Arrangement to adjust the homogeneity of a basic magnetic field

An arrangement for adjusting the homogeneity of a basic magnetic field in a magnetic resonance apparatus having a basic field magnet that generates a basic magnetic field having said homogeneity, said arrangement comprising:

• a shim tray containing a plurality of ferromagnetic shim elements at predetermined positions in said shim tray;
• a gradient coil support configured to support a gradient coil system of the magnetic resonance apparatus;
• said gradient coil support having at least one channel therein configured to receive said shim tray therein, with the respective positions of the ferromagnetic shim elements in said shim tray, when said shim tray is in said channel, adjusting the homogeneity of the basic magnetic field;
• said shim tray comprising a first locking element coupled to said shim tray and said channel comprising a second locking element that mates with said first locking element;
• and
• said first and second locking element being forced together into mechanical connection with each other by said basic magnetic field upon activation of said basic magnetic field.