invention of cyclotron - university of...
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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
3 April 16, 2008 Particle Physics
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
4 April 16, 2008 Particle Physics
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
5 April 16, 2008 Particle Physics
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
6 April 16, 2008 Particle Physics
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
7 April 16, 2008 Particle Physics
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
8 April 16, 2008 Particle Physics
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
9 April 16, 2008 Particle Physics
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
10 April 16, 2008 Particle Physics
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!
11 April 16, 2008 Particle Physics
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
+
12 April 16, 2008 Particle Physics
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)
13 April 16, 2008 Particle Physics
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
14 April 16, 2008 Particle Physics
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.
15 April 16, 2008 Particle Physics
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
16 April 16, 2008 Particle Physics
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
20 April 16, 2008 Particle Physics
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)
21 April 16, 2008 Particle Physics
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)
22 April 16, 2008 Particle Physics
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