Radial Retarding Grid (or Field) Energy Analyzer (RGEA)
This probe is designed to be inserted into a plasma and measure the energy of ions in the plasma. It is a variation on the classic "Langmuir Probe". The screeens are set at alternating positive and negative potentials, so as to filter out all electrons and any ions of energies (measured in eV) less than the voltage of the positive screen. The copper plate on the right is the "Faraday" plate, which is what actually measures the current produced by the collected ions.
The little amber pieces are Kapton insulators to keep the various screens from shorting to oneanother. This probe was less than 1/8 the size of previous probed used in the apparatus, minimizing its possible perturbation to the plasma structure. That said, it resulted in an extremely difficult probe to assemble.
The screens are 316 stainless steel, and spot-welded to 316-stainless steel back plates. Copper wire is spot-welded to the back plates. Since the probes live in high-vacuum, aluminum and brass were avoided for their tendencies to outgass. Since the probes are being used in a plasma lab with strong magnetic fields, no ferrous material could be used in their construction. hence the 316 stainless steel everywhere.
"Steerable" RGEA
This RGEA is identical in theory to the RGEA above, but points in a different direction in the plasma. It was also very difficult to assemble.
Assembled RGEAs
Shown is a picture of the assembled RGEAs, with the wrench used for disassembly and a ruler, extra screen/backplate and insulator for scale.
The little hole is where plasma is admitted to the steerable RGEA. The entrance hole for the radial RGEA is not visible.
Below is a .zip of the rough CAD files of the RGEAs from which the probes were built. The files are in Solidworks 2005 files.