Improvement of High Pressure Drift Tube for Negative Ion Mobility Measurement

Abstract

Negative ion mobility of oxygen molecules in oxygen has been measured by high pressure ion drift tube. The ion drift tube equips a positive corona gap as a negative ion detector. It allows for the measurement under the atmospheric pressure. The ion drift space is varied from 1 to 9 cm using a micrometer attached on a feedthrough of the chamber. The observed mobility decreases against E/p₀ and the tendency becomes remarkable in the shorter ion drift space. This would be caused by the field distortion effect near the mesh electrode. The electric field analysis is performed using a finite element method. It is found that field distortion is found by mesh electrode, separated the ion drift gap and the ion detecting gap. The mesh is changed in to new one of which diameter is 0.05mm. The obtained mobility can be improved and the reduced mobility μ₀^-=2.31±0.03cm²/V·s is obtained.