Comparison of plasma density measurements made with a double probe, a resonant cavity technique and an upper hybrid frequency method

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Abstract
Plasma density measurements are reported which were taken simultaneously on a plasma column by three different techniques. The diagnostic methods used were a double-probe method, a resonant microwave cavity technique and an upper hybrid frequency method. The density range covered was 109-1011 cm−3, and the plasmas employed were rf discharges in the lower density range and the positive column of arc discharges in the higher density range, each running in hydrogen, helium, neon or argon gas. It is shown that if sufficient care is taken and corrections are applied reliable results can be obtained. Further, reasonably good agreement (±25%) can be achieved between the three methods under these circumstances.