High Energy Gain IFEL at UCLA Neptune Laboratory

Abstract

We report on the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected in a 50 cm long undulator strongly tapered both in period and field amplitude. A CO 2 10.6 µm laser with power > 400 GW is used as the IFEL driver. The Rayleigh range of the laser (∼ 1.8 cm) is shorter than the undulator length so that the interaction is diffraction dominated. Few per cent of the injected particles are trapped in stable accelerating buckets and electrons with energies up to 35 MeV are detected on the magnetic spectrometer. Three dimensional simulations are in good agreement with the electron energy spectrums observed in the experiment and indicate that substantial energy exchange between laser and electron beam only occurs in the first 25-30 cm of the undulator. An energy gradient of > 70 MeV is inferred. In the second section of the undulator higher harmonic IFEL interaction is observed.

Beam by design: Laser manipulation of electrons in modern accelerators

“…(Courant et al, 1985) presented a comprehensive analysis for both planar and helical undulators that in-cluded the effects of synchrotron radiation losses, as well as energy transfer enhancements obtained from undulator tapering. Based on these principles, several single stage IFEL experiments followed, with accelerating wavelengths in the microwave regime (Yoder et al, 2001), at 1.6 mm (Wernick and Marshall, 1992), and at 10.6 µm, both at the fundamental undulator resonance (van Steenbergen et al, 1996), and including the second harmonic of a planar undulator (Musumeci et al, 2005b). The latter experiment at UCLA used a strongly tapered design to achieve a 70 MeV/m accelerating gradient for 5% of the electrons with a 2×10 14 W/cm 2 CO 2 laser.…”

“…A third challenge is to generate ultra-high power x-ray pulses, primarily for studies of matter in extreme conditions and for advanced imaging of biological samples using the novel concept of "diffraction before destruction" (Neutze et al, 2000). Because simplified FEL configurations typically saturate when beam energy spread becomes comparable to ρ and beam energy goes out of resonance with the amplified light, the FEL power can be enhanced both by increasing the beam peak current (and hence P b and ρ), and by tapering the undulator tuning to continue extracting power from the electron beam.…”

Role of Direct Laser Acceleration of Electrons in a Laser Wakefield Accelerator with Ionization Injection

“…In free space, the closest analog of the DLA process considered here is the inverse free electron laser mechanism [26][27][28] and the inverse ion channel laser [29]. The other so-called direct laser acceleration mechanism is acceleration in a dielectric [30] or plasma periodic [31,32] structure where the electric field of the laser pulse interacts with an electron in a periodic, slow-wave structure.…”

Simulation study of a photo-injector for brightness improvement in Thomson scattering X-ray source via ballistic bunching

“…Actually, velocity bunching could be carried out based on another configuration called ballistic bunching [9,10]. Ballistic bunching can be viewed as the "thin lens" version of phase space rotation.…”

“…As space charge force is neglected, the drift length needed for the strongest bunching could be estimated with the chirp from Eq. (3) by [9] submit to Chinese Physics C…”