Re: Inner plate on bcal

[whitey@jlab.org]

This sounds good! We will work out the details for supporting the CDC/FDC
rails with the plate.

Tim

>
> Hi Zisis,
>
> Thanks for your response.
>
> Tim: I guess we can go forward with refining a design with an 8 mm Al
> sheet at the inside of the Bcal.
>
> Cheers, Elton.
>
> On Wed, 6 Feb 2008, Zisis Papandreou wrote:
>
>> Hi Elton:
>>
>> a few remarks embedded in your text.
>>
>> On Feb 5, 2008, at 2:34 PM, Elton Smith wrote:
>>
>> >
>> > Hi George and Zisis,
>> >
>> > We had our weekly meeting with the JLab engineering/design team this
>> > morning and discussed bcal installation (along with other issues).
>> > There
>> > are many good reasons to have an inner skin to the bcal which can
>> > be used
>> > for mechanical assembly. We have discussed this previously, but
>> > wanted to
>> > try to pursue this a little further. We have a slightly different
>> > proposal
>> > now and some questions.
>> >
>> > The current thinking would be to attach an 8 mm Al skin (equivalent
>> > to the
>> > first 0.1 rad length of Pb sheet). This has structural advantages
>> > over the
>> > lead, and also would be symmetric to the Al plate on the outer
>> > layer, so
>> > you could use the same procedure for attachment.
>>
>> Fine, sounds ok.
>>
>> > Here we have some questions or be reminded of how the first layers are
>> > constructed: Is the layer of Pb next to the Al base the same
>> > thickness as
>> > the other layers? How is that it has a flat surface instead of a
>> > grooved
>> > surface? (We assume that the swaging machine groves the top and
>> > bottom of
>> > each layer at the same time). Finally, can one put grooves into the
>> > Al and
>> > use it instead of a Pb sheet?
>>
>> The very first Pb sheet is glued to the aluminum base plate with a
>> two-compound industrial epoxy.  We chose this as something expected
>> to be stronger than the BC-600 optical epoxy, and since there are no
>> fibers (actually there is only one, see below) between the Pb and Al;
>> the extra surface (and porosity?) of the fibers help the BC-600
>> adhere better and keep everything together.  This 1st Pb sheet is
>> identical in construction to all Pb sheets: it is grooved on both
>> sides of course, and has the same 0.5mm thickness.  The Al base plate
>> has a single 0.5mm groove (trench) machined along its entire length.
>> In it we glue a single fiber using BC-600.  This acts as a "guide
>> rail" for the 1st Pb sheet.  Once the BC-600 is cured, we then apply
>> the industrial epoxy and glue the 1st Pb sheet; the single fiber
>> keeps it from twisting/migrating under pressure when the industrial
>> epoxy is setting/curing.  We haven't seen the need to increase from 1
>> guide fiber to 3 or 5; 1 seems to do the job.
>>
>> Grooving the 8mm Al sheet that you are proposing to use at the other
>> end (inner side) of the modules, may not be the best way of tackling
>> this.  Reversing the above process would have us installing a single
>> fiber (or wire of equivalent diameter) in the middle of the topmost
>> (last) Pb sheet using BC-600, let it cure, and then use industrial
>> epoxy to glue the 8mm Al plate, once it has been machined with a
>> single groove for the guide fiber.  We should be able to do this easily.
>>
>> We have measured module thickness difference of ~1mm from one end of
>> the module to the other (over its 25cm thickness).  This is quite
>> good, but Tim you have to take into account that the 8mm Al plate
>> will not be perfectly parallel to the beam axis, and its inclination
>> will be slightly different from module to module (along all three
>> axes probably), since no two modules are precisely identical, due to
>> the nature of the construction process.   How is this best handled?
>> Using varying depths of bolts into threads (we assume you are
>> thinking of putting threads into the 8mm Al)?  What about spring-
>> loaded mechanisms?  Of course all this needs to be accurate and
>> reproducible for the alignment of the tracking packages.
>>
>> > These questions arise as we would like to see if an inner skin can be
>> > added because it increases the mechanical robustness of the
>> > calorimeter.
>> >
>> > Thanks for your patience, Elton.
>>
>> So the answer is yes on adding an inner skin.  We just have to think
>> things through.  On the BCAL side it is a more straight forward
>> issue, and we can certainly experiment with some small samples, to
>> ensure that the reversed process (fiber on lead first, then plate)
>> works as well as the regular process (fiber on Al first, then Pb
>> sheet).  The rest is up to you Tim!  :-)
>>
>> Cheers, Zisis...
>>
>>
>> >
>> > ---------- Forwarded message ----------
>> > Date: Tue, 5 Feb 2008 14:31:49 -0500 (EST)
>> > From: Elton Smith <elton@jlab.org>
>> > To: Tim Whitlatch <whitey@jlab.org>
>> > Cc: Elton Smith <elton@jlab.org>, Elke Aschenauer <elke@jlab.org>
>> > Subject: Inner plate on bcal
>> >
>> >
>> > Hi Tim,
>> >
>> > I checked the radiation lengths of materials to see how much we can
>> > afford
>> > to use for the inner plate of the calorimeter:
>> >
>> > rad len Al = 8.9 cm
>> > rad len Fe = 1.76 cm
>> > rad len Pb = 0.56 cm
>> > rad len W  = 0.35 cm
>> >
>> > We are nominally starting out with 0.5 mm Pb (0.09 rad len). So
>> > adding/replacing with another material of roughly the same
>> > thickness in
>> > rad lengths is reasonable. This corresponds to 8 mm of Al and 1.6
>> > mm of
>> > Fe (i.e. stainless). This is somewhat thinner than what we were
>> > considering this morning, but I wanted to get your feedback on how
>> > useful
>> > this would be.
>> >
>> > If Al is chosen, it was additional advantages. First it will be
>> > relatively
>> > thicker, so attachments are easier. Also, it may be possible to
>> > groove the
>> > Al sheet, which might allow us to replace the first layer of Pb and
>> > therefore increase the amount of backing structure. Finally,
>> > machining Al
>> > along with the rest of the pyramid should be very straightforward.
>> >
>> > Let me know what your thoughts are regarding Al/Fe before I run
>> > this by
>> > our Regina friends.
>> >
>> > Thanks, Elton.
>> >
>> >
>> > Elton Smith
>> > Jefferson Lab MS 12H5
>> > 12000 Jefferson Ave
>> > Suite # 16
>> > Newport News, VA 23606
>> > elton@jlab.org
>> > (757) 269-7625
>> > (757) 269-6331 fax
>> >
>>
>> ---
>> Dr. Zisis Papandreou		|  email: zisis@uregina.ca
>> Department of Physics	|  tel. : (306) 585-5379
>> University of Regina		|  tel. : (306) 585-4149
>> Regina, SK  S4S 0A2		|  fax. : (306) 585-5659
>> World Wide Web:    http://www.phys.uregina.ca/sparro/zisis/
>>
>>
>>
>