Minutes 4-4-2007
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FDC Weekly Meeting
Date: April 4, 2007
Participants: Daniel, Tim, Kim, Simon, Brian
Next Meeting: Wednesday, April 11, 2007 @ 1:30 p.m.
Contents
FDC Budget
- The FDC budget preparations for CD-2 are nearly complete. We are waiting for just a few last numbers. These include the quotes for the composite frames for the cathodes and the storage boxes for the wire planes. - When these numbers are available in the next few days, DSC will turn over our budget document, the manpower request for construction, and all backup information (quotes, pricing information, etc) to Elke. Note the FDC budget document is on the GlueX portal as GlueX-doc-735.
Short Term Work Plans
- DSC has produced a document listing all short term (i.e. this year) FDC work plans and distributed copies of this draft. Everyone should look this over and provide feedback as to items that have been overlooked. - Once we have a complete document (for now anyway), it will be posted on the FDC web site (http://www.jlab.org/Hall-D/detector/fdc/ for those who are not aware of this).
Cathode Sandwich Construction
- Brian has been working on producing new cathodes with the dummy cathode boards that just arrived. The latest version will be one without the Rohacell backing. He will make a single cathode frame and deliver it to the JLab Survey folks to test non-contact flatness measurement schemes using an optical system. His first step was to glue the 3 separate cathode boards together. The different strips have built-in fiducial/alignment marks to reduce the positioning uncertainty to a few mils. - Brian has been in contact with the board vendor regarding the defects that are apparent in these boards to see how we can eliminate them from our production planes. He has not gotten any feedback yet, although they are apparently aware of the problems. - Roger has been working to find a vendor who can supply the cathode board material in a size suitable to manufacture a single piece cathode board (remember it is the material that is the present limitation as the board manufacturer can handle the full-size boards). He has not had any luck as of yet, but feels confident that there is some company out there that can deliver. Presently he has 3 contacts that he is pursuing. The company needs to be able to provide boards on a 1 or 2 mil kapton backing with copper thicknesses down to 1 micron. - Tim is currently working on developing a test plan to measure the board deflection. There is still much to think about, but remember the goal is to calculate the expected cathode deflection in the electric field so that we can work to keep this below a level that would impact the cathode resolution. These deflection calculations need some numbers from measurements to determine the tension. More to come. - Before the new cathode boards are tensioned, we will measure the strip positioning so that we can have a reference to compare against after the tensioning. We need to understand what we are up against in terms of lateral cathode surface distortions. We then need to define a tolerance and then a procedure for reproducibility for the production boards. - A major concern with the no-Rohacell backing option for the cathodes is the deflection of the surfaces in the electric field produced by the wires. We need to study the deflection also as a function of the kapton thickness. If we use 1 micron Copper and eliminate the Rohacell, we could potentially afford to go with a thicker kapton backing to reduce the effects. Remember that we need to keep the tension on the cathode boards to a minimum to prevent distortions of the strips. We also discussed employing a Rohacell web behind the cathode that we could attach to. More to come on this issue.
Circuit Boards
- As Roger is on a chase (or a mission) to find a way to enable us to construct the cathode boards from a single piece, DSC also asked him to find a company that can produce our STBs and HVTBs as a single piece. This will simply the wire frame construction and will give us more flexibility in laying out the connectors on the STB side and more flexibility in laying out the HV busses on the HVTB side. - Kim has begun work on a layout of the HVTB boards. She began working on a single board first. The capacitors will again be located on the back of the boards. - We discussed the possibility of including cut-outs on the G10 frame to enable access to the capacitors on the STBs and HVTBs. This was viewed as a good idea that we should pursue.
Frames and Spacers
- We have a design for a composite cathode frame to replace the current 5-mm thick G10 frames in the current design. We have decided that these frames will represent our nominal design choice. The design of these frames (also 5-mm thick) has an outer surface layer of e-glass (non-conductive), a layer of carbon fiber, and an inner Rohacell foam layer. The thickness of these frames is effectively a factor of 3 or 4 smaller than the G10 frames. - Simon will pass the dimensions and material properties on to Richard, David, and Eugene for Monte Carlo studies of photon conversions. - We discussed replacing the CH2 spacers with the composite design, but the savings in terms of thickness is modest (less than 20%). Given how much easier it is to work with CH2, we have decided to keep this as our nominal material choice for now. Given that the costs for the composite and the CH2 are about the same, we can change our minds downstream if necessary.
Gas Ports
- Casey in the JLab machine shop developed a much simpler gas port than we had initially planned. He developed a nice gas port by crushing a piece of stainless steel tubing. The shaping of this tube still needs some fine tuning to give us the flared shape that we are after for better gas distribution. These ports can be inserted into the CH2 spacer or the G10 wire support frame. We have yet to make a decision.
Magnetic Field Studies
- The folks at BNL have gotten back in touch with us regarding a possible magnetic that we could use. However they have to check the field orientation. It appears that there may have been some confusion in what we told them. Brian will follow up on this. - Brian also gave the information on our magnet requirements to Elke so that she could communicate with her contacts at DESY. No word yet. - We discussed the options that may be available. At BNL (which is much closer and more convenient to get our equipment to), we would be doing field tests with cosmic rays. At DESY, we would have the opportunity to do the field tests in a beam. It is not clear if we want to do both studies simultaneously. We need to think about this in some detail.
Small-Scale Prototype Work
- Roger is working to finish the layout of the new +/-75 deg cathode boards for the small-scale prototype. He expecting to complete this work in a few more days. He will circulate the drawings upon completion so that we can get these out the door soon.
Ground Planes
- A minor complication has come up with the ground planes that go between each cathode layer if we do not use the Rohacell backing. How do we support them? Our goal is to define the ground plane so that it is equi-distant between the cathodes. We need to think about this issue and how close the ground planes can be to the cathodes and still do the job. This is a question for Fernando and for Gerard.
FNAL MOU
- The first draft MOU provided to Karen Kephart has been modified by DSC and sent back to her. DSC will follow up with Karen to find out the status of the draft. We want to get this to our procurement folks real soon to get the formal process underway to complete the agreement so that winding of test planes can proceed this summer.
GARFIELD Studies
- Simon will give a talk on his GARFIELD studies of various gas mixture options for the FDC system at the next Hall D meeting.
Minutes prepared by Daniel. Send any comments or corrections along.
