APV25 Magnetic Field Test (March 2001)

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APV25 Magnetic Field Test (March 2001)

The behavior of APV25S1 and optical lasers (see section , p. ) was tested in a strong magnetic field in collaboration with the Institute of Material Physics at the Vienna University [68]. The helium-cooled, superconducting magnet provides a homogeneous flux density of up to $14\,\rm T$ . Our tests were performed in the regime of up to $10\,\rm T$ , where handling is much easier at reduced helium consumption. Moreover, the magnetic field in the CMS tracker is only $4\,\rm T$ .

An APV25S1 chip was positioned in three orthogonal orientations with respect to the magnetic field. These positions are denoted A, B and C in fig. . The mechanical support is designed to fit into the magnet core which is $3\,\rm cm$ in diameter.

**Figure:** The three different orientations (A, B and C) of the APV chip (red) with respect to the magnetic field.
$\begin{figure}\centerline{\epsfig{file=bfield_apvpositions.eps,height=13cm}} \protect \protect\end{figure}$

Noise, internal and external calibration were measured at , and $10\,\rm T$ . The presence of the magnetic field was easily observed on the cathode ray tube (CRT) monitor, which was located in the stray field about $2\,\rm m$ away from the magnet. The distorted image of the DAQ software is shown in fig. .

**Figure:** Image of a CRT monitor, located approximately $2\,\rm m$ away from the magnet coil with an inner flux density of $10\,\rm T$ . The magnetic field not only rotates the picture geometry, but also disturbs the color representation.
$\begin{figure}\centerline{\epsfig{file=bfield_monitor.eps,height=10cm}} \protect \protect\end{figure}$

**Figure:** Overlay plot of the internal calibration waveform in deconvolution mode for the three different orientations (A, B and C) and magnetic fields of , and $10\,\rm T$ . Obviously the APV chip is not affected by a magnetic field.
$\begin{figure}\centerline{\epsfig{file=bfield_decintcal.eps,height=8cm}} \protect \protect\end{figure}$

The APV performance was completely indifferent to the presence of a magnetic field. Fig.

shows an overlay plot of the internal calibration waveform in deconvolution mode for the three different orientations (A, B and C) and magnetic fields between

and $10\,\rm T$ . The average noise deviation between any two measurements was less than $2\%$ , which is the usual tolerance and not related to the magnetic field.

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Markus Friedl 2001-07-14