A 3 CHANNEL SQUID-SYSTEM USING A MULTIPLEXED READOUT

Conventional multichannel SQUID systems require a number of wires connecting the individual SQUIDs and feedback coils to the room temperature electronics. In order to reduce the heat transport by these wires and to avoid the accompanied increased helium losses, we studied the possibility of using a multiplexed readout, requiring only a fraction of feed lines than needed by conventional systems. We used rf-SQUIDs in our experiments to avoid additional wires for dc-bias currents. A bias frequency of 100 MHz was chosen to achieve a sufficiently low flux-noise. The influence of modulation frequency and multiplexing frequency on the stability of the flux-locked loop and on the slew rate of the system was studied in some detail. Careful optimization of these parameters can lead to a multichannel system which requires only one coaxial cable between roomtemperature electronics and all SQUIDs.