Study of structural effects of Langmuir probe array on edge fluctuation measurement in the compact helical system heliotron/torsatron

A new type of Langmuir probe array is installed on the compact helical syst em heliotron/torsatron for the study of edge plasma turbulence. The probe a rray consists of four sets of the standard triple probes which are composed by four electrodes. Each triple probe set is slightly displaced both in th e toroidal and poloidal directions to minimize the shadow effects among the se probe sets. In order to investigate the structural effects of Langmuir p robe arrays, the results obtained by this new probe array are compared with the results previously obtained by the old probe array where the triple pr obe sets were displaced only in the poloidal direction from each other. Sta tionary plasma parameters near the plasma edge such as electron temperature , density, and plasma potential were consistently obtained by two probe arr ays. However, the new probe array displaced toroidally is more reliable to measure the particle flux induced by fluctuations where accurate measuremen t of the poloidal electric field fluctuations is required, compared with th e old probe array. (C) 2001 American Institute of Physics.