| Paper | Title | Page |
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| MOPJE075 | Tracking Through Analytic Quadrupole Fringe Fields With GPT | 489 |
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| In the early design stages it is customary to work with a highly simplified analytic model to describe the beam line. Dipoles and quadrupoles are often based on hard-edged approximations. This is not only unrealistic, it also significantly slows down time-domain spacecharge tracking codes such as the General Particle Tracer (GPT) code. The underlying reason for the poor performance is that despite the fact that the simple hard-edged field equations are fast to evaluate, they force the integration process to use excessively small step sizes near the fields discontinuities in order to achieve the desired accuracy. In other worlds, the apparently simple equations turn out to be the most difficult ones to evaluate numerically. An obvious solution is to switch to field-maps, but this is not practical in the early design stages. In this contribution we show a new solution implemented in the GPT code based on analytical expressions for the fringes where the transverse size of the magnet is properly taken into account. In addition to producing more realistic results, the smooth fields increase tracking speed by over an order of magnitude for typical test cases. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPJE075 | |
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| MOPJE082 | Analytical Approach to the Beam-Beam Interaction with the Hourglass Effect | 510 |
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Funding: STFC HL-LHC The HL-LHC upgrade will allow higher luminosities to be reached in the LHC. To achieve higher luminosities the β-function at the IP is decreased, which in turn will result in the hourglass effect becoming more prominent as the transverse bunch sizes become comparable to the length of the bunch. This effect reduces the luminosity since not all particles in the bunch will collide at the minimum IP. The standard derivation of the electric and magnetic fields of the beam-beam interaction is that undertaken by Bassetti and Erskine. The derivation by Bassetti Erskine does not include a coupling between bunch planes. When the transverse bunch sizes are comparable to the length of the bunch the magnitude of the transverse kick will be dependent on the longitudinal position. Currently only numerical methods are available to evaluate this effect. Here a theoretical framework is outlined that provides an analytical approach to derive the electric field for the beam-beam interaction with a coupling between the transverse and longitudinal planes. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPJE082 | |
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| TUPJE054 | Developments in CLARA Accelerator Design and Simulations | 1744 |
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| We present recent developments in the accelerator design of CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. The layout changes include a dedicated collimator in CLARA front end to provide some control over the dark current, changes to low energy diagnostics section and modifications to FEL modules. The progress in the design simulations mainly focus on injector simulations incorporating wake fields in ASTRA, comparison of using ELEGANT and CSRTRACK for the Variable Bunch Compressor and first considerations of requirement of laser heater for CLARA. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE054 | |
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| TUPJE056 | VELA Machine Development and Beam Characterisation | 1752 |
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| Recent developments on the VELA (Versatile Electron Linear Accelerator) RF photo-injector at Daresbury Laboratory are presented. These are three-fold; commissioning/installation, characterising and providing beam to users. Measurements for characterising the dark current (DC), 4-D transverse emittance, lattice functions and photoinjector stability are presented. User beam set ups to provide beam for electron diffraction and Cavity Beam Position Monitor development are summarised. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE056 | |
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| TUPTY070 | Strong-Strong Simulations of Beta star Levelling for Flat and Round Beams | 2192 |
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Funding: STFC HL-LHC The HL-LHC project aims to reach larger peak luminosities, however this can lead to a high pile up in the detectors. To control the pile up, luminosity levelling has been suggested. One proposed method is β*-luminosity levelling, in which beams collide at a larger than nominal β*. The β* is then reduced in steps as the beam intensity decays. This allows the luminosity to be kept constant over part of a physics fill. The use of round or flat optics will change the beam-beam effect of the head on collisions as well as the long range interactions. Here simulations of β* levelling are presented for the case of flat and round beam optics and the difference in terms of the beam-beam effect is highlighted. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPTY070 | |
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| TUPWI017 | Single-shot Multi-MeV Ultrafast Electron Diffraction on VELA at Daresbury Laboratory | 2278 |
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Funding: This work was funded by STFC Accelerator based Ultrafast Electron Diffraction (UED) is a technique for obtaining static structures and for studying sub-100 fs dynamic structural changes on the atomic scale. In this paper we present the first electron diffraction results obtained from the VELA accelerator in 2014. The accelerator was operated to provide typically 4MeV/c electron bunches. Diffraction patterns were observed with <<1 pC transported to the detection screen. Single shot and multi-shot accumulated diffraction data are presented from single crystal and polycrystalline samples, including Au, Al, Pt and C. Contamination of the diffraction pattern with dark current contributions is an issue. A variable size aperture directly in front of the sample offers some mitigation, but at the expense of reduced charge contributing to the diffraction pattern. We discuss future developments for electron diffraction on VELA including further beam optimization, measurement of bunch length with a newly installed Transverse Deflecting Cavity, and the planned developments for pump-probe studies. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWI017 | |
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