Tony's webpage
Klaus's Status Report
Allena's Status Report
Yongguang's Status Report
Qweak Simulation Forum
Dilution factor notes (Dave Bowman)
Previous Reports
Virginia Tech Update for Tracking Group,
Summary of previous working group:
Please click here for the working group summary
Aluminum Backgrounds:
Dave Mack asked us to look at elastic e-Al events. The distributions from the upstream and downstream
endcaps are shown in Figure 1. The elastic e-Al rate from the two windows totals about 12 MHz.
Figure 1 - This plot shows the distribution of electrons elastically scattered from the downstream (top) and
upstream (bottom) Al target endcaps. The ep elastic peak is shown in the middle for reference.
Primary Collimator Update:
Version
Elastic Rate (MHz)
Inelastic Rate (MHz)
Percent Inelastic (%)
< Q2>
FOM
Reference Design
801
0.212
0.026
0.02994
0.7182
Updated Reference Design
727
.191
.03
.03070
.6858
Increase phi, theta ranges
809
.188
.02
.02996
.7264
Increase phi, theta ranges with crude "detector collimator"
801
.513
.06
.02988
.7152
Klaus discovered that the location of the Region II chambers interfered with the support structure of the main
magnet, so Mark proposed moving the second half of the primary collimator downstream and placing the chambers
between the two halves of the primary collimator. There are several issues that have come up as a result of
this change.
Impact on Region II Chamber Design
- see Chambers Update below
Impact on Primary Collimator Design
- second half moved further downstream
- openings in second half appropriately updated
- certain beamline elements appropriately updated
"Housekeeping" changes needed in the geometry
- two halves of collimator entirely separated
- collimator material goes all the way down to beampipe sheilding
- target endcaps now included in the geometry
- second half of primary collimator has larger phi range than first half
- beamline mother volume large enough to include all beam elements
Table 1 - Comparison of rates with various changes to the reference design.
The target material in the reference design was beryllium. Changing it back to aluminum, along with all of the
changes listed above, and the new elastic ep rate is 727 MHz (See Table 1, second row). By far the largest loss
in rate was due to changing the target cell back to aluminum. The tube around the target cell is 20 mils thick
in the radial direction. Changing the thickness of this tube for either material affects the rate, as shown in
Figure 2. We believe this difference in rate is mostly due to bremsstrahlung in the target tube which alters
the energy enough that the electrons no longer make it into the detector acceptance at the focal plane.
Figure 2a - A plot of rate vs. target tube thicknesses for beryllium and aluminum target cells.
An attempt was made to gain back the lost rate by increasing the theta and phi acceptance of the primary
collimator. The theta acceptance was increased by half a degree at low angles and the phi acceptance was
increased by a degree on both sides. The rate became 809 MHz, but the ep peak at the focal plane now
extended past the end of the detector by about 5 to 10 cm on either side (See Figure 3a). In order to
avoid this, a crude detector collimator was used for the purpose of cutting out those events (See Table 1,
rows 3 and 4, and Figure 3b).
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Figure 3a - Shows ep peak position without detector collimator. |
Figure 3b - Shows ep peak position with detector collimator. |
Chambers Update:
Figure 4a - Current vs. Field Wire Voltage Figure 4b - Efficiency vs. Field Wire Voltage Figure 4c - Singles Rate vs. Field Wire Voltage
We now have a functioning prototype and have set up a cosmic ray test stand. See Drift Chamber Page. We're
in the process of setting up the DAQ, and in the mean time have performed current, efficiency and singles rate
tests on the chambers (See Figures 4a-4c).
We can't finalize our drift chamber sizes until the primary collimator design is fixed, as we already need
larger chambers and may even have to use a trapezoidal shape. We also have had our chamber separation
shortened from half a meter to 40 centimeters.
Future plans:
We need to optimize the primary collimator and return to the optimization of the minitorus
We plan to have arrival time plots for our prototype drift chamber in time for the collaboration meeting to compare
to our GARFIELD results
