BigBite Spectrometer

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BigBite dipole magnet

Electron Package

Electron package electronics

Electron package layout drawings

o  Detector package with dimensions, updated by Al Gavalya 10/27/2008. side view and top view

BigBite spectrometer layout drawings, with the electron detector package

o  Magnet and detector relative to target center, with dimensions, in the "ideal position", not the reality !!! 
   Updated by Susan Esp  10/28/2008. side view pdf file 
o  Closer to the reality, !!! still not the reality yet !!! after Al made some measurements on 10/28/208. 
   Update by Susan Esp 10/29/2008. side view pdf file 

BigBite stack position: closest to reality.

  PDF file is Susan's drawing from Oct 29, 2008 annotated with some measurements made by Brad on Jan 11, 2009
   Big_Bite_Spectrometer_Sect_Oct29-annot.pdf
   Summary:
     - 'Big_Bite_Spectrometer_Sect_Oct29-annot.pdf' is an accurate
       representation of where the BB stack sits in the Hall A coord system.
       There are two caveats (see the notes below for more detail):
     1) The top of the front wire chamber is 2.5cm closer to the magnet than
        it is shown in the model.  Perhaps the stack is racking forward under
        its own weight?
     2) In real-life the stack should be ~1cm higher than shown in the model.

Horizontal fiducials measured on Jan 11, 2009:

   NOTES: 
   - The bottom horizontal fiducial was measured to be 44.875" vs. the CAD model at 44.88"
     - max error on measurement was 1/16"
     - This was the fiducial Ed and I used to set the radial position of the stack.
   - The top horizontal fiducial was measured to be 18.50" vs. the CAD model at 19.47"
     - max error on measurement was 1/16"
     - Measurement was made using a 2' bubble-level to project the top of the
       BB yoke to the front of the Al wire-chamber support bar.  This ensured
       that the tape measure was level and consistent with the distance
       represented in the CAD model.
Vertical fiducials re-measured on Oct 29, 2008:
Laser on RHRS-Q1.jpg
Vert offset.jpg
   NOTES: 
   - A laser level was aligned to the RHRS Q1 centerline 
     With no shims, the electron stack sits 1/4" high relative to this laser line.
     - also BB_Postion_check-29Oct2008 
     - The same 1/4" offset exists at an independent fiducial on the Cerenkov tank 
       nearer the front of the stack. 
   - The vertical fiducial marks on the stack were located based on the
     beamline intersection as shown on the a model from Dec 12, 2007.  The
     rear fiducial mark has been added to the
     'Big_Bite_Spectrometer_Sect_Oct29-annot.pdf' drawing.  It doesn't quite
     match the beamline axis here.  I'm not sure if that's due to measurement
     error when the mark was originally drawn on the stack, some relative
     vertical displacement in the stack location in a subsequent model, or
     some difference between the model and how the Pb-glass "box" at the back
     of the stack was actually constructed.  Worst case discrepancy is on the
     order of 1--2 cm, so not too bad.
   NOTE:
   - On the _upstream_ side the holes on Q1 are 4mm higher than the nominal beam axis. 
       <http://www.jlab.org/~adaq/halog/html/0811_archive/081107002727.html>
     If that is also true for the holes on the _downstream_ side, then the
     electron stack is 10mm high (1/4"+4mm) relative to the beam axis.


Gas Cherenkov Detector

Scintillators

Shower/Preshower Detectors

  • Shower + Preshower + Scintillator geometry

Media:Shower.pdf

Position Survey

Sept 18, 2008

Notice: Terminology used in this section follows conventions of Hall A Tech Notes JLAB-TN-02-012:

BigBite Chamber center position are surveyed with laser markers and a hand held laser meter. Error could be between 1mm to 5mm.

  • Center of 1st Chamber Outer Aluminum Plate in BigBite Target Coordinate System:
    • X= -0.072m
    • Y= unknown
    • Z= 2.862m
  • Bigbite Magnetic in BigBite Target Coordinate System:
    • Front Shielding Plate @Z=1.154m
    • At Beam Height, Edge of Bigbite Coil at Detector Side @Z=2.46m

Oct. 28, 2008

  • This is the date on the survey report: Media:DT_A1191.pdf. The actual survey was done closer to Oct. 14th.

IMPORTANT NOTES:

o The electron detector stack was moved 9cm closer to the target on Oct. 24th.  That change is not reflected in this survey.

Oct. 28, 2008

  • Target survey report. Survey was done closer to Oct. 14th. pdf file