New method for negative ion diagnostics

Summary form only given. Recently a "test function" for measurements by Langmuir probes was introduced. This function is very sensitive to the body of electron distribution function (EDF), and useful for a plasma whose EDF is Maxwellian or bi-Maxwellian. The ion density can be also obtained from the test function values around the plasma potential. The test function method is an improved one, which was proposed to obtain the two electron group parameters in the bi-Maxwellian plasma. The method can distinguish the high electron energy group from the low one, even if the former is less than 2% that of the later. In this work we present how to use the test function for the negative ion diagnostics. The numerical procedures for processing a Langmuir probe characteristic in negative ion plasmas is established and errors included in this procedure is estimated.