We show that turbulence in a weakly ionized plasma can lead to a filam
entation of magnetic flux tubes as it reaches the ambipolar scale, whe
re the neutrals are imperfectly coupled to the ions. This results from
an instability mechanism, forcing the neutrals outside of the more io
nized regions and compressing the ions and the field in these regions.
It might have important consequences in such astrophysical contexts a
s the solar atmosphere or the interstellar medium.