  We have conducted pulsed transport measurements on c-axis oriented magnesium
diboride films over the entire relevant ranges of magnetic field $0 \alt H \alt
H_{c2}$ (where \hcu is the upper critical field) and current density $0 \alt j
\alt j_{d}$ (where $j_{d}$ is the depairing current density). The intrinsic
disorder of the films combined with the large coherence length and
three-dimensionality, compared to cuprate superconductors, results in a
six-fold enhancement of $H_{c2}$ and raises the depinning current density
$j_{c}$ to within an order of magnitude of $j_{d}$. The current-voltage
response is highly non-linear at all fields, resulting from a combination of
depinning and pair-breaking, and has no trace of an Ohmic free-flux-flow
regime.
  Keywords: pair, breaking, depairing, superconductor, superconductivity, flux,
fluxon, vortex, mgb2
