a is spaced apart from the tie bar 4 and nut 15 and encloses it to further reduce heat transfer via conduction it will be appreciated that some embodiments may not require this heat shield the rotor moves relative to a stator this comprises a number of components which will be familiar to the person skilled in the art but in fig2 there are shown an end plate 19 in the four of an annulus with the rotor 2 protruding through the central hole into the enclosure 5 a labyrinth seal 20 is provided to prevent hot gases escaping into the enclosure cavity the end plate 19 is also insulated to prevent heat transmission the stator also includes a series of support spokes 21 two of which can be seen these are fixed towards the radially outerwards part of the end plate 19 and are inclined inwards in a direction towards the axis of rotation 18 the radially inner ends of the spokes 21 are bolted to an annular shroud 22 this is provided with a central portion which is generally cylindrical which extends in a direction substantially parallel to the axis 18 this part of the arrangement is shown in greater detail in fig3 as is shown in fig3 a and 3 b the turbulator cylinder 16 is provided with a plurality of turbulators in the form of ribs 16 c milled.