Operation of bicrystal junction high-T_c direct current-SQUID in a portable microcooler

A bicrystal junction high-Tc direct current-SQUID has been operated successfully at 77 K in a portable battery operated microcooler. The microcooler products magnetic signals which are harmonics of 43 Hz and a band of frequencies from 400 Hz to 4 kHz. It is possible to operate the SQUID in a flux-locked-loop mode using a 10 kHz modulation signal. The performance of the SQUID in the microcooler, in the frequency range 1-10 Hz, is almost identical to that in a Dewar. © 1994 American Institute of Physics.