STELLA‐II: Staged Monoenergetic Laser Acceleration ‐ Experiment Update

The goal of STELLA‐II is to demonstrate staged monoenergetic laser acceleration of microbunches using an inverse free electron laser (IFEL) buncher and IFEL accelerator. A key feature of this experiment is the usage of a single high‐intensity laser beam to simultaneously drive both the buncher and accelerator. A chicane between the buncher and accelerator causes microbunches to form at the entrance to the accelerator. All hardware has been installed at the Accelerator Test Facility (ATF) located at Brookhaven National Laboratory, including a new laser beam transport system to permit delivering higher laser power. Preliminary test results indicate that modulation and acceleration of the microbunches are occurring with the new system. Energy gains >13% have been observed. Current experiments are being conducted with the ATF CO₂ laser operating at a pulse length of ∼180 ps. In late autumn 2002, the ATF CO₂ laser will be upgraded to produce pulse lengths of <10 ps at approximately the same output pulse energy. This higher peak power will enable higher acceleration and more complete trapping of the laser‐generated microbunches in the accelerator. This higher acceleration and trapping will also result in a clean separation of the accelerated microbunch electrons from the unaccelerated ones while at the same time maintaining a narrow energy spread.