  A new experimental method for creating void-free complex (``dusty'') plasmas
under microgravity conditions is presented. The method is based on a pulsed
operation mode of a four-channel radio-frequency generator for plasma
sustainment. A dust cloud of micrometer-sized particles can be immersed in the
bulk of a low temperature plasma under microgravity conditions. It typically
contains a central volume depleted of particles - the void - that prevents the
generation of large, continuous clouds. Experiments performed at different
neutral gas pressures and discharge volumes during the microgravity phase of a
parabolic flight show that the central void is closed completely once the
pulsed operation mode is applied. The particle cloud shape, and the density
distribution within the cloud, are practically independent on the pulse period
within the investigated parameter range, and mainly depend on the overall
discharge parameters neutral gas pressure and discharge volume. This indicates
that the pulsed operation of the plasma source does not introduce new physical
effects on the particles aside from the void closure. The proposed method has
great potential for future application in experimental facilities dedicated to
fundamental studies of large three-dimensional, homogeneous complex plasma
systems in microgravity.
