Welcome to the SI-Tee Sunday, June 28, 2015 Accelerators and Ion Sources CHARMS Basic Physics Topics series November 2 nd, 2005

Accelerators and Ion Sources 2 Outline 1.Accelerators 2.Ion Sources (This is logically reverse order, but it is easier to present things this way)

Accelerators and Ion Sources 3 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 4 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 5 Cockroft-Walton High voltage source using rectifier units Voltage multiplier ladder allows reaching up to ~1 MeV (sparking). First nuclear transmutation reaction achieved in 1932: p + 7 Li → 2· 4 He CW was widely used as injector until the invention of RFQ Fermilab 750 kV C-W preaccelerator

Accelerators and Ion Sources 6 Van de Graaff Voltage buildup by mechanical transport of charge using a conveyor belt. Builds up to ~20 MV

Accelerators and Ion Sources 7 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:  IReS Strasbourg  25 MV ORNL  18 MV JAERI  20 MV Tandem in Buenos Aires

Accelerators and Ion Sources 8 Induction linac Creation of electric field by magnetic induction in a longitudinal evacuated cavity in magnetic material N. C. Christofilos et al., Rev. of Sci. Inst. 35 (1964) 886 Very high intensity beams (up to thousands of Amperes)

Accelerators and Ion Sources 9 Betatron 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 10 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 11 RF LINAC – basic idea Particles accelerated between the cavities Cavity length increases to match the increasing speed of the particles EM radiation power P = ω rf CV rf 2 –  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 12 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 13 LINAC – Examples SLAC – 3 km, 50 GeV electrons, GHz GSI – HI IRMM Geel – 150 MeV electrons GELINA maquette

Accelerators and Ion Sources 14 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 Idaho State Univ.

Accelerators and Ion Sources 15 Cyclotron The cyclotron frequency of a non-relativistic particle is independent of the particle velocity: ω 0 = eB 0 / γ m ≈ eB 0 / m E. O. Lawrence in 1929 Limitations: relativistic effects break the isochronism → E pmax ≈ 12 MeV

Accelerators and Ion Sources 16 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 17 Synchrocyclotron 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 18 Synchrotron 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, CERN (28, 450, 7000 GeV)  GSI

Accelerators and Ion Sources 19 CERN Accelerator Complex

Accelerators and Ion Sources 20 GSI The Present and the Future

Welcome to the SI-Tee Sunday, June 28, 2015 Ion Sources

Accelerators and Ion Sources 22 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 (μm 2 to m 2 )

Accelerators and Ion Sources 23 Types of Ion Sources (selection) Surface ionization Plasma beam Field ionization Duoplasmatron Sputter Hollow cathode Laser Pigatrons Electron beam ionization Multifilament Arc discharge Cyclotron resonance Multipole confinement Surface plasma Pennings Magnetrons Charge exchange RF plasma source:

Accelerators and Ion Sources 24 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 25 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 26 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 GSI Penning Ion Gauge (PIG) Ion Source

Accelerators and Ion Sources 27 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 GSI

Accelerators and Ion Sources 28 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 GSI, Dubna, LBNL, CERN

Accelerators and Ion Sources 29 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 EXTRACTION ELECTRODE

Accelerators and Ion Sources 30 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 31 Laser Ion Source Stepwise resonant excitation and photoionization of the atom Chemically selective – wavelength tuned to the specific element Pulsed

Accelerators and Ion Sources 32 Electron Sources Thermionic emission – escape of electrons from a heated surface. Condition: E e > φ High field emission (fine point cathode) Photo emission: λ < hc/φ

Welcome to the SI-Tee Sunday, June 28, 2015 The End Questions? Comments? Tea? Coffee?