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FDC Weekly Meeting

Date: April 17, 2008

Participants: Daniel, Simon, Fernando, Roger, Mark, Kim

Next Meeting: April 24, 2008 @ 1:30 p.m.

Cathode Planning

 - Roger has received a quote from Allflex for the cathode boards
   for the full-scale prototype.  This quote was for roughly $10k
   for 5 sets of boards.  Allflex is in contact with Nippon Steel 
   Chemical Co (the board material supplier) about availability
   and delivery of the 1 mil Kapton/2 micron Cu board material.  Roger
   is expecting to hear back from his contact at Allflex within the
   next several days.
 - Fernando needs to prepare the electrical specifications (board
   tests) for the cathodes to be built into the order.  This should
   be completed within about a week or so (if possible).
 - Once we are assured that Allflex can make the boards, Roger will
   hash out how we should specify the flatness/handling/defect
   specifications in the order.
 - Roger has heard back from Multek and they stated that they would
   not enter a bid because they cannot handle our board widths.  Roger
   will continue to look for material suppliers and board houses for
   our cathodes.
 - Greg Arnold's group made a first attempt at soldering the rigid
   flex assembly to a semi-realistic cathode board.  The process used
   a standard soldering iron, and the results were somewhat mixed in
   that the solder region was a bit wavy/uneven.  They have purchased
   an air pencil system and will use this on their next attempt.  
   Fernando will also look into obtaining conducting epoxy for Greg's
   group to use.  Roger ordered a total of five sets of test boards and
   it seems clear that by the time Greg's group is done, we will have
   finalized the rigid flex soldering procedure and specifications.
 - Note that due to the height of the solder connection between the 
   cathode board and the rigid flex assembly, we will have to revisit
   the design from the standpoint of adding clearance pockets on the
   surfaces that mate up against this solder region.

Full-Scale Prototype

 - The G10 for the frames has arrived.  The only remaining frame
   component that is missing is a portion of the Rohacell order that
   should be in soon.  This is the 2-mm thick Rohacell for the cathode
 - The rail order has arrived.  Bill still needs to provide drawings
   on the attachment brackets to the FSU shop where they will be made.
   This is not a super critical item for us at the moment.
 - Brian spoke with Dennis Skopik about clean room space and it is
   clear that this will be an issue.  Dennis is trying to work something
   out to satisfy the short term needs of all groups, but the FDC
   assembly needs to be in the clean space for essentially all work, so
   sharing the clean tent with other groups does not seem like a viable
   solution.  DSC will follow up with Brian and Dennis on our requirements.
   Dennis did ask that we not purchase the second construction station
   if the only place that we can store it is in the clean room, i.e.
   wait for him to give us the green light.  We need to keep applying
   pressure to him to have the best chance of giving us a move-in date
   that is compatible with our schedule.
 - Roger has communicated with Greg Arnold about our need for his
   group's services for the cathodes and cathode assemblies in the
   next few months.
 - Brian talked to Casey in the machine shop about completing the
   modifications on our aluminum tooling plate for the wire frame
   construction.  Casey thought it best to do this until just before
   construction.  DSC has suggested that this work is completed first
   thing after Brian returns from IUCF (April 28-30) so that it is
   ready after Brian gets back to JLab from vacation on May 6.

Test Frame Wire Winding

 - IUCF has now blessed the entire wire winding facility and Brian
   is scheduled to leave for IUCF on Saturday April 19.  Once there
   he will enjoy a week of fun and relaxation.  Keith Solberg at
   IUCF believes that by Friday April 25, all of the Phase I winding
   will be completed with all measurements carried out.
 - DSC will arrange for several teleconferences with IUCF during the
   week that Brian is visiting so that we can keep up to speed on 
   progress and issues throughout the Phase 1 winding process.
 - DSC is working with Steve Christo to prepare a wire specification
   document for the tungsten and CuBe wires leading up to procurement.
   Steve is preparing a document for the Hall B chambers and we will
   most likely adopt this document for Hall D.  DSC reviewed the
   existing Hall B documents to give folks a flavor of how these
   documents have been prepared in the past.  We need to make decisions
   on what is required for the FDCs.

Stack Assembly Procedures

 - DSC, Brian, Tim, and Bill will work to finalize the stack assembly
   construction document that has been prepared.  This document should
   be in place before we get too far in the construction process.

Composite Cathode Updates

 - Brian and Denny have made another backed cathode using our standard
   construction procedure.  Brian incorporated the grounding tabs for
   the ground plane using Fernando's suggestion of add small copper
   strips around the perimeter of the back of the G10 cathode frame.
   The faston tabs will be attached (via solder or conductive epoxy)
   to the copper tabs.
 - Fernando has gotten the laser measurement system from Acquity Laser
   fully working and is now ready to hand this over to Brian to
   measure the level of bulging on one of our prototype cathodes.
   We are concerned that the plane is too "floppy" and has too much 
   gravitational sag (the old beer gut problem).  The measurement should 
   quantify this problem and give us feedback into the need for
   increased tensioning of our cathodes.  It might be that Denny could
   take this on next week's in Brian's absence.
 - Brian will also work to make a "tensioned" cathode plane without
   the Rohacell backing.  So far he has put together the 3 cathode
   board pieces and set them aside until the tensioning apparatus is
   set up again.  We need to quantify how much tension we can put on
   the planes without distorting the electrodes (or only distorting 
   them within allowed tolerances)?  Is the Rohacell (only 2-mm thick) 
   actually worsening the problem due to its weight and flimsiness?  
   Of course, if we can successfully design a cathode plane without the 
   Rohacell backing, the issue of sealing the Rohacell becomes moot.

Grounding Issues

 - Fernando has nearly completed preparations of an overall grounding 
   specification document.  This is needed for pre-brief material for
   the upcoming system review.  It should be ready in the first part of
   next week.

Cooling System Tests

 - Denny has nearly completed the set up of the cooling system.  He
   still has to include the thermistors for reading out the coolant
   temperature local to the preamplifier board.  DSC will contact
   Bill Crahen to get the aluminum and copper brackets for these

Gas System Design

 - Vladislav (Slava) Razmyslovich is working on a preliminary layout
   of the gas handling system for the CDC and FDC in preparation for
   the upcoming systems review.  We will sit down with him in a
   specialized meeting to review the design concepts after the review
   is over.

Gas Volume Definition

 - No progress on new calculations during the past week.  We will
   revisit the issue of modeling the gas in the drift cell region
   if the input is in the wire frame or spacer after the systems

STB/HVTB Discussion

 - Kim raised an issue with the design of the wire frame circuit boards.
   She stated that she believed the overlap regions on neighboring
   boards (the half-lap regions) are too flimsy and not mechanically
   strong enough.  She would prefer if we moved to a butt joint design.
   DSC talked to Tim after the meeting and he stated that the overlap
   is absolutely crucial for the mechanical strength.  His suggestion
   was to make the thickness of the overlap portion closer to 13 to
   14 mils instead of 10.  Perhaps we are leaving too much room for
   epoxy clearance.
 - Kim needs to provide an instructional writeup for the Phase 1 and
   Phase 2 wire frame PCB component attachment.  This is on her to-do
   list, but is not a high priority for now.

Cathode Board Discussion

 - Roger needs to prepare a document for QA/stuffing/cleaning for the
   cathode boards and a similar document for the cathode daughter
   boards and ground boards.
 - Roger was planning to do some test soldering for the rigid flex
   cables to a sample cathode board.  No update was given during the

Small-Scale Prototype

 - Simon has collected data with a 40/60 gas mixture and measured the
   resolution of the cathodes using the Hall B SIPs and charge integrating
   ADC (the standard picket fence measurement).  The results are fully 
   comparable with the 90/10 mixture.
 - Simon has measured the gas gain of the chamber with the 40/60 mixture
   and found a value of about 5x104, which is compatible with
   our calculated vale of about 1x105.
 - Simon has reconfigured the readout now using the ASICs, shaper, and
   FADCs to move on to the next step in the ASIC characterization.
   So far he has the readout working with the ASICs/shaper/FADC working
   on a set of anode wires (using a 100-MHz FADC).  He is trying to
   get the FADC readout working for a set of cathode strips, but is
   having some minor technical difficulties getting the second 100-MHz
   FADC to readout.  This will be a solvable problem in the near term.
 - We discussed how we need to quantify/measure the dynamic range on
   the cathodes and anodes.  The procedure will be to measure the
   FADC spectrum amplitude distribution for all peaks in the spectrum
   above a baseline-subtracted threshold of 20 mV.  Simon has posted 
   some FADC spectra in the FDC logbook for the anode wires.  These
   distributions typically have 3 to 5 peaks in them due to the
   arrival of the clusters on the wires.  These plots will be posted in
   the logbook once they are made.  To determine the FDC dynamic range,
   we then need to understand the amplification/attenuation in the
   system with the GAS-1 ASICS, shapers, attenuators and then scale
   the measurements from the minimum ionizing muons to the more heavily
   ionizing hadrons that will be in the FDC.
 - In FDC log book entry #357, Simon posted an X vs. Y plot from the 
   small-scale prototype measurements with the 2 micron cathodes.  He saw 
   evidence of waves in the reconstructed wire positions.  We need to 
   understand if this is an issue with the pulser calibration.  Simon believes 
   that this could be part of the problem.  Fernando also measured the resistance
   across strips with a sample of the 2 micron cathode boards.  Here the
   strips were all about 5 inches long.  He found resistance values 
   typically below 3 to 4 Ohms.  However, there were several strips with
   values above 10 Ohms, and one measured 100 Ohms.  We need to understand
   if this is due to an inherent problem with the board.


 - DSC has collected all of the available FDC subsystem design drawings
   and placed them on the FDC website.  The URL is:
   http://www.jlab.org/Hall-D/detector/fdc/drawings.html.  Folks should
   go through the drawings and let DSC know what drawings and/or categories
   are missing for a complete design set.
 - Also folks should send DSC the latest design drawings where there
   have been changes to keep this web site up-to-date through the
   review season.

Work List

 - The FDC short-term work list has been posted on the FDC web site
   (see http://www.jlab.org/Hall-D/detector/fdc/).  This is continually
   being updated and DSC welcomes any feedback or comments from the group.

Minutes prepared by Daniel. Send any comments or corrections along.