To: E614 Collaboration
From: Robert Henderson (TRIUMF)
Re: Design concept of Cradle/track
Date: 30 May 00


  Hans Wattlitzer and I have been working on the Cradle/Track concept.
In
this report I will try to bring the collaboration up to date about the
general concept without going into great detail. The concept is NOT
finished,
hopefully within 2-3 weeks it will be. There are eight postscript files
included, they are as follows:

  W1.EPS - Three sections views of cradle/track/detector. These sections

           are at: Uptream cradle endcap (left)
                   Central region of cradle and showing a detector
(center)
                   Downstream cradle endcap (right)

  W2.EPS - Section view of cradle/track at Upstream cradle endcap
  W3.EPS - Section view of cradle/track.detector at Central region of
cradle

  W4.EPS - Zoom of W3.EPS showing region near right cable bundle
  W5.EPS - Section view of cradle/track at Downstream cradle endcap
  W6.EPS - Zoom of W5.EPS showing DS endcap near right cable bundle
  W7.EPS - Same view as W6.EPS but including `plug' and cable tray
  W8.EPS - Side View of cradle/track in solenoid.

  Figures W1.EPS thru W7.EPS are from my acad drawings and do NOT
include all
the details Hans has incorporated in his drawing. I made figure W8.EPS
from
two drawings Hans made, deleting many deatils.

                  Current Cradle/Track Concept
                   =====================

  Going from Guys Stanford's initial concept, I modified it somewhat,
the
collaboration endorsed the new scheme and we dropped the cradle/track
scheme
based on arcs.

  Initially, I had the thick cradle endcaps filling the circular
enclosure of
the top half. In our meetings, the collaboration realised the thick Al
need
only be a smaller rectangle and the rest could be light-weight bolt-on
extensions.  In tals with the design office, they feel this just
complicates
the whole design, I agree. So the present concept has solid encaps with
circular top half, if the weight increase is a problem, they can easily
machine down some areas (I'd rather not). Going back to thick endcaps
nread
the cable trays started me re-thinking that interface, I'll discuss that

below.

Rolling and Landing
--------------------

  Hans has been working mainly on the Cradle-Track interface, i.e. how
will
the cradle roll. Guy's initial hurried concept had rollers to support
the
cradle, but none to prevent side-to-side motion and `rubbing' or even
binding. Plus no details of cradle `landing'. Hans has added a second
roller
to control side-to-side motion, he's still working on landing scheme.

Tension Rods
--------------

  We considered several ways of doing this, but soon came back to my
initial
concept.

  Each tension rod is inserted thru a hole in the DS endcap, passes
close to
the detectors modules, then screws into a tapped blind hole on the
inside
face of the US endcap (no gas leak).

  In principle, all that is required at the DS encap is to screw a nut
onto
each rod until it contacts the DS endcap, then lock it in pleace with
another
nut. Unfortunately, this is not failsafe. Someone unclear of the concept

might keep tightening the first nut, putting huge forces on the cradle
and
modules. Therefore, in the present design, a machined `spacer' goes on
before
the first nut. This spacer has two surfaces, one that contacts the
endcap
face, the other a step on the tension rod. The spacer will have to be
skimmed
to the correct spacing when first assembled, but thereafter it prevents
over
tightening.

  To gas seal this DS end of the tension rods, a `cap' will cover both
rods
and o-ring seal to the DS face of the endcap. Vent holes to this capped
volume ensure it's flushed. The cover also prevents people undoing the
rods
by mistake.

Gas Outlets
------------

  My inital concept had a flange on the encap extension, and a bellows
inside
connecting to the gas manifold.

  This has now been simplified. Each outlet will consist of a 0.5" dia,
pipe
glued into the DS endcap. A simple brass VCO fitting will connect to the

manifold. This is simpler and required less space. Hans and I have
started
working on the manifold support/alignment scheme. Ouside the helium
volume,
the outputs connect to 0.5" polyflo.

Gas Inlets
----------

  It is clear to me that the two inlet hose bundles should NOT be
incorporated in the cable bundle. If we move the cradle/detector stack
to
another location (cleanroom say), we do NOT want to have to disconnect
all
gas inlets and sample lines at the modules (75 hoses). Aslo if in aother

location we want to flow gas, it is far more convenient if the inlet
hoses
are still attached.

  There are two possible locations for the gas inlet bundles, at the
bottom
of the cradle or near the cable bundles. After some thought, I decided
that
near the cable bundle is better. Why?

  If the hose bundles are at the cradle bottom, the only way to
disconnect a
chamber is to remove the large cradle bottom-plate, disconnect and cap,
then
lift out the module. Doing this while under the `track extension cart'.

  If the hose bundle is near the cable bundle, we have TWO options. The
first is the same as discussed above, the second is to lift the module
vertically (usual removal technique), but with the inlet hoses still
attached. W3.EPS shows, a set of four gas fitting and a 1/4" hose
`floating'
above the in-situ module. These are a copy of the module gas inlets
positioned 820 mm above in-situ location. The hose is same length as the
the
in-situ, but obviously follows a different path to the gas bundle. The
idea
is to illustrate that, with the hose bundle near the cable bunbdle, the
module can be lifted clear WITH the those hoses attached. Then it is
trivial
to undo and cap them, without removing the bottom-plate at all. I
beleive we
should retain the bottom cover plate, this just enhances our options.
This
scheme would NOT work with the hose bundles at the bottom of the cradle,

since where and how would we store the 1 meter of extra hose in the
in-situ
position.

  On the subject of gas inlet and sample lines. Robert Opensahw and I
have
discussed it at length. The sample lines were origionally my idea, but
if is
unclear if they do anything for us except use up valuable space. If
there,
we have to figure some way of flushing those sample lines (not trivial).
All
a smaple line could do is possibly confirm that a helium is leaking into
a
module, something we should know from perfomance far sooner.

Cradle and Track
------------------

  For some reason, Willy's drawing to Hans showed the cradle extending
beyond
the track at both US and DS ends!? I don't understand this! Making the
cadle
overly long just uses up valuable space during removal and makes it more

unwieldy to transport. Also, unless other concerns arise, the DS end of
the
track should entend almost to the steel. This shortens the length of the

`track extension cart' and requires less distance to roll the cart
before it
can be lifted via crane.

  The present concept has the cradle 8.4" shorter than the tack on the
US
end, the track end 4.7" from the steel. At the DS end, the track is only
1"
from the steel, so the cradle is 12.1" shorter. The cradle is simply
supported from teh rail with pairs of rollers are each `corner' of the
cradle. The `landings' would be in the same area. This means the cradle
is
resting on the rails 7" from the point where the rails are attached to
the
external supports. I think this is definately close enough. The latest
scheme
for Z-axis alignment fo the cradle is to view targets from the side of
the
magnet, getting a direct measure of Z locations. With the cradle the
present
length, target extensions would need to be attached to the cradle
corners,
holding targets 4.5" beyond the ends. These extensions could be dowelled
and
bolted so they can be removed and re-installed easily.

  The US cradle endcap has two braces (gussets) to the top surface of
the
longitudional beams.  These braces are 10" long, 19.5" high and 1.5"
thick.
There are no such braces on the DS endcap of the cradle, since we care
only
about the stiffness of the US endcap and also because they would
interfere
with the cable bundles.

Upstream Cradle Endcap
-------------------------

  Shown in W2.EPS. Very simple. Has bumpers that will screw in to touch
the
G10 endcap during initial alignment. They are then locked with lock nuts
and
hopefully never touched again. On the US face, these four locations will
have
screw-on covers with an o-ring seal and vent holes to the covered
volume.

  On the Inside face there will be blind holes for manifold US
support/alignments etc. There will be a helium inlet pipe glued into
this
endcap. At the central circular cutout, there will be a `lip' with blind

tapped holes and an o-ring groove. The input window assembly will be
screwed
onto this lip.

  The lower half of the endcap will be bolted and glued to the
longitudional
beam and to a 0.5" permanent baseplate. The 3.16" shell comes into
contact
with the upper circular half of the endcap. Gas seal will be by gasket
compressed to say 2 mm final thickness.

Downstream Cradle Endcap
----------------------------

  Shown in W5.EPS, W6.EPS and W7.EPS. Has four bumpers that will slid
thru
holes in the endcap and contact the DS G10 ring. On the DS side of the
encap,
each of the bumpers will attach to a brass pneumatic cylinder (about
2.75"
dia bore). These cylinders will be attached and supported from the
endcap.
Flanges with o-rings will ensure Gas seal and there will be vent holes
to
these volumes.

  There will be a helium outlet pipe glued into this endcap. At the
central
circular cutout, there will be a `lip' with blind tapped holes and an
o-ring
groove. The output window assembly will be screwed onto this lip.

  The lower half of the endcap will be bolted and glued to the
longitudional
beam and to a 0.5" permanent baseplate. The 3.16" shell comes into
contact
with the upper circular half of the endcap. Gas seal will be by gasket
compressed to say 2 mm final thickness.

  The big difference between the US and DS endcaps is the need to bring
the
cable and hose bundles out the DS end. I have spent considerable time
designing a scheme I hope will be as convenient as possible. Instead of
glueing (RTV) the cable bundle into notches in the DS endcap, I have
deigned
a `pug' that will allow a gasket seal to be used.

  When trying to seal with a gasket, corners must be avoided. Also, all
parts
of the gasket need to be compressed at the same time. To accomplish
this,
I make a curved cutout in the DS encaps (see figure W6.EPS). The bottom
edge
of the cutout is horizontal, the left edge vertical and of course the
corners
are rounded. The upper suface surls around the hose bundle area and goes
to
the outer rim again. The upper sufaces are at 10 degrees from the
horizontal.
Why? The idea is that the `plug' piece will hav a matching contour, but
seperated by 2 mm, the final compression thickness. If the plug is
inserted
into the notch along a 5 degree line, then all surfaces come into
contact and
are compressed at the same time. The plug has a large machined cutout
into
which the cable bundle is permantently glued. Thus the plug becomes part
of
the cable bundle. The thinnest part of this aluminium plug at the outer
wall,
here it is 0.25" thick.

  The figure shows three brackets attached to the plug, two for bolts
and one
for a pin. There will probably actually be five, the two bolts being
replicated on the iside face of the plug to avoid `twisting'. There are
three
(or five) matching brackets attached to the endcap, two (or four)
threaded
and one with a hole for the pin.

  This scheme should allow relatively easy removal and re-installation
of the
cable bundle without the need for RTV. The plug would be as thick as the

endcap (2-3 inches), it's outer surface would be similar to that of the
endcap, with tapped holes for the outer shell and its gasket. In
principle
the only leak point (except for within the cable bundle) is the point
where
shell gasket and plug gasket meet. If the plug gasket protrudes a little
at
that point, I believe a seal will occur. If not, this one location may
need a
bead of RTV which would be easy to remove.

  Hans is studying the notch/plug concept, but doesn't see a problem.

Central region
--------------

  This region is shown in figures W3.EPS and W4.EPS. I have used just
about
all the available sapce for the hose bundle and cable bundle.

  The hose bundle has  3.2 mm thick wall and is shown with thirty-two
0.25"
dia. hoses. If we have sample lines, we need:

  56 + 19 + 4(spare) = 79 lines. This is 40 for each hose bundle.

  If we drop the sample lines, we need (56+4)/2=30 for each hose bundle.

  I could make the hose bundle bigger at the expense of the cable
bundle. It
is fine if we drop the sample lines.

  The cable bunbdle is shown with fifty-one 8.34 mm cables, that
represent
SHV and LV cables. We need 56+4(spare)=60 SHV and 38+4(spere)=42 LV
cables.
Thats 102 total, 51 for each cable bundle.

  Grant and I considered the idea of having our mini-coax cables put in
a
weave similar to that on the VTX chamber. This greatly reduces the
chance of
dmaaging the coax and makes it far easier to attach the connectors to
the
ends.

  I did some measurements and found for the 17-way ribbon of the VTX
chamber,
this weave increases the cable area by a factor of 2.26. For out larger
coax
and bundles of eight, I estiamte the same weve would cause an area
increase
of 1.6 for us. In talking to the company, Grant found that they can also
bond
the mini-coax together, this option causes little or no increase in
area.
Each ribbon effectievely becomes a 10 mm wide by 1.25 mm thick
rectangle,
with an area of 12.5 mm2.

  In the figures I show 321 bonded 8-way cable ribbons, each occupying
an
area of 15.6 mm2, 25% more than true cross section.

  Each fully instrumented detector layer requires 10 ribbons. If only
the
central 48 channels are instrumented, 6 ribbons are required. If we
fully
instrument all the layers in the dense stacks and only the central
regions of
the target, we need 568/2=283 ribbons in each cable bundle, So the 321
shown
represents 13% spares. There is still some space in the cable tray, but
we also need pulser cables (10 per tray) and 8-signal temperature
readout
cables (10 per tray). My view is that the cable tray should be no
smaller
than shown. Clearly, the alternative of a weave on the mini-coax would
be a
risky choise.

  Between cradle encaps, I show a bar extension to the beam `lips'. Hans
had
the same idea, except he `hogged out' a groove for the attachment
screws.
These extensions would be permanently bolted and glued to the beams. The

outer edge of the extension is angled and has blind tapped holes for the

shell and its gasket. This provides the helium seal.

  Hans and I are considering the possibility of making the shell in two
pieces, but I won't report on that yet

Filename: w1.eps

Filename: w2.eps

Filename: w3.eps

Filename: w4.eps

Filename: w5.eps

Filename: w6.eps

Filename: w7.eps

Filename: w8.eps

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