Re: FDC Material and Noise Rates

[Matthew Shepherd <mashephe@indiana.edu>]

Hi Dan,

I think Richard's revisions to geometry include revisions in both the  
active an inactive areas.  It would be helpful if you could examine  
Richard's notes on revision and comment on how that geometry (that is  
currently checked into the repository) aligns with your options  
below.  For example, is the current geometry "option 1" with revised  
chamber frames.  How does your description for the material in the  
inactive area match GlueX-doc 800 that Richard used to create the  
revised geometry?

If we are currently at option 1 with revised inactive area then we  
simply just need to create an alternate that is option 2 that removes  
the Rohacell.  Once that is done, we can redo studies.

Mihajlo is working now to study conversion rates and efficiencies in  
both the BCAL and FCAL using simulation.

Finally, do you really want rates for every active element in the  
FDC?  The last time I did this, you asked for rates in just a few  
planes.

-Matt


On May 17, 2007, at 11:44 AM, Daniel S. Carman wrote:

>
>
> Richard, Matt, David, et al.,
>
> I have seen some of the rate studies that have recently come out.  As
> I do not know what you are planning or what you have completed fully,
> I thought that I would send a follow up email on what we need to push
> forward with the FDC design and to complete the documentation needed
> for CD2 to address the questions raised by the DC review.  The  
> questions
> that we need to address have to do with 1). material in the active  
> area
> and 2). material in the inactive area of the FDCs.
>
> Questions on material in the active area:
> -----------------------------------------
> To simplify the situation, I would like to know what the rates are
> per cathode strip and per anode wire for all planes in the FDC system
> for the two options that we are pursuing.
>
> Option 1: 5-mm Rohacell backing with 10-cm diameter hole cut about the
>           beam line.  1 mil kapton + 2 micron copper strips for the
>           cathode planes.  In this option the copper strips about the
>           10-cm diameter hole are split in two and the hole in the
>           cathode board matches the hole in the Rohacell backing (i.e.
>           the strips and kapton do not go through the beam line hole).
>
> Option 2: Same as option 1 but with the Rohacell removed.
>
> The relevant gas mixture is 40/60 argon-CO2.  Note that we are also
> starting to consider a design to replace the Rohacell backing with a
> composite foam that should be significantly less material that a solid
> Rohacell piece.  However, with the results for the two options, we at
> least have set reasonable upper and lower limits for the rates that
> hopefully can serve to help us set a design spec.  We will also need
> MC run for both cases to show momentum resolution vs. p and theta.
>
> Questions on material in the inactive area:
> -------------------------------------------
> We would like the photon conversion studies that were presented about
> a month ago repeated for the FDC design where the 5-mm thick cathode
> frames are replaced by the 5-mm thick composite carbon-fiber/Rohacell
> frames.  We are also considering replacing the CH2 spacers with a
> composite frame, but this should be considered in a separate study
> as it is not part of our nominal design.  Again, the goal is to use
> these studies to set a design spec.  So we all need to think about
> what photon conversion rate in the frames and cables is allowable.
>
>
> Let me know if you have any questions.
>
>
> 			    Regards,
>
> 				Daniel
>
>
> **********************************************************************
> *                                                                    *
> * Dr. Daniel S. Carman                   e-mail : carman@jlab.org    *
> * Staff Scientist                        office : (757)-269-5586     *
> * Jefferson Laboratory                   web: www.jlab.org/~carman   *
> *                                                                    *
> **********************************************************************
>
>
>
>
>