FDC Weekly Meeting
Date: February 14, 2007
Participants: Daniel, Tim, Fernando, Kim, Simon, Brian, Chuck
Next Meeting: Wednesday, February 21, 2007 @ 1:30 p.m.
Drift Chamber Review
- As previously announced, the GlueX drift chambers (FDC and CDC) will be undergoing an external review on Mar. 6, 2007. Folks have been asked to provide brief write-ups of various sections (Brian - bas, sandwich construction, cathode flatness measurement, Tim - sag, cooling, stress calculations, thermal calculations, Fernando - preamps, daughter boards, cooling) for the FDC technical design report. Folks will also be asked to provide up-to-date drawings for the FDC design. This documentation is an essential part of the review. - Folks should make sure that they go over the posted talks and provide feedback on any issues that are unclear or (gasp) presented incorrectly. - Folks should also make sure that they are available to attend the practice talks and, of course, the real talks to assist in answering questions that come up.
Cathode Mechanical Mockups
- Brian has completed the construction of the first dummy cathode sandwich mechanical mock-up. The flatness of the cathode was measured by the JLab Survey Group using their Faro laser tracker. - The measurements had an accuracy of about 50 microns. The measurement results were quite encouraging and demonstrated flatness of better than +/- 100 microns on average. The flatness went out of spec where there were imperfections in the kapton surface and along the g10/kapton edge due to the difference in thickness of the materials. - Brian has been told that our dummy cathode boards with copper strips are being held up as the board manufacturer cannot get the material quickly. As soon as it arrives at the manufacturer, the turn-around time will only be several days before delivery to us. - Brian will make another mechanical mock-up with these new boards (using the lessons learned from the first prototype) to understand what issues the copper strips bring about in the manufacture. - Brian has been asked to make a cathode plane using the tensioning system and to measure the surface to quantify the lateral distortions of the cathode strips. The details on what the set tension should be are still unclear. At the present moment, this is more of a visual and "feel" process.
Circuit Board Material
- Our current planning for the STB and HVTB circuit boards is the standard FR-4. However DSC brought up another board material called HVPF that Chris Cuevas was talking about for Hall B. This material has a much higher dielectric constant than FR-4 and issues with spacing of traces, thickness of layers, leakage currents, etc are much less of an issue. This material also has a much higher surface resistivity than FR-4. - Fernando will follow up with Chris on this material. The big issue here is the rumored cost of this material. It is not expected to be cheap.
Ground Plane Thickness
- Gerard Visser was given a sample of the aluminized mylar that we nominally plan on using for our ground planes and he was going to give us feedback on the suitability of this material. No word yet. - After the meeting, DSC sent Gerard email to ask him to weigh in on this issue.
- We have been discussing at our last two meetings a current issue with the design regarding the space available for the daughter board and connector on the cathode plane face that is closest to the anode board. Presently there is no straightforward way to fit these connectors in without trimming down the g10 spacer or adding clearance notches to the anode board (which leads to flexing of the now weakened board). - Fernando believes that he has located some slimmer profile connectors that are below 5 mm thick. This should help. - We also discussed an option of putting the connectors for the cathodes on the back side of the cathodes. In other words, the connectors could fit in the middle of the cathode sandwich. This would save us from having to notch the anode boards. After working out the basic ideas, this seemed to be a promising avenue. DSC asked Tim to prepare some drawings/sketches of what we had talked about and we will continue down this design road discussion at our next meeting.
- Joe B. did not attend the meeting this week so we could not discuss the latest drawings on the cable layout. - DSC actually put the wrong idea in last week's meeting minutes. The readout cables will indeed go all the way around the FDC package. However the daughter board connectors will be fixed to be on the FDC perimeter above the rails so that they are accessible.
- Tim has done a number of calculations of stress and thermal environment. After the meeting, Tim passed along what he had to DSC.
Minutes prepared by Daniel. Send any comments or corrections along.