It now appears feasible to deposit positrons (e+) in a tokamak plasma by injecting bursts of neutral positronium atoms (e+e−), which are then ionized by the plasma. The annihilation time of these positrons in the plasma is long compared with typical particle containment times. Thus the subsequent transport of the positrons can be studied by monitoring the time dependence of the annihilation, gamma radiation produced when the positrons strike a limiter. This paper discusses the design of such an experiment, the kinds of data which can be obtained, and the physics questions which this experiment might address. This diagnostic technique could also be useful in studying transport in other magnetic confinement devices such as reversed-field pinches and magnetic mirrors.

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A simple scheme for bunching spatially distributed charged particles is described. In the present application, sub-nanosecond width pulses are obtained from a milliliter volume containing slow «2 e V) positrons. The utility of this technique is demonstrated by a qualitative observation of the temperature dependance of the surface state lifetime for positrons on aluminum.

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