Particle tracking in the ILC extraction lines with DIMAD and BDSIM

The study of beam transport is of central importance to the design and performance assessment of modern particle accelerators. In this paper, we benchmark two contemporary codes, DIMAD and BDSIM, the latter being a relatively new tracking code built within the framework of GEANT4. We consider both the 20 mrad and 2 mrad extraction lines of the 500 GeV International Linear Collider (ILC) and we perform particle tracking studies of heavily disrupted post-collision electron beams. We find that the two codes give an almost equivalent description of the beam transport

Benchmarking of Tracking Codes (BDSIM/DIMAD) using the ILC Extraction Lines

The study of beam transport is of central importance to the design and performance assessment of modern particle accelerators. In this work, we benchmark two contemporary codes - DIMAD and BDSIM, the latter being a relatively new tracking code built within the framework of GEANT4. We consider both the 20 mrad and 2 mrad extraction lines of the International Linear Collider (ILC) and we perform tracking studies of heavily disrupted post-collision electron beams. We find that the two codes mostly give an equivalent description of the beam transport.Comment: Contribution to the Tenth European Particle Accelerator Conference `"EPAC'06'', Edinburgh, United-Kingdom, 26-30 June 200

Optimization of the e-e- option for the ILC

The e-e- running mode is one of the interesting physics options at the International Linear Collider (ILC). The luminosity for e-e- collisions is reduced by the beam-beam effects. The resulting beamstrahlung energy loss and beam-beam deflection angles as function of the vertical transverse offset are different compared to the e+e- collisions. In this paper, the dependence of these observables with the offset for different beam sizes has been analyzed to optimize performances for the e-e- mode, taking into account the requirements of the beam-beam deflection based intra-train feedback system. A first study of the implications for the final focus and extraction line optics is also presented for the cases of the 20 mrad and 2 mrad ILC base line crossing angle geometries

Luminosity, beamstrahlung energy loss and beam-beam deflections for e+e−e^+e^- collisions at the ILC with 500 GeV and varying transverse beam sizes

At the interaction point of the International Linear Collider, beam-beam effects due to the strong electromagnetic fields that the bunches experience during collisions cause a mutual focusing called pinch effect, which enhances the luminosity in the case of $e^+e^-$ collisions. The opposite is true for $e^+e^-$ collisions. In this case the luminosity is reduced by mutual defocusing, or anti-pinching. The resulting beamstrahlung energy loss and beam-beam deflection angles as function of the vertical transverse offset are also different for both modes of operation. The dependence of these quantities with transverse beam sizes are presented for the case of $e^+e^-$ collisions

The 2mrad horizontal crossing angle IR layout for a TeV ILC

The current status of the 2mrad crossing angle layout for the ILC is reviewed. The scheme developed in the UK and France is described and the performance discussed for a TeV machine. Secondly, the scheme developed at SLAC and BNL is then studied and modified for a TeV machine. We find that both schemes can handle the higher energy beam with modifications, and share many common features.Comment: The proceedings of the 2005 International Linear Collider Workshop, March 2005. 4 pages, 5 figure

Luminosity, beamstrahlung energy loss and beam-beam deflections for e+e- and e-e- collisions at the ILC with 500 GeV and varying transverse beam sizes

At the interaction point of the International Linear Collider, beam-beam effects due to the strong electromagnetic fields that the bunches experience during collisions cause a mutual focusing called pinch effect, which enhances the luminosity in the case of $e^+e^-$ collisions. The opposite is true for $e^+e^-$ collisions. In this case the luminosity is reduced by mutual defocusing, or anti-pinching. The resulting beamstrahlung energy loss and beam-beam deflection angles as function of the vertical transverse offset are also different for both modes of operation. The dependence of these quantities with transverse beam sizes are presented for the case of $e^+e^-$ collisions

Linear collider test facility: ATF2 final focus active stabilisation pertinence

International audienceBeam motion at the Interaction Point (IP) of ATF2 has to be less than 10nm relative to the instrumentation used for measurements. Due to ground motion (GM), the beam can pass off-axis through the quadrupoles of the beam line and hence be deflected. It was shown in previous studies that good spatial coherence of the GM over a few meters makes the relative motion of the Final Doublets (FD) small enough for the tolerance not to be exceeded. However, since the coherence drops rapidly with distance, other quadrupoles further upstream can be expected to induce significant effects. In this paper, an evaluation taking into account all ATF2 quadrupoles is presented, using a GM generator with parameters tuned to dedicated measurements done recently along the ATF2 beam line and propagating to the IP with the optical transfer matrices. It was shown that although large IP beam motion can indeed be induced by some specific upstream quadrupoles, the combined effect of all is small because of compensations. The tolerance can thus be achieved without specially stabilising these quadrupoles

Linear Collider Test Facility: Twiss Parameter Analysis at the IP/Post-IP location of the ATF2 beam line

THPD077International audienceAt the first stage of the ATF2 beam tuning, vertical beam size is usually bigger than 3um at the IP. Beam waist measurements using wire scanners and a laser wire are usually performed to check the initial matching of the beam through to the IP. These measurements are described in this paper for the optics currently used (?x=4cm and ?y=1mm). Software implemented in the control room to automate these measurements with integrated analysis is also described. Measurements showed that beta functions and emittances were within errors of measurements when no rematching and coupling corrections were done. However, it was observed that the waist in the horizontal (X) and vertical (Y) plane was abnormally shifted and simulations were performed to try to understand these shifts. They also showed that multiknobs are needed in the current optics to correct simultaneously ?x, ?y and the horizontal dispersion (Dx). Such multiknobs were found and their linearity and orthogonality were successfully checked using MAD optics code. The software for these multiknobs was implemented in the control room and waist scan measurements using the ?y knob were successfully performed

Comparison of ILC Fast Beam-Beam Feedback Performance in the e−e−e^- e^- and e+e−e^+ e^- Modes of Operation

Several feedback loops are required in the Beam Delivery System (BDS) of the International Linear Collider (ILC) to preserve the luminosity in the presence of dynamic imperfections. Realistic simulations have been carried out to study the performance of the beam-beam deflection based fast feedback system, for both e+e- and e-e- modes of operation. The beam-beam effects in the e-e- collisions make both the luminosity and the deflections more sensitive to offsets at the interaction point (IP) than in the case of the e+e-collisions. This reduces the performance of the feedback system in comparison to the standard e+e- collisions, and may require a different beam parameter optimization

Extraction of the x-dependence of the non-perturbative QCD b-quark fragmentation distribution component

Using recent measurements of the b-quark fragmentation distribution obtained in $e^+e^- \to b \bar{b}$ events registered at the Z pole, the non-perturbative QCD component of the distribution has been extracted independently of any hadronic physics modelling. This distribution depends only on the way the perturbative QCD component has been defined. When the perturbative QCD component is taken from a parton shower Monte-Carlo, the non-perturbative QCD component is rather similar with those obtained from the Lund or Bowler models. When the perturbative QCD component is the result of an analytic NLL computation, the non-perturbative QCD component has to be extended in a non-physical region and thus cannot be described by any hadronic modelling. In the two examples used to characterize these two situations, which are studied at present, it happens that the extracted non-perturbative QCD distribution has the same shape, being simply translated to higher-x values in the second approach, illustrating the ability of the analytic perturbative QCD approach to account for softer gluon radiation than with a parton shower generator.Comment: 13 page