Tagger microscope prototype construction

The design of the Tagger Microscope prototype is currently underway. 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.

= Project Branches =

R&D into Fiber-Array Fabrication Techniques


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 of broken up into 2 mm2 patches (as shown in the adjacent figure) representing the cross-sections of the square scintillating fibers. 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 Carl Nettleton
 * Main article: Fiber Array Fabrication Techniques

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, the electronics provides for 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 ambient temperature. 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

Mechanical design of the Tagger Microscope has begun. 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 an internal pulser for testing and a three-point remote-control-adjustable plane for the fiber array are under design.