The helium sensor comprises a housing that encloses a detection chamber. A side of the housing is closed by a permeable wall that is selective for helium. In the detection chamber, there is located an ion getter pump comprising an anode, a cathode and a magnetic field. The cathode, or a cathode leg is made of beryllium. Beryllium has a low atomic mass, whereby the likewise light-weight helium ions can be better incorporated into the cathode material.