FEL/Duke University, Durham, North Carolina
High repetition rate linacs and ERLs are preferred accelerators to drive high power FELs in the kW to hundreds of kW region. The storage ring FEL, given its well-known extracted power limit, has not been considered as a high power photon source. A high-intensity Compton gamma source requires a high-power photon source, which can be made available inside an FEL resonator. The Duke storage ring FEL has been developed as a high intracavity photon source for a world-class Compton gamma-ray source, High Intensity Gamma-ray Source (HIGS). Recently, the HIGS has reached a total flux of few 110 g/s at few to 10 MeV, enabled by a few-kW intracavity average power storage ring FEL. In this work, we report our recent experimental study of kW intracavity FEL operation in visible and near-IR wavelengths. In particular, we will present our novel approach to suppress wiggler power loading on the downstream FEL mirror using in-cavity apertures, a critical step to achieve kW intracavity power. We envision that this wiggler radiation power control technique be adopted by other high power resonator FELs driven by linacs and ERLs in their pursuit of further increasing the FEL power.
ANL, Argonne
An x-ray free-electron laser oscillator (XFELO)[1] promises to be an ideal hard x-ray source, particularly for applications requiring high spectral purity such as Moessbauer spectroscopy and inelastic scattering. Progress has been made in several areas of XFELO study: Performance of concrete XFELO cases with tunable, four-diamond crystal cavities[2] in the 9-20 keV range was calculated using the modified GINGER code[3]. We measured the reflectivity of the diamond crystal at 23.7 keV to be near the theoretical value and the thermal expansion coefficient below 100K to be small, indicating that the heat load will not adversely affect XFELO operation. A null feedback system has been implemented that stabilizes the crystal orientation to within 50 nr of the Rocking curve maximum, an encouraging first step towards achieving the <10 nr stability requirements. We are refining the conceptual design of an injector satisfying the XFELO requirements, starting from a thermionic cathode in a low-frequency rf cavity and followed by various beam filtering and manipulation stages. A 300-kV DC cathode assembly is under construction to demonstrate the production of ultralow-emittance beams.
[1] K.-J. Kim, Y. Shvyd’ko, and S. Reiche, PRL 100, 244802 (2008).
[2] K.-J. Kim and Y. Shvyd’ko, PRST-AB, 12, 030703 (2009).
[3] R.R. Lindberg and K.-J. Kim, submitted to PRST-AB.
JLAB, Newport News, Virginia
ATF, Boulder
Twente University, Laser Physics and Non-Linear Optics Group, Enschede
We report the design, and broadly tunable operation, for the first time, of a high average power free-electron laser using edge-outcoupling. Using the FEL in this configuration, we achieved a maximum stable output power of 270W at 2.53 μm, and could tune with an output of 20 W or higher from 0.8 to 4.2 μm. The output was in the form of a continuous train of sub-ps pulses at 4.68 MHz. Measurements of gain, loss, and the output mode are compared with models.
JLAB, Newport News, Virginia
In this paper we report a direct experimental investigation of optical frequency chirping effects induced by ultrashort electron bunches in a high-gain energy-recovery-linac (ERL) free-electron laser (FEL) cavity. Our measurement and analysis shows clear evolution of the optical pulse chirp verses the electron bunch energy chirp. Further study also provides important evidence that under certain conditions much shorter FEL pulses can be obtained through properly chirping electron bunches and optical pulse compression. Although studies about the chirp measurement on Self-amplified-spontaneous-emission (SASE) FEL were reported recently, we believe this paper for the first time provides a comprehensive and close observation into the very unique temporal and spectral characteristics of ultrashort optical pulses from a high-gain ERL FEL. This is made possible by the stable operation and unique capability of the Jefferson Lab machine to change the electron bunch energy chirp with no curvature. Preliminary simulations will also be presented.