[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: CDC Endplate Design
Hi David -
I tried shortening the chamber to 135cm, but that did not do it.
I then reduced the tolerance between the tubes. That did not do it.
I then moved the first layer from 10.93cm to 10.675 cm. That also
did not do it.
If I make all three changes and am very close to having 28 layers.
I then tried to change the CDC back to 140cm from 135cm. That made it not
possible. I do not believe that 135cm is smart, I might tolerate 140cm.
I then went back to nominal spacing and changed the stereo angle from 6 to
5.7 degrees. That did not do very much.
Then I moved the inner layer to 10.675, reduced to tolerance, changed the stereo
to 5.7 degrees and shortened the chamber to 140cm. That got me again very close
to having 28 layers.
These are all probably ok changes to make, but we need to make a decision on
this for Slava to get the end-plate design finished. I am not sure what happens if
the ID of the CDC comes in by 2.5 mm. That will have an impact on something.
Curtis
On Tue February 24 2009, David Lawrence wrote:
>
> 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$ \\
> >
> >
>
--
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/