1. Lecture 1 - Overview of Accelerators I
ACCELERATOR PHYSICS
MT 2011
E. J. N. Wilson

2. Links Author’s e-mail: ted.wilson@cern.ch “Engines of Discovery”:
“Particle Accelerators”

3. Lecture 1 – Overview I- Contents
History of accelerators
Need for accelerators
Linear accelerator
Acceleration on a wave
Magnetic rigidity
Cyclotron
Vertical focussing
Components of a synchrotron
Phase stability
Weak focusing synchrotrons
Weak focusing in a synchrotron

4. The history of accelerators

5. Need for Accelerators

6. The race to high energies
Earnest Rutherford was born, 1871, in Nelson, New Zealand, the fourth child in a family of twelve. His father, James Rutherford, a Scottish wheelwright, emigrated to New Zealand with Ernest's grandfather and the whole family in 1842.
1910, came his greatest contribution to physics when scattering of alpha rays showed the "nucleus" containing almost all the mass of the atom to be concentrated in a minute space at its center.
He was a great believer in apparatus improvised from string and sealing wax – My own physics teacher who was a student of Rutherford confirmed this and ironic in that accelerators were to become the most advanced forms of experimental equipment we know.
Rutherford fired the starting pistol
At the Royal Society in 1928 he said
“I have long hoped for a source of positive particles more energetic than those emitted from natural radioactive substances”.

7. Cockcroft and Walton - Electrostatic
On the right we see one of the first accelerators to make a discovery in nuclear physics– a far cry from the accelerators you have have learned about at CERN today and you may say, not much relevance to High Energy Physics (300 keV) Burt it was a start..

8. Van der Graaf
Van de Graaff's was a Rhodes Scholar at Oxford when he first thought about electrostatic machines. This is very large accelerator built at MIT's Round Hill Experiment Station in the early 1930s.
Under normal operation, because the electrodes were very smooth and almost perfect spheres, Van de Graaff generators did not normally spark. However, the installation at Round Hill was in an open-air hanger, frequented by pigeons, and here we see the effect of pigeon droppings.
Van de Graaff was a Rhodes Scholar at Oxford when he first thought about electrostatic machines. This is very large accelerator built at MIT's Round Hill Experiment Station in the early 1930s.
Under normal operation, because the electrodes were very smooth and almost perfect spheres, Van de Graaff generators did not normally spark. However, the installation at Round Hill was in an open-air hanger, frequented by pigeons, and here we see the effect of pigeon droppings.

9. Linear accelerator Particle gains energy at each gap
Lengths of drift tubes follow increasing velocity
Spacing becomes regular as v approaches c
Wideroe’s first linac:

10. Wideroe’s Linac
Someone who was inspired by Rutherford was a Norwegian – Rolf Wideroe. A prolific inventor, he is variously credited with the invention of the betatron, the linac, the synchrotron, and storage rings for colliding beam and certainly he built the first pair of linac drift tubes for his Dr. Ing. thesis at Aachen in 1927.
During the war years he had indeed been working in Berlin on betatrons which he was told would serve as a compact X-ray source in field hospitals. (Actually, The Nazi leadership hoped to use it to blind bomber pilots.) He agreed to do this when promised the release of his brother, Viggo, who had been imprisoned by the Nazis on suspicion of spying in Norway.
Can you imagine why this device had to remain (on the shelf) for 15 years before it could be used.
His many other claims as an innovator, though substantiated by patents were often hidden from the free world of science by the clouds of war and had to be re-invented , either independently or subsequently by others. It does seem clear however that his enthusiasm for storage ring colliders prompted his good friend Touschek, himself imprisoned by the Nazis, to build the first such device after the war.

11. Fermilab linac (400MeV)

12. Inside the Fermilab linac

13. The Stanford Linear Accelerator

14. The International Linear Collider (ILC)
TESLA technology: these superconducting accelerator structures are built of niobium, and are the crucial components of the International Linear Collider.

15. Cyclotrons –an inspired discovery
Lawrence read Wideroe's thesis – why not accelerate repetitively.
He built many machines for medicine encouraged by his brother John who was a doctor – irradiated his grandmother was a master of fund-raising and publicity. Berkeley University president is reported as complaining that “Instead of a University with a Cyclotron Berkeley has become a cyclotron with a University attached. People told him relativity would limit energies to 30 MeV but he just pushed on and built a 184 inch machine.
A picture of the 11-inch cyclotron built by Lawrence and his graduate students, David Sloan and M. Stanley Livingston, during 1931.

16. Cyclotron
Magnetic rigidity
Constant revolution frequency

17. Magnetic Rigidity from resolution of momenta that:
the magnitude of the force may be written:
Equating the right hand sides of the two expressions above, we find we can define a quantity known as magnetic rigidity:
A common convention in charged particle dynamics is to quote pc in units of electron–volts. Whereupon:

18. Vertical Focusing People just got on with the job of building them.
Then one day someone was experimenting
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

19. Discovery of the Synchrotron
Marcus Oliphant – an Aussie – later to become Governor of South Australia
Cyclotrons scale with the cube of the energy – there had to be a better way. Oliphant – an Aussie – later to become Governor of South Australia was on sabbatical from Birmingham to Oak Ridge supervising gaseous diffusion of Uranium for the WWII atom bombs – shame! you may say but at the time many great scientists were too naïve to do otherwise. His boss was a famous cyclotron builder – MacMillan.
Marcus Oliphant, (See Sidebar for Oliphant) an Australian physicist who had been working in England at Birmingham University, found himself at Oak Ridge supervising the business of transforming a laboratory experiment for isotope separation into a large scale industrial process. As deputy to E.O. Lawrence he was often given the owl watch and "with little to do unless troubles developed" occupied his time by speculating on plans for his return to Birmingham when war was over. He began to think about the difficulty of scaling up cyclotrons with their huge magnets to higher energy. He suddenly realized that you need only construct the rim of the cyclotron if you pulsed its field to follow the rising energy of a short burst of injected ions. With only a thin ring of magnets to build the whole device should be many meters (nowadays km) in diameter.
He wrote a memo to the Directorate of Atomic Energy, UK in which he proposed a new method of acceleration- the synchrotron. His new idea was not greeted with enthusiasm at a time, when more important business was afoot, but, as he left for England at the end of the war, he was encouraged by Lawrence to pursue the idea further.
After his return to Birmingham, Oliphant read the comprehensive and beautiful papers by McMillan (a student of Nobel prize-winning Lawrence) and Veksler (a soviet physicist). McMillan described Oliphant’s pulsed ring-magnet idea and announced his own plan to build such a machine — without a single reference to Oliphant.
Late in World War II the Woolwich Arsenal Research Laboratory in the UK had bought a betatron to "X-ray" unexploded bombs in the streets of London. Frank Goward converted the betatron into the first “proof of principal” synchrotron.
The Arsenal Synchrotron- Late in World War II the Woolwich Arsenal Research Laboratory in the UK had bought a betatron to "X-ray" unexploded bombs in the streets of London. Frank Goward converted the betatron into the first “proof of principal”

20. Components of a synchrotron

21. Phase stability
PHS.AD5

22. Cosmotron
COSMOTRON.PCT

23. Weak focusing in a synchrotron
The Cosmotron magnet
Vertical focusing comes from the curvature of the field lines when the field falls off with radius ( positive n-value)
Horizontal focusing from the curvature of the path
The negative field gradient defocuses horizontally and must not be so strong as to cancel the path curvature effect

24. Summary History of accelerators Need for accelerators
Linear accelerator
Acceleration on a wave
Magnetic rigidity
Cyclotron
Vertical focusing
Components of a synchrotron
Phase stability
Weak focusing synchrotrons
Weak focusing in a synchrotron