High Frequency Electromagnetic Interference Reduction on the SQUID Attached in Pulse Tube Cryocooler

Measurements of the high frequency electromagnetic interference (EMI) of a pulse tube cryocooler are made in a typical laboratory environment using laboratory-made current transformers. The inverter makes high frequency EMI which could cause severe interference with SQUID operation inside the pulse tube cryocooler. By covering the power lines, including a neutral line, of the valve motor with a copper mesh cover, as a ground line, one order de- crease in the magnitude of the EMI noise is successfully obtained. This paper describes an example to show how to observe and reduce conducted high frequency noise currents in a precision experimental system.