Observation of a long-wavelength hosing modulation of a high-intensity laser pulse in underdense plasma

Hosing of a Long Relativistic Particle Bunch in Plasma

Experimental results show that hosing of a long particle bunch in plasma can be induced by wakefields driven by a short, misaligned preceding bunch. Hosing develops in the plane of misalignment, self-modulation in the perpendicular plane, at frequencies close to the plasma electron frequency, and are reproducible. Development of hosing depends on misalignment direction, its growth on misalignment extent and on proton bunch charge. Results have the main characteristics of a theoretical model, are relevant to other plasma-based accelerators and represent the first characterization of hosing.

Mitigation of the Onset of Hosing in the Linear Regime through Plasma Frequency Detuning

The hosing instability poses a feasibility risk for plasma-based accelerator concepts. We show that the growth rate for beam hosing in the linear regime (which is relevant for concepts that use a long driver) is a function of the centroid perturbation wavelength. We demonstrate how this property can be used to damp centroid oscillations by detuning the plasma response sufficiently early in the development of the instability. We also develop a new theoretical model for the early evolution of hosing. These findings have implications for the general control of an instability's growth rate.

Laser-based synchrotron X-ray radiation experimental scaling

We review the results obtained in several experimental campaigns with the INRS high-power laser system and determine the X-ray emission scaling from synchrotron radiation produced during laser wakefield acceleration (LWFA) of electrons. The physical processes affecting the generation of intense and stable X-ray beams during the propagation phase of the high-intensity ultrashort pulse in the gas jet target are discussed. We successfully produced stable propagation in the gas jet target of a relativistic laser pulse through self-guiding on length larger than the dephasing and depletion lengths, generating very intense beams of hard X-rays with up to 200 TW on target. The experimental scaling law obtained for the photon yield in the 10-40 keV range is presented and the level of X-ray emission at the 1 PW laser peak power level, now available at several laser facilities, is estimated.

Laser and electron deflection from transverse asymmetries in laser-plasma accelerators

We report on the deflection of laser pulses and accelerated electrons in a laser-plasma accelerator (LPA) by the effects of laser pulse front tilt and transverse density gradients. Asymmetry in the plasma index of refraction leads to laser steering, which can be due to a density gradient or spatiotemporal coupling of the laser pulse. The transverse forces from the skewed plasma wave can also lead to electron deflection relative to the laser. Quantitative models are proposed for both the laser and electron steering, which are confirmed by particle-in-cell simulations. Experiments with the BELLA Petawatt Laser are presented which show controllable 0.1-1 mrad laser and electron beam deflection from laser pulse front tilt. This has potential applications for electron beam pointing control, which is of paramount importance for LPA applications.

Generation of femtosecond γ-ray bursts stimulated by laser-driven hosing evolution

The promising ability of a plasma wiggler based on laser wakefield acceleration to produce betatron X-rays with photon energies of a few keV to hundreds of keV and a peak brilliance of 10²²–10²³ photons/s/mm²/mrad²/0.1%BW has been demonstrated, providing an alternative to large-scale synchrotron light sources. Most methods for generating betatron radiation are based on two typical approaches, one relying on an inherent transverse focusing electrostatic field, which induces transverse oscillation, and the other relying on the electron beam catching up with the rear part of the laser pulse, which results in strong electron resonance. Here, we present a new regime of betatron γ-ray radiation generated by stimulating a large-amplitude transverse oscillation of a continuously injected electron bunch through the hosing of the bubble induced by the carrier envelope phase (CEP) effect of the self-steepened laser pulse. Our method increases the critical photon energy to the MeV level, according to the results of particle-in-cell (PIC) simulations. The highly collimated, energetic and femtosecond γ-ray bursts that are produced in this way may provide an interesting potential means of exploring nuclear physics in table top photo nuclear reactions.

Optical control of hard X-ray polarization by electron injection in a laser wakefield accelerator

Laser-plasma particle accelerators could provide more compact sources of high-energy radiation than conventional accelerators. Moreover, because they deliver radiation in femtosecond pulses, they could improve the time resolution of X-ray absorption techniques. Here we show that we can measure and control the polarization of ultra-short, broad-band keV photon pulses emitted from a laser-plasma-based betatron source. The electron trajectories and hence the polarization of the emitted X-rays are experimentally controlled by the pulse-front tilt of the driving laser pulses. Particle-in-cell simulations show that an asymmetric plasma wave can be driven by a tilted pulse front and a non-symmetric intensity distribution of the focal spot. Both lead to a notable off-axis electron injection followed by collective electron–betatron oscillations. We expect that our method for an all-optical steering is not only useful for plasma-based X-ray sources but also has significance for future laser-based particle accelerators.

Radiation sources driven by laser-plasma accelerators have the potential to produce shorter bursts of radiation at lower cost than those based on conventional accelerators. Schnell et al. demonstrate the ability to control the polarization of the bursts of hard X-rays produced by such a source.

Laser hosing in relativistically hot plasmas

Electron response in an intense laser is studied in the regime where the electron temperature is relativistic. Equations for laser envelope and plasma density evolution, both in the electron plasma wave and ion acoustic wave regimes, are rederived from the relativistic fluid equations to include relativistic plasma temperature effect. These equations are used to study short-pulse and long-pulse laser hosing instabilities using a variational method approach. The analysis shows that relativistic electron temperatures reduce the hosing growth rates and shift the fastest-growing modes to longer wavelengths. These results resolve a long-standing discrepancy between previous nonrelativistic theory and simulations or experiments on hosing.

Anticorrelation between ion acceleration and nonlinear coherent structures from laser-underdense plasma interaction

In laser-plasma experiments, we observed that ion acceleration from the Coulomb explosion of the plasma channel bored by the laser is prevented when multiple plasma instabilities, such as filamentation and hosing, and nonlinear coherent structures (vortices or postsolitons) appear in the wake of an ultrashort laser pulse. The tailoring of the longitudinal plasma density ramp allows us to control the onset of these instabilities. We deduced that the laser pulse is depleted into these structures in our conditions, when a plasma at about 10% of the critical density exhibits a gradient on the order of 250 μm (Gaussian fit), thus hindering the acceleration. A promising experimental setup with a long pulse is demonstrated enabling the excitation of an isolated coherent structure for polarimetric measurements and, in further perspectives, parametric studies of ion plasma acceleration efficiency.