Recommissioning of the University of Hawai‘i LINAC and Free Electron Laser

The electron beam linear accelerator (linac) at the free-electron-laser (FEL) laboratory of the University of Hawai‘i at Mānoa, originally developed by Prof. John Madey, has undergone recommissioning. The S-band linac delivers 45 MeV electron beams with 170 mA pulse current and 4–8 $\mu$s pulse duration to drive an infrared FEL oscillator. Recent efforts include restoration of the microwave thermionic gun with a new LaB$_6$ cathode, upgraded vacuum and RF systems, and development of a Python-based beam dynamics model to recover operational magnet settings and optimize beam transport. These upgrades address key technical challenges to restart the accelerator and pave the way for future FEL experiments, including coherent pulse shaping and inverse Compton scattering x-ray generation.