  Understanding and controlling the motion of superconducting vortices has been
a key issue in condensed matter physics and applied superconductivity. Here we
present a method for macroscopically manipulating the vortices based on
travelling wave flux pump to accurately output industrial-scale DC current into
high-temperature superconducting (HTS) magnets. DC magnetic fields are used to
adjust the polarity of the vortices and thus modulate the direction of the
output current, which demonstrates that the DC current of the flux pump
originates from the motional electromotive force ( e.m.f. ) other than the
induced e.m.f.. In addition, applying different strengths of DC fields can
modulate the magnitude of the output current. Further numerical simulation
suggests how the flux inside the superconducting tape is controlled by
different applied fields. We build a controlled flux flow model to correctly
explain the behavior of vortices controlled by the flux pump, and how the
motional e.m.f. is created by manipulating the vortices. Based on the method,
we achieve high precision regulation of output current using adaptive control
of the DC magnetic field, allowing the flux pump to output DC current just as
accurate as a typical commercial power supply. This work advances the technic
for macroscopic manipulation of vortices.
