We describe a method of cooling an axial flux permanent magnet machine, the machine having a stator comprising a stator housing enclosing a set of coils wound on respective stator bars and disposed circumferentially at intervals about an axis of the machine, and a rotor bearing a set of permanent magnets and mounted for rotation about said axis, and wherein said rotor and stator are spaced apart along said axis to define a gap therebetween in which magnetic flux in the machine is generally in an axial direction, the method comprising: flowing a coolant through said stator housing around said coils such that said coolant flows between said coils; and controlling said coolant flow between said coils by controlling a gap between adjacent said coils; wherein said controlling of said gap comprises: providing each of said coils with a single layer of windings over said stator bar, said layer of windings comprising a ribbon-shaped wire having a greater width across a surface of the ribbon than thickness through the
