Cryogen Liquids
In order to keep the inner temperature of the magnet low enough to maintain supra-conductivity, the magnet is filled with liquid helium (magnet types US and USR) and liquid nitrogen (magnet type: US, only). If the inner temperature of the magnet increases above a certain threshold, the magnet is going to quench. This can be caused by low levels of cryogen liquids.
During normal operation, the USR type magnet does not lose any relevant amount of helium. Following special conditions like power failure, malfunctions of the cold head or maintenance activities, liquid helium has to be refilled by the Bruker Service. All work at the magnet including filling of helium is considered a service action and must therefore be performed by other persons than trained Bruker Service.
During normal operation of US type magnets, the helium and nitrogen levels decrease by evaporation with time. In adequate intervals, the cryogenic liquids must be refilled. All work at the magnet including filling of helium and nitrogen is considered a service action and must be performed by trained Bruker Service.
Properties of liquid helium and liquid nitrogen:
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- Extremely low temperature:
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- Helium: - 270 °C
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- Nitrogen: - 190 °C
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- Oxygen in ambient air is displaced during boil-off
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- Odorless
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- Non-flammable
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- Non-toxic
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Risk of severe personal injury or explosion - •
- Only Bruker Magnet Service may perform work on the magnet.
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- Do not open or remove any safety valves and/or burst disks of the magnet dewar.
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Risk of asphyxiation or severe burns by cryogen liquids The handling of cryogen liquids bears potential risk of severe personal injuries like burns or asphyxiation. Rapidly escaping helium or nitrogen as it occurs during the filling process of a magnet can possibly displace the air in the magnet room and can therefore be a potential risk for asphyxiation. - •
- Only authorized and trained personnel may refill cryogen liquids.
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- Always have a second person supervising from outside while handling liquid cryogens.
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- Wear suitable protective gloves and eye protection.
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- Use only non-magnetic dewars and carts.
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- Store cryogen liquids in sufficiently ventilated rooms only.
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- No humans are permitted inside an elevator (or any other insufficient and closed room) that hosts dewars with cryogen liquids.
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Risk of fire by condensation of oxygen Helium and nitrogen are non-combustible. However, oxygen in the room may condense at the quench line or into relief ports and vents which are in contact with liquid helium. If these fittings are coated with flammable oils and grease, a potential fire hazard exists. - •
- All flammable material must be removed from the immediate vicinity of the magnet.
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