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Line 38: − + + + + + + + + + + − 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
Tagger Microscope Mechanical Design (view source)
Revision as of 01:19, 27 August 2008
, 01:19, 27 August 2008no edit summary
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 and deviating from this parallel arrangement. It can be shown that the natural alignment of the fiber modules contains 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 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 and deviating from this parallel arrangement. It can be shown that the natural alignment of the fiber modules contains allows a small angular shift from one fiber module to the next, satisfying to the necessary extent the alignment with the electron trajectories.
Each rail mentioned above consists of two rigid metal strip 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 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.
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.
== Coupling Waveguide to Photo-sensor ==
[[Image:Chimney-AmpBoard.png|left|315px]]
In the current design, each fiber module (containing an array a square bundle of 25 fibers) is paired with a detector PCB (referred to here as "analog" or "amplifier" card to distinguish from digital control electronics separately under design.) These circuit boards attach to female card-edge connectors on the ceiling of the tagger enclosure. The 32 photo-sensors (SiPMs) form a row along the bottom edge of the card with amplifier and summing circuitry occupying the rest of it. This arrangement allows easy access for the fibers without interfering with the neighboring cards. A 32 "chimney" array block allows for prices alignment of the fiber waveguides to their SiPMs. This is essentially a plastic block with square channels which hold the fibers. This block is with respect to the amplifier board via holes in the card itself and in the tagger enclosure frame.