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: 8.2 Linac: 66.7 PSB: 28 PS: 20 SPS: 16 LHC: 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 cavities can 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 =  I L N: number of expected events of a certain type  : cross section of those types of events I L : integrated luminosity

Calculating luminosity from beam parameters Intersecting storage ring, identical beams k b : number of bunches, N b : protons per bunch f r : revolution frequency,  n : emittance  : beta function at intersection

LHC luminosity goals In the first year, the expected LHC luminosity is (cm 2 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 , G Arduini et. al., “Beams in the CERN PS Complex After the RF Upgrades for LHC,” Proc. EPAC, P Collier, “The SPS as Injector for the LHC,” CERN-SL DI, K Schindl, “The Injector Chain for the LHC,” Chamonix IX, CERN, N Tahir et. al., “Impact of 7 TeV/c large hadron collider proton beam on a copper target,” J. Appl. Phys. 97, C. Rembser, “LHC - Machine and Detectors,” CERN, 2005 Photos courtesy of CERN