SQUIDs De-fluxing Using a Decaying AC Magnetic Field

Matlashov, Andrei Nikolaevich¹  Semenov, Vasili Kirilovich²  Anderson, Bill³ 

[1]Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

[2]State Univ. of New York (SUNY), Plattsburgh, NY (United States)

[3]Senior Scientific, LLC, Albuquerque, NM (United States)

关键词: Biological Science;    High Magnetic Field Science;    SQUID;    SPMR;    MRX;    ULF MRI;    de-fluxing;    de-magnetization;    flux trapping;   

DOI  :  10.2172/1257119
RP-ID  :  LA-UR--16-23994
PID  :  OSTI ID: 1257119

学科分类：凝聚态物理

美国|英语

来源: SciTech Connect

【 摘 要 】

Flux trapping is the Achilles??? heel of all superconductor electronics. The most direct way to avoid flux trapping is a prevention of superconductor circuits from exposure to magnetic fields. Unfortunately this is not feasible if the circuits must be exposed to a strong DC magnetic field even for a short period of time. For example, such unavoidable exposures take place in superparamagnetic relaxation measurements (SPMR) and ultra-low field magnetic resonance imaging (ULF MRI) using unshielded thin-film SQUID-based gradiometers. Unshielded SQUIDs stop working after being exposed to DC magnetic fields of only a few Gauss in strength. In this paper we present experimental results with de-fluxing of planar thin-film LTS SQUID-based gradiometers using a strong decaying AC magnetic field. We used four commercial G136 gradiometers for SPMR measurements with up to a 10 mT magnetizing field. Strong 12.9 kHz decaying magnetic field pulses reliably return SQUIDs to normal operation 50 ms after zeroing the DC magnetizing field. This new AC de-fluxing method was also successfully tested with seven other different types of LTS SQUID sensors and has been shown to dissipate extremely low energy.