Development of ccr based variable temperature insert for cryogen free superconducting magnet system

Abstract

Cryogen free magnet systems using close cycle refrigerator(CCR) is gaining more attention nowadays with continuously increase in advancement of performance and reliability of the close cycle refrigerator. In research lab and institutes, material characterisation is done which includes study for basic material science. As it is evident that sample properties depend on the sample space temperature, which require variation of magnetic field with variable sample temperature. Hence, the need for variable temperature insert for cryogen free magnet system came into existence. This thesis reports the design and fabrication of variable temperature insert for cryogen free magnet system with temperature variation from 4.2K to 300K and sample space of 25mm. The experimental set up comprises of GM cryocooler, vacuum jacket, thermal shield, heat exchangers, charcoal adsorber, sample bore and sample holder, buffer tank, scroll pump for circulation of gas. It also includes the manufacturing of three conduction-cooled (Helical coil) heat exchangers(HX) by using copper tube which are cooled with the help of the CCR. In this experimental set up, Thermal shield is connected with 1st stage of the CCR and maintained at temperature of 1st stage of the CCR i.e. at 30 K whereas two heat exchangers are connected on 1st and 2nd stage of cryocooler. The objective of this work is to develop a system to cool sample space from 300 K to 4.2 K. It can be achieved by the circulation of helium gas. The helium gas is cooled by the HX ,cooled by the CCR. It takes 15 hrs cool the helium gas to the desired temperature. Multiple test runs are done to test the stability of the system under fine controlled flow rate and system is working extremely well, Variable temperature insert(VTI) is successfully integrated with the cryogen free magnet system and experiment with variable temperature and varying magnetic field can be performed as the system is in fully working state.