Operational Experience with the CMS Hadron Forward Calorimeters Phase I Upgrade

The Phase I Upgrade of the CMS Hadron Forward Calorimeters was completed during the Extended Year End Technical Stop of 2016 - 2017. In the framework of the upgrade, the front-end electronics were replaced and the PMT boxes were reworked to implement two-channel readout in order to exploit the benefits of the multi-anode PMTs. The new PMTs with two channel readout allow background tagging and signal recovery. In addition, the front-end electronics implement a 6-bit TDC to provide an additional handle to eliminate the background. The Hadron Forward Calorimeters were commissioned and operated successfully in 2017 data taking period. Here we describe the details and the components of the upgrade, and discuss the operational experience with the Phase I Upgrade.