OXFORDphysics, Oxford, Oxon
JAI, Oxford
Funding: This work was supported by EPSRC grant EP/E032869/1.
PAMELA is a design study of a non-scaling FFAG for hadron therapy aiming to deliver 250 MeV protons and 400 MeV/u carbon ions. This paper outlines the general magnet design required for the 250 MeV proton case. The magnet design is challenging because of the combination of required field strength (up to 4T), geometric constraints (the magnets need to be short) and large beam aperture (up to 160 mm). All magnets are combined function magnets with dipole, quadrupole, sextupole and octupole field components of good field quality.
LBNL, Berkeley, California
Electron microscopes and streak cameras are "mini accelerators". Advanced techniques in electron optics have been successfully applied to the design and optimization of electron microscopes and streak cameras. This talk is an overview of the status and unique designs that have arisen, with emphasis on the theoretical aspects.
BESSY GmbH, Berlin
PTB, Berlin
The Metrology Light Source (MLS)* is in user operation since April 1st, 2008. It is the first storage ring designed and built for operation in the low α mode, which relies on the control of higher order terms of the momentum compaction factor α with respect to the momentum deviation dp/p, α=a0+a1*dp/p+a2*(dp/p)**2. The a0 term is controlled by quadrupoles, a1 by 3 families of sextupoles for controlling the chromaticity in the transverse and longitudinal planes, the a2 term is controlled by an octupole family. The a0 value can be varied by more than a factor of {10}00. The low α mode is also called 'isochronous' operation, it is used for short bunch operation, where intense signals of coherent sub-THz radiation are produced. We report on operation experience of this scheme.
*R. Klein et al., 'Operation of the Metrology Light Source as a primary radiation source standard',
PHYSICAL REVIEW SPECIAL TOPICS - ACCELERATORS AND BEAMS 11, 110701 (2008).
CERN, Geneva
The implementation of new Multi-turn extraction at the CERN Proton Synchrotron required major hardware changes for the nearly 50-year old accelerator. The installation of new PFNs and refurbished kicker magnets for the extraction, new sextupole and octupole magnets, new power converters, together with an in-depth review of the machine aperture leading to the design of new vacuum chambers was required. As a result, a heavy programme of interventions had to be scheduled during the winter shut-down 2007-8. The newly installed hardware and its commissioning is presented and discussed in details.
BINP SB RAS, Novosibirsk
The influence of resonances on the beam dynamics in storage rings is of substantial interest to accelerator physics. For example, a fast crossing of resonances occurs in the damping rings of future linear colliders during the beam damping (due to the incoherent shift) can result in a loss of particles. We have studied experimentally the crossing of resonances of different power near the working point of the VEPP-4M storage ring. Observation of the beam sizes and particle losses was performed with a single-turn time resolution. Comparison with the numerical simulation has been made and will be presented alongside the experimental results.
CERN, Geneva
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
IHEP Beijing, Beijing
LAL, Orsay
KEK, Ibaraki
UMAN, Manchester
SLAC, Menlo Park, California
The CLIC Final Focus System has considerably larger chromaticity than those of ILC and its scaled test machine ATF2. We propose to reduce the IP betas of ATF2 to reach a CLIC-like chromaticity. This would also allow to study the FFS tuning difficulty as function of the IP beam spot size. Both the ILC and CLIC projects will largely benefit from the ATF2 experience at these ultra-low IP betas.
CERN, Geneva
BNL, Upton, Long Island, New York
In early LHC commissioning, linear and "higher-order" polarity checks were performed for one octant per beam, by launching suitable free betatron oscillations and then inverting a magnet-circuit polarity or strength. Circuits tested included trim quadrupoles, skew quadrupoles, lattice sextupoles, sextupole spool-pieces, Landau octupoles, and skew sextupoles. A nonzero momentum offset was introduced to enhance the measurement quality. The low-intensity single-pass measurements proved sufficiently sensitive to verify the polarity and the amplitude of (almost) all circuits under investigation, as well as the alignment of individual trim quadrupoles. A systematic polarity inversion detected by this measurement helped to pin down the origin of observed dispersion errors. Later, the periodic "ring dispersion" was reconstructed from the full first-turn trajectory of an injected off-momentum beam, by removing, at each location, the large incoming dispersion mismatch, forward-propagated via the optics model. Various combinations of inverted trim quadrupoles were considered in this model until reaching a good agreement of reconstructed dispersion and prediction.
CERN, Geneva
Phase I collimators, equipped with Carbon-Carbon jaws, effectively met specifications for the early phase of LHC operation. However, the choice of carbon-based materials is expected to limit the nominal beam intensity mainly because of the high RF impedance and limited efficiency of the collimators. Moreover, C/C may be degraded by high radiation doses. To overcome these limitations, new Phase II secondary collimators will complement the existing system. Their extremely challenging requirements impose a thorough material investigation effort aiming at identifying novel materials combining very diverse properties. Relevant figures of merit have been identified to classify materials: Metal-diamonds composites look a promising choice as they combine good thermal, structural and stability properties. Molybdenum is interesting for its good thermal stability. Ceramics with non-conventional RF performances are also being evaluated. The challenges posed by the development and industrialization of these materials are addressed in a collaboration program, involving academic and industrial partners and complementing material research with an innovative design.
CERN, Geneva
INFN-Roma, Roma
BNL, Upton, Long Island, New York
The UA9 experiment will take place in 2009 at the CERN-SPS and will evaluate the feasibility of silicon crystals as primary collimators for a storage ring. A crystal placed at 6 σ from the beam core will deviate protons towards two roman pots and a tungsten absorber (TAL). In this paper the authors show simulations of the expected beam dynamics and of the capture efficiency into the secondary collimator. The result of these simulations will guide us in interpreting the experimental data expected in UA9.
BNL, Upton, Long Island, New York
Fermilab, Batavia
The University of Texas at Austin, Austin, Texas
An AC dipole magnet produces a sinusoidally oscillating dipole field with frequency close to betatron frequency and excites large sustained oscillations of beam particles circulating in a synchrotron. Observation of such oscillations with beam-position-monitors allows direct measurements of a synchrotron's nonlinear parameters. This paper presents experimental studies to measure effects of sextupole and octupole fields, such as tune dependence on amplitude and resonance driving terms, performed in the Fermilab Tevatron using an AC dipole.
CERN, Geneva
For several years, a large variety of beams have been prepared in the LHC injectors, such as single-bunch and multi-bunch beams, with 25 ns, 50 ns and 75 ns bunch spacings, nominal and intermediate intensities per bunch. As compared to the nominal LHC beam (i.e. with nominal bunch intensity and 25 ns spacing) the other beams can be produced with lower transverse emittances. Beams of low transverse emittances are of interest during the commissioning phase for aperture considerations and because of the reduced long-range beam-beam effects. On the other hand machine protection considerations might lead to prefer nominal transverse emittances for safe machine operations. The purpose of this paper is to present the results of controlled transverse emittance blow-ups using the transverse feedback and octupoles. The procedures tested in the SPS in 2008 allow to tune the transverse emittances up to nominal values at SPS extraction.
JAEA/TARRI, Gunma-ken
CNS, Saitama
It is possible to fold the tails of the transverse beam profile into the inside, or even to uniformize the beam distribution in the properly-designed nonlinear beam transport system. A two-dimensionally uniform beam profile was formed using sextupole and octupole magnets at the azimuthally-varying-field cyclotron facility of Japan Atomic Energy Agency. Such a uniform beam exhibits a unique feature in the viewpoint of a uniform irradiation system; as compared to the raster scanning system, it enables us to perform uniform irradiation over the whole area of a large sample at a constant particle fluence rate. For the application of materials sciences, uniformization of heavy-ion beams as well as protons has been performed. In order to reduce undesirable beam halos at the target, tail-folding of the spot beam is also planed using the nonlinear focusing method.
BINP SB RAS, Novosibirsk
INFN/LNF, Frascati (Roma)
A project of the SuperB Factory in Italy with the crab-waist collision scheme and extremely large luminosity addresses new challenges to the nonlinear beam dynamics study. Among these challenges are: low emittance lattice requiring strong sextupoles for chromatic correction, sub-mm vertical betatron function at the IP, crab sextupoles placed at both sides from the IP, etc. In this report we describe the results of the DA limiting sources analysis and optimization of the arrangement of the IR and Crab sextupoles and octupoles for the Low Energy Ring (LER).
USTC/NSRL, Hefei, Anhui
IHEP Beiing, Beijing
SINAP, Shanghai
IHEP Beijing, Beijing
SSRF, Shanghai
In this paper, we introduce the BxB transverse feedback systems at Hefei Light Source (HLS), which employ an analog system and a digital system. The construction and commissioning for two feedback systems, as well as the instability analysis of beam and the experiment result of the feedback system in HLS are also presented in this paper.
USTC/NSRL, Hefei, Anhui
JASRI/SPring-8, Hyogo-ken
Hefei Light Source (HLS) is an 800MeV storage ring with bunch rate of 204 MHz, the harmonics of 45, and circumference of 66 meters. HLS injection works at 200MeV, where the multi-bunch instabilities limit the maximum stored current. A digital transverse bunch-by-bunch feedback system has recently been commissioned at HLS to suppress the multi-bunch instabilities during injection. We employ the SPring-8 FPGA based feedback processor and modified it at NSRL to process horizontal and vertical oscillation signals, independently and simultaneously by one single processor. The design of the digital transverse feedback system and the experiment results are presented in this paper.
CERN, Geneva
UMAN, Manchester
EPFL, Lausanne
Honorary CERN Staff Member, Grand-Saconnex
The LHC phase 2 collimation project aims at gaining a factor ten in cleaning efficiency, robustness and impedance reduction. From the impedance point of view, several ideas emerged during the last year, such as using dielectric collimators, slots or rods in copper plates, or Litz wires. The purpose of this paper is to discuss the possible choices, showing analytical estimates, electro-magnetic simulations performed using Maxwell, HFSS and GdFidL, and preliminary bench measurements. The corresponding complex tune shifts are computed for the different cases and compared on the stability diagram defined by the settings of the Landau octupoles available in the LHC at 7 TeV.