John Arthur Urbahn

Dynamic nuclear polarization polarizer for sterile use intent.

A novel polarizer based on the dissolution‐dynamic nuclear polarization (DNP) method has been designed, built and tested. The polarizer differs from those previously described by being designed with sterile use intent and being compatible with clinical use. The main features are: (1) an integral, disposable fluid path containing all pharmaceuticals constituting a sterile barrier, (2) a closed‐cycle cryogenic system designed to eliminate consumption of liquid cryogens and (3) multi‐sample polarization to increase throughput. The fluid path consists of a vial with the agent to be polarized, a pair of concentric inlet and outlet tubes connected to a syringe with dissolution medium and a receiver, respectively. The fluid path can operate at up to 400 K and 2.0 MPa and generates volumes as high as 100 mL. An inline filter removes the amount of electron paramagnetic agent in the final product by more than 100‐fold in the case of [1‐13C]pyruvate. The system uses a sorption pump in conjunction with a conventional cryocooler. The system operates through cycles of pumping to low temperature and regeneration of the sorption pump. The magnet accommodates four samples at the same time. A temperature of less than 1 K was achieved for 68 h (no sample heat loads) with a liquid helium volume of 2.4 L. The regeneration of the liquid helium could be achieved in less than 10 h, and the transition to cold (< 1.2 K) was achieved in less than 90 min. A solid state polarization of 36 ± 4% for [1‐13C]pyruvic acid was obtained with only 10 mW of microwave power. The loading of a sample adds less than 50 J of heat to the helium bath by introducing the sample over 15 min. The heat load imposed on the helium bath during dissolution was less than 70 J. The measured liquid state polarization was 18 ± 2%. Copyright

The Thermal Performance of a 1.5 MVA HTS Generator

A 1.5‐MVA high temperature superconducting ( HTS ) generator of novel design has been designed, built and successfully tested by the General Electric Company. The 1.5‐ MVA generator has served as the engineering prototype for a much larger 100‐MVA beta unit now under design.The HTS coil in the 1.5 ‐ MVA demonstrator is designed to operate in the range of 20–40 K and is cooled with a closed‐cycle helium refrigeration system employing GM type cryocoolers. This paper will discuss the calculation of the thermal loads to the rotor from all anticipated sources. These sources include conduction losses through the coil suspension system, radiative heat loads to the cold‐system components, residual gas conduction losses, helium‐transfer coupling losses and lead losses. These predicted losses were compared to those measured during actual electrical testing of the rotor at 3600 RPM in order to validate the predictive calculations employed for the 100 MVA machine.