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Accelerators and Ion Sources. CHARMS Basic Physics Topics series November 2 nd , 2005. Outline. Accelerators Ion Sources (This is logically reverse order, but it is easier to present things this way). Accelerators – basic ideas. Charged particles can be accelerated in the electric field.

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Accelerators and ion sources

Accelerators and Ion Sources

CHARMS Basic Physics Topics series

November 2nd, 2005


  • Accelerators

  • Ion Sources

    (This is logically reverse order, but it is easier to present things this way)

Accelerators and Ion Sources

Accelerators basic ideas
Accelerators – basic ideas

  • Charged particles can be accelerated in the electric field.

  • Examples from the nature – electrostatic discharge, α- and β-decays, cosmic rays.

  • Rutherford's experiments with α-particles

    • Discovery of the nucleus in 1911

    • First artificial nuclear reactions

    • Inspiration for high-voltage particle accelerators

  • Muons and pions were discovered in cosmic-ray experiments with emulsions.

  • Everyday life: TV-set, X-ray tubes...

Accelerators and Ion Sources

Types of accelerators used in science
Types of Accelerators Used in Science

  • Electrostatic: Cockroft-Walton, Van de Graaff

  • Induction: Induction linac, betatron

  • Radio-frequency accelerators: LINAC, RFQ, Cyclotron, Isochronous cyclotron, Synchrocyclotron, Microtron, Synchrotron

Accelerators and Ion Sources

Cockroft walton

  • High voltage source using rectifier units

  • Voltage multiplier ladder allows reaching up to ~1MeV (sparking).

  • First nuclear transmutation reaction achieved in 1932: p + 7Li → 2·4He

  • CW was widely used as injector until the invention of RFQ

Fermilab 750 kV C-W preaccelerator

Accelerators and Ion Sources

Van de graaff
Van de Graaff

  • Voltage buildup by mechanical transport of charge using a conveyor belt.

  • Builds up to ~20 MV

Accelerators and Ion Sources

Tandem van de graaff
Tandem Van de Graaff

  • Negative ions accelerated towards a positive HV terminal, then stripped of electrons and accelerated again away from it, doubling the energy.

  • Negative ion source required!

  • Examples:

    • VIVITRON @ IReS Strasbourg

    • 25 MV Tandem @ ORNL

    • 18 MV Tandem @ JAERI

    • 20 MV Tandem in Buenos Aires

Accelerators and Ion Sources

Induction linac
Induction linac

  • Creation of electric field by magnetic induction in a longitudinal evacuated cavity in magnetic material

  • Very high intensity beams (up to thousands of Amperes)

N. C. Christofilos et al., Rev. of Sci. Inst. 35 (1964) 886

Accelerators and Ion Sources


  • Changes in the magnetic flux enclosed by the circular beam path induce a voltage along the path.

  • Name derived from its use to accelerate electrons

  • To the left: Donald Kerst with two of the first operational betatrons (2.3 and 25 MeV)

Accelerators and Ion Sources

Rf accelerators
RF Accelerators

  • High voltage gaps are very difficult to maintain

  • Solution: Make the particles pass through the voltage gap many times!

  • First proposed by G. Ising in 1925

  • First realization by R. Wiederöe in 1928 to produce 50 kV potassium ions

  • Many different types

Accelerators and Ion Sources

Rf linac basic idea
RF LINAC – basic idea

  • Particles accelerated between the cavities

  • Cavity length increases to match the increasing speed of the particles

  • EM radiation power P = ωrfCVrf2 –

    • the drift tube placed in a cavity so that the EM energy is stored.

    • Resonant frequency of the cavity tuned to that of the accelerating field

Accelerators and Ion Sources

Rf linac phase focusing
RF LINAC – phase focusing

  • E. M. McMillan – V. Veksler 1945

  • The field is synchronized so that the slower particles get more acceleration

Accelerators and Ion Sources

Linac examples
LINAC – Examples

  • SLAC – 3 km, 50 GeV electrons, 2.856 GHz


  • GELINA @ IRMM Geel – 150 MeV electrons

GELINA maquette

Accelerators and Ion Sources

Rf quadrupole
RF Quadrupole

  • Simultaneous generation of a longitudinal RF electric field and a transverse focusing quadrupole field

  • Low-energy, high-current beams

  • Compact

  • Replacing Cockroft-Walton as injectors

2 MeV RFQ @ Idaho State Univ.

Accelerators and Ion Sources


  • The cyclotron frequency of a non-relativistic particle is independent of the particle velocity:ω0 = eB0 / γm ≈ eB0 / m

  • E. O. Lawrence in 1929

  • Limitations: relativistic effects break the isochronism → Epmax≈ 12 MeV

Accelerators and Ion Sources

Isochronous cyclotron
Isochronous Cyclotron

  • In order to restore the isochronism, the magnetic field needs to be shaped in function of the radius to match the change of the frequency with the particle energy.

  • However, such configuration leads to vertical orbit instability → restoration of the orbit stability using the Azimuthal Varying Field (AVF) L. H. Thomas (1938)

Accelerators and Ion Sources


  • Instead of modifying the magnetic field, the radio frequency can be modulated → pulsed beams

  • Limit at ~1GeV

  • Example: SC in CERN (600 MeV)

Accelerators and Ion Sources


  • Use of the phase-focusing principle in a circular orbit with a constant radius

  • RF and magnetic fields are tuned to synchronize the particle revolution frequency and confine its orbit.

  • Examples:

    • PS, SPS, LHC @ CERN (28, 450, 7000 GeV)

    • SIS @ GSI

Accelerators and Ion Sources

Cern accelerator complex
CERN Accelerator Complex

Accelerators and Ion Sources

Gsi the present and the future
GSI The Present and the Future

Accelerators and Ion Sources

Ion sources1
Ion Sources

  • Very broad field with many applications:

    • Material science and technology (e.g. ion implantation)

    • Food sterilization

    • Medical applications

    • Military applications

    • Accelerators

    • ...

  • Beams of nanoamperes to hundreds of amperes

  • Very thin to very broad beams (μm2 to m2)

Accelerators and Ion Sources

Types of ion sources selection
Types of Ion Sources (selection)


Accelerators and Ion Sources

Plasma ion sources
Plasma ion sources

  • Ionization is actually a process of creation of a plasma

  • Plasma ion source: Ionization mechanism: eˉ-eˉ collisions

  • Most widely used – many different types

  • Types differ according to plasma production and confinement mechanisms.

Accelerators and Ion Sources

Metal vapor vacuum is mevva
Metal Vapor Vacuum IS (MEVVA)

  • Electrostatic discharge between a cold anode and a hot cathode in a vacuum

  • Evaporation and ionization of cathode atoms

Accelerators and Ion Sources

Penning ion sources
Penning Ion Sources

  • Arc discharge in a magnetic field – electrons confined radially by the magnetic field and axially by electrostatic potential well

  • In cyclotrons it is possible to use the magnetic field of the accelerator

  • One PIG is used @ GSI

Penning Ion Gauge (PIG) Ion Source

Accelerators and Ion Sources

Multi cusp ion source mucis
Multi-Cusp Ion Source (MUCIS)

  • Cusp-like magnetic field lines

  • Most of the plasma volume in a relatively weak magnetic field

  • Large volume of uniform and dense plasma possible (2.5 cm – 1m size)

MUCIS used @ GSI

Accelerators and Ion Sources

Electron cyclotron resonance is ecris
Electron Cyclotron Resonance IS (ECRIS)

  • Vapor held in a cavity with high magnetic field

  • Microwaves with frequency that coincides with eˉ cyclotron frequency in the field heat the electrons (and only electrons).

  • No electrodes, no arc discharge – very reliable, high currents

  • 14 GHz, 0.5 T @ GSI, Dubna, LBNL, CERN

Accelerators and Ion Sources

Surface ion source
Surface Ion Source

  • Hot surface of a metal with high work function ionizes elements with low ionization potential (like alkalis)

  • Negative surface ion source also in use


Surface Ion-Source

Accelerators and Ion Sources

Sputter ion source
Sputter Ion Source

  • Cesium vapor, hot anode, cooled cathode

  • Some of the vapor gets condensed on the cathode, some gets ionized on the anode and accelerated towards the cathode where it sputters atoms from the cathode

  • Produces negative ions of all elements that form stable negative ions

Accelerators and Ion Sources

Laser ion source
Laser Ion Source

  • Stepwise resonant excitation and photoionization of the atom

  • Chemically selective – wavelength tuned to the specific element

  • Pulsed

Accelerators and Ion Sources

Electron sources
Electron Sources

  • Thermionic emission – escape of electrons from a heated surface. Condition: Ee > φ

  • High field emission (fine point cathode)

  • Photo emission: λ < hc/φ

Accelerators and Ion Sources

The end

The End