We propose a self-consistent simulation model for particle beams in accelerators, which includes the impact of electromagnetic wakefields caused by the geometry of the accelerator chamber. The method is based on a scattered-field formulation for the beam-driven Maxwell's equations. The total electromagnetic field seen by the particles is obtained as the solution of two coupled problems: a purely wakefield problem and a space charge field problem, where for each of these problems, specialized and numerically efficient approaches can be used. To assess the accuracy of the method, we compare simulation results with the analytical solution for a relativistic beam in a uniform accelerator pipe. The numerical efficiency of the method is, furthermore, demonstrated in the beam dynamics study of the multi-cell RF photo-gun installed at the SuperKEK collider facility. We show that electromagnetic wakefields have a non-negligible impact on the quality of the generated beam and, therefore, should be taken into account in the design of high-brilliance electron sources.
Photon acceleration (PA) driven by ultra-relativistic electron beams offers a promising approach to generating high-power, high-frequency coherent radiation sources. While current methods typically rely on external optical laser pulses injected into beam-driven plasma wakefields, they face significant challenges in synchronization and alignment between electron accelerators and laser systems. We propose utilizing transition radiation (TR) generated by the drive electron bunch transversing the vacuum-gas interface as the seed photons of PA. Using a 1 GeV electron bunch, we demonstrate acceleration of TR from 4.4 μm to 184 nm in 1.6 mm of two-stage uniform plasma, achieving more than a 20-fold frequency boost. Further frequency increases can be achieved with optimized setups. This scheme addresses the synchronization and alignment issues present in previous approaches, providing a practical path toward beam-driven photon acceleration.
We study the effects of irradiating water with 3 MeV protons at high doses by observing the motion of charged polystyrene beads outside the proton beam. By single-particle tracking, we measure a radial velocity of the order of microns per second. Combining electrokinetic theory with simulations of the beam-generated reaction products and their outward diffusion, we find that the bead motion is due to electrophoresis in the electric field induced by the mobility contrast of cations and anions. This work sheds light on the perturbation of biological systems by high-dose radiations and paves the way for the manipulation of colloid or macromolecular dispersions by radiation-induced diffusiophoresis.
We study electron acceleration in a plasma wakefield under the influence of the radiation-reaction force caused by the transverse betatron oscillations of the electron in the wakefield. Both the classical and the strong quantum-electrodynamic (QED) limits of the radiation reaction are considered. For the constant accelerating force, we show that the amplitude of the oscillations of the QED parameter $χ$ in the radiation-dominated regime reaches the equilibrium value determined only by the magnitude of the accelerating field, while the averaged over betatron oscillations radiation reaction force saturates at the value smaller than the accelerating force and thus is incapable of preventing infinite acceleration. We find the parameters of the electron bunch and the plasma accelerator for which reaching such a regime is possible. We also study effects of the dephasing and the corresponding change of accelerating force over the course of acceleration and conclude that the radiation-dominated regime is realized both in cases of single-stage acceleration with slow dephasing (usually corresponding to bunch-driven plasma accelerators) and multi-stage acceleration with fast dephasing (corresponding to the use of laser-driven accelerators).
A detailed study of direct laser-driven electron acceleration in paraxial Laguerre-Gaussian modes corresponding to helical beams $\text{LG}_{0m}$ with azimuthal modes $m=\left\{1,2,3,4,5\right\}$ is presented. Due to the difference between the ponderomotive force of the fundamental Gaussian beam $\text{LG}_{00}$ and helical beams $\text{LG}_{0m}$ we found that the optimal beam waist leading to the most energetic electrons at full width at half maximum is more than twice smaller for the latter and corresponds to a few wavelengths $Δw_0=\left\{6,11,19\right\}λ_0$ for laser powers of $P_0 = \left\{0.1,1,10\right\}$ PW. We also found that for azimuthal modes $m\geq 3$ the optimal waist should be smaller than $Δw_0 < 19 λ_0$. Using these optimal values we have observed that the average kinetic energy gain of electrons is about an order of magnitude larger in helical beams compared to the fundamental Gaussian beam. This average energy gain increases with the azimuthal index $m$ leading to collimated electrons of a few $100$ MeV energy in the direction of the laser propagation.
We report on a successful test of a new method for intense ion beam formation using an extraction with inhomogeneous electric field. Its key feature is a special shape of the extraction electrodes providing a higher rate of ion acceleration. It is applicable to any ion source type and could be used to improve performance of a wide range of plasma devices. The proof of concept was carried out using a high-current electron-cyclotron resonance ion source SMIS 37. High efficiency of the new extraction and proton beam formation with a record current density of up to 1.1 A cm-2 was demonstrated.
Stewart Boogert, Andrey Abramov, Laurence Nevay
et al.
Creating and maintaining computer readable geometries for use in Monte Carlo Radiation Transport (MCRT) simulations is an error-prone and time-consuming task. Simulating a system often requires geometry from different sources and modelling environments, including a range of MCRT codes and computer-aided design (CAD) tools. PYG4OMETRY is a Python library that enables users to rapidly create, manipulate, display, read and write Geometry Description Markup Language (GDML)-based geometry used in simulations. PYG4OMETRY provides importation of CAD files to GDML tessellated solids, conversion of GDML geometry to FLUKA and conversely from FLUKA to GDML. The implementation of PYG4OMETRY is explained in detail along with small examples. The paper concludes with a complete example using most of the PYG4OMETRY features and a discussion of extensions and future work.