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Described is the system for positioning, and arresting the poloidal field coil in the FM-l machine. The ring is held in the proper position, on centerline of the machine by four positioner assemblies. Rotation of the ring to proper azimuth for filling, venting and charging is provided. The positioner assemblies are lowered to the vacuum vessel floor during ring levitation or for ring maintenance. In the event of a system failure, resulting in loss of ring stabilization the ring must be quickly arrested to prevent damage to the Dewar or machine. Four scissors type, mechanisms are positioned in the vacuum vessel for this purpose. A cylinder mounted solenoid poppet valve is fired by a capacitor bank resulting in a signal to closure time of 60 msec. A slow mode catch may also be actuated, through externally mounted valves, resulting in a cycle time of 150 to 200 msec. Upon closure and contact with the ring, the ring energy is absorbed by uncoupled slide and tilt spring systems. After a catcher closure cycle the positioners are again inserted and the ring returned to the proper position.