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Re: CDC Endplate Design
Hi Beni -
we need to be able to glue the straws together going around a ring
for the non-closepack. Otherwise, they have the possibility of sagging
which is not good. At least construction-wise, they do need to be very
close to touching as we go around a ring.
-- Curtis
On Tue February 24 2009, Beni Zihlmann wrote:
> 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$ \\
> >
> >
>
>
--
Professor Curtis A. Meyer Department of Physics
Phone: (412) 268-2745 Carnegie Mellon University
Fax: (412) 681-0648 Pittsburgh PA 15213-3890
cmeyer@ernest.phys.cmu.edu http://www.curtismeyer.com/