Download An Introduction to particle Accelerators

5th Particle Physics Workshop
National Centre for Physics
Quaid-i-Azam University Campus, Islamabad
PARTICLE BEAMS, TOOLS FOR MODERN SCIENCE
Hans-H. Braun, CERN
¾ History and Physics Principles of Particle Accelerators
Origins
From Zyklotron to Synchrotron
Defocusing + Focusing = Focusing
Particle Colliders
¾ An Overview of Accelerator Applications
Synchrotron Radiation, from Nuisance to Bright Light
Beams for Medicine
Particle Accelerators for Particle Physics
¾ Introduction to Linear e+/e- Colliders and CLIC
Linear Colliders - Motivation and Concept
Technical Challenges for Linear Colliders
CLIC
5th Particle Physics Workshop
National Centre for Physics
Quaid-i-Azam University Campus, Islamabad
PARTICLE BEAMS,
TOOLS FOR MODERN SCIENCE
Hans-H. Braun, CERN
1st Lecture
History and Physics Principles
of Particle Accelerators
o Origins
o From Zyklotron to Synchrotron
o Defocusing + Focusing = Focusing
o Particle Colliders
Origins
One of the first particle beam set-up’s
(Marsden didn’t get a stamp)
The Rutherford-Geiger-Marsden Experiment (1906-1913)
Showed that the Thomson (or Plum Pudding) model of the atom is wrong !
Atoms consists of extremely small nucleus of positive electric charge,
carrying almost all the mass of the atoms. The nucleus is surrounded by a
diffuse cloud of almost weightless electrons with negative charged.
Rutherford experiment started
interest in subatomic length scales
Ernest Rutherford cajoled for years British industry
to push development of high voltage sources as
replacement for the α-emitters in his experiments.
Why ?
• Higher flux of particles
• Particles of higher velocity ⇔ higher momentum
⇔ higher kinetic energy
Motivations for higher beam energies I
Theory of microscope:
Only objects larger than the wavelength λ of light
can be resolved
Louis De Broglie 1923:
Particles have wave properties
with wavelength given by
h
h
h
=
λ= =
P
2m E KIN
2m q U
de Broglie wavelength of α particles vs. kinetic energy
-14
10
λ (m)
strongest α
sources
size of
proton
-15
10
-16
10
6
10
7
8
10
10
Accelerating Voltage (MV)
9
10
Motivations for higher beam energies II
Coulomb barrier for charged-particle reactions
+
elect
ric
forc
e
+
+
+
+
Motivations for higher beam energies III
Einstein* 1905: Energy equivalent to mass
E = m c2
⇒ Collisions of energetic particles can create
new particles, if kinetic energy is sufficient
Traces of particles produced in
collision of gold atoms at 100 GeV
*many stamps
Electrostatic Generators
Van de Graaff Generator, 1931
Limited to
K20MV
by electrical sparking
Linear accelerator (Rolf Wideroe 1928)
… and half an RF period later
L=
‹
Lengths of drift tubes follow increasing velocity
‹
Particle gains energy at each gap, total acceleration
Applied acceleration is
N
1 v
2 f
NGAP ·VRF
times higher than electric voltage !
Wiederoe’s first LINAC
In 1928 voltage from RF oscillators was small and the linear accelerator,
(or LINAC ) not competitive with electrostatic accelerators
RADAR technology boosted the development of RF sources during
World War II. This eventually made LINAC’s the accelerator of
choice for many applications.
Fermilab proton linac (400MeV)
Inside proton linac
Electron Linacs
Because of higher particle velocity (≈c0), higher frequency (1.3-30 GHz)
and different accelerating structure types.
Most common building block it traveling wave structure.
pulsed RF
Power
source
Electric field
RF wall currents
d
Electrically coupled TM010 resonant cavities
Condition for acceleration Δϕ = ω/c·d,
with Δϕ the phase difference between adjacent cells
RF
load
TM
010
"pill box cavity mode"
E 0 J 0 ( ωc r ) cos(ωt )
EZ =
Bφ
E0
J 1 ( ωc r ) sin(ωt )
c
Resonant frequency given by 1st zero
c
of Bessel function, ω = 2.405
R
ω independent of d !
Bφ = −
EZ
R
d
Stored Energy
∫∫
0 0 0
=
π
2
2
( E + c Bφ ) r dr dφ dz
2
Z
ε 0 d E Z2 R 2 J 1 (2.405) 2
Power loss given by
P=-
ω
Q
W, Q ≈
100
0.2
50
0.1
2
7 ⋅ 10 8
f
(typical Q value for copper
accelerating structures)
0
0
0.5
1
ω/c r
1.5
2
0
2.5
Bφ (T)
W=∫
ε0
EZ (MV/m)
d 2π R
d
Coupled chain of resonators
″
″
″
Ei + ω 0 E + aEi −1 + Ei +1 = 0
i-1
Ansatz
i
i+1
Ei −1 = e i (ωt +ϕ ) , Ei = e iωt , Ei +1 = e i (ωt −ϕ ) ;
⇒ Dispersion relation
wavenumber
⇒ Group velocity
ω=
k=
ω0
1 + 2a cosϕ
ϕ
d
a d ω 0 sin kd
dω
vG =
=
3
dk
(1 + 2a cos kd ) 2
ω
ω0
vP =
ω
k
=
ωd
= v ELECTRON
ϕ
ϕ
3 GHz accelerating structure of CTF3
Input power
Pulse length
Length
Beam current
Acceleration
Frequency
30 MW
1.5 μs
1m
3.5 A
9 MV
2.99855 GHz
Dipole modes suppressed by slotted iris
damping (first dipole’s Q factor < 20)
and HOM frequency detuning
Damping
slot
SiC load
Cyclotron
Lawrence & Livingston 1932
The same acceleration gap
traversed many times !
Lorentz Force = Centrifugal Force
m v2
ev B =
R
mv
Radius of trajectory R =
eB
2π R 2π m
T=
Revolution time
=
v
eB
Cyclotron frequency f =
eB
2π m
Independent of velocity !
R
Example: a typical proton Zyklotron
B = 1.7 T
R = 0.75 m
f =
EKIN
eB
= 25.92 MHz
2π m
2
(
e B R)
=
2 mP
= 1.247 ⋅10 −11 J = 77.86 MeV
Cyclotron frequency f =
Theo
ry
relat of
ivity
eB
2π m
Independent of velocity ?
meffective
⎛ EKIN ⎞
⎟
= m0 ⎜⎜1 +
2 ⎟
⎝ m0c ⎠
⇒ Cyclotron principle works only for beam energies
EKINh m0 c2
For example for protons
EKINh 938 MeV
(with some tricks ¡600 MeV can be obtained)
The Synchrotron
Proposed independently and simultaneously 1945
by McMillan in the USA and Veksler in the USSR
E.M. McMillan
V. Veksler
magnetic field
Electromagnet of
variable strength
Magnetic cycle synchrotron
ion
rat
e
l
e
acc
injection
extraction
injection
time
RF electric field with
variable frequency
f=g(t)
N
S
Beam on circular orbit
with constant radius
B(t)
To make synchrotron work
magnetic field, RF frequency and voltage have
to be controlled following a system of coupled
equations:
dEkin(t)
= e VRF f (t )
dt
m c ( Ekin(t) + m c 2 ) 2
B (t ) =
−1
eR
m 2c 4
f(t)
VRF
EKIN(t)
Layout of an early proton synchrotron
f (t ) =
v(t)
2π R
m 2c 4
v(t ) = c 1 −
( Ekin(t) + m c 2 ) 2
Taken relativistic mass increase into account !
⇒ Synchrotron can be build for very high energies.
For proton beams limits are given by achievable magnetic field
and size.
Largest synchrotron LHC at CERN (under construction),
27km circumference, BMAX=8.3 T, EKIN=7.000.000 MeV
Variation of parameters with time in a proton synchrotron
Proton Synchrotron, R= 10m, VRF=10 kV, EKinetic at injection=10MeV
2.5 ´ 108
particle velocity m s
4000
EKinetic MeV
3 ´ 108
@
D
5000
3000
2000
1000
2 ´ 108
1.5 ´ 108
1 ´ 108
5 ´ 107
0
0.2
0.4
@
D
0.6
0.8
1
0
0.2
2
@
D
0.4
0.6
0.8
1
Time s
Time s
@
D
5
1
@
D
1.75
0.75
2
4
1.25
fRevolution MHz
magnetic field T
1.5
3
0.5
1
0.25
0
0.2
0.4
@
D
0.6
Time s
0.8
1
0
0.2
0.4
@
D
0.6
Time s
0.8
1
How to keep beam particles together ?
In light optics an array of focusing lenses
is used to keep light rays together
An electromagnet in quadrupole configuration
will have a similar effect on a particle beam.
Δφ
iron yoke
x
The action of each lens can be described
as an angle change of the trajectory
x
Δφ = −
f
N
S
S
N
coil
quadrupole magnet
However there is one big difference,
considering the direction of Lorentz force
you find that it focuses in one plane,
but defocuses in the other !
1952 Courant, Snyder and Livingston
propose “alternating gradient focusing”
focusing
+ defocusing = focusing
E. Courant
defocusing +
H. Snyder
S. Livingston
focusing = focusing
Introduction of AG focusing had tremendous impact
on beam quality and accelerator size and cost !
In turned out that Christofilos from Athens had filed an
U.S. patent on this idea already in 1950, but nobody had noticed !
N. Christofilos
C
l
el
Quadrupole
focusing
Dipole
(B=Bend)
Quadrupole
defocusing
FODO lattice
for synchrotron
Particle Colliders
Frascati and Novosibirsk, 1961
Reaction products
extracted beam
Reaction
products
e
acc
injection
extraction
injection
time
“Interaction point”
Storage ring
Synchrotron
Magnetic cycle synchrotron
n
tio
a
r
le
A. Budker
Detectors
“Fixed target”
magnetic field
magnetic field
Detectors
B. Touschek*
Magnetic cycle storage ring
e
acc
injection
n
tio
a
r
le
storage
time
*with
Lola
What is the advantage of collider?
Fixed target
Colliding beams
beam particle
with energy E
new particle
of mass mX
particle of clockwise
beam with energy E
interaction
new particle
of mass mX
interaction
particle at rest
of mass mT
particle of counterclockwise
beam with energy E
Conservation of energy and momentum
E>
m X 2c 2
2 mT
E>
mX c2
2
Same pages from Bruno Touscheks
1960 notebook
2007
1961 VEP 1, Novosibirsk, USSR
1971 ISR, CERN, Switzerland
2000 RHIC, Brookhaven, USA
e+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ee+/ep/p
p/p
p/p
e+/ee+/ee+/ee+/- /p
e+/ee+/ee+/ee+/ee+/ep/p and Pb/Pb
e-/ep/p
ion/ion
DAΦNE
LNF Frascati
500 MeV e+/e- collider
In the tunnel of the CERN SppS proton antiproton collider
450.000 MeV, 7 km circumference
1967 Unified Theory of electromagnetic and weak interaction
Field quanta γ, W± and Z0
1979 Nobel price for Glashow, Weinberg, Salam
1983 Discovery of W± and Z0 at SppS /CERN
1984 Nobel price for Rubbia and van der Meer
UA1 detector
SppS
7 km
W event
Enabling technologies for accelerators
¾ Electron, proton and ion sources
¾ Vacuum systems
¾ Magnet technology
ƒ Iron/copper magnets
ƒ Fast pulsed ferrit magnets
ƒ Superconducting magnets
ƒ Permanent magnets
¾ RF power sources
¾ Accelerating RF structures
ƒ Normal conducting
ƒ Superconducting
¾ Cryogenic Systems
¾ Electromagnetic sensors
¾ High speed electronics
¾ High precision electronics
¾ Electric power systems
¾ Large scale precision alignment
¾ Large scale computer control systems
¾ Laser
¾ Tunnel construction techniques
¾...
Accelerators
Many technological
developments were
promoted by
accelerator needs
Recommended literature
Accelerator physics general
H. Wiedemann, “Particle Accelerator Physics,” (2 volumes), Springer 1993
K. Wille, “The Physics of Particle Accelerators : An Introduction,”
Oxford University Press, 2001
S.Y. Lee, “Accelerator Physics,” World Scientific, 2004
A. Chao and M. Tigner (editors), “Handbook of Accelerator Physics and Engineering,”
World Scientific, 1999
T. Wangler, “RF Linear Accelerators,” John Wiley 1998
M. Minty and F. Zimmermann, “Measurement and Control of Charged Particle Beams,”
Springer 2003
Accelerator key technologies
M.J. Smith and G. Phillips, “Power Klystrons Today,” John Wiley 1995
M. Sedlacek, “Electron Physics of Vacuum and Gaseous Devices,” John Wiley 1996
H. Padamsee, J. Knobloch, T. Hays, “RF Superconductivity for Accelerators,”
Wiley 1998
J. Tanabe, “Iron Dominated Magnets,” World Scientific 2005
K. Mess, P. Schmüser, S. Wolff, “Superconducting Accelerator Magnets,”
World Scientific, 1996
For more accelerator book references http://uspas.fnal.gov/book.html
PARTICLE BEAMS, TOOLS FOR MODERN SCIENCE
Hans-H. Braun, CERN
2nd Lecture
Examples of Modern Applications and their Technological Challenges
o Synchrotron Radiation,
from Nuisance to Bright Light
o Beams for Medicine
o Particle Accelerators for Particle Physics