Edge temperature and density measurements by helium line intensity ratios in the reversed field experiment RFX with high time resolution

In the reversed field experiment the electron temperature and density at th e edge are measured from the intensity ratio of selected lines emitted by a n atomic helium beam injected into the plasma. Helium is injected through a single microtube 30 mm long and with 150 mum of internal diameter. Four be am splitters allow three interference filters, coupled to linear array came ras or alternatively to photomultipliers, and a charge coupled device camer a to observe the same beam volume. The application of photomultipliers as d etectors has recently increased the time resolution of the diagnostic. This allows following the time evolution of edge density and temperature during nonstationary processes. Moreover, the enhanced time resolution increases the capability of the diagnostic to measure the edge electron temperature a nd density fluctuations, which are relevant to the edge electrostatic trans port studies. (C) 2001 American Institute of Physics.