Berkeley Lab

TREX Undulator Beamline

Developing techniques to apply LPAs to seeded free electron lasers

Photograph of the undulator.

Photograph of the undulator

The high current femtosecond electron beams generated by LPAs make them attractive drivers for future free-electron lasers (FELs), while at the same time the radiation produced is a powerful diagnostic for improving the LPA. Research in these areas is carried out using THUNDER, the Tapered Hybrid Undulator, originally built by Boeing and Spectra Technology and installed on the GeV-class LPA beamline driven by the TREX laser.

The LPA electron beam driven by the TREX laser is coupled into the undulator using quadrupole magnetic lenses, and measured via beam-position monitors and Optical Transition Radiation (OTR) foils. Undulator radiation spectroscopy allows resolution of beam emittance and energy spread.

3D model of the XUV spectrometer to study the wavelength dependence of the emitted undulator radiation.

3D model of the XUV spectrometer to study the wavelength dependence of the emitted undulator radiation

Techniques are being developed tested towards an LPA based FEL, including improvement of beam phase space tuning via injection control, and electron beam phase space manipulation in magnetic optics after the LPA. Novel methods of seeding the FEL are also being investigated, including Laser harmonics at XUV wavelengths generated by the interaction of a moderately-intense laser with an overcritical plasma (solid) by the coherent wake emission (CWE) mechanism. A spooling tape-based solid target configuration enables high-repetition rate (multi-Hz) operation.