Dr gang zhou (Technical Institute of Physics and Chemistry, CAS)
A system for high precise control of the sample temperature using a 4K GM cryocooler is described. The maximum temperature fluctuations in a GM cryocooler without a high heat bath or thermal resistance are typically of the order of 400mK between 4K and 20K. It is particularly difficult to dramaticallydiminishthefluctuation of the sample cooled by the cryocooler at low temperatures. In this system, the temperature fluctuations of 0.5mK could be achieved when the temperature were controlled between 7K and 20mK using a PID temperature control system with supercritical helium and PTFE thermal resistance. In addition, shutting off the cryocooler significantly reduces sample motion that results from vibration and expansion/contraction of the cold head housing. Precise temperature control at 18.7K was attained when the cryocooler is shut off in present study, and the fluctuations of the sample temperature was less than 2mK even when the cryocooler is shut down for 30 minutes. This technique makes it possibleto control and stabilize the temperature regardless of the cryocooler is on or off.
Dr Kongrong Li (Technical Institute of Physics and Chemistry,CAS)