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Longitudinal impedances at high frequencies, which extend far beyond the width of the beam spectrum, can pose a threat to the performance of modern low-emittance electron storage rings, as they can establish a relatively low threshold for microwave instability. In such rings, coherent synchrotron radiation (CSR) emerges as a prominent contributor to these high-frequency impedances. This paper undertakes a systematic investigation into the effects of CSR on electron rings, utilizing Elettra 2.0, a ring of fourth-generation light sources, and the SuperKEKB low-energy ring, a ring of $e^+e^-$ circular colliders, as illustrative examples. Our work revisits theories of microwave instability driven by CSR impedance, extending the analysis to encompass other high-frequency impedances such as resistive wall and coherent wiggler radiation. Through instability analysis and numerical simulations conducted on the two aforementioned rings, the study explored the impact of high-frequency impedances and their interactions with broadband impedances from discontinuities in vacuum chambers., Comment: 16 pages, 21 figures

Calin Galeriu(CG) has commented [1] about our manuscript, "Doppler signature in electrodynamic retarded potentials" [2], that must be properly addressed, amending at the same time of notation errors [3] to clarify some formal aspects which were discussed and criticized in C. Galeriu's comments. The same author (CG) has published three papers concerning the origin of the Doppler term, v/c, in the Li\'enard-Wiechert (L-W) potentials [4-6]., Comment: Reply to arXiv:2302.13404, a comment on arXiv:2202.05393, https://doi.org/10.1016/j.physo.2023.100136

Diamond sensors (DS) are widely used as solid-state particle detectors, beam loss monitors, and dosimeters in high-radiation environments, e.g., particle colliders. We have calibrated our DS with steady $\beta$- and X-radiation, spanning a dose rate in the range 0.1-100 mGy/s. Here, we report the first systematic characterization of transient responses of DS to collimated, sub-picosecond, 1 GeV electron bunches. These bunches, possessing a charge ranging from tens to hundreds of pC and a size from tens of microns to millimeters, are suitably provided by the FERMI electron linac in Trieste, Italy. The high density of charge carriers generated by ionization in the diamond bulk causes a transient modification of electrical properties of DS (e.g., resistance), which in turn affects the signal shape. We have modeled a two-step numerical approach, simulating the effects on the signal of both the evolution of charge carrier density in the diamond bulk and the changes in the circuit parameters. This approach interprets features observed in our experimental results to a great extent., Comment: contribution to the proceedings of ICHEP2022

With the best of modern standard lasers, high-energy $\gamma\gamma$ colliders from electron beams of E larger than 250 GeV are only possible at the expense of photon luminosity, i.e. 10 times lower than for photon colliders at c.m. energies below 0.5 TeV. For existing state-of-the art lasers, an optimistic upper energy limit for x=4.8 is an electron beam of less than 250 GeV. This Snowmass21 Contributed Paper shows how Free Electron Lasers (FEL) pave the way for High Energy & High Luminosity $\gamma\gamma$ colliders. We present and assess a conceptual design study of a FEL with wavelength of 2.4 $\mu$m and an x-factor in the range of 2 to 40, to maximize the luminosity of a $\gamma\gamma$ collider as second interaction region of 0.5 TeV to 10 TeV c.m. $e^+e^-$ colliders., Comment: Contribution to Snowmass 2021

The presence of the term $\left(\case{v}{c}\right)$ that characterizes the electrodynamic retarded potentials, also known as Li\'enard-Wiechert potentials, is thought to be reminiscent of a Doppler effect. Here, we show that these potentials are consistent with the Doppler shifted electromagnetic (e.m.) field generated by a charge moving along a generic trajectory with respect to the laboratory reference frame. Of course, the retarded potentials derived here are formally the same as those reported in the current literature. Nonetheless, this work sheds a new light on the origin of the electrodynamics retarded fields, while offering a direct physical interpretation of the term $\left(\case{v}{c}\right)$ characterizing the related potentials., Comment: 11 pages, 1 figure

The statistical features of the radiation emitted by Free-Electron Lasers (FELs), either by Self-Amplified Spontaneous Emission (SASE-FELs) or by seeded emission (seeded-FELs), are attracting increasing attention because of the use of such light in probing high energy states of matter and their dynamics. While the experimental studies conducted so far have mainly concentrated on correlation functions, here we shift the focus towards reconstructing the distribution of the occupation numbers of the radiation energy states. In order to avoid the various drawbacks related to photon counting techniques when large numbers of photons are involved, we propose a Maximum Likelihood reconstruction of the diagonal elements of the FEL radiation states in the energy eigenbasis based on the statistics of no-click events. The ultimate purpose of such a novel approach to FEL radiation statistics is the experimental confirmation that SASE-FEL radiation exhibits thermal occupation number statistics, while seeded-FEL light Poissonian statistics typical of coherent states and thus of laser light. In this framework, it is interesting to note that the outcome of this work can be extended to any process of harmonic generation from a coherent light pulse, unlocking the gate to the study of the degree to which the original distinctive quantum features deduced from the statistical photon number fluctuations are preserved in non-linear optical processes., Comment: 8 + 10 pages, 5 figures

The dynamical effects inducing geometrical and phase space misalignment of bunch slice in X-ray operating Free Electron Lasers can be traced back to a plethora of phenomena, both in the linac accelerating section or inside the beam transport optic magnet. They are responsible for a spoiling of the beam projected qualities and induce, if not properly corrected, an increase of the saturation length and a decreasing of the output power. We discuss the inclusion of these effects in models employing scaling formulae.

Light can be strongly confined in sub-wavelength spatial regions through the interaction with plasmons, the collective electronic modes appearing in metals and semiconductors. This confinement, which is particularly important in the terahertz spectral region, amplifies light-matter interaction and provides a powerful mechanism for efficiently generating non-linear optical phenomena. These effects are particularly relevant in Dirac materials like graphene and Topological Insulators, where massless fermions show a naturally non-linear optical behavior in the terahertz range. The strong interaction scenario has been considered so far from the point of view of light. In this paper, we investigate instead the effect of strong interaction on the plasmon itself. In particular, we will show that Dirac plasmons in Bi$_2$Se$_3$ Topological Insulator are strongly renormalized when excited by high-intensity terahertz radiation by displaying a huge red-shift down to 60% of its characteristic frequency. This opens the road towards tunable terahertz non-linear optical devices based on Topological Insulators.