6 is arranged axially in the direction of the axis of the room temperature bore containing the room temperature tube 4 during operation within the vacuum lock 5 the passive shim apparatus 3 or parts thereof being able to be moved with the ram the cryostat 1 contains one or more radiation shields 7 arranged in a radially nested manner a cover apparatus 8 for one sided sealing of the opening on the side of the room temperature bore is attachable to the magnet side end of the ram 6 in particular for one sided sealing of the radially innermost radiation shield adjacent to the room temperature tube 4 the cover apparatus 8 seals the opening in the thermal shield and serves as a thermalization of the ram in order to keep the thermal load on the coil tank low the passive shim apparatus 3 or parts thereof may be attached in a heat conducting manner to a radiation shield 7 during the operation of the magnetic resonance installation alternatively or in a complementary manner the passive shim apparatus 3 or parts thereof may be attached in a heat conducting manner in the cold region of the cryostat 1 on the outer side of.