  We explore the cosmological consequences of the superconductivity of QCD
axion strings. Axion strings can support a sizeable chiral electric current and
charge, which alters their early universe dynamics. Shrinking axion string
loops can become effectively stable remnants called vortons, supported by the
electromagnetic force of the string current. Generically, vortons produced by
axion strings overclose the universe, unless there are efficient current
leakage processes. Furthermore, if a primordial magnetic field (PMF) exists in
the early universe, a large current is induced on axion strings, creating a
significant drag force from interactions with the surrounding plasma. As a
result, the strings are slowed down, which leads to an orders of magnitude
enhancement in the number of strings per Hubble volume. Finally, we study the
implications for the QCD axion relic abundance. The QCD axion window is shifted
by orders of magnitude in some parts of our parameter space.
