  High-accuracy spectroscopic comparisons of trapped antihydrogen atoms
($\overline{\text{H}}$) and hydrogen atoms ($\text{H}$) promise to stringently
test the fundamental CPT symmetry invariance of the standard model of particle
physics. ATRAP's nested Penning-Ioffe trap was developed for such studies. The
first of its unique features is that its magnetic Ioffe trap for
$\overline{\text{H}}$ atoms can be switched between quadrupole and octupole
symmetries. The second is that it allows laser and microwave access
perpendicular to the central axis of the traps.
