Progress Report of Region3


1) VDC progress

The wires will be strung on the wire frame over a precision bridge (highlighted in red) which define the absolute vertical wire position.

The bridge is 0.25” wide and surrounds the inner cutout (80.5”x21”).

A vertical offset of 50um translates 1:1 into a drift time offset of 1ns. The wire is 25um thick (hair thickness: ~50um.

Received the first feedback from some companies about their machining capabilities of G11 or 4411W and their concerns.

Main problem is handling a raw sheet size of 96”x48” and the achievable tolerance and flatness of the wire bridge.

The estimated tolerances over the length of 80.5” are +-250um (10mil) for G11 and +-100um (4mil) for 4411W from Stesalit.

Stesalit could do better with a new milling machine, but this one might not be available before summer 2006 …

Reminder : For the Liquid Argon Calorimeter at CERN 3m long G10 bars were machined with a thickness precision of +-20um (~1mil)

Remember : One 48”x96”x0.625 G11/FR5 sheet after stress relieve (sandblasting) costs ~$2000 , so we can not make test runs

on every machine shop.

The company Stesalit did some test runs with 4411W and they measured the surface roughness: +-5um (pretty good)

Pic below: Simplified sketch of the precision bridge of the wire frames. The contact area/surface is marked in red and defines

the vertical wire poison similar to a guitar bridge

Last week we purchased a used glue dispenser with (EFD 1500XL kit for $750 instead of ~$2000) which allows a precision gluing of the wires on the frame.

We will use the CERN approved glue Araldite AY 103 + hardener HY 991 with a low viscosity. The Hall A VDCs were glued with Araldite AW 106 which is not

recommended by CERN due to outgassing and effecting wire chamber ageing.

I’m about to purchase metallized Mylar foil, preferable coated with copper instead of aluminum (if we can afford it). The company Sheldahl is using Mylar type S1 or Type EL for metallizing but these types have a pretty

high transmission for oxygen and water vapor. Metallizing Mylar reduces the transmission, but to which factor (10 or even 100)? DuPont has a Mylar-G series (elog) with a superior barrier for oxygen

and water vapor with a factor 100 and better. Sheldahl can metallize them but does not stock them; for an order you have to buy at least one spool (minimum quantity) from DuPont for ~$10k … anyone interested ?

2) Wire Scanner

The research priority of our graduate student Joe Katich has changed: since this semester he is working mostly on projects related with polarized 3He supervised by Todd Averett. In the spare time Joe is

working on a LabView interface for steering and controlling the wire scanner stepper motor. The CCD camera + optics for reading out the horizontal wire position is assembled but we have to build a

platform for mounting it on the translation stage.

Currently I’m thinking of attaching a second CCD camera tilted at e.g. 45deg for measuring the vertical height of the wires.

3) Electronics: I2C interface

The work of graduate student Pjerin Luli will be continued by undergraduate student Graham Giovanetti who just started his first steps using EAGLE (printed circuit layout program)

Main part will be to debug and optimize a mockup I2C receiver for switching on/off individual wire signal channels symbolized by LEDs. Later on he is supposed to write a Linux program

for controlling the I/O chips hooked up to the I2C bus.

Pic below:  The schematics of the I2C receiver is shown on the feft , the derived board layout is shown on the right
.

4) Frame quality control project

We need some kind of quality control once we have received the frames. The most critical part is the flatness of the bridge which defines the height of the wires (acts like a precision guitar bridge).

Any vertical displacement from a reference plane translates 1:1 into a time arrival error (rule of thumb: 50 micrometer drift length= 1ns drift time, 50 micrometer = 2 mils ~ thickness of an hair).

Mentioned before: measuring the z position of each glued wire with a second CCD camera

Painful PVA4 experience (precision wedged aluminum frames for calorimeter): the company who machines the parts should *not* be the company who provides the flatness survey you have to rely on.

ð Senior thesis student Brett Appleton (just started): Feasibility study for a “poor man’s” flatness survey using a laser, a gage block, and a photodiode.

Basic idea: A gage block will block a part of the laser light seen by the photodiode. The detected intensity then will be a function of the vertical

displacement of the gage block positioned at various locations along the laser beam.

If a photodiode is insufficient, we have to measure the edge of the intensity drop / shift of the intensity centroid with a CCD camera (LabView DAQ)

First test to be done: Measure the unknown 2D flatness of the laser table, esp. the shape (flat, tilted, concave, convex ?!)

..

That's all folks !