A new network of electric field mills at the Pierre Auger Observatory

The Pierre Auger Observatory is the largest ground-based instrument for the detection of ultra-high energy cosmic rays via extensive air showers. As part of the current detector upgrade, called AugerPrime, the new Radio Detector (RD) is being deployed, which will finally consist of 1661 radio antennas covering an area of more than 3000 km2. A crucial ingredient for the interpretation of data taken with the RD is monitoring the atmospheric electric field over the observatory. Large atmospheric electric fields, typically in the presence of thunderstorms, can significantly alter the radio emission from air showers. Therefore, these kinds of conditions have to be flagged.
We present a new network of five electric field mills (EFM) that was installed at the Pierre Auger Observatory to tackle this task. The network is designed such that each EFM measures the electric field with an absolute calibration. The setup of the network and the deployment process are shown. First data are presented.