  Observations have shown that continuous radio emission and also sporadic
H-alpha and X-ray emission are prominent in singular, low-mass objects later
than spectral class M. These activity signatures are interpreted as being
caused by coupling of an ionised atmosphere to the stellar magnetic field. What
remains a puzzle, however, is the mechanism by which such a cool atmosphere can
produce the necessary level of ionisation. At these low temperatures, thermal
gas processes are insufficient, but the formation of clouds sets in. Cloud
particles can act as seeds for electron avalanches in streamers that ionise the
ambient gas, and can lead to lightning and indirectly to magnetic field
coupling, a combination of processes also expected for protoplanetary disks.
However, the precondition is that the cloud particles are charged.
  We use results from Drift-Phoenix model atmospheres to investigate
collisional processes. We show that ionisation by turbulence-induced dust-dust
collisions is the most efficient kinetic process. Dust-dust collisions alone
are not sufficient to improve the magnetic coupling of the atmosphere inside
the cloud layers, but the charges supplied either on grains or within the gas
phase as separated electrons can trigger secondary non-linear processes. Cosmic
rays are likely to increase the global level of ionisation, but their influence
decreases if a strong, large scale magnetic field is present as on Brown
Dwarfs.
  We suggest that although thermal gas ionisation declines in objects across
the fully-convective boundary, dust charging by collisional processes can play
an important role in the lowest mass objects. The onset of atmospheric dust may
therefore correlate with the anomalous X-ray and radio emission in atmospheres
that are cool, but charged more than expected by pure thermal ionisation.
