A new compact electron cyclotron resonance (ECR) plasma source for future plasma-assisted processing was developed. The source allows for improved control and direct monitoring of the discharge. Control of the ion energy distribution by movement of the magnetic field is demonstrated for the first time in a compact ECR plasma source. The ion energy can be tuned from 10 to 30 eV. An explanation based on different ambipolar diffusion coefficients for different magnetic fields is outlined. Nitrogen-plasma-induced surface reaction processes on sapphire substrates, with a view to achieving growth of a thin AlN buffer layer prior to group III nitride growth, was investigated using this novel energy-selective ECR plasma source.