Transcript Van de Graaff Accelerator

Particle Physics: Status and Perspectives
Part 3: Accelerators
Manfred Jeitler
electron microscope
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Van-de-Graaf generator
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Changing the
Particle Energy
F. Sannibale
Van de Graaff Accelerator:
Applications
Tandem Scheme
1st Stage
•Negative ions (H- for example) are
created and accelerated through the
first stage
•At the end of the first stage the
electrons are ‘stripped’ out from the
ions (by a gas target for example)
++ +
+
+ +
2nd Stage
+
•In the second stage the positive ions
(protons in our example) are
accelerated. The net energy gain is
twice the voltage of the Van de Graaff
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Fundamental Accelerator Theory, Simulations and Measurement Lab – Arizona State University, Phoenix January 16-27, 2006
Electrostatic Accelerators:
The Simplest Scheme
Changing the
Particle Energy
F. Sannibale
Cathode
-
-
--
E
Anode
-
-
W = -q VHV
Diode Pierce
Geometry
VHV
Still one of the most used schemes for electron sources
Budker Institute
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Fundamental Accelerator Theory, Simulations and Measurement Lab – Arizona State University, Phoenix January 16-27, 2006
Cockroft-Walton
accelerator
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Cockroft-Walton accelerator at CERN
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Changing the
Particle Energy
F. Sannibale
RF Accelerators:
Wideroe and Alvarez Schemes
In 1925-28 Ising and Wideroe conceived the first linear accelerator (linac). The
revolutionary device was based on the drift tubes scheme.
During the decelerating half period of the RF, the beam is shielded inside the
conductive tubes.
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Synchronicity condition: Li @ vi TRF
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At high frequency the Wideroe scheme becomes lossy due to electromagnetic
radiation.
In 1946 Alvarez overcame to the
inconvenient by including the Wideroe
structure inside a large metallic tube
forming an efficient cavity where the
fields were confined.
200 MHz RF
source from radars
The Alvarez structures are still widely used as pre-accelerator for protons and
ions. The particles at few hundred keV from a Cockcroft-Walton for example, are
accelerated to few hundred MeV.
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Fundamental Accelerator Theory, Simulations and Measurement Lab – Arizona State University, Phoenix January 16-27, 2006
inside of an Alvarez-type
accelerating structure
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The cyclotron
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Cyclotron
p
rµ
eB
r.............orbit radius
p...........particle momentum
e............particle charge
B............magnetic field
revolution frequency must be
independent of the particle‘s
momentum !
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Changing the
Particle Energy
F. Sannibale
Cyclotron and
Synchro-cyclotron
Uniform
Magnetic
Field
Electric
Field
Proton Source
Accelerated
Protons
The first cyclotron
4.5” diameter (1929).
In an uniform magnetic field:
TR =
2p r 2p p 2p mv 2p m
=
=
=
v
veB
veB
eB
for v << c
E. O. Lawrence
1939 Nobel Prize
For non-relativistic particles
the revolution period
does not depend on energy
• If the RF frequency is equal to the particles revolution frequency synchronicity is
obtained and acceleration is achieved.
• The synchro-cyclotron is a variation that allows acceleration also of relativistic
particles. The RF frequency is dynamically changed to match
the changing revolution frequency of the particle
• In 1946 Lawrence built in Berkeley the 184” synchro-cyclotron with an orbit radius of
2.337 m and capable of 350 MeV protons. The largest cyclotron still in operation is in
Gatchina and accelerates protons to up 1 GeV for nuclear physics experiments.
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Fundamental Accelerator Theory, Simulations and Measurement Lab – Arizona State University, Phoenix January 16-27, 2006
Changing the
Particle Energy
F. Sannibale
The Cyclotron:
Different Points of View
From LBNL Image Library
Collection
By Dave Judd and Ronn MacKenzie
…the operator
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Fundamental Accelerator Theory, Simulations and Measurement Lab – Arizona State University, Phoenix January 16-27, 2006
Synchrotron
elements of a
synchrotron
dipole magnet: to keep
particles on track
quadrupole magnet:
focussing
high-frequency
accelerating cavity
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SPS Tunnel
Super-Proton-Synchrotron (Geneva)
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first electron-electron collider:
Novosibirsk / Russia
VEP-1
130+130 MeV
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Particle production at a collider
 particles do not
disintegrate and show
what is inside but
 the kinetic energy of
the colliding particles
(protons) is transformed
into the mass of another
particle
Fixed-target accelerators and colliders
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layout of a circular
collider
quadrupole
dipole
resonator
reaction products
interaction zone
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LHC dipole
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layout of the LHC storage ring
(built into the former LEP tunnel)
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the world‘s largest accelerators
accelerator
accelerated
particles
Ebeam
start
luminosity
[ 1030 cm-2 s-1]
TEVATRON
pp
2 x 900 GeV
1987
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PEP II
e+ e-
10.5 GeV
1999
5000
KEK B
e+ e-
10.5 GeV
1999
13 000
HERA
p e±
26 + 820
GeV
1992
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pp
2 x 4000
GeV
2009
10 000
LHC
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luminosity
 (instant) luminosity is rate per cross section
 usual units: cm-2 s-1
 e.g., 1030 cm-2 s-1 corresponds, for a reaction cross section of 10-30
cm-2 ( = 1 μbarn), to a rate of 1 event per second
 for a collider, the luminosity can be calculated as follows:
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integrated luminosity
 number of events collected divided by the cross section
 usual units: fb-1 (“inverse femtobarn”),
ab-1 (“inverse attobarn”)
 an integrated luminosity of 1 fb-1 means that for a process
with a cross section of 1 fb, 1 event (on average) should
have been collected
 or 1000 events for a cross section of 1 nb, etc.
 so, 1 inverse attobarn = 1000 inverse femtobarns :
 1 ab-1 = 1000 fb-1
 physicists are now looking for very rare events, so it is
vital to reach not only high energies (so that heavy
particles can be produced) but also high luminosities
 handling the resulting data rates is a challenge also for the
detectors, trigger systems, and readout electronics
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“Accelerator”: do particles really get faster?
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Years of Design, Construction and
Commissioning of the LHC
slide
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accelerator centers worldwide
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photon collider
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layout of a muon storage ring
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