Coated conductors allow the fabrication of closed superconducting loops of arbitrary size. Various mechanisms can play a role in the decay of a persistent current in one such loop and in an assembly of multiple loops magnetically coupled with each other. We report recent experimental results on the relaxation rate of the persistent current in an assembly of closed superconducting loops made out of the currently manufactured coated conductors. One of the main goals of this study is to find the effective ways to control the relaxation rate so as to make it small enough to enable such high temperature persistent magnets to be considered as potential alternatives for energy storage, MRI magnets, and magnetic levitation applications. Here we report the effect of appropriately modified current sweep reversal method on the relaxation rate.Index Terms-Coated conductor, current sweep reversal method, MAGLEV, MRI, persistent current, relaxation rate, SMES, 2G HTS.
A fifty meter proof of concept demonstrator was developed utilizing gaseous helium as a cryogen for the use in a High Temperature Superconductor (HTS) based degaussing system for use on Navy ships. Increased signature requirements as Navy future missions move into littoral waters have resulted in a new copper degaussing system. This system has an increased weight and installation cost because of the additional copper cable required. High temperature superconductors have been suggested as a replacement to the copper based cable to reduce system weight while maintaining the desired ship's magnetic signature. A feasibility study was conducted in 2004 that showed that a superconductive system provided the same performance at a lower cost and at a lower system weight. Many terrestrial superconducting cable projects use liquid nitrogen as the cryogen to keep the cable cold. However, an inert, gaseous cryogen would be preferred for naval applications, but such a cooling system has never been demonstrated in a power cable. This paper describes the experimental setup and preliminary results of testing a helium cooled loop for use in a HTS based degaussing system.
Experiments conducted to determine the resistance of demountable HTS lap joints with variations in compressive stress are reported here. A joint fixture was constructed that enabled the simultaneous testing of multiple joints of different configurations. The joint fixture was installed in a loading facility, comprising a pneumatic press mounted in a vacuum bell jar and connected to a GM cryocooler. The resistance across each joint was measured by means of voltage taps over a range of compressive joint forces.The test results demonstrated that joint resistances less than 2 were possible with only light joint loading.
The need for increased magnetic signature control on Navy ships has lead to the development and adoption of a three axis advanced degaussing system. While this system is effective in reducing the ship magnetic signature, it requires significantly more copper cable than the legacy two axis systems. Degaussing only requires DC currents for field manipulation. Since DC applications is where HTS use excels, a feasibility study was conducted in FY04 to determine the benefits of HTS when used in an advanced degaussing system. Results showed reduced system size and weight, while remaining cost neutral. A series of lab based demonstrations were conducted proving out key aspects of an HTS DG system, most notably cooling a long length of flexible cryostat with gaseous helium. This led to an at sea demonstration of a single HTS DG loop aboard the USS Higgins. This was the first HTS system installed on an active combatant, and it made a successful magnetic range run in April 2009 demonstrating its capability to perform in a naval environment. This paper details the development of the HTS DG system from the initial feasibility study through the successful demonstration onboard the USS HIGGINS.
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