Shahin Pourrahimi

Powder metallurgy processed Nb/sub 3/Sn(Ta) wire for high field NMR magnets

Powder metallurgy together with a multi-tin core approach was used to fabricate industrial scale lengths of Ta alloyed Nb/sub 3/Sn wire. The wire produced high critical currents (I/sub c/) along with high critical current densities (J/sub c/) at fields up to 20 tesla and 4.2 K. The wire was produced for a program funded by Battelle Pacific Northwest. One objective of the program was to compare various commercially available wires for applications in high field NMR magnets. The 1.5 mm diameter PM wire compares well with other wires tested in the program. More than 250 m of the 1.5 mm diameter wire was used to fabricate a superconducting model coil. The coil exhibited an I/sub c/ equal to that of a short sample. The performance of the Ta doped wire examined here was lower than those of similar PM wires which were produced earlier using Ti doping. Diffusion dynamics of the tin inside the wire was studied at various stages of heat treatment and was correlated to the properties of the wire.<<ETX>>

Performance of the US quench detection systems in the QUELL experiments

The Quench of Long Length (QUELL) experiments have been completed. The US contribution was to develop and implement both conventional and novel techniques in quench detection. The results of the quench detection experiments demonstrate that all US systems functioned as expected. The most important criteria for the comparison of the various quench detection systems were the time constant of the response and noise rejection by the system. The novel US internal (inside the CICC) sensors included; (1) a cowound voltage sensor, and (2) a fiberoptic temperature sensor. The internal sensors combined fast response with high noise rejection capacity, and proved to offer potentially high reliability for ITER. The conventional sensors, namely the absolute pressure transducer and Venturi flowmeters, confirmed inherent thermo-hydraulic time response limitations in measurements of pressure and flow that excludes them as quench detectors for ITER and other large scale CICC applications.

Principles of advanced quench detection design in cable-in-conduit (CICC) magnets

The design and development of novel quench detection systems for the International Thermonuclear Experimental Reactor (ITER) and the Tokamak Physics Experiment (TPX) has advanced our knowledge of design principles governing quench detection systems. Design studies have quantified the detection signal-noise ratios for several types of quench detector, including external and cowound voltage sensors, fiber optic temperature sensors, and optical and piezoresistive flow meters. The effects of sensor placement and subdivision have also been studied. Sensor topologies with the highest signal-noise ratios are identified. Fiber-optic and voltage sensors have been fabricated for the ITER QUELL experiment, that have demonstrated the capacity to survive cabling and compaction, heat treatment, and cooldown to low temperature with tight conduit bend radii. Extraction techniques have been developed that use redundant seals and coefficient-of-expansion matching to guarantee leak-tightness. Electrical integrity is guaranteed in a design through the control of electrical fields in the feedthrough geometry and insulation material selection.

Correlation between quench pressure and normal zone voltage observed in the QUELL experiment

An interesting correlation between the quench pressure and the generated power was observed in the quench runs of the QUELL experiment. The experimental results indicate that the instantaneous values of the quench pressure and power generated by the normal zone are linearly correlated during the quench propagation. For quenches with constant operating current, the linear correlation holds for quench pressure and the normal zone resistance or voltage. This correlation can be used to improve the accuracy of the quench detection systems based on voltage taps. It could be also a useful tool for the validation of numerical codes for quench propagation.

Structural Analyses of the Cold Mass for High Field Dusty Plasma Experiment

A magnet to study the properties of dusty plasmas in the presence of a magnetic field has been proposed. This magnet has four operating modes to vary the experimental test region and target magnetic field values. The design of the cold mass for the high field magnetized dusty plasma experiment is presented and analyzed. The cold mass includes four coils, ground insulation covering the winding packs, and coil cases used to safely support the coils. Dimensions of the four coils are specified by the magnetic design, and the equipment used to view the dusty plasma apply spatial constraints to the cold mass design. The design also considers the manufacturing process for the cold mass and the stresses resulting from electromagnetic loads coupled with thermal loads. Only one operating mode is considered in this analysis as the others produce significantly lower electromagnetic forces. Resulting stresses compare favorably to failure criteria at critical locations.

Progress in Commercialization of Cable-in-Tube Approach to Manufacturing of Internal-Tin

With funding provided by US Department of Energy SSI has been able to reach significant milestones in manufacturing of Nb3Sn wires by the innovative cable-in-tube method. Development of wires for consideration for the International Thermonuclear Experimental Reactor (ITER) project has reached the stage where single billets produce single piece-lengths of wire without any breaks. Wires in the range of 1-1.5 km have been produced. An early stage sample wire produced by the CIT approach has shown a non-copper Jc of 940 A /mm2 at 12 T and 4.2 K combined with plusmn3 T hysteresis loss of 560 mJ/cc. Another wire designed and produced for High Energy Physics applications has shown a non-copper Jc of more than 2200 A/mm2. These results and the research to achieve them are described in this article.