Nuclotron superconducting magnets and their improvement for use in the SIS100 heavy-ion synchrotron in the fair project

Abstract

At the beginning of the 1970s, the stage of development and assimilation of magnetic and accelerator technologies based on superconductivity started in the leading scientific centers in world which were studying the fundamental problems of nuclear physics and the structure of matter. Superconductivity for developing magnets for the proton synchrotron with field amplitude much greater than the limit for ordinary magnets (B ~ 2 T) was harnessed at Fermi Lab (Batavia, USA). The magnetic system of the Tevatron with field amplitude in the working aperture to 4.7 T, placed inside the synchrotron tunnel at energy 500 GeV, made it possible to double the energy of the accelerator. The field in the Tevatron magnets is formed by a multi-turn winding, fabricated on precision equipment. The accuracy of its geometric dimensions determines the quality of the magnetic field in the aperture. Superconducting magnets of this type in their modern form were used in the designs of other accelerators and were termed cos θ magnets. The magnets are cooled successively; the cool-down time of the magnetic system to the working temperature is weeks. A precision cos θ magnet, cryostat with a vessel for liquid helium, heat screen, vacuum jacket, and anchoring of the magnet are integral parts of an extremely labor-intensive, metal-intensive, and expensive cryogenic-magnetic system. Magnets of a new type [3] were developed in the High-Energy Laboratory at the Joint Institute for Nuclear Research (OIYaI) to considerably simplify and reduce the cost of the construction of the superconducting magnet and its cryostating system for the Nuclotron ‐ a specialized synchrotron for relativistic nuclei [1, 2]. Their fundamental difference lay in the use of a magnetic with a window-frame cross-sectional geometry instead of the cos θ precision magnet and a specially developed tubular superconducting cable, intended for pulsed magnets with rapid ramping of the field, instead of the flat superconducting Rutherford cable. In the case of tubular cable, as opposed to Rutherford cable, there is no coil or frame electric insulation in the path of heat flow from the superconductor to the helium; this improves considerably the conditions for cryostating of the superconductor. In addition, the use of two-phase helium as the cryogenic coolant makes the conditions for cooling the superconductor in the tubular cable of the pulsed magnets of the accelerator unique, making it possible to operate with record high field ramping 4 T/sec and higher [4]. On the whole, the concept adopted made it possible to minimize the transverse cross section of the Nuclotron magnet, eliminate the helium vessel inside the cryostat, secure an operating regime with field rise and fall rate 4 T/sec, economize on materials and power supply, simplify the external infrastructure, and most importantly organize the fabrication and testing of the magnets on the basis of the production capacity of OIYaI. OIYaI Nuclotron ‐ SIS100 Prototype. The development of the Nuclotron, a superconducting, strongly focusing accelerator of relativistic heavy nuclei, was motivated by the problems of relativistic nuclear physics and quantum chromodynamics and investigations of the color degrees of freedom in atomic nuclei. To study these problems experimentally, it was necessary to have appropriate beams of accelerated particles, which could not be obtained with the proton synchrotron operating at the time without creating an essentially new accelerator complex. The choice of the maximum energy of the new