High frequency electromagnetic interference reduction on the squid attached in pluse 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, which include a neutral line, of the valve motor with a copper mesh cover, as a ground line, one order decrease in the magnitude of the EMI noise is successfully obtained. This paper describes one example to show how to observe and reduce conducted high frequency noise currents in a precision experimental system.