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April 16, 2008 Particle Physics

Invention of Cyclotron

Physics 363 April 16, 2008

Satomi Shiraishi

First cyclotron (4.5 inch)

Ernest O. Lawrence, Noble Prize in 1939 “for the invention and development of the cyclotron and for results obtained with it,

especially with regard to artificial radioactive elements”

http://nobelprize.org/nobel_prizes/physics/laureates/1939/

2 April 16, 2008 Particle Physics

Outline • A brief history of E. O. Lawrence • Physics that was going on at that time • Limitation of DC High Voltage accelerators • Lawrence & Livingston’s cyclotron

– Physical Review 40 (1932) • Seeking higher and higher energy • Crucial researches using cyclotrons • Even higher energy -- synchrocyclotron @ U of C

– 170-inch Synchrocyclotron Progress Report • More recent accelerators • Conclusion


Ernest Orlando Lawrence

• Born in South Dakota in 1901 • Ph.D from Yale on photoelectric effect under

professor W.F.G. Swann • His early work was on ionization phenomena

and the measurement of ionization potentials of metal vapours.

• He was appointed Associate Professor of Physics at Berkeley in 1928 and became a Professor two years later.

“I felt out one of the most brilliant experimental young men in the East”

--Leonard Loeb, Berkeley physicist-recruiter's view on Lawrence

http://www.aip.org/history/lawrence/youth.htm


History of Physics in early 1900’s • 1911: Rutherford found that

the atom has a small nucleus by bombarding atoms with alpha particles.

• 1913: Niels Bohr succeeds in constructing a theory of atomic structure

• 1919: Rutherford finds evidence for proton

• 1921: James Chadwick and E.S. Bieler finds that some strong force holds the nucleus together. “a prerequisite to a successful experimental

attack on the nucleus was the development of means of accelerating charged particles to high velocities”

E. O. Lawrence, December 11, 1951

http://www.aip.org/history/lawrence/larger-image-page/1930s-solvay.htm


Limitation of DC High Voltage Earlier accelerators were electrostatic field based

Cathode Ray Tubes ~ late 1800s

Van de Graff ~1930

Cockroft and Walton ~1920

Practical limitations using high voltage: problem with corona, insulation and design

of vacuum tubes were difficult


One evening in 1929… Lawrence was in the University library and came across an article in electrical engineering journal on multiple acceleration of positive ions.

He thought of a way to reach 1MeV range and realized that it would be “rather awkwardly long for laboratory purposes.” (Lawrence, Nobel Lecture)

So he thought of a way of using circular paths instead of linear paths


Repeatedly applying voltage: Cyclotron

Electrodes (Semi-circular hollow plates)

Oscillating E-field

http://nobelprize.org/nobel_prizes/physics/articles/kullander/

Connected to high frequency

oscillator

B-field

Peak value 4000 V

€

F = q( v × B ) =

mv2

r

€

f =Bec2πE


Apparatus : 11-inch cyclotron

A

B 24 cm Ion source

Vacuum pump

Oscillating electrode

window

11 inch

collector

Hydrogen

Protons spiral around 150 times 300 increments of energy Acquire 1.2 MeV


Keys to Success of Cyclotron

• Easy way to create uniform B-field: • If ions were to circulate 100 times, the B-field has to be uniform to a fraction of 0.1% • Uniform B-field can be created easily by using shims.

• Focusing effect on beam: • E and B field have focusing effect

Lawrence wanted to make the production of particles with ~MeV a matter that can be done with modest lab equipment


Focusing Ions travel several meters within the cyclotron. Spreading of space

charge, thermal velocities, inhomogeneities of fields seemed that ions would spread

E-field The beam of high speed ions had a width of less than 1 mm!

B-field

Fields provide focusing effect!


Experimental Results

B-field

B-field

Cur

rent

at

the

dete

ctor

Wav

elen

gth

Resonance wavelength as a function of B-field

Current as a function of B-field for a given ion

H+ H2+

H+ H2

+


Bigger and bigger … 27-inch (3.6 MeV protons, 1932)

60-inch (16 MeV deutrons, 1939)

37-inch (8 MeV deutrons, 1937)

184-inch completed in 1946 as Synchrocyclotron (340 MeV protons)


Crucial Researches using Cyclotrons Plutonium was discovered at Berkeley by E.M. McMillan and G.T.Seaborg

(1940) – Bombarded uranium with 16 MeV deutrons using 60’ cyclotron

“Calutron” Berkeley’s 32’’ and 184’’ cyclotrons were modified as mass spectrographs to study separation of rare U-235 isotope from abundant U-238 for the atomic bomb.

€

238U92+2H1→238Np93 +21n0

238Np93→238Pu94 + e− + ν e

www.atomicarchive.com/ History/mp/p2s9.shtml


Synchrocyclotron

In 1946, Berkeley commissioned 184’’ synchrocyclotron that produced 196 MeV deutrons

Synchrocyclotron Frequency is decreased

continuously to maintain the resonance

Can accelerate to higher energy than cyclotrons

€

E = m0 c2+ Ekin

f =ecH2π E

RF frequency and oscillation frequency of ion must be in resonance for acceleration

Cyclotrons Oscillation frequency becomes out of phase when the kinetic

energy of ions become comparable to the rest energy

Lawrence and his stuff posing with the magnet for the 184-inch synchrocyclotron. Source: LBL News Magazine.


170-Inch Synchrocyclotron at Chicago

“The energy of the protons which [the synchrocyclotron] produces is sufficiently great to create mesons, perhaps more than one at a time, out of nuclear matter.”

-- 170-Inch Synchrocyclotron Progress Report

Pi mesons has just been discovered by C. Powell and G. Occhialini in 1947


170-Inch Synchrocyclotron at Chicago Proton energy ~450 MeV Magnet : 2,200 tons Pole diameter : 170’’ B field: ~1.86 T RF frequency: 28.3 MHz ~ 18.3 MHz

E, f, ∆r as a function of radius


In 1948 …


In 1949 …


In 1950 …


Recent Accelerators

Wolfgang K. H. Panofsky: The Evolution of Particle Accelerators & Colliders (1997)

LHC

faculty.fullerton.edu/ cmcconnell/304/LHC.htm

Wim Leemans lab @ LBNL

Laser driven accelerator fits on a large tabletop (~1 GeV electrons)


Conclusion • E. O. Lawrence invented cyclotron which was a key to a study of

nuclear physics – Wanted to accelerate particles to high energies with modest lab

setting

• Cyclotrons have had an enormous influence on the society

• Initiated a big science, a new way of doing science – Tevatron, LHC etc. – Effort to accelerate particles with modest lab setting is also

going on using new technologies (ex. Laser driven accelerator)


References • “170-inch Synchrocyclotron Progress Report.” University of Chicago.

Institute for Nuclear Studies. 1947-1948, 1948-1949, and 1949-190. • Physical Review 37 (1931) 1707 • Physical Review 38 (1931) 834 • Physical Review 40 (1932) 19 • Ernest O. Lawrence, “The Evolution of the cyclotron.” Noblel Lecture,

December 11, 1951. • http://bancroft.berkeley.edu/Exhibits/physics/bigscience02.html • http://www.nature.com/physics/looking-back/lattes/index.html • http://nobelprize.org/nobel_prizes/chemistry/laureates/1951/mcmillan-

lecture.pdf • http://www.nap.edu/readingroom/books/biomems/handerson.html • http://chem.ch.huji.ac.il/_history/graaff.html • http://www.aip.org/history/lawrence/first.htm

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