Changes

=UNDER CONSTRUCTION=

=UNDER CONSTRUCTION=

==Tagger Microscope Placement in the Tagger Hall==

=Tagger Microscope Placement in the Tagger Hall=

When discussing the location of the Tagger Microscope (TAGM) within the Tagger Hall it is often easiest to reference the starting point of the energy spectrum being tagged. For example, if the TAGM is said to be placed at 9.2 GeV this would indicate that the location of the most upstream column of fibers, with respect to the beamline, is such that a post-bremsstrahlung electron associated with a 9.2 GeV emitted photon will pass through the longitudinal axis of this column of scintillating fibers (SciFi). This column is referenced as column #1 in Figure 1 below. As the column numbers increase the electrons' energy increases, and as such the energy of the associated photon being tagged decreases.  

When discussing the location of the Tagger Microscope (TAGM) within the Tagger Hall it is often easiest to reference the starting point of the energy spectrum being tagged. For example, if the TAGM is said to be placed at 9.2 GeV this would indicate that the location of the most upstream column of fibers, with respect to the beamline, is such that a post-bremsstrahlung electron associated with a 9.2 GeV emitted photon will pass through the longitudinal axis of this column of scintillating fibers (SciFi). This column is referenced as column #1 in Figure 1 below. As the column numbers increase the electrons' energy increases, and as such the energy of the associated photon being tagged decreases.  

The ideal configuration of the each fiber column would allow the center of the front face of the fibers to sit on the focal plane, as shown in Figure 2. Unfortunately, this configuration does not permit sufficient space to provide a method for holding the fibers in place, and during the prototyping phase testing showed that gluing the fibers to the bundle support was not an option due to unacceptable light loss. A 5x5 configuration per bundle was used during prototyping, but unfortunately having 25 silicon photomultipliers (SiPM) per preamplifier board led to too much electronic cross-talk and the likelihood of optical cross-talk due to limited spacing between SiPM. Using a bundle support with 6 or more columns side-by-side, as in Figure 3, extends the fibers too far past the focal plane in the y-direction. Bundle supports with smaller fiber array configurations have too narrow of a base and could lead to improper alignment of the fibers due to the instability of the bundle support on the mounting rails. A compromise was reached by designing a bundle support with 30 fibers (5x6 array), which was split into two 5x3 fiber arrays (forward and rear bundle halves) offset to one another. This configuration shown in Figure 4 limits the fibers' intrusion past the focal plane (± Y_FP) and reduces the number of SiPM to 15 per pramplifier board by using one board per bundle half. The offset of the bundle halves is such that when placed at a β = 12^o the focal plane will pass through the center face of the center fiber in each bundle half.  

The ideal configuration of the each fiber column would allow the center of the front face of the fibers to sit on the focal plane, as shown in Figure 2. Unfortunately, this configuration does not permit sufficient space to provide a method for holding the fibers in place other than gluing. During the prototyping phase testing showed that gluing the fibers to the bundle support was not a viable option due to unacceptable light loss, not to mention the difficult that would arise when trying to replace fibers. A 5x5 fiber configuration per bundle was used for the prototype, which was optically linked to a single preamplifier board. Unfortunately, having 25 silicon photomultipliers (SiPM) per preamplifier board led to too much electronic cross-talk and the likelihood of optical cross-talk between channels due to limited spacing between SiPM. Bundle supports with smaller fiber array configurations have too narrow of a base and could lead to improper alignment of the fibers due to the instability of the bundle support on the mounting rails. While using a bundle support with 6 or more columns side-by-side, as in Figure 3, extends the fibers too far past the focal plane in the y-direction.  A compromise was reached by designing a bundle support with 30 fibers (5x6 array), which was split into two 5x3 fiber arrays (forward and rear bundle halves) offset to one another. This configuration shown in Figure 4 limits the fibers' intrusion past the focal plane (± Y_FP) and reduces the number of SiPM to 15 per preamplifier board by using one board per bundle half. The offset of the bundle halves is such that when placed at a β = 12^o the focal plane will pass through the center face of the center fiber in each bundle half.