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The LHC: an Accelerated Overview

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Title: The LHC: an Accelerated Overview


1
The LHC an Accelerated Overview
  • Jonathan Walsh
  • May 2, 2006

2
LHC in a nutshell
  • LHC beam from start to finish
  • Expected beam statistics
  • What is luminosity, and what can it do for me?
  • Beam properties and difficulties unique to the LHC

3
Overview staging in LHC beam production
  • Duoplasmatron 300mA beam current at 92 keV
  • RFQ to 750 keV
  • Linac 2 to 50 MeV
  • PSB to 1.4 GeV
  • PS to 28 GeV
  • SPS to 450 GeV
  • LHC to 7 TeV at 180mA beam current

Increase factors RFQ 8.2 Linac 66.7 PSB
28 PS 20 SPS 16 LHC 15.5
4
Duoplasmatron H source
  • Hydrogren gas is fed into a cathode chamber with
    electrons
  • The hydrogen dissociates and forms a plasma
    confined by magnetic fields
  • The plasma is constricted by a canal and
    extracted through the anode
  • The plasma is allowed to expand before forming
    the proton beam
  • The LHC Duoplasmatron operates at 100 kV

5
The Duoplasmatron
gas feed
canal
expansion cup
anode
cathode
6
RF Quadrupole shaping the beam
  • 4 vanes (electrodes) provide a quadrupole RF
    field
  • The RF field provides a transverse focusing of
    the beam
  • Spacing of the vanes accelerates and bunches the
    beam

7
Linac-2 the MeV weapon of choice
8
Linac Tank RF accelerator
  • The linac tank is a multi-chamber resonant
    cavity tuned to a specific frequency
  • RF is sent into the tank by waveguides, and
    normal modes can be excited in the cavity
  • These normal modes create potential differences
    in the cavities that accelerate the particle

9
Resistive losses in RF cavitiescan overwhelm
accelerators
  • The walls of a linac tank or other RF cavity
    begin converting input RF power into heat due to
    finite wall resistance
  • Solution make the cavity superconducting

10
Linac 2 is already at LHC spec
  • LHC spec (achieved)
  • 180 mA beam current (192 mA)
  • 30 ?s pulse length (120 ?s)
  • 1.2 ?m transverse rms emittance (1.2 ?m)

11
Down to the Proton Synchrotron Booster (PSB)
  • The beam line to the PSB from the Linac is 80m
    long
  • 20 quadrupole magnets focus the beam along the
    line
  • 2 bending and 8 steering magnets direct the beam
  • The PSB will boost the protons up to 1.4 GeV
    (factor of 28)

12
The Fellowship of the Rings
  • PSB Proton Synchrotron Booster
  • PS Proton Synchrotron
  • SPS Super Proton Synchrotron
  • LHC Large Hadron Collider

13
The PS Booster
  • Output energy has been increased to 1.4 GeV from
    1 GeV for the LHC
  • 16 sectioned synchrotron consisting of bending
    magnets, focusing magnets, and RF cavities
  • PSB upgrades are largely to the high power RF
    system for the energy boost

14
Proton Synchrotron Last low energy step
synchrotron
  • The PS has been upgraded for 40 and 80 MHz RF
    operation and new beam controls have been added
  • The PS is responsible for providing the 25 ns
    bunch separation for the LHC

15
PS accelerating sections
16
SPS Converted for LHC
  • The SPS boosts protons up to 450 GeV for LHC
    injection
  • SPS was the injector for the LEP system, and the
    injection system was upgraded as well as the RF
    systems (at 200, 400, and 800 MHz)
  • SPS is fully LHC dedicated during fills
  • (1-2 per day)

17
LHC Injection Chain
  • 81 bunch packets produced in the PS with 25 ns
    spacing
  • Triplets of 81 bunches are formed in the PS and
    injected into the SPS, taking up 27 of the SPS
    beamline
  • The total LHC beam consists of 12 supercycles
    of the 243 bunches from SPS

18
LHC The Lord of the Rings
19
LHC acceleration and beam steering system
  • Entire beamline run cold
  • RF cavities run at 400 MHz
  • 1232 Dipole magnets for beam steering
  • 386 Quadrupole focusing magnets
  • Many (thousands) of small correcting magnets also
    in place

20
The LHC Dipole Magnet
21
An RF Cavityshiny
22
Luminosity the other key to the puzzle
  • N ?IL
  • N number of expected events of a certain type
  • ? cross section of those types of events
  • IL integrated luminosity

23
Calculating luminosity from beam
parametersIntersecting storage ring, identical
beams
  • kb number of bunches, Nb protons per bunch
  • fr revolution frequency, ?n emittance
  • ? beta function at intersection

24
LHC luminosity goals
  • In the first year, the expected LHC luminosity is
    1033 (cm2 s)-1 5 times that of Fermilab
  • Target luminosity is ten times this value,
    believed to be achievable in the second year,
    with 25 times in the future

25
Beam Parameters
26
Beam Difficulties
  • Magnet quenching is a real danger, with only a
    small fraction (10-6) needed to quench a SM
  • A quenched dipole will require a beam dump in a
    single turn - 7 TeV (690 MJ) dissipated in 89 ?s!
  • An error in dumping the beam will expose
    accelerator components to serious radiation risk

27
The future of particle accelerators
  • Ring accelerators are on their way out - the
    strongest magnets (8.33 T) are employed to steer
    the LHC beam
  • The ILC has the brightest future (more than the
    VLHC), with wakefield plasma acceleration
    achieving limited gradients of 1 GeV/m

28
References
  • M Benedikt (ed.), The PS Complex as Proton
    Pre-Injector for the LHC - Design and
    Implementation Report,CERN 2000-03, 2000
  • G Arduini et. al., Beams in the CERN PS Complex
    After the RF Upgrades for LHC, Proc. EPAC, 2004
  • P Collier, The SPS as Injector for the LHC,
    CERN-SL-97-07-DI, 1997
  • K Schindl, The Injector Chain for the LHC,
    Chamonix IX, CERN, 1997
  • N Tahir et. al., Impact of 7 TeV/c large hadron
    collider proton beam on a copper target, J.
    Appl. Phys. 97, 2005
  • C. Rembser, LHC - Machine and Detectors, CERN,
    2005
  • Photos courtesy of CERN
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