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Accelerators

Accelerators. We want to study submicroscopic structure of particles. Spatial resolution of a probe ~de Broglie wavelength = 1/p => increase energy of probes. probe. r. target. p. The collider is the most efficient way to get the max usable energy:. (E cm ) 2 =. collider with.

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Accelerators

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  1. Accelerators We want to study submicroscopic structure of particles. Spatial resolution of a probe ~de Broglie wavelength = 1/p => increase energy of probes. probe r target p The collider is the most efficient way to get the max usable energy: (Ecm)2= collider with fixed target of mass m2 A. Bay Beijing October 2005

  2. General structure RF from Klystrons In addition: sophisticated instrumentation for the control of the orbit A. Bay Beijing October 2005

  3. gg A cavity A. Bay Beijing October 2005

  4. Energies of Colliders vs time LHC: starting date 2007 A. Bay Beijing October 2005

  5. Max Energy limiting factors * Need powerful magnets to curb the orbit * Synchrotron radiation in a machine of radius r and energy E goes like E4 : Consider like baseline design the LEP machine with a radius of 4.3 km. At 50 GeV/beam the power dissipated is of the order of 10-7 W per electron. There are ~ 1012 electrons in the LEP => 105 W needed from the klystrons. Suppose you want an energy of 500 GeV. With electrons you must increase the klystron power by ~ (500/50)4 ! 2 possibilities: use protons (mp=2000me) or increase r. A. Bay Beijing October 2005

  6. The proton collider Because the p is a composite particle the total beam E cannot be completely exploited. The elementary collisions are between quarks or gluons which pick up only a fraction x of the momentum: quarks spectators proton momentum available is only x1p1+ x2p2 p2 x2p2 x1p1 p1 proton quarks spectators A. Bay Beijing October 2005

  7. Luminosity Interaction rate for a process of cross-section s rate [s-1] = sL The luminosity of a collider is proportional to the currents of the 2 beams I1, I2, and inversely proportional to their section A, ni are the number of particles per bunch, b the number of bunches, f the frequency of the orbit. For gaussian bunch profiles: sy sx A. Bay Beijing October 2005

  8. Example: LEP A. Bay Beijing October 2005

  9. Example of L calculation for LEP I= 1.38 and 1.52 mA e=1.6 10-19 C b = 8 ... close to the real (measured) value of ~ 4 - 5 1030 A. Bay Beijing October 2005

  10. Example of rate calculation for LEP Cross sections for processes at the Z peak: where from rate [s-1] = sL assuming we obtain an hadronic rate of 0.3 s-1 In one year 3x107 s, assuming that the system is on duty for 1/3 of the time, we have an "integrated luminosity" of 107 x 1031 = 1038 cm-2 = 105nb-1 The number of hadronic events/year is ~ 0.3 107 A. Bay Beijing October 2005

  11. Luminosity vs time A. Bay Beijing October 2005

  12. The Large Hadron Collider Build a 7 GeV/beam machine in the LEP tunnel. A. Bay Beijing October 2005

  13. LHC jet d'eau Alps Pb Pb Geneva Leman lake LHCb point 8 LHCb LHC A. Bay Beijing October 2005

  14. viewed from the sky on July 13, 2005 Salève Jet d’eau Genève ALTAS surface buildings CERN new wood building A. Bay Beijing October 2005

  15. LHC magnets Lowering of 1st dipole into the tunnel (March 2005) Joining things up Cryogenic servicesline • ~1650 main magnets (~1000 produced) + a lot more other magnets • 1232 cryogenic dipole magnets (~800 produced, 70 installed): • each 15-m long, will occupy together ~70% of LHC’s circumference ! B fields of 8.3 T in opposite directions for each proton beam Cold mass (1.9 K) A. Bay Beijing October 2005

  16. LHC schedule • Beam commissioning starting in Summer 2007 • Short very-low luminosity “pilot run” in 2007 used • to debug/calibrate detectors, no (significant) • physics • First physics run in 2008, at low luminosity • (1032–1033 cm–2s–1) • Reaching the design luminosity of 1034 cm–2s–1 • will take until 2010 A. Bay Beijing October 2005

  17. LHC parameters detector a 25 ns • Ecm = 14 TeV • Luminosity ~ 3 1034 cm-2 s-1 generated with • 1.7 1011 protons/bunch • Dt = 25 ns bunch crossing • bunch transverse size ~15 mm • bunch longitudinal size ~ 8cm • crossing angle a=200 mrad The proton current is ~1A, ~500 Mjoules/beam (100kg TNT) A. Bay Beijing October 2005

  18. CLIC The Compact LInear Collider CLIC is the name of a novel technique to produce the RF required for acceleration, based on a Two Beam Acceleration (TBA) system. The goal is to have a gradient of acceleration of the order of 150 MeV/m. Aa 250+250 GeV machine would be 5 km long sub-nanometer beam !!!!!!!!! 30 GHz A. Bay Beijing October 2005

  19. CLIC electron beam to be accelerated Low E, very high intensity beam used to produce RF A. Bay Beijing October 2005

  20. The CLIC idea A gradient of 150 MeV/m requires a RF of ~30 GHz. Klystrons are limited at ~10 GHz => go to TBA: 1) create a beam of ~ 1 GeV electrons made of bunches 64 cm apart 2) reorganize in time the bunches so that they are 2 cm apart: this corresponds to 0.67 ns at the speed of light 3) send the bunches into passive microwave devices (Power Extraction and Transfer Structure, PETS) where a 30 GHz radio-wave is excited and then transferred by short waveguides to the main accelerator. A. Bay Beijing October 2005

  21. CLIC Test Facility 3 CTF3 Produce a bunched 35 A electron beam to excite 30 GHz PETS. Accelerate a 150 MeV electron beam up to 0.51 GeV A. Bay Beijing October 2005

  22. CTF3 first phase has proven the possibility to reduce the pulse spacing to the nominal value of 0.67 ps. A. Bay Beijing October 2005

  23. Nanometer size beam Requires a nanometric stability of all the components, in particular the last quadrupole. geophone Need to fight (hard) against several possible sources of vibrations (ex.: cooling liquid), ground motion, etc. A. Bay Beijing October 2005

  24. Stabilization ground motion Use a combination of active and passive stabilization techniques 1 quadrupole motion A. Bay Beijing October 2005

  25. Luminosity gain w/wo stabilization Simulation of the beam collision behaviour ~70% of the nominal luminosity has been obtained A. Bay Beijing October 2005

  26. The experiments e+e- collisions and g g collisions A. Bay Beijing October 2005

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