This thesis describes an in-depth series of investigations into electromagnetic and thermal behaviour of a brushless permanent-magnet electrical generator and technologies that would provide additional power density. It has a particular focus on a 50kW generator operating at speeds up to 17,000rpm which is coupled to an uncontrolled diode rectifier for DC power generation for a 'more electric' RollsRoyce model 250 turbine engine. To be competitive for this application, an active power density target of 15kW/kg was set. An electromagnetic design study has been carried out on a 15-slot, 10-pole surfacemounted permanent magnet topology. The design is optimised in order to maximise output power at the uncontrolled rectifier terminals and to limit the current density to a thermally sustainable level, ultimately operating near its electromagnetic limit. Having established a baseline design, a prototype generator was constructed and tested both in its normal operating mode of power generation and statically using DC currents for precise thermal characterisation of the cooling strategy. The scope to further increase the power density is explored drawing on analysis of several novel features: additively manufactured coils, aluminium winding design variant, and current waveform optimisation.