Pre zaujimavost - detektor Alice zaznamenal prve castice (z vesmiru)
Pátek Červen 30 16:11:27 CEST 2006
preposielam clanok, v texte su dve linky na celkom zaujimave fotky...
ALICE joins the cosmic ballet
ALICE has detected its first real events. On 16 June, the time
projection chamber started to record and reconstruct the tracks of
Peter Glassel, technical coordinator for the ALICE time projection
chamber, sits in the middle of the completed TPC.
One of the first cosmic-ray events recorded and reconstructed in two
sectors of the TPC. A shower induced by cosmic rays is seen on this 3-D
In its quest for the quark-gluon plasma, a state of matter that is
believed to have existed just after the Big Bang, ALICE will use a very
accurate tracker system. The major part of this system is the time
projection chamber (TPC), wherein the trajectories of electrically
charged particles are reconstructed and their identity is determined.
The ALICE TPC, a cylinder of 5 metres in diameter and 5 metres in
length, is the largest of its kind worldwide. Nearly completed, it now
has all read-out chambers installed with the custom electronics complete
for the approximately 560000 read-out channels.
Before being lowered to the underground experimental area,
commissioning the TPC has begun in the large clean room on the surface,
where it has been assembled. The team involved in this operation, with
around 20 people, began to put the readout electronics into service at
the beginning of March. The gas and high voltage systems were then
commissioned (see Bulletin No. 21-22/2006). This continuous effort was
rewarded on 16 May when the first cosmic rays were detected and their
tracks reconstructed in the TPC.
The TPC consists of a field cage, made of carbon-fibre composites,
containing 95 m3 of a mixture of gas, across which an electric field is
applied. The read-out system is partitioned into 18 sectors on either
side, each sector comprising an inner and outer read-out chamber based
on the principle of multiwire proportional chambers with pad read-out.
Due to the ultra-low power consumption of the electronics, the whole
TPC needs about 25 kW of electrical power for full operation. Only a
fraction of that power and of the corresponding water-cooling plant is
available in the clean room. That is why commissioning the read-out
system currently proceeds with two sectors at a time, using the ALICE
cosmic-muon trigger detector ACORDE, as well as a specially designed UV
laser system for the generation of tracks in the detector.
Preliminary analysis of the cosmic events recorded and of
laser-induced tracks show that the drift velocity and diffusion of
electrons liberated by traversing charged particles, as well as spatial
resolutions, are very close to the design values.
All of the 36 sectors will be turned on and their performance
studied during this commissioning phase, which will last until October
2006. The TPC will then be transported into the ALICE underground area
later this year, where it will be put into service in the spring of 2007.
Did you know?
In a time projection chamber (TPC), an electric field is applied
across a large volume of gas. When a charged particle traverses the TPC,
it ionizes the gas and the liberated electrons drift in the electrical
field to the endplates. The position on the endplate gives two
coordinates. The third is given by the time of arrival of the electrons-
hence the name of time projection chamber.
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