Future Accelerators

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Future Accelerators

• Lutz.Lilje_at_desy.de
• DESY -MPY-
• Maria Laach 2007
• Part I

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References (Real Paper)

• Accelerator Physics Courses
• Physik der Teilchenbeschleuniger und
  Synchrotronstrahlungsquellen, Klaus Wille,
  Teubner Verlag, Studienbücher, 2. Auflage 1996
• Proceedings of CERN ACCELERATOR SCHOOL (CAS),
  Yellow Reports
• General Accelerator Physics, and topical schools
  on Vacuum, Superconductivity, Synchrotron
  Radiation, Cyclotrons, and others
  http//schools.web.cern.ch/Schools/CAS/CAS_Proceed
  ings.html
• E.g. 5th General CERN Accelerator School, CERN
  94-01, 26 January 1994, 2 Volumes, edited by
  S.Turner
• Accelerator Physics General
• Handbook of Accelerator Physics and Engineering,
  A.W.Chao and M.Tigner, World Scientific, 1998
• Technology Topics
• Superconducting Accelerator Magnets, K.H.Mess,
  P.Schmüser, S.Wolff, WorldScientific 1996
• RF Superconductivity for Accelerators, H.
  Padamsee, J. Knobloch, and T. Hays, John Wiley
  Sons, 1998.
• The Superconducting TESLA Cavities, B. Aune et
  al., PRST-AB, 3, September 2000, 092001.
• Historical and Sociological Aspects
• A BRIEF HISTORY AND REVIEW OF ACCELERATORS, P.J.
  Bryant, CERN, Geneva, Switzerland, CERN 94-1
• Pions to Quarks, edited by L. M. Brown, M.
  Dresden and L. Hoddeson, (New York Cambridge
  Univ. Press, 1989).
• The Birth of Particle Physics, edited by L. M.
  Brown and L. Hoddeson (New York Cambridge
  University Press, 1983).
• Galison, Peter u. Bruce Hevley (Hg.) Big
  science the growth of large-scale research.
  Stanford Univ. Pr., 1992
• Traweek, Sharon Beamtimes and lifetimes the
  world of high energy physicists. Harvard
  University Press 1988
• Rhodes, Richard, Die Atombombe

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References (Virtual)

• Wikipedia
• http//en.wikipedia.org/wiki/Particle_accelerator
• Accelerators
• Lecture by Rüdiger Schmidt (german)
• http//rudi.home.cern.ch/rudi/lectures20darmstadt
  /overview.htm
• LHC http//lhc.web.cern.ch/lhc/
• XFEL http//xfel.desy.de/tdr/tdr/index_eng.html
• ILC http//www.linearcollider.org/cms/

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Outline

• History of particle accelerators
• Particle accelerators concepts
• New particle accelerators for HEP
• LHC
• ILC
• Technology challenges in particle accelerators
  e.g.
• Superconducting Magnets
• Superconducting Cavities
• Outlook

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History of particle accelerators

• One can try to identify three main lines
• Electrostatic
• E.g. tandem accelerators
• Resonant acceleration
• Accelerating structures in virtually every
  accelerator built today
• E.g. RF Linacs
• Betatrons

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Electrostatic Accelerators

• 1857 Heinrich Geissler
• Gas discharge tubes
• http//www.infogr.ch/roehren/roehren.htm
• 1858 Julius Plücker
• First cathode ray tubes electron sources
• 1886 Eugen Goldstein
• Kanalstrahlen ion sources
• 1895 Lenard.
• Electron scattering on gases (Nobel Prize). lt 100
  keV electrons.
• One of the initiators of the Deutsche Physik
  in the 1930/40s
• 1913 Franck and Hertz
• excited electron shells by electron bombardment.
• 1906 Rutherford
• bombards mica sheet with natural alphas and
  develops the theory of atomic scattering.
• 1911 Rutherford
• publishes theory of atomic structure.
• 1919 Rutherford induces a nuclear reaction with
  natural alphas
• 1928
• ... Rutherford believes he needs a source of many
  MeV to continue research on the nucleus. This is
  far beyond the electrostatic machines then
  existing, but ...

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Rutherfords Dream

• It has long been my ambition to have available
  for study a copious supply of atoms and electrons
  which have an individual energy far transcending
  that of the alpha- and beta-particles from
  radioactive bodies. I am hopeful that I may yet
  have my wish fulfilled... .
• E. Rutherford Proc. of the Royal Society of
  London, 117300 (1927)

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Cathode Ray Tubes (Railway tube Crookes)
http//www.infogr.ch/roehren/roehren.htm
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Kanalstrahlen http//www.infogr.ch/roehren/roehren
.htm
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Van de Graaff Generator

• hollow metallic sphere (with positive charges)
• electrode connected to the sphere, a brush
  ensures contact between the electrode and the
  belt
• upper roller (for example in plexiglass)
• side of the belt with positive charges
• opposite side of the belt with negative charges
• lower roller (metal)
• lower electrode (ground)
• spherical device with negative charges, used to
  discharge the main sphere
• spark produced by the difference of potentials
• Tandem concept with stripping for doubling the
  voltage

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25 MV Tandem (Oak Ridge)
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Towards Resonant Acceleration

• Electrostatic accelerators are limited to a few
  Megavolts because
• therefore use resonant acceleration
• Accelerating structures in virtually every
  accelerator built today
• E.g. Radiofrequency (RF) Linacs
• Power Sources are readily available (e.g.
  klystrons from radar or TV)
• 1924 Ising
• proposes time-varying fields across drift tubes.
• This is "resonant acceleration", which can
  achieve energies above that given by the highest
  voltage in the system.
• 1928 Wideröe
• demonstrates Ising's principle with a 1 MHz, 25
  kV oscillator to make 50 keV potassium ions.
• 1929 Lawrence
• inspired by Wideröe and Ising, conceives the
  cyclotron.
• 1931 Livingston
• demonstrates the cyclotron by accelerating
  hydrogen ions to 80 keV.
• 1932 Lawrence
• cyclotron produces 1.25 MeV protons and he also
  splits the atom just a few weeks after Cockcroft
  and Walton (Lawrence received the Nobel Prize in
  1939).

Sparking during conditioning the 25 MV Tandem in
Oak Ridge
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Linear Accelerator (LINAC)
l1
l2
l3
l4
l5
l6
l7
Teilchen quelle
HF-Sender mit fester Frequenz
Driftröhren aus Metall

• Particles from the source are accelerated towards
  the first drift tube
• While passing through the tube the potential
  changes the sign
• When leaving the first drift tube they will be
  accelerated towards the second drift tube
• As the speed increases the distance between tubes
  increases (and their length

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li

• Energy of the particles after tube i
• U0 maximum Voltage of the HF source,
• and ?s the average phase during the passage
  between the tubes of the particle

• Consequence
• No continuous beam can be accelerated,
• Need particle bunches
• Length from few 10 um upto 1m

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Linac at FERMILAB

• 1971, upgraded in 1993
• Linac can accelerate beam to 400 MeV
• Low energy end of the Fermilab linac is an
  Alvarez style drift tube linac.
• The accelerating structures are the big blue
  tanks shown in the photo.
• The five tanks of the low energy end take the
  beam from 750 KeV to 116 MeV.
• The resonant frequency of the cavities is 200
  MHz.

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• FERMILAB Linac

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FLASH (VUV-FEL) Facility at DESY
TTF / FLASH
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Circular Accelerators Betatrons

• Basic idea
• A time varying magnetic field induces a circular
  electrical field
• 1923 Wideröe
• a young Norwegian student, draws in his
  laboratory notebook the design of the betatron
• Two years later he adds the condition for radial
  stability but does not publish.
• 1927 Wideröe
• makes a model betatron in Aachen, but it does not
  work.
• Discouraged he changes course and builds the
  linear accelerator (see above)
• 1940 Kerst
• re-invents the betatron and builds the first
  working machine for 2.2 MeV electrons.
• 1950 Kerst
• builds the world's largest betatron of 300 MeV.

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Circular Accelerators Cyclotron Principle

• Particle moving in perpendicular magnetic field
• results in a circular motion
• Equilibrium of Lorentz- and centrifugal forces
• Revolution time is constant, thus the frequency
  of the acclerating field
• Independent of energy and velocity
• If B constant, R will increase!

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History Excursion Ernest Orlando Lawrence

• Born August 8, 1901
• Died August 27, 1958
• 1930 4 inch cyclotron
• 1932 27-inch
• 1945184-inch
• Relativity speed limit, frequency ramp needed

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History Excursion Ernest Orlando Lawrence
N.B. Tubealloy was the WW II code word for
uranium

• Lawrence is one of the founders of what is called
  Big Science
• Big Science as opposed to the small laboratory
  work has certain features
• Big budgets
• By government
• Big staffs
• Diversification into specialist areas
• Big machines
• See slide before.
• Big laboratories
• Big national labs in the US, CERN, DESY,
• Several methods for getting money to built larger
  machines were explored by Lawrence
• Medical application e.g. cancer treatments
  already before world war II (WW II)
• Military applications e.g. Isotope separation
  with the Calutron and isotope production with the
  cyclotron during WW II

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Vertical Focusing in the Cyclotron
People just got on with the job of building
them. Then one day someone was experimenting
The Figure shows the principle of vertical
focusing in a cyclotron In fact the shims did not
do what they had been expected to do
Nevertheless the cyclotron began to accelerate
much higher currents
E.Wilson Lectures 2001
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• Cyclotron at CERN

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Cyclotron at PSI

• Medical cyclotron for proton therapy at PSI
• 90 t and 3,2 m diameter
• Protons with 60 of speed of light
• Superconducting coils
• Work of Michigan State University, PSI and Accel
  Instruments GmbH

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Early Synchrotrons

• Synchrotrons
• RF frequency is changed
• Magnetic field is ramped
• Energy is increased
• Early Synchrotrons with only weak focussing (see
  below)
• Large aperture magnets
• Avoid saturation
• Large vacuum chambers
• Cosmotron (BNL, 1953)
• 3 GeV
• 2000 tons mainly for the magnets
• 288 C-shaped

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Bevatron (Berkeley, 1954)

• 6 GeV, 10000 tons

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Synchrophasotron (Dubna, 1957)

• Effectively a synchrotron
• 10 GeV
• 36000 tons
• Vacuum tube 150 x 40 cm

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Beam Optics and Focussing

• Particles with different initial conditions
  (position, angle) will depart from each other
• Assume a divergence between two particles of
  10-6 rad
• After 106 m they would have a distance of a meter
• E.g. LEP (circumference 26860 m) after 50 turns
  (5 ms)
• Compensate Gravity
• Need defined conditions at interaction point (IP)
• Small dimensios desirable for higher interaction
  rate (luminosity)
• Different energy particles should reamin together

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Geometrical (Weak) Fokussing in Homogenous Dipole
Field
s

• Two particles with identical energy at the same
  position with slightly different angle will meet
  evry half turn
• Fokussing only perpendicular to magnetic field
• In the other direction there is no focussing and
  particles would diverge
• A focussing force is needed

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Dispersion in Dipole field
Two particles with different energy and the same
momentum will come back to initial position after
each turn.
Nominal Orbit Momentum p0
B
Dispersion orbit with momentum p1
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Strong Focussing

• 1950 Christophilos
• 1952 Courant, Snyder, Livingston
• Alternate magnet types e.g combined function
  magnets
• Provide focussing
• Smaller vacuum chambers (e.g. compare Cossmotron
  with AGS)

From M.C. Crowley-Milling Rep. Prog. Phys
46,1983, 51ff.
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Early Strong Focusing Synchrotrons

• PS (CERN)
• 1959
• 25 GeV
• AGS (BNL)
• 1960
• 33 GeV
• 4000 tons

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Magnet Types

• Today accelerators mainly use seperated function
  magnets
• Dipole magnet constant Field in Aperture
• Quadrupole magnet Zero Field in center , linear
  increase
• Lense like in light optics
• Sextupole magnet - Zero Field in center ,
  quadratic increase
• Chromaticity correction
• Off-energy particles

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Dipole magnet
Iron Yoke
Coil
N
N
Parallele poles
Bz
S
S
Vacuum- chamber
z
Coils
Iron yoke
z
N
S
Quadrupole magnet
N
S
x
x
S
N
S
N
Hyperbolic Pole shoes
Vacuum- chamber
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Real Life Dipole magnet and Quadrupole magnet
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Magnet for SNS

• Beams eye view of an SNS half cell.
• From front to back
• corrector,
• quad polefaces,
• sextupole faces
• the dipole

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Summary of History Part

• Several accelerator types were developed in the
  third decade of the last century
• Other applications like medicine were also
  considered, but were of minor importance in the
  early years
• Driving force was primarily nuclear physics
• Particle accelerators are an excellent example
  for Big Science
• The main type of accelerator used today are
  Radiofrequency Accelerators with bunched beams
• Especially as power sources are readily available
• e.g Klystrons from radar or TV applications
• Several important principles known until mid of
  last century
• E.g. Strong focussing in modern synchrotrons
• Most of the building blocks of modern
  accelerators have been described
• But of course there is more (not in this
  lecture..)
• Space-charge
• Collective effects
• Beam-beam effects
• ..
• In the next lecture, we look at how people to put
  these pieces together
• Accelerator concepts

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