  On the basis of the time-dependent Ginzburg-Landau equation we studied the
dynamics of the superconducting condensate in a wide two-dimensional sample in
the presence of a perpendicular magnetic field and applied current. We could
identify two critical currents: the current at which the pure superconducting
state becomes unstable ($J_{c2}$ \cite{self1}) and the current at which the
system transits from the resistive state to the superconducting state
($J_{c1}<J_{c2}$). The current $J_{c2}$ decreases monotonically with external
magnetic field, while $J_{c1}$ exhibits a maximum at $H^*$. For sufficient
large magnetic fields the hysteresis disappears and $J_{c1}=J_{c2}=J_c$. In
this high magnetic field region and for currents close to $J_c$ the voltage
appears as a result of the motion of separate vortices. With increasing current
the moving vortices form 'channels' with suppressed order parameter along which
the vortices can move very fast. This leads to a sharp increase of the voltage.
These 'channels' resemble in some respect the phase slip lines which occur at
zero magnetic field.
