Pair-ion plasmas, consisting of positive and negative ions with the equal mass, are generated using fullerene as an ion source and processes of electron-beam impact ionization, electron attachment, and radial diffusion of ions in an axial magnetic field. When a central and a hollow electron beam are injected into a gas of sublimated fullerene molecules, the pair-ion plasmas with almost no electrons are found to be generated in a periphery and a core region of the plasma column, respectively. A dumb-bell-shaped dimer of fullerene is directly produced in the plasma. This is a novel method of dimer formation without utilization of catalysts or non-allotropic fullerene derivatives. (C) 2003 Elsevier Science B.V. All rights reserved.