Accelerators

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Accelerators
We want to study submicroscopic structure of
particles. Spatial resolution of a probe de
Broglie wavelength 1/p gt increase energy of
probes.
probe
r
target
p
The collider is the most efficient way to get the
max usable energy
(Ecm)2
collider with
fixed target of mass m2
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General structure
RF from Klystrons
In addition sophisticated instrumentation for
the control of the orbit
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A cavity
gg
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Energies of Colliders vs time
LHC starting date 2007
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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
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
gt 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 (mp2000me) or
increase r.
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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 spectators
proton
momentum available is only x1p1 x2p2
p2
x2p2
x1p1
p1
proton
quarks spectators
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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
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Example LEP
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Example of L calculation for LEP
I 1.38 and 1.52 mA e1.6 10-19 C b 8
... close to the real (measured) value of 4 -
5 1030
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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
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Luminosity vs time
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The Large Hadron Collider
Build a 7 GeV/beam machine in the LEP tunnel.
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LHC
LHC
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viewed from the sky on July 13, 2005
new wood building
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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
  LHCs circumference !

B fields of 8.3 T in opposite directions for
each proton beam
Cold mass (1.9 K)
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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
• (10321033 cm2s1)
• Reaching the design luminosity of 1034 cm2s1
  
• will take until 2010

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LHC parameters

• 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 a200 mrad

The proton current is 1A, 500 Mjoules/beam
(100kg TNT)
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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
250250 GeV machine would be 5 km long
sub-nanometer beam !!!!!!!!!
30 GHz
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CLIC
electron beam to be accelerated
Low E, very high intensity beam used to produce RF
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The CLIC idea
A gradient of 150 MeV/m requires a RF of 30
GHz. Klystrons are limited at 10 GHz gt 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.
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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
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CTF3 first phase
has proven the possibility to reduce the pulse
spacing to the nominal value of 0.67 ps.
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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.
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Stabilization
Use a combination of active and passive
stabilization techniques
1
quadrupole motion
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Luminosity gain w/wo stabilization
Simulation of the beam collision behaviour
70 of the nominal luminosity has been obtained
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The experiments
ee- collisions and g g collisions