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Virginia Tech Update for Tracking Group,
GARFIELD simulations have been used to compare the old and new region II prototypes with the HERMES chamber. Shown below are comparisons of the contour plots of potential, drift lines with isochrones spaced by .02 &mu s, and arrival time distributions. The ratio of our cathode plane spacing to our wire spacing is ~2:1 for both prototypes, and 1:1 for the Hermes chamber. The gas in the simulation was the same, so the only difference is the cell geometry.
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Figure 1a - Contours of V for the old prototype (-1800 C, -1800 F). |
Figure 2a - Contours of V for the new prototype (-1800 C, -1800 F). |
Figure 3a - Contours of V for the Hermes geometry (-1410 C, -1550 F). |
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Figure 1b - Drift lines (yellow) and isochrones (green) for the old prototype. |
Figure 2b - Drift lines (yellow) and isochrones (green) for the new prototype. |
Figure 3b - Drift lines (yellow) and isochrones (green) for the Hermes geometry. |
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Figure 1c - Histogram of arrival times of first electron for the old prototype. |
Figure 2c - Histogram of arrival times of first electron for the new prototype. |
Figure 3C - Histogram of arrival times of first electron for the Hermes geometry. |
We have been able to get the chamber to work at a higher threshold than originally anticipated. Shown below are singles rates and efficiency curves vs. cathode voltage and vs. threshold. It seems that a threshold of 3V and a cathode voltage of 2200V is reasonable.
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Figure 4a - Singles rates vs. cathode voltage (threshold 2.5V). |
Figure 4b - Efficiency vs. cathode voltage (threshold 2.5V). |
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Figure 5a - Singles rates vs. threshold (cathode= 2200V). |
Figure 5b - Efficiency vs. threshold (cathode= 2200V). |
We would like to begin construction on an actual chamber soon. When we started to think about the final design, however, we realized that while we had considered the frame size (Figures 6a and 6b), we hadn't considered that the readout boards and cables would be in the acceptance of the adjacent octants (Figures 7a and 7b). Getting around this (if it is even possible) would take considerable redesign of our readout electronics. We may also possibly require having two different size chambers for the upstream and downstream chambers, which we were hoping to avoid.
The question for the tracking group is, can we accept either having part of the frame (and electronics?) in the acceptance of the adjacent octants? Or is it going to be possible to "plug" the adjacent octants for the calibration runs?
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Figure 6a - Upstream Region II chamber frame with ep peak. |
Figure 6b - Downstream Region II chamber frame with ep peak. |
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Figure 7a - Same as above, but also showing cards. |
Figure 7b - Same as above, but also showing cards. |
