Primary Collimator Live Page
Katherine's Status Report
Tony's Status Report
Klaus's Status Report
Michael's Web Page
Burnham's Web Page
Burnham's collimator pics
Keep Out Zones a la Allena
Previous Reports
The following pages require a username and password:
Qweak elog at JLab
Qweak Simulation Forum
Virginia Tech Update for Tracking Group,
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Watch out for all the spoooooky things happening this month - Friday the 13th and Halloween! Russ and I have a hard time avoiding our black cat, George! |  |
Definitions:
VT collimator - as defined by row 20 at the Primary Collimator Live Page
25cm upstream collimator - same extreme angles as VT collimator, 25cm upstream
extreme upper (lower) angle - the angle from the downstream (upstream) end of the target to the upper (lower) edge of the collimator opening at its upstream face
Collimator simulation/design:
Katherine and I have been working together to figure out how to define the collimator when it is moved 25cm upstream. It turns out that the way I thought the collimators had been defined was not exactly how they were defined, so that led us to question the reasons for the exact collimator definition. Katherine had some confusion about how the angles of the upper and lower edges of the openings should be defined, and the reason is because the angles did not match the explanation I was giving her!
The nominal collimator definition is that the extreme upper and lower angles of the collimator are 11.84° and 5.84° respectively. It also has upper and lower edges parallel to the normal angles. The problem is that this is not actually the case with VT collimator! The angles of the edges of the openings of the collimators was not optimized in any way, and though I thought that this was how I defined them, they really were arbitrary - instead of being something specific and arbitrary.
It was hoped that defining them "properly" might help the backgrounds, but Katherine checked this and it doesn't seem to affect the background coming from the collimator significantly.
So then we decided that there should be a section in the primary collimator report (which hasn't been posted in the Qweak document database yet) to explain what would need to be done to move the collimator or change its thickness, should it need to be done again.
So that brings up some questions:
1) Should we change the collimator definition so that the upper and lower edges actually are parallel to the normal angles? | |
2) Based on the fact that Burnham saw some issues with the definition in SolidWorks, we propose changing the euclid definition to be a TRAP volume. Among other things, this would allow us to more easily define the phi angle of the collimator opening. We propose to start with the opening parallel to the normal rays (yet to be defined) while keeping the extreme rays the same as the current VT collimator. | |
3) Katherine tried to upload things from CVS and it said the location was wrong or something... where are the GEANT3 files being stored? | |
4) Jim and Willie have a new field map. I have downloaded the map, but haven't tested it yet. We were wondering if Jim had a new code for reading it in, and if we could get our hands on it! |
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Figure 1 - Definition of normal (red) and extreme (black) angles for the collimator openings. |
Since we were checking the definitions, Katherine made some plots that show the accepted and actual ep profiles at various locations. We were a little confused because our first guesses for the sizes of the 25cm upstream collimator did not give exactly the same size profile at the location of the downstream face of that collimator. We are still thinking about this, and will update the new section of the report if necessary. Click here to see more details about this.
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Figure 2 - All and accepted elastic electrons at the GEM location with the VT collimator. |
Figure 3 - All and accepted elastic electrons at the GEM location with the 25cm upstream collimator. |
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Figure 4 - All and accepted elastic electrons 25cm upstream with the VT collimator. |
Figure 5 - Accepted elastic electrons 25cm upstream with the 25cm upstream collimator. |
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Figure 6 - Accepted elastic electrons after the VT collimator with the VT collimator. |
Figure 7 - Accepted elastic electrons after the VT collimator with the 25cm upstream collimator. |
Drift chamber:
In the last two weeks we have built new U and V sense planes. They have a new circuit board design with better spacing between HV and ground. They were tested up to 1900V in a test box prior to being assembled into a chamber. The chamber was assembled and leak checked with Helium. It has an X,U,V,X wire plane configuration. This week we flushed it with 88%Argon, 10% CO2 and 2% CH4 and ran a simple efficiency curve on one plane as we did before. It looks good. The current is low ~100nA/plane and the efficiency looks good >98% with 1800V on both field wires and cathode planes. All four planes are at operating voltage and we are proceeding to the next step of reading out all four planes with the TDCs.
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Figure 8 - A picture of the current setup with the improved mechanical and electrical supports. |
