W&M  report 07-29-2004


1) Clean room status

- Last week we moved the laser table (4'x10') from the laser room into the detector lab and installed it on the laser table stands (elog).
- Found more softwall clean room conpanies, quotes are around ~15k$ (elog).

2) Wire Scanner project

Gathering information in order to build a wire scanner (elog) like UVA is using for their HDCs in order to measure/verify the wire location. Instead of a fine pitch threaded rod we intend to use a long ball screw (elog).

3) Garfield simulation, Hall A tracking

Since my computer and I are busy working on SolidWorks drawings (Windows), our new computer at W&M is dedicated and setup for Garfield and Geant simulations. Up to now Garfield was running on wmg0.jlab.org and was committed to frequent mysql zombies of the G0 analysis eating up all the CPU and/or memory 8-(
Started to write a first version of a ROOT macro (class) which can display and fit the XT and Arrival-Time results  given by Garfield. At present our summer student Carissa is still analysing the results with Maple 9 which can not handle (nonlinear) fits with (x)y -errors without major efforts.

Last week we started to install the Hall A analyser, so our summer student Joe Katich has a working platform
in order to understand and modify the Hall A  VDC tracking.

4) Man power ...

... is in my opinion an issue and is getting more and more crucial with increasing parallel work load coming up
in the next months. We have to get (keep?) at least one grad student after the semester starts end of august, otherwise
we will not switch gears with the current constellation ... enough said.


5) Region 3 implemetation into Qweak Geant

  ... is still pending

6) Progress on Region 3 Drawings

On Monday Stan Sobczynski released his QTOR Solidworks drawings (QTOR_pdf, QTOR_Front.jpg, QTOR_Back.jpg)
- This finally answers the question about how much space  is left between the end of the magnet and
   start of the shielding wall: ~74cm (see pdf or jpg).
- Seems like that Stan is using an older?  electron track  profile  ?!  His profile is slightly higher than the openings
   of the octants (pdf or jpg) .

- I checked for possible exposure of the VDC to the adjacent octants and found an interference (pdf or jpg1and jpg2).
  The problem can be resolved by reducing the length of first VDC a little bit. Fortunatly this is possible due to
  the divergency of the electron profile at the corners of an octant.
 
6) An alternative drift chamber design proposal for region 3
   
Last week Roger Carlini, Greg Smith, Allena Opper and I (Klaus) had an extra meeting where
Roger et al. proposed a different region 3 design.
The motivation for this proposal are some concerns about the design and implementation of the VDC
proposed by W&M.

VDC Concerns:
                        - out-dated work shop, no precise CNC machines
                        - increased dimensions (active area: 210cm x 50cm)
                             - might lead to reduced shielding wall thickness (100->70cm)
                             - tight spacing (Cerenkov, Scintillator)
                             - DC retraction not thought through (collision)
                        - design parameter still beeing discussed (see report 07-01-2004)
                             - Pending Geant simulations:
                                      - best tilting angle for Dual VDCs and wire orientation
                                      - preserveration of minimun 3 drift cells beeing hit
                       - rate limitation due to delay line readout (~multiplexing due to budget restrictions)
                       - implementation of non traditional techniques
                             - flexible Kapton PCBs
                             - MAD chip preamplifier PCB checkout and design
                      




Proposal A :  Translational octant scanner

Roger: A small area HDC package is moving parallel along the octant opening
          (e.g. linear motion system: stepper motor + rods)
          The HDC package should be parked between the octants

 Here are my SolidWorks drawing in order to see how a design
for the proposal A would look like : overview 

overall width of HDC:      270mm including side frames etc ...
active  width of HDC:   ~>150mm

=> tentative design conclusion:
       - while the front chamber can be parked between the octants, the rear chamber
          is exposed to electrons. It means if we don't include some kind of retraction
         (e.g. pulling everthing to smaller radius)  we will scatter ALWAYS electrons
          on a drift chamber. The scintillator and cerenkov detectors see never a quiet
         enviroment.

Proposal B :  Rotating octant scanner (proposal A spin off)

Roger: A small area HDC package is moving along a circle/arc over the octant openings.
          The HDC package should be parked between the octants

Here are my SolidWorks drawings in order to see how a design
for the proposal B would look like : overview 

overall width of HDC:     300mm including side frames etc ...
active  width of HDC:    ~>180mm

=> tentative design conclusion:
          Rotating HDCs can be parked between the octants without beeing exposed to electrons.
 
          However scanning one octant will take a while ...

Proposal advantage: - using standard HDC techniques and equipment used at JLab, UVA and VT
                                             - faster implementation
                                 - HDC are much smaller than W&M VDCs
                                              -  cheaper design ?!
                                              - could handle higher rates
                                              - no need for delay-line readout, 1 wire = 1 channel (preamp + TDC)

General Proposal disadvantage: The drift chamber frames are exposed to the octants (electrons)

Roger proposed to place scintillators on the exposed side frames of the drift chambers.
The scintillators will act as veto counters, indicating that an electron has hit the frame.

Well, let's take a look into what will be exposed :

Material	Radiation Length [cm]	Assumed Thickness [cm]	Fractional Radiation Length [%]
		(per drift chamber)	(2 drift chambers)
G10	19.4	5.5	57
Aluminium	8.9	1.5	34
Scintillator	42.4	1.0	5
		sum for 2 HDC:	96

(I have neglected the copper planes and mylar foils of the drift chambers)

Klaus: With this proposal it is not advisable to have any electronics exposed to
the octant. Therefore the preamplifiers, which should be as close to the signal wire
as possible, have to be relocated to the top and bottom of the chambers. The raw signal
path will be ~30cm longer (max), we have to correct for signal delays due to different  path length.

=> I have no clue about additional noise etc picked up while the signal path is exposed to electrons.
      Certainly the signal paths (wire->preamp) have to be shielded (external noise pickup).


                        To be continued ...