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Re: CDC Endplate Design
Hi Curtis,
Out of curiosity, would shortening the CDC by 5 or 10 cm remove the
overlaps and allow us to keep the 28 layers?
Regards,
-David
Curtis A. Meyer wrote:
> Dear Trackers -
>
> Tim and Slava are currently implementing the 4-4-4 hole pattern
> into the CDC endplates. In doing this, Slava noticed a small inconsistency
> when one goes from a close-packed stereo to the next layer. In particular,
> for several of the innermost transitions, the tubes had a small overlap
> between layers at the endplates. In particular, layers 6+7 8+9 and 10+11
> all showed small overlaps.
>
> Yves and I then carefully looked at the code that did the stereo close pack
> and noticed that because the close-pack stereo angle is slightly larger than
> 6 degrees, the tube moves out in the radial direction at the endplate slightly
> more than it would for the nominal 6-degrees. However, the spacing was
> between layers was computed based on the straws at the center of the
> chamber. While our code is different from the code Beni used to generate
> the geometry, the two codes produced the same radial positions at the
> center, and the same numbers of tubes per layer. Thus, we suspect that
> the same problem exists in the geometry file for the CDC.
>
> In order to fix this, we now check the gap at both the endplates and at the
> center to make sure that they both work. We then regenerated the hole
> patterns. This very small "fix" had the effect of moving layer 28 out too far
> radially. It went from 54.973cm (center) to 56.250cm (center). In fact
> layer 27 is now at 54.867cm (center). The easiest way to implement these
> close packs is to remove layer 28, leading to a "4-4-4-4-4-4-3" layout.
>
> We also suspect that the small overlaps that we found exist in the
> version-C CDC geometry and may be contributing to some ineffeciencies.
> Layer 6 is at roughly 13.5 degrees and layer 11 is at 18.5 degrees. Hits
> that are near the sides of the tubes may have been reconstructed in the
> wrong strawtube, though the overlap is small. The following table gives
> the locations of the straws
>
>
> Curtis
> --------------------------------------------------------------------------------------------------------------
> Instrumented Layers is 28
> Instrumented Channels is 3580
> Instrumented Channels is 3365 excluding layer 28.
>
> layer number radius(center) radius(plate) stereo gap
> $ 1$ & $ 43$ & $ 10.955$ & $ 10.955$ & $ 0.000$ & $ 10.955$ \\
> $ 2$ & $ 43$ & $ 12.310$ & $ 12.310$ & $ 0.000$ & $ 1.356$ \\
> $ 3$ & $ 55$ & $ 14.021$ & $ 14.021$ & $ 0.000$ & $ 1.711$ \\
> $ 4$ & $ 55$ & $ 15.385$ & $ 15.385$ & $ 0.000$ & $ 1.364$ \\
> $ 5$ & $ 66$ & $ 17.013$ & $ 18.750$ & $ 0.105$ & $ 1.628$ \\
> $ 6$ & $ 66$ & $ 18.396$ & $ 20.274$ & $ 0.113$ & $ 1.383$ \\
> $ 7$ & $ 80$ & $ 20.627$ & $ 22.081$ & $ 0.105$ & $ 2.231$ \\
> $ 8$ & $ 80$ & $ 22.014$ & $ 23.566$ & $ 0.112$ & $ 1.387$ \\
> $ 9$ & $ 93$ & $ 23.982$ & $ 25.244$ & $-0.105$ & $ 1.968$ \\
> $10$ & $ 93$ & $ 25.371$ & $ 26.706$ & $-0.111$ & $ 1.389$ \\
> $11$ & $106$ & $ 27.337$ & $ 28.450$ & $-0.105$ & $ 1.965$ \\
> $12$ & $106$ & $ 28.728$ & $ 29.898$ & $-0.110$ & $ 1.391$ \\
> $13$ & $125$ & $ 31.895$ & $ 31.895$ & $ 0.000$ & $ 3.167$ \\
> $14$ & $125$ & $ 33.273$ & $ 33.273$ & $ 0.000$ & $ 1.378$ \\
> $15$ & $137$ & $ 34.958$ & $ 34.958$ & $ 0.000$ & $ 1.685$ \\
> $16$ & $137$ & $ 36.337$ & $ 36.337$ & $ 0.000$ & $ 1.379$ \\
> $17$ & $148$ & $ 38.174$ & $ 38.979$ & $ 0.105$ & $ 1.837$ \\
> $18$ & $148$ & $ 39.569$ & $ 40.403$ & $ 0.108$ & $ 1.395$ \\
> $19$ & $161$ & $ 41.528$ & $ 42.269$ & $ 0.105$ & $ 1.959$ \\
> $20$ & $161$ & $ 42.924$ & $ 43.690$ & $ 0.108$ & $ 1.396$ \\
> $21$ & $173$ & $ 44.624$ & $ 45.315$ & $-0.105$ & $ 1.700$ \\
> $22$ & $173$ & $ 46.020$ & $ 46.732$ & $-0.108$ & $ 1.396$ \\
> $23$ & $185$ & $ 47.720$ & $ 48.366$ & $-0.105$ & $ 1.700$ \\
> $24$ & $185$ & $ 49.117$ & $ 49.782$ & $-0.108$ & $ 1.397$ \\
> $25$ & $203$ & $ 51.804$ & $ 51.804$ & $ 0.000$ & $ 2.688$ \\
> $26$ & $203$ & $ 53.187$ & $ 53.187$ & $ 0.000$ & $ 1.382$ \\
> $27$ & $215$ & $ 54.867$ & $ 54.867$ & $ 0.000$ & $ 1.680$ \\
> $28$ & $215$ & $ 56.250$ & $ 56.250$ & $ 0.000$ & $ 1.383$ \\
>
>
--
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David Lawrence Ph.D.
Staff Scientist Office: (757)269-5567 [[[ [ [ [
Jefferson Lab Pager: (757)584-5567 [ [ [ [ [ [
http://www.jlab.org/~davidl davidl@jlab.org [[[ [[ [[ [[[
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