Prototype Construction

The prototype electromagnetic calorimeter is a lead+scintillator sampling calorimeter, having a sampling fraction of 6.5%. Its construction is similar to an earlier design of the full endcap electromagnetic calorimeter (EEMC) and shower-maximum detector that will be built for the STAR detector.

The calorimeter is constructed as a 24-layer stack consisting of

5-mm thick lead sheets produced by Vulcan lead.

4-mm thick scintillator sheets (Kuraray SCSN-81).

The first two layers of the stack differ from the others in that 5-mm thick scintillator is used, allowing their future use as a ‘preshower’ detector. In the top view of the calorimeter below, the red hatched layers are lead and the black hatched layers are scintillator. The first layer in the stack is a lead converter sheet. The beam enters the calorimeter from the bottom. Following the sixth layer of lead, two planes of triangular cross section scintillator strips were used as a shower-maximum detector (SMD). In the SMD, there were 60 vertical strips to measure the transverse shower profile in the horizontal direction and 100 horizontal strips to measure the transverse shower profile in the vertical direction.

In the drawing above, the dimensions shown are in inches.

The scintillator sheets within the calorimeter were machined into ‘megatiles’. Optical isolation grooves were machined into a single scintillator layer and were then filled with titanium dioxide loaded epoxy. Following curing of the epoxy, ‘sigma grooves’ were machined into the scintillator to allow the insertion of 0.83-mm (Y11 doped) wavelength shifting (WLS) optical fibers produced by Kuraray. Each layer had 12 tiles machined into it, in a 3 x 4 pattern resembling the inner radius of an earlier design of the STAR endcap electromagnetic calorimeter. The 24 scintillator sheets thereby defined twelve projective calorimeter towers.

An optical connection was made, use a ten-fiber optical connector produced by DDK Electronics, at the wall of the light-tight box housing the megatiles. The optical connection is between the WLS fibers, collecting scintillation light from the individual tower tiles, and clear optical fibers, used to carry the light to a photomultiplier tube box. Optical fibers from the 24 layers associated with a given tower were then coupled to a single Burle 83101 photomultiplier tube. There was one Burle 83101 for each of the calorimeter towers (12 total).

The primary objective of the prototype construction was to test the operation of a shower-maximum detector. That detector consists of two planes of triangular cross section scintillator strips, formed by extrusion, with a centered hole into which a WLS optical fiber is inserted for light collection. The strips have a transverse profile approximating an equilateral triangle, with an apex-to-base height of 0.5 cm. The individual triangular strips are wrapped by 50 microns of aluminized mylar to optically isolate them from their neighbors. This design for theSMD follows closely the original design of the segmented preshower detector under construction by the D0 group. The wrapped scintillator strips are then epoxied between two G-10 sheets to form two planes. The first plane in the stack consists of 100 horizontal strips (y plane), followed by the second plane constructed of 60 vertical strips (x plane).

The WLS optical fibers collecting light from the SMD scintillator strips are then connected to clear fibers. The clear fibers transport the scintillation light from the 160 fibers onto individual pixels of ten Hamamatsu 6568 multi-anode photomultiplier tubes (MAPMT). Each MAPMT has 16 pixels to which the clear optical fibers are coupled. A front view showing a megatile layer and an overlay of the WLS fiber layout for the shower maximum detector is shown below.

The units shown in the above drawing are in inches.

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L.C. Bland (IUCF), for the T-438 collaboration

Last revised: 31 October 1999