In a method and a device for precooling the helium tank of a cryostat, in particular one for accommodating a superconductive magnet coil, contamination of the he lium tank is avoided by the fact that helium gas is cooled down to the temperature of boiling nitrogen in a closed circuit, the helium gas is then circulated through the helium tank and thereafter cooled down again to the temperature of boiling nitrogen. The helium tank is cooled by means of the helium gas, which has a temper ature of 77 K, until the tank has reached that tempera ture. The interior of the helium tank getting into contact exclusively with helium, the helium tank can be filled with liquid helium immediately after it has reached the precooling temperature, without the need to clean the tank first.
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