Download Physics and Technology of Particle Accelerators

Physics and Technology of
Particle Accelerators
Basics, Overview and Outlook
Simone Di Mitri,
Elettra – Sincrotrone Trieste
University of Trieste, Dept. of Engineering
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Prologue
This seminar samples the history of particle accelerators, and
contents of my “Particle Accelerators” Course.
This is a seminar primarily for students and young scientists.
We aim to provide a taste of what particle accelerators are, how
they work and why they have been developed.
Use a qualitative approach, no mathematics, focus on existing
cases (whenever possible), such as Elettra – Sincrotrone Trieste.
Credits: Physics of Particle Accelerators, Prof. S. Tazzari, University of
Roma Tor Vergata, 2006 – 2007.
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Particle Acceleration
Charged Particles: electron, proton, ion and anti-particles
E = T + m0c2 = γm0c2
r r
p = βγm0c 2
r r r
FL = q (E + v × B )
Special Relativity is all we need. Includes
kinematics and dynamics of relativistic
charged particles.
2
γ = 1 1− β
Static and time-varying electric field increases the particle kinetic
energy.
Radiofrequency (RF) accelerating structures: cavities, diskloaded waveguides.
Static and time-varying magnetic field bounds the particle motion
into the vacuum chamber, possibly on a closed orbit.
Dipole, quadrupole and multi-pole magnetic elements for
controlling the particles direction (orbit) and beam size (focusing).
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Why High Energy Particles ?
3Li 7 +
p = 2 2He4
∆x∆p ≥ h
λ =h p
Proton (p) energy has to overwhelm the Coulomb barrier of the
target atoms (He). Rutherford’s exp. in 1911 led to investigation of
the atomic structure & (sub-)nuclear reactions.
Heisenberg’s Uncertainty Principle + De Broglie Wavelength point that
the spatial/energy resolution for observing the matter structure is
inversely proportional to the particle energy.
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Accelerator Facilities
“Beam on Fixed Target” (p = t):
ECM = 2γ b m0c 2
“Collider” (p1 = p2):
ECM = 2γ bm0c 2
“Synchrotron Radiation”:
U turn [keV ] = 88.5
Eb4 [GeV ]
R [m ]
3 cγ b3
ωc =
2 R
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Colliding Proton Beams: the Tevatron
(Chicago, IL)
Neutrinos from
fixed target exp.
The search for
Higgs boson
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Synchrotron Radiation Light Source:
ESRF (Grenoble, FR)
observer
matter
sample
synchrotron light
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Electrostatic Accelerators
5 MeV electrons, Van De
Graaf, MIT 1931
Few MeVs protons, Cockroft
and Walton, CERN 40’s
∆T = q∆V
Au- ions
15MV
Stripper,
Q = 15e-
Seminar on Particle Accelerators, Univ. of Trieste
T = 14x15MV
= 210 MV !!
Simone Di Mitri, 19-05-2014
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Resonant Linear Accelerators
Ising (1924), Wideroe (1928), Sloan and
Lawrence (1931), Alvarez (1945),…
Gap
Drift-Tubes
Disk-Loaded
Waveguide
Structure
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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RF Structure
Pill-box
(in vacuum)
•
Accel. field:
•
Synchronism:
•
Traveling Wave:
•
Energy Gain:
(TM010)
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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RF Electron Linac:
SACLA (Hyogo Pref., Japan)
50 m
Experimental Hall
200 m
Undulator Hall
400 m Accelerator
Tunnel
Klystron
Gallery
May 2010
Machine
Assembly Hall
Source: T. Inagaki, T. Shintake
8 GeV e-linac
C-band (5.7 GHz)
35 MV/m acc. gradient
13000 cells mass production
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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RF Proton Linac: TULIP (CERN)
Source: A. Degiovanni, U. Amaldi
80–210 MeV p-linac
C-band (5.7 GHz)
<38 MV/m acc. gradient
Rep.rate, 200 Hz
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Resonant Circular Accelerator: the
Cyclotron (E.O.Lawrence & M.S.Livingstone, Berkeley 1931)
“Dees”
top view
side view
Synchronism
Energy gain / turn
Lorentz force
• Spiraling motion:
1 ∆T
∆T m0c 2
∆ρ = ρ
=
2 T
q cB 2T
• Maximum kinetic energy:
Classical approximation
(e.g., massive particles)
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Cyclotron for Relativistic Particles
ωc =
B
1 B
=
≡ CωRF
q m γ q m0
To maintain the synchronism, which ensures the
multi/turn acceleration, one has two ways:
1. Increase B(t) synchronous to γ(t), ∝ ρ(t)
CERN SC
“sector cyclotron”
TRIUMPH, Canada
2. Increase ωRF (t) synchronous to γ(t)
“sincro-cyclotron”
N.B.: here the beam is bunched, over
one period of modulation of ωRF !!
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Betatron
The “focusing issue” of the “sector cyclotron”, to keep the beam orbit stable,
had already been faced by R. Wideröe in 1923 (“ray transformer”), but only
solved by D.W. Kerst in 1940 (“betatron”).
Few tens of MV/m average
accelerating gradient
• Unlike the cyclotron, the betatron is not resonant, as the accelerating field
is here generated by the time-varying magnetic field.
• Here the beam is bunched, over one period of modulation of B(t) (typically,
< 50Hz).
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Synchrotron
RF acceleration in linacs turned out to be very efficient for reaching high energies
(T>100s MeV). At the same time, a closed orbit minimized the cost of the facility.
But, closed orbit implies transverse focusing, synchronized with the energy ramping.
Idea: split the electric and the magnetic action, and distribute it on a ring. The
magnetic fields are “ramped” with the beam energy, for a fixed RF.
… to LEP (1987) and LHC (2007), synchrotron
colliders in Geneva, Switzerland.
From AdA, e+e- synchrotron collider
in Frascati, Rome (1961)….
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Livingstone Chart
eV
Average 10-fold
increase in energy
every 6 years.
New branches
correspond to
technological
advances.
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Resumé
Particle accelerators developed from atomic physics research at the beginning of
the 20th century (Rutherford, 1911). The nuclear structure of stable atoms was
investigated with electrostatic accelerators driving < 30 MeV protons and ions
(Cockroft-Walton, Van De Graaf, until 1940s).
Nuclear transmutation and radioactive elements were studied. In US, research
started being driven by the army (mainly fusion and nuclear bomb).
Kinetic energy gain reached 100s of MeV with linear (Ising, Wideroe, Alvarez)
and circular (Lawrence and Livingstone’s cyclotron, 1931) resonant accelerators.
Stability issues faced in the sector-cyclotron, the sincro-cyclotron and the
betatron. These are currently used for nuclear physics and medical applications.
Kinetic energy gain reached the GeV level with resonant accelerators, splitting
the accelerating (RF) and the focusing (magnets) action. Stability was ensured
over long time periods, in all 3-planes of motion. Synchrotrons are used to store
leptons, hadrons and ions.
Applications include: particle physics, astrophysics (collider), imaging, biology,
lithography, radiology (light sources), medical applications (protons).
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Elettra – Sincrotrone Trieste
Elettra – Sincrotrone Trieste is a nonprofit shareholder company of Italian national
interest, established in 1987 to construct and manage synchrotron light sources as
international facilities.
ELETTRA Synchrotron Light Source:
FERMI@Elettra FEL:
up to 2.4 GeV, top-up mode,
100 – 4 nm, fully funded
768 proposals from 39 countries in 2010
Sponsors:
Italian Minister of University and
Research (MIUR)
Regione Auton. Friuli Venezia Giulia
European Investment Bank (EIB)
European Research Council (ERC)
European Commission (EC)
Collaborations:
and many others…
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Science Needs and Goals (examples)
High resolution at small spatial scales
short wavelength
Most of the photons at the same wavelength
narrow bandwidth
Stroboscopic picture of chimical processes
short pulse
Large statistics in single-shot
large number of photons per pulse
Large statistics in multi-shot
high repetition rate
multi-color
wide source
×
×
multi-color
collimated
×
monochromatic
wide source
Coherence
×
Brilliance
monochromatic
collimated
= coherent !
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Elettra Synchrotron Light Source
Main Ring
Hill’s equation:
Dipole Magnet (bend)
Quadrupole (focus)
RF cavity (energy)
x ' '+ k ( s ) x = δ ρ ( s )
electrons
B
ref. orbit
\
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Electron Beam Dynamics in Rings
1.
2.
3.
The machine is modelled with codes.
From orbit measurements, machine imperfections are evaluated.
The machine model is upgraded and corrections applied to the machine.
Beam “optics” along the lattice
Multi-turn nonlinear dynamics
Other crucial issues:
• injection into the main ring,
• beam-beam collisions,
• collimation,
• single- and multi-bunch instability (excited modes)
• ….
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Why a Linac-Driven Light Source?
An accelerated charge particle radiates: Pcirc
2 e 2 γ 2 r& 2
2
=
p
,
P
=
γ
Plin
circ
2
3
3 c m0
Leptons (i.e., electrons) radiate more than hadrons (i.e., protons) when
subjected to the same force. Circular acceleration is more efficient (and
typically cheaper) than the linear one.
But, e-beams in SLS reach equilibrium properties that are typically far from
providing radiation as wished by FEL users (synchrotron radiation damping
of particles’ velocities is balanced by the quantum excitation due to
random emission of photons in time) .
An electron linac can be used to overcome the SLS equilibrium dynamics
and to “shape” the e-beam as desired. However, a more efficient radiating
process is still needed to surpass the SLS’s brilliance level…
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Gap ∼ mm’s
Undulator Radiation & FEL
λu∼cm’s
∼N
Source: T. Shintake, R. Bakker, E. Allaria
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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FERMI Free Electron Laser
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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FERMI Free Electron Laser
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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FERMI Free Electron Laser
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Electron Beam Dynamics in Linacs
“Emittance compensation”:
r ′′ =
r’
r
qI
r
Kr
=
2πε 0 mc 3 β 3γ 3 R 2 R 2
z
(Figure by P.G. O’Shea)
r
emittance
slice
“Wakefield (Impedance)”:
“Bunch Length Compression”:
Electron w/ higher
energy is behind
=−
=−
Electron w/ higher
energy travels on shorter
path and catches up
Reference
particle
Electron w/ lower
energy is ahead
=−
Electron w/ lower
energy falls
behind
Source: J.R. Harris, M. Venturini, P. Craievich
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Achievements
… and many
others in Phys.
Rev. Letters.
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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Conclusions
• SLSs are complementary to FELs as for multiple-users access, stability,
pulse rate, λ-tunability, brilliance and coherence.
• Successful (i.e., interesting and delivering) projects are those that reach
the right equilibrium between pushing the boundaries and setting
achievable goals.
• The gap between what current technology/proven designs can deliver
and what is desirable for the users provides opportunities (R&D! jobs!
fun!) for physicists and engineers (and scientists in general).
Thank you for Your Attention
Contact: [email protected]
Course: Acceleratori di Particelle, in Ing. Elettronica, Laurea Magistrale (6 CU)
Seminar on Particle Accelerators, Univ. of Trieste
Simone Di Mitri, 19-05-2014
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