are formed there is no metal isolation between the rotor and the stator for cutting through the magnetic lines of force so that the eddy current loss is relatively small meanwhile with mud flowing through the passages as lubricant overheating of the generator can be prevented and high power output can be ensured application_number US 201214241903 A description a specific embodiment according to the present disclosure will be described below with reference to fig1 the downhole rotating magnetic field generator 100 according to the present disclosure mainly comprises a stator assembly and a rotor assembly the stator assembly comprises a stationary cylindrical body 1 the cylindrical body 1 as a mounting base of the whole generator is configured as an elongated shaft shaped member all the components of the generator 100 can be mounted on the cylindrical body 1 windings 20 are arranged on a certain region of the body 1 namely a first region l1 in one specific embodiment a projection 25 in form of an integral step is arranged on one end the right end in fig1 of the first region l1 so that the windings 20 can be positioned axially thereon in a preferred embodiment an insulation layer 13 is arranged radially outside of the windings 20 and a set of laminations 19 is arranged radially inside of the windings 20 during operation the body 1 does not rotate therefore the windings 20 the set of laminations 19 and the insulation layer 13 do not rotate during operation either according to the present disclosure the rotor assembly comprises a permanent magnet 10 arranged in the first region l1 of the body 1 the magnet 10 is also located radially outside of the windings 20 and one end the right end in fig1.