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2. The Cyclotron

T

he story of the cyclotron braids together into a single experimental technology so many strands of Berkeley physics that it might be the most instructive way to understand how the department gained its pre-eminent place in physics during the post-war era.


The story begins on a spring evening in 1929, when a young Ernest Lawrence happened to be browsing the Archiv fuer Elektrotechnik (reportedly to stave off boredom in a meeting). He read about a new method for accelerating charged particles.


In that moment, Lawrence thought of a way to dramatically improve the design. Hurrying back to LeConte Hall, he encountered a colleague’s wife and announced, “I’m going to be famous.”


Browsing p. 390 of Wideroee’s article – possibly this very volume, the Library’s copy he would have used -- Lawrence discovered the central idea leading to his invention of the cyclotron


"Ueber Ein Neues Prinzip Zur Herstellung Hoher Spannungen," Von Rolf Wideroee. Archiv Fuer Elektrotechnik, Band XXI, Heft 4, Dezember 17, 1928 "Ueber Ein Neues Prinzip Zur Herstellung Hoher Spannungen," Von Rolf Wideroee. Archiv Fuer Elektrotechnik, Band XXI, Heft 4, Dezember 17, 1928
"Ueber Ein Neues Prinzip Zur Herstellung Hoher Spannungen," Von Rolf Wideroee
Archiv Fuer Elektrotechnik, Band XXI, Heft 4, Dezember 17, 1928
[pg. 390, pg. 391] additional [cover as shown above]
[tK3.a7 v.21]


"Prinzip Einer Methode Zur Herstellung Von Kanalstrahlen Hoher Voltzahl," Von Gustav Ising. Arkiv Fuer Matematik, Astronomi Och Fysik, Band 18, Haefte 4, 1928 "Prinzip Einer Methode Zur Herstellung Von Kanalstrahlen Hoher Voltzahl," Von Gustav Ising. Arkiv Fuer Matematik, Astronomi Och Fysik, Band 18, Haefte 4, 1928
"Prinzip Einer Methode Zur Herstellung Von Kanalstrahlen Hoher Voltzahl," Von Gustav Ising
Arkiv Fuer Matematik, Astronomi Och Fysik, Band 18, Haefte 4, 1928
[pg. 1, 2-3] additional [cover]
[MAIN Q4.A8]


Widerloee, in turn, had found inspiration in this earlier article in a Swedish periodical. The illustration is a proposal for a linear particle accelerator.


The First Cyclotron

Model for Cyclotron Chamber, 1931 Model for Cyclotron Chamber, 1931
[Courtesy Lawrence Hall of Science]

W

ith the aid of graduate students, especially Stanley Livingston, Lawrence built an ingenious device with a remarkably resourceful hand – he scrounged together shards of glass, metal, wires, and wax to produce the unassuming gadget seen here. The art of accelerator building was learned gradually, as a process that combined ingenuity, fabrication and apprenticeship.


At root, its operation was straightforward. It used magnetic fields to hold charged particles in a narrow, spiraling path. When the particles crossed the gaps, an electric field would accelerate them ahead, from the right side to the left side, then from the left to the right. On each round, the particles picked up speed. They were shot out at high energy and put to work.


It was with this relatively simple technique that Berkeley’s legacy of experimental pragmatism and Lawrence’s training in engineering and physics collided and “big science” was born.


11" Cyclotron, 1931

B

y summer 1931, Lawrence and Livingston had managed to build a model more powerful than their first tentative effort. They increased the size of the machine and the magnet in order to push charged particles through the equivalent of a million volts. As they competed with physicists elsewhere, accelerating particles in devices with different designs, they launched an experimental culture in which expansion became a defining feature.


The accompanying image offers a rare glimpse of the glow of the cyclotron beam, before a cover was added in 1933.


Glow from 11" Cyclotron Beam
Glow from 11" Cyclotron Beam
[BANC PIC 1984:022:50953--PIC]


 

Lawrence and Colleague Beside the 27" Cyclotron, 1932
Lawrence and Colleague Beside the 27" Cyclotron, 1932

[Courtesy Lawrence Berkeley National Laboratory]


Lawrence at Work on the 37" Cyclotron, 1937
Lawrence at Work on the 37" Cyclotron, 1937
[UARC PIC 10n:13]


60" Cyclotron, 1939

T

hrough the 1930s, Lawrence’s machines grew larger. They served different experimental purposes, too. Starting from straightforward nuclear physics – replicating artificial radioactivity and exploring nuclear reactions – the Rad Lab expanded its program. It turned its cyclotron beams to manufacture radioisotopes that other scientists and medical doctors could use. Eventually the huge 60” cyclotron, the largest in the laboratory through the decade, was principally given over to medical uses.


Why was it so large and why did Berkeley need it? Asked this question, Lawrence responded simply. “Because we can get the money,” he said.


The cyclotron’s particle beams could also be collided with target materials to create entirely new elements. This was a field in which Berkeley physicists and chemists excelled from the outset, beginning with the discovery of neptunium (and its secret by-product plutonium) in 1940 by future Berkeley Nobel laureates Edwin McMillan, Glenn Seaborg, and Emilio Segre; and Philip Ablest.


184" Cyclotron, ca 1942

I

n 1939, Lawrence announced plans for a “large-scale” cyclotron. His contemporaries may have scoffed at his ambitions, but the onset of World War II made his project a wartime priority.


Armed with a magnet face 184” in diameter, Berkeley physicists opened up an entirely new frontier beyond 100 MeV (100 million electron volts), where there lurked (its boosters said) “discoveries of totally unexpected character and of tremendous importance.” But it was soon diverted to other purposes, even before it was built. The magnet for the 184” cyclotron was used to separate the fissile, or explosive, part of natural uranium, U-235, from its much more plentiful companion isotope, U-238.


After the war, the 184” cyclotron was completed as a synchrocyclotron, or synchrotron, incorporating the principle of phase stability developed by McMillan. It would help physicists identify the first known subnuclear particle discovered with an accelerator (the neutral pi-meson, or pion), carry out studies of proton-proton and neutron-proton interactions, and serve as a valuable instrument for biological and medical research.


184" Cyclotron Before Installation of Fifteen-Foot-Thick Concrete Shielding, ca. 1940
184" Cyclotron Before Installation of Fifteen-Foot-Thick Concrete Shielding, ca. 1940



Lawrence Above 184" Cyclotron Building, ca. 1941
By Richard F. Hoosn
[BANC PIC 1984.022--PIC]