Axial Momentum Lost to a Lateral Wall of a Helicon Plasma Source

Momentum exerted to a lateral wall of a helicon plasma source is individually measured for argon, krypton, and xenon gases. A significant loss of the axial plasma momentum to the lateral wall, which has been assumed to be negligible, is experimentally identified when an axially asymmetric density profile is formed in the source. This indicates that the radially lost ions deliver not only the radial momentum but also the axial momentum to the lateral wall. The formation of the axial asymmetry causing the momentum loss is interpreted with competition between the magnetic field and neutral depletion effects.

Figure 1

(a) Schematic diagram of the experimental setup. (b) Axial profile of the magnetic field strength on axis for $I_B=1\mathrm{A}$.

Figure 2

(a) Measured forces to the back plate ($T_s$; filled symbols) and to the lateral wall ($T_w$; open symbols) as a function of the solenoid current $I_B$ for argon (triangles), krypton (circles), and xenon (squares). (b) Sum of the forces $T_s+T_w$ for argon (open triangles), krypton (open circles), and xenon (open squares). (c) Plasma density versus $I_B$ for the argon ($z=-12\mathrm{cm}$; open triangles), krypton ($z=-11\mathrm{cm}$; filled circles), and xenon ($z=-11\mathrm{cm}$; open squares) cases, where the data for argon are from Ref. [19].

Figure 3

Radial profiles of the plasma density taken at $z=-11\mathrm{cm}$ for argon (open triangles), krypton (filled circles), and xenon (open squares) for $I_B=7\mathrm{A}$. The dotted, solid, and dotted-dashed lines are the fitted Bessel functions of order zero for visual guides.

Figure 4

Axial profiles of (a) the plasma density and (b) the normalized density for argon (open triangles), krypton (filled circles), and xenon (open squares) for $I_B=7\mathrm{A}$.