Minutes-7-17-2008
From GlueXWiki
FDC Weekly Meeting
Date: July 17, 2008
Participants: Daniel, Simon, Chuck, Beni, Elke, Brian, Fernando, Mark, Eugene, Bill, Micah, Kim, Roger
Next Meeting: July 24, 2008 @ 1:30 p.m.
Contents
Cathode Planning
- Cathode delivery date is expected within roughly 2 weeks. - Our transport box has arrived at Allflex. Due to our change in plans for the length of the boards, we need to provide Allflex with instructions on how to prepare the shipment. DSC suggested to have Allflex stack the boards and then roll up the naked ends on cylinders. Roger will communicate this to the Allflex representatives. We will modify this box upon arrival at JLab to include the ability to flow nitrogen or dry air to prevent oxidation of the copper traces. - Fernando has received the probes for the electrical checkout and characterization of the cathodes and will work to put together a test plan document. This should be ready for review next week. - Bill and Brian have begun discussing planning of how to cut the cathode board edges. They will do some trial cuts with pieces of test Kapton and then converge on a procedure. More details to come so stay tuned. - Roger plans on ordering a set of 3 to 5 of the new cathode daughter boards that we plan to use with the full-scale prototype. We expect that with the copper fingers extending off the flex cable, that soldering to the cathode surface will be a very straightforward procedure. - Roger circulated the cathode board material specification sheets that we received for the material supplier. DSC has asked Fernando for comments or impressions. - 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. Chuck understands the issue and will work to make some pictures for us to look at. We most probably will add thin pockets in the G10 frame skins to allow for the clearance. Once we get a look at some relevant design pictures, we can make sure that there are no issues with these pockets. This work needs to be brought to conclusion in the next few weeks as we need to do the machining on the skins as part of the wire frame construction procedures. - Brian will modify his Lucite box design for storage of the completed cathode planes. The cathode planes can stack upon one another (unlike the strung wire frames). As this box is not needed for at least several months, this work is not super high priority. - DSC circulated a cathode R&D planning document to the group for feedback. Brian and Simon are now going over this document to ensure that the task list is necessary and sufficient to complete our design work on the cathode construction procedure. DSC will meet with Brian to go over this list. Once we have a complete task list, DSC will prepare a time line so that we can understand the impact on FDC design completion and the start of construction. This will also give us some clues as to manpower issues.
Full-Scale Prototype
- The work on the assembly jigs is in queue in the JLab machine shop. The work should be completed in about a week. Once the jigs are ready, we will move to begin construction of the full-scale prototype wire frames. As there is no money to spend on a new A-frame for the lifting, Tim has investigated borrowing equipment already at JLab. He has identified two A-frames and we need to look them over to see if they will work for us. Brian will be in contact with Tim to have a look at the equipment. Once we decide if they are useful for the FDC work, we can then work out a loan agreement. - The granite table that we ordered will be arriving August 1. Another group will occupy the clean tent for the first week of August, and then we will take over. Note that we expect the cathode construction work to take place in the clean tent and the wire frame construction work to take place in EEL 126. - Brian will work to prepare a wire frame construction document during the construction of the full-scale prototype frames. This work should begin once we get the assembly jigs from the shop. Due to R&D budget time lines, the funds for the Phase 2 wire winding have to be obligated before the end of September. This mean that the prototype wire frames need to be basically constructed by the end of August. - We discussed a few remaining items that we need for the prototype. We need to provide Elke with a list so that she can understand the budget fully. - Elke said that she has a Ph.D. student available that she can assign to the FDC project. This student could be responsible for HV testing of the wire frame circuit boards, cathode testing, full-scale prototype testing, etc.
Cathode Prototyping
- Brian has been in discussion with some outside companies about
our technique of joining the three separate cathode boards together.
There are some important points that are coming to light:
> The use of 2-in wide Kapton tape is certainly not be best
joining material that we can use as there are much better adhesives
out there. We would be much better served to use Hysol adhesive
on blank Kapton strips. Brian is still digging up information
on whether the improved strength is against peeling or sheer
forces.
> The strength of the bond of neighboring boards will be improved
if we use a wider strip of tape. We may ultimately need to
consider this.
> The 20-in wide Kapton rolls that Allflex receives are sliced from
60-in wide rolls made by the material vendor. Apparently it is
the case that the tensile strength of the middle pieces have a
different profile that the outer pieces. Once the 60-in roll
is slices up, they do not keep track of inner and outer pieces.
This is problematic if we require a large tension to be applied
to our 3-piece cathode. The distortion of the electrodes would
be different for the different pieces! This would demand that
we want the tension to be as low as possible. This also could be
a problem if we want to use a fixed weight to define the cathode
tension. With different tensile strengths in the different
pieces, we could not guarantee a fixed tension. Anyway, some
things to consider as we move forward.
> The key in all of this is how flat the cathode pieces from Allflex
are. In the past, our technique has been to apply enough tension
to remove the wrinkles. If the delivered cathode pieces are very
flat, we are certainly in a much more advantageous position. We
also eliminate the worry about stretching the cathodes if we can
employ a low enough tension and also eliminate worries about the
joints between boards pulling apart.
- From the flatness measurements that have been made on our prototype
cathodes to date, the version with the 2-mm thick foam backing will
not work. The bulging profile is too large. This is presumably
due to gravitational sag of the foam. We are doing measurements now
that will address this. The apparent bulging that we have seen in
the unbacked (tensioned) cathode may not be fully real in that the
measurement system could not force the cathode to flat. The bulging
is like associated with a potato-chipping of the support frame under
the tension load.
- Brian has received a Kapton roll 48 inches wide. We will use this
to test various cathode construction techniques and to study methods
of attaching the cathode to the frame. Brian will work to develop
a system to measure the cathode membrane tension while on the
tensioning fixture. This system will use the laser measurement
head that we have for the flatness measurement system. This process
will begin setup within the next week.
Test Frame Wire Winding
- The paperwork for the continuation of the Phase 1 wire winding contract with IUCF is finalized. The agreement is that this work will be completed in full by August 22. DSC and Keith are finalizing the details of the work plans. - The technique to scan the wire placement on the winding table before attaching to the frame will use the technique of Moire interference fringes of the wires and an overlaid mask. The reference for this work is H.B. Dijkstra et al., NIM 188, 59 (1981) (a wonderfully brief article). This technique is simple and fast and should tell us placement accuracy to easily better than 50 microns. IUCF has requested that JLab provide the mask that is laid on top of the wires. Keith will provide details on what is needed before the end of the day and DSC will work with Kim to see if the mask can be made at JLab. - DSC talked with Steve Christo about the quality of our Cu-Be wire. He did not think that there was any reason to discard the existing sample and that using it in our prototype would not lead to any noticeable problems. - 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. - As the time to complete Phase 1 and Phase 2 winding before the end of the fiscal year will be super tight, DSC will work with Elke to complete as much of the required Phase 2 paperwork as we can in the next few weeks so that we can move quickly to getting Phase 2 in place before time runs out.
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.
Cathode Flatness Measurements
- Bill is working to finish the engineering design of the cathode flatness measurement system. He will have some design drawings to walk us through at our next FDC meeting. - Micah will continue making measurements of the surface profile of our backed and unbacked cathode prototypes as a function of rotation angle. He will also disturb the cathode surface and study repeatability of the measurements. - We need to work to define the allowable surface flatness variations for the cathodes. What can we tolerate and still deliver a system that can meet the resolution requirements for the cathodes and the wire plane? Eugene has volunteered to take this on. Simon will pass along the relevant notes that he has to Eugene.
Cooling System Tests
- Bill installed the flow valve in the cooling system in F117. Bill and Fernando will continue the cooling system tests this week.
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 when we get a chance.
STB/HVTB Discussion
- 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.
Small-Scale Prototype
- Simon and Fernando have taken some more Fe-55 measurements with the small-scale prototype in an effort to finalize the FDC dynamic range specifications for the anodes and cathodes. Simon and Fernando should be able to complete the analysis of this new data within a week and Simon can then work to update the results document. What we have so far is posted as GlueX-doc-1070. - We still have the lingering issue of the problematic x-y plots from the 2-micron Cu cathodes. Simon will revisit this problem by taking some new pulser calibration data to see if this makes the apparent problem go away.
Drawings
- 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.
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.
