Abstract: A cooling apparatus for a low temperature magnet system includes a superconducting magnet coil (32) which encircles a test space (36). The magnet coil (32) is surrounded by at least one intermediate shield (26, 29) and is contained in an evacuated outer shell (22). On the outer shell (22) is a motor driven refrigerator (11) which actively cools the at least one intermediate shield (26, 29) by means of a cooling arm (18) extending through the outer shell (22). For compensating the disturbing fields emitted by the motorized drive of the refrigerator (11) a sensing device is provided for picking up these magnetic and/or mechanical disturbing signals. The sensor signal controls at least one coil (62) for compensating the disturbing field effective in the test space (36).