  We investigate the effect of magnetic helicity on the stability of buoyant
magnetic cavities as found in the intergalactic medium. In these cavities, we
insert helical magnetic fields and test whether or not helicity can increase
their stability to shredding through the Kelvin-Helmholtz instability and, with
that, their lifetime. This is compared to the case of an external vertical
magnetic field which is known to reduce the growth rate of the Kelvin-Helmholtz
instability. By comparing a low-helicity configuration with a high helicity one
with the same magnetic energy we find that an internal helical magnetic field
stabilizes the cavity. This effect increases as we increase the helicity
content. Stabilizing the cavity with an external magnetic field requires
instead a significantly stronger field at higher magnetic energy. We conclude
that the presence of helical magnetic fields is a viable mechanism to explain
the stability of intergalactic cavities on time scales longer than 100 Myr.
