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 µs pulse length (120 ?s)
• 1.2 µm transverse rms emittance (1.2 µm)

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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
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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)

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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
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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 sIL
• N number of expected events of a certain type
• s cross section of those types of events
• IL integrated luminosity

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Calculating luminosity from beam
parametersIntersecting storage ring, identical
beams

• kb number of bunches, Nb protons per bunch
• fr revolution frequency, en emittance
• ß 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
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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 µs!
• 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