The Optical Sensors in FM-1

In the PPL FM-1 Machine, the plasma containment volume is shaped, in part, by a levitated superconducting ring which is stabilized and positioned by servoed currents in stationary tilt and slide coils. The instantaneous position of the ring is sensed, in the required five degrees of freedom, by external non-contacting reflex optical sensors. Design and construction of these sensors is described and results of performance tests, both off and on the FM-1, are presented.