Plasma-Wakefield Accelerator Group

Abstract:

Precise characterization and tailoring of the spatial and temporal evolution of plasma density within plasma sources are critical for realizing high-quality accelerated beams in plasma wakefield accelerators. The simultaneous use of two independent diagnostics allowed the temporally and spatially resolved detection of plasma density with unprecedented sensitivity and enabled the characterization of the plasma temperature in discharge capillaries for times later than 0.5 µs after the initiation of the discharge, at which point the plasma is at local thermodynamic equilibrium. A common-path two-color laser interferometer for obtaining the average plasma density with a sensitivity of 2 × 10¹⁵ cm^-2 was developed together with a plasma emission spectrometer for analyzing spectral line broadening profiles with a resolution of 5 × 10¹⁵ cm^-3. Both diagnostics show good agreement when applying the spectral line broadening analysis methodology of Gigosos and Cardeñoso in the temperature range of 0.5 eV-5.0 eV. For plasma with densities of 0.5-2.5 × 10¹⁷ cm^-3, temperatures of 1 eV-7 eV were indirectly measured by combining the diagnostic information. 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. These measurements pave the way for highly detailed parameter tuning in plasma sources for particle accelerators and beam optics.

Abstract:

Energy-efficient plasma-wakefield acceleration of particle bunches with low energy spread is a promising path to realizing compact free-electron lasers and particle colliders. High efficiency and low energy spread can be achieved simultaneously by strong beam loading of plasma wakefields when accelerating bunches with carefully tailored current profiles [M. Tzoufras et al., Phys. Rev. Lett. 101, 145002 (2008)PRLTAO0031-900710.1103/PhysRevLett.101.145002]. We experimentally demonstrate such optimal beam loading in a nonlinear electron-driven plasma accelerator. Bunches with an initial energy of 1 GeV were accelerated by 45 MeV with an energy-transfer efficiency of (42±4)% at a gradient of 1.3  GV/m while preserving per-mille energy spreads with full charge coupling, demonstrating wakefield flattening at the few-percent level.

Abstract:

This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years.

Abstract:

A novel mechanism for injection, emittance selection, and postacceleration for laser wakefield electron acceleration is identified and described. It is shown that a laser prepulse can create an ionized plasma filament through multiphoton ionization and this heats the electrons and ions, driving an ellipsoidal blast-wave aligned with the laser-axis. The subsequent high-intensity laser-pulse generates a plasma wakefield which, on entering the leading edge of the blast-wave structure, encounters a sharp reduction in electron density, causing density down-ramp electron injection. The injected electrons are accelerated to ∼2 MeV within the blast-wave. After the main laser-pulse has propagated past the blast-wave, it drives a secondary wakefield within the homogenous background plasma. On exiting the blast-wave structure, the preaccelerated electrons encounter these secondary wakefields, are retrapped, and accelerated to higher energies. Due to the longitudinal extent of the blast-wave, only those electrons with small transverse velocity are retrapped, leading to the potential for the generation of electron bunches with reduced transverse size and emittance.