Region 3 Statuts Report

0) Man power

- Summer student Brian Walsh is continuing the flatness scanner studies in the framework on a senior thesis. In addition he and I are working on an alignment system for the wires that ensures
  the correct spacing and tilting angle of the wires on the wire frame. He became an expert on SolidWorks and did a great job on the flatness scanner.
- Summer student Thomas Ruscher has chosen a different topic for his senior thesis (high speed photography, a hobby of him). But he wants to continue working on the front-end electronics for a few hours per week. Thomas did a great job on characterizing the Bigbite MAD chip board.
- Graduate stiudent Brian Hahn has passed the qualifier ! Sadly he has to be a TA for this semester before our group can  fund him. Brian did a great job on the wire scanner and became an expert on LabView. Well, chances are high that he will choose a thesis topic related to Hall A ...

1) Rotator
 
The W&M procurement office is administrating the purchase order of the region 3 rotator based on the technical drawings and good faith estimates provided by JLab. In July the technical drawings have been updated due to minor changes related to the trigger scintillator support that will be mounted on the rotator.
The solicitation of quotes has been delayed by one month caused by a job change of the responsible senior procurement officer ...
Beginning of September an invitation of sealed bids for the region 3 rotator with a due date for end of September has been sent out.
Only  3!!! quotes out of 10 invitations have been received ...  Based on the W&M procurement procedure the awarding must go to the lowest bidder which is
B&L  Machine & Fabrication Inc. in Norfolk . However even the lowest quotes are ~40k$ higher than was accounted for in the budget ...
And there was a significant $10-15k rise in price compared to the good faith estimates given by the same companies this summer.
On Oct 31 B&L has been officially awarded by the W&M procurement.

The fitted parts of the rotator will be shipped to JLab where the assembly will be done presumably at the test lab where space has been requested.
    
2) Flatness Scanner

A granite surface plate has been used for an initial height sensitivity calibration where the total height of stacked gage blocks has been varied with a stepping size of 2.54um (0.1 mil).
While scanning a range of  +-1mm the height sensitivity has been determined to be 3.35 mV/um. This sensitivity is more than sufficient to resolve a local wire offset of 25um
which would relate to a photodiode output voltage of 84um which is easy to measure. However one has to keep in mind that the calibration was only done for a max. distance of 12" between laser and receiver, which is only limited by the size of the used granite surface table.
Currently the Flatness Scanner is mounted at various distances on the 10'x4' large laser table at W&M for extracting the total amount of detected light as a function of distance. In addition the height sensitivity will be measured as a function of the location along the laser beam. The laser table seems to flat in order of +-200um.
Afterward the same measurements will be repeated using a 10' long precision granite surface plate at JLab where a permission for this project has been granted by the JLab machine shop.

Pic below: The flatness scanner is set up for maximum distance (~9'). Gage blocks are currently stacked at various locations
along the laser beam blocking partially the laser spot. This allows to measure the height sensitivity as a function of location


Pic below: The laser spot has been blocked stacking gage blocks with a stepping size of 2.54um at one
location along the laser beam. The height sensitivity for this location -3.345 mV/um

3) Wire scanner

The W&M machine shop finished a small aluminum board equipped with a precision dowel pin array, that allows to string wires with an angle of 26.565 grad and 90 grad over a 1/4" wide slotted hole (window) for a length of 6". This board represents a mock-up wire plane with a reference wire grid for evaluating the wire scanner under semi-realistic conditions.
A LabView script was setup for moving the wire scanner camera automatically from wire to wire for extracting the intensity profile of the CCD image. Initially the wires
were strung with an angle of 90 grad on the mockup board which allows an unambiguous position reconstruction. The measurement results of the wire scanner revealed that the the distance from to wire to wire showed fluctuations in the order of 150um. These unexpected fluctuations could be traced back to the fact that the used CNC milling machine of the W&M machine shop was operating with such an inaccuracy even though the CNC position display suggest a position accuracy of 25um and better.
Currently the W&M machine shop is awaiting a brand new 3-axis CNC milling machine

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4) Wire Properties

The wires have to be strung with a certain tension when gluing then on the wire frame. A too low tension leads to sagging and related gain loss, a too high tension might break the wire
causing a long down time for repair. At W&M the elongation for a 136cm long wire has been measured using a dedicated setup: While one end of the wire was fixed,
various weights between 20g and 120g have been attached to the other end of the wire that runs over a pulley system.
A CCD camera with a zoom optics has been used for reading out the position of a marker on the wire which was running parallel to a stainless steel ruler with a grading of 1/100".
The measurements were done for a 25um thick (VDC default) and a 20um thick gold plated tungsten wire.
When pulled, the wire stretches in two distinct stages. The first is the elastic stage, when if the load is removed, the wire springs back to its original length.
If pulled further, into the second or plastic stage, the wire elongates but does not spring back when the load is removed. The wire elongates considerably in the plastic stage before it breaks.
The change from the elastic to the plastic stage has been measured to be ~80g for the default 25um wire and ~60g for the 20um wire. The break point seems to be higher than 120g. Currently a 25um wire has been strung with 60g for 4 weeks and no creeping effects (loss of tension) have been observed.



Graduate student Carissa Capuano has looked into various methods of measuring the wire tension. In principle the wir tension is determined through the resonace frequency
of  a vibrating wire (like a guitar string) . The most promising methode for planar wire chambers is this:

     A magnetic field of strength B is applied transversely to the wire over a short length around the midpoint of the wire.A very short pulse of total charge Q is
     passed down the wire, which therefore starts vibrating. The voltage induced between the two ends of the  vibrating wire is measured as a function of time and a
      Fourier analysis yields the various frequencies present.
     See: http://dilbert.physics.wm.edu/elog/Construction/061012_171937/fulltext.pdf
      -Some claim that they can determine the resonace frequency by eye (looking for maximum deflection)

5) Front-end Electronics

Using small pulses at the rate of 500kHz, tests were perfomed to determine the useful range of the MAD chip (boards), dependent upon the threshold.
A threshold of approximately 8.0-10.0mV is the lower limit before noise overwhelms the system. All inputs were perfomed on Channel 5 with a 1pF SMD
capacitor replacing the 0.1uF capacitor. Most of the crosstalk is mainly seen on the adjacent channels (there are exceptions for very low thresholds).
Significant crosstalk is defined as one or more fake hits on any channel for every 10.000 real hits on one channel.
Dave Mack made an interesting point: one should check for "soft cross-talk":  Do the input/output signal of  neighbor channels effect the timing of the current channel?
Initial quick tests do not indicate such a behaviour, but this has to be repeated.



6) Misc

The photolab that is used as a Qweak storage room is now used for fast prototyping of printed circuit boards. We purchased an etching tank with heater control, a Dremel mini
drill press (50.000 rpm) and a laminator for a "toner transfer". The circuit layout (e.g. using Eagle) is printed on a special paper using a laser printer. A laminator is then used
for transfering this printout image on a (double sided) copper cladded board which can be etched afterwards. Prototyping time for a board: ~20min.
We tested this technique successfully with some test layouts and want to apply it for building test boards for embedding I2C electronics on the MAD chip front-end board.

See http://www.pulsar.gs/PCB/a_Pages/3_Direct_Etch/3b_The_15min_PCB/The_15min_PCB.html