  The application of resonant magnetic perturbations (RMPs) with a toroidal
mode number of n=4 or n=6 to lower single null plasmas in the MAST tokamak
produces up to a factor of 5 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. 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. During the ELM mitigated stage clear lobe
structures are observed in visible-light imaging of the X-point region. The
size of these lobes is correlated with the increase in ELM frequency observed.
The characteristics of the mitigated ELMs are similar to those of the natural
ELMs suggesting that they are type I ELMs which are triggered at a lower
pressure gradient. The application of the RMPs in the n=4 and n=6
configurations before the L-H transition has little effect on the power
required to achieve H-mode while still allowing the first ELM to be mitigated.
