engines of discovery - university of toronto
TRANSCRIPT
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Engines of Discovery
R.S. Orr
Department of Physics
University of Toronto
Berkley 1930
1 MeV
Geneva
14 TeV 20089
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Birth of Particle Physics and Accelerators
• 1909 Geiger/Marsden MeV a backscattering - Manchester
• 1919 Rutherford disintegrates Nitrogen - Manchester
• 1927 Rutherford demands accelerator development
Particle accelerator studies - Cavendish
• 1929 Cockcroft and Walton start high voltage experiments
• 1932 The goal achieved: Cockcroft + Walton split Li nucleus
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Cockcroft-Walton Generator
665 kV
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Ising – 1924
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Resonant Accelerator Concept
• The acceleration occurs in the electric field between cylindrical drift tubes.
• The RF power must be synchronised with the motion of the electrons, so that acceleration occurs in every gap.
Wideroe - 1928
Linear Accelerator = LINAC
Alternating (radio frequency) fields allow higher voltages
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Recirculation Concept - Cyclotron
Radio frequency alternating voltage
Hollow metal drift tubes
time t =0
time t =½ RF period
D-shaped RF cavities
• Orbit radius increases with momentum
• Orbital Frequency independent of momentum
• Particle motion and RF in phase
Lawrence:
4” – 80 keV
11” - 1.2 MeV
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B mv
ep
ef rev
v
2v
2
eB
mveB
2m
Magnetic rigidity Constant revolution frequency
Equilibrium Orbit
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Orbit Stability
Slight Displacement from Equilibrium Orbit Particle Lost
Vertical and Horizontal Focusing
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Vertical Orbit Stability in Lawrence’s Cyclotron
Cross Section Thru Ds Electrostatic Focusing Lens
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Orbital Stability in a Cyclotron
qF v B
c
SHIMS
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Horizontal Vertical
0z
n
zR
B Br
0
2
0zmv e
vBR c
2
x zmv e
F vBr c
2
1xmv x
FR R
n
1x nv
R
1n
2
2 xd y e
m vBcdt
0x zB B
z x
2
2z
znBd y e
m v FR cdt
2 2
2 20n
d y vm m
dt R
2
2zR
nv
0n
Field Index
Equilibrium Orbit
Centrifugal = Lorentz on equilibrium orbit
Restoring Force
Simple Harmonic
Stable Oscillations around Equilibrium orbit
Weak Focusing
Betatron Oscillations
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This machine is just a model for a bigger
one, of course
This machine is just a model for a bigger
one, of course
This machine is just a model for a bigger
one, of course
1931 410 Volts
1932
1953
610 Volts
910 Volts
1960 1010 Volts
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Marcus Oliphant
– later to become
Governor of South Australia
Invention of the Synchrotron
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Synchrotron Ring Schematic
Focusing magnets
Vacuum
tube
Accelerating
cavity
Bending magnets
• Increase magnetic field
during acceleration.
• Constant orbital radius
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1 0 1 01
1 11 10 1
L
f f
2
1
1
LL
f
L L
f f
2
1 0
1L
f
L f Net Focusing
• FODO Lattice
• Strong Focusing
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Strong Focusing
• Field Index set by Pole Face Shape
• Weak, n = 0.5
• Strong, n = 3500
• Strong Focusing = Alternating Gradient
• “Combined Function” Magnet
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Weak Focusing Magnet
Strong Focusing Magnet
Enormous Cost Saving
• Strong Focusing = Alternating Gradient
• Reduce amplitude of betatron oscillations
• Reduce diameter of vacuum pipe
• Reduce Aperture of Magnets
• 35 GeV (CERN PS, AGS) costs same as 7 GeV (NIMROD)
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2
20
d YK s Y
ds
cosY s A s s
cosY s s s
2
2 3
1dK s
ds
2s s
TRAJECTORY
BEAM ENVELOPE
Amplitude of betatron oscillations
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• Single Particle Phase Space
• Beam Envelope
position
angle
Shape of phase space changes along accelerator lattice
Area constant -> Liouville
• Real Accelerator
• Non-linear
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2 2
1 1
A B C
1
sins s sn nE E eV
Successive turns around accelerator lattice
• B is synchronous with RF phase
• A too energetic to be in phase
• B not energetic enough to be in phase
Closed Oscillations in Phase
(non relativistic)
Change in transit time around lattice
Synchronous particle
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1 1
1
1
2
2
s
s
in sin
ins s s
n n n
n
n n
s
n s
E E eV
c
vE
E E eV
E
• Symplectic Mapping
• Preserves Phase Space
Synchronous Particle
Non-Synchronous Particle
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Transformed “s” into “Φ” position around lattice
Particle orbits in energy-phase
separatrix Stable oscillations
Trapped by RF
Unconfined motion = “lost” particles
Synchronous particle
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1
2
2
sin si
sin
n
s n
s
s
s snE E eV
cdE
dn
d EeV
dn
v E
Non-linear equations
Describing deviation in phase and energy from synchronous orbit
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2 2
2cos s
1constant = Η in=
2s
s
c
v
d
dn E
RF Bucket
separatrix
cos sin s
H
Initial condition
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CERN Seen from the Air
• Tunnels of CERN accelerator complex superimposed on a map of Geneva.
• Accelerator is 50 m underground
• 25 km in circumference
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Superconducting Magnet
8 Tesla
•In order to accelerate protons to high energy, must bend them in circular accelerator
•7 TeV momentum needs intense magnetic field
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LHC 2002
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LHC 2003
Dipole Cold Masses
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Ph. Lebrun ATLAS Plenary Meeting
18 February 2005
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Infrastructure completed in 2003
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Underground
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Dipole-dipole interconnect
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March 2006
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Descent of the Last Magnet, 26 April 2007
300 m underground at 2 km/h!
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RF Modules
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Sector 7-8 Sector 8-1
Point 8
Su
rfa
ceC
ave
rn
QSCA QSCB
QSRB
QURC
QUIC
QURA
Sh
aft
QSCC QSCC
Tu
nn
el
Storage
QURC
QSRA
IHI Linde Air Liquide
Refrigeration Units at 1.8 K
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Sector 7-8 Sector 8-1
Point 8
Su
rfa
ceC
ave
rn
QSCA QSCB
QSRB
QURC
QUIC
QURA
Sh
aft
QSCC QSCC
Tu
nn
el
Storage
QURC
QSRA
Cryogenic Distribution
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DFBA Electrical Feed Box
Low current module 6kA & 600A leads
High current module 13kA & 6kA leads
Shuffling module
Vacuum equipment VAA
Connection to
magnets
Jumper cryo
connection to QRLSHM/HCM
interconnect
HCM/LCM
interconnect
Supporting beam
600A leads
6kA leads
6kA leads
13kA leads
Current lead chimneys
Removable door
x 16
2 per LHC Point
1.9K
4.5K
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13 kA HTS Current Leads
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6 kA current leads with water-cooled cables
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Lyn Evans – EDMS docment no. 970483 45
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Beam 2 first beam – D-Day
46
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Beam on turns 1 and 2
47 Courtesy R. Bailey
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No RF, debunching in ~ 25*10 turns, i.e.
roughly 25 mS
48 Courtesy E. Ciapala
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First attempt at capture, at exactly the wrong
injection phase…
49 Courtesy E. Ciapala
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Capture with corrected injection phasing
50 Courtesy E. Ciapala
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Capture with optimum injection phasing,
correct reference
51 Courtesy E. Ciapala
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LHC longitudinal bunch profile Beam 2
52
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Lyn Evans – EDMS document no. 970483
H wire scan
53
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Kick response compared with
theoretical optics
54
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Alors, c’est fini!
Et maintenant?
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• Storage Ring
• Stable phase =
• No acceleration
0
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2 2
2 2
2
2
cos 0
2 0
s
s
s
d c eV
dn v E
d
dn
0 ; ; cos 0
0 ; ; cos 0
t s
t s
Synchrotron (phase) oscillations