We investigate singly and doubly charged flux tubes in U(1) lattice ga
uge theory. By simulating the dually transformed path integral we are
able to consider large flux tube lengths, low temperatures, and multip
ly charged systems without loss of numerical precision. We simulate fl
ux tubes between static sources as well as periodically closed flux tu
bes, calculating flux tube profiles, the total field energy and the fr
ee energy. Our main results are that the string tension in both three
and four dimensions scales proportionally to the charge - which is in
contrast to previous lattice results - and that in four-dimensional U(
1) there is an attractive interaction between flux tubes for beta appr
oaching the phase transition. (C) 1998 Elsevier Science B.V.