A.M. Dawson

A data base of magnet failures and its relevance to magnet design

This data base of magnet failures is the formalization of a process that began a number of years ago as an effort to see what could be learned from failures to assist in the design process for new magnet systems, whether they were one-of-a-kind or the next in a series. The learning and evaluation process applies equally to resistive and to superconducting magnets and both are represented in the data base. The information has been obtained from numerous sources including open literature and from a survey of members of this community. The updated study was performed with a particular focus of assessing the safety potential of magnet systems for magnetically levitated vehicles.

Conceptual design of a superconducting magnet for a 200 MW e MHD engineering test facility

A 6 T superconducting magnet system conceptual design has been completed for the U.S. Department of Energys 200 MW e Engineering Test Facility. The 1000 tonne magnet will be built of two grades of pool-cooled NbTi cable superconductor supported in 26 layers of stacked epoxy-plastic plates which form each 60° rectangular saddle coil half. Each coil half will be enclosed in a stainless steel vessel which contains the liquid helium that cools the coils and provides some structural support against the electromagnetic forces. The main force containment structure, external to the LHe vessels and located in the vacuum chamber, is designed for maximal access to structural and coil containment vessel welds for purposes of routine inspection. An LN 2 -cooled thermal radiation shield is situated between the force containment structure and the outer vacuum vessel. Fiberglass-epoxy low-heat-leak struts position and hold the cold mass in place in the vacuum vessel and also withstand gravity, seismic and magnetic interaction loading. The magnet system, warm bore liner and roll-aside mechanism provided for channel changeout will be discussed as well as such interfacing considerations as fringe field effects on personnel and control instrumentation.

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.

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. >

Comparison of two ICCS conductors for MHD application

Two subscale, internally cooled, cabled superconductors (ICCSs) have been examined as candidates for use in a retrofit MHD (magnetohydrodynamic) topping cycle magnet. One of these was a 3*3*3 cable in which all the strands were multifilamentary NbTi stabilized with copper. The other was a 3*3*3 cable in which two strands in each of the nine triplets wa OFHC copper and one was multifilamentary NbTi. The overall copper-to-superconductor ratio for each of the two 27-strand cables was approximately the same. The two conductors were cowound onto a grooved mandrel in such a way that they could be tested alternately. Each sample was instrumented with a heater at the center of the conductor length and with a pressure transducer, four pairs of voltage taps, and one iron-doped gold/constantan thermocouple. Performance tests of the conductors were made at 6-, 7-, and 7.8-T background magnetic fields and at heater input energies ranging from 60 mJ/cm/sup 3/ to 1758 mJ/cm/sup 3/ of conductor. The results of these tests and their significance for MHD magnet design and economics are discussed. >

Tests of DC Cable-in-Conduit Superconductors for Large Detector Magnets

At the previous IISSC conference, a novel cable-in-conduit conductor (CICC) was proposed that offered not only the many advantages of traditional CICC such as helium containment within the conduit and integral structural support, but also increased protection characteristics. The latter is achieved by separating the protection and stabilization functions in the conductor so that the protection function is incorporated in a conduit with relatively low electrical resistivity, and the stability function is retained by the cable. An embodiment of this approach was the addition of a braided dacron sleeve surrounding the cable, acting as an electrical barrier between cable and conduit. The results of comparison tests performed on two samples, one without the barrier, one with, have been dramatic, indicating clearly the improved protection capabilities of the latter conductor. This new configuration of CICC, with improved protection characteristics should be desirable for all types of detector magnets, but especially for those requiring radiation-thin windings.

A. 7.9 T Cryogenic Magnet for a Space-Based Mhd Disk Generator Test Facility

A 7.9 T, 0.7 m bore, liquid-nitrogen-cooled, long pulse solenoid has been designed and is now under construction. The magnet will be a part of a ground-based test and demonstration facility for a single-sided, disk MHD generator system under development by TRW for multimegawatt, space-based power generation.

Advanced superconducting MHD magnet design for a retrofit power plant

A magnet has been designed for an MHD (magnetohydrodynamic) topping cycle retrofit of a conventional power plant. The channel power output will be approximately 35 MWe. The magnet which will have 4.5-T peak on-axis field, will be constructed of an unusual NbTi superconductor wound into four subunits per dipole half. These will consist of three 45 degrees saddle coils with circular or ellipsoidal end turns and a single planar coil with a modified racetrack shape that will serve principally as a field-shaping coil. This planar coil also allows a substantial reduction in the ratio of peak to central field strength. Among the unique features of this design will be the use of flexible bands in tension as the primary element of the transverse force containment structure. The conductor will be of the cable-in-conduit type with a cable having a low copper-to-superconductor ratio and a thick-walled aluminum conduit sheath. The sheath will support the axial loads on the saddles and will also provide thermal mass for protection against overheating in the event of an energy dump. The analysis and design of this magnet system and its projected advantages in both performance and economics are discussed. >

Testing Organic Composite Insulators for Fusion Magnets

Descriptions are presented of problems associated with acquiring mechanical property data on organic composite electrical insulators for fusion magnets. Magnet environments are identified and are shown to differ from test conditions because of simulation difficulties, foremost among which is the reactor radiation field. Other problems involve the development of reliable test procedures for such properties as interlaminar shear. Examples are presented. Recent advances in test procedures are summarized and the survivabilities of newer composites are described.

Superconducting MHD Magnet Engineering Program

MHD has the potential to become the first large-scale commercial application of superconductivity. Recent accomplishments of the DOE/MHD development program have shown this fossil-fueled power generation technique to be capable of higher efficiencies and lower-per-kilowatt-hour cost than any other near-term technology.