GlueX Graduate Student Workshop Newport News, VA
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Photon Tagging in the Hall D Beamline
James McIntyreUniversity of Connecticut
13 May 2010
GlueX Graduate Student Workshop Newport News, VA
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Outline
• How we tag photons• Photon production• Tagger Microscope– Components– Construction
13 May 2010
GlueX Graduate Student Workshop Newport News, VA
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• Our interest is in determining the energy of the photons which produce an event in the target.
• The energy of an electron that produced (via bremsstrahlung) a photon of interest is measured so that the counterpart photon can be “tagged” with a correct energy.
• Things to consider:– Not all photons produced will create a usable event in the
target.– Not all electrons will produce a photon.– Need a way to limit & filter accidental tags and noise from the
data stream.• Limiting – Occurs due to our design choices.• Filtering – Statistically process the data stream.
13 May 2010
Tagging
GlueX Graduate Student Workshop Newport News, VA
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Photon Production• As the electrons pass through the 20 µm diamond radiator
photons can be produced via bremsstrahlung.• The angle of deflection off the beamline varies.
13 May 2010
GlueX Graduate Student Workshop Newport News, VA
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• Distance between the Tagger Microscope and Target is ~ 300 feet.
• Over such a large distance even small angles of deflection become considerable.
13 May 2010
Hall D Beamline
GlueX Graduate Student Workshop Newport News, VA
613 May 2010
~97 Ft41 Ft~161 Ft~91 Ft
Location of TargetLocation of Tagger Microscope
Hall D Beamline
e- Beam
GlueX Graduate Student Workshop Newport News, VA
713 May 2010
e- Beam
Tagger Magnet
Tagger Area
Photon Beam
e- Beam
GlueX Graduate Student Workshop Newport News, VA
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• We can use the deflection to our advantage.– Use collimator to filter out photons that have large angles.– Use Scintillating Fibers (SciFi) size to our advantage.
• The electron which produced a photon with a large angle will also have a larger angle.
• Based on Monte Carlo simulations SciFi length and cross-sectional area was selected to provide optimum filtering of incoming electrons (along with other considerations).– 2 mm square multi-clad fibers– 2 cm long
13 May 2010
Tagging
GlueX Graduate Student Workshop Newport News, VA
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• Scintillating Fibers– Fast Green Scintillator (BCF – 20)– Decay time 2.7 ns• Other faster fibers were considered but not chosen due
to problems such as shadow signal after event, etc.
• Waveguide– BCF-98– ~23 inches long per channel
13 May 2010
Fiber Selection
GlueX Graduate Student Workshop Newport News, VA
1213 May 2010
Parallel Railing System
Parallel Railing Unit
GlueX Graduate Student Workshop Newport News, VA
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Parallel Railing Unit
13 May 2010
• Ability to adjust bundle angle to permit alignment with electron beam.
• Step motors permit 3-point adjustment of railing height & angle (remotely).
GlueX Graduate Student Workshop Newport News, VA
1413 May 2010
Bundle Support Unit (aka Pop-Sickle Stick)
• 5x5 Bundle will mount on it via epoxy.• Permits adjustment of bundle angle.• Nuts on the underside of the rails will secure unit in
place.
Parallel Railing Unit
GlueX Graduate Student Workshop Newport News, VA
1513 May 2010
Fiber Array (Full Scale)
Full Scale Tagger Microscope• Fiber Array
• 500 Fibers• 20 – 5x5 Fiber Bundles• Note: Prototype will only have a single bundle (25 fibers) of which only 20 channels will be utilized.
• 5 horizontal rows• Allow for proper alignment to the incoming beam by using all channels, then secure all except one
row during the test runs.• Provides longer operational lifetime, since radiation damaged fibers can be shifted via the step
motors (instead of being changed out) to keep running using another viable row.
• 100 vertical rows• Determines the amount of curvature of the electron due to the Tagger Magnet, therefore allowing
us to calculate its energy and thus know the energy of the counterpart photon created during bremsstrahlung.
End on view. The electrons would be going into the page.
GlueX Graduate Student Workshop Newport News, VA
1613 May 2010
Gluing Station
Gluing Station• Allows for close alignment of the two fibers• Permits fine adjustment of the gap between the fibers• Al construction allows for quicker curing on a heat plate
Gap Adjustment Screw
GlueX Graduate Student Workshop Newport News, VA
1713 May 2010
Polishing: End-Mill to paper sanded
Sanded fibers (400 grit)
Straight edge when sanded (in contrast to the rounding shown above)
Prep for Gluing (Old vs. New)
GlueX Graduate Student Workshop Newport News, VA
1913 May 2010
Painting Fibers
Glued fiber joint showing light transmission.
Air Gun used to paint the individual fibers after gluing.
GlueX Graduate Student Workshop Newport News, VA
2013 May 2010
Bundle of Fibers
Glued fiber bundles (3x3 practice bundles)• Foreground: Trial bundle with painted individual fibers. BC-600 epoxy was used.• Background: Unpainted trial bundle using Elmer’ Glue.
Tin Foil
GlueX Graduate Student Workshop Newport News, VA
2113 May 2010
Splicing Fibers
MSU Splicing Unit• Most promising way to connect SciFi to Waveguides
• As strong as a single fiber• Quick production (once setup correctly)
• Uses a high intensity lamp to heat the fiber to the melting point and fuse them• Was made for round fibers
• Need ferrule for square fibers to maintain shape during slicing
Use of MSU Splicing Unit courtesy of Ron Richards
GlueX Graduate Student Workshop Newport News, VA
2213 May 2010
Digital Control Board
Backplane Board Amplifier
Board
Electronics
Electronics• Backplane is secured to the top plate via six 6-32 machine screws.• A Sponge Gasket provides a light seal for the penetration of the electronics.• Not pictured – Card Guides and Chimney
GlueX Graduate Student Workshop Newport News, VA
2313 May 2010
Electronics
Card Guide
Backplane Board
Chimney
WaveguideSiPM
Amplifier Board96 Pin Euro Connector
Amp Board Guard
Amplifier Board Guard & Guides/Chimney• Amp Board Guard protects SiPMs by preventing rubbing with the waveguides and other components.• Card Guides/Chimney provide for alignment with respect to the waveguides, both vertical and horizontal.• Designed to allow for ease of fiber mounting and removal.
GlueX Graduate Student Workshop Newport News, VA
2413 May 2010
Electronics
Amp Board Guard SiPM
Leveling strip