Roger Pizzato Nunes

While laser wakefield acceleration (LWFA) in the bubble regime demands ultra-short, high-peak-power laser pulses, operation in the self-modulated regime (SM-LWFA) works with more relaxed pulse conditions, albeit at the cost of lower beam quality. Modern laser systems can deliver few-terawatt pulses with tens of femtoseconds at kilohertz repetition rates. These systems are well-suited for developing SM-LWFA applications where high average energy and charge are prioritized over beam quality. Such beams could be used to generate high-energy bremsstrahlung photons, capable of triggering photonuclear reactions to produce radioisotopes like molybdenum-99. This isotope decays into technetium-99m, the most widely used medical radioisotope, with over 30 million applications worldwide per year. This work explores the use of Bayesian optimization to maximize the energy and charge of electron beams accelerated via SM-LWFA. Particle-in-cell (PIC) simulations model a 5 TW, ∼60 fs-long (FWHM) Gaussian laser pulse, propagating through tailored hydrogen gas-density profiles. In these simulations, over multiple iterations, the algorithm optimizes a set of input parameters characterizing the gas-density profile and the laser focal position. Three distinct profiles, with lengths ranging from 200 to 400 μm and combining ramps and plateaus, were investigated. Optimal configurations produced electron beams with median energies ranging from 14 to 17 MeV and charges of 600 to 1300 pC, considering electrons with energies above 8 MeV. Preliminary estimates of molybdenum-99 yields for the optimal beams were obtained using their phase space data from PIC simulations as radiation sources in Monte Carlo simulations irradiating a tantalum-molybdenum target.

Plasma wakefields driven by high power lasers or relativistic particle beams can be orders of magnitude larger than the fields produced in conventional accelerating structures. Since the plasma wakefield is composed not only of accelerating but also of decelerating phases, this paper proposes to utilize the strong decelerating field induced by a laser pulse in the plasma to absorb the beam energy, in a scheme known as the active plasma beam dump. The design of this active plasma beam dump has considered the beam output by the EuPRAXIA facility. Analytical estimates were obtained, and compared with particle-in-cell simulations. The obtained results indicate that this active plasma beam dump can contribute for more compact, safer, and greener accelerators in the near future.

This work presents a study on laser wakefield electron acceleration in the self-modulated regime (SM-LWFA) using 50-fs laser pulses with energy on the mJ scale, at λ = 0.8 µm, impinging on a thin H₂ gas jet. Particle-in-cell simulations were performed using laser peak powers ranging from sub-terawatt to a few terawatts and plasma densities varying from the relativistic self-focusing threshold up to values close to the critical density. The differences in the obtained acceleration processes are discussed. Results show that bunched electron beams with full charge on the nC scale and kinetic energy in the MeV range can be produced and configurations with peak density in the range 0.5–5 × 10²⁰ atoms/cm³ generate electrons with maximum energies. In this range, some simulations generated quasimonoenergetic bunches with ∼0.5% of the total accelerated charge and we show that the beam characteristics, process dynamics, and operational parameters are close to those expected for the blowout regime. The configurations that led to quasimonoenergetic bunches from the sub-TW SM-LWFA regime allow the use of laser systems with repetition rates in the kHz range, which can be beneficial for practical applications.

Beam dumps are indispensable components for particle accelerator facilities to absorb or dispose beam kinetic energy in a safe way. However, the design of beam dumps based on conventional technology, i.e., energy deposition via beam–dense matter interaction, makes the beam dump facility complicated and large in size, partly due to the high beam intensities and energies achieved. In addition, specific methods are needed to address the radioactive hazards that these high-power beams generate. On the other hand, the European Plasma Research Accelerator with eXcellence in Application (EuPRAXIA) project can advance the laser–plasma accelerator significantly by achieving a 1–5 GeV high-quality electron beam in a compact layout. Nevertheless, beam dumps based on the conventional technique will still produce radiation hazards and make the overall footprint less compact. Here, a plasma beam dump will be implemented to absorb the kinetic energy from the EuPRAXIA beam. In doing so, the overall compactness of the EuPRAXIA layout could be further improved, and the radioactivity generated by the facility can be mitigated. In this paper, results from particle-in-cell simulations are presented for plasma beam dumps based on EuPRAXIA beam parameters.

Beam dumps are indispensable components for particle accelerator facilities to absorb or dispose beam kinetic energy in a safe way. However, the design of beam dumps based on conventional technology, i.e. the energy deposition via beam-dense matter interaction, makes the beam dump facility complicated and large in size, partly due to nowadays’ high beam intensities and energies achieved. In addition, these high-power beams generate radioactive hazards, which need specific methods to deal with. On the other hand, the EuPRAXIA project can advance the laser-plasma accelerator significantly by achieving 1-5 GeV high quality electron beam in a compact layout. Nevertheless, the beam dump based on conventional technique will still produce radiation hazards and make the overall footprint less compact. Here, we propose to implement a plasma beam dump to absorb the kinetic energy from the EuPRAXIA beam. In doing so, the overall compactness of the EuPRAXIA layout will not be impacted, and the radioactivity generated by the facility can be mitigated. In this paper, results from particle-in-cell (PIC) simulations are presented for plasma beam dumps based on EuPRAXIA beam parameters.

Plasma-based deceleration could greatly improve the overall compactness of accelerator facilities. In the so-called passive plasma beam dump, collective oscillations of plasma electrons are used to absorb kinetic energy of spent high-energy electron beams. Moreover, due to the high-amplitude decelerating gradient and the low-density plasma medium, deceleration is achieved in a compact and safer way, if compared to conventional beam dumps. Adoption of this novel decelerating scheme might be critical for facilities aiming for high-energy, high-repetition-rates, as well as for transportable applications built upon plasma-based accelerator technology. However, key issues such as, for example, particle re-acceleration, need to be addressed. In this work, tailored plasma-density profiles are used to shift the defocusing phase of the beam self-driven transverse wakefield towards re-accelerated beam particles, and transversely eject them. PIC simulations are used to evaluate the total beam energy, energy deposited in the plasma, and energy transversely ejected, for each of the investigated plasma density profiles. Moreover, the average energy per ejected particle is estimated for each case. In particular, it is shown that the energy of ejected particles is affected by the rate at which the plasma wavelength decreases, since it determines the time that particles experience re-acceleration before being defocused.

This work analyses the counterpropagation of transversal plane waves in a linear, homogeneous, nondispersive, and isotropic medium. Although this is a traditional subject in disciplines associated with wave phenomena, a propagation analysis is not found in the literature. With this purpose, the resultant wave and consecutively its phase velocity in such system are obtained analytically. Instead of what happens with the individual waves, the analytical results demonstrate that the phase velocity of the resultant wave actually is not a constant and depends explicitly of the time or the spatial coordinates, and principally depends of the amplitudes of the individual waves. This last remarkable feature, when considering as example electromagnetic systems, can be used to adequately control and accelerate particles in a charged medium. Full agreement between the analytical and numerical results is found.

This work presents an energy criterion to define the halo of homogeneous and mismatched charged particle beams. In the simulations used in this work, the beam is considered to be azimuthally symmetric, initially cold and is confined by an external constant magnetic field inside a cylindrical conducting pipe. The energy criterion is established through the analysis of the beam energy distributions with time. The obtained results are in reasonable agreement with the past results that considered the beam phase-space topology, for many values of the beam initial envelope mismatch.

This work presents a particle-core model for an inhomogeneous and mismatched nonneutral charged particle beam. The beam is azimuthally symmetric, initially cold, and is confined by an external constant magnetic field inside a cylindrical conducting pipe. The core description is based on a previous developed Lagrangian approach. The relaxation time and the phase-space topology of the particle-core model is in reasonable agreement with full self-consistent N-particle beam numerical simulations.