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Re: CDC Endplate Design
HI Curtis,
I rechecked again Geometry C in the repository using root and hdgeant++
in both cases I did not
find any overlap of any straw with another straw. However this geometry
is somewhat different
from what you have in your list. The major difference is that I do not
insist that the distance
between the straws in all the layer has to be the same. I choose the
smallest radius that is closest to
the previous layer but reasonably and put as many straws in as possible.
This has the consequence
that not all layers have the same distance between straws. I do not
claim that the geometry in the
repository is perfect. in particular the angles might be not perfect.
However, if one insists on an
equal distance of straws in all layers (first layer of any closed pack
packedg of two layers) then
we have a problem. If you are willing to give up that constraint then I
think it is still possible
to put 28 layers into the CDC.
cheers,
Beni
> 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$ \\
>
>
--
***********************************************************
Benedikt Zihlmann
TJNAF
HallD 12C/ F350
Suite 8
12000 Jefferson Av.
Newport News VA, 23606
tel: 757 269 5310
fax: 757 269 6331 zihlmann@jlab.org
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