Journal
CRYOGENICS
Volume 76, Issue -, Pages 16-22Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.cryogenics.2016.03.007
Keywords
Closed-cycle helium recycler; Magnetoencephalography (MEG); Pulse-tube cryocooler; Superconducting quantum interference device (SQUID); Gifford-McMahon cryocooler
Categories
Funding
- NSF [0958669, 0959294]
- Division Of Behavioral and Cognitive Sci
- Direct For Social, Behav & Economic Scie [0959294, 0958669] Funding Source: National Science Foundation
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A closed-cycle helium recycler was developed for continuous uninterrupted operation for magnetometer-based whole-head magnetoencephalography (MEG) systems. The recycler consists of a two stage 4 K pulse-tube cryocooler and is mounted on the roof of a magnetically shielded room (MSR). A flexible liquid helium (LHe) return line on the recycler is inserted into the fill port of the MEG system in the MSR through a slotted opening in the ceiling. The helium vapor is captured through a line that returns the gas to the top of the recycler assembly. A high-purity helium gas cylinder connected to the recycler assembly supplies the gas, which, after it is liquefied, increases the level of LHe in the MEG system during the start-up phase. No storage tank for evaporated helium gas nor a helium gas purifier is used. The recycler is capable of liquefying helium with a rate of similar to 17 L/d after precooling the MEG system. It has provided a fully maintenance-free operation under computer control for 7 months without refill of helium. Although the recycler is used for single-orientation operation at this initial testing site, it is designed to operate at +/- 20 degrees orientations, allowing the MEG system to be tilted for supine and reclining positions. Vibration of the recycler is dampened to an ultra-low level by using several vibration isolation methods, which enables uninterrupted operation during MEG measurements. Recyclers similar to this system may be quite useful even for MEG systems with 100% magnetometers. (C) 2016 Elsevier Ltd. All rights reserved.
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