Primary Collimator Live Page
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Yongguang's Status Report
Qweak Simulation Forum
Keep Out Zones a la Allena
Previous Reports
Virginia Tech Update for Tracking Group,
Unless otherwise stated, all dimensions are in cm, and rates in MHz/octant. You can view a larger version of most plots by clicking on the picture, and get back to this page by using your browser's back button. All of the results shown are with the minitorus OFF and helium as the global volume, unless otherwise stated.
Final Version of Primary Collimator
Having chosen a general shape and trim at the time of the last meeting, the next step was to make a straight sided collimator, and to investigate making the entire "unradiated" profile fit on the chosen size of cerenkov bar (18cm x 2m) at the chosen z location of 570cm. The following is a summary of this process and a description of the final choice and its parameters. The euclid file for this geometry is provided at the primary collimator working group page as well as the ntuples for minitorus on and off in rows 20 and 21. Figure 1 shows the global volume and Figures 2a-c show the upstream cleanup, primary and downstream cleanup collimators.
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Figure 1 - Picture of the global volume from the euclid file. |
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Figure 2a - Upstream cleanup collimator |
Figure 2b - Primary collimator |
Figure 2c - Downstream cleanup collimator |
The chosen version (See previous report) was version 5. It was decided that straight top and bottom edges would be preferable. With the unradiated profile fitting entirely on the bar, the rate decreases by 100 MHz/octant, but the error only increases by .08% (See Table 1). The rate is higher with minitorus off, which will be the status for production running. A preliminary study shows that turning the minitorus on lowers the profile at the focal plane by about 3cm in the radial direction and causes some additional dispersion in the phi direction, leaving the dispersion in the radial direction relatively unaffected (see Figures 3a and b).
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Figure 3a - ep profile at focal plane for minitorus off. |
Figure 3b - ep profile at focal plane for minitorus on. |
Description |
ep rate (MHz) |
inelastic rate (MHz) |
inelastic percentage (%) |
Q2 |
Error on Qpweak |
Moller Rate (kHz/nA) |
version 5, minitorus on |
761 |
.554 |
.073 |
.0285 |
4.18 |
----- |
version 5, straight sides, minitorus on |
798 |
.631 |
.079 |
.0282 |
4.15 |
----- |
version 5, straight sides, minitorus off |
911 |
.665 |
.073 |
.0267 |
4.03 |
---- |
straight sides, unradiated profile fits on bar, minitorus off |
875 |
.364 |
.042 |
.0258 |
4.11 |
2402 |
same as above, minitorus on |
773 |
.365 |
.047 |
.0272 |
4.19 |
38 |
Table 1 - Shows the rates for the progression from version 5 to current collimator.
We are now planning to have the minitorus off during production running following extensive conversations with Dave Mack. The statistical error should have an additional factor of 1.03 because of additional statistical error associated with the cerenkov bar thickness. These errors are reflected in rows 20 and 21 at the primary collimator working group page though not in the tables on this page.
The results with minitorus on (last row in Table 1 and row 21 on primary collimator working group page) are for the highest integral B*dl we can imagine. We are working with vendors to see what we can afford, but the minitorus will likely be slightly smaller. Those investigations will begin in earnest now that the primary collimator is more or less fixed.
In order to fit the unradiated profile on the bar, I plotted the events that hit the bar at the entrance to the primary collimator. I then superimposed the events that hit the focal plane above the bar (See figure 4a). The primary collimator was then trimmed to be below that x value. Figure 4b shows how the unradiated profile fits on the bar. With the radiation turned on, the profile shifts slightly upward, so the bar is in the correct place.
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Figure 4a - ep profile at entrance to primary collimator for accepted (black) and unaccepted (red) events. |
Figure 4b - unradiated ep profile at focal plane fits on the bar. |
In order to test the primary collimator and quartz bar response to beam energy changes or QTOR magnetic field changes, I varied the BFIL factor +/- 1% and used 3 different beam energies, 50 MeV apart. Table 2 gives the rates. The ep profiles for the BFIL changes are shown in Figures 5a and c, with the chosen setting shown in Figure 5b for reference. The profiles for changing the beam energy are shown in Figures 6a-c.
Description |
ep rate (MHz) |
Q2 |
Error on Qpweak |
lower x (cm) |
straight sides, unradiated profile fits on bar |
875 |
.0258 |
4.11 |
313 |
same as row 1, BFIL =.99 |
850 |
.0259 |
4.14 |
313 |
same as row 1, BFIL =1.01 |
889 |
.0257 |
4.09 |
313 |
same as row 1, beam energy = 1065 MeV |
998 |
.0218 |
3.94 |
322 |
same as row 1, beam energy = 1115 MeV |
922 |
.0238 |
4.04 |
317 |
same as row 1, beam energy = 1215 MeV |
793 |
.0276 |
4.25 |
307 |
Table 2 - The rate and error information for testing the primary collimator.
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Figure 5a - ep profile for BFIL =.99 |
Figure 5b - ep profile for BFIL =1.00 |
Figure 5c - ep profile for BFIL =1.01 |
The following plots, corresponding to the last three rows in Table 2, are all made with BFIL = 1. It may be possible to vary the QTOR magnetic field so these profiles fit on the bar in the same place as the nominal bar location. How the focus changes would have to be considered.
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Figure 6a - ep profile for beam energy of 1065 MeV |
Figure 6b - ep profile for beam energy of 1115 MeV |
Figure 6c - ep profile for beam energy of 1215 MeV |
* So we propose that the primary collimator cutout and location (and the cutout and location of the upstream "cleanup" collimator be declared "frozen" at this point). This is a version that Jim Birchall can use to do his sensitivity checks (combined with Dave Mack's quartz detector sizes).
* The mini-torus design will evolve as we discuss things with vendors, but we think it won't affect the primary collimator/upstream collimator.
* The "downstream" cleanup collimator was not carefully thought through. It was simply made bigger than the primary by some amount. This probably needs to be designed carefully in collaboration with the design of the region 3 detector shielding. Volunteers?
* Other issues that probably need simulations to decide (with proposed people to work on them):
* Choice of material, thickness, and "slant" for upstream cleanup collimator. These choices probably effect Region 1 most, so they should probably be the ones to worry about the details of this collimator
* Choice of material, thickness, and "slant" for primary collimator. This collimator is nearest to the region 2 chambers and it is the mini-torus "Moller dump". So Region 2 volunteers to work on the simulations for the final choice for this collimator.
* Choice of material, thickness, and "slant" for downstream cleanup collimator. The group mentioned above needs to think about this.
* Exact choice of beamline,shielding: We had a beamline in the simulation before that was Mark's modification of Neven's original beamline. Mark will take another look at it given the new geometry and Roger's desire to have the "initial scatter" occur as far upstream as possible.
The CAEN VME V767 TDC is performing correctly in simple tests. We'll begin taking data on drift time distributions for the prototype chamber with the goal of having some results for the next teleconference.
