Good confinement of alpha particles in a large magnetic fusion device is a precondition for building a magnetic fusion reactor. The direct measurement of alpha particle losses is of particular interest. Appropriate diagnostics are now being prepared for the Joint European Torus tokamak: a scintillator probe and a set of Faraday cups. Both systems are capable of measuring charged fusion products and ion cyclotron resonance heating tail ions. The design of the lost alpha particle scintillator probe is in the scope of this article. It will allow the detection of particles with a gyroradius between 20 and 140 mm (15% resolution) and a pitch angle between 30° and 86° (5% resolution). As scintillating material P56 will be used. The light emitted by the scintillator caused by charged particles that pass the collimator and hit the scintillator will be detected via a set of optical lenses and a coherent image fiber bundle with a charge coupled device camera and a photomultiplier array. In the following the present design of the scintillator probe with emphasis on the performance of the system, structural resistance against plasma disruptions, and the requirements on the heat protection against plasma and neutral beam induced thermal loads will be described.

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A regenerative or peripheral compressor has been developed with aerodynamic blading in place of the usual straight radial vanes on the rotor. The blades are shrouded by a core, around which a helical toroidal flow path is established. Two compressors have been constructed, the first with a single row of blades and the second with two rows side by side to provide parallel counterrotating flow paths. The diameter of the impellers is 0.30 m. The characteristics of the compressor resemble those of a Rootes blower, with a steep variation of pressure with respect to flow rate. At a speed of 4000 rpm the isothermal efficiency reaches a maximum of 57 percent when the pressure ratio is 1.17 and the flow rate is 0.2 m3/s. When the flow rate is reduced by throttling to 0.165 m3/s the pressure ratio is raised to 1.50, but the isothermal efficiency is reduced to 44 percent. The theory, design, and development of the compressor are discussed.

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