| In high energy physics (HEP) a fundamental parameter is the measurement of the total energy of the collision fragments of a beam interaction, performed by a detector called calorimeter, one of the most important subsystems in the experiments at the Large Hadron Collider (LHC) at CERN.; Ionization chamber calorimeters using liquified noble gas as their active medium, among of the most reliable and precise thanks to their simple electrode geometry and their ease of calibration, are described. Two different approaches to the signal readout from capacitive sources are analyzed: the direct connection of the electronics to the detector, requiring a cryogenic preamplifier, and the connection via a transmission line, which has the advantage of removing the preamplifier from the high radiation detector region and allowing access for maintenance. It is shown that for the fast shaping times required at the LHC, a better signal to noise ratio could be achieved with a transmission line connection. Closed expressions for the signal to noise ratio are derived and the general case in the presence of skin effect losses is treated numerically.; Two realizations of the preamplifier are presented. The first one is a radiation hard preamplifier capable of cryogenic operation based on a monolithic JFET technology. Device characteristics are analyzed both at room and cryogenic temperatures as well as the radiation damage due to gamma and fast neutrons. Monolithic JFETs are remarkably resistant to ionizing radiation. The main effect of neutron irradiation is a decrease of the maximum drain current IDSS, and an increase in noise. The devices continue to operate at the 10 14n/cm2 neutron fluence foreseen at LHC.; A radiation resistant line terminating preamplifier which, by assigning the functions of low noise and large dynamic range to different transistors, achieves a linearity better than 0.2% over the 16 bit dynamic range of the input current while also allowing a significant reduction of the power dissipation is described. Its noise performance and stability are analyzed in detail. The design, construction and performance of the four channel ceramic hybrid module for the Atlas calorimeters is described. |
