Changes

* if possible, have the ability to work at all usable energies (not just ~9 GeV of GlueX)

* if possible, have the ability to work at all usable energies (not just ~9 GeV of GlueX)

* motorized, internal, 3-point adjustment to bring the fiber array plane to appropriate alignment with that of the electrons

* motorized, internal, 3-point adjustment to bring the fiber array plane to appropriate alignment with that of the electrons

* plan for SiPM bias and amplifier board alignment to fiber waveguides (out of the electron plane)

* plan for SiPM amplifier board alignment to fiber waveguides (out of the electron plane)

* appropriate room for bending these stiff 2 mm square fibers

* appropriate room for bending these stiff 2 mm square fibers

* pulser assembly for testing the Tagger without beam

* pulser assembly for testing the Tagger without beam

{|

{|

|  [[Image:ParallelRailingConcept.png|370px]]

|  [[Image:ParallelRailingConcept.png|370px]]

|| [[Image:FiberModuleMounting.png]]

|| [[Image:FiberModuleMounting.png]]

|}

|}

A simple dynamic parallel railing system was devised to allow flexibility for the electron crossing angle. In the range of useful photon energies (3-12 GeV) the crossing angle (measured from the focal plane) is calculated to change from 8 to 60 degrees. The adjacent figure illustrates a set of "rails" kept apart by beams parallel to electron trajectory. As shown, this allows for properly positioned mounting sites for both ends of the fiber modules. Additionally, in the high energy photon range (where electrons have low energy and bend significantly) the errors accumulating from keeping the fibers parallel are no longer insignificant. The right-hand side of the parallelogram shown is actually equipped with a slot to allow the lower rail to rotate inward, deviating from this parallel arrangement. It can be shown that the natural alignment of the fiber modules allows a small angular shift from one fiber module to the next, satisfying to the necessary extent the alignment with the electron trajectories.

A simple dynamic parallel railing system was devised to allow flexibility for the electron crossing angle. In the range of useful photon energies (3-12 GeV) the crossing angle (measured from the focal plane) is calculated to change from 8 to 60 degrees. The figures above show plots of crossing angle dependence on electron energy. Diagrams are shown illustrating a set of "rails" kept apart by beams parallel to electron trajectory that allow proper alignment to the crossing angle. Additionally, in the high energy photon range (where electrons have low energy and and show steep angle dependence with energy) the errors accumulating from keeping the fibers parallel are no longer insignificant. The right-hand side of the parallelogram shown is actually equipped with a slot to allow the lower rail to rotate inward, deviating from this parallel arrangement. This allows a small angular shift from one fiber module to the next. The crossing angle plot for low electron energies shown above demonstrates a close match possible between the alignment of the fiber modules and the trajectory of the electrons. Thus the geometry of the rails specifies the alignment of the fiber modules.

Each rail mentioned above consists of two rigid metal strips spaced to allow a standard 4-40 bolt between them. Each module sinks two long 4-40 bolts (3" apart on the module) into the slot of the two corresponding rails. They may be tightened against the rail from below, if desired. Thus the geometry of the rails specifies the alignment of the fiber modules.

Each rail mentioned above consists of two rigid metal strips spaced to allow a standard 4-40 bolt between them. Each module sinks two long 4-40 bolts (3" apart on the module) into the slot created between the two corresponding rails. They may be tightened against the rail from below, if desired.  

Angles as low as 8 degrees require ~60" rails to fit all 100 channels. Rails made out of aluminum (chosen for the ease of machining and to keep the load on the adjustable supports light) will sag significantly compared to the thickness of the fiber, if they are supported on the edges. Optimized positions have been found (roughly 28% of the way from the edge) to minimize the sag. Also, thickening the rail in the direction perpendicular to the ground to the maximum reasonable degree helps significantly (the sag is inverse to the third power of this dimension). Using these methods, the calculated sag has been reduced to about 35 μm. The brackets shown in blue in the above illustration represent the mounting structures to which the motors (described above) are attached.

Angles as low as 8 degrees require ~60" rails to fit all 100 channels. Rails made out of aluminum (chosen for the ease of machining and to keep the load on the adjustable supports light) will sag significantly compared to the thickness of the fiber, if they are supported on the edges. Optimized positions have been found (roughly 28% of the way from the edge) to minimize the sag. Also, thickening the rail in the direction perpendicular to the ground to the maximum reasonable degree helps significantly (the sag is inverse to the third power of this dimension). Using these methods, the calculated sag has been reduced to about 35 μm. The brackets shown in blue in the above illustration represent the mounting structures to which the motors (described above) are attached.