The Camera of the Fluorescence Detector Telescopes

The camera of the Fluorescence Detector telescopes is the sensitive part of the system.  The camera body, a rigid aluminium structure holds a matrix of 440 photomultipliers.  Light collectors (mercedes) are used to rescue light that falls in between the photocathodes of adjacent photomultipliers. The overall system is a common effort of  INFN-Catania (camera body and support), INFN-Milano (photomultipliers basis and driver), INFN-Roma (light collectors, distribution boards and cabling), INFN-Torino (input stage of the analog electronics), Forschungszentrum of Karlsruhe, FZK (read-out electronics, data acquisition and computing system).

Sketch of the Fluorescence Detector telescope. 

The main  components  are:  Shutter, Diaphragm,  UV filter, PMT camera, Spherical mirror and Read-out crate

A close front view of the camera body.

The camera body mounted on its support. On the left a laser distance meter mounted on the top of a vertical column. 

The laser is used to align the camera  with respect to the reference point which is the centre of curvature of the telescope mirror .

Front view of the camera with all 440 PMTs mounted.

Back view of the camera showing the head electronics of the 440 PMTs. The head electronics (HV divider and signal driver) is mounted on two small printed boards of round shape.

The light collectors (mercedes) are mounted in between the photocathodes of the photomultipliers.

The special crate for holding the distribution boards.

The distribution boards mounted on the back of the camera. Short cables from the distribution boards bring LV and HV to the PMT units, and carry the signals from the PMTs.

The overall system is very compact.

The signal cables from the camera to the FZK read-out crate run into the camera support legs to avoid additional shadow of the mirror.

View of the back of the camera  with the HV and LV cables  connected to the distribution boards.

Front view of the FZK read-out crate. The crate is placed in the camera support base.

Back view of the FZK crate.

The signal cables from the distribution boards are connected.

Picture of the first camera completely mounted in the lab with analog and digital electronics.

Notice the Mirror PC from FZK on the side of the camera support base.


Example of a shower candidate  as seen by the on-line Monitoring Program.

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Example of a background event as seen by the on-line Monitoring Program.

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Another example of a background event .

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An example of a shower candidate.

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The longitudinal profile of a shower with energy  of about  2x1018 eV.  The  number of shower particles  is shown as a function of the atmospheric depth.


The longitudinal profile of a shower with energy close to 1019 eV. 

The number of particles at the maximum of the shower development is about 6x109 !



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