
312 Compact Plasma and Focused Ion Beams
be realized and sustained in MC waveguides with the cross sections below
cutoff values for the fundamental waveguide mode [1–6]. Both circular and
square cross-sectional MCs were studied [2,3]. The reduction in size of the
MC is favorable because it increases the power density deposited in the
plasma, thereby enhancing the plasma density. Also, a small source size is
crucial for beam focusing (demagnication factor) and hence important for
FIB systems. In sub-cutoff dimensional waveguides, plasmas with densities
above the ordinary mode (O-mode) cutoff density (10
11
cm
−3
) could be pro-
duced and maintai ...