Detector Page

The ADAMO magnetic spectrometer is composed by three sub-systems:

Magnetic system (old system)

Tracking system

Trigger system (old system)

 The magnetic system is formed by two main blocks of permanently magnetized material, a Nd-Fe-B alloy, with a residual magnetization Br=1.3 T. In the current configuration each of these two blocks is realized with four smaller blocks disposed in such a way that they form a magnetic cavity of 6 cm × 14 cm × 10 cm. The two main block are kept at a distance of 1cm and the two cavities aligned along their axes, so that they form a whole cavity of 6 cm × 14 cm × 21 cm. The mean field inside the cavity is about 0.4 T. The whole magnet is fixed on an altazimuth platform that allows to define the measuring direction of the detector (setting the azimuth and zenith angles). The approximate weight of magnet and platform is 100 kg.

The tracking system was initially composed by three detection unit made of high resolution microstrip silicon sensors used to determine three points (x and y coordinates) along the track of particles. In 2003 two units were added and currently it is composed by five silicon planes. Each layer consists of two silicon sensors 5.3 cm × 7 cm × 300 μm, and a hybrid circuit where the front-end electronics is housed. The silicon sensors are the same used for the PAMELA experiment and are double sided, with double metalization and integrated decoupling capacitors. The resolutions achieved by these silicon sensors with standard approximate algorithms are about 5μm along x (bending view) and 10μm along y (but more sophisticated algorithms have been implemented within the PAMELA collaboration in such a way that on the x view the spatial resolution is better than 3 μm).

The trigger system was originally made of four 12 cm × 12 cm × 1 cm plastic scintillators. The scintillating medium was BICRON BC-408. Two long light guides were used for two of them to draw light signals to the photomultipliers, located in a zone where the intensity of magnetic field is not critical. For the two other scintillators, light signals were driven far away from the magnetic cavity by wavelength shifter fibers (BICRON BCF-91A). These fibers were optically coupled to the scintillating material by mean of optical grease.
In the current version the original trigger system has been replaced by a new one made of two 7 cm × 17 cm × 1 cm layers of BC-408 scintillator readout through both the 7 cm × 1 cm faces by means of two lightguides coupled with two PMTs PHOTONIS XP-2020. The two PMTs are screened with respect to the dispersed magnetic field, produced by the magnetic system, by means of mu-metal foil and a soft iron shield. Althought this system could be used as a Time Of Flight (TOF) system, because the scintillator is fast and PMT are suitable for timing measurement, the dispersed magnetic field is intense and spoils the PMT performance. Thus time measurements cannot be exploited in the current configuration.

Mechanics (old system)

 

 

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