Ultrasensitive Superconducting Magnetic Gradiometer.
Final rept. 1 Jan-31 Dec 71,
NATIONAL BUREAU OF STANDARDS BOULDER COLO CRYOGENICS DIV
Pagination or Media Count:
A compact battery-operated superconducting magnetic gradiometer with 10 to the minus 11th power gausscm Hz to the 12 power sensitivity has been built. It has been balanced to better than 50 ppm of the projected axial area in all three orthogonal directions. The sensor SQUID is a multihole fractional turn type, coupled to multi-turn pickup loops made of fine wire to minimize flux trapping and jumping. The cryostat is a light-weight, non-metallic dewar with vapor-cooled radiation shields which holds one liter of liquid helium and operates in excess of 24 hours on one filling. An uhf 300 MHz low-noise bias system has been developed which can provide a considerable increase of sensitivity when it is incorporated into the system. A data recording system is described which utilizes a battery-operated tape recorder with frequency modulation and demodulation circuits to improve the linearity. A new type of SQUID has been developed for use in the gradiometer and other applications. It combines the reliability of a Nb thin-film microbridge with the low inductance of a bulk Nb ring. Author
- Test Facilities, Equipment and Methods