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New version of Hall-D Detector geometry
Hi Richard,
We've recently had some local discussions here on the current state
of the geometry for the Hall-D detector. At this point, we'd like to get
the simulation up to the most current designs for all detectors. The FDC
group would like to get a new revision implemented that involves a new
composite design for the frames as well as a thinner Rohacell backing.
We'd also like to include the stripped-back FDC cables that should
remove a lot of material in front of the calorimeters. At the same time,
we would like to implement the changes to the CDC design that were
presented at the drift chamber review in March. We had not wanted to
include those up until now so that we could study the effects of the FDC
changes alone. Below is a list of the changes. Note that they assume FDC
"option 1" as the starting point.
1. Change the composite design of the FDC support frames. Here is
Simon's e-mail describing the new design:
"The current plan is to replace all the frames with a composite consisting of 3.4 mm thick 0.075 g/cm3 Rohacell with skins on either side made up of 0.8 mm thick FR4 attached to the foam with 25 microns of epoxy. This means that the polyethylene spacer is now composed of this composite as well. Unless Daniel disagrees, the original composite for the Cathode support rings that was composed of foam/E-glass/carbon fiber would be replace with the new design as well."
2. Change the Rhoacell backing from 5mm to 2mm. The volume revealed by
shrinking this should be filled with air.
3. The latest design for the FDC has the cathode strip connectors in the
annulus region between chambers. This is going to introduce an
additional gap between neighboring chambers that will be at least 1cm.
This means a six chamber package will extend 5cm further in z than what
is currently in hdds. The gap should contain the circuit boards that are
currently implemented as tubes that are thin in the radial direction
with ones that are thin in the z direction.
Note that some drawings are being requested from the engineers and will
be made publicly available once we get them. That may take a little time
though.
4. Modify the FDC cable definition to reflect the newest design that has
the outer copper shield pulled off for the part of the cable in the
detector and a heat-shrink wrapping added. Details from Simon are:
"I've extracted the following estimates from the Amphenol spec sheet. I
have assumed that the cables will be covered with 0.06 cm thick PVC heat
shrink in place of the copper braid and the original jacket. The
fractions by mass are 0.38 Cu/ 0.61 PVC /0.01 Polyester. To simplify the
model I would say we just make it 0.62 PVC and not add the polyester,
which is of comparable density to PVC anyway. The effective
diameter/cable is 0.6 cm. There are 144 signal cables per package (I have
added one extra cable per cathode plane to deal with the hole in the
center for the beam) for a grand total of 576. There are 24 HV cables
(6/package) with 1 cm diameter. There are 6 low voltage cables with 0.36
cm diameter. Since the original estimate for the signal cables using
17-pair cable everywhere was 720, we should be occupying less space
with cables than the previous model, so the density should go down."
5. There will be a thin aluminum mesh between FDC chambers for heat
dissipation. We'd like to model this by adding a tube of Al between each
of the chambers with a radius of 60.0cm and a thickness of 0.5mm.
6. Change the CDC endplate to 4mm carbon fiber. I think this was already
done, but please confirm.
7. Remove the outermost CDC layer and add the 3 inner ones. The number
of wires and the layer radii should be changed to reflect what Curtis
presented at the DC Review. These can be found in GlueX-doc-746 on slide
9. For convenience, I copy them here.
" Straight Layers Stereo Layers
Layer Wires Radius Layer Wires Radius Angle
1 43 11.0 cm
2 50 12.7 cm 4 64 16.3 cm +6
3 57 14.5 cm 5 71 18.1 cm +6
8 99 25.2 cm 6 78 19.9 cm -6
9 106 27.0 cm 7 85 21.7 cm -6
10 113 28.8 cm
11 120 30.6 cm 13 134 34.1 cm +6
12 127 32.3 cm 14 141 35.9 cm +6
17 166 42.3 cm 15 148 37.7 cm -6
18 173 44.1 cm 16 155 39.5 cm -6
19 180 45.8 cm
20 187 47.6 cm
21 194 49.4 cm
22 201 51.2 cm
23 208 53.0 cm
24 215 54.8 cm
25 222 56.5 cm
"
8. We need to start using the correct magnetic field map. The one we
have been using was produced at too low of a current. I have gathered
the various maps that I have (there are 4) and organized them with a
consistent naming scheme and format so that they can be read in through
the new calibration database. I would like to change how the field is
implemented in hdds so that one specifies the field map's location
within the calibration database rather than an absolute file.
Specifically, I suggest we change the /map/ attribute of the
/mappedBfield/ tag to be "Magnets/Solenoid/solenoid_1500". For the
reconstruction, I have copied the rotation/interpolation algorithm from
hddsGeant3.F and placed it in a DMagneticFieldMap class. I would like to
get the simulation to use this so that we make the simulation and
reconstruction consistent. I have started working on a prototype version
of hdgeant that will do this. It can be checked out from the repository
via:
svn co https://halldsvn.jlab.org/repos/users/davidl/devel/HDGeant
It currently only reads in the map and does not use it, but we can use
this as a common development area for now without affecting the main trunk.
Please let me know if you have any questions.
Regards,
-David
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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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