Invention of Cyclotron - HEP

Invention of Cyclotron
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”
First cyclotron (4.5 inch)
http://nobelprize.org/nobel_prizes/physics/laureates/1939/
Physics 363
April 16, 2008
Satomi Shiraishi
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
April 16, 2008
Particle Physics
2
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
April 16, 2008
Particle Physics
3
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
http://www.aip.org/history/lawrence/larger-image-page/1930s-solvay.htm
• 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
April 16, 2008
Particle Physics
4
Limitation of DC High Voltage
Earlier accelerators were electrostatic field based
Cathode Ray Tubes ~ late 1800s
Cockroft and Walton ~1920
Van de Graff ~1930
Practical limitations using high voltage:
problem with corona, insulation and design
of vacuum tubes were difficult
April 16, 2008
Particle Physics
5
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
April 16, 2008
Particle Physics
6
Repeatedly applying voltage: Cyclotron
  mv 2
F = q(v × B) =
r
Connected to
high€frequency
oscillator
B-field
http://nobelprize.org/nobel_prizes/physics/articles/kullander/
Electrodes
(Semi-circular hollow plates)
Oscillating E-field
Bec
f =
2πE
Peak value 4000 V
April 16, 2008
Particle Physics
7
Apparatus : 11-inch cyclotron
Oscillating electrode
Hydrogen
Vacuum pump
A
window
24 cm
B
Ion source
11 inch
collector
April 16, 2008
Protons spiral around 150 times
 300 increments of energy
 Acquire 1.2 MeV
Particle Physics
8
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
April 16, 2008
Particle Physics
9
Focusing
Ions travel several meters within the cyclotron. Spreading of space
charge, thermal velocities, inhomogeneities of fields seemed that
ions would spread
Fields provide focusing effect!
E-field
The beam of high speed ions had
a width of less than 1 mm!
B-field
April 16, 2008
Particle Physics
10
Experimental Results
H+
Resonance wavelength as a function
of B-field
H 2+
Wavelength
Current at the detector
Current as a function of B-field for a given ion
H+
H 2+
B-field
B-field
April 16, 2008
Particle Physics
11
Bigger and bigger …
27-inch (3.6 MeV protons, 1932)
60-inch (16 MeV deutrons, 1939)
April 16, 2008
37-inch (8 MeV deutrons, 1937)
184-inch completed in 1946 as
Synchrocyclotron (340 MeV protons)
Particle Physics
12
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
€
238
U92 + 2 H1→238 Np93 +21 n0
238
Np93 →238 Pu94 + e− + ν e
“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.
www.atomicarchive.com/ History/mp/p2s9.shtml
April 16, 2008
Particle Physics
13
Synchrocyclotron
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
€
E = m0 c 2 + E kin
ecH
f =
2π E
Synchrocyclotron
Frequency is decreased
continuously to maintain the
resonance
Can accelerate to higher
energy than cyclotrons
In 1946, Berkeley commissioned 184’’
synchrocyclotron that produced
196 MeV deutrons
Lawrence and his stuff posing with the magnet
for the 184-inch synchrocyclotron. Source: LBL
News Magazine.
April 16, 2008
Particle Physics
14
170-Inch Synchrocyclotron at Chicago
Pi mesons has just been discovered by C. Powell and G. Occhialini in 1947
“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
April 16, 2008
Particle Physics
15
170-Inch Synchrocyclotron at Chicago
E, f, ∆r as a function of radius
Proton energy ~450 MeV
Magnet : 2,200 tons
Pole diameter : 170’’
B field: ~1.86 T
RF frequency: 28.3 MHz ~ 18.3 MHz
April 16, 2008
Particle Physics
16
In 1948 …
April 16, 2008
Particle Physics
17
In 1949 …
April 16, 2008
Particle Physics
18
In 1950 …
April 16, 2008
Particle Physics
19
Recent Accelerators
LHC
faculty.fullerton.edu/ cmcconnell/304/LHC.htm
Laser driven accelerator fits on a
large tabletop (~1 GeV electrons)
Wolfgang K. H. Panofsky: The Evolution of Particle Accelerators & Colliders (1997)
April 16, 2008
Particle Physics
Wim Leemans lab @ LBNL
20
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)
April 16, 2008
Particle Physics
21
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/mcmillanlecture.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
April 16, 2008
Particle Physics
22