Upgrade of Mid-Infrared Free Electron Laser at Kyoto University by Long Macro-pulse Photocathode Operation of the Existing RF Gun

A mid-infrared Free Electron Laser (MIR-FEL) is a candidate to realize a high-repetition-rate atto-second hard X-ray source based on the high harmonic generation (HHG). A new project to conduct a proof of principle experiment of HHG driven by a MIR-FEL has been started since 2018. For this purpose, upgrade project of MIR-FEL at Kyoto University (KU-FEL) has been started to achieve high peak power and ultrashort pulse operation. As the first step of the upgrade, a photocathode drive laser was improved to enable long macro-pulse photocathode operation. The results of the long macro-pulse photocathode operation of KU-FEL will be presented.