Cascaded high-voltage power supplies for the ALICE TPC upgrade with GEMs

For the upgrade of the Time Projection Chamber (TPC) of the ALICE experiment at the CERN LHC it is planned to replace the present MWPC-based readout chambers with detectors that employ stacks of four GEMs. At the same time, new HV power supplies are needed to provide the voltages to the eight GEM electrodes. To this end, a new generation of power supplies is being developed where the voltages are cascaded in such a way, that no over-voltages can occur in case of a GEM discharge. At the IKF in Frankfurt, a test board was developed that simulates the electric network of a 4-GEM system. This board allows to study the characteristics of a cascaded power supply prototype in terms of noise and study its behavior in case of a discharge. In this presentation, results of such tests are presented.