Changes

Moving the TAGM to a new energy range not only involves the physical relocation of the microscope and its shielding along the tagger magnet's focal plane, but also requires internal realignment of the fiber, which is the subject of this page. The realignment of the scintillating fibers' longitudinal axes requires all 17 bundle supports to have new, individual crossing angles (β angle) with respect to the focal plane. These angles are derived from a table generated based on a TOSCA map of the post-bremsstrahlung electrons' crossing angles as they pass through the magnet's focal plane. Since the crossing angle changes with energy (e.g. displacement along the focal plane) each bundle support will have a slight "kick" or "tow" from the adjacent bundle support. The tow is typically on the order of 0.1^o.

Moving the TAGM to a new energy range not only involves the physical relocation of the microscope and its shielding along the tagger magnet's focal plane, but also requires internal realignment of the fiber, which is the subject of this page. The realignment of the scintillating fibers' longitudinal axes requires all 17 bundle supports to have new, individual crossing angles (β angle) with respect to the focal plane. These angles are derived from a table generated based on a TOSCA map of the post-bremsstrahlung electrons' crossing angles as they pass through the magnet's focal plane. Since the crossing angle changes with energy (e.g. displacement along the focal plane) each bundle support will have a slight "kick" or "tow" from the adjacent bundle support. The tow is typically on the order of 0.1^o.

Since the bundle supports have varying β angles, the parallel railing system that holds these supports in place are no longer representative of their namesake. That is, the front and rear rails of the parallel railing system are not parallel to each other and have a pitch with respect to one another. Figure 7 is a pictorial explanation of this and shows that for two equal length rails (front & rear), the length of the upstream and downstream alignment bars differ by 0.039 ± 0.001 in. at a starting photon energy (E_γ) with a required tow of 0.09^o between bundle supports. For each individual photon energy range covered by the microscope, or more simply stated for each energy that the microscope starts at, a new pitch for the parallel rails must be determined and three components (upstream alignment bar, downstream alignment bar, and upstream guide plate) unique to that starting energy must be fabricated. For this reason CAD drawings, an Excel spreadsheet, and this wiki page were created to provide the information needed to realign and move the TAGM to the following starting photon energies: 11, 10, 9, 8, 7, 6.5, 6, 5.5, and 5 GeV. The turnaround time for the machining components is typically two to five days, while the realignment of fibers will take no more than two days with inexperienced workers, and that's being conservative.

Since the bundle supports have varying β angles, the parallel railing system that holds these supports in place are no longer representative of their namesake. That is, the front and rear rails of the parallel railing system are not parallel to each other and have a pitch with respect to one another. Figure 7 is a pictorial explanation of this and shows that for two equal length rails (front & rear), the length of the upstream and downstream alignment bars differ by 0.039 ± 0.001 in. at a starting photon energy (E_γ) with a required tow of 0.09^o between bundle supports. For each individual photon energy range covered by the microscope, or more simply stated for each energy that the microscope starts at, a new pitch for the parallel rails must be determined and three components (upstream alignment bar, downstream alignment bar, and upstream guide plate) unique to that starting energy must be fabricated. For this reason CAD drawings, an Excel spreadsheet, and this wiki page were created to provide the information needed to realign and move the TAGM to any starting photon energy between 11 and 5 GeV. The turnaround time for the machining components is typically five to seven days, while the realignment of fibers will take no more than two days with inexperienced workers.

[[Image:Beta-Angle-Explanation-White.png|center|thumb|1000px|Figure 7: Pictorial representation of the alignment of the front and rear rails of the parallel railing system, which supports and aligns the optical fiber bundle supports along the tagger magnet's focal plane. The red circles represent the locations of the support rods that extend below the bundle supports and are used to secure them to the railings. This representative image was created from a 3D CAD drawing of the microscope which has a precision of ± 0.001 in.]]

[[Image:Beta-Angle-Explanation-White.png|center|thumb|1000px|Figure 7: Pictorial representation of the alignment of the front and rear rails of the parallel railing system, which supports and aligns the optical fiber bundle supports along the tagger magnet's focal plane. The red circles represent the locations of the support rods that extend below the bundle supports and are used to secure them to the railings. This representative image was created from a 3D CAD drawing of the microscope which has a precision of ± 0.001 in.]]