Hisashi Isogami

Continuous superconducting-magnet filtration system

We developed a new water purification system using a continuous superconducting-magnet filtration system that removes phytoplankton. The system consists of twin-type magnets with a helium refrigerator: a reciprocating magnetic main filter, and a rotating magnetic sub-filter. This system removes phytoplankton from lake water by separating coagulated magnetic flocks with the magnetic filters. The filters can be continuously cleaned and regenerated under low magnetic fields while flocks are being separated under high magnetic fields. This system removed more than 93% of the phytoplankton from lake water at flow rates of 400 m/sup 3//day.

Beneficial effect of solid nitrogen on a BSCCO-2223/Ag composite tape subjected to local heating

Abstract This paper presents results of a quench/recovery experiment for a BSCCO-2223/Ag composite tape in the presence or absence of a thin layer of solid nitrogen on each side of the tape. Voltage and temperature data were recorded for a 20-cm long BSCCO-2223/Ag tape operating in the range 20–55 K and subjected to a heat pulse of a 10–600 s duration applied over a short distance at its midpoint. The data clearly show that solid nitrogen is beneficial to the stability of high-temperature superconductors operating in this temperature range and subjected to transient heating disturbances.

Transient electrical and thermal responses of a 2-section BSCCO-2223 coil under overcurrent pulses

This paper presents experimental and numerical simulation results of 2-section coil subjected to overcurrent pulses in the temperature range 20-60 K. The experiment simulates a high-temperature superconducting (HTS) magnet for electric devices such as fault-current limiters, transformers, motors, and power lines under fault-mode overcurrent pulses. Each section of the test coil is layer-wound with Bi-2223/Ag composite tape, 3.5 mm wide and 0.23 mm thick, with the outer section wound directly over the inner section. A pulse current exceeds the critical current of each conductor and may drive each section normal. A constant current that follows the pulse current leaves each section in three possible conditions: completely superconducting, recovering, and quenching. Simulation agrees reasonably well with experiment.

Small 3.7K closed-cycle refrigerator without auxiliary vacuum pumps

The neutral beam injection (NBI) system is the equipment for heating the plasma within the fusion reactor to an even higher temperature and driving the current by means of high-rate injection of neutralized hydrogen into the plasma. There is a need for high performance cryopumps cooling at 3.7 K for exhausting the large amount of hydrogen gas that remains in the NBI chamber. This paper proposes to provide multiple small systems to cool individual cryopanels. A small helium refrigerator consisting of a Gifford-McMahon expander with a Joule-Thomson circuit with no auxiliary vacuum pumps was designed and tested to demonstrate the feasibility of applying this type of small closed-cycle refrigerator as an alternative to liquid helium supplied-cryopumps for operating temperatures below 4 K. The prototype system is adjustable to provide up to 6.6 watts of cooling at 3.7 K. Furthermore, the authors have achieved a no-load temperature of 2.2 K.