chapter 2 particle accelerators: from basic to applied research rüdiger schmidt (cern) – 2011 -...
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Chapter 2
Particle accelerators: From basic to applied research
Rüdiger Schmidt (CERN) – 2011 - Version E1.0
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Scientific motivation for accelerators
The interest in accelerators came first from nuclear physics
Particles from radioactive decays have energies of up to a few MeV. The interest was to generate such particles, e.g. to split the atomic nuclei, which was for the first time done in 1932 with a Cockroft-Walton Generator.
Ernest Rutherford 1928:
I have long hoped for a source of positive particles more energetic than those emitted from natural radiaoactive substances
Cockcroft, Rutherford and Walton soon after splitting the atom
http://www.phy.cam.ac.uk/alumni/alumnifiles/Cavendish_History_Alumni.ppt
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Dimensions in our universe
Typical dimension of atomic and subatomic matter:
• Distance of atoms in matter: 0.3 nm = 3•10-10 m• Atomic radius: 0.1 nm = 1•10-10 m• Proton / Neutron radius: 1•10-15 m • Classical electronenradius: 2.83•10-15 m• Quark: 1•10-16 m• Range of strong interaction : < 1•10-15 m• Range of Weak interaction : << 1•10-16 m
• Mass of an electron: 9.11•10-31 kg• Mass of a proton : 1.673•10-27 kg
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Particle energy and basic research
For studies of the structure of the material, “probes“ are required which are smaller than the structure to be examined, for example: Light microscope ( - Quants with an energy of about 0.25 eV)
• Electron microscopes• Particle accelerators – the probe is the particle• Particle accelerators – the probe is the radiation emitted by the particles (light
quantum with an energy of some eV up to few MeV)• Particle accelerators - the probe is a neutron. Neutrons are in general generated
with intense high energy proton beams on a target
The production of new particles requires particles with enough energy
Examples: Particle accelerators
Cosmic rays
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Particle energy and basic research
Extension of the probe to study material structures
Light, typical wavelength: 500 nm = 5•10-7 m
For particles, the De Broglie wavelength becomes smaller with increasingkinetic energy:
)( 20kk
planckB
cm2EE
ch
p
hplanckB
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Research on small structures requires high energy
Example for the De Broglie wavelength:
Kinetic energy of a proton:
De Broglie wavelength for the proton:
Kinetic energy of an electron:
De Broglie wavelength for the proton:
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Kinetische Energie
= v / c = E / E0 pc Broglie * 10
18
[GeV] [GeV] [m]1 0.875 2.066 1.696 732.00
10 0.996 11.65 10.89 113.80100 ~1 107.6 100.93 12.29
1000 ~1 1067 1000 1.2310000 ~1 10660 10000 0.12
Kinetische Energie
= v / c = E / E0 pc Broglie * 10
18
[GeV] [GeV] [m]0.1 ~1 196.7 0.101 12340
1 ~1 1958 1.001 123910 ~1 19570 10.01 124
100 ~1 195700 100.001 12.41000 ~1 1957000 1000 1.24
PROTONS
ELECTRONS
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Energy spectrum: Cosmic radiation and accelerators
Cosmic radiation is free of charge!
Investment for particle physics with accelerators: ~GEuro
But:
Cosmic rays at 1 TeV: <0.001 particles / m2 / sec
LHC 7 TeV: >1026 protons / m2 / sec
LHC am CERN
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Creation of secondary particles in fixed target experiments
An accelerator that directs particles on a target:
Particles from the accelerator with the kinetic energy E and
mass m0
Particles in the target with mass m1
Conservation of momentum and energy
Secondary particles from the collision with momentum p and mass m
Fixed Target Experiment
Example: kinetic energy of a proton with Ek 450GeV with the rest mass:
mp 1.673 1027 kg :
Ecm 2 mp c2 1
Ek
2 mp c2
1
Ecm 27.244 GeV
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Production of secondary beams
Sekundary beam:• Positrons• Antiprotons• Neutrinos• Myons• Pions• Kaons
Primary beam
Target
Magnet
Parameters: Beam Intensity and Particle type
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Production of “new” particles with colliding beams
Accelerator where two particles collide:
Conservation of momentum and energy:
New particle with momentum = 0 and mass m0
Note: to produce a Z0 needs e+ e- beams with each about 46 GeV. For the production of W+ W-pair, the accelerator requires the double energy (conservation of charge!)
Particles from the accelerator with the kinetic energy E and
mass m0
Collider
Colliding particles with Ek 450 GeV
Ecm 2 Ek
Ecm 900 GeV
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Particle physics: cross section
Approximation (example): to investigate the inside of a proton, a high-energy proton beam collides with another proton
„Protonradius“: ~10-15 m
„Area“ is in the order of: ~10-30 m2
Definition: Barn 10-24 cm2 = 10-28 m2
Diameter of the beam: 10-3 m (1 mm)
Number of protons in the beam: 1014
Probability, that a proton in the beam collides with another proton: 10-30 m2 / 10-6 m2
In order to obtain a collision rate of 1 Hz, about 1024 colliding protons per second are required
• Small cross section of the beams• Intense particle beams
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Colliding Beams: Energy and Luminosity
e+e- storage rings: LEP-CERN until 2001, B-Factories at SLAC and KEK (USA, JAPAN)e+e- linear accelerators (Linacs): - being discussed – ILC (Int. Linear Collider) und CLIC – CERN
Proton-Proton: ISR until 1985, und LHC – CERN from 2008Proton-Antiproton Collider: SPS – CERN until 1990, TEVATRON – FERMILAB (USA) just finished e+ or e- / Proton: HERA (DESY) – until 2007
Number of "new particles"“: ][][ 212 cmscmLtN
LEP (e+e-) : 3-4 1031 [cm-2s-1]
Tevatron (p-pbar) : 3 1032 [cm-2s-1]
B-Factories : >1034 [cm-2s-1]
LHC nominal : 1034 [cm-2s-1]
LHC today: 3-4 1033 [cm-2s-1]
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L = N2 f n b / 4 p s x s y
N ......... Number of particle per bunch
f ......... Revolution frequency
nb......... Number of bunches
sx s y ... Transverse beam dimensions at collision point (Gaussian)
Luminosity
Protons N per bunch: 1011
f = 11246 Hz, Number of bunches: nb = 2808
Beam size σ = 16 m
L = 1034 [cm-2s-1] Example for LHC
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Z0 Teilchen bei LEP
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Energy and power of a particle beam
The energy that is stored in a particle beam is given by:
The power in the beam is given by:
For many new projects high power of the beam is of crucial importance (power exceeding one MW).
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Energy stored in the beam
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10 100 1000 100000.01
0.10
1.00
10.00
100.00
1000.00
10000.00
Momentum [GeV/c]
En
erg
y st
ore
d i
n t
he
bea
m [
MJ] LHC top
energy
LHC injection(12 SPS batches)
ISR
LEP2
SPS fixed target and CNGS
HERA
TEVATRON
SPSppbar
SPS batch to LHC
Factor~200
RHIC proton
LHC energy in magnets
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Importance of particle physics for the development of accelerators
• The driving force behind the development of accelerators came from particle physics
• Particle physicists are still the most demanding user of particle accelerators
• This is starting to change – now progress in accelerator physics is being also driven by other users
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The use of Accelerators (R.Aleksan)
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This « market » represents ~15 000 M€ for the next 15 years, i.e. ~1000M€/year
Projects Science field Beam type Estimated cost
LHC Particle Physics proton 3700M€
FAIR Nuclear Physics Proton /ion 1200M€
XFEL Multi fields electron aphoton 1050M€
ESS Multi fields Proton aneutron 1300M$
IFMIF Fusion Deuteron aneutron
1000M€
MYRRHA Transmutation Proton aneutron 700M€
In past 50 years, about 1/3 of Physics Nobel Prizes are rewarding work based on or carried out with accelerators
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Clinical accelerators Industrial accelerators
Total accelerators sales increasing more than 10% per yearCourtesy: R. Aleksan
and R. Hamm
radiotherapy electron therapy hadron (proton/ion)therapy
ion implanters electron cutting & welding electron beam and X-ray irradiators radioisotope production …
Application Total systems (2007) approx.
System sold/yr
Sales/yr ($M)
System price ($M)
Cancer Therapy 9100 500 1800 2.0 - 5.0
Ion Implantation 9500 500 1400 1.5 - 2.5
Electron cutting and welding 4500 100 150 0.5 - 2.5
Electron beam and X-ray irradiators 2000 75 130 0.2 - 8.0
Radioisotope production (incl. PET) 550 50 70 1.0 - 30
Non-destructive testing (incl. security) 650 100 70 0.3 - 2.0
Ion beam analysis (incl. AMS) 200 25 30 0.4 - 1.5
Neutron generators (incl. sealed tubes) 1000 50 30 0.1 - 3.0
Total 27500 1400 3680