The world's demand for hydrogen is increasing rapidly as the basic raw material in the petroleum, chemical and fertilizer industries. Some of these demand is satisfied by the process of the cryogenic hydrogen recovery from the hydrogen-containing waste gas streams that are a by-product of refineries and ammonia plants. The hydrogen is recovered at purities 95-98% and at yields 92-98% by this process. Because of the process is simple, the investment and recovery cost are cheap.
The superconducting magnet with hollow conductor has various merits, when it is compared with the conventional superconducting magnet, and it will be applicated for big bubble chamber, big spark chamber, etc. in near future. In this article, its merits, refrigeration systems, optimum operation, examples of superconducting hollow conductor, examples of actual magnets and future projects for big magnet in the world are presented.
This paper describes the design and performance of 4.5°K closed-cycle refrigerator. Using a Gifford-McMahon cycle refrigerator (manufactured by Cryomech Inc.) for cooling helium gas down to 16°K, the addition of a Joule-Thomson expansion circuit provides 1 watt (using Cryomech GB 02 refrigerator, without LN2), and 1.6 watts (using Cryomech GB 12 refrigerator, with LN2) of refrigeration power at 4.5°K. Performance is shown in Table 1. The refrigerators feature (1) to be automatic, maintenancefree and compact size, which can run continuously for about 3, 000 hours without operator, (2) to have a high efficient small heat exchangers, (3) to have a simple thermal switch to make short the cool-down time by automatically precooling the low temperature parts, (4) to have a fixed J-T valve and an automatic by-pass valve.
Thin films of the superconducting compound NbN were deposited at atmospheric pressure on fused quartz substrates using the chemical reaction of the gaseous niobium pentachloride with ammonia & hydrogen gases in a quartz apparatus. NbN films prepared by this method had a wide range of resistivities, temperature coefficients of resistance and superconducting transition temperatures depending on the deposition conditions. The maximum transition temperature obtained was 15.75°K for the films deposited at 900°C. The deposition rate varied with the reaction conditions from 20 to 1, 500Å/sec, and deposits ranged from smooth films to polycrystals in which the individual crystal faces were 20 microns in length. The X-ray diffraction data for the niobium nitride films deposited at 900°C and 1, 000°C revealed face-centered cubic structure with cube edges of about 4.334Å and 4.358Å, respectively.