  We present the mid-infrared spectrum, obtained with the Spitzer Infrared
Spectrograph (IRS), of HD 98800, a quadruple star system located in the
10-Myr-old TW Hydrae association. It has a known mid-infrared excess that
arises from a circumbinary disk around the B components of the system. The IRS
spectrum confirms that the disk around HD 98800 B displays no excess emission
below about 5.5 micron, implying an optically thick disk wall at 5.9 AU and an
inner, cleared-out region; however, some optically thin dust, consisting mainly
of 3-micron-sized silicate dust grains, orbits the binary in a ring between 1.5
and 2 AU. The peculiar structure and apparent lack of gas in the HD 98800 B
disk suggests that this system is likely already at the debris disks stage,
with a tidally truncated circumbinary disk of larger dust particles and an
inner, second-generation dust ring, possibly held up by the resonances of a
planet. The unusually large infrared excess can be explained by gravitational
perturbations of the Aa+Ab pair puffing up the outer dust ring and causing
frequent collisions among the larger particles.
