Versatile TV system for PBX‐M plasma control

In advanced tokamak research involving complex magnetic geometries, midplane visible plasma TV images can indicate the need for tokamak control corrections not evident from other diagnostics. Suitable midplane viewports are often unavailable. The PBX‐M plasma TV system uses four tangential midplane vacuum viewports. One tangential vacuum viewport is on a standard re‐entrant midplane port flange. The other three vacuum viewports are tangentially aligned along the inside vessel wall and connected to port flanges 40 cm from the midplane via 60‐cm‐long re‐entrant bellows. Fiber optic bundles transmit images from the re‐entrant viewports through the off‐midplane ports and out to TV cameras positioned beyond the TF coils. The VCR recorded images from each discharge were used to obtain information not available from other diagnostics.