First Edition
Synchrotron
Radiation
1FA555
2013-2014 Lecture Notes
Jan-Erik Rubensson
Introduction
1
Some historical notes on
the development of
synchrotron radiation
techniques, and a very
brief view on what it is
good for
Section 1
History
Lorem Ipsum
Introduction
The cartoons made David Judd and Ron MacKenzie to describe a cyclotron cover
also common reactions of various people when introduced to a synchrotron. I assume that most of you are users, and have also been visitors at a synchrotron. The
aim of this course is to give you glimpse inside the black box, not only to remove any
remaining feeling of magic, but also to learn about ultimate possibilities and limits. Of
course, I also want you to see a possible system in the chaos that you experienced
as a visitor.
The'cyclotron…'as'seen'by…'
1. Lorem ipsum dolor sit amet, consectetur.
2. Nulla et urna convallis nec quis blandit odio
mollis.
…the'inventor'
3. Sed metus libero cing elit, lorem ipsum. Adip
inscing nulla mollis urna libero blandit dolor.
4. Lorem ipsum dolor sit amet, consectetur.
5. Sed metus libero cing elit, lorem ipsum. Quis que
euismod bibendum sag ittis.
6. Sed metus libero cing elit, lorem ipsum.
…the'user'
Catoons'by'David'Judd'and'Ron'MacKenzie,'LBNL1966'
…the'governmental'funding'agency'
7. Quis que euismod bibendum sag ittis.
There are many good books describing synchrotron radiation from this perspective.
2
We use Attwood: ‘Soft X-ray and Extreme Ultraviolet Radiation’, and these lecture
notes that you will find (updated) on Studentportalen. They basically contain summaries of Attwoods’s chapters on synchrotron radiation, and also some addenda. On his
homepage you can find many excellent lectures on themes we treat in this course.
31/10 10-12 Basic ideas 1: Properties of synchrotron radiation: angular distribution,
energy distribution, power, brilliance, polarization, time structure, coherence
7/11 10-12 Basic ideas 2: Properties of synchrotron radiation: angular distribution,
energy distribution, power, brilliance, polarization, time structure, coherence
I also recommend:
14/11 10-12 10-12 Insertion devices: Wigglers and Undulators
Philip Willmott: An Introduction to Synchrotron Radiation: Techniques and Applications, John Wiley & Sons (2011).
20/11 10-12 Optical properties in the X-ray range. Absorption-ReflectionTransmission
Giorgio Margaritondo: Elements of Synchrotron Light: For Biology, Chemistry, and
Medical Research, Oxford University Press (2002)
27/11 10-12 Beamlines and monochromators
Jens Als-Nielsen, Des McMorrow, Elements of Modern X-ray Physics, Wiley (2001)
5/12 10-12 Free electron lasers
Thesis writing and dissertations will follow in December.
Schedule and Examination
The lectures will be interspersed with expert presentations. The examination includes
handed-in solved problems (e.g. in connection to the expert presentations), and a
laboratory work at MAX-lab. In addition, you will write a beamtime proposal, which
you must defend in a ‘dissertation’, and you will also act as opponent on one occasion. These dissertations will take place during December.
The course is given in collaboration with KTH, where the course “Characterization
Techniques in Materials Physics using Neutron and Synchrotron Radiation” is given
in parallel. The expert presentations at KTH relevant to synchrotron radiation at KTH
are included in this Uppsala course.
The lectures in Uppsala are as follows.
8/10 10-12 Information meeting
17/10 10-12 Introduction, history, sources of electromagnetic radiation, accelerating
charged particles at high speed.
3
Historical Notes
Synchrotron radiation was first observed in the General Electric
synchrotron accelerator built in 1946 and announced in May
1947 by Frank Elder, Anatole Gurewitsch, Robert Langmuir,
and Herb Pollock in a letter entitled “Radiation from Electrons in
a Synchrotron”
"On April 24, Langmuir and I were running the machine and as
usual were trying to push the electron gun and its associated
pulse transformer to the limit. Some intermittent sparking had
occurred and we asked the technician to observe with a mirror
around the protective concrete wall. He immediately signaled to
turn off the synchrotron as "he saw an arc in the tube." The vacuum was still excellent, so Langmuir and I came to the end of
the wall and observed.”
First observation of synchrotron light at the General Electric
(GE) laboratory 1947 in the 70 MeV synchrotron.
The first attempts to characterize synchrotron radiation over a
large energy range was made by Hartman and Tomboulian in
1953:
“An attempt was ... made to extend the region of observation to
the vacuum ultraviolet.Since a grazing incidence spectrograph
was available and could readily be modified for this purpose, it
was decided ... to proceed directly with the exploration of the
soft x-ray region {50Å to 500Å}.”
4
The same authors followed up with thorough investigation and
in their 1956 paper one can find this nice hand-drawn figure,
which compares the angular distribution of the radiation for a
charge at classical speeds and a charge at relativistic speed:
standing the basic properties of synchrotron radiation. For
those who are interested in the theoretical details there are
other courses given at this department, and the free on-line
book “Electromagnetic Field Theory” by Bo Thidé is recommended.
The development of synchrotron radiation techniques since the
early days is a success story. The 1st generation synchrotrons
were built for collision experiments, with synchrotron radiation
as an unwanted by-product. The usage of the radiation was
termed “parasitic”. The 2nd generation storage rings were dedicated to and optimized for producing synchrotron radiation, and
the 3rd generation sources features so-called insertion devices
(wigglers and undulators), magnetic structures with which the
the radiation can be taylored for specific purposes. For the next
generation the ultimate storage ring is envisioned, for which the
performance is limited by fundamental principles only. Closely
related is the recent development of free-electon lasers, which
provide radiation with fascinating properties.
The theoretical prediction was already worked out in the classical paper by Julian Schwinger, entitled “On the Classical Radiation of Accelerated Electrons”, Phys. Rev. 75, 1912-1925
(1949). In this course we will take a heuristic approach to under-
Taking the brilliance of the radiation as a figure of merit the improvement since the discovery beats Moore´s law for microelectronics integration: Whereas computer speed is only doubled in
18 months, synchrotron radiation brilliance is tripled. The concept of brilliance will be discussed in more detail later, but
briefly it reflects the number of photons of a certain wavelength
that can be focussed in a small area (as opposed to the number
5
of microelectronic functions in a small area). This development
creates overwhelming new opportunities, especially for experiments which rely on X-rays, where there are no alternative
sources.
Development of Synchrotron Radiation Brilliance
vs. Microelectronics Integration
the development, e.g., via strong traditions in X-ray spectroscopy and scattering techniques. Swedish researchers have developed crucial synchrotron radiation instrumentation and methods, and are frequent users of the international facilities. In addition, the development at MAX-lab in Lund, has led to the construction of MAX IV, a (the) world-leading synchrotron, which
will start operation in 2016. Apart from the European Spallation
Source this will be the largest infrastructure for science in the
country.
SR:
x 3 in 18 months
Moore´s law:
x 2 in 18 months
There are now a large number of dedicated synchrotrons
around the globe, and they are easy to find via their hompages.
Many of them have a lot of information and nice animations
which describe synchrotron radiation. Sweden has been part of
6
Basic Concepts
2
A general overview of how
the merits of a radiation
source is described
Section 1
Flux, emittance, and brilliance
Flux, emittance, and brilliance
Electromagnetic radiation transports energy, because there is
energy in electric and magnetic fields. For an electromagnetic
plane wave the energy density u [J/m3] is
u = ϵ0 E 2
Lorem Ipsum
1. Lorem ipsum dolor sit amet, consectetur.
2. Nulla et urna convallis nec quis blandit odio
mollis.
3. Sed metus libero cing elit, lorem ipsum. Adip
inscing nulla mollis urna libero blandit dolor.
4. Lorem ipsum dolor sit amet, consectetur.
5. Sed metus libero cing elit, lorem ipsum. Quis que
euismod bibendum sag ittis.
6. Sed metus libero cing elit, lorem ipsum.
(1)
where ϵ0 = 8.8541878 ⋅ 10−12 As/Vm is the vacuum permittivity,
and E is the electric field [V/m]. Intensity is defined as the average energy per unit time and unit area. For a harmonic wave in
vacuum the intensity is
I = uaveragec =
1
ϵ0cE02!
2
(2)! !
!
where c = 2.99792458 ⋅ 108 m/s, is the speed of light in vacuum
and E0 is the amplitude of the wave [V/m]. Intensity therefore
gets the unit of W/m2, as expected. If you don’t feel comfortable
with this, you must consult your Electricity and Optics books. It
is covered e. g., in Hecht: Optics, chapter 3.3.
In a quantum mechanical description the intensity is related to
number of photons per time and area. The energy density is related to the number of photons, nph, and their frequency, ν:
7. Quis que euismod bibendum sag ittis.
8
,u =
nphhν
V
!
!
!
!
!
(3)
where V is the volume of a beam with cross section A, and
h = 6.626076 ⋅ 10−34 Js is Planck’s constant. Assuming a constant flux of photons, the intensity ((average) energy per unit
time and unit area) is then
I = uc =
nphhν
AΔt
!!
!
!
one-photon-at-a-time, it is convenient to count the number of
photons, as opposed to considering the E-field amplitude. Thus,
equation (4) is a more convenient starting point, and an obvious
question is what is required from a radiation source, to get a
large intensity. In addition, many experiments require monochromatic radiation. Therefore, the spectral purity of the source is
an important parameter. One has therefore introduced a number of concepts which are relevant for experiments. On most of
these concepts there is no consensus on the terminology, so
one has to be careful and look at the definition in each specific
case.
(4)
The flux of a source is normally defined:
The volume of photons travelling at the speed of light.
A"
cΔt"
The classical equation (2) and the quantum mechanical equation (4) appear very different. As long as we are doing experiments in the ‘linear regime’, where excitations are made with
Φ=
nph
Δt 0.1 % BW
! (5)
‘Flux’ does take the spectral purity into account, since it explicitly measures the number of photons/second in a 0.1% bandwidth (BW), e. g, at a nominal photon energy of 1000 eV, only
photons/second within the 999.5-1000.5 eV band contributes to
Φ.
The usefulness of a source is also critically dependent on its
size and angular distribution. Since the size boundary is not
abrupt, but the intensity can be considered to be a distribution,
the spatial extensions are often given as the standard deviation
of this distribution, and in the horizontal and vertical direction,
9
respectively. Similarly, the angular distribution of the flux is characterized by the standard deviation of the intensity around a
nominal direction, and , with respect to the horizontal or vertical
plane, respectively. Note that these measures contain an implicit assumption of a statistical distribution of the intensity. In
addition since the two dimensions are separated the solid angle
defined by gets the unit [rad2] rather than [sterad]. This is convenient as long as small angles are considered.
10