Upgrade of the sPHENIX TPC High Voltage System

sPHENIX (super Pioneering High Energy Nuclear phyIcs eXperiment) is a particle detector at RHIC (Relativistic Heavy Ion Collider) at Brookhaven National Lab in Long Island, New York, USA. sPHENIX is optimized to study the Quark-Gluon Plasma (QGP) created in the Au+Au ion collisions at √s_NN = 200 GeV that RHIC provides. sPHENIX is a multimodal detector which includes silicon and gaseous detectors for tracking/momentum and calorimeters for energy measurement. sPHENIX uses a Time Projection Chamber (TPC) filled with Ar:CF4:Isobutane in a 75:20:5 by volume ratio for its track momentum measurement. The sPHENIX TPC is a double-sided TPC with a radial acceptance of 30-78 cm, drift length of ~100 cm and nominal drift field of ~400 V/cm. The sPHENIX TPC uses 72 HV modules with GEM (Gaseous Electron Multiplier) foils arranged in 4 foils/module across its ends for its amplification stage. In 2023 and 2024, the modules were powered from an ISEG HV power supply, using one channel per module and a chain of 8 resistors to distribute the voltage across the 4 GEM foils. At the end of 2024 into 2025, the sPHENIX TPC was upgraded to a CAEN cascaded HV power supply, using 8 floating channels per module to distribute the voltage across the 4 GEM foils. The upgraded system improves high voltage stability, allows for active gain adjustment under load, provides GEM-by-GEM monitoring, and significantly lowers maintenance. This talk will discuss the upgrade process and the successful running status during the 2025 Au+Au run.