Minutes-7-24-2008
From GlueXWiki
FDC Weekly Meeting
Date: July 24, 2008
Participants: Daniel, Simon, Chuck, Beni, Brian, Fernando, Eugene, Bill, Micah, Kim, Herun
Next Meeting: July 31, 2008 @ 1:30 p.m.
Contents
Cathode Planning
- Cathode delivery date is expected within roughly 1 to 2 weeks. - As the cathodes have been extended in length, we discussed last week how Allflex should ship them to us. Roger will have to let us know if these instructions have been communicated. DSC sent him an email to follow up on this. - Fernando has posted GlueX-doc-1082 detailing the electrical QA test plan for the cathode boards. Folks should look it over and provide feedback to Fernando (this should be sent on to Gerard Visser for his comments). This will need to happen immediately on receipt of the boards from Allflex. Once we characterize and perform QA on the boards, we want to communicate this information to Allflex and if everything is acceptable to us, move to complete the order for the remainder of the cathode boards for the prototype. Fernando showed us the probes that he has put together to do this work. The process, while perhaps a bit time consuming, should work quite well. - Bill has done some thinking on a technique to cut the edges of the cathode boards. He will put together a sketch of his design and we will then begin procurement of the necessary parts n' pieces. - 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. - Fernando has looked over the polyimide specification sheets provided to us through Allflex for the 2 micron Cu boards and the 5 micron Cu boards. While these materials are similar to Kapton, they are slightly different. Fernando saw nothing in the specifications that caused him any worry. - Due to the height of the solder connection between the cathode board and the rigid flex assembly, as well as the height of the rigid flex cable itself, we will have to revisit the design from the standpoint of adding clearance pockets on the surfaces that mate up against this assembly. One flex cable goes in the space above the spacer ring, so perhaps no modifications on this surface are necessary. However, the the cathode ring that goes up against the wire frame will need some pocket cuts. Chuck has started to look into this and has done some initial layout in the CAD model. He still has some things to check with Roger about to finalize this work. We talked about when these pockets need to cut, and it was agreed that it was best to do this after the wire board frame was constructed to minimize rotational alignment issues. We will have to find a way to have these cuts made without significant handling problems with the circuit boards. This design work and related decisions need to be completed very shortly as wire frame construction for the full-scale prototype will begin in about 1 week. - 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 has prepared a more detailed draft of the cathode R&D planning document. This document has been passed on to Simon, Brian, Bill, and Elke. Folks should be looking this over to make sure that the task list is complete, and accurately detailed with respect to the individual steps in each task, the time estimates, and the assigned manpower. This document will be turned over to Chuck Hutton next week to turn into a Gantt chart. We need to understand better how the delay in the cathode R&D work planning will affect the FDC schedule now and into construction. - Brian and Bill should begin to layout a detailed outline for the cathode construction steps and circulate for feedback. - DSC discussed a more concrete plan for attaching ground connections to the cathode plane. It seemed to be a reasonable approach given what we have discussed in the past. This work will be incorporated in the cathode R&D planning document. We expect that the same system used to connect the external ground to the cathode plane can be used to connect the external ground to the ground plane.
Full-Scale Prototype
- The work on the assembly jigs is in queue in the JLab machine shop. No update today on when they will be done. Brian will check with the shop. Once the jigs are ready, we will move to begin construction of the full-scale prototype wire frames. - Brian circulated a construction plan outline for the wire frames. It has been passed on to Bill Crahen for feedback. - Fernando reminded us that we need to perform HV checks on the STBs and HVTBs before frame construction begins. He will work to prepare a test plan and get this work underway. It should be completed by the first week in August to avoid delays to construction. - Tim Whitlatch helped us located an A-frame for lifting of the aluminum tooling plate for the frame construction. He will work to set up a formal arrangement so that we can have it during frame construction. He will try to have it available for us during the first week of August. More to come. - The granite table that we ordered will be arriving August 1. Another group will occupy only until the end of July and should be out of our hair before we want to move in. - We talked about the schedule for wire frame construction. We are aiming to construct 4 frames for the Phase 2 winding. Brian felt that a realistic time frame to aim for would be the end of August. The delays are not due to his time, but in getting the frames through the machine shop. We will have to make some of these shop submissions through appropriate higher-level channels to get them done with relevant turn-around time. - Anyone that has items that they know need to be ordered for the FDC full-scale prototype effort must contact Elke to let her know the plans, otherwise money most likely will NOT be available. One thing that we did discuss were the LV cables and signal cable connectors. Fernando and Kim will work on preparing this information and placing the order. - The Ph.D. student, Herun Yang, showed up today for her first FDC meeting. Elke has assigned her to work on the FDC project. She could be responsible for HV testing of the wire frame circuit boards, cathode testing, full-scale prototype testing, etc. - Chuck has included the FDC gas windows in the 3D CAD model.
Cathode Prototyping
- Brian has been in discussion with some outside companies about
our technique of joining the three separate cathode boards together.
The following information was included in last week's meeting minutes.
However, as it is so important, I repeat it again for emphasis (for
emphasis!). 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 is now staring 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. He is currently starting to think about a system
to deliver a controlled puff of air to the cathode to induce the
vibrations. Some initial data (with Simon serving as a calibrated
source of air) showed that, in principle, the system should work, but
we still have some work to complete to bring this all into working
order.
Test Frame Wire Winding
- IUCF has been working on other projects and has not yet started work in earnest on the Phase 1 project. DSC and Keith have instead been working on details of planning, and specifically where in the work plan they need to communicate with us before proceeding to the next step. Two things have happened this week. DSC and Keith have agreed on a plan to use Moire patterns to verify the relative wire positions on the winding table before attaching the wires. Secondly, the sag of the frame support jig on the winding table has been measured and preliminary discussions have taken place on how to proceed. - 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. Roger and Kim have taken care of finding a vendor, making the drawings, and placing the order. The masks are expected to be at IUCF by the end of this week. - 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 stepped us through some pictures of his design and he is nearly ready to begin parts procurement. He indicated that the three linear bearing that he will order should take about 2 weeks to come in. - One thing that we discussed is exactly what we will want to measure with this system. Will it just be single cathode frames without a ground plane, or will it be required to measure the fully completed cathode sandwiches. We decided that we would design in the flexibility to adjust the laser measurement head to accommodate these different options. - Micah completed measurements of the cathode flatness profile as a function of rotation angle for the high tension cathode and the foam backed version. The data, while not fully clean to interpret due to the known frame warping issues, seemed to indicate that some of the profile was locked into the cathode and rotated as the frame rotated. Clearly these measurements will have to be repeated when Bill's design changes are fully incorporated. - 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 gotten into this and is starting to make progress. He plans on giving a detailed update on his work either next week or the following week. - As there are no further flatness measurements planned on the prototype cathodes until Bill's work is completed, Micah will concentrate now fully on preparing the control and display software for the new system.
Cooling System Tests
- Bill and Fernando completed the planned cooling system measurements for the daughter boards. Fernando is working to put together a document of the test results. He indicated that no further cooling system tests are planned until we have more cards and can test a bigger portion of the system. So far, things are working according to expectations.
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. - The next combined FDC/CDC meeting focussing on the dynamic range measurements will take place on Monday July 28. - 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.
