Tagger microscope prototype construction

The tagger microscope is a movable, high-resolution hodoscope that counts post- bremsstrahlung electrons corresponding to the photon energy band of interest to the GlueX experiment in Hall D at Jefferson Lab. While designed as a general-use device, it has been optimized primarily for use in the GlueX experiment, covering the E&gamma; range of 8.4-9 GeV (Ee 3-3.6 GeV)

Construction of the tagger microscope prototype is now complete. Below are topics concerning the branches of the work required for its completion and testing in preparation for the construction of the fully-instrumented tagger for Hall D in Jefferson Lab.

R&D into Fiber-Array Fabrication Techniques

 * Main articles: Fiber Array Fabrication Techniques and Fiber Array Prototype and Mass Production



The design concept for the tagger microscope calls for a scintillating fiber detector array along the focal plane of the spectrally-analyzed beam of electrons. This is a two-dimensional array broken up into 2 mm2 patches (as shown in the adjacent figure) representing the cross-sections of the square scintillating fibers. The choice cross-section of the channels is driven largely by considerations of rate. Sensitivity in the vertical direction provided by this two-dimensional array allows for a boost in tagging efficiency (matching electron angular acceptance to that of the photons they produced, which undergo collimation.) To avoid placing photo-sensors along the path of the electronics, the scintillation light will be delivered to separately-mounted sensors and electronics via clear fiber waveguides.

Development of fiber cutting, polishing and gluing techniques to enable the most efficient capture and delivery of scintillation light is being conducted by Brendan Pratt and James McIntyre

Scintillation Detection Sensors



 * Main article: Characterizing SiPMs

A search for a solid state photo-sensor satisfying the tagger requirements has been conducted. The new Silicon Photomultipliers (SiPMs) are thought to fit this application better than the traditional Photo-Multiplier Tubes (PMTs) due to the nice properties of the former, including match of fiber cross section, low bias voltage and other factors. See the main page of this project for this design choice justification as well as detailed performance analysis of tested SiPMs produced by Igor Senderovich and Richard Jones.

Photo-Sensor Support Electronics

 * Main article: Design and prototyping of SiPM electronics

A project pertaining to design and prototyping of electronics pertaining to bias, amplification and control of the photo-sensors described above has been conducted by Brendan Krueger, Igor Senderovich, and Woody Underwood. Due to the expected variability of performance of these solid-state sensors as well as variation in optical efficiency among the channels, the electronics has been designed to provide individually selectable bias voltage, controlled amplification over a wide range of light intensities, as well as feedback on "board health": state of key voltages and temperature readings at various points. Additionally, the summation of signals over scintillator channels vertical in the focal plane is incorporated. Communication with the tagger electronics for monitoring and bias control will be done of Ethernet.

Mechanical Design of the Tagger Microscope

 * Main article: Tagger Microscope Mechanical Design (Igor Senderovich, James McIntyre)

Mechanical design of the full-scale tagger microscope is well underway. The design is intended to simplify the repetitive components necessary while maximizing the flexibility of the device. In particular, the drastic dependence of the electron crossing angle with energy has been taken account: the device will have the ability for orientation of its fiber modules to match any segment in the useful energy range. Additionally a movable internal pulser for testing and a three-point remote-control-adjustable plane for the fiber array are under design.

Beam Test in Hall B at Jefferson Lab
The ideal place to test the prototype is near another tagger magnet such as the one in Hall B. Thus the plan is to set the prototype downstream of Hall B's hodoscope.


 * Beam Test Plan
 * Delivery of the Tagger Microscope Prototype to JLab - James McIntyre
 * Spring 2011 Beam Test of Tagger Microscope Prototype - online logbook