Experimental Study On Cryogenic Temperature Measurement And Control System Of The High Accuracy

The temperature measurement is the most basic measurement in cryogenictemperature physics experiment. Compared with the temperature measurement at roomtemperature, cryogenic temperature in the system is stricter. Some ignored problems atroom temperature, such as lead heat leakage, radiant heat, Joule heat and thermal contactresistance, become important under the cryogenic temperature. Cryostat cooled by theGM cryocooler has been widely used in many fields. It has the advantages of simplestructure, convenient operation, low operating and maintenance costs. However, limitedby its structure and working principle of the GM cryocooler, the temperature fluctuationand vibration of the cold head is large, which is harmful in many applications requiringhigh stable temperature. Based on the above analysis, this article has carried on thecryogenic temperature measurement and control system research cooled by cryocooler.The specific work content is as follows.The cryocooler cold head temperature fluctuation model is analyzed. According to theanalytical solution, the temperature fluctuation amplitude is mostly influenced bymaterial thermal diffusivity and the cold head wave frequency. Decreasing the thermaldiffusivity or increasing the frequency can reduce the temperature fluctuation amplitude;thereby improve the temperature stability of the sample stage. Thermal resistance, heliumtank and thermal resistance combined helium tank experiments were carried on. Theexperiment results show that the thermal resistance can effectively restrain temperaturefluctuations, and the cryostat has more simple structure and easier operation. In thehelium tank experiments, in addition to the4.2K, temperature fluctuations can’t get goodinhibition in other points. Experimental results show that the combined use of thermalresistance and helium tank can control the peak-to-peak values within3mK.The experimental study on the temperature control of the cryostat cooled by cryocooler has carried on. Control the cooling rate of the sample stage by using themethod of PID. Samples collected when the PID controls on the temperature fluctuationsof short-term stability and long-term stability data. Experimental results show that theperformance is limited by the cryocooler itself; there exist a maximum cooling rate and aslowest heating rate. Adopted PID control, the long-term stability is good. Temperaturefluctuation was controlled in±1.5mK, the standard deviation is0.339mK.A system for maintaining a sample at constant temperature after stopping thecryocooler is designed and some preliminary experimental verification were done.Measuring the total thermal contact resistance between the connecting parts and analyzed.After stooping the cryocooler, the temperature of the sample stage keep around7K forabout650seconds and the fluctuation range is6.9990K to7.0030K. The stable time andstability meet the experimental requirements.