  The 25.4m Giant Magellan Telescope (GMT) will be amongst the first in a new
series of segmented extremely large telescopes (ELTs). The 25.4 m pupil is
segmented into seven 8.4 m circular segments in a flower petal pattern. At the
University of Arizona we have developed a novel pupil slicer that will be used
for ELT extreme adaptive optics (ExAO) on the up and coming ExAO instrument,
GMagAO-X. This comes in the form of a six-sided reflective pyramid with a hole
through the center known as a "hexpyramid". By passing the GMT pupil onto this
reflective optic, the six outer petals will be sent outward in six different
directions while the central segment passes through the center. Each segment
will travel to its own polarization independent flat fold mirror mounted on a
piezoelectric piston/tip/tilt controller then onto its own commercial 3,000
actuator deformable mirror (DM) that will be employed for extreme wavefront
control. This scheme of seven DMs working in parallel to produce a 21,000
actuator DM is a new ExAO architecture that we named a "parallel DM," in which
the hexpyramid is a key optical component. This significantly surpasses any
current or near future actuator count for any monolithic DM architecture. The
optical system is designed for high-quality wavefront (lambda/10 surface PV)
with no polarization errors and no vignetting. The design and fabrication of
the invar mechanical mounting structure for this complex optical system is
described in this paper.
