This paper describes the development of detector magnets from the mid-1960s to the LHC detector magnets. The discovery of cryogenic stability in March, 1965, made large detector magnets possible. A number of bubble chamber magnets were built as a result. In the 1970s, the quest for thin magnets started. This led to the development of quench protection through quench-back and the development of indirect cooling with two-phase helium in tubes. The late 1970s and 1980s led to the development of a conductor with ultrapure aluminum as a stabilizer. This led to large coils that were wound inside a strong aluminum mandrel. The LHC saw the development of magnets that are open and they return their own flux without iron. This paper describes the development of detector magnets that have been used in high-energy physics.

The Development of Superconducting Detector Magnets From 1965 to the Present

The application of superconductivity to the large magnets required for charged particle spectroscopy in high energy physics experiments, and for plasma containment in fusion experiments, has resulted in a spectacular leap in the efficiency of these devices. First applied in the late 1960s, the technology has progressed to meet increasingly demanding goals of the experiments and has stimulated important development of the associated conductors. In this article we describe briefly the basic requirements that determine the design of the different types of magnets. This is followed by descriptions of examples of representative working and projected magnets, as well as essential auxiliary equipment. An overview is provided of ongoing development that may impact on the design of future magnets.

Superconducting Magnets for Particle Detectors and Fusion Devices

The toroidal system consists of three air core superconducting toroids. The barrel toroid covers the central region over a length of 26 m with an inner bore of 9.4 m and an outer diameter of 19.5 m. The two end cap toroids are inserted in the barrel at each end over a length of 5.6 m with an inner bore of 1.26 m. Each toroid consists of eight fiat coils assembled around the beam axis and carrying 3 MAt each. The present paper describes the barrel toroid. Features of the design which are presented include the electromagnetic design, field and forces calculations, the basic concept of indirectly cooled aluminium conductor and monolithic fully impregnated winding, the description of the alu-alloy mechanical structure, the thermal analysis and the quench protection. Cryogenics principles, cryostat and toroid assembly procedures are summarized. Unsymmetric loadings, fault sensing and stability are discussed, in relation with the requirements of transparency.

Progress in the design of a superconducting toroidal magnet for the ATLAS detector on LHC

The Compact Muon Solenoid (CMS) is one of the experiments, which are being designed in the framework of the Large Hadron Collider (LHC) project at CERN. The design field of the CMS magnet is 4 T, the magnetic length is 12.5 m and the free aperture is 6 m in diameter. This is achieved with a 4 layer and 5 module superconducting Al-stabilized coil energized at a nominal current of 20 kA at 4.5 K. In the CMS coil the structural function is ensured, unlike in other existing Al-stabilized thin solenoids, both by the Al-alloy reinforced conductor and the external cylinder. The calculated stress level in the cylinder at operating conditions is particularly severe. In this paper the different possible fabrication techniques are assessed and compared and a possible welding specification for this component is given.

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Possible fabrication techniques and welding specifications for the external cylinder of the CMS coil

An automatic gain calibration method based on model reference adaptation for HDD servo is presented. Variations in VCM gain may cause variations in servo control stability margins and thus need to be compensated. The traditional model reference adaptive method is modified in this paper to generate the compensation gain adaptively. Experimental results show that after the compensation, the DC gain of the open-loop responses can be maintained nearly constant despite the variations in head position and operating temperature

HDD servo loop gain calibration based on MRA method

An aluminium stabilized, thin superconducting solenoid is required for the central field of 1.5 T for the BABAR detector. The winding is supported by an aluminium alloy outer cylinder, which provides hoop strength to the coil. The coil has dimensions of 3 m in diameter and 3.7 m in length. The current density is graded to meet the field uniformity requirements of /spl plusmn/2%. A hexagonal flux return, comprised of a barrel and two end doors provides the external flux path for the field. Additional material is required in the end caps to shield the flux from the beam line magnets. To accommodate the muon detectors, the barrel and end caps are segmented into 20 plates of different thickness. Special attention is given to the support of the coil and cryostat to account for seismic loading. The coil is indirectly cooled to 4.5 K using the liquid helium thermo-siphon technique and cooling channels welded to the support cylinder. Automatic cooldown and cryogen supply to the coil and its 40 K radiation shield is done by a helium liquefier/refrigerator via coaxial, return gas screened, flexible transfer lines.

The superconducting magnet for the BABAR detector of the PEP-II B Factory at SLAC

The ATLAS experiment proposed for LHC will use a toroidal magnet system to achieve high efficiency muon momentum resolution. The end cap toroids are designed to provide bending powers in the range 4-8 Tm over the rapidity span 1.5-2.8 in the important forward/backward regions. Each end cap toroid will have an outer diameter of approximately 11 m and an axial length of 5.6 m. This paper presents the magnetic, mechanical and cryogenic design of the end cap toroid magnet systems. Particular emphasis is placed on the interactive design issues imposed by the close proximity of the ATLAS barrel toroid. Proposals for the magnet fabrication and assembly are given.

R.J.G. Greenhalgh

Papers

The superconducting magnet for the BABAR detector of the PEP-II B Factory at SLAC

Design of the superconducting end cap toroids for the ATLAS experiment at LHC