Synchrotron Radiation Storage Rings

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Synchrotron Radiation Sources Past, Present and
Future
By Vic Suller
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• Contents
• The Origins of Synchrotron Radiation
• Synchrotron Radiation Characteristics
• Storage Rings as Sources
• Insertion Devices
• The Future with 4th Generation Sources

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Crab Nebula - the first Synchrotron source
observed??
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CAMD in Baton Rouge, LA
Center for Advanced Microstructures and Devices
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Accelerator Synchrotron Radiation
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Discovery of Electron JJ Thompson October 1897
Accelerated Charge Radiation Lienard July 1898
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ELECTROMAGNETIC RADIATION
Field lines from a stationary charge
Field lines from an accelerated charge
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z
Spatial distribution of radiation from a charge
accelerated along the z axis
x
y
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Acceleration by Induction - The Betatron
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Prediction of Energy loss by radiation in an
accelerator Iwanenko Pomeranchuk June 1944
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GEC(USA) electron accelerators 1946
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First attempt to Detect Synchrotron
Radiation John Blewett 1947 used a microwave
receiver expecting Harmonics of the orbit
frequency (100 MHz) - nothing found!
First correct theory of Synchrotron
Radiation Julian Schwinger 1947 showed the
importance of relativistic effects
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Light from the GE Synchrotron 1947
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Betatron - CERAMIC
Synchrotron - GLASS
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Relativistic effects in Synchrotron Radiation

• Contraction of the orbit in the electron frame
• Result- Orbit frequency increases by factor
  g
• Relativistic Doppler shift from the electron
  frame to the lab
• Result- Frequency further increases by factor
  2g
• Relativistic forward focusing of the emission
• Result- Frequency further increases by factor
  2pg

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Relativistic focusing of Synchrotron Radiation
tan q g-1 sin f (1b cos f )-1
Transformation between frames-
If f 900 then q g-1
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Relativistic effects in Synchrotron Radiation
(cont)
The effect of 3 relativistic processes upshifts
the orbit frequency by g3 For example 2 GeV
electrons in a 100m orbit orbit frequency 3
MHz g 3914 g3 6.0 1010 100m Þ 1.7 nm
(0.7 keV) For protons to radiate equivalently in
a 100m orbit Energy 3.7 TeV and magnetic
field 10 kT
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Synchrotron Radiation Features

• Continuum source from IR to X-rays
• Source in a clean UHV environment
• High Intensity and Brightness
• 4. Highly Polarized
• 5. Stable controllable pulsed characteristics

highly attractive for research applications!!!
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Synchrotron Radiation Features
The synchrotron radiation spectrum is described
with reference to a characteristic (often called
'critical') wavelength lc, or photon energy ec
where B is the bending magnetic field.
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Synchrotron Radiation Spectral Flux Intensity
When the radiation at a given wavelength is
integrated over all angles of vertical emission
the resultant Spectral Flux Intensity is given by
photons/sec/mr/0.1 bandwidth
is a numerical factor which essentially governs
the shape of the spectrum.
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Synchrotron Radiation Spectra
Examples of spectra produced by electron storage
rings-
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Typical Synchrotron Radiation Spectra
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Typical Synchrotron Radiation Spectra 2
APS
CAMD
VUV
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1st Generation Synchrotron Radiation Sources
Originally built for some other purpose (1965
1975)
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2nd Generation Synchrotron Radiation Sources
Dedicated, purpose designed (1975 1985)
Some examples-
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Synchrotron Radiation Brightness
Notice that Brightness, as here defined, is often
referred to as Brilliance, with an accompanying
incorrect use of the term brightness for the
Spectral Flux Density. It is best to avoid
confusion by using the well established
radiometric definitions as given here.
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Note that source Brightness as defined is
anisotropic, the value depends on the source
density distribution and on the observation
angle. It is often more convenient to use, as a
figure of merit, an average brightness which for
dipole sources is defined
Average Spectral Brightness
is the vertically integrated flux,
2.36sx is the fwhm of the horizontal electron
beam size, 2.36sz is the fwhm of the vertical
electron beam size, and 2.36sg/ is the fwhm of
the photon emission angle in the vertical plane.
The latter is a combination of the electron beam
vertical divergence and the photon emission angle
thus
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Radiation excitation and damping of oscillations
Radiation excitation
Radiation damping
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Minimum emittance of Chasman-Green lattice
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Theoretical Minimum Emittance lattice
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3rd Generation Synchrotron Radiation Sources
Dedicated, high brightness, designed to
include Insertion Device Sources (1985 2005?)
Some examples-
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APS at Argonne National Laboratory
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Trends in 3rd Generation Light Source Performance
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Proposed South East Advanced Light Source (1)
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Proposed South East Advanced Light Source (2)
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Wiggler or Wavelength Shifter

• Placed in a straight section
• Net deflection zero
• High magnetic field 5-10T
• Large horizontal fan 200 mr

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CAMD Wiggler

• Central pole 7 Tesla
• End poles 1.5 Tesla
• Made by Budker Institute

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SRS Daresbury 6 Tesla Wiggler
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Multi Pole Wiggler

• Multiple alternating poles
• High magnetic field 2-5T
• Small horizontal fan 20 mr
• Superposition of source points

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SRS Daresbury 2.4 Tesla Permanent Magnet MPW
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Undulator

• Multiple alternating poles
• Period lu 10s of mm
• Beam deflection lt 1/g
• Interference makes line spectrum
• Very high brightness

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Undulator approximate theory
In the laboratory frame the electron travels
towards the undulator magnetic field at
relativistic velocity.

• In the electron frame the undulator appears as an
  EM-wave relativistically contracted to 1/g . lu.
• There is then a relativistic Doppler shift 1/2g
  back to the laboratory frame.
• Thus the undulator produces monochromatic
  radiation of

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Undulator correct theory
It is essential to account for the transverse
motion of the electron in the undulator.
Introduce the deflection parameter k
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Undulator constructive interference
As an electron moves from A to B the photon moves
ahead. A photon emitted at point A will
constructively interfere with one emitted at
point B if it gains by a whole number of
wavelengths-

n 1,3,5,
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Undulator Spectrum (calculated)
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ESRF Undulator
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In vacuum Undulators for small gap / period
SRC
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SRC Wisconsin 6 EM Undulator
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Elettra SLS Helical Wiggler/Undulator
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SE-ALS Undulator 50 mm
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4th Generation Synchrotron Radiation Sources

• What could be their characteristics?
• Extremely high brightness
• Ultra short electron bunches
• Coherent radiation

Conclusion- It must be based on a Free Electron
Laser
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Oscillator type Free Electron Laser
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SASE type Free Electron Laser

• SASE Self Amplification of Spontaneous Emission

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Free Electron Laser- present limitations

• Wavelength limited by mirrors
• - use SASE
• Low rep rate hence low average brightness
• - use Energy Recovery Linac

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Energy Recovery Linac
Superconducting RF
High brightness cw e-gun
Low energy beam dump
SASE Free Electron Laser
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ERLs Past and Future
TJNAL (USA) 160 MeV BINP (Rus) 100 MeV 4GLS (UK)
600 MeV KEK ERL (J) 2.5GeV PERL NSLS (USA) 2.7
GeV LUX LBL (USA) 3 GeV ERLSYN (D) 3.5
GeV Cornell-TJNAL (USA) 5 GeV MARS BINP (Rus) 6GeV
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Conclusion for Synchrotron Radiation The Future
is EVEN BRIGHTER than this!
Thank You!
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BRIGHTNESS of Undulators
The brightness of an undulator is calculated
slightly differently. The flux in the central
cone of an undulator Fn at a specified
wavelength is averaged over the emission angle of
that cone to give the Average On-axis Brightness.
Because of the usually very small source size
and divergence in an undulator diffraction
effects must be taken into account.
Average On-axis Brightness
sgz, sgz are the photon source sizes in both
planes and sgz/, sgz/ are the photon source
divergence in both planes, taking into account
diffraction effects.
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L undulator length lu undulator
period Radiation in the nth harmonic in an
undulator deflection parameter k 93.4
lu(m)Bo(Tesla)
flux in the central cone Fn1.43 1014 I0
Qn(k) photons/sec/0.1 bandwidth
fn is a numerical factor, related to k.