The FEE Server Control Engine of the ALICE-TRD - Westfälische ...

Average pulse height (mV)
4 The ALICE Transition Radiation Detector
120
100
80
60
40
20
0
e dE/dx+TR
e dE/dx
π dE/dx
p=2 GeV/c
0 0.5 1 1.5 2 2.5 3
Drift time (μs)
Figure 4.4: Average pulse height as a function of drift time for pions and electrons with a momentum
of 2 GeV/c (with and without transition radiation) (image taken from [And04]).
induce a measurable image charge on the cathode pads. This charge is read out by the
front end read out electronics every 100 ns.
Figure 4.4 shows the time evolution of the signal for different particles. One can divide
the signal in four sections. The first three points are recorded before the particle crosses
the chamber. Then the particle flies through the chamber and liberates electrons along
its path. First the electrons liberated in the amplification region reach the anode wires.
Since electrons from both sides of the anode wire plane reach the wires the number of
avalanches and therefore the number of created ions is high. This results in a sharp
increase of the signal. A few time bins later the electrons liberated in the amplification
region all have reached the anode wires. Now the first electrons liberated in the drift
region near the cathode wires reach the anode plane. Since no electrons reach the anode
plane from the pad plane side anymore, the number of avalances decreases. This leads to
a decreasing signal. In case of electrons, at the end of the drift time additional electrons
liberated by the transition radiation reach the anode plane. The number of avalanches
and therefore the number of created ions increases again and leads to a rising signal.
4.2 Infrastructure Services
A supermodule needs for operation four infrastructure services: low voltage and cooling
for the front end readout electronics and high voltage and the correct gas mixture for the
drift and amplification region of the chamber.
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