EXPERIMENTAL SCALING OF PARTICLE CONFINEMENT IN TOKAMAKS

Experimental measurements on particle confinement in tokamaks are reviewed. The global particle confinement is mainly determined by recycling of the particle flux at the edge, which can be evaluated from H(alpha) emission. The global particle confinement time scales with the line-averaged electron density in small tokamaks, while it decreases with rising electron density in large tokamaks because particle recycling is more localized at the edge. The particle confinement appears to be degraded as heating power increases, like the energy confinement. Other parameter dependences, for example on the ion species, have not been clarified. The database for particle confinement is too limited for designing tokamak reactors.