardiff, UK, 2007, Vol.2, p.797-798. |
||
| WEPP134 | Ultra-short x-ray Radiation coming from a Laser Wakefield Accelerator | 2809 |
|
||
|
A Laser Wakefield Accelerator (LWFA) is under development at LLNL Jupiter Laser Facility to produce multi-GeV electron bunches promising to provide a bright and compact source of x-ray radiation for high energy density studies. The interaction of a high power (200 TW), short laser (50 fs) pulse with neutral He gas can accelerate monoenergetic electrons up to 1 GeV in a stable self-guiding regime*, over a dephasing length of 1 cm (for a plasma density of 1.5x1018 cm-3), overcoming the limitation of vacuum diffraction and allowing long interaction lengths for LWFA. The waveguide can be extended over several centimeters by using a novel scheme, which employs an external magnetic field (up to 5 T uniform along 12 cm) to control the radial heat flux** resulting from the interaction of a high energy (100 J), long pulse (1 ns) laser with a gas tube. The acceleration of electrons over several centimeters can produce multi-GeV bunches and thus a powerful x-ray source. Analysis will be presented on femtosecond x-ray radiation produced by wiggling an electron bunch with energy above 1 GeV in this new LWFA scheme.
* W. Lu et al., Phys. Rev. Spec. Top-ac 10, 061301 (2007) |
||
| WEPP136 | Femtosecond and Attosecond Bunches of Electrons upon Field Emission in a Combined Quasi-static and Laser Electric Field | 2812 |
|
||
|
Obtaining short pulses of particles and of electromagnetic radiation is of interest for investigating fast processes in physics, chemistry, biology and medicine*,**. A new method of modulating an electron beam is proposed to obtain electron bunches of 100-as to 20-fs duration. For this purpose, two electric fields – quasi-static and the variable field of a laser with wavelength in the 0.25 – to 10 microns range – simultaneously act on a single-spiked or multi-spiked cathode. Current from 0.01 to 100 A from one spike having a curvature radius of 1 micron corresponds to a maximal intensity of total electric field of 70 to 280 MV/cm for a 10-micron laser wavelength. For a 1-micron laser, total fields of 300 – 400 MV/cm should be used for 1 – 20 A currents. A regime of device operation was determined for which the emitting surface of a copper cathode is not damaged. Obtaining a single bunch or a sequence of bunches with a repetition rate up to1330 THz was considered. Using multi-spiked cathodes permits to obtain bunches with current up to 10 kA.
*P. Emma. Issues and challenges for short pulse radiation production, Proc. EPAC04, p. 225, Lucerne, Suisse. |
||
| WEPP137 | Accelerating and Transporting Attosecond and Femtosecond Bunches of Electrons | 2815 |
|
||
|
Dynamics of short bunches of electrons obtained upon field emission in a quasi-static electric field and a variable electric field of a laser has been studied*. The equation of longitudinal motion of electrons was numerically integrated. Emitted electrons are accelerated by quasi-static potential applied to the spike and this drastically reduces initial energy spread in the bunch preventing its fast elongation. When the forces of space charge have little effect, grouping part of the beam due to velocity spread acquired in the laser field permits to obtain bunches of about 200-as duration when using a carbon dioxide laser and about 6-as with a neodymium laser. Analytical models were used to evaluate the influence of the space charge of the bunch on the longitudinal motion of electrons in it. It has been shown that the proper choice of the intensities of both fields can cancel such an influence. There have been considered methods of lateral focusing of the beam taking into account possible initial angular divergence and space charge effects. Such electron bunches could be used directly in experiments or for generation of short pulses of coherent UV- and X-ray radiation.
*V. A. Papadichev, Femtosecond and Attosecond Bunches of Electrons Upon Field Emission in a Combined Quasi-static and Laser Electric Field, submitted to this Conference. |
||
| WEPP138 | Experimental Demonstration of Ultrashort μJ-Class Pulses in the Terahertz Regime from a Laser Wakefield Accelerator | 2818 |
|
||
|
Ultrashort terahertz pulses with energies in the μJ range can be generated with laser wakefield accelerators (LWFA), which are novel, compact accelerators that produce ultrashort electron bunches with energies up to 1 GeV* and energy spreads of a few-percent. Laser pulses interacting with a plasma create accelerated electrons which upon exiting the plasma emit terahertz pulses via transition radiation. Because they are only tens of femtoseconds long, electron bunches can radiate coherently (CTR) in a wide bandwidth (~ 1 - 10 THz) yielding terahertz pulses of high intensity**,***. In addition to providing a non-invasive bunch-length diagnostic**** and thus feedback for the LWFA, these high peak power THz pulses are suitable for high field (MV/cm) pump-probe experiments. Here we present energy-based measurements using a Golay cell and a single-shot electro-optic technique which were used to characterize the full waveform of these μJ-class THz pulses, including phase and amplitude information.
*W. P. Leemans et al. N. P. 2/696 (2006). |
||
| WEPP139 | The CTF3 Two-beam Test-stand Installation and Experimental Program | 2821 |
|
||
| The Two-beam Test-stand in CTF3 will be used to investigate the power-generation and accelerating structures for the Compact Linear Collider CLIC. We report on its design and construction which was recently completed and discuss the imminent commissioning phase as well as the following experimental program that initially will be devoted to the test of power generation structures in the drive-beam. | ||
| WEPP140 | X-band PASER Experiment | 2824 |
|
||
| The PASER concept for particle acceleration entails the direct transfer of energy from an active medium to a charged particle beam. The PASER was originally formulated for optical (laser) media; we are pursuing a PASER demonstration experiment based on an optically pumped paramagnetic medium active in the X-band. We report on the development of a relatively high energy density microwave active medium consisting of a fullerene (C60) derivative in a toluene solution. We discuss both the bench test of an amplifier and a beam acceleration experiment under construction that employ this medium as a power source. Applications of the technology to accelerators and microwave components will be presented. | ||
| WEPP142 | Simulation of and Progress towards a Micron-scale Laser-powered Dielectric Electron Source | 2827 |
|
||
| A dielectric, slab-symmetric structure for generating and accelerating low-energy electrons has been under study for the past two years. The resonant device is driven by a side-coupled laser and is configured to maintain field provide necessary for synchronous acceleration and focusing of nonrelativistic particles. Intended applications of the structure include the production of radiation for medical treatments, imaging, and industrial uses. The details of the structure geometry and its resonant properties have been studied with 2D and 3D electromagnetic codes, the results of which are present here. | ||
| WEPP146 | Generation of Electron Microbunches Trains with Adjustable Sub-picosecond Spacing for PWFA and FEL applications | 2830 |
|
||
| We demonstrate that trains of subpicosecond electron microbunches, with subpicosecond spacing, can be produced by placing a mask in a large dispersion region of the beam line where the beam transverse size is dominated by the correlated energy spread. The particles are selected based on the scattering of their emittance at the mask. The electrons that hit the solid arts of the mask are subsequently lost. The mask spatial pattern is converted into a time pattern in the dispersion-free region of the beam line. The experiment was performed with the Brookhaven National Laboratory Accelerator Test Facility 60 MeV beam. We show that the number, length, and spacing of the microbunches can be controlled through the parameters of the beam and the mask. Trains with one to eight equidistant microbunches are produced. The microbunches spacing is adjusted in the 100 to 300 microns or 300 fs to 1 ps range and comparable microbunch length. The train structure is measured using CTR interferometry, and is stable in time and energy. Such microbunch trains can be further compressed and accelerated, and have applications to free electron lasers (FELs) and plasma wakefield accelerators (PWFAs). | ||
| WEPP147 | Aberration-free Muon Transport Line for Extreme Ionization Cooling: a Study of Epicyclic Helical Channel | 2833 |
|
||
| Once the normalized transverse emittances of a muon beam have been cooled to some hundreds of microns, new techniques such as Parametric-resonance Ionization Cooling and Reverse Emittance Exchange can be used to focus the beam very tightly on beryllium energy absorbers for further transverse emittance reduction. The transport lines for these techniques have stringent requirements for the betatron tunes so that resonance conditions are properly controlled and for the dispersion function so that the longitudinal emittance can be controlled by emittance exchange using wedge-shaped absorbers. The extreme angular divergence of the beam at the absorbers implies large beam extension between the absorbers such that these techniques are very sensitive to chromatic and spherical aberrations. In this work we describe general and specific solutions to the problem of compensating these aberrations for these new muon cooling channels. | ||
| WEPP148 | Generation of High Gradient Wakefields in Dielectric Loaded Structures | 2835 |
|
||
| Dielectric loaded wakefield structures have potential to be used as high gradient accelerator components. Using the high current drive beam at the Argonne Wakefield Accelerator Facility, we employed cylindrical dielectric loaded wakefield structures to generate accelerating fields of up to 100 MV/m. Short electron bunches (13 ps FWHM) of up to 86 nC are used to drive these fields, either as single bunches or as bunch trains. These recently tested standing-wave structures have a field probe near the outer edge of the dielectric to sample the RF fields generated by the electron bunches. Monitoring of these high intensity RF fields serves to verify the absence of electric breakdown. | ||
| WEPP149 | Advances in Parametric-resonance Ionization Cooling | 2838 |
|
||
| Parametric-resonance ionization cooling (PIC) is a muon-cooling technique that is useful for low-emittance muon colliders. This method requires a well-tuned focusing channel that is free of chromatic and spherical aberrations. The dispersion function of the channel must be large where the correction magnets are placed for aberration control but small and non-zero where the ionization cooling beryllium wedges are located to provide emittance exchange to maintain small momentum spread. In order to be of practical use in a muon collider, it also necessary that the focusing channel be as short as possible to minimize muon loss due to decay. A compact PIC focusing channel is described in which new magnet concepts are used to generate the required lattice functions. | ||
| WEPP151 | Metallic Photonic Band Gap Accelerator Structure Experiments and Design | 2841 |
|
||
| Damping wakefields is a critical issue in the next generation of high gradient accelerators. Photonic bandgap (PBG) structures have unique properties that offer significant wakefield damping. The goal of this work is to quantify the higher order mode (HOM) wakefield content of a constructed metallic PBG accelerator structure, in order to test the theory of wakefield excitation in these structures and to provide direction for future structure design. Experimental measurements of wakefields excited by an 18 MeV electron beam in a 6 cell, 17.14 GHz metallic PBG traveling wave accelerator structure are reported. Because the electron beam used to generate wakefields in the PBG structure is bunched at the 17.14 GHz rf frequency, all wakefields observed were at integer multiples of 17.14 GHz. Using diode detectors, radiation has been observed at the input and output coupler ports as well as through a quartz window in the surrounding vacuum vessel. Estimates of wakefield radiation, made using HFSS and basic wakefield theory, compare well with experiment. | ||
| WEPP153 | Status of the MANX Muon Cooling Experiment | 2844 |
|
||
| MANX is an experiment to prove that effective six-dimensional (6D) muon beam cooling can be achieved a Helical Cooling Channel (HCC) using ionization-cooling with helical and solenoidal magnets in a novel configuration. The aim is to demonstrate that 6D muon beam cooling is understood well enough to plan intense neutrino factories and high-luminosity muon colliders. The experiment consists of the HCC magnets that envelop a liquid helium energy absorber, upstream and downstream instrumentation to measure the particle or beam parameters before and after cooling, and emittance matching sections between the detectors and the HCC. Studies are presented of the effects of detector resolution and magnetic field errors on the beam cooling measurements. | ||
| WEPP154 | Linac-LHC ep Collider Options | 2847 |
|
||
| We describe various parameter scenarios for a ring-linac ep collider based on LHC and an independent s.c. electron linac. Luminosities of order 1032/cm2/s can be achieved with a standard ILC-like linac, operated either in pulsed or cw mode, with acceptable beam power. Reaching much higher luminosities, up to 1034/cm2/s and beyond, would require the use of two linacs and the implementation of energy recovery. Advantages and challenges of a ring-linac ep collider vis-a-vis an alternative ring-ring collider are discussed. | ||
| WEPP155 | Laser Driven Linear Collider | 2850 |
|
||
| We continue detailed description of scheme allowing long term acceleration with >10 GeV/m in multi-cell microstructures side-illuminated by laser radiation. The basis of the scheme is a fast sweeping device for the laser bunch. After sweeping the laser bunch has a slope ~45° with respect to the direction of propagation. So the every cell of microstructure becomes excited locally only for the moments, when the particles are there. Self consistent parameters of collider based on this idea allow consideration this type of collider as a candidate for the near-future accelerator era. | ||
| WEPP156 | Spherical Aberrations-free Wiggler | 2853 |
|
||
| We represented details of design of a wiggler with linear piecewise longitudinal field dependence. This type of field distribution eliminates spherical aberrations in wiggler. This wiggler can be recommended for usage in cooler rings including ILC ones. | ||
| WEPP157 | Lithium Lens for Positron Production System | 2856 |
|
||
| We represent optimized parameters for undulator-based positron production scheme for ILC-type machine. In particular we describe details of Lithium lens design suggested for usage in collection optics. | ||
| WEPP158 | Simulation of beam Halo in CLIC Collimation Systems | 2859 |
|
||
| Full simulation of the CLIC and ILC collimation systems are performed to take account of collimator wakefield effects from the core beam on the halo. In addition full simulation of the interaction of the halo with the collimator material is performed to study the effect of multiple scattering and also the production of neutrons in the electromagnetic showers. The effect of beam-gas scattering downstream of the collimators is also included. | ||
| WEPP161 | Preliminary Experiments on a Fluidised Powder Target | 2862 |
|
||
| In order to achieve higher resolutions the next generation of accelerator facilities is designed to operate with beam powers orders of magnitude higher than that handled by the current technology. So it is believed that the existing target and beam dump designs will be unsuitable to survive beam interactions depositing powers in the order of several megawatts. Good target design is important for the physics yield from experiments and crucial to the reliable operation of the facility. Furthermore the choice of target is strongly associated with the safety and cost of design (i.e., economic viability) of the entire facility. This article proposes a new target technology based on fluidised powder believed to be suitable for application at higher beam powers whilst avoiding some of the problems associated with other technologies. A conceptual system design for the application of the fluidised powder target to the requirements of a future neutrino facility, is presented. The preliminary experimental results presented, show the effect of some of the parameters which are expected to determine the performance, physics yields and reliability of operation of the new powder system. | ||
| WEPP162 | Beam Impact Studies on ILC Collimators | 2865 |
|
||
| Spoilers in the ILC Beam Delivery System are required to survive without failure a minimum of 1-2 direct impacts of 250 GeV-500 GeV bunch of electrons or positrons, in addition to maintaining low geometric and resistive wall wake fields. Simulations were completed to determine the energy deposition of an ILC bunch to a set of different spoiler designs. These shower simulations were used as inputs to thermal and mechanical studies using ANSYS. This paper presents the results of testing carried out at the Accelerator Test Facility at KEK used to validate the simulations. Results from the first phase of testing, in which electron bunches of varying charge were incident on TI-6Al-4V foils, are presented and compared with simulations. | ||
| WEPP163 | Measurements of Collimator Wakefields at End Station A | 2868 |
|
||
| The angular kicks imparted to an electron beam with energy of 28.5 GeV when it passes through a collimator jaw with a certain offset, generating a wakefield, were measured in End Station A (ESA) in SLAC for fifteen different collimator configurations of geometry and material. Some configurations were chosen in order to compare with previous measurements while others served to study the effect of geometry and taper angles (geometrical contribution to the wakefield) and the effect of the material resistivity (resistive contribution) to the kick. This paper summarises the final experimental results. The reconstructed kick factor is compared to analytical calculations and simulations. | ||
| WEPP164 | Beam Collimation Studies for the ILC Positron Source | 2871 |
|
||
| The results of collimation studies for the ILC positron source beam line are presented. The calculations of primary positron beam loss are done using the ELEGANT code. The secondary positron and electron beam loss, synchrotron radiation along the beam line and bremsstrahlung radiation in the collimators are simulated using the STRUCT code. The first part of the system, located right after the positron source target at 0.125 GeV, is used for protection of super-conducting RF Linac from heating and radiation. The second part of the system is used for final collimation of the beam before injection to the Damping Ring at 5 GeV. The calculated power loss in the collimation region is about 100 W/m, with loss in the collimators of 0.2-5 kW. The beam transfer efficiency from target to the Damping Ring is 13.5%. | ||
| WEPP165 | GdfidL Simulations of International Linear Collider Candidate Collimator Assemblies | 2874 |
|
||
| Collimator performance is critical to the successful operation of any collider. Building on previous GdfidL simulations of collimator jaws, this paper describes simulations where STL files of the complete assembly are investigated and wakefield performance is determined and optimised. | ||
| WEPP166 | Comparison of Collimator Wakefields Formulae | 2877 |
|
||
| There is an extensive literature on transverse wakefield kick factors in collimators. We present a compendium of the formulae and discuss their agreement and disagreement with each other and with experimental results. | ||
| WEPP167 | Effect of Collimator Wakefields in the Beam Delivery System of the International Linear Collider | 2880 |
|
||
| The collimators in the design of the International Linear Collider (ILC) Beam Delivery System (BDS) may be a significant source of wakefields and significantly degrade luminosity. New simulations are used to predict the effect of BDS collimator wakefields, and compared with previous analytical methods. BDS lattices optimised for improved collimation performance are also examined. | ||
| WEPP168 | Mechanical Design of Collimators for the ILC | 2883 |
|
||
| Much attention has been paid to the optimisation of the geometry and material of collimators in the ILC to mitigate the effects of both short-range transverse wakefields and errant beam impacts. We discuss the competing demands imposed by realistic engineering constraints and present a preliminary engineering design for adjustable jaw spoilers for the ILC. | ||
| WEPP169 | The MERIT High-power Target Experiment at the CERN PS | 2886 |
|
||
| The MERIT experiment was designed as a proof-of-principle test of a target system based on a free mercury jet inside a 15-T solenoid that is capable of sustaining proton beam powers of up to 4MW. The experiment was run at CERN in the fall of 2007. We describe the results of the tests and their implications. | ||
| WEPP170 | A 15-T Pulsed Solenoid for a High-power Target Experiment | 2889 |
|
||
| The MERIT experiment, which ran at CERN in 2007, is a proof-of-principle test for a target system that converts a 4-MW proton beam into a high-intensity muon beam for either a neutrino factory complex or a muon collider. The target system is based on a free mercury jet that intercepts an intense proton beam inside a 15-T solenoidal magnetic field. Here, we describe the design and performance of the 15-T, liquid-nitrogen-precooled, copper solenoid magnet. |