  During Phase-2 of the LHC, known as the High Luminosity LHC (HL-LHC), the
accelerator will increase its instantaneous luminosity to 5 $\times$ 10$^{34}$
cm$^{-2}$ s$^{-1}$, delivering an integrated luminosity of 3000 fb$^{-1}$ over
10 years of operation starting from 2027. In view of the HL-LHC, the CMS muon
system will be upgraded to sustain efficient muon triggering and reconstruction
performance. Resistive Plate Chambers (RPCs) serve as dedicated detectors for
muon triggering due to their excellent timing resolution, and will extend
$|\eta|$ (pseudorapidity) up to a region of 2.4. Before Long Shutdown 3 (LS3),
the RE3/1 and RE4/1 stations of the endcap will be equipped with new improved
Resistive Plate Chambers (iRPCs) having different design and geometry than the
present RPC system. The iRPC geometry configuration improves the detector's
rate capability and its ability to survive the harsh background conditions of
the HL-LHC. Also, new electronics equipped with excellent timing precision
measurements with a resolution of less than 150 ps are developed to readout the
RPC detectors from both sides of the strips to allow for good spatial
resolution along them. The performance of the iRPC has been studied with gamma
radiation at the Gamma Irradiation Facility (GIF++) at CERN. Ongoing longevity
studies will help to certify the iRPCs for the HL-LHC running period. The main
detector parameters such as the currents, rate and resistivity are regularly
monitored as a function of the integrated charge. Preliminary results of the
detector performance will be presented.
