The dynamics of energetic particles in strong electromagnetic fields can be heavily influenced by the energy loss arising from the emission of radiation during acceleration, known as radiation ...reaction. When interacting with a high-energy electron beam, today's lasers are sufficiently intense to explore the transition between the classical and quantum radiation reaction regimes. We report on the observation of radiation reaction in the collision of an ultra-relativistic electron beam generated by laser wakefield acceleration (\(\varepsilon > 500\) MeV) with an intense laser pulse (\(a_0 > 10\)). We measure an energy loss in the post-collision electron spectrum that is correlated with the detected signal of hard photons (\(\gamma\)-rays), consistent with a quantum (stochastic) description of radiation reaction. The generated \(\gamma\)-rays have the highest energies yet reported from an all-optical inverse Compton scattering scheme, with critical energy \(\varepsilon_{\rm crit} > \) 30 MeV.
We report on the first experimental observation of a current-driven instability developing in a quasi-neutral matter-antimatter beam. Strong magnetic fields (\(\geq\) 1 T) are measured, via means of ...a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma.The experimentally determined equipartition parameter of \(\epsilon_B \approx 10^{-3}\), is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by Particle-In-Cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma for thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets.
Over the last decades, significant advances in high-power laser systems have enabled rapid progress in the development of laser-driven plasma accelerators. Today, the results obtained in beam ...stability and reproducibility present laser plasma acceleration as a viable and promising alternative to conventional accelerators. As several electron beam and secondary sources applications require high average currents, a major focus is now on increasing the beam's repetition rate. In the following, we introduce a novel plasma source for kHz electron acceleration, providing a continuous and spatially confined gas flow, while minimising the gas load in the acceleration chamber.
We report on the laser-driven generation of purely neutral, relativistic electron-positron pair plasmas. The overall charge neutrality, high average Lorentz factor (\(\gamma_{e/p} \approx 15\)), ...small divergence (\(\theta_{e/p} \approx 10 - 20\) mrad), and high density (\(n_{e/p}\simeq 10^{15}\)cm\(^{-3}\)) of these plasmas open the pathway for the experimental study of the dynamics of this exotic state of matter, in regimes that are of relevance to electron-positron astrophysical plasmas.
We present few-femtosecond shadowgraphic snapshots taken during the non-linear evolution of the plasma wave in a laser wakefield accelerator with transverse synchronized few-cycle probe pulses. These ...snapshots can be directly associated with the electron density distribution within the plasma wave and give quantitative information about its size and shape. Our results show that self-injection of electrons into the first plasma wave period is induced by a lengthening of the first plasma period. Three dimensional particle in cell simulations support our observations.
Laser-wakefield acceleration is a promising technique for the next generation of ultra-compact, high-energy particle accelerators. However, for a meaningful use of laser-driven particle beams it is ...necessary that they present a high degree of pointing stability in order to be injected into transport lines and further acceleration stages. Here we show a comprehensive experimental study of the main factors limiting the pointing stability of laser-wakefield accelerated electron beams. It is shown that gas-cells provide a much more stable electron generation axis, if compared to gas-jet targets, virtually regardless of the gas density used. A sub-mrad shot-to-shot fluctuation in pointing is measured and a consistent non-zero offset of the electron axis in respect to the laser propagation axis is found to be solely related to a residual angular dispersion introduced by the laser compression system and can be used as a precise diagnostic tool for compression oprtimisation in chirped pulse amplified lasers.
Energy-transfer efficiency is an important quantity in plasma-wakefield acceleration, especially for applications that demand high average power. Conventionally, the efficiency is measured using an ...electron spectrometer; an invasive method that provides an energy-transfer efficiency averaged over the full length of the plasma accelerator. Here, we experimentally demonstrate a novel diagnostic utilizing the excess light emitted by the plasma after a beam-plasma interaction, which yields noninvasive, longitudinally resolved measurements of the local energy-transfer efficiency from the wake to the accelerated bunch; here, as high as (58 \(\pm\) 3)%. This method is suitable for online optimization of individual stages in a future multistage plasma accelerator, and enables experimental studies of the relation between efficiency and transverse instability in the acceleration process.
Precise characterization and tailoring of the spatial and temporal evolution of plasma density within plasma sources is critical for realizing high-quality accelerated beams in plasma wakefield ...accelerators. The simultaneous use of two independent diagnostic techniques allowed the temporally and spatially resolved detection of plasma density with unprecedented sensitivity and enabled the characterization of the plasma temperature at local thermodynamic equilibrium in discharge capillaries. A common-path two-color laser interferometer for obtaining the average plasma density with a sensitivity of \(2\times 10^{15}\) cm\(^{-2}\) was developed together with a plasma emission spectrometer for analyzing spectral line broadening profiles with a resolution of \(5\times 10^{15}\) cm\(^{-3}\). Both diagnostics show good agreement when applying the spectral line broadening analysis methodology of Gigosos and Carde{ñ}oso. Measured longitudinally resolved plasma density profiles exhibit a clear temporal evolution from an initial flat-top to a Gaussian-like shape in the first microseconds as material is ejected out from the capillary, deviating from the often-desired flat-top profile. For plasma with densities of 0.5-\(2.5\times 10^{17}\) cm\(^{-3}\), temperatures of 1-7 eV were indirectly measured. These measurements pave the way for highly detailed parameter tuning in plasma sources for particle accelerators and beam optics.
