This object consists of a set of two or three nested solenoids housed within stainless steel cylindrical frames The solenoids are wound from niobium-zirconium (25%) copper coated cable. The frames have holes and slots for circulation of liquid helium within. The solenoid was designed to be used as a high-field magnet for the Argonne 10-inch liquid helium bubble chamber.
Disjoint part 1978.0469.01.2 is a retaining ring (or flange) with notches and bolt holes that was originally mounted with 2 studs inside the outer rim of one face of the cylindrical housing of the solenoid magnet (disjoint part 1978.0469.01.1). Originally, three curved strips, each covering one third of the ring circle, were attached over the ring. These strips, the screws, that presumably held them, and the two studs are not now with the ring. The three arc strips comprise disjoint part 1978.0469.01.3.
When acquired, the Argonne superconducting solenoid consisted of its 3 disjoint parts joined together as the original single object in the acquisition. For display in the "Atom Smashers" exhibit at the National Museum of American History, the ring .01.2 and its 3 associated strips .01.3 were removed to expose the coils of the solenoid assembly .01.1.
In addition, three among the set of nine spacers (irregularly shaped, thin, flat non-metallic pieces) that were mounted with an adhesive on the annular face of the solenoid frame have become separated. The three separated spacers (not numbered) have been retained in storage with the disjoint parts.
Basic Principles and History
A magnetic field is an essential feature in a bubble chamber in order to distinguish the sign of charged particles and to measure their momenta from the curvature of their bubble tracks. Charged particles moving through a magnet field are deflected in a circular path in a direction that is perpendicular to both the magnetic field lines and their direction of motion. In a chamber of a given size, higher momentum particles require correspondingly stronger magnetic fields in order to produce particle tracks of sufficiently small radius of curvature for measurement purposes.
To analyze the tracks from high-energy collisions, it is necessary to maintain the entire chamber in a strong uniform magnetic field (in excess of 20 kilogauss). Conventional (copper-coil) electromagnets that carry the high currents necessary to produce these magnetic fields can be prohibitively massive and can have attendant high cooling requirements. The discovery of superconductivity over a century ago raised the prospect of producing extremely intense electric currents – and thereby, the ability to generate correspondingly high magnetic fields using coils carrying those currents. Niobium was used in the various superconducting materials from which these coils were fabricated. Such niobium-based alloys must be cooled to cryogenic temperatures with liquid helium to become superconductive. In 1955 coils made with drawn niobium wire produced 5.3 kilogauss at a temperature of 1.2 degrees Kelvin. By the 1960’s, coils made of a compound of niobium and tin reached 40 kilogauss at 4 deg. K. The further development and application of these coils was subsequently carried out almost entirely at high-energy accelerator laboratories.
In 1963, a group at Argonne National Laboratory (ANL), together with physicists from Carnegie-Mellon University, began fabricating the first “large” superconducting solenoid magnet. Although built for use with a 10-inch diameter liquid helium bubble chamber, the Argonne superconducting solenoid was intended to test materials and fabrication techniques for building much larger superconducting magnets. The solenoid was originally composed of three concentric nested coils; in that form it produced 67 kilogauss. When used with the 10-inch bubble chamber, the innermost coil was removed. The coils are wound with several types of cable, with multiple strands in case any individual one should prove faulty. Holes and slots in the stainless steel casing, and stainless steel mesh between layers of winding, allow liquid helium to circulate through the magnet.
Success with this first large solenoid led the ANL group to use superconducting coils to provide the magnetic field for a 12-foot diameter liquid hydrogen bubble chamber. Completed in 1969, they were larger by an order of magnitude than any previous superconducting coils. Thereafter, superconducting magnets were use in other bubble chambers of the same size around the world. Among other attributes, superconducting magnets had the benefit of reducing total consumption of electrical power by more than 97%.
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