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.

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.

Superconducting homopolar motor concepts with accompanying auxiliary systems have been examined in a quick‐look assessment for their impact on ship designs utilizing the Navy's Advanced Surface Ship Evaluation Tool (ASSET) developed by the Naval Surface Warfare Center Carderock Division. An existing ASSET DDG51‐FLT2A “like” ship model was used as a convenient means of evaluating the ship impact of the superconducting homopolar, and other advanced electric propulsion systems. For simplicity, all ship impact benefits due to increased power density and efficiency are taken in increased fuel capacity and thus, increased ship operating range. Previous studies have shown that superconducting homopolar motors are well suited to Navy propulsion systems due to their inherent low noise generation, high power density, and efficiency. Homopolar motors are the only true direct current electrical motors and produce very smooth torque because they have no magnetic field pulsations or alternating currents. The Annapolis Laboratory of the Naval Surface Warfare Center is reexamining superconducting homopolar motor technology in light of the resurgent interest in a more electric Navy and because of significant advancements in two key homopolar component technologies. Extensive development of mechanical cryogenic refrigerators has resulted in liquid cryogen‐free superconducting magnets. Magnet systems utilizing cryogen‐free technology have been kept at superconducting temperatures for over two years (18,000 hrs.) with no maintenance. Development of dry copper‐fiber and multiple‐foil copper brushes has eliminated the need for liquid metal current collectors used in early homopolar motors. Basic wear measurements imply replacement times of tens of thousands of full‐power motor hours. Superconductive homopolar motor designs utilizing the new solid collectors are comparable in size to those for previous designs, and show only small increases in machine size as voltage increases from 200V to 2,000V As a result, the operating voltage of a homo‐polar machine can now be selected on an overall system basis in the same way as conventional alternating current systems. Advances in these key technologies and the promising results of the ship impact assessments indicate that a closer examination of superconducting homopolar motors for propulsion is warranted.