The Compact Linear Collider (CLIC) study team at CERN is working on the design of an electron-positron linear collider, with the main focus on a machine with a centre-of-mass energy of Ecm=3 TeV and a luminosity of 1035cm-2s-1. Because of the high energy and high luminosity, the background in this machine is expected to be higher than in low-energy linear colliders. These backgrounds need to be carefully investigated in order to verify that the experimental conditions are acceptable. For the same reason the luminsoity spectrum needs careful consideration. This paper gives a brief update on the status of the necessary machine/detector interface studies for CLIC

Schulte, Daniel

CERN Document Server

EUROPEAN ORGANISATION FOR NUCLEAR RESEARCHCERN – PS DIVISIONCERN-PS 2001-074 (AE)CLIC Note 502Update of the Status of Machine Detector Interface Studies for CLICD. SchulteAbstractThe Compact Linear Collider (CLIC) study team at CERN is working on the design of an electron-positronlinear collider, with the main focus on a machine with a centre-of-mass energy of Ecm = 3 TeV and a luminosityof 1035 m−2s−1 [1]. Because of the high energy and high luminosity, the background in this machine is expectedto be higher than in low-energy linear colliders. These backgrounds need to be carefully investigated in orderto verify that the experimental conditions are acceptable. For the same reason the luminsoity spectrum needscareful consideration. This paper gives a brief update on the status of the necessary machine/detector interfacestudies for CLIC.APS/DPF/DPB Summer Study of the Future of High Energy Particle Physics (Snowmass 2001),Snomass, Colorado, 30 June-21 July 2001Geneva, Switzerland21 October 2001Update of the Status of Machine Detector Interface Studies for CLICD. SchulteCERNThe Compact Linear Collider (CLIC) study team at CERN is working on the design of an electron-positron linear collider, with the main focus on a machine with a centre-of-mass energy of Ecm =3 TeV and a luminosity of 1035 m−2s−1 [1]. Because of the high energy and high luminosity, thebackground in this machine is expected to be higher than in low-energy linear colliders. Thesebackgrounds need to be carefully investigated in order to verify that the experimental conditionsare acceptable. For the same reason the luminsoity spectrum needs careful consideration. Thispaper gives a brief update on the status of the necessary machine/detector interface studies forCLIC.I. INTRODUCTIONA short summary of the background in the detector due to beam-beam interaction can be found in ref-erences [2][3] and in the references therein. The latter paper also describes the masks used to reduce thebackground. This paper will concentrate on the new developments.II. BEAM DELIVERY SYSTEM AND MUON BACKGROUNDThe last quadrupoles of the nal focus system will be positioned inside of the detector. Depending on whichof the two options for the nal focus system is used, the distance of the nal quadrupole to the interaction point(IP) will be l? = 2 m or l? = 4.3 m. The available space for the nal quadrupoles is very limited, especially inthe case of l? = 2 m, where the outer radius must stay below 20 mm [4]. Several dierent designs for the nalquadrupole were considered [5]. A design that is based on permanent magnets is very promising. It should bepossible to achieve the required small outer radius with this approach.In the collimation system, the tails of the beams are scraped o to avoid background in the detector. It alsoserves to protect both the nal focus system and the detector in case of machine failures. A rst design of thissystem has been developed [6]. It is based on a design for the Next Linear Collider (NLC) [7] which was scaledto achieve the required performance. The total length is 5.6 km. The rst part of the system collimates thebeam in energy, the second part performs collimation of transverse tails. It is anticipated that energy errorsfrom one pulse to the next are common, while large transverse errors are rare. Therefore the beam size atthe energy collimators must be large enough so that they are not damaged, while the transverse collimatorsare sacricial [6]. Possible failures that can lead to large energy or position errors of the beam have beeninvestigated [8] [9]. This work needs to continue.When beam particles hit the collimators, they induce electro-magnetic showers in which muons are produced.Since muons can easily penetrate material, they have a signicant probability to reach the detector and causebackground. The study of the potential muon flux is continuing. A modied version of the GEANT basedprogram MUBKG, which was used for the TESLA study [10], has been developed [6]. This allows to study themuon rate in the detector. First results show that it is much more dicult to reduce the background flux inCLIC with iron absorbers than in lower energy machines. One of the goals of the study is to implement thedierent muon production processes into GEANT4.In CLIC the beams collide with a crossing angle of θc = 20 mradian at the IP. This is the smallest angle whichis compatible with the necessity to provide enough space for the outgoing coherent pairs which are created inthe interaction point [11]. Also the multi-bunch kink instability [12] sets a lower limit [13]. This instabilityis due to parasitic crossings of bunches in the detector. A more complete treatment of the multi-bunch kinkinstability, which includes the non-negligible eect of the coherent pairs, has been performed [3]. It also showedthat θc = 20 mradian is acceptable. When the beams have a crossing angle at the IP, they are deflected by thelongitudinal magnetic eld in the detector. This leads to the emission of synchrotron radiation, which modiesthe particle trajectories and leads to an increase of the spot size in the IP. For a solenoid eld of Bz = 4 T thespot size growth is acceptable if the crossing angle is θc ≤ 20 mradian [14].3a)b)c)1488149014921494149614981500150215041506-80 -60 -40 -20 0 20 40 60 80E [GeV]z [µm]FIG. 1: The left side schematically shows the modification of the bunch shape in the linac (a). Usually, for furthercalculations the final bunches are modeled by broader ones which are straight (b), while realistic calculations need totake into account the correlation of the transverse and longitudinal position within the bunch. The right side shows thecorrelation of the final beam energy to the longitudinal position within the bunch. The head of the bunch is at z < 0.051015202530354045502980 2990 3000 3010 3020dL/dE cm [1032cm-2 s-1 GeV-1 ]Ecm [GeV]perfect machinecase 1case 2case 3case 40510152025303540452980 2990 3000 3010 3020dL/dE cm [1032cm-2 s-1 GeV-1 ]Ecm [GeV]initial machinecase 1case 2case 3case 4FIG. 2: The luminosity spectrum in the peak. On the left side four examples of the spectrum are shown for differentinitial misalignments. For comparison the case of a perfectly aligned machine is also displayed. On the right side a singlemachine is shown together with four examples of how the spectrum could look like 10 minutes later, when the machineis moving together with the ground.III. WAKEFIELD EFFECTS AND THE LUMINOSITY SPECTRUMIn the main linac the shape of the bunches will be distorted due to transverse wakeelds. The energy spreadwithin the bunch also leads to a distortion due to dispersion, since particles at dierent energies are focuseddierently by the same quadrupole. The left side of Fig 1 schematically shows how the bunches are deformedwhile passing through the linac (a). Conventionally these bunch deformations have been described by the growthof the projected emittance, i.e. the overall transverse size of the bunch. In the simulation of the following partof the machine, the correlation of transverse and longitudinal position was therefore neglected. In the gurethis is shown for the example of beam-beam interaction (b). Simulation of the real situation, shown in (c), mayhowever lead to very dierent results, as has been shown in recent quantitative investigations for TESLA [15]and CLIC [16]. The actual luminosity loss due to bunch deformations can be more than an order of magnitudelarger than calculated without the correlation. The impact this has on the dierent tolerances needs to beinvestigated in detail.In normal-conducting accelerators, the nal beam has a correlated energy spread along the bunch, see Fig. 1(right). Since the dierent slices of the beam also have dierent osets, the luminosity spectrum will be aectedby the bunch shape. This has been simulated using the following procedure. The beam has been trackedthrough the main linac using PLACET [17] and a simplied beam delivery system has been used to transport itto the IP. The beam-beam interaction has then been simulated using Guinea-Pig [18]. A realistic beam deliverysystem, which adds to the bunch deformations due to non-linear and energy dependent eects, will be includedin the simulations in the near future.When the elements of the linac are put into the tunnel they have small misalignments with respect to thenominal position. The resulting eect this has on the beam is largely corrected using beam-based alignment.4While the average amplitude of these initial misalignments is approximately known, their actual distributionis not. Several dierent misalignments have been simulated and some examples of resulting luminosity spectraare shown on the left side of Fig. 2. Obviously they can signicantly depend on the initial misalignments of thelinac.When the linac has been installed it will move continuously due to the motion of the ground. A single machinehas been simulated with given misalignments. Then 10 minutes of ground motion and the appropriate reactionby the feedbacks were simulated. As the right side of Fig. 2 shows, the luminosity spectrum can change quitesignicantly in this time.IV. CONCLUSIONCalculation of the beam delivery system of CLIC is progressing. A rst design of the complete beam lineexists. However, further evaluation of the performance of this system is necessary. The availability of theprogram to simulate the muon background is a major step towards this goal. Also the search for possibleimprovements of the system is continuing. The nal quadrupoles are however posing a challenge. A design hasbeen developed that can meet this challenge. It has been veried that the chosen crossing angle between thetwo beams is compatible with a solenoid eld of Bz = 4 T.It has been shown that the actual bunch shapes need to be taken into account in simulations of the beam-beam interaction. They not only modify the luminosity loss signicantly, but they also aect the luminosityspectrum. These eects need further study.[1] G. Guignard (ed) et al. (2000), CERN-2000-008.[2] D. Schulte (1999), workshop on the Development of Future Linear Electron- Positron Colliders for Particle PhysicsStudies and for Research Using Free Electon Lasers, Lund, Sweden, 23 -26 Sep 1999.[3] D. Schulte (2001), prepared for 5th International Linear Collider Workshop (LCWS 2000), Fermilab, Batavia, Illinois,24-28 Oct 2000.[4] D. Schulte (1999), International Workshop on Linear Colliders, Sitges, Spain, 28 Apr - 5 May 1999.[5] M. Aleksa et al. (2001), CERN-SL-2001-045-AP.[6] R. Assmann et al. (2001), prepared for IEEE Particle Accelerator Conference (PAC 2001), Chicago, Illinois, 18-22Jun 2001.[7] P. Tenenbaum, R. Helm, L. Keller, and T. O. Raubenheimer, eConf C000821, MOA08 (2000),arXiv:physics/0010078.[8] D. Schulte and F. Zimmermann (2001), IEEE Particle Accelerator Conference (PAC 2001), Chicago, Illinois, 18-22Jun 2001.[9] R. Assmann et al. (2000), CERN-SL-2000-058-AP.[10] H. J. Schreiber (1999), presentation at the 7th Workshop of the 2nd ECFA/DESY Study of Physics and Detectorsfor a Linear Electron Positron Collider.[11] D. Schulte (1999), IEEE Particle Accelerator Conference (PAC 99), New York, 29 Mar - 2 Apr 1999.[12] K. Yokoya and P. Chen (1991), tsukuba KEK - KEK-Prepr.-91-002 (91/04,rec.Jul.) 36 p.[13] O. Napoly (1999), CERN-SL-99-054-AP.[14] D. Schulte and F. Zimmermann (2001), IEEE Particle Accelerator Conference, Chicago, IL, USA, 18- 22 Jun 2001.[15] R. Brinkmann, O. Napoly, and D. Schulte (2001), IEEE Particle Accelerator Conference (PAC 2001), Chicago,Illinois, 18-22 Jun 2001.[16] N. Leros and D. Schulte (2001), IEEE Particle Accelerator Conference, Chicago, IL, USA, 18- 22 Jun 2001.[17] E. T. D’Amico, G. Guignard, N. Leros, and D. Schulte (2001), IEEE ParticleAccelerator Conference, Chicago, IL,USA, 18-22 Jun 2001.[18] D. Schulte (1999), CERN-PS-99-014.

Update of the Status of Machine Detector Interface Studies for CLIC

Schulte, D

  CERN – EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH             CLIC Note 502 CERN/PS 2001-074 (AE)      UPDATE OF THE STATUS OF MACHINE DETECTOR INTERFACE STUDIES FOR CLIC   D. Schulte     Abstract   The Compact Linear Collider (CLIC) study team at CERN is working on the design of an electron-positron linear collider, with the main focus on a machine with a centre-of-mass energy of Ecm=3 TeV and a luminosity of 1035cm-2s-1. Because of the high energy and high luminosity, the background in this machine is expected to be higher than in low-energy linear colliders. These backgrounds need to be carefully investigated in order to verify that the experimental conditions are acceptable. For the same reason the luminosity spectrum needs careful consideration. This paper gives a brief update on the status of the necessary machine/detector interface studies for CLIC.   Presented at  the SAPS-DPF-DPB Summer Study on the Future of Particle Physics - Snowmass 2001, 30 June - 21 July 2001, Snowmass, CO, US       Geneva, Switzerland 20 December 2001 Update of the Status of Machine Detector Interface Studies for CLICD. SchulteCERNThe Compact Linear Collider (CLIC) study team at CERN is working on the design of an electron-positron linear collider, with the main focus on a machine with a centre-of-mass energy of Ecm =3TeV and a luminosity of 1035 m−2s−1 [1]. Because of the high energy and high luminosity, thebackground in this machine is expected to be higher than in low-energy linear colliders. Thesebackgrounds need to be carefully investigated in order to verify that the experimental conditionsare acceptable. For the same reason the luminsoity spectrum needs careful consideration. Thispaper gives a brief update on the status of the necessary machine/detector interface studies forCLIC.I. INTRODUCTIONA short summary of the background in the detector due to beam-beam interaction can be found in ref-erences [2][3] and in the references therein. The latter paper also describes the masks used to reduce thebackground. This paper will concentrate on the new developments.II. BEAM DELIVERY SYSTEM AND MUON BACKGROUNDThe last quadrupoles of the ﬁnal focus system will be positioned inside of the detector. Depending on whichof the two options for the ﬁnal focus system is used, the distance of the ﬁnal quadrupole to the interaction point(IP) will be l = 2m or l = 4.3m. The available space for the ﬁnal quadrupoles is very limited, especially inthe case of l = 2m, where the outer radius must stay below 20mm [4]. Several diﬀerent designs for the ﬁnalquadrupole were considered [5]. A design that is based on permanent magnets is very promising. It should bepossible to achieve the required small outer radius with this approach.In the collimation system, the tails of the beams are scraped oﬀ to avoid background in the detector. It alsoserves to protect both the ﬁnal focus system and the detector in case of machine failures. A ﬁrst design of thissystem has been developed [6]. It is based on a design for the Next Linear Collider (NLC) [7] which was scaledto achieve the required performance. The total length is 5.6 km. The ﬁrst part of the system collimates thebeam in energy, the second part performs collimation of transverse tails. It is anticipated that energy errorsfrom one pulse to the next are common, while large transverse errors are rare. Therefore the beam size atthe energy collimators must be large enough so that they are not damaged, while the transverse collimatorsare sacriﬁcial [6]. Possible failures that can lead to large energy or position errors of the beam have beeninvestigated [8] [9]. This work needs to continue.When beam particles hit the collimators, they induce electro-magnetic showers in which muons are produced.Since muons can easily penetrate material, they have a signiﬁcant probability to reach the detector and causebackground. The study of the potential muon ﬂux is continuing. A modiﬁed version of the GEANT basedprogram MUBKG, which was used for the TESLA study [10], has been developed [6]. This allows to study themuon rate in the detector. First results show that it is much more diﬃcult to reduce the background ﬂux inCLIC with iron absorbers than in lower energy machines. One of the goals of the study is to implement thediﬀerent muon production processes into GEANT4.In CLIC the beams collide with a crossing angle of θc = 20mradian at the IP. This is the smallest angle whichis compatible with the necessity to provide enough space for the outgoing coherent pairs which are created inthe interaction point [11]. Also the multi-bunch kink instability [12] sets a lower limit [13]. This instabilityis due to parasitic crossings of bunches in the detector. A more complete treatment of the multi-bunch kinkinstability, which includes the non-negligible eﬀect of the coherent pairs, has been performed [3]. It also showedthat θc = 20mradian is acceptable. When the beams have a crossing angle at the IP, they are deﬂected by thelongitudinal magnetic ﬁeld in the detector. This leads to the emission of synchrotron radiation, which modiﬁesthe particle trajectories and leads to an increase of the spot size in the IP. For a solenoid ﬁeld of Bz = 4T thespot size growth is acceptable if the crossing angle is θc ≤ 20mradian [14].a)b)c)1488149014921494149614981500150215041506-80 -60 -40 -20 0 20 40 60 80E [GeV]z [µm]FIG. 1: The left side schematically shows the modiﬁcation of the bunch shape in the linac (a). Usually, for furthercalculations the ﬁnal bunches are modeled by broader ones which are straight (b), while realistic calculations need totake into account the correlation of the transverse and longitudinal position within the bunch. The right side shows thecorrelation of the ﬁnal beam energy to the longitudinal position within the bunch. The head of the bunch is at z < 0.051015202530354045502980 2990 3000 3010 3020dL/dE cm [1032cm-2 s-1 GeV-1 ]Ecm [GeV]perfect machinecase 1case 2case 3case 40510152025303540452980 2990 3000 3010 3020dL/dE cm [1032cm-2 s-1 GeV-1 ]Ecm [GeV]initial machinecase 1case 2case 3case 4FIG. 2: The luminosity spectrum in the peak. On the left side four examples of the spectrum are shown for diﬀerentinitial misalignments. For comparison the case of a perfectly aligned machine is also displayed. On the right side a singlemachine is shown together with four examples of how the spectrum could look like 10 minutes later, when the machineis moving together with the ground.III. WAKEFIELD EFFECTS AND THE LUMINOSITY SPECTRUMIn the main linac the shape of the bunches will be distorted due to transverse wakeﬁelds. The energy spreadwithin the bunch also leads to a distortion due to dispersion, since particles at diﬀerent energies are focuseddiﬀerently by the same quadrupole. The left side of Fig 1 schematically shows how the bunches are deformedwhile passing through the linac (a). Conventionally these bunch deformations have been described by the growthof the projected emittance, i.e. the overall transverse size of the bunch. In the simulation of the following partof the machine, the correlation of transverse and longitudinal position was therefore neglected. In the ﬁgurethis is shown for the example of beam-beam interaction (b). Simulation of the real situation, shown in (c), mayhowever lead to very diﬀerent results, as has been shown in recent quantitative investigations for TESLA [15]and CLIC [16]. The actual luminosity loss due to bunch deformations can be more than an order of magnitudelarger than calculated without the correlation. The impact this has on the diﬀerent tolerances needs to beinvestigated in detail.In normal-conducting accelerators, the ﬁnal beam has a correlated energy spread along the bunch, see Fig. 1(right). Since the diﬀerent slices of the beam also have diﬀerent oﬀsets, the luminosity spectrum will be aﬀectedby the bunch shape. This has been simulated using the following procedure. The beam has been trackedthrough the main linac using PLACET [17] and a simpliﬁed beam delivery system has been used to transport itto the IP. The beam-beam interaction has then been simulated using Guinea-Pig [18]. A realistic beam deliverysystem, which adds to the bunch deformations due to non-linear and energy dependent eﬀects, will be includedin the simulations in the near future.When the elements of the linac are put into the tunnel they have small misalignments with respect to thenominal position. The resulting eﬀect this has on the beam is largely corrected using beam-based alignment.While the average amplitude of these initial misalignments is approximately known, their actual distributionis not. Several diﬀerent misalignments have been simulated and some examples of resulting luminosity spectraare shown on the left side of Fig. 2. Obviously they can signiﬁcantly depend on the initial misalignments of thelinac.When the linac has been installed it will move continuously due to the motion of the ground. A single machinehas been simulated with given misalignments. Then 10 minutes of ground motion and the appropriate reactionby the feedbacks were simulated. As the right side of Fig. 2 shows, the luminosity spectrum can change quitesigniﬁcantly in this time.IV. CONCLUSIONCalculation of the beam delivery system of CLIC is progressing. A ﬁrst design of the complete beam lineexists. However, further evaluation of the performance of this system is necessary. The availability of theprogram to simulate the muon background is a major step towards this goal. Also the search for possibleimprovements of the system is continuing. The ﬁnal quadrupoles are however posing a challenge. A design hasbeen developed that can meet this challenge. It has been veriﬁed that the chosen crossing angle between thetwo beams is compatible with a solenoid ﬁeld of Bz = 4T.It has been shown that the actual bunch shapes need to be taken into account in simulations of the beam-beam interaction. They not only modify the luminosity loss signiﬁcantly, but they also aﬀect the luminosityspectrum. These eﬀects need further study.[1] G. Guignard (ed) et al. (2000), CERN-2000-008.[2] D. Schulte (1999), workshop on the Development of Future Linear Electron- Positron Colliders for Particle PhysicsStudies and for Research Using Free Electon Lasers, Lund, Sweden, 23 -26 Sep 1999.[3] D. Schulte (2001), prepared for 5th International Linear Collider Workshop (LCWS 2000), Fermilab, Batavia, Illinois,24-28 Oct 2000.[4] D. Schulte (1999), International Workshop on Linear Colliders, Sitges, Spain, 28 Apr - 5 May 1999.[5] M. Aleksa et al. (2001), CERN-SL-2001-045-AP.[6] R. Assmann et al. (2001), prepared for IEEE Particle Accelerator Conference (PAC 2001), Chicago, Illinois, 18-22Jun 2001.[7] P. Tenenbaum, R. Helm, L. Keller, and T. O. Raubenheimer, eConf C000821, MOA08 (2000),arXiv:physics/0010078.[8] D. Schulte and F. Zimmermann (2001), IEEE Particle Accelerator Conference (PAC 2001), Chicago, Illinois, 18-22Jun 2001.[9] R. Assmann et al. (2000), CERN-SL-2000-058-AP.[10] H. J. Schreiber (1999), presentation at the 7th Workshop of the 2nd ECFA/DESY Study of Physics and Detectorsfor a Linear Electron Positron Collider.[11] D. Schulte (1999), IEEE Particle Accelerator Conference (PAC 99), New York, 29 Mar - 2 Apr 1999.[12] K. Yokoya and P. Chen (1991), tsukuba KEK - KEK-Prepr.-91-002 (91/04,rec.Jul.) 36 p.[13] O. Napoly (1999), CERN-SL-99-054-AP.[14] D. Schulte and F. Zimmermann (2001), IEEE Particle Accelerator Conference, Chicago, IL, USA, 18- 22 Jun 2001.[15] R. Brinkmann, O. Napoly, and D. Schulte (2001), IEEE Particle Accelerator Conference (PAC 2001), Chicago,Illinois, 18-22 Jun 2001.[16] N. Leros and D. Schulte (2001), IEEE Particle Accelerator Conference, Chicago, IL, USA, 18- 22 Jun 2001.[17] E. T. D’Amico, G. Guignard, N. Leros, and D. Schulte (2001), IEEE ParticleAccelerator Conference, Chicago, IL,USA, 18-22 Jun 2001.[18] D. Schulte (1999), CERN-PS-99-014.

Update of the Status of Machine Detector Interface Studies for CLIC

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