SQUID-based rock magnetometer with open-ended horizontal room-temperature access

We constructed a 3-channel SQUID-based rock magnetometer with an open-ended horizontal room-temperature access having an inner diameter of 38 mm. A refrigerator is incorporated for cooling two radiation shields so that an operating time can be realized of about 10 weeks with a reservoir volume of 26.7 litres. The temperature variation along the access is about 9 K. The rock magnetometer is equipped with a special sensing-coil set of which the signal uniformity with respect to magnetic dipoles is about a factor of two better than that of conventional vertical-access systems. The intrinsic noise level of the system is 10
^-11
Am
²
/
\sqrt{Hz}
.