Real-time reconstructor for adaptive secondary control of the 6.5-m single-mirror MMT

We describe the proposed real-time reconstructor algorithm and hardware design for the planned 6.5 m MMT monolithic primary upgrade. The real-time reconstructor will use a linear matrix multiply to calculate the command values to be applied to the actuators of an adaptive secondary mirror using input data from a Shack-Hartmann type wavefront sensor which samples the atmospheric turbulence. Each mirror actuator will be controlled by a high- speed inner control-loop which uses capacitive position sensors located at each actuator as feedback. The real-time reconstructor algorithm is designed to take advantage of the presence of this inner control-loop to achieve better overall correction of the atmospheric aberration. The reconstructor design also provides the ability to use wave-front sensor measurements obtained in previous cycles as part of the input vector in the reconstruction algorithm. The real-time reconstructor hardware uses commercially available hardware to implement the reconstruction algorithm at high bandwidths and small latencies.