Basic principles of accelerators

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Basic principles of accelerators (part II) Linear
accelerators

• Classification
• History
• Applications

for some slides courtesy to Dr. A.Sidorin
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Classification
High Voltage Induction Radio Frequency or Resonant or Linac
1. HV transformers (up to 1 MV) 2. Electrostatic accelerators 3. Cascade HV generators 4. Powerful pulse generators First device provided voltage larger than 1MV was invented and constructed by N. Tesla in 1896. A time varying magnetic field is generated resulting in an electric field It was used firstly by Kerst and Serber in circular electron accelerator named betatron. The linear induction accelerator is called Linear betatron Two principles of classification 1. The type of an accelerating structure standing or traveling wave structures. 2. The particle velocity v ltlt c proton or ion linacs v c electron linacs

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Cascade generator First accelerator used for
nuclear physics cascade generator on 700 keV
energy was created by J.Cockraft and A.Walton
England 1931. 
First controlled nuclear reaction
Step-up transformer
The basic method implemented in the cascade
generator is a voltage multiplication across the
plates of a capacitor. A set of capacitors are
charged through appropriately placed diodes from
an alternating current source
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Electrostatic accelerators
Van de Graaf (1931) generator Electrostatic
generator particles or ions are accelerated
due to passing through huge constant potential V
(which reach magnitude up to 20 MV). Particle
having charge Ze takes in such an accelerator
kinetic energy TZeV. The great advantage of
such a machine continuous very intensive and
very stable in energy (0,01 ) accelerated
beam. Beam current is about several mA.
metal brush takes electrons from the high
voltage electrode
Isolating column
moving rubber tape delivers positive charge

negatively charged metal plate
positively charged metal brush takes electrons
from the tape


Voltage source


1937, St. Bartholomews Hospital, London, 1 MeV
HV accelerator
First medicine application
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Betatron First circular electron accelerator.
Electrons are in the wire of a secondary coil
accelerated by an electro motive force generated
by a time varying magnetic flux penetrating the
area enclosed by the secondary coil. Electron
beam is circulating in a closed doughnut shaped
vacuum chamber.
D.Kerst near his betatrons. Small 2,3 MeV Big
25 MeV
Wideroe ½ condition
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In the linear betatron a time varying azimuthal
magnetic field is used to provide a high dipole
electric field across a gap along the particle
trajectory. The accelerator consists of many
transformer units which are lined up along a
straight path and are triggered in synchronism
with the particles. Induction accelerator can
accelerate a beam current up to a tens of kA to
energy up to a few tens of mega electron volts.
Accelerating structure of induction accelerator.
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First RF accelerator (Drift Tube Linac DTL
structure)
In DTL ions are accelerated in a gap between
drift tubes. When the field becomes decelerating
the ions drift inside the tube
synchronism
(R.Wideroe, 1928)
DESY, Hamburg
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Alvarez type DTL (E-cavities)
In Alvaretz structure the electric field in all
the gaps has the same direction and phase,
therefore the synchronism condition is
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Particle transverse motion in DTL
The radial components are focusing at the gap
entrance and defocusing at the end. Stability of
the particle longitudinal motion corresponds to
unstable transverse motion (defocusing prevails)
Methods of the focusing

1. Greed focusing
2. Solenoidal focusing
3. Focusing by Static Quadrupoles (Strong focusing)
4. Focusing by the accelerating field

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Beginning of accelerator history
The end of the Second World War

• 1944. V.Veksler auto phasing principle
• 1945. L.Alvarez first RF proton accelerator
• 1945. Biggest cyclotron in the world Tokio,
  Nishina
• 1949. Phasotron in Dubna
• 1952. Strong focusing in Linacs by J.P.Blewett

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Atomic projects
Isotop separation Reactor breeder Accelerator breeder
To increase concentration of 235U from 0.7 to 95 1. Centrifugal 2. Gas diffusion 3. Electromagnetic (mass spectrometers) Irradiation of U by neutrons leads to formation of Pu. Chemical separation. First reactor was constructed by E.Fermi, in SU I.Kurchatov The same as reactor. Instead of neutrons protons at 50 -100 MeV and 1 A of continuous current (!!!). Livermore (Naval research laboratory) Cheljabinsk-sity in SU
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First proton accelerators
The first one constructed in 1945 was 17 m in
diameter and 19 m of length. The drift tubes had
inner diameter of 2 m and aperture diameter of 90
cm. It worked at ? 12.5 m (41.6 MHz). Inside
the drift tubes focusing solenoids were located.
Second Alvarez-type accelerator for 80 MHz
After strong focusing application typical
frequency is 150 300 MHz (d 1.5 3 m)
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Alvarez type DTL
First Alvaretz type accelerator in SU injector
into Synchrophasatron (1957) under leading by
K.Sinelnikov (focusing by grids)
CERN, LINAC-2, griders with drift tubes.
IHEP, Protvino, I-100 proton linac Will be used
for carbon therapy
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Alvarez type DTL
To the end of 70-th the proton (ion) Linacs are
used mainly as injectors of large cyclic
accelerators. Standard configuration HV
foreinjector ( 700 kV) Alvarez (up to 600
MeV). Quadrupole lenses are located inside the
drift tubes
JINR Alvarez injector for the Nuclotron
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Electron Linacs
1960 first clinical 6 MeV resonant electron
accelerator with 3600 gantry (Varian)
In 2002 more than 7500 medicine electron Linacs
were in the world
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Traveling wave structures
For acceleration of relativistic particles
different types of traveling wave structures
operated at frequency from a few hundreds of MHz
to a few GHz are used.
Disc loaded round wave guide
Side coupled structure
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Episode IV Star wars
The idea was proposed in Los Alamos laboratory
in the beginning of 70-th
Usage of a neutral particle beam in the cosmic
space to destroy electronics on Enemies rockets

1. Generation of H- beam
2. Acceleration to the energy of 50 100 MeV
3. Neutralization in a gas or plasma target
4. Required beam current is about 50 mA

1971-discovery of Cesium Catalysis in Budker
Institute (Novosibirsk) The current was
increased from 100 ?A up to 1 A (Dudnikov, Dymov)
1972 commissioning of first RFQ accelerator
(V.Tepljakov, I.Kapchinsky, IHEP Protvino)
1983 USA Strategic Defender Initiative
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RFQ
Four-road line with quadrupole symmetry
The RFQ is a four-vanes resonator with quadrupol
symmetry which provides a transverse electric
gradient for transverse focusing (at low
velocity, magnetic focusing is not efficient
because of the v term which appears in the force
equation). Modulated pole shapes lead to a
longitudinal variation of the transverse field
gradient giving a longitudinal electric component
for acceleration and bunching.
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RFQ
Does not require HV foreinjector, provides
current up to 0.5 A
2H cavity
IHEP, Protvino, initial part of URAL-30
GSI, RFQ based on IH cavity for medicine
accelerator
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Bear on a rocket
13 July 1989 in 8-30 AM from White Sand in New
Mexico Areas rocket was started with BEAR
facility on a board BEAR Beam Experiment Aboard
a Rocket After 11 minutes of flight the BEAR was
successfully landed without mechanical damages.
1 MeV, 10 mA of equivalent current the neutral
particle beam was injected into space
Price of the experiment was 794 M 1993 the
program was closed.
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BEAR goes from Los Alamos to Washington DC
international airport to aerospace museum (2006)
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Structures based on Interdigital H- cavity
Firstly realized by V.Tepljakov (IHEP, USSR) RFQ
DTL
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RFQ - DTL
IHEP, Protvino, URAL-30
RF model for CERN 352.2 MHz linac for SPL
project. (Developed in IHEP)
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Alternative-Phase-Focused (APF) linac
The method first proposed in 50-s in USSR
utilizes focusing and defocusing strengths
provided with the RF acceleration field by
choosing the positive and negative synchronous
phases alternately at each gap.
ALTERNATING-PHASE-FOCUSED IH-DTL FOR
HEAVY-ION MEDICAL ACCELERATOR (HIMAC) NIRS, Japan
(2007)
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Hybrid focusing
U. Ratzinger (1988)
GSI, Darmstadt, Heavy ion linac
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Superconductivity in Linacs
Standing wave accelerator consists of a multi-gap
RF cavity. Synchronism between a particle and RF
voltage is provided by appropriate phase shift
between the fields in the cavities
Electric Field
Electron (positron)?
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Super-Conducting cavities for electron
accelerators
CERN, LEP SC cavity
IHEP, Protvino, niobium SC cavity
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SNS Titanium Helium Vessel
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SC cavities for ion linacs
?/4 cavity
?/2 cavity
The accelerator is a chain of independent cavities
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Applications of linear accelerators

• Medicine and technology
• Neutron generators
• Neutral particle beams
• Energy recovery linacs ERL (synchrotron radiation
  sources)
• X-ray free electron laser X-FEL
• High energy phisics Linear collider

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Typical scheme of injector for medicine
synchrotron
Heidelberg Ion Therapy (HIT) facility
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European X-Ray Laser Project XFEL (started June
2007)
In cooperation with international partners, DESY
is realizing a facility for short-wavelength
laser light with unique properties. The XFEL
opens up new promising experimental possibilities
for almost all natural sciences. The extremely
intensive and ultrashort X-ray laser flashes will
enable scientists to "film" with atomic
resolution the behaviour of, for example,
materials or biomolecules.
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Linear colliders

• Stanford Linear Collider - SLC
• CLIC Compact Linear Collider
• ILC International Linear Collider

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Why ee- Collisions ?

• elementary particles
• well-defined
• energy,
• angular momentum
• uses full COM energy
• produces particles democratically
• can mostly fully reconstruct events

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Stanford linear accelerator
L 3.2  km W 50 GeV
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CLIC
Overal layout of the CLIC complex
Two beam acceleration scheme, normal conducting,
high acceleration rate (150 MeV/m)
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• The International Linear Collider

2 linacs 32 (50) km length e-e at 500 GeV
(1TeV) 21034 luminosity 5 x 500 nm bunch size
Dubna ?
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For conclusion
What do and can we expect "soon"?
2011 (2012) ? LHC
2017 (?) ? NICA, FAIR
2020 (2025 ???) ? ILC or CLIC
2025 (?) ? Muon collider
2030 (?) ? Wake Field Accelerator (100 GeV/m)
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For conclusion What do and can we expect ?
The Goals
GUT (Grand Unification Theory) 1023 eV
The Hopes
Tevatron 1.81012 eV LHC
1.41013 eV Wake Field Collider
61014 eV (2x100 km)
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Thank you for attention !