Primary Collimator Live Page
Tony's Status Report
Klaus's Status Report
Michael's Status Report
Yongguang's Status Report
Jim's Status Report
Qweak Simulation Forum
Keep Out Zones a la Allena
Previous Reports
Virginia Tech Update for Tracking Group,
There are now ep profiles available for download at the primary collimator optimization page. The z locations are spaced 18cm apart starting at the end of the target and going to 700cm after the center of QTOR. I plotted the events accepted on the quartz bar and chose the points of the corners. Those points are placed in a data file at the same location as the pictures which show the outline given by the chosen points. Figures 1a and b show the difference between the profiles for the accepted events and that for all of the events making it through the primary collimator. We are recommending simulations to check the rates on the affected QTOR supports.
A primary collimator technical report is now in the works.
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Figure 1a - An ep profile close to the end of QTOR for events accepted on the quartz bar. |
Figure 1b - An ep profile close to the end of QTOR for all events. |
The VME DAQ system to take drift time data with the prototype HDC is working. First results are shown in Figure 2a for the drift time distribution for one of the wires for an input distribution of cosmic rays defined by scintillators in a cone that is roughly ± 7 degrees about the normal to the chamber. The high voltages were -1500 V for the field wires and -2000 V for the cathode plane. The gas is 90% Ar, 10% CO_2; we are using this because we want something non-flammable for now. The drift cell size is 1.2 cm, so we expect a maximum drift time of about 120 nsec under these conditions. For comparison, see Figure 2b from the Garfield simulation generated under similar conditions. Our experimental data doesn't look like it should. We are just getting started, so we haven't yet ruled out the fact that we may be doing something simple incorrectly. Currently, we are trying different chamber voltages to see if the observed distribution changes.
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Figure 2a - Experimental drift time histogram for prototype chamber (100pF). |
Figure 2b - GARFIELD drift time histogram for similar chamber. |
We originally put a 1000pF capacitor on the nanometrics card to get rid of the high frequency noise that we couldn't seem to get rid of any other way. Unfortunately, as shown in Figures 2 a,b above, we got a drift time distribution which still doesn't match GARFIELD simulation. In order to investigate the effects of the capacitor, we tried 3 additional values of capacitor, 100pF, 10pF and 1.5pF. The results are shown in Figures 3a-d. We plot the drift time distribution for one wire, number 17. There seems to be some long drift time events that we can resolve more clearly as we decrease the capacitance. The distribution in the 0-200 range, however, more closely approximates the expected distribution as suggested by GARFIELD.
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Figure 3a - Experimental drift time histogram with 1000pF capacitor. |
Figure 3b - Experimental drift time histogram with 100pF capacitor. |
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Figure 3c - Experimental drift time histogram with 10pF capacitor. |
Figure 3d - Experimental drift time histogram with 1.5pF capacitor. |
We have tried two different field wire voltages with the 10pF capacitor so far. See Figures 4a,b.
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Figure 4a - Experimental drift time histogram with 10pF, -1700V. |
Figure 4b - Experimental drift time histogram with 10pF, -1500V. |
Norm has also decided on a Region II chamber size based on the new ep profiles for the semi-finalized primary collimator acceptance. The chambers will be the same size, so we looked at the back face of the second chamber, and with what we hope is a reasonable buffer around the profile, the chosen chamber size is a rectangle approximately 30cmx45cm. The "buffer" that we chose is 2cm on each side.
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Figure 5 - The new design for the Region II chambers based on the new ep profiles. |
