Defined the 15 cm thick Pb primary collimator using the proper description, so this is different from the dimensoins given in Paulo's latest drawing (sent out 20-sept). Took out minitorus (no longer use) and QTOR supports (temporarily unsure about position). Geometries:
So we have the following plots of the accepted electrons at the upstream and downstream face of the collimator where the red outlines the aperture of the that face. (Upstream on left, Downstream on right.)
- v0: This is the starting point
- v5: v0 changed in the following ways:
-Changed the "top sides" to be parallel, before they had a .5 degree tilt out. Width equal to the original width at the intersection between top and bottom sides.
-Changed the upstream opening so that the top (bottom) is 0.26 cm higher (lower) to allow for machining tolerances.
-Redefined the volume defining the bottom side as a GEANT trap: changed the downstream side so that the downstream lower edge is ~0.25 cm less and changed the upstream side so that the upstream lower edge is 0.26 cm larger so that the downstream face defines the acceptance.
For "v0": we can see that there is a gap at the lower bottom side on the downstream edge:
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Add to After making the stated changes to "v5" we see that the downstream aperture is completely filled so that it now defines the acceptance:
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Table 1: Comparing Rate, Q2, Error for geometries
| Rate | Q2 | Error | |
| v0 | 795.244 | 0.025907 | 4.309 |
| v5 | 801.326 | 0.025907 | 4.298 |
Table 2: Comparing backgrounds (weighted properly) for geometries
| Elastic Photons | Elastic Photons from coll. region | Inelastic Photons | Inelastic Electrons | Moller Photons | Moller Electrons | |
| v0 | 0.14460 +/- 0.00467 | 0.00819 +/- 0.00079 | 0.00971 +/- 0.00042 | 0.09186 +/- 0.00279 | 0.18861 +/- 0.01117 | 0.62727 +/- 0.02893 |
| v5 | 0.14108 +/- 0.00471 | 0.00611 +/- 0.00060 | 0.01094 +/- 0.00045 | 0.09860 +/- 0.00291 | 0.20002 +/- 0.01161 | 0.76878 +/- 0.03401 |
Conclusion: We see very little effect from changing the primary (coll. 2) so that the downstream face defines the acceptance.
Geometry says it is there (email from Roger 24-oct)- but we don't see it to the same level in the simulation. And there is no effect on Rate, < Q^2 >, or Figure of Merit when going from the nominal 4x4 mm beam to a 9x9 mm beam. We used the most up to date geometry file (v5 primary collimator) to consider beam sizes from 4x4 mm to 9x9 mm. Considered octant 1 and octant 2. We also plotted the XY distribution of accepted electrons at the upstream and downstream face of collimator 1 and collimator 2. Collimator 1 was removed from the geometry so that at no time would it become defining.
Table 1: Comparing Rate, Q2, Error for different beam sizes
| Octant 1 | Octant 2 | ||||||||
| size | Rate | Q2 | Error | size | Rate | Q2 | Error | ||
| 4x4 | 798.466 | 0.025854 | 4.306 | 4x4 | 800.251 | 0.025783 | 4.308 | ||
| 5x5 | 796.518 | 0.025944 | 4.303 | 5x5 | 796.828 | 0.025877 | 4.307 | ||
| 6x6 | 795.686 | 0.025876 | 4.309 | 6x6 | 800.057 | 0.025907 | 4.299 | ||
| 7x7 | 797.636 | 0.025859 | 4.307 | 7x7 | 799.958 | 0.025820 | 4.305 | ||
| 8x8 | 802.759 | 0.025938 | 4.294 | 8x8 | 801.790 | 0.025847 | 4.301 | ||
| 9x9 | 799.799 | 0.025859 | 4.303 | 9x9 | 795.307 | 0.025848 | 4.311 |
The plots show that there is no effect on the Q^2 distribution:
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Below are the XY profiles of electrons at the upstream face of collimator 1, where there is possible interference. Shown is for a 9x9 mm beam. To see all the plots go to this page.
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Below is an image showing the original aperture (red) and the aperture of Paulo's newly shaped collimator 1 (black) at the upstream (Z=-583.41 cm) and downstream (Z = -568.17 cm) face.
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And finally the XY distribution with Paulo's collimator design superimposed.
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