Construction of a Cryogenic Magnet for Quasi-Steady High Magnetic Fields

1.低温磁体的设计与制作(1)线圈：该磁体工作在液氮温度下，由外置BIT线圈和内置多螺旋线圈组成。在设计中仔细考虑了电磁力和焦耳散热的影响。(2)电源：将稳恒高场磁体的大功率直流电源改装成脉冲运算电路，以满足准稳态低温磁体的需要。将电流增加到23kA/1或2s，并保持在23kA下0-3秒。(3)低温恒温器：液氮由一个容量为9m_3的大型储液器提供，在低温下通过磁体线圈循环。低温磁体的测试(1)室温励磁：线圈在室温下的电阻很大，只有很小的电流可以通过线圈。然而，在这种情况下，测试了电源和线圈的加热特性。(2)冷却到液氮温度：将线圈从300K冷却到77K需要10分钟。(3)在液氮温度下激励：线圈的电阻降低到室温下的约1/8，从而使大电流通过线圈。虽然应在液氮循环期间进行励磁，但在本试验中，在励磁之前停止了循环：由励磁加热的盘管再次由循环液氮冷却。该磁体产生的磁场与设计值吻合较好。低温磁体还没有应用于高场物理性能的测量。然而，应该强调的是，这项研究的主要目的是澄清准稳态低温磁体的特性。

1. Design and fabrication of cryogenic magnet(1) Coil : This magnet is operated at liquid nitrogen temperature, consisting of an outer Bitter coil and an inner polyhelix coil. The electromagnetic force and the Joule heat dissipation were carefully taken into account for designing the magnet.(2) Power supply : A high-power DC source for steady high field magnets was modified with a pulse operation circuit so as to serve for the quasi-steady cryogenic magnet. The current is increased to 23 KA ror 1 or 2 seconds, and kept at 23 KA for 0-3 seconds.(3) Cryostat : Liquid nitrogen is supplied from a large reservoir of 9 m_3 capacity, and circulated through the magnet coils in a cryostat.2. Test of cryogenic magnet(1) Excitation at room temperature : The resistance of the coils is so large at room temperature that only a small current can be passed through the coils. Under this condition, however, the characteristics of the power supply and the heating of the coils were tested. No unexpected results were obtained.(2) Cooling down to liquid nitrogen temperature : It took 10 minutes to cool down the coils from 300 K to 77 K.(3) Excitation at liquid nitrogen temperature : The coil resistance is reduced to about 1/8 of that at room temperature so that a large current is passed through the coils. Although the excitation should be made during the circulation of liquid nitrogen, the circulation was stopped before the excitation in the present test : the coils heated by the excitation was cooled again by circulating liquid nitrogen. The field produced by the magnet was in good agreement with the designed value. The cryogenic magnet has not been applied for the measurement of physical properties at high fields. It should be emphasized, however, that the main purpose of this research is to clarify the characteristics of the quasi-steady cryogenic magnet.