| As an important tool, high magnetic field, as well as ultrahigh voltage and ultralow temperature, has been widely used to explore the mysteries in biology,chemistry, engineering, metallurgy and physics. High magnetic field is also considered as the cradle of the Nobel prize by the scientists all over the world, that is why efforts are made in many countries to establish high magnetic field facilities.After nine-years' design and construct, a 40T steady-state high magnetic field facility has been built in High Magnetic Field, Chinese Academy of Sciences (CHMFL). It was accomplished in August. 2016 and successfully checked and accepted in May,2017. It marked that China, following France, Poland, Japan, German and America,has become the leading country to have the high magnetic field facility. The hybrid magnet which is comprised of a resistive insert and a superconducting outsert, will produce at least 40 T steady field on axis.This subject is focused on the fabrication of cryogenic system for the magnet, as well as the thermo-hydraulic analysis and cooldown performance of the outsert. The main research work of the paper is shown as follows:(1) Learn about the 360 W/4.5 K cryogenic system comprehensively, including system composition, operation mode and general performance. Learn about the integrated operation of cryogenic system and magnet system, learn about the cryogenic subsystem and the cooldown technique, make preparations for the cooldown performance.(2) According to the requirement of cooldown superconducting magnet, this paper shows the numerical analyse of the cooldown process which can be divided into 2 period: firstly cooldown from 300 K to 80 K, secondly cooldown from 80K to 5K.Based on the simplified assumption of the coils' structure, a mathematical model was developed for the cooldown to 80 K of the coils. The simulation results obtained from this model explained the temperature profiles along the different cooling channels decrease with time homogeneously and also showed the characteristics of helium during the cooling process. The results also met the requirement that max temperature differences in coils should be less than 50 K. As to cooldown process from 80K to 5K,the refrigerating capacity was obtained from the running expanders. The results showed that all coils can be cooled synchronously, and the total cooldown prcocess can be finished in 580 h.(3) Before the cooling process, warm gas in the pipeline should be evacuated,purified and substituted by pure helium. This process worked with an external purifier which can purify helium gas to the concentration of 99.999%. During the first 100 h,the maximum temperature difference exceeding 50 K was caused by the immoderate nitrogen supply rate. After the over-supply nitrogen control strategy was changed, the maximum temperature differences were decreased and maintained to be 50 K to maximize the cooling rate. The turbine cooling started in 420 h when the inlet temperature reached 80 K and the outlet temperature was 110 K. Then, it took about 130 h to cooldown to 5K.(4) In this paper, we revise the friction factor equation, analyse experimental data, compare it with simulation results to find difference. As to the experimental cooldown process, there were many unpredictable problems existed, for example: the temperature sensors and vacuum gauge are affected by the magnetic field, causing the wrong number display. In that case, the magnetic shielding has been designed and installed. With the development of 2nd generation high temperature superconducting material YBCO, update and improve the current leads design is around the corner.This paper presents the magnetic shielding design and the welding of YBCO to copper using solder layers research. |
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