Test of a visible/near-ultraviolet transmitting, coherent fiber-optic bundle for ultrahigh-vacuum applications

A visible/near-ultraviolet transmitting, coherent fiber-optic bundle designed for vacuum applications was tested for vacuum compatibility under ultrahigh vacuum conditions at temperatures up to 310 °C. This development was motivated by the need to view the light emitted by neutrals recycling in the throats of large pump limiters, such as the Advanced Limiter Test-II (ALT-II) and the Tore Supra outboard limiter, without access to a direct, unobstructed optical view from an external port at the back end of the limiter. The temperature inside the pump limiter chamber is typically high (—250 to 300 °C), and the outgassing rate of the fiber-optic bundle must remain low at these temperatures. The fiber bundle that was tested was built as a prototype for a bundle to be eventually used in a pump limiter and is now installed in the pumping duct of the ALT-II pump limiter on TEXTOR. The bundle was designed to be coherent to allow the possibility of imaging a region of the limiter throat onto a spatially resolving instrument.