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Moving the Tagger Microscope (view source)
Revision as of 14:30, 30 March 2021
, 14:30, 30 March 2021→Calculating Position of Each Bundle Support Mounting Rod
<ul>
<ul>
<li>Select a starting energy for the photon tagging array (highest γ energy to tag)</li>
<li>Select a starting energy for the photon tagging array (highest γ energy to tag)</li>
[[Image:Bundle_support_displacement.jpg|right|thumb|400px|Figure : Sketch showing the X-displacement along the focal plane (Δx) from the center of the first fiber column to the center of the sixth fiber column of the first bundle support.]]
<li>Using [https://halldweb.jlab.org/wiki/images/b/b6/Counterbounds2017%28b%29.xlsx hodoscope energy bin bounds] interpolate the crossing angle with respect to the focal plane (β<sub>1</sub>) of an electron associated the highest energy to be tagged (starting E<sub>γ</sub>)</li>
<li>Using [https://halldweb.jlab.org/wiki/images/b/b6/Counterbounds2017%28b%29.xlsx hodoscope energy bin bounds] interpolate the crossing angle with respect to the focal plane (β<sub>1</sub>) of an electron associated the highest energy to be tagged (starting E<sub>γ</sub>)</li>
<ul>
<ul>
<li> These electrons will pass through the center of the first column of SciFi fibers</li>
<li> These electrons will pass through the center of the first column of SciFi fibers</li>
</ul>
</ul>
<li>Using β<sub>1</sub> calculate the X-displacement along the focal plane (Δx) from the center of the first fiber column to the center of the sixth fiber column of the first bundle support</li>
<li>Using β<sub>1</sub> calculate the X-displacement along the focal plane (Δx) from the center of the first fiber column to the center of the sixth fiber column of the first bundle support</li>
<ul>
<ul>
The 5x6 fiber bundle supports were designed with two 5x3 bundle halves offset such that the center of the front face of the middle column in each bundle half would sit on the magnetic focal plane for a β angle of 12.0<sup>o</sup>. This angle was selected as a compromise that would allow coverage through the photon energy range of 10 - 5.6 GeV. <i><u>As a side note</u> - If required and finances permit, the 17 bundle supports can be easily redesigned for a different β angle. This redesign would take less than an hour of CAD work, with a manufacturing turn-around time in as little as two days. Costs are estimated to be around $2k. A CAD drawing of a new bundle support design already exists, which incorporates updated locations of the threaded holes for mounting the clamps that keep the bundle straps in place. The best time to replace/modify the bundle supports, if so desired, would be during fiber replacement. This way the new fibers can be mounted to the new bundle support outside the tagger hall, before ever making it to JLab. A conservative time estimate for changing the TAGM fiber configuration would be approximately two days (16 hours).</i>
The 5x6 fiber bundle supports were designed with two 5x3 bundle halves offset such that the center of the front face of the middle column in each bundle half would sit on the magnetic focal plane for a β angle of 12.0<sup>o</sup>. This angle was selected as a compromise that would allow coverage through the photon energy range of 10 - 5.6 GeV. <i><u>As a side note</u> - If required and finances permit, the 17 bundle supports can be easily redesigned for a different β angle. This redesign would take less than an hour of CAD work, with a manufacturing turn-around time in as little as two days. Costs are estimated to be around $2k. A CAD drawing of a new bundle support design already exists, which incorporates updated locations of the threaded holes for mounting the clamps that keep the bundle straps in place. The best time to replace/modify the bundle supports, if so desired, would be during fiber replacement. This way the new fibers can be mounted to the new bundle support outside the tagger hall, before ever making it to JLab. A conservative time estimate for changing the TAGM fiber configuration would be approximately two days (16 hours).</i>
Each bundle has a "pivot point" that when placed on the focal plane, provides the optimal y-displacement from the focal plane for each fiber column in that bundle. If the bundle β angle ≠ 12<sup>o</sup>, then the 1<sup><u>st</u></sup> & 6<sup><u>th</u></sup>, 2<sup><u>nd</u></sup> & 5<sup><u>th</u></sup>, and 3<sup><u>rd</u></sup> & 4<sup><u>th</u></sup> fiber columns will have the same magnitude offset from the focal plane in Y, but with opposite signs. This is all provided that when the bundle support is mounted on the parallel railing system the tagger magnet's focal plane passes through the midpoint between the front and rear bundle halves (the so called pivot point).
Each bundle has a "pivot point" that when placed on the focal plane, provides the optimal y-displacement from the focal plane for each fiber column in that bundle without encroaching too close to the tagger magnet window. If the bundle β angle ≠ 12<sup>o</sup>, then the 1<sup><u>st</u></sup> & 6<sup><u>th</u></sup>, 2<sup><u>nd</u></sup> & 5<sup><u>th</u></sup>, and 3<sup><u>rd</u></sup> & 4<sup><u>th</u></sup> fiber column pairs will have the same magnitude offset as one another from the focal plane in Y, but with opposite signs, see Figure ???. This is all provided that when the bundle support is mounted on the parallel railing system the tagger magnet's focal plane passes through the midpoint between the front and rear bundle halves (the so called pivot point).
[[Image:popsicle_stick_fiber_angle_top_view.png|center|thumb|800px|Figure : Sketch showing the "pivot point" that should always sit on the focal plane to provide the optimal fiber alignment. The green line running through the pivot point represent the placement of the focal plane for a bundle support with β = 12<sup>o</sup>, while the red line shows the placement for β > 12<sup>o</sup>.]]
As shown in Figure ??? by the red and green lines, if β ≠ 12<sup>o</sup> then the front face of the first column of SciFi no longer sits on the focal plane. This offset must be accounted for. The Excel spreadsheet starts by finding the optimal first bundle support crossing angle (β<sub>avg</sub>) and places the front center of the first column of SciFi on the X<sub>FP</sub> location corresponding to E<sub>γ<sub>o</sub></sub>. Depending on β's departure from 12<sup>o</sup> the pivot point will be displaced from the focal plane. The spreadsheet calculates the (Δx, Δy) needed to return the pivot point to the focal plane and keep the first fiber column's longitudinal axis on the E<sub>γ<sub>o</sub></sub> electron's path. The spreadsheet's title for this is "Pivot Point Move" and the description is detailed below.
<i><u>NOTE:</u> &beta<sub>avg</sub> is used to determine this displacement. While the E<sub>γ<sub>o</sub></sub> electron's β angle differs slightly &beta<sub>avg</sub> and would keep the column's centerline on the proper electron path, this discrepancy is so small that it does not come close to the TAGM machining parts' tolerance. Additionally, the sixth column's β angle has the same magnitude difference from the bundle support's β, but with a different sign. For these reasons β<sub>avg</sub> was used.</i>
<gallery caption="Pivot Point Move for β ≠ 12<sup>o</sup>" widths="300px" heights="300px" class="center">
popsicle_stick_pivot_point.png|Figure ???: Dimensions of the pivot point to the front center of the first column of fibers. The three 2 mm<sup>2</sup> boxes at the end of each 5x3 bundle half are <i>only</i> included to represent the width of a fiber column and have no meaning in length in the longitudinal axis direction.
popsicle_stick_fiber_angle9.png|Figure ???: Dimensions of the pivot point to the front center of the first column of fibers. The three 2 mm<sup>2</sup> boxes at the end of each 5x3 bundle half are <i>only</i> included to represent the width of a fiber column and have no meaning in length in the longitudinal axis direction.
popsicle_stick_inch_angle.png|Figure ???: Dimensions of the bundle support as viewed from below. This view shows the location of the bundle support mounting rods at 2.75 in. and 8 in. from the front of the bundle support.
popsicle_stick_fiber_angle8.png|Figure ???: Dimensions of the pivot point to the front center of the first column of fibers. The three 2 mm<sup>2</sup> boxes at the 5x3 bundle half are <i>only</i> included to represent the width of a fiber column and have no meaning in length in the longitudinal axis direction.
</gallery>
[[Image:Bundle_support_FP_shift.jpg|center|thumb|600px|Figure : Sketch showing the displacement needed to move the "pivot point" to the focal plane for β ≠ 12<sup>o</sup>, while maintaining the first fiber column on the E<sub>γ<sub>o</sub></sub> electron's path.]]
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