The ALICE Time-Projection Chamber (TPC) is the main device, in the ALICE ‘central barrel’, for tracking of charged particles and particle identification. The ALICE TPC was designed to cope with the highest conceivable charged particle multiplicities produced in central Pb–Pb collisions at LHC energies. Its acceptance covers 2π in azimuthal angle and a pseudo-rapidity interval |eta| < 0.9.

The ALICE TPC is a 90 m^3 cylinder filled with gas and divided in two drift regions by the central electrode located at its axial centre. The field cage secures the uniform electric field along the z-axis. Each of the two end plates is divided into 18 sectors, each holding one Inner ReadOut Chamber (IROC) and one Outer ReadOut Chamber (OROC). In total, the TPC readout is based on 36 IROCs and 36 OROCs.

Charged particles traversing the TPC volume ionise the gas along their path, liberating electrons that drift towards the end plates of the cylinder. The necessary signal amplification is provided by Gas Electron Multipliers (GEMs) in an optimized multilayer configuration, which stand  up to the technological challenges imposed by continuous TPC operation at high rate. The requirement to keep the ion-induced space-charge distortions at a tolerable level leads to an upper limit of 2% for the fractional ion backflow, i.e. the ion escape probability per effective electron-ion pair produced in the gas amplification stage, at the operational gas gain of 2000 in a Ne-CO2-N2 (90-10-5) gas mixture. At the same time, the readout system provides a local energy resolution better than 14% at the ^{55}Fe-peak, which translates into the required dE/dx resolution of the TPC.

The readout of the signal is done by the 524160 pads that form the anode plane of the GEM chambers located at the TPC end plates. Each pad is connected to a front-end electronics channel. 160 front-end channels are
combined in Front-End Cards (FEC). On each FEC, the signals are transformed into differential, semi-Gaussian voltage signals, and continuously digitized in five custom-made ASICs (SAMPA). The FEC further incorporates two optical readout links for the digitized data, and one control link, which also provides the reference clock to the digital circuitry on the FEC. In total, 6552 optical TX (transmit) links are needed to send the digitized data off-detector. This leads to an unprecedented data throughput of 3.28 TB/s. 360 FPGA-based readout cards (Common Readout Unit, CRU) receive the data and perform online processing (common mode correction and data reduction).

TPC Documents

TPC Internal:

Photo Galleries


Participating Institutes:

  • Comenius University Bratislava, Faculty of Mathematics, Physics and Informatics, Bratislava, Slovakia
  • Helmholtz-Institut fur Strahlen und Kernphysik, Rheinische Friedrich-Wilhelms-Universitat Bonn, Bonn, Germany
  • High Energy Physics Group, Universidad Autonoma de Puebla, Puebla, Mexico
  • Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania
  • Institut fur Kernphysik, Johann Wolfgang Goethe-Universitat Frankfurt, Frankfurt, Germany
  • Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico
  • Istanbul University, High Energy Physics Department, Istanbul, Turkey
  • Lund University Department of Physics, Division of Particle Physics, Lund, Sweden
  • Nagasaki Institute of Applied Science, Nagasaki, Japan
  • Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
  • Physics department, Faculty of science, University of Zagreb, Zagreb, Croatia
  • Physikalisches Institut, Ruprecht-Karls-Universitat Heidelberg, Heidelberg, Germany
  • Physik Department, Technische Universitat Munchen, Munich, Germany
  • PINSTECH, Islamabad, Pakistan
  • Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum fur Schwerionenforschung GmbH, Darmstadt, Germany
  • The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland
  • The University of Texas at Austin, Austin, Texas, United States
  • Universidade de Sao Paulo (USP), Sao Paulo, Brazil
  • University of Houston, Houston, Texas, United States
  • University of Tennessee, Knoxville, Tennessee, United States
  • University of Tokyo, Tokyo, Japan
  • Wayne State University, Detroit, Michigan, United States
  • Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, Hungary
  • Yale University, New Haven, Connecticut, United States
TPC installation



TPC picture