Fast time projection chamber for ALICE experiment

The ALICE experiment on LHC is especially designed to study quark-gluon plasma (QGP). During the first run of the experiment, fundamental processes in QGP were studied. For the second run the main field of study will be shifted to rare processes with low effective cross-sections in QGP. Studying such processes requires a lot more data to be acquired, meaning the increase of collision frequency and a thorough upgrade for ALICE are needed. This paper rounds up the upgrade of the slowest of all the detectors on ALICE - the time-projection chamber (TPC). Making this detector faster means not only a higher effectiveness of the electronics, as well as the acceleration of particles drifting through the detector volume or fast ion back-flow (IBF) suppression. Solution of the slow charge drift seems to be lying within CF₄ gas mixtures, where electron drift velocities have proved to be up to four times higher than in standard mixtures with CH₄ or CO₂. But positive ion drift velocities are still an unknown territory in such mixtures. Ion back-drift on the other hand should be effectively suppressed by a self-gate system of Gas Electron Multiplier foils (GEMs). Question is if with these foils the same space point resolution for track recognition can be preserved. This paper provides positive drift ion velocity measurements in various mixtures of inert gases Ar, Ne and He with different concentrations of CF₄, CH₄ and CO₂ as well as a simulation of a triple GEM system with pad readout for space-point resolution evaluation. (author)