Oak Ridge 60 Inch Vertical Heavy-ion Cyclotron Dees

Oak Ridge 60 Inch Vertical Heavy-ion Cyclotron Dees

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Description
This object is the dee assembly from the Oak Ridge 63-inch cyclotron, as adapted for the Atom Smashers exhibition at the National Museum of American History.
The object consists of copper hollow D-shaped electrodes (dees) mounted on heavy stems placed through a steel plate. The dee assembly is positioned vertically, rather than the common practice of being positioned horizontally as in most cyclotrons. The assembly is mounted on a flat painted rectangular base, constructed with unspecified construction board material. After the assembly was received at NMAH, the metal casing enclosing the dee stems was removed and discarded, and prior to being exhibited in the Atom Smashers exhibition, the stems were truncated in length by approximately two feet.
History and basic principles of the Oak Ridge 63-inch cyclotron
In 1951 the Oak Ridge National Laboratory was authorized by the Atomic Energy Commission to construct a heavy-particle cyclotron. An accelerator, designated the OREL 63-Inch Heavy-Particle Cyclotron, was then designed and built by the Electronuclear Research Division of the Laboratory. The first beam was obtained on May 20, 1952 and a productive research program was initiated shortly afterwards. The past usefulness of this cyclotron is indicated by the amount of nuclear data derived from its operation.
This cyclotron was the first built expressly to accelerate ions heavier than hydrogen and helium. Designed by Alexander Zucker, this cyclotron helped open a very active field of atomic and nuclear research, which is now pursued with much larger and costlier accelerators. It constructed was constructed to determine whether the explosion of a very powerful thermonuclear bomb might trigger a chain reaction of nitrogen nuclei, igniting the earth’s atmosphere; experiments with this cyclotron, colliding nitrogen ions with nitrogen ions, established that this fear was unwarranted.
The basic design of the 63-inch is that of a conventional, fixed-frequency cyclotron. In operation, triply charged nitrogen ions were produced by the ion source and were accelerated in a magnetic field of 15,500 gauss. The ions were then electrostatically deflected at the radius of 25.6 inches yielding an external beam of nitrogen ions with a mean energy of about 28 MeV. The accelerating system operated at a frequency of 5.1 MHz/sec and employed dee-to-earth voltages between 35 and 50 kV.
The vertical position of the dees is characteristic of cyclotrons designed at Oak Ridge. This departure from common practice at the time originally arose from parasitical use of the Calutrons, the large, ganged electromagnetic mass separators built during the Second World War to produce uranium-235 for the first atomic bombs. This and earlier Oak Ridge cyclotrons were “plugged into” Calutron magnets, in place of one of the scores of uranium isotope separation units.
Basic principles of the cyclotron
The cyclotron is the simplest of circular particle accelerators. (Go to https://www.physics.rutgers.edu/cyclotron/theory_of_oper.shtml to see a diagram of a typical cyclotron.) At its center is a vacuum chamber which is placed between the pole pieces of a large electromagnet. Within the chamber is a pair “dees” - two flat D-shaped hollow metallic shells - positioned back-to-back forming a cylindrical space, with a uniform gap between the straight sides of the two dees. The plane of the dees is parallel to the faces of the magnet pole pieces. An alternating voltage is applied across the gap between the dees, creating an associated time-varying electric field in that space.
Electrically charged particles, such as protons, alpha particles or heavier ions, are introduced into the chamber from an ion source at the center. The charged particles are constrained to travel in a circular path inside the dees in a plane perpendicular to the direction of the static uniform magnetic field produced by the electromagnet. The electric field accelerates the particles across the gap between the dees. The electric field is made to alternate with the “cyclotron period” of the particle (determined by magnetic field strength and the particle’s mass and charge). Thus, when the particles complete a semi-circle and arrive at the gap again, the electric field has reversed, so that the particles are again accelerated across the gap. Due to their increased speed in the constant magnetic field, the particles now move in a larger circle.
The increasing speed of the particles causes them to move in a larger radius with each half-rotation, resulting in a spiral path outward from the center to the outer rim of the dees. When they reach the rim the particles are pulled out by a deflecting electrode, and hit a target located at the exit point at the rim of the chamber, or leave the cyclotron through an evacuated beam tube to hit a remote target. Nuclear reactions due to the collisions of the particle beam and the target atoms will create secondary particles which may be guided outside of the cyclotron and into instruments for analysis.
Location
Currently not on view
Object Name
Cyclotron, 63 Inch, dees
Date made
May 20, 1952
maker
Oak Ridge National Laboratory
place made
United States: Tennessee, Oak Ridge
Physical Description
copper; steel (overall material)
Measurements
overall (approx.): 172 cm x 329 cm x 58 cm; 67 23/32 in x 129 17/32 in x 22 27/32 in
base: 44 cm; 17 5/16 in
dee stems (diam.): 10 cm; 3 15/16 in
dee stems (ctr. to ctr.): 46 cm; 18 1/8 in
steel plate thickness: 3.7 cm; 1 15/32 in
ID Number
1977.0359.41.1
accession number
1977.0359
Credit Line
Oak Ridge National Laboratory
subject
Science & Scientific Instruments
See more items in
Medicine and Science: Modern Physics
Science & Mathematics
Modern Physics
Energy & Power
Data Source
National Museum of American History
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