Basic principles of accelerators
(part II)
Linear accelerators
•Classification
•History
•Applications
… for some slides courtesy to Dr. A.Sidorin
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
A time varying magnetic
field is generated
resulting in an electric

field
Two principles of
classification:
1. The type of an
accelerating structure:
standing or traveling
wave structures.
2. The particle velocity:
v << c – proton or ion
linacs;
v = c – electron linacs
rotE  
1 B
.
c t
It was used firstly by
Kerst and Serber in
circular electron
accelerator named
First device provided
voltage larger than
“betatron”.
1MV was invented and The linear induction
constructed by N. Tesla accelerator is called
in 1896.
“Linear betatron”
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
pLi
2He
4U0
3U0
Step-up transformer
2U0
U0
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
3
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 T=ZeV. 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
moving rubber
tape delivers
positive charge
positively charged
metal brush takes
electrons
from the tape
Isolating
column
negatively
charged
metal
plate
Voltage
source
1937, St. Bartholomew’s Hospital, London, 1 MeV HV accelerator
First medicine application
4
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.

V
I
D.Kerst near his
betatrons.
Small – 2,3 MeV
Big – 25 MeV

B

1
d
Ф
1
d
(
E
,
dl
)







(
B
,
ds
)


c
dt
c
dt
Wideroe ½
condition
1
B
(R
) B(R
)
2
5
Linear induction accelerator
Accelerating structure
of induction accelerator.
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.
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:
L

2
(R.Wideroe, 1928)
DESY, Hamburg
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
L  
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.
2.
3.
4.
Greed focusing
Solenoidal focusing
Focusing by Static Quadrupoles (Strong focusing)
Focusing by the accelerating field
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
Atomic projects
Isotop separation
Reactor breeder
Accelerator breeder
To increase
Irradiation of U by
The same as reactor.
concentration of
neutrons leads to
Instead of neutrons –
formation of
protons at 50 -100
235U from 0.7% to 95%
1. Centrifugal
Pu. Chemical separation.
MeV and ~ 1 A of
2. Gas diffusion
First reactor was
continuous current
3. Electromagnetic
constructed by
(!!!).
(mass spectrometers)
E.Fermi, in SU –
Livermore (Naval
I.Kurchatov
research laboratory)
Cheljabinsk-sity in SU
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)
Alvarez – type DTL
First Alvaretz type accelerator in SU – injector into Synchrophasatron (1957)
under leading by K.Sinelnikov (focusing by grids)
IHEP, Protvino, I-100 proton linac
Will be used for carbon therapy
CERN, LINAC-2, griders with drift tubes.
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
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
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
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.
2.
3.
4.
Generation of H- beam
Acceleration to the energy of 50 – 100 MeV
Neutralization in a gas or plasma target
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
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.
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
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.
BEAR goes from Los Alamos
to Washington DC international airport to aerospace museum (2006)
Structures based on Interdigital H- cavity
Firstly realized by V.Tepljakov
(IHEP, USSR): RFQ DTL
RFQ - DTL
IHEP, Protvino, URAL-30
RF model for CERN 352.2 MHz linac
for SPL project. (Developed in IHEP)
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)
Hybrid focusing
U. Ratzinger (1988)
GSI, Darmstadt, Heavy ion linac
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
電場
Electric
Field
(陽)電子
Electron
(positron)
28
Super-Conducting cavities for
electron accelerators
CERN, LEP SC cavity
IHEP, Protvino, niobium SC cavity
SNS Titanium Helium Vessel
Stiffening Rings
Titanium Bellows
NbTi Dished
Head
2 - Phase Return Header
NbTi Dished
Head
HOM
Coupler
Field
Probe
HOM
Coupler
Fundamental
Power Coupler
Medium Beta Cavity
30
SC cavities for ion linacs
/4 cavity
/2 cavity
The accelerator is a chain of independent cavities
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
Typical scheme of injector for
medicine synchrotron
Heidelberg Ion Therapy (HIT) facility
European X-Ray Laser Project XFEL (started June 2007)
In cooperation with international partners, DESY is realizing a facility for shortwavelength 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.
Linear colliders
• Stanford Linear Collider - SLC
• CLIC – Compact Linear Collider
• ILC – International Linear Collider
Why e+e- Collisions ?
• elementary particles
• well-defined
– energy,
– angular momentum
• uses full COM energy
• produces particles
democratically
• can mostly fully
reconstruct events
36
Stanford linear accelerator
L = 3.2 km
W = 50 GeV
CLIC
Overal layout of the CLIC complex
Two beam acceleration scheme,
normal conducting, high acceleration rate (~150 MeV/m)
The International Linear Collider
2 linacs
Dubna ?
32 (50) km length
e-e+ at 500 GeV (1TeV)
2·1034 luminosity
5 x 500 nm bunch size
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)
40
For conclusion: What do and can we expect ?
The Goals:
GUT (Grand Unification Theory) ~ 1023 eV
Tevatron
LHC
The Hopes:
1.8·1012 eV
1.4·1013 eV
Wake Field Collider 6·1014 eV (2x100 km)
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