High repetition-rate wakefield electron source generated by few-millijoule, 30 fs laser pulses on a density downramp

Abstract

We report on an experimental demonstration of laser wakefield electron acceleration using a sub-TW power laser by tightly focusing 30 fs laser pulses with an 8 mJ pulse energy on a 100 µm scale gas target. The experiments are carried out at an unprecedented 0.5 kHz repetition rate, allowing 'realtime' optimization of accelerator parameters. Well-collimated and stable electron beams with quasi-monoenergetic peaks in the 100 keV range are measured. Particle-in-cell simulations show excellent agreement with the experimental results and suggest an acceleration mechanism based on electron trapping on the density downramp, due to the time-varying phase velocity of the plasma waves.

Coherent control of plasma dynamics

“…Parameters similar to the experiment conditions were used, with a Gaussian plasma density profile to enable trapping of electrons in the density down ramp (see ref. 27 and Methods for details on the simulation).…”

“…The plasma electron density is measured to be in the range (0.5-2) Â 10 19 cm À 3 using ARTICLE transverse interferometry. Electrons are accelerated in the density down ramp with a final energy in the 100-keV range 27 and detected by a high-resolution scintillating screen (J6677 FOS by Hamamatsu), which is placed about 35 cm downstream from the source and imaged with a lens coupled 12-bit CCD camera for a 4 Â 4 cm 2 effective area. The scintillator sensitivity was calibrated using an electron microscope for the energy range in the spectrum measurement.…”

High-Flux Femtosecond X-Ray Emission from Controlled Generation of Annular Electron Beams in a Laser Wakefield Accelerator

“…This process can also be accomplished by tailoring the plasma density profile. Specifically, self-injection can be localized to a region in space by introducing density gradients along the laser pulse propagation path [14,16]. These gradients affect the evolution of the wave buckets and can be used to minimize the electron beam energy spread [17][18][19][20].…”

Electron diffraction using ultrafast electron bunches from a laser-wakefield accelerator at kHz repetition rate

“…However, the scalability of laser wakefield accelerators has been recently demonstrated 24 and can be extended to a few mJ kHz laser system for producing electrons. 25,26 This electron source has strong potential for UED experiments: (i) After removing the linear (2013) chirp, the bunches should be sub-100 fs, (ii) electron bunches are intrinsically synchronized to the laser source, (iii) the gas target and the high repetition rate permit an ease of use as well as the possibility to accumulate data.…”

“…16,17 This might be due to the fact that a kHz laser system is usually more compact and stable than a multi-joule laser system. In addition, the injection mechanism that is used in this experiment relies on downramp injection, 26,29 and it does not rely on the non FIG. 1.…”