  We present experimental studies of the current pumped through a dynamic
quantum dot over a wide range of magnetic fields. At low fields we observe
repeatable structure indicating increased confinement of the electrons in the
dynamic dot. At higher fields (B>3T), we observe structure which changes
markedly from device to device suggesting that in this regime the transport is
sensitive to local disorder. The results are significant for the development of
dynamic quantum dot pumps as quantum standards of electrical current.
