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The CERN Large Hadron Collider LHC Abstract EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH Europ ean Lab oratory for Particle Physics Large Hadron Collider Pro ject LHC Project Rep ort 83 The CERN Large Hadron Collider LHC Eb erhard Keil Abstract The Large Hadron Collider Pro ject LHC was approved by the CERN Council in December 1994. Commissioning with b eam will start in the second half of 2005. The pap er discusses the most imp ortant parameters, the general layout of the LHC o ctants, and the status of the exp eriments ALICE, ATLAS, CMS and LHC-B. Also describ ed are some asp ects of the b eam- b eam interactions, the transverse coupled-bunch instability,aswell as the technical developments of the cryogenics, the tests of half an arc cell, and the new civil engineering needed. Invited talk at the 34-th Eloisatron Workshop, Erice, Italy, 4{13 Novemb er 1996 Administrative Secretariat LHC Division CERN CH-1211 Geneva23 Switzerland Geneva, Decemb er 6, 1996 1 INTRODUCTION The LHC pro ject was approved by Council in December 1994. Big contracts start b eing placed. In Septemb er 1996, the Finance Committee approved contracts for the whole 50000 t of steel supply, the sup ervision of the civil engineering work, and eight magnet measuring b enches. I assume for the remainder of the milestones that enough funds are available to construct the LHC in a single stage. By the end of 1999 most of the big contracts will have b een placed, the prices will be known, and a nal decision on the con guration can be taken. We assume that LEP will stop op eration at the end of 1999. Continuing LEP op eration into 2000 must be justi ed on scienti c grounds and money must be found. Dismantling LEP will start in Octob er 2000 when the civil engineering work for LHC is advanced such that it b ecomes necessary to break into the tunnel, in particular for the ATLAS and CMS caverns. Injection tests are foreseen from Octob er 2003. Commissioning with b eam will start in the second half of 2005. The latest conceptual design rep ort [1] for the LHC was issued in Octob er 1995. The remainder of this pap er is organised as follows: Chapter 2 discusses the most imp ortant parameters, the overall layout, the state of the exp eriments, and the layout and optical functions in the neighb ourho o d of Pit 5, Chapter 3 the b eam-b eam fo otprints and the choice of the crossing angle, and Chapter 4 the cryogenics, the string tests of half an arc cell, and the new civil engineering needed are presented in Chapter 5. Finally, Chapter 6 contains the conclusions. 2 PARAMETERS, LAYOUT, EXPERIMENTS, OPTICAL FUNCTIONS This chapter is divided into three sections, discussing the most imp ortant parame- ters, the overall layout of the LHC, and the detailed layout and optical functions in the neighb ourho o d of the CMS exp eriment in Pit 5. Table 1: LHC Parameters Circumference C 26659 m Energy E 7 TeV Dip ole eld B 8.4 T Bunch spacing s 25 ns 11 Bunch p opulation N 10 Bunch radius = 16 m x y Bunch length 75 mm s Beam-b eam parameter 0.0034 1 1 Luminosity L 10 nb s Distance to nearest quadrup ole ` 23 m Q Events/collision n 19 c 2.1 Parameters Tab. 1 shows the LHC parameters. The circumference C is that of LEP, and known to even more digits than shown. The maximum energy E is a round gure, achieved at the dip ole eld B listed. The bunch spacing s corresp onds to 10 RF wavelengths. Together with the distance from the interaction p oint IP to the separating dip oles it determines the numb er of parasitic collisions, ab out 15 on either side of the IP. The bunch p opulation N 1 and the bunch radii and are shown at the interaction p oint IP. They are adjusted x y such that the b eam-b eam tune shift parameter falls into range b elieved to b e achievable from exp erience with other hadron colliders which were or are in op eration [2], and that the luminosity L is in a range which the exp eriments b elieve they can handle. The total b eam-b eam tune spread from the nearly head-on collisions and from all parasitic collisions should b e small enough to t b etween nonlinear resonances of order up to twelve. Not all the space ` between the IP and the front face of the nearest quadrup ole is available to Q the exp eriments. At the assumed inelastic non-di ractive cross section =60 mb, the pp number of events in a single collision is n = 19. c Low ß (pp) High Luminosity CMS RF & Future Expt. Dump Octant 5 Octant 6 Octant 4 Octant 7 Cleaning Cleaning Octant 3 Octant 2 Octant 8 Octant 1 ALICE Injection LHC-B Injection Low ß (Ions) ATLAS Low ß (B physics) Low ß (pp) High Luminosity Figure 1: Layout and Exp eriments 2.2 Overall Layout and Exp eriments Fig. 1 shows the layout of the LHC. The pits are at the centres of the o ctants. The two LHC rings cross in Pits 1, 2, 5, and 8. The circumferences of the two rings are the same, since b oth rings have four inner and four outer arcs. The two large exp eriments, ATLAS and CMS, are diametrically opp osite in Pits 1 and 5, resp ectively. Both are approved exp eriments with a cost ceiling of 475 MCHF each. Technical prop osals were published in 1994 [3, 4]. The LHCC exp ects technical prop osals for the subsystems. The heavy-ion exp eriment ALICE will b e in Pit 2. The technical prop osal for the core exp eriment [5] was published in 1995. The LHCC is waiting for the technical prop osal for the muon arm. The LHC-B exp eriment is dedicated to the study of CP violation and other rare phenomena in the decay of Beauty particles. It uses colliding b eams and a forward detector, contrary to the HERA-B exp eriment which uses a single b eam and a gas jet target. A letter of intent [6] has b een submitted to the LHCC. The LHCC wants an R&D programme for the detector. The two b eams are injected into LHC into outer arcs upstream of Pits 2 and 2 8. The b eam cleaning insertions to steer the b eam halo into staggered sets of collimators rather than the sup er-conducting magnets are in Pits 3 and 7. Pit 4 houses the RF system. Pit 6 is reserved for the b eam dumping system. 2.3 Layout and Optical Functions near Pit 5 Fig. 2 shows the layout and optical functions near Pit 5. The mimic diagram shows the LHC layout schematically over ab out 500 m in the neighb ourho o d of Pit 5. The low- interaction p oint IP5 and CMS are close to the centre. On either side of IP5 is a quadrup ole triplet, actually consisting of four quadrup oles. Because of the antisymmetry designed into LHC, the rst quadrup ole of the triplet fo cuses horizontally on the left, and defo cuses on the right, and similarly for all other quadrup oles. The b oxes b ehind the rst triplet are the dip ole magnets which rst separate the two b eams, and then make them parallel again at the correct distance of 194 mm at 1.9 K. Just b efore the disp ersion p suppressors there is a second triplet. The graph shows the optical functions in black, x q in red. They are prop ortional to the horizontal and vertical b eam radii. The and y antisymmetry of LHC makes them swap values when passing through IP5. Their values at IP5, = =0:5 m, are to o small to show clearly. Their maximum values in the rst x x triplet are quite large. The green curve shows the horizontal disp ersion D . It is matched x 0 to D = D = 0 at IP5, and has asymmetric nonzero values b ehind the rst separating x x dip oles. The layout and optical functions near Pit 1 are the same as those near Pit 5. The layout and optical functions near Pits 2 and 8 are very similar. LHC4.2 near IP5 HP/UX version 8.17/3 18/06/96 09.12.11 ) 70. .40 1/ 2 63. .35 (m) x (m D 56. .30 1/ 2 49. .25 42. .20 35. .15 28. .10 21. .05 14. 0.0 7. -.05 0.0 -.10 13.05 13.25 13.45 s (m) E /p0c= 0. Table name = TWISS ∗10∗∗( 3) Figure 2: Layout and Optical Functions near Pit 5. The interaction p oint is close to the centre of the abscissa. The diagram ab ove the graph schematically shows the horizontally fo cusing (defo cusing) quadrup oles as rectangles ab ove (b elow) the axis, and the separating dip oles as centred rectangles. The curves are the square ro ots of the horizontal and vertical amplitude functions in black and red and the horizontal disp ersion in green. 3 3 BEAM-BEAM EFFECTS The tune spread caused by the nonlinearityof the b eam-b eam force is usually dis- played in the form of \fo otprints" which show the horizontal and vertical tune shifts Q x and Q for combinations of horizontal and vertical b etatron amplitudes a and a .
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