First operation of an FEL in same-cell energy recovery mode
Neil GR., Benson S., Biallas G., Bohn CL., Douglas D., Dylla HF., Evans R., Fugitt J., Gubeli J., Hill R., Jordan K., Krafft G., Li R., Merminga L., Oepts D., Piot P., Preble J., Shinn M., Siggins T., Walker R., Yunn B.
The driver for Jefferson Lab's kW-level infrared free-electron laser (FEL) is a superconducting, recirculating accelerator that recovers 75% of the electron-beam power and converts it to radio frequency power. As reported in FEL'98, the accelerator operated "straight-ahead" to deliver 38 MeV, 1.1 mA cw current for lasing at wavelengths in the vicinity of 5 μm. The waste beam was sent directly to a dump, bypassing the recirculation loop. Stable operation at up to 311 W cw was achieved in this mode. The machine has now recirculated cw average current up to 4.7 mA, and has lased cw with energy recovery up to 1720 W output at 3.1 μm. This is the first FEL to ever operate in the "same-cell" energy recovery mode. Energy recovery offers several advantages (reduced RF power and dramatically reduced radio-nuclide production at the dump) and several challenges (potential for instabilities and difficult beam transport due to large energy spreads). Solutions to these challenges will be described. We have observed heating effects in the mirrors which will be described. We will also report on the additional performance measurements of the FEL that have been performed and connect those measurements to standard models. © 2000 Elsevier Science B.V. All rights reserved.