D.B. Montgomery

Design and manufacture of the US-ITER pre prototype joint sample

The US-ITER pre prototype joint sample which has been fabricated at the MIT Plasma Fusion Center is the first attempt to fabricate an optimized full size joint which can be stably operated in ITER required AC background fields at reduced coupling losses. This paper presents an overview of the joints construction and fabrication, highlighting some of the procedural steps that have since been incorporated into fabrication of current terminations for the inner module ITER central solenoid (CS) model coil.

The future prospects for large scale applications of superconductivity

Predictions of future market growth for large scale applications of superconductivity are very bullish. This paper discusses there predictions in the context of research applications, defense and space, instruments for science and medicine, machine tools, materials processing, transportation, energy and national security. The status and the technical and non-technical market factors likely to influence growth for each of these applications are discussed.

Anatomy of the PF magnet failure in Alcator C-MOD

The Alcator C-MOD tokamak began operation in late March, 1992. The terminal of one of the poloidal field magnets, located inside the TF magnet, suffered a structural failure in routine service on April 10, 1992. The protective systems functioned as designed and there was virtually no associated damage. Post mortem analysis showed that the terminal might well have failed at or near the design current limit, but a satisfactory explanation for the failure at 17% of design stress has not been produced. The terminal details of the failed magnet were present in 9 other PF magnets. A new design was developed and applied to all affected magnets. The replacement of the magnet terminals and restart of the experimental facility took 13 months. The terminal assembly that failed was on a relatively simple magnet with only moderately high applied loads. The toroidal field magnet and ohmic heating solenoid are both much more complex and subjected to higher loads. The TF magnet, for example, utilizes an innovative sliding joint construction method to carry loads to a massive external superstructure. Yet the TF magnet continues to perform well and is now operating routinely at over 50% of design current. This presentation will examine the factors and decisions that led to the original PF terminal design and subsequent failure. The new design will be presented, followed by a discussion of the lessons learned from this experience.

US contributions to the development and calibration of quench detectors for the ITER QUELL

The ITER QUELL (quench experiment on long length) experiment calls for the development and demonstration of new methods of quench detection for cable in conduit (CIC) superconductors. These will directly monitor temperature and pressure changes within the CIC. The use of single mode optical fibers is being investigated for measurement of temperature during a quench. A full-length pressure sensor/switch consisting of two conducting strips enclosed in a flattened stainless steel capillary has also been developed. Above a threshold He pressure of about 1 MPa, tube walls will deflect enough to short the otherwise open strips to trigger a current relay switch and also reflect microwave pulses that are generated at the strips ends. These signals can independently indicate the occurrence and the location of a quench. These new sensors will be integrated with more conventional instruments which include co-wound insulated voltage sensors placed inside the CIC, strain gauge pressure transducers, and flowmeters to measure quench parameters.<<ETX>>

The TPX superconducting magnet system

The Tokamak Physics Experiment (TPX) at Princeton will be the first tokamak with an all superconducting magnet system, including both the toroidal field (TF) and poloidal field (PF) coils. The conductors are all cable-in-conduit (CIC) superconductors with a single conduit, similar to those in the International Thermonuclear Experimental Reactor (ITER).

Characterization of Bougienage Electromagnetic Forces

Infants born with esophageal atresia can be treated by an electromagnetic bougienage method to lengthen the esophageal segments. This method uses magnetic forces generated between magnetic bullets (bougies) by a background magnetic field. Two types of bougies, solid rounded rod and hollow cylinder bullets, have been characterized using a fabricated prototype bougienage magnet. Analytical methods have been developed to obtain the magnetic forces on bougienage bullets. The calculation results were confirmed to agree well with the experimental results.

Effect of Magnetic Field Direction on the Critical Current of Twisted Multifilamentary Superconducting Wires

Critical currents of a twisted Nb3Sn multifilamentary superconducting wire are investigated in longitudinal, transverse and intermediate-angled fields. The critical current in a longitudinal field may be as much as 2.6 times that in a transverse field. It was found that the reciprocal of the critical currents normalized by the critical current of the transverse field gives a linear equation of the sine of the angle between the field and the superconductor. The actual angle between the field and the superconductor may require a correction of the twist for a wire with a large twist angle.

Preliminary design of a US ITER model poloidal coil

A preliminary design of a central solenoid model coil for ITER (International Thermonuclear Experimental Reactor) has been made. The preliminary conductor and coil design described should achieve the model coil performance requirements with minimum cost and maximum reliability. The design is based on a Nb/sub 3/Sn cable-in-conduit conductor incorporating a conduit made from the new superalloy Incoloy 908. This alloy has excellent mechanical properties and a COE (cost of electricity) well matched to the COE of the superconducting wire. Major advantages in coil performance result, due to reduction of the thermal strain-induced degradation of the critical properties of the Nb/sub 3/Sn superconductor. The principal performance advantages include higher critical current density and higher critical temperature, particularly at high fields, which results in increased operating margins of critical current and stability. A prediction of enhanced operating performance is made relative to conductor designs by other ITER parties which rely on conduits made from austenitic stainless steels with relatively high coefficients of thermal expansion.<<ETX>>

Application of superconducting cable-in-conduit conductors to coil systems for Maglev vehicles

Significant system advantages result if the superconducting levitation and propulsion coils can be operated at temperatures higher than 4.2 K, which can be achieved with cable-in-conduit conductors (CICCs) using Nb/sub 3/Sn and supercritical helium as the working fluid. The authors compare the relative advantages of NbTi and Nb/sub 3/Sn for this application. They also discuss the system aspects surrounding the selection of operating temperature, current density and number of modules. The features of a suitable CICC Nb/sub 3/Sn conductor which has been manufactured are described.<<ETX>>

US conductor R&D and small scale experiments for the ITER magnets

During the Engineering Design Activity (EDA) of the ITER program a major effort is being devoted to conductor R&D for the ITER magnets systems. This program includes all aspects of cable-in-conduit-conductor (CICC) manufacturing development such as superconducting strand, large multistage cables, and fabrication of thick-wall and thin-wall conduits. It also includes an extensive program of small scale laboratory measurements and experiments designed to predict the full-size conductor and magnet performance, and to quantify elements of the conductor design guidelines. A description of the manufacturing development and experimental program is given, including experiments for determining AC losses in the superconductor, CICC stability under BC and fast ramped conditions of field and current, and development of novel quench detection techniques.