Characteristics of the Helium Circulation System on the 440 CH Vector type MEG
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1
University of Tokyo , Japan
We report the characteristics of the Helium Circulation System (HCS) mounted on the 440 CH vector type MEG of the University of Tokyo Japan, that re-liquefies all the evaporating helium gas, consumes far less electric power and has low magnetic noises. It collects warm helium gas about 300 K, cools it to about 40K and returns it to the neck tube of the Dewar of the MEG to keep it cold. It also collects helium gas just above the liquid helium surface while it is still cold, re-liquefies and returns it to the Dewar. A special transfer tube (TT) about 2 m length with 7 multi-concentric pipes was developed to allow the dual helium streams. It separates the HCS with a MEG to reduce magnetic noise. A refiner to collect the contaminating gases such as oxygen and nitrogen effectively by freezing the gases is developed. It has an electric heater to remove the frozen contamination in the form of gases into the air. A gas flow controller is also developed, which automatically control the heater to cleanup the contamination. The developed TT has very low heat inflow less than 0.1W/m to the liquid helium ensuring the efficient operation. The HCS can re-liquefy up to 35.5 l/D of liquid helium from the evaporated helium gas using two 1.5W@4.2K GM cryocoolers (SRDK-415D, Sumitomo Heavy Industries, Ltd.). It has been confirmed that the HCS could be used with the real MEG system without any noise problem for about two year. The noise level is below 10 fT/Hz1/2 for 2-40 Hz, below 30 fT/Hz1/2 at 1 Hz, and 200 fT/Hz1/2 at 50 Hz, which is the power supply frequency. As the amount of liquid helium used decreases less than one percent, the maintenance cost of the MEG becomes less than one-tenth of the previous cost.
Conference:
Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010.
Presentation Type:
Poster Presentation
Topic:
Instrumentation and Multi-modal Integrations: MEG, Low-field MRI,EEG, fMRI,TMS,NIRS
Citation:
Takeda
T,
Okamoto
M and
Katagiri
K
(2010). Characteristics of the Helium Circulation System on the 440 CH Vector type MEG.
Front. Neurosci.
Conference Abstract:
Biomag 2010 - 17th International Conference on Biomagnetism .
doi: 10.3389/conf.fnins.2010.06.00026
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Received:
19 Mar 2010;
Published Online:
19 Mar 2010.
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Correspondence:
Tsunehiro Takeda, University of Tokyo, Kashiwa, Japan, takeda@brain.k.u-tokyo.ac.jp