1. 09 February 2011 1

2. The LHC tunnel is 27 km, or 17 miles, in circumference. It’s depth underground ranges from 50 to 175 meters. It contains two parallel beam pipes, one containing protons traveling clockwise, one containing protons traveling anticlockwise. Trillions of protons circle the ring 11,245 times per second, at.9999991c (that’s 3 meters per second slower than light). Each beam will reach a maximum energy of 7 TeV, yielding collisions of 14 TeV (10 12 eV). There will be at maximum 600 million collisions per second. Maximum luminosity will be 1.7×10 34 cm -2 s -1 (Tevatron record is 4.04 x 10 32 cm -2 s -1 (404 inverse microbarns/s) 2

3. The accelerator chain Accelerator Duoplasmatron Linac 2 Proton Synchrotron Booster Proton Synchrotron Super Proton Synchroton LHC Maximum energy 100 keV 50 MeV 1.4 GeV 25 GeV 450 GeV 7 TeV 3

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5. Duoplasmatron http://psdoc.web.cern.ch/PSdoc/acc/ad/Visite GuidePS/Animations/Duoplasmatron/Duoplas matron.html http://psdoc.web.cern.ch/PSdoc/acc/ad/Visite GuidePS/Animations/Duoplasmatron/Duoplas matron.html Hydrogen is ionized by firing electrons off a cathode into hydrogen gas, forming a plasma of positive ions. The proton plasma is then accelerated through charged grids, and directed by RF quadrupole magnets, becoming a beam and leaving to the LINAC at 100 keV. 5

6. LINAC 2 Accelerates the proton beam up to 50 MeV. The LINAC is a multichamber cavity into which RF waves of a specific frequency are directed. AC voltage is applied along the LINAC. A proton experiencing one full cycle of the AC voltage would undergo first an acceleration and then a deceleration, resulting in no net acceleration. But drift tubes are placed to shield the particles during periods of negative voltage, preventing their deceleration and resulting in a net acceleration. A separate LINAC, LINAC 3, is used to accelerate heavy ions. LINAC 2 be replaced by LINAC 4, currently under construction. 6

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9. Synchrotron chain After the LINAC phase, the proton beams are injected into the Proton Synchrotron Complex, which comprises the Proton Synchrotron (PS) and the lower energy Proton Synchrotron Booster (PS). These serve two main purposes: (1) accelerating the protons to an output energy of 25 GeV, and (2) bunching the beam to its final 25 ns spacing. Both are accomplished using the time-varying RF standing wave system. 9

10. Synchrotron chain, cont. The protons are accelerated by an electrostatic radiofrequency (RF) kicker system. Time-varying RF standing waves are generated in a sinusoidal cavity. The system is constructed so that particles only experience positive potential, which means that the beam must be bunched. In the preaccelerators (PS, SPS) superconducting magnet technology is not used, but there is an upgrade under discussion that would introduce that technology into the SPS. The LHC uses the same RF system, but with superconducting magnets. 10

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14. Proton Synchrotron Booster 20 quadrupole magnets focus the beam on its way to the PSB, 2 bending magnets and 8 steering magnets direct it. The PSB is four rings, each with 16 sections with bending and focusing magnets and RF cavities. The PSB operates on the first harmonic. Each ring bunches its protons in a single bunch. They then release their bunches into the PS so that their incidence corresponds to a higher harmonic wave in the PS. 14

15. Proton Synchrotron Six PSB bunches are captured on harmonic h = 7 in the PS. The bunches are then split into three by operating on harmonics h = 7, 14 and 21. The beam is accelerated up to 25 GeV where each bunch is split twice. Now each of the six original bunches has been split into 12, and 72 bunches have been created on harmonic 84. Finally, the 80 MHz systems shorten the bunches to ∼ 4 ns, so as to fit into the SPS 200 MHz buckets. Protons exit at 25 GeV. 15

16. Super Proton Synchrotron The SPS was the injector for the Large Electron Positron collider (LEP) – the largest and highest-energy accelerator at CERN before the LHC Filling the LHC requires 12 cycles of the SPS (cycling time: 21.6 s), and filling the SPS requires 3 or 4 cycles of the PS (cycling time: 3.6 s). With “warm-up” and calibration, total injection time is about 16 minutes. For the LHC to be significantly upgraded, the SPS will likely have to be upgraded. Ideally, the extraction energy would be increased to 1 TeV, necessitating the introduction of superconducting magnets. 16

17. LHC: Injection The beam is directed from SPS into the injection line by a series of dipoles. The injection kicker system comprises four fast pulsed magnets per injection. The magnets are housed in a vacuum tank containing both beam pipes, for injection into Ring 1 and Ring 2. The injection points are at Point 2 and Point 8. The transfer line brings the beam near Point 2 for injection into Ring 1, and another line delivers the beam to near Point 8 for injection into Ring 2. Up until then, they have shared a beam pipe; once they are injected, they travel in opposite directions in separate beampipes. The injection kick occurs in the vertical plane with the two beams arriving at the LHC from below the LHC plane. The beams cross from one magnet bore to the other at four interaction locations. Once in the LHC, it takes 20 minutes for the particles to ramp up from 450 GeV to 7 TeV, and 20 minutes for the mangets to ramp down after a beam dump. Total theoretical turnaround time is 70 minutes, actual turnaround time is closer to 7 hours.. RF system of frequency 400.8 Hz, compatible with this bunch length (1.6 ns) is used to capture the beam 17

19. LHC: geometry The LHC was constructed in the existing LEP tunnel. The tunnel has 8 straight sections and 8 arcs, and it tilts toward Lake Geneva. Each straight section is 528 m long. Found of the straight sections house detectors; the other four are used for machine utilites, the RF system, collimation and beam abort. Two transfer tunnels, 2.5 km each, link the LHC to its injection system. 19

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22. The two beams are made to collide at four points along the ring: High luminosity experiments: CMS: Point 1 ATLAS: Point 5 Two more experimental insertions are located at Point 2 and Point 8, which also include the injection systems for Beam 1 and Beam 2, respectively. 22

23. Two chief systems: magnets and RF kicker A synchrotron has three main jobs: acceleration, steering, and focusing. Acceleration is accomplished by the radiofrequency kicker system, which administers a series of electrostatic boosts. Steering and focusing are accomplished using a complex network of many, diverse magnets. 23

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25. Radiofrequency system The RF system is designed to add energy to accelerate the protons, and also to compensate for loss. Loss comes primarily from synchrotron radiation. 25

26. Radiofrequency system The RF system is located at point 4. The ring intermittently contains a series of sinusoidal cavities made of niobium sputtering on copper (reduces quenching). Each cavity is driven by an individual RF system. They are timed to that the particles experience positive potential during their stay there. This is why the beam must be bunched. The RF of the LHC is 400.8 MHz The 400 MHz superconducting RF cavities have three different and independent types of vacuum systems: for the cavity, the secondary beam and the cryostat. 26

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28. Energy Beam: 362 megajoules. LHC magnet system: 600 MJ. 28

29. Magnets The LHC is the first and only superconducting synchrotron to operate below 2 K. Other large accelerators, like the Tevatron, HERA and RHIC use the same superconducting magnets with NbTi (niobium titanium) windings, cooled by supercritical helium. However, their systems are only cooled to 4.2 K, yielding fields around 5 T. The LHC magnet system uses superfluid helium to cool to 2 K, yielding fields about 8 T. A quench can thus be triggered at much lower energies in the LHC. In September 2008, a faulty connection between two giant quadropole magnets in sector 3-4 caused a quench, shutting down the LHC for months. A smaller quench can disrupt the machine for hours or days. 29

30. Magnets The magnets are responsible for bending the protons on a circular path, via the Lorentz force, and focusing the beam. 30 The LHC contains 9300 magnets;more than 7000 are superconducting 1232 dipole magnets, 15 m long each. These are for bending the beam 392 quadropole magnets, 5-7 m in length. These are for focusing the beam

31. Magnets: kinds Dipole magnets are used to steer the protons into the ring, along their path, and then out of the ring. However, dipole magnets alone can only provide weak focusing. And arrangement of quadropole and sextopole magnets are used to focus the beam. A single quadropole that focuses a beam in one direction defocuses the beam in the orthogonal direction. The lattice of magnets must be built accordingly, to achieve net focusing. Sextopole, octopole and decapole magnets are for correcting, dispersion suppression and matching. 31

32. Magnets: dipoles The LHC lattice was designed to maximize the amount of bending power by making the dipoles as long as possible. The dipoles are 15 meters long, with 23 regular lattice periods per arc. Each period is made up of six dipoles and two short straight sections (SSS) containing the main quadrupoles and lattice correctors. 32

33. Magnets, quadrupoles The main quadrupole focusing magnets are found in the short straight sections at the edges of the arcs, along with various corrector magnets. On the upstream end, these can be either octupoles, MO, tuning quadrupoles, MQT, or skew quadrupole correctors, MQS. The quadrupole magnets are arranged in a “FODO” lattice structure. “F quadrupoles” focus horizontally but defocus vertically, and “D” quadrupoles focus vertically but defocus horizontally. 33

34. Magnets, more kinds 34

35. Magnets, cont. There is not enough room in the LEP tunnel for two sets of magnets, so the LHC uses twin- bore magnets that consist of two sets of coils and beam channels within the same mechanical structure and cryostat. The peak beam energy of 7 TeV requires a field of 8.33 T 35

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42. Vacuum system and cryogenics The LHC has three vacuum systems: the insulation vacuum for cryomagnets, the insulation vacuum for helium distribution (QRL), and the beam vacuum. The requirements for the beam vacuum are much more stringent, driven by the required beam lifetime and background at the experiments. 300 kTons coldmass, 90 tons He 42

43. Beam cleaning/collimation Straight sections at points 3 and 7 contain two collimation systems for capturing stray particles. Point 3: momentum collimation Point 7: betatron collimation 43

44. Luminosity loss and beam dump The luminosity decays during a run, due to the degradation of intensities and emittances of the circulating beams. The main cause of loss is from the collisions: decay time τ = N/Lσk = 44.85 hours for peak initial luminosity, yielding a luminosity decay time of 29 hours. 44

45. Beam Dumping The dedicated beam dumping system of the LHC is situated at IP 6. The beam is extracted from both rings to an external absorber, in a way that does not overheat the absorber material. Given the destructive power of the LHC beam, the dumping system must meet extremely high reliability criteria. The system comprises, for each ring, 15 extraction kicker magnets (deflect horizontally), 15 steel septum magnets (deflect vertically, above the LHC cryostat), and 10 modules of dilution kicker magnets (sweeps beam to graphite absorber core). 45

46. The detectors There are 6 detectors on the LHC ring: CMS (Compact Muon Solenoid): general-purpose (supersymmetry, Higgs, dark matter, extra dimensions) ATLAS (A Toroidal LHC Apparatus): like CMS, but less cool. LHCb (Large Hadron Collider Beauty): investigates matter- antimatter asymmetry by investigating beauty quark ALICE (A Large Ion Collider Experiment): quark-gluon plasma. TOTEM (ToTal Elastic and diffractive cross-section Mesasurement): measure proton size, monitor beam luminosity. LHCf (Large Hadron Collider Forward): cosmic ray simulation. 46

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48. What the beam looks like when it comes to us The number of events per second generated in the LHC collisions is given by N = Lσ Maximum total integrated luminosity over one year: 80 to 120 inverse femtobarns (100x Tevatron). The protons are in bunches of 1.06 ns, spaced by 25 ns. There are about 10 11 protons per bunch. 48

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52. Acknowledgements Thanks very much to Ken for letting me use his very excellent paper as a primary reference. Two other very good and detailed references are the LHC design report on the CERN website and an article, courtesy of Ellie, in the Journal of Instrumentation (3) 2008. 52