Discussion of the LP endplate and field cage geometry

1
Discussion of the LP endplate and field cage
geometry
Dan Peterson Cornell University

15-November-2006
A version of the LP endplate to field cage
interface was discussed at Valencia,
06-November-2006 . This describes the next
iteration.
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Overview
The endplate (shown in blue) attaches to the
field cage flange (a sort-of copper color) that
is an integral part of the field cage but is made
of a more durable material. Readout panels, or
modules, attach to the endplate from the inside
(but are inserted through the endplate from the
outside). Readout panels include a metal frame
(red) that is common to all readout technologies
and provides all interface to the endplate.
The readout structure is mounted on the panel
frame. This includes a pad panel (dark green) and
the gas-amplification and gate (light green). The
example shown is a 3-GEM plus gate.
Martin Killenberg has suggested 26 mm as the
maximum module thickness from the endplate
surface. This includes structure 8mm
pad plane 2mm
3GEM 6mm
GEM gate 10mm sum
26mm. This design maintains
the thicknesses of the pad plane, GEM and gate
but differs in the thickness allocated to the
structure, which extents into the endplate.
FileEndplateFieldCageGeometry5
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Geometry details end flange
Refer to the drawing on page 5.
The field cage includes an end flange of more
durable material. The end flange now has a flat
mating surface. Concerns about the limited amount
of material in the endplate outer ring, at the
point where the endplate steps into the field
cage, have been addressed. The end flange
includes a long section that extends further
into the low-density material to increase the
strength of the connection. The long section has
an inner radius of 37.8 cm, which provides a
clearance of 1.2 cm from the field shaping bands.
The end flange is also located at 1.2 cm from the
field bands in the longitudinal direction. The
end flange includes the threaded holes which will
be used to attach the endplate. These are shown
as 8-1.25-15 Helicoils. With a flattened flange
surface and with an adjustment of the location of
the long section, there should be enough
clearance for this size Helicoil. I suggest that
we have 36 bolts, with an arc spacing of
6.8cm. The end flange includes the o-ring slot.
If, after considering the relative geometry of
the end flange and field band, it is still
preferable to have a fiber end flange, the o-ring
slot should be moved to the aluminum end plate.
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Geometry details longitudinal locations of the
field bands, readout modules, and end flange.
Refer to the drawing on page 5.
The endplate has a step that places the
panel-mounting surface at the same longitudinal
location as the inner surface of the field cage
end flange. This shape also increases the overall
thickness and, therefore, the stiffness of the
endplate. The face surface of the readout panels
is displaced by 2.20 cm from the endplate
surface. It is the intent that all readout
modules place the face surface at this location
as described by Martin Killenberg. The face
surface of the readout panels defines the
location of the intermediate contact to the
field shaping bands necessary to define the end
of the drift field. A critical dimension of the
design is that the face surface of the readout
panels is located 4.30 cm from the surface of the
field cage end flange. The field shaping bands
extend beyond the face surface by 1.0 cm, the
offset of a possible gate. A final contact to the
field shaping bands allows field shaping over the
offset of the gate. A radial clearance of 2 mm
is provided between the step in the endplate and
the inner wall of the field cage.
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Geometry details
FileEndplateFieldCageGeometry5
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Geometry details endplate.
Refer to the drawings on page 5 and 7.
The drawing on page 5 shows the cross section at
a location where a panel does not extend to the
maximum available radius of the instrumented
area. This is the case except for the few
instances where a corner of a panel reaches the
maximum radius. In this case, there is a biased
surface located at the same longitudinal position
as the face of the readout panel. With the
panel displaced from the maximum radius, there
can be more metal in the region of the step in
the endplate. This will provide extra stiffness
for the entire endplate structure. I have not
calculated the details. The geometry in the
locations where a corner of a readout panel
reaches the maximum radius is shown in on page 7.
The section between the thick out ring and the
surface on which the panels are mounted is very
thin. However, this region is very small an will
not affect the strength. The mullions are shown
on page 2. Note that the cross section has been
modified to include a wing section extending to
the outside in the longitudinal direction. This
stiffens the mullion. For an example case of a
(30cm)2 panel, with 6millibar overpressure, the
sagitta of the local bowing of the of a 30cm long
mullion is calculated to be 25 microns. The
addition of the wing section increases the
stiffness by a factor of 3. Panels are drawn
to the endplate with an additional frame mounted
on the outside. Screws will pull the panel into
the frame. With this arrangement, panels can
still be located with precision surfaces.
Alternatively, panels may be located with dowels
through the frame, into the panel and the
endplate.
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Geometry at a corner of a module that comes to
the maximum radius