  The application of resonant magnetic perturbations (RMPs) with a toroidal
mode number of n=3 to connected double null plasmas in the MAST tokamak
produces up to a factor of 9 increase in Edge Localized Mode (ELM) frequency
and reduction in plasma energy loss associated with type-I ELMs. A threshold
current for ELM mitigation is observed above which the ELM frequency increases
approximately linearly with current in the coils. The effect of the RMPs is
found to be scenario dependent. In one scenario the mitigation is only due to a
large density pump out event and if the density is recovered by gas puffing a
return to type I ELMs is observed. In another scenario sustained ELM mitigation
can be achieved irrespective of the amount of fuelling. Despite a large scan of
parameters complete ELM suppression has not been achieved. The results have
been compared to modelling performed using either the vacuum approximation or
including the plasma response. The requirement for a resonant condition, that
is an optimum alignment of the perturbation with the plasma, has been confirmed
by performing a scan in the pitch angle of the applied field.
