A magnetic duct is inserted between the cathodic arc plasma source and the chamber to eliminate the macroparticles. In this paper, the plasma output of the magnetic duct is determined as a function of the magnetic field and thebias voltage under the Bilek biasing mode and entire duct biasing mode. The computer simulation and the experimentalresult indicate that the E × B drift results in an extra diffusion flux under the Bilek biasing mode. The test verifyingthe electron oscillation was conducted in the magnetic duct biased in the Bilek mode. The electron behaviour underBilek biasing mode is different from that under entire duct biasing mode. The Bilek biasing mode has a lower plasmaoutput than the entire duct biasing mode.