P.G. Marston

Design concept for the GEM detector magnet

The magnet has two symmetric and independent halves, each containing a cold mass assembly operating nominally at 4.5 K, a set of vapor cooled leads, a cold mass support system, a liquid nitrogen shield system, and a vacuum vessel. Also included in each half is a forward field shaper which provides a component of magnetic induction normal to the path of low angle muons in the forward region, thereby improving their resolution. The unique features of this magnet are the conductor design itself and the large coil diameter, which demands an on-site winding and assembly operation. The use of a natural convection thermosiphon loop for thermal radiation cooling eliminates plumbing complications. Locating the aluminium sheath outside the conduit for quench protection permits optimizing the copper-to-superconductor ratio inside the conduit for stability alone. The conceptual design for the magnet, including the design for the detector dependent magnetics, the superconducting coils and coil structure (cold mass), the coil winding process, the vacuum vessel and liquid nitrogen shields, the cold mass supports, and the magnet assembly procedure, are described.<<ETX>>

Cable-in-conduit conductor concept for the GEM detector magnet

A conceptual design for a conductor based on cable-in-conduit (CIC) technology is presented for application to the proposed GEM detector magnet for the Superconducting Super Collider. The conductor design is driven by the enormous scale of the magnet, which will be composed of two coil halves each approximately 19 m in diameter and 14 m long. Each coil half will be assembled from 12 winding modules, each comprising of a single layer winding. The nominal operating current of 50 kA generates a central field of 0.8 T and a peak field at the winding of 1.6 T. Although the field requirements are low and operation is DC, the CIC concept is preferred because of its large intrinsic stability. The GEM detector requires the highest level of stable, quench-free operation to minimize risk and maximize reliability. The conductor consists of a 450 strand multistage cable made from NbTi/copper composite wires enclosed in a stainless steel tube which is surrounded by a large rectangular block of low resistivity aluminum. The aluminum sheath offers quench protection for the 2.5-GJ coil system, while the fast transient stability is provided by copper in the strand and the supercritical helium inside the conduit. Details of the conductor design, operating performance, and manufacturing process are described.<<ETX>>

Design of an opposing pair magnet system for ASTROMAG

A magnet system comprising a pair of self-supporting disk-shaped coils has been designed for the ASTROMAG facility on the space station Freedom. The coils are connected in a quadrupole configuration in order to eliminate their dipole moment. One of the primary requirements of this design is that the magnet coils must have near-perfect structural integrity. To this end, each coil would be manufactured as a monolithic composite in which the superconducting wire is incorporated as one of the components. By utilizing a precision X-Y numerically controlled wiring machine, the coil can be built up in pancake layers by alternating prepreg sheets of fiber/epoxy (e.g. carbon or Kevlar fiber) with a layer of NbTi wire that spirals from OD to ID in one layer, from ID to OD in the next. and so on. Each disk magnet will have an ID of 0.4 m and an OD of 1.7 m. The peak field at the winding will be 7.2 T. The system is to operate at 1.8 K. and I/sub op//I/sub c/=0.5. Results of magnetic field and force calculations are presented, and the structural characteristics of the system are described.

GEM detector conductor manufacturing experience

Feasibility studies and manufacturing experience on the GEM Magnet conductor are presented, including all components-NbTi strand, cable, conduit manufacture, cable pulling, and aluminum sheath application.<<ETX>>

CONDUCTOR DESIGN FOR THE GEM DETECTOR MAGNET

The Gammas, Electrons, Muons (GEM) Detector, one of the two large detectors planned to be built at the SSC, features high muon momentum resolution. This is achieved by magnetization (by a huge magnet, about 20 m in diameter and 31 m long) of roughly 10,000 m3 of space within the muon chambers. The GEM Detector Magnet1 should be designed to operate with highest possible reliability level to ensure maximum availability of the Detector Systems. That means that the magnet and the conductor should be as stable as practically possible. The conductor should be reliably protected against overheating and electrical breakdown in the case of a quench or fast discharge. For reliability reasons, the magnet dump voltage is relatively low, 500 V to ground, which implies low current density in the conductor. Table 1 lists general requirements for the conductor.

Plans for building the largest thin solenoid ever

The superconducting solenoid magnet for the GEM detector poses unusual fabrication and handling challenges because of its extraordinary size. It will be more than 30% larger in diameter than the largest existing particle detector coils. Each of the two coil elements that compose the air-core solenoid, will be about 19 meters in diameter and 15 meters long. Major components weighing as much as 1500 Mg must be transported and manipulated at the Interaction Region 5 (IR5) fabrication site of the SSC Laboratory as the magnets are fabricated. Because of their large size, the magnets will be fabricated, assembled and tested at special purpose facilities at the IR5 site. The site-use plan must accommodate the fabrication of other detector components and the assembly of large flux shaping iron structures in a timely manner to allow subsequent testing and defector assembly. Each cold mass will be composed of twelve 45-Mg coil windings that are joined prior to assembly into the 19-m diam annular cryostat. >

The superconducting solenoid magnet system for the GEM detector at the SSC

The design of the magnet for the GEM detector at the SSC is described. It is an 18 m inner diameter, 30 m long superconducting solenoid, with a magnetic field of 0.8 T. The basic solenoidal field is shaped by large ferromagnetic cones, to improve detector performance in the ends of the solenoid. Because of the systems large size and mass, field-fabrication on-site at the SSC is required. The challenges in this process, together with the large stored energy of the system 2.5 GJ, have lead to novel design choices in several areas, including the conductor. The design of the conductor, cold mass, vacuum vessel, cold mass supports, thermal shields, forward field shapers, and auxiliary systems are described. >

Electrical joints between superconducting coil modules in the GEM detector magnet

The GEM detector magnet at the Superconducting Super Collider is built in two halves each of which is comprised of 12 single layer superconducting coil modules wound on a 19 m mean diameter and joined with a low resistance lap joint employing the superconducting strands and a copper stabilizer. Each joint half is attached to the sheathed cable-in-conduit conductor end, and assembly of the mating halves is completed in the field. The target resistance per joint is 5/spl times/10/sup -10/ /spl Omega/ at an operating current of 50 kA. Details of the joint design, its cooling and results of tests on prototypical sub- and full-scale models using superconducting strands are presented. >

Design of a retrofit magnet using advanced cable-in-conduit conductor

The excellent properties of the new MIT cable-in-conduit conductor have made possible the design of a retrofit-scale superconducting MHD (magnetohydrodynamic) magnet using a momentless force containment structure. The authors describe the magnet design and compare its weight, cost, and manufacturing logistics with the prior art pool-cooled designs. The magnet system has a peak on-axis field of 4.5 T, has an aperture of 0.8*1.0 m at the inlet end of the magnet and 1.3*1.6 m at the outlet end, and has stored energy of approximately 490 MJ. >

Overview of the Superconducting Magnet Subsystem for the GEM Detector at the SSC

The SSC Laboratory plans to deploy two “large” detectors for the essential highenergy physics experiments at the initial startup of the collider. The GEM detector is optimized to emphasize precise measurement of photons and electrons, as well as precise tracking of high-energy muons. An essential part of the GEM detector is the magnet subsystem, which provides the magnetic field necessary for identification and highresolution tracking of charged particles. This large superconducting magnet system, with ferromagnetic field-shapers, presents a variety of engineering challenges in superconductor technology, in magnet-winding technology, fabrication, assembly and installation of large and heavy components, and in ensuring the required high operating availability.