  High-Luminosity running at the LHC, which is planned for 2022 and beyond,
will imply an order of magnitude increase in radiation levels and particle
fluences with respect to the present LHC running conditions. The performance
evolution of the CMS electromagnetic calorimeter (ECAL), comprising 75,848
scintillating lead tungstate crystals, indicates that an upgrade of its endcaps
will be needed for HL-LHC running, to ensure an adequate performance. Results
from LHC collision periods, beam tests and laboratory measurements of
proton-irradiated crystals are combined to predict the performance of the
current detector at the HL-LHC. In addition, an overview is given of various R
and D studies towards a replacement of the ECAL endcaps for the HL-LHC running
period.
