Fiber Tracker
The primary task of Fiber Tracker on HERD is to measure the tracks of incident particles. Under the current design, the FIT system is composed of five sided sub-FITs (one top sector and four lateral sectors) surrounding the CALO. Each sector contains 7 x-y superlayers. FIT modules on x layers are rotated of 90° with respect to the FIT modules on y layers to measure the x and y coordinate. The x and y layers of the top and lateral sectors are composed of FIT modules of different lengths to form sufficient coverage area. All superlayers are mechanically supported by honeycomb layers sandwiched between two thin carbon fiber-reinforced polymer (CFRP) face sheets.
A FIT module includes one scintillating fiber mat and three highly segmented SiPM arrays to read out the scintillation light induced by the particles hitting the mat. The mat is composed of six layers of fibers with a diameter of 250 μm.
