An LED-Based Calibration System for the ATLAS and CMS ZDC in the HL-LHC Era*

The high radiation environment of the CERN high-luminosity (HL) LHC will present new challenges for its detectors. Among these challenges is the damage that this radiation may

cause to the photo-multiplier tubes (PMTs) of the new HL-Zero Degree Calorimeter (HL-ZDC) of the ATLAS and CMS experiments. To address this, an LED-based calibration system was included in the detector design to monitor the PMT performance and calibrate accordingly. This calibration is critical for distinguishing radiation damage from the physics signal in the detector, ensuring the quality of the recorded by the HL-ZDCs during Run 4 and beyond.

The University of Illinois Urbana-Champaign is collaborating with Kansas University to develop a new LED pulser board to use in this calibration system. In between events, the board will be triggered to drive multiple colors of LEDs to pulse the PMTs of the HL-ZDC and monitor the PMT performance in response to different wavelengths. In this contribution, we present results for extensive tests of the board, as well as different light distribution systems designed for it.