arXiv · physics/0203036
Enhanced radiative cooling of ion beams in storage rings and Robinson's damping criterion are discussed.
Explore connections, maps & timelines
E. G. Bessonov. 2002-03-13. Enhanced radiative ion cooling. https://arxiv.org/abs/physics/0203036
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Laser-plasma accelerators (LPAs) sustain accelerating gradients of order $100\,\mathrm{GV/m}$, but routine operation remains difficult: electron beam metrics drift over an operating shift, and the root physical cause is often invisible to the available diagnostics. We formulate LPA operation as a latent state-space model in which three effective interaction-point variables, the normalized laser amplitude $a_0$, the normalized plasma electron density $\tilde n_e$ and the residual pulse chirp $\mathcal{C}$, are inferred from routine electron beam observations by an extended Kalman filter. The emission model, which maps the latent state to the diagnostics, is kept structurally separate from the {transition} model, which describes how the latent state evolves between shots. The separation supports diagnosis in two stages, one asking which latent variable moved and one asking what moved it. The implemented emission model is a toy model, yielding an expected performance in line with current facilities and using 3D blow-out regime dependencies where relevant. We conduct synthetic sessions to test the effectiveness of the detection and attribution protocols, finding that attribution is limited by excitation rather than by shot count or diagnostic resolution. Because the construction needs only a set of physical latent variables, an emission model and a family of hardware-derived transition models, it transfers to other drift-prone subsystems. We argue that the accuracy of the whole procedure is limited by the emission model rather than by the inference method.
A new semi-analytical model for electron scattering in foils is presented valid for thin foils and electron-beam kinetic energies up to roughly $100$ keV and from 20 keV at a dimensionless foil thickness of $20$, and higher energies for thinner foils. To perform calculations, an approximate solution is constructed by Hankel transforms of an adapted Bethe transport equation for electron scattering. The Wentzel differential cross section is used in the Bethe transport Eq. and resulting integrals are solved analytically or approximated. These approximate solutions of the transport Eq.'s were compared to the Goudsmit-Saunderson solutions in gold, for thin samples with dimensionless thicknesses $λ=5,10,20$. We also compare to the Kawrakow \cite{Kawr} model, which uses the small angle approximation. We show that in the regime of $20$ to $100$ keV beam energies, our model performs better than Kawrakow's model and this is opposite above about 100 keV. Exactly, some angularly distributed beams and the influence of energy loss of the beam can be simulated with our model.
Slow positron beams enable diverse applications, from surface-sensitive materials studies to positronium physics, but progress is limited by source intensity and brightness. In linac-based sources, mono-energetic, slow positrons are produced by moderating the broad, divergent distribution of fast positrons produced by high-energy electrons incident on a high-Z target. This process is intrinsically inefficient. Conventional linac-based designs place the moderator close to the target. Tungsten moderators become less efficient when heated by high-power, fast positrons, leading to defect-related losses. Cryogenic moderators, like solid neon, melt when exposed to high-power, fast positrons. Following the method of O'Rourke et al., we use Monte Carlo simulations combined with a diffusion model to investigate how moderator geometry, material, and incident fast positron energy affect slow positron production. We compare single tungsten foil and multi-foil configurations with solid neon moderators in reflection and transmission geometries. We find that for fast positron energies below 300 keV, solid neon offers order-of-magnitude higher efficiency than tungsten due to its larger diffusion length, whereas at MeV-scale energies multi-foil tungsten has higher efficiency due to the maximization of scattering. We also find that including a target proxy in simulation increases low-energy efficiency up to fourfold by allowing a fraction of initially reflected positrons to return to the moderator. We conclude that substantial gains in start-to-end efficiency at linac sources will likely require combining a decelerating cavity with a decoupled cryogenic moderator.