| Superconducting technology is applied more and more widely,and the application of superconducting magnet is one of the main research directions.As one of the large superconducting magnets,superconducting solenoid magnet(SSM)is often used as the high energy accelerator component due to its outstanding unimpeded current-carrying capacity.Nowadays,the pursuit of the SSM in engineering is to be the better central magnetic field and uniformity.In the aspect of cryogenic thermostat providing temperature conditions for superconducting magnets,the conduction-cooled system with direct cooling by the refrigerator occupies a simpler structure and safer working state as well as no requirement of adding or replacing the liquid working medium,which will play a major role in the structural design of superconducting magnets in the future.However,improper design of the conductive-cooled superconducting magnet can lead to excessive temperature rise during operation of the magnet exceeding the cooling capacity limit of the refrigerator,and even lead to damage to the superconducting coil.Therefore,it is extremely important to conduct thermal analysis for the magnet system in advance during the design stage.Base on the Heavy Ion Accelerator Facility(HIAF)driving project,the thermal analysis and experiment study in the design stage of the high field SSM with a GM double-stage refrigerator for conductive cooling are investigated.Firstly,a conduction-cooled cryogenic system was designed to investigate and verify the thermal analysis method of conduction-cooled superconducting magnet.According to the heat transfer calculation result of the parameterized model,a double-stage GM refrigerator of KDE422 SA was selected.Through the simulation of temperature distribution after cooling the thermal shield and the sample stage,it was found that the minimum temperature of the thermal shield and the sample stage is 39.46 K and 2.38 K respectively,and the corresponding maximum temperature difference is 0.83 K and 0.003 K respectively,which shows that the temperature distribution uniformity meets the target requirement.By several cooling and temperature control tests on the system,it was found that the minimum temperature of the thermal shield could reach 39 K,and the minimum temperature of the sample stage could reach 2.3 K.The experimental results were in a good agreement with the simulation results.The temperature error of the thermal shield is less than 1.5 K and the maximum relative error is 3.52%,while the error of the sample stage temperature is less than 0.01 K and the maximum relative error is 0.25%.The uniformity of temperature distribution met the requirements of the system and verified the accuracy of the heat transfer analysis method.Meanwhile,the precise temperature control of 12 temperature points within the temperature range of 280～50 K was successfully achieved,and the experimental temperature control effect was good,which verified the reliability of temperature control of the device.Base on the verified heat transfer analysis method,the heat transfer calculation of 10 T conduction-cooled superconducting magnet with more complex structure was realized.The temperature distributions of magnet system,coil assembly and current leads under the static condition after stabilized cooling and under stable current running at 142.6 A were simulated.The results show that the system could accommodate the regular working temperature of the magnet.By probing the temperature distributions of the thermal shield with different materials and the same boundary conditions as well as considering contact thermal resistance or ignoring contact thermal resistance,Al 1100 was finally selected as the main material of the thermal shield,which was supplemented by red copper and some oxygen-free copper.In addition,the cooling capacity accounting to the selected refrigerator in this superconducting magnet system was carried out,and the results showed that the selected model SRDK-415 D GM refrigerator met the refrigeration requirements.The experimental investigation on cooling and excitation of the 10 T conduction-cooled superconducting magnet was completed.The cooling time was about 52.5 hours.The minimum temperature of the primary cold head was 28 K,and the minimum temperature of the each component near the secondary cold head was 2.5 K.After the temperature dropped and stabilized,the magnet was subjected to three differential energization rates of excitation to the required central magnetic field(142.6 A-10 T).The current was stabilized for 10 min after reaching the designed current strength.After that,the magnet was de-energized at the same rate.The temperature fluctuation during the whole excitation process was always lower than the regular working temperature of the magnet,which indicated that the thermal design of the magnet was reasonable.Comparing the simulation value and experimental value of the temperature change of the secondary cold head components during the excitation process,it was found the trend of the experimental value curve and the simulation value curve was similar.The maximum error was between 0.6 K and 0.7 K,and the maximum relative error was 12.4%.The comparison results were in a good agreement,which indicated that the magnetic field and cryogenic performance of the magnet system met the design indicators and the requirements of the thermal magnetic design.Thus,it could be put into use normally. |
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