CHICOX, the latest upgrade of CHICO

CHICO (Compact Heavy Ion COunter) was designed and fabricated almost three decades ago and proved to be a successful and productive auxiliary charged-particle detector array for Gammasphere for the nuclear gamma-ray spectroscopy study. With the gamma-ray detector array evolved to GRETA, CHICO upgrade is needed to CHICO2, a pixelated parallel-plate avalanche counter with matching position resolution, to fully realize the potential for ultimate gamma-ray energy resolution. It was done about 10 years ago and proved to be another successful and productive auxiliary detector array for GRETINA in three science campaigns in ANL. To fit physically into the cavity of GRETA, CHICO2 requires another upgrade to CHICOX by resizing the detector chamber that leads to redesigning the pixelated position-sensing board and the flexible transmission line. This latest upgrade project has been completed and field tested successfully at ANL. CHICOX is ready for the GRETINA science campaign at ANL in FY25. Some significant improvements in the new design to enhance the performance among other details of this detector array will be presented.