Pair-Ion Plasma Generation using Fullerenes

We have developed a novel method for generating pure pair plasma which consists of positive- and negative-charged particles with an equal mass. The pair-ion plasma without electrons is generated using fullerene as an ion source through the processes of hollow-electron-beam impact ionization, electron attachment, preferential radial diffusion of ions, and resultant electron separation in an axial magnetic field. Basic characteristics of this plasma are discussed in terms of the differences from ordinary electron-ion plasmas, such as a phenomenon in the absence of sheath and potential structure formation.

Figure 1

Schematic drawing of the experimental setup. An electron beam for ionization takes the form of a hollow tube. Pure pair-ion plasma using a fullerene (${\mathrm{C}}_{60}^{+}$, ${\mathrm{C}}_{60}^{-}$) is generated by electron-impact ionization, electron attachment, and preferential diffusion of ions.

Figure 2

(a) Characteristic of ${\mathrm{C}}_{60}$ discharge depending on electron-beam energy. (b) Typical current-voltage characteristic of Langmuir probe is displayed (electron energy: 100 eV).

Figure 3

Spatial (axial-radial) profile of pair-ion plasma density in the downstream region from the annulus.

Figure 4

(a) Pair-ion plasma density depending on electron-beam energy and annulus bias: voltage $V_{cy}$. (b) Positive-ion saturation current vs $V_{cy}$ (electron energy: 100 eV).