High Temperature Superconducting Magnet Control Actuators for the NGST

Executive Summary In this program, the use of high temperature superconducting monoliths for drivers for actuators was investigated. The properties of commercially available bulk YBCO and BSCCO monoliths were measured, and compared with those obtained in laboratory samples. The monoliths were charged, and the capability of holding field was determined. It was found that the properties of commercially available YBCO monoliths was substantially lower than that of laboratory samples that had been carefully manufactured. The reason is that the material is not single crystal, as advertised by the commercial vendors. Carefully manufactured, single crystal disks can be manufactured, but are not commercially available. For BSCCO, on the other hand, multigrain commercially available material is all that is commercially available, and its performance agrees with reported properties. Two charging schemes were investigated: saturation pumping and flux pumping. A simple driver consisting of a capacitor, a switch, a load-matching transformer and driven by triggers from a computer system was built. The computer system also provided the data acquisition necessary for the system. It was found that even though the superconductor was truly persistent, there were transients. The transients lasted varying amounts, and as long as 12 hours, and the amount of the transient was ~10 % of the field. The transient time-constant as well as the fraction of the field variation during a transient, have a large distribution of values, lasting in some cases from a few minutes to 24 hours. At this point, the nature of the transient is not well understood. A total of 19 actuators, with different geometries and materials, were tested. It is concluded that because of the transients, the best application of this type of magnets is for controlling actuators that do not require very sensitive setting, such as on-off actuators, or gross-motion actuators. Abstract The use of monolithic high temperature superconductors in solenoical configurations for use as actuators is analyzed in this report. The properties of monolithic high temperature superconductors are documented. Monolithic tubes, disks and rods of different cross section and sizes can presently be obtained from several commercial vendors. In this report, design issues solenoidal magnets using single crystal or highly textured YBCO monoliths are addressed, as well as multigrain BSCCO 2212. The properties of these materials operating at elevated temperatures (> 10 K) are summarized. High field, cryo-stable, highly complex solenoidal magnets can be manufactured in the proposed manner. The charging schemes for …