Minutes-12-3-2009
From GlueXWiki
FDC Weekly Meeting
Date: December 3, 2009
Participants: Daniel, Mark I., Brian, Fernando, Tim, Kim, Chuck, Bill, Casey, Simon, Eugene, Glenn
Next Meeting: December 10, 2009 @ 1:30 a.m.
Contents
General Construction Updates
- We identified several big leaks in the first of our cathode sandwiches. It is suspected that they arose from uneven clamping pressure during the sandwich lamination. Casey mounted the cathode to the granite table vertically after we disassembled the stack and went around and epoxied the gap more thoroughly. This same operation will have to be completed on the second cathode sandwich as well. - During the step of epoxy sealing of the first cathode sandwich, epoxy inadvertently filled one of the rigid-flex power connectors. This was not found until after the epoxy cured. The rigid-flex assembly was broken off and replaced. - The through-holes on all stack layers used for the first two layers were re-epoxied. This time pressure was applied so that the epoxy got deeper into the Rohacell. One issue is that during stack assembly, the threaded rods that go through the holes were removing epoxy, which led to potential leak paths. - Given that Bill was not satisfied with the gusset arcs that he made out of plastic, he had a new beefy aluminum set made in the shop to replace them. - Immediately after the FDC meeting, we reassembled the two layers of the stack for leak checking, as well as HV testing and signal checkout on the second layer wire board and cathodes. During assembly, we noted that the o-rings in one of our spacer rings were compressed and were below the surface level of the spacer. We replaced these o-rings (which were made from the 50 durometer material) with the soft o-rings (made from the 8 durometer material) mounted on top of pinstriping tape to raise these level by about 8 mils in the o-ring groove. Leak checking will proceed this week. - Before adding the third (and final) layer to the full-scale prototype, we will do signal checkout. We will hopefully have a leak-tight chamber and can let gas flow over the weekend to purge the two layers. Stay tuned. - Fernando completed his test plan on the single layer prototype using a single anode preamp board and a single cathode preamp board, both stuffed with the new GAS-II preamps. He has posted GlueX-doc-1384 that folks should take a look at. These few plots have taken us a long time to acquire and the news is quite encouraging as a first series of measurements. Obviously, there is much more to come to finalize and checkout the FDC system design. - Brian prepared the wire samples from the CDC/FDC wire spools that arrived. They were delivered to the W&M folks who will be doing the check out. They have already been provided with samples of our sense and field wire to set up their machines to carry out the planned measurements. The test procedures for wire spool acceptance have been prepared by Bill and are on the FDC web page. - Bill will follow up on getting us access to an oxygen sensor to check the oxygen levels in our chamber outflow. - The preliminary FDC stack assembly document draft is located at: /u/group/halld/Engineering/PRELIMINARY DOCUMENTS. The document will continue to be fleshed out during the assembly procedure for the full-scale prototype. We will have to add steps in our construction plans for leak checking. - DSC pushed for better tracking of our epoxy freshness. We need to check the dates on the epoxy before using. If it is too old, then the epoxy needs to be discarded so that it is not used in the construction.
Wire Frame Update
- Wire frame P3 needs to have its final preparations completed. This includes electrical QA/repairs, final cleaning, HV components potted in Humaseal, recheck of epoxy seals. It then needs to be laminated to its cathode. We hope that this work will proceed on Monday so that the frame is ready for stack assembly on Tuesday. Stay tuned. - We need to have a dedicated meeting to design what the schedule for work on the Phase 3 wire winding will be. The highest priority for work scheduling will be doing work on upgrades of the wire winding facility. This includes a better strongback design, the design and construction of precision combs, modification to the wire winding table, and a list of other items with the system. Stay tuned, more to come. - DSC received a message from Keith Solberg at IUCF regarding the status at IUCF. They are in the midst of a management shake-up. It is time to schedule a meeting of a more formal nature so that firm committments can be made. DSC will set a meeting up. - The wire frame construction document is located at: /u/group/halld/Engineering/PRELIMINARY DOCUMENTS. We will include the information on the wire electroplating process shortly. - The parts of the jig to use for the wire electroplating operation are in our hands. They will be assembled as we find time. - We need to prepare a document for the electrical QA of the preamp connectors on the wire boards. - DSC, Bill, and Fernando will plan a meeting to go over the circuit board design work for Kim. - Kim is following up with the contacts obtained from Peter Monaghan regarding large-area PCBs. Kim is still in back and forth with the board house and the board material supplier. The outlook may be rosier than it was a few years ago. Stay tuned.
Cathode Update
- Soldering of all rigid-flex assemblies for the full-scale prototype has been completed. - The current draft of the cathode construction document is located at: /u/group/halld/Engineering/PRELIMINARY DOCUMENTS. - We need to prepare a document for QA/stuffing/cleaning for the cathode boards and a similar document for the cathode daughter boards and ground boards. - The order for the cathode material was scheduled to arrive on Dec. 26. Roger asked that it be held for delivery until the first week of January when shipping and receiving is open for business. Tim suggested that before we store away the board material, that we do an inspection and quick QA check to be sure that there are no obvious problems before we store the material away.
Leak Issues
- The second half of the meeting was focussed on the leak issues that have
been plaguing us during stack assembly so far. DSC began by listing some
of the known issues:
* Leaks in middle of cathode sandwich due to uneven clamping pressure.
* Leaks through the via on the wire frame PCBs. This can be solved by
having board house fill the vias and then to cover all with solder mask.
* Better sealing of the I.D. of the wire frames.
* Defining the torque applied to the stack bolts so that we don't
over-tighten and crush the Rohacell.
* Better sealing of the through holes on all layer frames.
* Modify the PCB design so that no traces are directly under the o-ring.
* Modify the spacer groove design to allow us to eliminate using the
instant adhesive to hold the o-rings in place.
* With the design problem with the capacitor position on the back side
of the STB, there is no support under the o-ring, i.e. the
unsupported circuit board is to flexible to push up against the o-ring
for a reliable seal. This will not be present with the final circuit
board design.
- Bill presented a much more aggressive design replacing the gas spacer
and inner cathode frames with solid G10. His design incorporates a
wide gasket seal.
* Fernando had a few concerns with potential gas leaks from the foam
gaskets. He suggested getting more information such as:
a. material composition
b. outgassing
c. adhesive
d. long term performance with Ar-CO2
e. radiation "hardness".
Most foam gaskets and contact adhesives loose their properties over
time. In particular, most foam gaskets loose their elasticity and
crumble, even with closed cell compositions. He is concerned that
after 2 years of operation leaks will develop.
* Obviously the amount of material he is proposing adding back in is
of concern. Bill will provide a listing of the parts n' pieces to
Simon for his proposed design and we can check the background issues
and photon losses for BCAL and FCAL.
* DSC raised concerns about straying too far from the nominal design as
we will not be able to full vet and study the ideas within the
full-scale prototype. There are lots of tight spaces and potential
conflicts can be (and have been) missed just relying on our 3D CAD
model.
* Bill is concerned about the crushing of the Rohacell. We discussed
the notion of using inserts in through holes on the frames.
* Tim's notes from the discussion:
1. Causes and potential fixes for the production packages were discussed
2. Some known and Possible causes of leaks include leaks through the
Rohacell bonding boudaries, deflection of unsupported wireplane PC board
under o-ring, grounding vias on pc board, bond voids on cathode
sandwich, protrusion of traces (3-4 mils) on pc board, not enough
compression on o-ring, too much compression on Rohacell, not enough
stiffness in outer channel supports.
Action items:
a. Develop test plan for testing existing design, slightly changed
design and addition of G10 ring to support bolts and gas seal (Bill
Crahen)
b. Get worst case additional material to Simon for background analysis
(Bill Crahen)
c. Perform background analysis on increased material (Indiana U?)
d. Gather all changes needed for production pc board (Kim Shinault).
* Obviously lots of ideas and discussion that question the nominal
design at this late stage made folks nervous and edgy. More discussion
and planning will continue as we move forward.
Preamplifier Boards
- An order for more ASIC chips is expected very shortly. Fernando expects that we will have ~40 boards ready by the end of November.
Cosmic Ray Test Stand
- Several meetings ago we focussed on the wiggles seen in the reconstructed wire position from the cathodes (see log entry 419) in the FDC logbook. We believe that the periodicity seen is due to the algorithm Beni is using to determine the U and V centroids. Beni get back to this soon. Stay tuned.
Work List
- The FDC short-term work list has been posted on the FDC web site. 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.
