Muon Veto Insert - tube and light guides

This is the tube section which runs the length of the cryostat tail.

The main structure is a moulded fibreglass shell (blue) with internal walls to guide the sample rod (orange) and protect the counters (cyan).

The fibreglass shell has much less thermal expansion than do the Lucite light guides. Therefore, by holding the counters against the end of the shell, the scintillators are held at the proper position over varying temperatures.

Cross-sections (magnified 1.5×) are shown to the right of the main image.

The bottom cross section shows how the light guides (cyan) mate with the scintillators (violet) just above the sample. The five segments of the veto light guide immediately begin bending to assume a more compact arrangement.

The middle cross section shows the arrangement at the location arrowed - where the veto counter light guides finish bending and join to a solid semi-circular light guide. Note that the light guide for the (thin) muon counter extends up the whole tube as a thick strip with beveled corners.

When they get up to the wider barrel section, both light guides spread apart and transform to circles, to facilitate vacuum seals. The veto's light guide, which had been a circle with some cut away, becomes fully circular with a step. The muon counter's guide forms three strips which bend adiabatically to join a circular light guide.