The design luminosity for the future linear colliders is very demanding and
challenging. Beam-based feedback systems will be required to achieve the
necessary beam-beam stability and steer the two beams into collision. In
particular we have studied the luminosity performance improvement by
intra-train beam-based feedback systems for position and angle corrections at
the interaction point. We have set up a simulation model which introduces
different machine imperfections and can be applied to both the International
Linear Collider (ILC) and the Compact Linear Collider (CLIC).Comment: 4 pages, 4 figure

Burrows, P. N.

Latina, A.

Resta-Lopez, J.

Schulte, D.

English

arXiv

The design luminosity for the future linear colliders is very demanding and challenging. Beam-based feedback systems will be required to achieve the necessary beam-beam stability and steer the two beams into collision. In particular we have studied the luminosity performance improvement by intra-train beam-based feedback systems for position and angle corrections at the interaction point. We have set up a simulation model which introduces different machine imperfections and can be applied to both the International Linear Collider (ILC) and the Compact Linear Collider (CLIC)

Resta-López, J

Burrows, Philip

Latina, A

Schulte, D

Oxford University Research Archive

Luminosity performance studies of linear colliders with intra-train feedback systems

The design luminosity for the future linear colliders is very demanding and challenging. Beam-based feedback systems will be required to achieve the necessary beam-beam stability and steer the two beams into collision. In particular we have studied the luminosity performance improvement by intra-train beam-based feedback systems for position and angle corrections at the interaction point. We have set up a simulation model which introduces different machine imperfections and can be applied to both the International Linear Collider (ILC) and the Compact Linear Collider (CLIC).The design luminosity for the future linear colliders is very demanding and challenging. Beam-based feedback systems will be required to achieve the necessary beam-beam stability and steer the two beams into collision. In particular we have studied the luminosity performance improvement by intra-train beam-based feedback systems for position and angle corrections at the interaction point. We have set up a simulation model which introduces different machine imperfections and can be applied to both the International Linear Collider (ILC) and the Compact Linear Collider (CLIC)

Burrows, P.N.

CERN Document Server

Luminosity Performance Studies of Linear Colliders with Intra-train Feedback Systems

The design luminosity for the future linear colliders is very demanding and
challenging. Beam-based feedback systems will be required to achieve the
necessary beam-beam stability and steer the two beams into collision. In
particular we have studied the luminosity performance improvement by
intra-train beam-based feedback systems for position and angle corrections at
the interaction point. We have set up a simulation model which introduces
different machine imperfections and can be applied to both the International
Linear Collider (ILC) and the Compact Linear Collider (CLIC)

Resta-Lopez, J

Burrows, PN

University of Liverpool Repository

arXiv:0902.2915v1  [physics.acc-ph]  17 Feb 2009Luminosity Performance Studies of Linear Colliderswith Intra-train Feedback SystemsJ. Resta-Lo´pez1, P. N. Burrows1, A. Latina2 and D. Schulte31- John Adams Institute at Oxford University, Oxford, OX1 3RH, UK2- Fermilab, Batavia, IL 60510-5011, USA3- CERN, 1211 Geneva 23, CHThe design luminosity for the future linear colliders is very demanding and challenging.Beam-based feedback systems will be required to achieve the necessary beam-beamstability and steer the two beams into collision. In particular we have studied theluminosity performance improvement by intra-train beam-based feedback systems forposition and angle corrections at the interaction point. We have set up a simulationmodel which introduces different machine imperfections and can be applied to both theInternational Linear Collider (ILC) and the Compact Linear Collider (CLIC).1 Introduction 0 0.2 0.4 0.6 0.8 1 1.2 0  1  2  3  4  5L/L0∆y/σyrigid modelCLIC (3 TeV cm)ILC (500 GeV cm)Figure 1: Luminosity loss versus the relativebeam-beam position offset.The design luminosity of the future high-energy electron-positron colliders requirestransverse beam sizes at the nanometre levelat the interaction point (IP), as well as sta-bilisation of the electron and positron beamcollision overlaps at the sub-nanometrelevel.Static and dynamic imperfections of themachine generate beam jitter, which candramatically degrade the luminosity. Fig. 1shows an example of luminosity loss versusthe relative offset of the colliding beams forboth ILC [1] and CLIC [2] with nominalbeam parameters. The red curve is the ge-ometric luminosity analytically calculated.The blue and green curves correspond to the luminosity loss for ILC and CLIC, respectively,computed using the code GUINEA-PIG [3]. For instance, in order to maintain the lumi-nosity 10% of nominal the electron and positron beam vertical position overlap needs to bestabilised to within ≈ 0.5 σy for ILC and ≈ 1 σy for CLIC.In order to achieve the required beam stability goals, beam-based feedback (FB) systems,operating at different timescales, are designed to be distributed in the linac and the beamdelivery system (BDS). In this paper we concretely study the luminosity performance withfast intra-train beam-based FB systems at the IP in presence of dynamic imperfections, e.g.ground motion (GM). Simulation results are presented and discussed in section 3 for bothILC and CLIC.To illustrate the train structure of linear colliders Table 1 shows some relevant designparameters of ILC and CLIC. The ILC is an example of ’cold-’RF based design (supercon-ducting RF cavities) [1]. The ILC repetition frequency is 5 Hz, and the bunch train comprisesLCWS/ILC 2008Property ILC 500 GeV CLIC 3 TeV unitsElectrons/bunch 2.0 0.37 1010Bunches/train 2820 312Train Repetition Rate 5 50 HzBunch Separation 308 0.5 nsTrain Length 867.7 0.156 µsHorizontal IP Beam Size (σx) 655 45 nmVertical IP Beam Size (σy) 5.7 0.9 nmLongitudinal IP Beam Size 300 45 µmLuminosity 2.03 6.0 1034cm−2s−1Table 1: Some nominal parameters of the ILC and CLIC designs for the linear collider.2820 bunches with a nominal inter-bunch separation of 308 ns. This time structure wouldallow the bunch-to-bunch feedback correction using digital FB processors. CLIC is based ina so-called ’warm’-RF design (see e.g. Ref. [2] for details), with beam time structures muchshorter than for the ILC. For CLIC with a nominal inter-bunch separation of 0.5 ns and anominal train length of 156 ns the design of an IP intra-pulse FB system is very challenging.2 Intra-train feedback systemKickerBPMProcessorDelayAmp+IPFigure 2: Schematic of IP intra-train feedbacksystem.The beam-beam jitter induced by imperfec-tions of the machine can be counteracted byusing fast intra-train feedback systems nearthe IP. The IP-FB systems could be consid-ered as the last ’weapon’ of defence against,for example, transverse jitters of the finalfocus magnets.A fast IP-FB system for linear collidersis based on the measurement of the incom-ing trajectories of the early bunches in theelectron or positron trains. This informa-tion is then used as the input to the feed-back system for steering the later bunchesinto collisions at the IP. Fig. 2 shows a basic scheme of a beam-based IP-FB system. Thekey components of the system are a beam position monitor (BPM) for registering the beamorbit, and a kicker for applying a position (or angle) correction to the beam. Additionalhardware components, such as BPM signal processor board, FB circuit and fast amplifier,are described in detail elsewhere [4].3 Beam transport and luminosity simulationsWe have developed a beam transport model for linear colliders based on the tracking codePLACET [5]. Sliced bunches are tracked along the main linac. The linac simulations includeboth short and long-range transverse and longitudinal wakefield effects of the acceleratingcavities. For the tracking through the BDS each bunch is binned in a certain number ofmacro-particles (here we have used 50000 macro-particles). Survey alignment errors anddynamic imperfections (ground motion) can be included in the model.LCWS/ILC2008The code GUINEA-PIG [3] is used to evaluate the luminosity and the beam-beam de-flection for electron-positron beam collisions at the IP.3.1 Results for ILC0 50 100 150 200 250 300 3500.40.60.811.21.41.61.82Bunch #L [*1034 cm−2 s−1 ]  with GM model Awith GM model Bwith GM model Cwith GM model KFigure 3: Total luminosity versus bunch num-ber within a train for the ILC. Example fora single random seed for different models ofground motion: A, B, C and K.Intra-train IP position FB corrections canbe applied using a stripline kicker locatednear the IP in the incoming beamline be-tween the sextupole SD0 and the finalquadrupole QF1. At pi/2 phase advancedownstream of the IP a BPM measures thebeam positions to determine the deflectionangle of the beams. Usually BPM resolu-tions of ∼ 1 µm are sufficient for these mea-surements. On the other hand, to correctthe angle, a stripline kicker is located atthe entrance of the final focus system witha downstream BPM at pi/2 phase advance.For the simulations we use a FB loop basedin a proportional and integral (PI) controlalgorithm [6].We have studied the performance of theFB system in terms of correcting the posi-tion jitter generated by ground motion. Using the GM models [7], 0.2 s of GM is appliedto both e− linac+BDS and e+ linac+BDS. The resulting luminosity for a single seed of GMas a function of bunch number in a train is shown in Fig. 3, where different scenarios ofGM are compared. For the noisiest site (model C), applying fast position FB stabilisation,a recovery of the luminosity up to 85% of the nominal value is obtained. On the otherhand, for quiet sites (models A and B) practically 100% of the nominal luminosity would beachievable with the IP-FB correction.3.2 Results for CLICLatency times of about 20 ns have experimentally been demonstrated by the FONT3 system[8] using an analogue FB processor. Therefore, for the CLIC simulations we have considereda correction iteration every 20 ns. Taking into account the CLIC nominal bunch separationof 0.5 ns, this system performs approximately a correction every 40 bunches (≈ 8 iterationsper pulse).For the CLIC IP position FB simulations, the kicker or corrector has been located in theincoming beamline immediately downstream of the final quadrupole QD0. At pi/2 phaseadvance downstream of the IP a BPM, with 1 µm resolution, measures the beam positions.In this case we have employed a FB control loop based in a simple proportional controlalgorithm. Unlike the angle bunch-to-bunch FB system for ILC, due to latency constraintsno angle intra-train FB system has been designed for CLIC.In this case, applying the model C of GM, simulations of CLIC (Fig. 4) has shown arecovery of about 20% of the nominal luminosity using the intra-train position FB systemat the IP. With model K the FB system manages to recover about 80% of the nominalLCWS/ILC 2008luminosity. For quiet sites (models A and B) practically 100% of the nominal luminositywould be achievable.4 Summary and outlook0 100 200 300 400 500 60000.20.40.60.811.2t [ns]L/L0  GM model AGM model BGM model CGM model KFigure 4: Relative luminosity versus time forCLIC. Example for a single random seed fordifferent models of ground motion: A, B, Cand K.Beam-based feedback systems will bemandatory to achieve the required luminos-ity goals of the future electron-positron lin-ear colliders. In particular we have simu-lated the performance of intra-train beam-based FB systems at the IP. These FB sys-tems reduce the transverse beam-beam jit-ters and steer the electron and positronbeams into collision. Simulation results arepresented for ILC and CLIC in terms of cor-recting the transverse vertical jitters gen-erated by ground motion. For quiet sites(models A and B) practically 100% of thenominal luminosity would be achievable us-ing the IP-FB systems. However, assumingthe most severe scenario (GM model C),intra-train FB systems at the IP are notenough to achieve the nominal luminosity.This is due to remaining uncorrected pulse-to-pulse jitter, which could in principle be cor-rected with additional upstream slower FB systems in the BDS.5 AcknowledgmentsThis work is supported by the Commission of the European Communities under the 6thFramework Programme ”Structuring the European Research Area”, contract number RIDS-011899.References[1] James Brau (Ed.) et al., ILC Reference Design Report: ILC Global Design Effort and World WideStudy, arXiv:0712.1959[physics.acc-ph] (2007).[2] Frank Tecker (Ed.) et al., CLIC 2008 Parameters, CLIC-Note-764 (2008).[3] D. Schulte, PhD Thesis, TESLA-97-08 (1996).[4] P. N. Burrows et al., Design and Performance of a Prototype Digital Feedback System for the Interna-tional Linear Collider Interaction Point, Proc. of EPAC 2008, Genoa, Italy (2008).[5] D. Schulte et al., Simulation Package based on Placet, Proc. of PAC 2001, Chicago, Illinois (2001);https://savannah.cern.ch/projects/placet.[6] T. Himmel, Annu. Rev. Nucl. Part. Sci. 49 157 (1997).[7] A. Seryi et al., Simulation Studies of the NLC with the Improved Ground Motion Models, Proc. ofLINAC 2000, Monterey, California (2000).[8] P. N. Burrows et al., Tests of the FONT3 Linear Collider Intra-train Beam Feedback System at theATF, Proc. of PAC 2005, Knoxville, Tennessee (2005).LCWS/ILC2008

Luminosity Performance Studies of Linear Colliders with Intra-train Feedback Systems

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