An air-gap is between a rotor and a stator. The stator comprises a number of stacked laminate-plates. The laminate-plates are positioned and fixed by a structural support and by end-plates in relation to a central-part of the stator to achieve the air-gap. A cavity is formed by the end-plates, the central-part of the stator, the air-gap and an internal surface of the rotor. An air-cooling arrangement is arranged and used to circulate a gaseous medium for cooling purposes inside the cavity.