# Summary

Document Sample

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

The collider is the most efficient way to get the max usable
energy:
(Ecm)2=
collider with

fixed target of mass m2
A. Bay   Beijing October 2005             1
General structure
RF from
Klystrons

In addition: sophisticated instrumentation for the control of the orbit

A. Bay   Beijing October 2005                      2
A cavity

A. Bay   Beijing October 2005   3
Energies of Colliders vs time

LHC:
starting
date 2007

A. Bay   Beijing October 2005                4
Max Energy limiting factors

* Need powerful magnets to curb the orbit
* Synchrotron radiation in a machine of radius r and
energy E goes like E4 :                                   4
2Ke 2c  4 E 
Power             ~  
3   r2
m 

Consider like baseline design the LEP machine with
a radius of 4.3 km. At 50 GeV/beam the power dissipated

is of the order of 10-7 W per electron.
There are ~ 1012 electrons in the LEP => 105 W needed from
the klystrons.
Suppose you want an energy of 500 GeV. With electrons
you must increase the klystron power by ~ (500/50)4 !

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

A. Bay   Beijing October 2005                    5
The proton collider
Because the p is a composite particle the total beam E cannot
be completely exploited. The elementary collisions
are between quarks or gluons which pick up only a fraction
x of the momentum:

quarks
proton                                                        spectators
momentum available
p2                  x2p2                            is only x1p1+ x2p2
x1p1
p1

quarks                                                            proton
spectators

A. Bay   Beijing October 2005                        6
Luminosity
Interaction rate for a process of cross-section srate [s-1] = sL

The luminosity of a collider is proportional to the currents
of 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:
sy

sx
A. Bay   Beijing October 2005                     7
Example: LEP

A. Bay   Beijing October 2005   8
Example of L calculation for LEP

I= 1.38 and 1.52 mA      e=1.6 10-19 C
b=8

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

A. Bay   Beijing October 2005      9
Example of rate calculation for LEP
Cross sections for processes at the Z peak:

where

from rate [s-1] = sL assuming                                we
obtain an hadronic rate of 0.3 s-1

In one year 3x107 s, assuming that the system is on duty
for 1/3 of the time, we have an "integrated luminosity" of
107 x 1031 = 1038 cm-2=105nb-1

The number of hadronic events/year is ~ 0.3 107

A. Bay   Beijing October 2005             10
Luminosity vs time

A. Bay   Beijing October 2005   11
The Large Hadron Collider

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

A. Bay   Beijing October 2005   12
LHC                    jet d'eau
Alps
LHC
Pb Pb
Geneva
Leman lake
LHCb
point 8

LHCb

A. Bay   Beijing October 2005               13
viewed from the sky on July 13, 2005

new wood building
Salève
Jet d’eau

Genève

ALTAS surface
buildings                              CERN

A. Bay    Beijing October 2005            14
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 !

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

Joining things up

A. Bay   Beijing October 2005                                15
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

A. Bay   Beijing October 2005         16
LHC parameters
detector

a

—Ecm = 14 TeV
—Luminosity ~ 3 1034 cm-2 s-1 generated with
—1.7 1011 protons/bunch
— Dt = 25 ns bunch crossing
—bunch transverse size ~15 mm
—bunch longitudinal size ~ 8cm
— crossing angle a=200 mrad

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

A. Bay   Beijing October 2005              17
CLIC
The 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 of
150 MeV/m. Aa 250+250 GeV machine would be 5 km long

30 GHz                        sub-nanometer
beam !!!!!!!!!

A. Bay   Beijing October 2005               18
CLIC
electron beam to be accelerated

Low E, very high intensity beam used to produce RF
A. Bay   Beijing October 2005   19
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 apart
2) reorganize in time the bunches so that they are 2 cm apart:
this corresponds to 0.67 ns at the speed of light
3) send the bunches into passive microwave devices (Power
Extraction and Transfer Structure, PETS)
where a 30 GHz radio-wave is excited
and then transferred by short
waveguides to the main accelerator.

A. Bay   Beijing October 2005                20
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

A. Bay   Beijing October 2005             21
CTF3 first phase
has proven the possibility to reduce the pulse spacing to
the nominal value of 0.67 ps.

A. Bay   Beijing October 2005           22
Nanometer size beam
Requires a nanometric
stability of all the components,
in particular the last quadrupole.

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

A. Bay   Beijing October 2005                         23
Stabilization
Use a combination of active and
passive stabilization techniques

1

motion

A. Bay   Beijing October 2005                   24
Luminosity gain w/wo stabilization
Simulation of the beam collision behaviour

~70% of the
nominal luminosity
has been obtained

A. Bay   Beijing October 2005                        25
The experiments

e+e- collisions      and        collisions

A. Bay   Beijing October 2005         26

```
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 0 posted: 3/28/2013 language: English pages: 26
How are you planning on using Docstoc?