Study On Measurement Of Low Temperature Thermometer In High Magnetic Fields

With the development of science,it is becoming more and more difficult to make scientific research breakthroughs using conventional experimental conditions.In addition to an extreme experimental condition,high magnetic field has played an important role in discovering new phenomena,understanding new phenomena and catalyzing new technologies.However,due to the influence of magnetoresistance,the indication value of the low temperature thermometers will change with the magnetic fields,which will affect the results of low temperature physics experiments or actual running state of the superconducting device.Even small temperature fluctuations may even cause quench.The persuit of higher magnetic field is one of the inevitable development trends of steady high magnet field facility,which puts forward higher requirements for the accuracy of low temperature thermometer under high magnetic fields.Based on the development of low temperature measurement in high fields,this paper carried out the experimental study of low temperature thermometer measurement in high fields relying on steady high magnet field facility.The main research work of this article is shown as follows:Firstly,based on the transport properties of metal and semiconductor,the mechanism of factors affecting the measurement accuracy of low temperature thermometer in high field was described,such as magnetoresistance,magnetic properties of materials,and eddy current losses.A low temperature thermometer measuring platform which can be applied to 35 T high field is designed.The thermal load analysis of the cryostat,temperature distribution and temperature stability analysis,the structure design,decompression and cooling system design,eddy current loss calculation,measurement and control system design,and platform uncertainty analysis were carried out.The temperature measurement experiments of seven metal and semiconductor resistance thermometers including platinum,rhodium-iron,low-temperature linear thermometer,ruthenium oxide.Cernox,carbon ceramic,and germanium,etc.were carried out at a maximum field intensity of 35T.The variation of magnetoresistance with temperature and field intensity,anisotropic magnetoresistance and the errors caused by magnetoresistance were analyzed.The magnetoresistance of metal resistance and semiconductor resistance was compared and analyzed.The magnetoresistance mechanism of typical resistance thermometers was explained.Based on the comparative analysis,the best thermometer types for LHe temperature and LN2 temperature under high field were were obtained by comparative analysis.In this paper,new types of low temperature sensor material CrN thin film which may be used in high magnetic field were explored,and the electrical properties and magnetoresistance of the new CrN thin film were analyzed,and the magnetoresistance mechanism of CrN film was explained.CrN thin film has presented semiconductor conduction behavior,good temperature sensing characteristics and low magnetic field sensitivity.The magnetoresistance of CrN thin film is lower than Cernox thermometer which is the best thermometer under the magnetic field.So CrN thin film can be regarded as a low-cost thin-film resistance temperature sensor with potential application in magnetic field.But the temperature and resistance curve of CrN thin film are not continuous at the Neel temperature,and the film sensitivity also can be furtherly improved.Our experimental data prove that the smaller the CrN film thickness,the higher the sensitivity,and the higher the CrN film resistance,therefore,it maybe necessary to find the optimal balance point of film sensitivity,film thickness,and resistance in future.