October 7, 2010 FDC meeting
- Blue Crab status
- Frame production
- Update on PCBs, fADC125 and other (Fernando, Chris, Gerard)
- Wire stringing: fixtures, movement system (Bill, David)
- Update on tension measurements (Lubomir)
- Wire tension requirements (Lubomir)
- Other: gas system using methane
- Full-scale prototype
Participants: Eugene, Fernando, Chris, Simon, Beni, Glenn, Gerard (on the phone), and Lubomir. Bill, David, and Casey were busy at 126 laminating the first wire frame.
- There was a meeting between JLab people and AdvanceTEC that will build the clean room. Completion date: January 7th. AdvanceTEC had two concerns: the power coming to building (from Dominion Power) is close to the expected use and has to be checked. The second is related to the quality of the floor, not good enough for 10K clean room. AdvanceTEC will send a quote to re-seal the floor.
- Bill, David and a machinist from our machine shop visited "Vision machining". The frame production has started. About half of the spacer rings are ready. Two of the wire frames are here at JLab, being laminated in the moment with the Rohacell rings in 126. Five Rohacell rings were made by Casey and David. Tomorrow morning David with techs will be at Blue Crab to turn up the two granite tables there. The idea is to start using some space at Blue Crab for the lamination because of the limited space in 126.
- Gerard will use the pulses generated from Garfield to study the timing of the fADC125 and will try different interpolation algorithms. He's working now on the firmware.
- Chris: all 28x4 boards were shipped to the company for stuffing and will have 2x4 (two of each type) ready within a week.
- Fernando will finalize the rigid-flex design (Roger is busy the next several weeks) and then submit it to the procurement. In a week (Oct. 14) we must hear from the procurement about the cathode foils.
- Wire stringing. According to Bill: the strong-back has been machined ready to be put on the granite table. The pin bars are in the machine shop to be attached to the spacer bars. The mounts for the micrometers (that will be used to adjust the chamber position w.r.t. pin bars) was designed and will go to the machine shop today. David was working on the motion system: capable of 0.2 microns increment, good repeatability, but needs more tests. He ordered ISA-USB converter to connect the stepper motor controller to a new computer. Bill and David are looking for a sensor to be used for automatic mapping of the wire positions.
- According to Vladimir Nelyubin from UVA, they demonstrated that the proposed tension measurement system works. They used a functional generator, audio amplifier, transformer to produce +/-400V pulses in an electrode. The electrode was 15cm copper tape placed along the wire at 5mm distance. The wires were connected to ground. To generate vibrations they had to apply in addition some constant voltage ~1kV (it is not so clear why and has to be discussed further). The vibrations are visible and just visually one can identify the resonance frequency of the order of 200Hz with ~2Hz precision.
- Lubomir re-visited the previous calculations (Gluex-doc 1431 v1) of the wire tensions. There, a formula used for proportional chambers, was used to calculate the critical tension below which uncontrollable oscillations will begin. In case of drift chambers, the oscillations are not a concern. Still, if we have 20g on the sense wires, there will be a sag of 40microns in the middle of the longest wire, which is good enough. If we want to have the same sag on the field wires the tension must be 8 times bigger (reflecting 8 times bigger linear density), or 160g as in the above document. If we had 80g, the distance between the field and sense wires in the middle would change by 40microns. Lubomir will run Garfield simulations to estimate the effect on the resolution, most likely it will be small. Based on this, Fernando and Eugene made remarks that we don't need a very good precision in the tension and maybe the pulley system is not needed.
- Mathew Wright will do the ODH and flammability calculations for the argon/CO2/methane gas mixture. In this calculation one is allowed to separate the chamber volume from the gas bottle if we install a valve on the pipe in between.
- Beni installed the fADC125 module and incorporated it in the CODA system successfully. He had to play with the trigger time to adjust the fADC125 window to the signals. Gerard: do we need to have the timing window programmable? Beni: later yes, but in the moment it's not needed. Beni is working now on the data analysis software.
- Last week Beni was scanning the HV plateau for the 80/20 gas mixture. It turned out, the plateau is rather wide (compared to 40/60) starting from ~1500 up to 1700-1750 where we start seeing after-pulses. Field wire at -100V.
- Lubomir showed results for the measured resolutions (from the Beni's studies) for different gas mixtures 40/60, 80/20, 85/15 and 90/10. So far, 40/60 has the best resolution but we were not able to reach the same high gain with the high Ar mixtures because of the after-pulses. To do this we need methane, an organic quencher. The proposed gas mixture is Ar/CO2/CH4 of 85/10.5/4.5% which has properties very similar to 90/10 but, hopefully, better quenching properties.
- Simon showed results for the momentum resolution with a "realistic" smearing, like before for 40/60, this time for the 90/10 gas mixture. 40/60 is a little better. Simon assumed the same magnetic field effects for the two gases. He will do the same comparison by turning off the magnetic field effects. Lubomir will give him the latest Garfield results with lower threshold to be used in these simulations.