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The resistance of high temperature superconductor (HTS) lap joints under compressive loading is measured and two different HTS tape configurations are tested. The results have shown that joint resistances less than 2 [micro][omega] are possible with only light joint loading configuration.

An electromagnetic bougienage method has used magnetic forces generated between magnetic bullets by a background magnetic field. Analytical methods are developed to obtain the magnetic forces on bougienage bullets and the results have agreed well with the experimental results.

Voltage-current characteristics of semiconductor contact junctions between superconducting wires are examined by means of a voltage-driving method.

Fabrication and testing of a high temperature superconductor (HTS) Levitated Dipole Experiment (LDX) levitation coil is described and discussed.

An overview is presented of research needs involving superconducting magnets for fusion applications.

Tests of NbTi superconducting prototype quadrupole magnets, built for the High Current Transport Experiment (HCX), are described and discussed.

Design of the Muon-to-Electron Conversion Experiment (MECO) solenoids is described and discussed.

The Levitated Dipole Experiment approach to the study of magnetic confinement of a fusion plasma, using a superconducting ring coil, is described.

Experiments with local field sensors are described.

The test program for a second lap joint sample conducted at the MIT Pulse Test Facility is described. Test was conducted in both parallel and transverse time-varying fields at ramp rates from 0.05 to 1.5T/s and background induction to 4T to qualify its performance subject to ITER-relevant operating conditions. The joint was observed to have a dc resistance below 2.5 nOhm and pulsed, transverse field losses for a 1.5s ramp at 0.4T/s below 90J.

A magnetic Pulse Test Facility was built at the Massachusetts Institute of Technology Plasma Fusion Center for testing cable-in-conduit conductor electrical joints for the International Thermonuclear Experimental Reactor (ITER) project. The remote-controlled facility is equipped with a state-of-the-art, multiple channel data acquisition system for digitally recorded sensor signal processing. ITER teams can securely access test data from the facility 24-hours a day through the Internet.

The current distribution of each of the 12 strands of a Nb3Sn cable-in-conduit conductor was measured during current/external magnetic field ramping. The strand currents exhibited severe non-uniformity before quenching. A simple model was developed to represent the ramp rate phenomenon causing the peculiarities in the current characteristics of the conductor strands.

A pulsed magnetic field test facility is under construction at Massachusetts Institute of Technology for testing large scale cable-in-conduit superconductor and joint samples. Separate, demountable split-pair solenoid and saddle coils provide a combination of fields which can be either transverse or parallel to the sample axis. The solenoid and saddle magnets together can provide transverse peak fields as high as 8.4 T. Peak parallel fields of 6.6 T can be generated with the solenoid alone. Ramp-up rates of 1.5 T/s and ramp-down rates of 20 T/s are possible. Sample currents up to 50 kA are provided by a superconducting current transformer. The sample is connected to the transformer secondary through a pair of low resistance joints. Supercritical helium is provided to the sample at flow rates up to 20 g/s, pressures up to 1 MPa, and temperatures from 4.7 to 10 K. Programmable logic controllers provide coordination of the magnetic field, sample current, and helium flow rate and temperature in the sample. Sample and facility instrumentation signals are processed and data is stored on a workstation-based data acquisition system with comprehensive data reduction capability. Facility details and status are described.

Two types of mechanical contact joint termination methods for a 2G YBCO cable have been developed. Each YBCO tape of a cable is connected to a BSCCO tape while the other ends of BSCCO tapes are bundled together and soldered inside a copper tube. Another termination method uses only YBCO tapes. It has been confirmed that both joint termination methods are very useful for 2G HTS cables. Mechanical contact joint resistances between YBCO-BSCCO tapes and YBCO-YBCO tapes have been measured under various contact pressures and contact surface conditions at 77 K. Joint resistance distribution among the tapes in the cable have been also evaluated for both termination methods. These contact joint methods can be used for a demountable joint. Joint resistance is greatly reduced with increasing applied pressure especially for YBCO-YBCO joints. However, in the case of a YBCO-BSCCO joint, the BSCCO tapes may degrade at high pressure. The contact pressure should be optimized to obtain low joint resistance. [ABSTRACT FROM PUBLISHER]

The sensitivity of superconducting magnets to AC losses is well known. If superconducting magnets are this sensitive to AC fields, why not use AC fields for magnet protection, and in particular, for internal energy dump when a quench has been detected? The answer is the large reactive power needed to provide the rate of change of the fields required to quench of a large fraction of the magnet. In this paper we describe a novel approach where quench protection secondary windings external to the magnet are used to minimize the power to initiate the energy dump. The main requirement of these secondary windings is that the mutual inductance between the primary winding and the protection secondary windings has to be small, ideally zero. One means to provide for zero mutual inductance between the protection secondary winding and the primary winding is by designing a protection secondary winding that produces AC fields that everywhere in the volume are normal to the fields produced by the primary winding. Alternatively, appropriate windings can be made so that the coupling in one region is the opposite to that of another region, with zero total mutual inductance. The latter approach results in low voltages at the leads, but could result in high voltages within the coil. We describe several circuit topologies applicable to solenoidal and toroidal windings that satisfy these requirements. Calculations of the heating due to AC fields are presented, including eddy current heating in cable-in-copper-channel conductors. If the quench inducing coil is optimally designed and powered, the hysteresis of the superconductor dominates the heating. Thus, as a portion of the superconducting magnet quenches, the heating power shifts to those zones that are not yet in the current-sharing regime. This approach is an alternative to the use of resistive heating elements, which need to be placed on, or embedded in, the winding pack. [ABSTRACT FROM PUBLISHER]

Recent International Thermonuclear Experimental Reactor (ITER) Model Coils and tests on Nb3Sn Cable in Conduit Conductors (CICC) showed a significant and unexpected increase in the broadness of the transition to the normal state, resulting in degradation of superconducting properties. To investigate these phenomena, two CICC samples were built with identical 144 strand cables but different conduit materials. One sample had titanium conduit with low coefficient of thermal expansion, the other had stainless steel conduit. The purpose of this experiment was to study changes in strand properties in the cable (critical current, current sharing temperature, n-value), the effects of cycling and high electromagnetic load, and the effect of the conduit on the CICC performance. [ABSTRACT FROM AUTHOR]

The International Thermonuclear Experimental Reactor (ITER) Central Solenoid and Toroidal Field Model Coils (CSMC, TFMC) and the CSMC Insert Coils using Nb33Sn had unexpectedly low current-sharing temperatures and cable "n-values." This paper argues that the anomalous effects can be explained by the high longitudinal strain due to transverse Lorentz loads. Simulated results of earlier experiments with A15 monoliths indicate that the transverse stress "multiplier" is actually a longitudinal strain multiplier due to transverse loading. Irreversible cyclic degradation effects in the cables with the lowest thermal contraction mismatches are explained by showing that a modest precompression is required to prevent tensile cracking of a significant number of individual filaments. Examination of filament breakage due to bending shows the possibility of a well-defined threshold for irreversible damage. [ABSTRACT FROM AUTHOR]

A cryostat housing a pair of previously tested quadrupole magnets has been constructed as a prototype focusing cell for the High Current Experiment (HCX) project. The doublet assembly was constructed with a room temperature beam tube. The magnets were reassembled, electrically connected in series, and tested to the short sample limiting current without further training. The doublet was more sensitive to the current ramping rate as compare with the previous performance. In order to build a compact vacuum jacket for the warm bore structure, a novel radiation insulation made of aluminum coated stainless steel foil was selected. The experiences in assembly of the doublet and fabrication of the cryostat are described. The thermal performances of the cryostat are reported. [ABSTRACT FROM AUTHOR]

Four NbTi superconducting prototype quadrupole magnets have been built for the High Current Transport Experiment (HCX) as part of the multi-beam heavy-ion fusion research activity, led by the Lawrence Berkeley National Laboratory (LBNL). MIT performed quench training and ramp rate tests of the two prototype magnets that were designed and built by the Advanced Magnet Lab, Inc. (AML), based on a novel concept featuring cable-in-groove and multi-layer stacking. Both magnets are splice-free without inter-layer or inter-quadrant joint. Each coil was wound with a continuous NbTi round cable, placed in precise grooves machined in G-11 plates. The two magnets differ in their cable construction and their coil and yoke configuration. Each magnet was tested more than once in liquid helium bath with a room temperature thermal cycle between cold tests. This paper describes the results of the performance tests as well as the instrumentation and the quench protection system. Possible improvements for future coil winding are discussed. [ABSTRACT FROM AUTHOR]

Describes the design, fabrication and test of the react-and-wind Nb[sub 3]Sn Levitated Dipole Experiment floating coil conductor developed in a joint project by Columbia University and the Massachusetts Institute of Technology. Magnetic levitation of a superconducting ring coil; Cable strain; Prevention of degradation of the critical current; Effect of fabrication, winding and operating strains on critical current.