  After the Long Shutdown 2 the LHC will provide lead-lead collisions at
interaction rates as high as 50kz. In order to cope with such conditions the
ALICE Time Projection Chamber (TPC) needs to be upgraded. After the upgrade the
TPC will run in a continuous mode, without any degradation of the momentum and
dE/dx resolution compared to the performance of the present TPC. Since readout
by multi-wire proportional chambers is no longer feasible with these
requirements, new technologies have to be employed. In the new readout chambers
the electron amplification is provided by a stack of four Gas Electron
Multiplier (GEM) foils. Their high voltage settings and orientation have been
optimised to provide an energy resolution better then 12% at the photopeak of
55Fe. At the same settings the Ion BackFlow into the drift volume is less than
1% of the effective number of ions produced during gas amplification and the
primary ionisations. This is necessary to prevent the accumulation of space
charge, which eventually will distort the field in the drift volume. To ensure
stable operation at the high loads during LHC run 3 the chambers have to be
robust against discharges, too. With the selected configuration in a quadruple
GEM stack the discharge probability is kept at the level of $10^{-12}$
discharges per incoming hadron. An overview of the ALICE TPC upgrade activities
will be given in these proceedings and the optimised settings foreseen for the
GEM stacks of the future readout chambers are introduced. Furthermore the
outcome of two beam time campaigns at SPS and PS (at CERN) in the end of 2014
is shown. At this campaigns the stability against discharges and the dE/dx
performance of a full size readout chamber prototype was tested. In addition it
is reported on charging-up studies of 4GEM stacks and on tests of
electromagnetic sagging of large GEM foils.
