Cosmotron Magnet Lamina
date: label: Date made
content: 1948-1952
name: label: originator
content: Brookhaven National Laboratory
label: manufacturer
content: Bethlehem Steel Company
notes: label: Description
content: Object 1988.0706.02 is a "C"-shaped steel plate (lamina) formed by cutting corners off a square to form an octagon and cutting central slot on one side for accelerator beam tube and magnet coil. For display in Atom Smashers exhibition, the lamina was mounted with four braces on a horizontal metal base, which was fastened to a platform with 4 screws and washers. This plate is one of the several thousand laminae forming the ring magnet of the first successful proton synchrotron, the Cosmotron at Brookhaven National Laboratory (BNL). The steel used was SAE 1020 low carbon steel.
label: Description
content: Brief History of Early Proton Synchrotrons; Brookhaven Cosmotron
label: Description
content: The use of a ring-shaped magnet, rather than the solid-core cyclotron magnet (see for example description for object EM.N-09130 Columbia University cyclotron), was the obvious way to obtain the larger orbits necessary for higher energies without building impossibly massive and expensive machines. But such an accelerator, a “proton synchrotron,” would have to do all that happens automatically in the cyclotron, and thus would have to be more complex than any previous type. The first to attempt it was a group in Birmingham, England, aiming for a proton energy of just one billion-electron volts (1 GeV). All agreed, therefore, that this first attempt in the United States at a proton synchrotron should be on a much more modest scale than the 10-GeV machine originally projected. A second, more ambitious, 6-GeV Bevatron, begun simultaneously at Berkeley, was completed in 1954. Meanwhile, unknown to the West, the Russians were at work on a 10-GeV synchrotron. (For basic principles and history of early electron synchrotrons see description for object EM.N-09261.01 McMillan synchrotron assembly.)
label: Description
content: The Cosmotron at Brookhaven was the first accelerator in the world to send particles to energies in the billion-electron volt, or GeV, region. The machine reached its full design energy of 3.3 GeV in 1953. Not only was the Cosmotron the world's highest energy accelerator, it was also the first synchrotron to provide an external beam of particles for experimentation outside the accelerator itself.
label: Description
content: Protons are first accelerated to 4 GeV by the Van de Graaff accelerator, and then injected into the synchrotron. The magnetic field gradually rises at a fixed rate, while the protons are first bunched and then accelerated by the oscillating electric field in the radio-frequency cavity. The frequency of the oscillator and the phase of the electric field it produces are continuously adjusted so the protons remain in step with the increasing magnetic field, that is, gain the right amount of energy to remain orbiting at the same distance from the center of the ring. At the end of the acceleration cycle a target is plunged into the path of the 3-GeV beam, or (as was done later) the beam is deflected out of the synchrotron by pulsed electric and magnetic fields.
label: Description
content: The magnets of pulsed accelerators (like the cores of alternating current transformers) are constructed of large numbers of thin laminae electrically insulated from each other to block currents induced in the iron by the rise and fall of the magnetic field. Object 1988.0706.02, a thousand-pound C-shaped plate, is one such lamina. A dozen of these welded together formed the six-inch-thick blocks of which the sixty-foot diameter Cosmotron magnet ring was built.
label: Description
content: The design and arrangement of the Cosmotron magnet blocks involved laborious measurements and hand calculations. The necessary magnetic field strength and its variation with position (“gradient”) in the magnet gap were set by the diameter and energy of the Cosmotron and the conditions of orbital stability. But to calculate just what size and shape gap would give the required field was a difficult matter. Laborious hand computation yielded a very approximate solution. (Later such problems would be solved by electronic digital computers.) The actual shape was determined by extensive measurements on scale models. Finally, over a hundred measurements on each of the several hundred magnet blocks established the small deviations of the actual from the prescribed performance. With these data the blocks were arranged in the ring so that the effects of the deviations canceled.
label: Description
content: When the accelerator was designed, and even when completed in 1952, the complex of experiments around the Cosmotron in 1959 was unimaginable. Neither the means for extracting beams of particles from the accelerator nor the means of guiding such extracted beams existed then. The development of both has been essential to the effective use of high-energy accelerators. After 14 years of service to the physics community, the Cosmotron ceased operation in 1966 and was dismantled in 1969. Knowledge gained from the Cosmotron's experiments would lead to revolutionary design improvements and pave the way for construction of Brookhaven's next big accelerator: the Alternating Gradient Synchrotron (AGS).
label: Location
content: Currently not on view
setName: label: See more items in
content: Medicine and Science: Modern Physics
creditLine: label: Credit Line
content: Brookhaven National Laboratory
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: 1988.0706.02
label: accession number
content: 1988.0706
label: catalog number
content: 1988.0706.02
objectType: label: Object Name
content: Cosmotron, C-Magnet Block
label: Object Name
content: Cosmotron Magnet Lamina
physicalDescription: label: Physical Description
content: metal; steel (overall material)
label: Measurements
content: overall: 102 in x 25 in x 95 in; 259.08 cm x 63.5 cm x 241.3 cm
label: Measurements
content: overall (approx.): 94 in x 94 in x 1/2 in; 238.76 cm x 238.76 cm x 1.27 cm
label: Measurements
content: slot at center: 9 5/16 in x 48 3/16 in x 1/2 in; 23.65375 cm x 122.39625 cm x 1.27 cm
label: Measurements
content: slot at right edge: 9 11/16 in x 48 3/16 in x 1/2 in; 24.60625 cm x 122.39625 cm x 1.27 cm