A Facility to Produce Uniform Space Charge for Evaluating ION Measuring Instruments

A low-speed wind tunnel containing space charge has been constructed and evaluated. The facility is used for testing the performance of ion counters and net space charge measuring devices. For different operating conditions, space charge densities in the test volume range from 2.5-5.7 x 10-8 C/m3. The space charge density is spatially uniform within 5% over more than than 900) of the cross sectional area of the test volume, but decreases by approximately 20% between two positions separated by 1 m. Ion densities achieved in this system are comparable to those found near high-voltage dc transmission lines but are free from the accompanying large electric fields.