Special Diagnostic Devices

In contrast to plasma diagnostic probes having linear motion only, recent years have seen an increase in the number of special diagnostic devices having multiple degrees of freedom. In addition, the single custom-built probe tip has gradually yielded to the concept of mounting several pre-set probe tips on "plug-in" type probe holders. Several of the special diagnostic devices, designed to solve particular positioning and measurement problems, are described and illustrated. In particular, the problems associated with achieving the various mechanical movements within a vacuum, and the methods employed in controlling the coaxial conductors from the probe tip to the vacuum feedthrough are discussed.