Abstract:
Magnetic fields correlated on kiloparsec scales are seen in disc galaxies. The origin could be due
to amplification of small scale seed fields by a turbulent dynamo. Helicity conservation imposes
constraints on dynamo action and one can study the minimal field strength of the large scale magnetic
field that could arise despite the constraint. The calculation of helicity is technically complicated
because of open boundaries and the usual form for the MHD invariant needs to be modified to take
this into account. A general formalism has been developed to calculate the field strength using a
quasi-linear dynamo model. As a first step, a galactic disk dynamo model has been built analytically
while making the usual assumptions of shear and the alpha effect. We find quadrupolar solutions that are
matched to a vacuum field with D = 11. The general approach to solving the quasi-linear dynamo
using the full set of relative helicity boundary conditions are described
