Active energy compression scheme is presently being investigated for future laser-plasma accelerators. This method enables generating laser-plasma accelerator electron beams with a small, $\sim {10}^{-5}$, relative slice energy spread. When modulated by a laser pulse, such beams can produce coherent radiation at very high, $\sim 100$th harmonics of the modulation laser wavelength, which are hard to access by conventional techniques. The scheme has a potential of providing additional capabilities for future plasma-based facilities by generating stable, tunable, narrow-band radiation.

Magnetized liner inertial fusion (MagLIF) is an attractive concept for producing thermonuclear fusion reactions. The MagLIF platform involves the operation of Helmholtz coils to apply a 15 Tesla axial magnetic field to the load region, where a cylindrical, fuel-filled metal liner is imploded by a $\sim 20\mathrm{MA}$ current pulse. The fringe field from these coils extends into the transmission line that delivers the current to the target. We investigated the extent to which this applied field disturbs the nominal power flow within that transmission line. A simplified model of the geometry shows that adding the applied magnetic field results in magnetic field lines that connect the cathode to the anode, suggesting electrons may not be magnetically insulated in this region. Particle-in-cell simulations indicated the addition of the applied magnetic field would not significantly impact the current delivery to the load. Velocimetry was used to experimentally assess the current delivery with and without the applied magnetic field. We find no measurable effects of the applied field on current delivery in the configuration investigated in this study.

The feasibility of gamma-ray light sources based on the channeling phenomenon of ultrarelativistic electrons and positrons in oriented single crystals is demonstrated using rigorous numerical modeling. Case studies are presented for 10 GeV and sub-GeV $e^{-}/e^{+}$ beams incident on ${10}^{-1}-{10}^0\mathrm{mm}$ thick diamond and silicon crystals. It is shown that for moderate values of the beam average current ($\lesssim 10\mathrm{\mu }\mathrm{A}$), the average photon flux in the energy range of ${10}^0–{10}^2\mathrm{MeV}$ emitted within the ${10}^1–{10}^3\mathrm{\mu }\mathrm{rad}$ cone and 1% bandwidth can be on the level of ${10}^{10}\mathrm{photon}/\mathrm{s}$ for electrons and ${10}^{10}–{10}^{12}\mathrm{photon}/\mathrm{s}$ for positrons. These values are higher than the fluxes available at modern laser-Compton gamma-ray light sources.

High-frequency longitudinal impedances, particularly at wavenumbers $k\gg 1/{\sigma }_z$ (where ${\sigma }_z$ is the bunch length), can drive microwave instability and potentially limit the performance of modern low-emittance electron storage rings. In such rings, the 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 the fourth-generation storage ring light source Elettra 2.0 and the low-energy ring of the SuperKEKB $e^{+}{e}^{-}$ circular collider 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 combined effects with broadband impedances caused by discontinuities in vacuum chambers.

Polarized x rays or gamma rays generated from inverse Compton scattering (ICS) sources are high-brightness, quasimonochromatic, and polarization-tunable and are widely applied in medical imaging, material science, and nuclear physics research. In this paper, to simulate ICS between electron beams and polarized laser beams, a Monte Carlo simulation code has been developed and implemented based on the geant4 toolkit. This code considers the polarization as well as the bandwidth of incident laser beams. The code is benchmarked by comparing its simulation results with those from the well-known Monte Carlo tool called cain and experimental results. The comparisons show that this code accurately reproduces the scattered photons, demonstrating its potential for various ICS-based applications.

The magnetic field optimization of RE-Ba-Cu-O (REBCO, $\mathrm{RE}=\text{rare}$ earth) bulk superconducting undulators is a fundamental step toward their implementation in an accelerator driven photon source, like a synchrotron or a free electron laser. In this article, we propose a sorting algorithm to reduce the undulator’s phase error based on the reconstruction of the trapped current inside the bulks of a staggered array undulator. The results obtained with a YBCO short prototype field-cooled down to 10 K in a 10 T magnetic field are reported. Finally, its performance is critically discussed in light of 2D magnetic field maps of its individual components, obtained at ${\mathrm{LN}}_2$ after the magnetization tests.

The Proton Power Upgrade initiative at Oak Ridge National Lab’s Spallation Neutron Source aims to greatly boost the capability of proton beam power. This upgrade involves the integration of seven additional cryomodules, each housing four six-cell high-beta ($\beta =0.81$) superconducting radio frequency cavities. These cavities, manufactured and processed by Research Instruments in Germany, underwent meticulous treatment, including electropolishing as the bulk and final vital step. Upon delivery to Jefferson Lab, a total of 28 cavities for seven cryomodules, along with an additional four cavities for a spare cryomodule, underwent thorough vertical qualification tests, meeting the required specifications. Following cavity tanking and subsequent rf testing, the assembly of eight cryomodules was successfully executed, with all 32 cavities demonstrating compliance with acceptance criteria. The transportation of the cryomodule to SNS for high-power testing in the tunnel yielded exceptional results. Notably, the performance surpassed specifications, in terms of quality factor and accelerating gradient.

Using a waveguide in a THz FEL has been shown to maximize the coupling and enable efficient extraction of relativistic electron beam energy from a single passage through a tapered helical undulator. An oscillator configuration can further boost energy extraction above the single-pass limits and open the door toward very high average power THz sources. Embedding the undulator in an oscillator cavity is particularly useful in combination with high repetition rate electron sources, even if at reduced peak brightness, since recycling a fraction of the radiation as an intense seed can compensate for lower single-pass gain. In this paper, we investigate the efficiency scaling of a tapering-enhanced waveguide oscillator, showcasing its capability for frequency-tuning operation and high-efficiency operation at different wavelengths. Using a thermionic-driven beamline equipped with compression elements, numerical start-to-end simulation results indicate a 16% efficiency at 200 GHz and a 2.1% efficiency at 1.5 THz, resulting in kW-level average power out-coupled in radiation pulses with few hundred $\mathrm{\mu }\mathrm{J}$ energy and tens of MW peak power.

In this paper, we present a Monte Carlo event generator for radiative Bhabha scattering, based on the method of equivalent photons, and optimized for multiturn tracking simulations in the xsuite framework. We demonstrate the accuracy of the event generator with successful benchmarks of the luminosity and event cross section against currently existing alternative tools. Consequently, we use it to investigate existing estimates of the radiative Bhabha scattering beam lifetime at the FCC-ee, as well as the impact of radiative Bhabha scattering on the beam dynamics, using full nonlinear tracking models.

The world’s first 1.3 GHz cryomodule containing eight 9-cell superconducting radio-frequency (rf) cavities treated by medium-temperature furnace baking (mid-T bake) was developed at the Institute of High Energy Physics, Chinese Academy of Sciences. The 9-cell cavities in the cryomodule achieved an unprecedented high average intrinsic quality factor ($Q_0$) of $3.8\times {10}^{10}$ at $16\mathrm{MV}/\mathrm{m}$ and $3.6\times {10}^{10}$ at $21\mathrm{MV}/\mathrm{m}$ in the horizontal test. The cryomodule can operate stably up to a total continuous wave rf voltage greater than 193 MV, with an average cavity usable accelerating gradient of more than $23\mathrm{MV}/\mathrm{m}$. The results significantly exceed the specifications of Circular Electron Positron Collider and Dalian advanced light source and the other high repetition rate free electron laser facilities [Linac Coherent Light Source II (LCLS-II), LCLS-II-high energy, Shanghai High Repetition Rate X-ray FEL and Extreme Light Facility, Shenzhen Superconducting Soft X-Ray Free Electron Laser, etc.]. There is evidence that the mid-T bake cavity may not require fast cooldown or long processing time in the cryomodule. This paper reviews the cryomodule performance and discusses some important issues in cryomodule assembly and testing.

In the CERN Large Hadron Collider (LHC), bent crystals are used to efficiently deflect beam halo particles toward secondary collimators used as absorbers. In this crystal collimation scheme, a crystal with a length of a few millimeters can produce a deflection equivalent to a magnetic field of hundreds of Tesla at LHC top energies, improving the cleaning performance of the machine. However, crystals must be in optimal alignment with respect to the circulating beam to maximize the efficiency of the channeling process. A newly developed machine learning model automatically classifies the channeling condition of crystals using beam loss monitor signals during slow rotation of the crystal. This advancement represents a crucial step toward refining the process of identifying the optimal channeling orientation. The algorithm has been tested for the fist time in operation with Pb ion beams at the record energy of 6.8 Z TeV demonstrating its reliability.

S-band high-gradient accelerating structures were proposed to accelerate protons from 30 to 230 MeV for a compact proton therapy linac in Institute of Modern Physics. A backward traveling wave structure and a single-periodic magnetically coupled standing wave structure were designed, and differences between these two structures were analyzed to select a more suitable one for the proton therapy linac. In this paper, a novel single-periodic magnetically coupled standing-wave accelerating structure was studied, with an optimized nose cone that related to a smaller peak surface electric field and higher shunt impedance, with the reduced number of coupling holes and mechanical von Mises stress thus making it possible for higher duty factor and longer rf pulse operation, also with larger coupling holes and improved cell-to-cell coupling thus making this structure suitable for operating in $\pi$ mode. An 11-cell high-power prototype for $\beta =0.26$ particles was developed with an active length of 143 mm. This prototype cavity is supposed to operate at an accelerating gradient of $30\mathrm{MV}/\mathrm{m}$ with 0.1% duty factor, corresponding to a maximum surface electric field of $105\mathrm{MV}/\mathrm{m}$ and a peak rf power of 3.43 MW. Cavity design, optimization, manufacture, rf measurement, and high-power test will be discussed in this paper.

New algorithms useful for the calculation of dynamic aperture and momentum acceptance in circular accelerators, particularly synchrotron light sources, are developed and presented. The flood-fill tool from raster graphics inspired us to efficiently compute dynamic apertures by minimizing required trackings on stable initial coordinates, leading to several factors of speedup with respect to standard algorithms. A novel technique for momentum acceptance calculations, Fast Touschek Tracking, is developed. Thorough benchmarking using modern accelerator codes shows that the new technique can provide one or two orders of magnitude faster computation of local momentum acceptances with only limited loss of accuracy.

Space-charge tune shifts can affect the beam quality in storage rings. Laslett’s method, a classical approach for calculating space-charge tune shifts, may not hold valid assumptions for rings with extremely short bunches and small bunch spacing, such as in steady-state microbunching (SSMB) storage rings. To overcome this limitation, we have developed new formulas that are suitable for arbitrary bunch lengths and spacings for calculating space-charge tune shifts. Additionally, simplified formulas have been provided for the calculations of space-charge tune shifts specifically in the context of extremely short bunch lengths. Numerical computations were carried out to demonstrate the validity of these newly derived formulas. Moreover, the formulas were applied to compute the space-charge tune shifts in an SSMB storage ring characterized by typical parameters.

Harmonic analysis has provided powerful tools to accurately determine the tune from turn-by-turn data originating from numerical simulations or beam measurements in circular accelerators and storage rings. Methods that have been developed since the 1990s are suitable for stationary signals, i.e., time series whose properties do not vary with time and are represented by stationary signals. However, it is common experience that accelerator physics is a rich source of time series in which the signal amplitude varies over time. Furthermore, the properties of the amplitude variation of the signal often contain essential information about the phenomena under consideration. In this paper, a novel approach is presented, suitable for determining the tune of a nonstationary signal, which is based on the use of the Hilbert transform. The accuracy of the proposed methods is assessed in detail, and an application to the analysis of beam data collected at the CERN Large Hadron Collider is presented and discussed in detail.

We present a new approach that demonstrates the deflection and guiding of relativistic electron beams over curved paths by means of the magnetic field generated in a plasma-discharge capillary. The active bending plasma (ABP) represents a promising solution that has been recently demonstrated with a proof of principle experiment. An ABP device consists of a curved capillary where large discharges (of the order of kA) are propagated in a plasma channel. Unlike conventional bending magnets, in which the field is constant over the bending plane, in the ABP, the azimuthal magnetic field generated by the discharge grows with the distance from the capillary axis. This features makes the device less affected by the beam chromatic dispersion so that it can be used to efficiently guide particle beams with non-negligible energy spreads. The study we present in the following aims to provide a theoretical basis of the main ABP features by presenting an analytical description of a single-particle motion and rms beam dynamics. The retrieved relationships are verified by means of numerical simulations and provide the theoretical matrix formalism needed to completely characterize such a new transport device.

Beam-driven plasma wakefield acceleration (PWFA) is a promising technique to generate high-energy electron bunches for future electron-positron colliders. Longitudinal shaping of high-charge drive beam is highly desired for achieving high-transformer ratio and loading high-charge witness beam. However, the existing shaping schemes either focused on relatively low-charge bunch shaping or accompanied with significant charge-loss rate (typically over 50%). In this paper, a coherent-synchrotron-radiation-free shaping scheme based on velocity modulation is proposed to generate a high-charge beam with a linearly ramped profile. A $>10\mathrm{kA}$-peak-current shaped beam containing $>50\mathrm{nC}$ charge with a low charge-loss rate is demonstrated by a start-to-end simulation, and the tunabilities of the beam charge and the peak current, and the robustness of the proposed shaping scheme are also discussed. When loaded by a 3 nC witness beam, a $>\mathrm{GV}/\mathrm{m}$ accelerating electric field with a transformer ratio larger than 4 can be achieved in a uniform plasma for the shaped drive beam, providing the possibility of high-transformer-ratio PWFA for a high-charge beam.