A. Bay Beijing October 20051 Accelerators We want to study submicroscopic structure of particles. Spatial resolution of a probe ~de Broglie wavelength

A. Bay Beijing October 2005 1

AcceleratorsWe want to study submicroscopic structure of particles.Spatial resolution of a probe ~de Broglie wavelength = 1/p=> increase energy of probes.

targetr

p

probe

The collider is the most efficient way to get the max usableenergy:

collider with

fixed target of mass m2

(Ecm)2=


General structure

RF fromKlystrons

In addition: sophisticated instrumentation for the control of the orbit


A cavity


Energies of Colliders vs time

LHC:starting date 2007


Max Energy limiting factors

* Need powerful magnets to curb the orbit* Synchrotron radiation in a machine of radius r andenergy E goes like E4 :

Suppose you want an energy of 500 GeV. With electronsyou must increase the klystron power by ~ (500/50)4 !

Consider like baseline design the LEP machine witha radius of 4.3 km. At 50 GeV/beam the power dissipatedis of the order of 10-7 W per electron.There are ~ 1012 electrons in the LEP => 105 W needed fromthe klystrons.

€

Power ≈2Ke2c

3

γ 4

r2~

E

m

⎛

⎝ ⎜

⎞

⎠ ⎟4

2 possibilities: use protons (mp=2000me) or increase r.


The proton collider

Because the p is a composite particle the total beam E cannotbe completely exploited. The elementary collisionsare between quarks or gluons which pick up only a fractionx of the momentum:

proton

proton

quarksspectators

quarksspectators

p2

p1

x1p1

x2p2

momentum availableis only x1p1+ x2p2


Luminosity

Interaction rate for a process of cross-section rate [s] = L

The luminosity of a collider is proportional to the currentsof 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: y

x


Example: LEP


Example of L calculation for LEP

I= 1.38 and 1.52 mA e=1.6 10 Cb = 8

... close to the real (measured) value of ~ 4 - 5 1030


Example of rate calculation for LEP

Cross sections for processes at the Z peak:

where

from rate [s] = L assuming we obtain an hadronic rate of 0.3 s

In one year 3x107 s, assuming that the system is on dutyfor 1/3 of the time, we have an "integrated luminosity" of107 x 1031 = 1038 cm 105 nb

The number of hadronic events/year is ~ 0.3 107


Luminosity vs time


The Large Hadron Collider

Build a 7 GeV/beam machine in the LEP tunnel.


LHC

LHC

LHCbpoint 8

LHCb

Pb PbGeneva

jet d'eau

Alps

Leman lake


viewed from the sky on July 13, 2005

Jet d’eau

ALTAS surface buildings CERN

Genève

Salève

new wood building


LHC magnets• ~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 !

Lowering of 1st dipole into the tunnel (March 2005)B fields of 8.3 T in opposite directions for each proton beam

Cold mass

(1.9 K)

Joining things up

Cryogenic services

line


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


LHC parameters

—Ecm = 14 TeV

—Luminosity ~ 3 1034 cm-2 s-1 generated with

—1.7 1011 protons/bunch

— t = 25 ns bunch crossing

—bunch transverse size ~15 m

—bunch longitudinal size ~ 8cm

— crossing angle =200 mrad

The proton current is ~1A, ~500 Mjoules/beam (100kg TNT)

25 ns

detector


CLICThe 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 of150 MeV/m. Aa 250+250 GeV machine would be 5 km long

sub-nanometerbeam !!!!!!!!!

30 GHz


CLICelectron beam to be accelerated

Low E, very high intensity beam used to produce RF


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 apart2) reorganize in time the bunches so that they are 2 cm apart:this corresponds to 0.67 ns at the speed of light3) send the bunches into passive microwave devices (Power Extraction and Transfer Structure, PETS)where a 30 GHz radio-wave is excitedand then transferred by shortwaveguides to the main accelerator.


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


CTF3 first phase

has proven the possibility to reduce the pulse spacing tothe nominal value of 0.67 ps.


Nanometer size beam

Requires a nanometricstability of all the components,in particular the last quadrupole.

geophone Need to fight (hard) againstseveral possible sources of vibrations(ex.: cooling liquid),ground motion, etc.


ground motion

StabilizationUse a combination of active and passive stabilization techniques

quadrupolemotion

1


Luminosity gain w/wo stabilization

~70% of thenominal luminosityhas been obtained

Simulation of the beam collision behaviour


The experiments

e+e collisions and collisions

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A. Bay Beijing October 20051 Accelerators We want to study submicroscopic structure of particles. Spatial resolution of a probe ~de Broglie wavelength