CERN 87-05 27 May 1987 ORGANISATION EUROPÉENNE POUR LA RECHERCHE NUCLÉAIRE CERN EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH THE LARGE HADRON COLLIDER IN THE LEP TUNNEL Edited by G. Brianti and K. Hubner GENEVA 1987 © Copyright CERN, Genève, 1987 Propriété littéraire et scientifique réservée pour Literary and scientific copyrights reserved in all tous les pays du monde. Ce document ne peut countries of the world. This report, or any part of être reproduit ou traduit en tout ou en partie sans it, may not be reprinted or translated without l'autorisation écrite du Directeur général du written permission of the copyright holder, the CERN, titulaire du droit d'auteur. Dans les cas Director-General of CERN. However, permission appropriés, et s'il s'agit d'utiliser le document à will be freely granted for appropriate non­ des fins non commerciales, cette autorisation commercial use. sera volontiers accordée. 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CERN 87-05 27 May 1987 ORGANISATION EUROPÉENNE POUR LA RECHERCHE NUCLÉAIRE CERN EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH THE LARGE HADRON COLLIDER IN THE LEP TUNNEL Edited by G. Brianti and K. Hubner A. Asner, Y. Baconnier, M. Bassetti*\ C. Benvenuti, D. Boussard, D. Brandt, G. Brianti, R. Calder, G. de Rijk, J. Dupin, A. Fassô, J. Gareyte, K. Goebel, O. Grôbner, G. Guignard, M. Gyr, D. Hagedorn, A. Hilaire, N. Hilleret, K. Hùbner, A. Ijspeert, E. Keil, K.H. Kissler, J.P. Koutchouk, J.M. Laurent, Ph. Lebrun, D. Leroy, M. Morpurgo, R. Perin, K. Potter, H.P. Reinhard, L. Resegotti, W. Scandale, J. Schmid, W. Schnell, G. Schroder, G.R. Stevenson, W. Thomi, T. Tortschanoff, A. Verdier, L. Vos, G. Vossenberg and E. Weisse CERN, Geneva, Switzerland GENEVA 1987 *) INFN, Frascati, Italy Ill ABSTRACT The status of the studies for the CERN Large Hadron Collider (LHC) is described. This collider will provide proton-proton collisions with 16 TeV centre-of-mass energy and a luminosity exceeding 1033 cm-2 s~ ' per interaction point. It can be installed in the tunnel of the Large Electron-Positron Storage Ring (LEP) above the LEP elements. It will use superconducting magnets of a novel, compact design, having two horizontally separated channels for the two counter-rotating bunched proton beams, which can collide in a maximum of seven interaction points. Collisions between protons of the LHC and electrons of LEP are also possible with a centre-of-mass energy of up to 1.8 TeV and a luminosity of up to 2 x 1032cm-2s_1. VI 4.4 Longitudinal instabilities 4.5 Transverse instabilities 4.6 Vacuum-chamber heating by the beam 4.7 Collective phenomena of ep option 5. MAGNET SYSTEM 5.1 Description of the magnet system 5.1.1 Layout, number, and types of magnets 5.1.2 Design criteria 5.1.3 Cryomagnets in the LEP tunnel 5.2 Dipoles 5.2.1 Main features of present design 5.2.2 Field quality 5.2.3 Energy deposition in dipoles 5.3 Quadrupoles 5.3.1 General 5.3.2 Cross-section of active part and main parameters 5.4 Combined sextupoles and correction dipoles 5.5 Tuning quadrupoles 5.6 Magnet protection 5.7 Powering and discharge of the machine 6. CRYOGENICS 6.1 Generalities 6.2 Magnet cryostat 6.3 General principles of the refrigeration scheme 6.3.1 Tasks 6.3.2 Steady operation at 1.8 K 6.3.3 Initial cooling-down 6.3.4 Recooling after a magnet quench 6.4 Details of a possible refrigeration scheme 6.4.1 Cooling scheme 6.4.2 Calculated performance 6.5 Safety 7. VACUUM SYSTEM 7.1 Design of the vacuum system 7.1.1 Vacuum chamber 7.1.2 Sectorization of the main vacuum system 7.1.3 Room-temperature lateral connections 7.1.4 Insulation vacuum 7.2 Expected vacuum performance 7.2.1 Static vacuum 7.2.2 Vacuum in the presence of beams 8. RADIO-FREQUENCY SYSTEM 42 8.1 Basic parameters and assumptions 42 8.2 Accelerating structure and high-power radio frequency 43 8.3 RF noise 44 8.4 Multibunch feedback 45 9. BEAM-DUMPING SYSTEM 47 9.1 General description and layout 47 9.2 Kicker magnets 48 9.2.1 Extraction kicker 48 9.2.2 Spiral kickers 49 9.3 Beam dump 49 10. INJECTION SYSTEM 51 10.1 General description 51 10.2 Injection process 51 10.3 Modifications and additions to the PS 52 10.4 Modifications and additions to the SPS 52 10.4.1 Polarity reversal 52 10.4.2 Injection 52 10.4.3 Ejection 53 10.5 Beam transfer lines from SPS to LEP 53 10.6 Injection into the LHC 54 10.6.1 Layout 54 10.6.2 Kicker magnets 54 10.6.3 Steel septum magnets 55 10.7 Injection for ep mode 55 11. RADIATION PROTECTION CONSIDERATIONS 56 11.1 Introduction 56 11.2 Prompt radiation 56 11.2.1 Hadron shielding of an accidental full-beam loss 56 11.2.2 Hadron shielding of the intersection regions 57 11.2.3 Muon shielding of the intersection regions 57 11.2.4 Scattered radiation 57 11.2.5 Muon-dump shielding 57 11.2.6 Environmental'exclusion'zones 58 11.3 Radiation heating 58 11.3.1 Thebeamdump 58 11.3.2 Beam losses in LHC magnets 59 11.3.3 Heating by beam-beam interactions 60 11.4 Induced radioactivity 60 11.4.1 Global radioactivity estimates 60 11.4.2 Remanent activity in the accelerator structure 60 11.4.3 Radioactivity in soil, rock and ground water 61 11.4.4 Radioactivity released by water 61 VIII 11.4.5 Radioactivity released by air 61 11.4.6 Tritium production in helium 62 11.5 Radiation damage and radiation-produced noxious compounds 62 REFERENCES 64 APPENDIX 1: LIST OF LHC PARAMETERS 67 APPENDIX 2: LIST OF LHC NOTES 70 FIGURES 73 1. INTRODUCTION This report describes the status of the work done for the Large Hadron Collider (LHC) in the LEP tunnel. After the ECFA-CERN Workshop [1] in 1984, studies continued [2-4] within the framework of the Long-Range Planning Committee chaired by Professor C. Rubbia. This continuation of the work has made it possible to single out the most promising options as far as the parameters and the development work are concerned. The study has concentrated on the pp and the ep modes of operation, promising top performance. The report explains the reasons for other choices made, it gives the updated performance figures, and it presents the research and development work for the superconducting magnets which are the most critical components of LHC. For proton-proton collisions, two proton beams of 8 TeV nominal energy circulate in opposite directions in two separate magnetic channels, which are side by side in the horizontal plane, 0.9 m above the median plane of LEP (see Fig. 5.4); the horizontal separation of the two channels is 180 mm. Since the circumference of the LHC orbit is fixed by the LEP tunnel, the magnetic field in the guiding dipoles must be as high as possible because it determines the top energy. Therefore the nominal level is chosen to be 10 T, which seems technically attainable and economically feasible provided a vigorous R&D programme is undertaken. The superconducting coils providing equal but opposite magnetic field in the two beam channels have a common iron yoke and force-retaining structure, the whole being housed in one cryostat. This 'two-in-one' solution allows the highest possible field in the restricted space above LEP, which has not only the advantage of compactness but also of lower cost, compared with that of two independent rings with separate cryostats. The disadvantages seem acceptable: i) the field distortions due to the coupling of the two magnetic channels must be attenuated by proper coil design; ii) the two channels can operate at two different field levels up to only a moderate field, which is however sufficient for the storage of the first injected beam at an intermediate energy level, should this be required during the injection of the second beam. The beam orbits, separated in the arcs and over most of the long straight sections, are combined in a single channel just in the region of the experiments, so that the counter-rotating bunches collide only in seven interaction points at a maximum. The eighth long straight section is reserved for the beam-dumping system, where the beams do not interact. The nominal peak luminosity is 1.4 x 1033 cm~ 2 s~ ' at 8 TeV beam energy with 3564 bunches per beam. This implies that there are bunch collisions every 25 ns per interaction point, yielding an average of 3.6 events per bunch collision for a total cross-section of 100 mb.