We introduce a new definition of the thermal partition function in string t
heory. With this new definition, the thermal partition functions of all of
the string theories obey thermal duality relations with self-dual Hagedorn
temperature beta (2)(H) = 4 pi (2)alpha (1). A beta --> beta (2)(H)/beta tr
ansformAtion maps the type I theory into a new string theory (type (I) over
tilde) with thermal Dp-branes, spatial hypersurfaces supporting a p-dimens
ional finite temperature non-Abelian Higgs-gauge theory for p less than or
equal to 9. We demonstrate a continuous phase transition in the behavior of
the static heavy quark-antiquark potential for small separations r(*)(2) m
uch less than alpha (1) transitioning through a precise inverse power law a
t a critical temperature T-D = T(H)r(*)/(2 alpha')(1/2)pi.