Rub-A-Dub-Dub, ICON EUV gets a scrub

In preparation for launch, the ICON EUV instrument recently went through a week long "scrub" activity at the Orbital ATK facility in Gilbert, Arizona. The detector in EUV is a microchannel plate (MCP), and the millions of tiny tubes in the MCP can develop different characteristics during all the testing done on the ground, and overall become less effective. The scrub involves running the detector at high voltage while it is illuminated by a bright EUV light source, which cleans off any molecules that weren’t there at the start of all that testing. When done for a sufficient amount of time (a week, in this case), the detector develops a more uniform and stable amplification, just like when it was new. It’s like a drink from the fountain of youth for the MCP.

This photo of ICON provides a nice view of the instrument suite and shows the scrub light source and vacuum plumbing. There are many reasons for the vacuum system, the first three being:

• Air is opaque to the EUV light used to illuminate the light source.
• Air, mainly nitrogen molecules, is what you are trying to scrub off the MCP in the first place.
• Air, under the high voltage that will be applied to the detector during scrub and in space, breaks down and ionizes, allowing lightning to form. It will come as no surprise to know we don't want lightning on our detector!

[contributed by Will Marchant]