  Large populations of cataclysmic variables (CVs) in globular clusters have
long been predicted, but the number of absolutely certain cluster CVs known in
globulars is still less than 10. HST and Chandra observers have recently found
dozens of cataclysmic variable candidates in several populous globular
clusters. Confirmation and characterization of these candidates are extremely
difficult, thus identification of unambiguous CVs remains important. We have
searched all archival HST images of the dense globular cluster M80 for erupting
dwarf novae (DN), and to check the outburst behaviors of two very blue objects
first identified a decade ago. Two new erupting dwarf novae were found in 8
searched epochs, making M80 a record holder for erupting DN. The quiescent
classical nova in M80 varies by no more than a few tenths of a magnitude on
timescales of minutes to years, and a similar faint, blue object varies by a
similar amount. Simulations and completeness tests indicate that there are at
most 3 erupting DN like SS Cyg and at most 9 U Gem-like DN in M80. Either this
very dense cluster contains about an order of magnitude fewer CVs than theory
predicts, or most M80 CVs are extremely faint and/or erupt very infrequently
like WZ Sge. We have detected a sequence of 54 objects running parallel to the
main sequence and several tenths of a magnitude bluewards of it. These blue
objects are significantly more centrally concentrated than the main sequence
stars, but not as centrally concentrated as the blue stragglers. We suggest
that these objects are white dwarf--red dwarf binaries, and that some are the
faint CV population of M80.
