DC induction acceleration in a circular ring can be realized by integrating a pair of induction cells with two insulating gaps for setting and resetting of induction magnetic cores and a magnetic flux storage system, which absorbs the magnetic flux emitted when resetting the induction cell. This scenario has been described with the help of theory and computer simulation. One possible application is a fixed field alternating gradient (FFAG) accelerator that provides D- beams of 1-2 MeV and a few amperes for neutral beam injection in the future magnetic fusion DEMOs. The other is an isochronous electron storage ring that could lead to an efficient constant wave free-electron laser.

Magnetically insulated electron flow lowers transmission line operating impedance with respect to particle-free vacuum impedance. This work establishes two simple rules: 1) transitioning from high to low impedance, magnetic fields on the high impedance line grow and, consequently, electrons are more tightly insulated; 2) transitioning from low to high impedance, magnetic fields on the high-impedance side weaken and the size of the electron flow region grows. In both cases, the impedance of the formerly high-impedance line drops to exactly match the lower operating impedance, but electron flow on the low-impedance line is unaltered.

Seeded free-electron lasers (FELs) generate short-wavelength light by high harmonic conversion of seed laser, but their performance is often limited by electron beam energy spread. In this study, we experimentally compare two key schemes, High-Gain Harmonic Generation (HGHG) and Echo-Enabled Harmonic Generation (EEHG). We show that EEHG’s ability to handle large energy spread makes it more reliable for producing fully coherent soft X-ray pulses. Using a laser heater to control energy spread, our results confirm EEHG’s advantages, offering a clear path forward for high-performance next-generation FELs.

Prebunched relativistic electron beams are central to coherent x-ray generation, but producing nanometer-scale bunching in compact plasma accelerators remains challenging. Here we propose an all-optical three-laser scheme in uniform plasma, where two low-intensity counter-propagating pulses create a density modulation that periodically controls injection into a nonlinear laser wake. The method generates ultrabright electron beams with nanometer-scale bunching and tunable exotic structures, opening a practical route to compact, high-power and coherent x-ray sources.

Precise alignment between laser-ionized plasma sources and ultrarelativistic beams is critical for plasma wakefield acceleration at collider-relevant energies. We introduce a simple, non-invasive technique that uses plasma afterglow imaging at two longitudinal locations to achieve micron-level alignment of an 85-cm plasma with a 10-GeV beam. The method achieves better than 10 μm transverse and 10 μrad angular accuracy and is directly validated through beam energy loss, energy transfer efficiency, and witness beam energy gain measurements. These results establish quantitative alignment tolerances essential for next-generation plasma-based accelerators and collider concepts.

This paper presents the first experimental demonstration of a nonlinear collimator in the SuperKEKB low-energy ring. By using a pair of skew-sextupole magnets, the system enables efficient beam halo removal while keeping the collimator jaws away from the beam core, thereby reducing impedance. Beam studies show that the nonlinear collimator achieves comparable or improved background suppression relative to conventional collimators without degrading beam lifetime or injection efficiency. Furthermore, it significantly raises the instability threshold, demonstrating its potential for future high-luminosity colliders.

We show that purely linear acceleration of ultra-short electron bunches results in emission of a significant amount of radiation in regimes within reach of current experiments. In cases relevant to plasma acceleration, with fields of 10’s of GV/m, radiation losses are around 100µJ with losses increasing for larger acceleration field strength and shorter bunches. We also predict that acceleration with field strengths accessible to traditional RF accelerating structures results in a measurable radiation pulse of energy of 100’s of nJ. These higher-than-expected losses are due to coherence effects such that the power of the emitted radiation scales with the square of the total charge.

Laser-Plasma Accelerators (LPAs) have emerged as novel, compact drivers for Free-Electron Lasers (FELs), demonstrated most recently by the results of high gain (>1000) and reliability (>90%) achieved by Barber et al. The work presented here serves as a follow-up to these results, highlighting the exceptional long-term stability of the hundred-terawatt laser system. Enabled by the unique integration of multiple active stabilization systems, we demonstrate over ten hours of stable electron beam production from our LPA source, resulting in reliable, long-term operation of an LPA-driven FEL in the self-amplified spontaneous emission (SASE) regime.

A comprehensive design is presented for the Booster-to-pEDM (BtP) injection line serving both clockwise and counterclockwise rings in the proposed proton Electron Dipole Moment (pEDM) experiment at BNL. The design builds upon a symmetric-hybrid lattice while reusing segments of the existing Booster-to-AGS transfer line, tackling key challenges in precision injection for pEDM searches—such as stringent optics matching, dispersion suppression, spin preservation within $\pm 20$ mrad, and systematic error control—required to reach the target sensitivity of ${10}^{-29}$ e$\cdot$cm. Multi-particle and spin tracking simulations validate beam containment and polarization stability, demonstrating design feasibility and robustness.

Double-RF systems are widely used in advanced storage-ring light sources, but they are generally implemented with separate accelerating and harmonic cavities. Here we propose a compact normal-conducting bimodal cavity that supports the TM${}_{010}$ and TM${}_{020}$ modes in a single cavity. A low-pass filter suppresses harmonic power leakage through the fundamental-mode coupler, while tunable band-stop filters provide selective isolation for higher-order-mode damping to protect the harmonic mode. The two operating modes remain largely independently controllable, providing a practical design approach for compact bimodal RF cavities in storage rings.

We present the results of analytical and numerical calculations of electromagnetic radiation generated by a charged particle bunch passing through two parallel grids composed of thin conductors. The longwave range of the radiation spectrum is studied, i.e., the wavelengths are assumed to be much greater than the cell size of each grid. We demonstrate, in particular, that the structure under consideration can be used for developing new methods of non-destructive bunch diagnostics.

he SHINE 3.9 GHz fundamental power coupler was improved from the original Eu-XFEL design by incorporating adjustable external quality factor $Q_{ext}$ and a double-braid copper strip for enhanced cooling. This paper details all aspects of coupler development, including requirements, design, RF simulations, fabrication techniques, power testing, cryomodule integration and RF conditioning. Sixteen production 3.9 GHz couplers were manufactured and integrated into two SHINE third harmonic cryomodules, which achieved maximum total cavity voltages of 63.6 MV and 59.8 MV, respectively. These cryomodules have since been successfully commissioned for online operation.

We introduce a novel beam-cooling concept for multicharge-state heavy-ion beams based on a new multi-zone stripper configuration in a charge stripper ring, where stochastic charge-state transitions combined with charge-state-dependent closed-orbit shifts turn charge exchange—normally associated with beam heating—into a mechanism for rapid cooling. Numerical simulations show substantial emittance reduction within tens of turns, allowing the scheme to overcome beam heating caused by beam-matter interactions. The concept opens new possibilities for sustaining beam-matter interactions and controlling intense heavy-ion beams in future accelerator facilities.

Laser compression of relativistic electron beams offers a pathway to ultrashort pulses, yet the relevant theory for tightly focused fields remains incomplete. We develop a covariant oscillation-center framework for dual-frequency traveling waves, identify a critical beam waist that delineates the transition between multi-cycle compression and sub-cycle breakdown, and derive scaling laws governing wavelength and focusing conditions—thereby enabling predictive optimization of laser compression for relativistic electron beams. Simulations incorporating space-charge effects demonstrate that, under realistic conditions, MeV-scale electron bunches can be compressed into the sub-femtosecond regime.

Modern synchrotron light sources strive for extreme parameters, where the resulting lowered dynamic aperture could be mitigated by reducing the required sextupole strength through a negative momentum compaction factor. This strategy significantly changes the longitudinal beam dynamics which must be investigated in detail. At KARA, this operation mode was studied in a regime dominated by the coherent synchrotron radiation impedance. The results include significant deviations from the usual positive momentum compaction dynamics, particularly in terms of bunch length and the micro-bunching instability, challenging existing theoretical predictions of the threshold current.