The LHC: an Accelerated Overview

Jonathan Walsh

May 2, 2006

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

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: 8.2Linac: 66.7PSB: 28PS: 20SPS: 16LHC: 15.5

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

The Duoplasmatron

gas feed

cathode anode

canal

expansion cup

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

Linac-2: the MeV weapon of choice

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

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

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)

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)

The Fellowship of the Rings

PSB: Proton Synchrotron Booster

PS: Proton Synchrotron

SPS: Super Proton Synchrotron

LHC: Large Hadron Collider

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

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

PS accelerating sections

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)

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

LHC: The Lord of the Rings

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

The LHC Dipole Magnet

An RF Cavity…shiny

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

Calculating luminosity from beam parameters

Intersecting storage ring, identical beams

kb: number of bunches, Nb: protons per bunch

fr: revolution frequency, n: emittance

: beta function at intersection

€

L =kbNb

2 f r4πεnβ

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

Beam Parameters

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

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

References

1. M Benedikt (ed.), “The PS Complex as Proton Pre-Injector for the LHC - Design and Implementation Report”,CERN 2000-03, 2000

2. G Arduini et. al., “Beams in the CERN PS Complex After the RF Upgrades for LHC,” Proc. EPAC, 2004

3. P Collier, “The SPS as Injector for the LHC,” CERN-SL-97-07-DI, 1997

4. K Schindl, “The Injector Chain for the LHC,” Chamonix IX, CERN, 1997

5. N Tahir et. al., “Impact of 7 TeV/c large hadron collider proton beam on a copper target,” J. Appl. Phys. 97, 2005

6. C. Rembser, “LHC - Machine and Detectors,” CERN, 2005

Photos courtesy of CERN