SUPRALEITENDE MAGNETANORDNUNG

摘要

A superconducting magnet arrangement of a nuclear spin tomographic apparatus comprises mutually coaxial metal tubes (1 to 9) in which eddy currents are induced when gradient fields are switched on. In turn, the eddy currents induce time-dependent magnetic fields which interfere with the gradient fields. To date, compensation of these interfering magnetic fields has proved only partly successful or prohibitively expensive. According to the invention, a shield (13) made of a material which is an excellent conductor of electricity, with a wall thickness not greater than 10 mm, or of a superconducting material is arranged in the region of the helium tank (10) of the magnet arrangement. All other tubes (1 to 9) of the magnet arrangement are made from a material which is a poor conductor of electricity, so that at the operating temperature of the magnet arrangement, the conductivity of the shield (13) is at least ten times the conductivities of the other tubes (1 to 9). The shield (13) generates an interference field of given magnitude and time constants, which, if necessary, can be easily compensated electronically.