Parametric x-ray radiation (PXR) is the quantum process analog to Laue diffraction where a pseudophoton is scattered out of a crystalline structure as a radiation photon. In this work, PXR emitted by electron beams generated in a compact laser-plasma accelerator and interacting afterward with a Si 220 crystal is observed in single-shot operations. The combination of laser wakefield acceleration and PXR is an efficient and table-top way to obtain monochromatic, pulsed, ultrashort, and stable emission of high-energy photons: to our knowledge such a complete set of performance parameters is new. Unlike other relevant radiation mechanisms, such as betatron radiation or incoherent bremsstrahlung, PXR is insensitive to the beam energy spread. With a long crystal, we demonstrate the stability of the PXR bandwidth toward shot-to-shot variations of the beam energy and divergence.

This study presents a general analysis of how the transverse rotational symmetry of a beam imposes equality constraints among transverse beam moments. Efficient analytic methods are developed to derive symmetry-imposed constraints among $k$th order moments in beams with continuous or $n$-fold rotational symmetry for arbitrary $k$ and $n$. The formalism also enables one to construct symmetry arguments based on how discrete and continuous rotational symmetries manifest themselves differently in terms of beam moments. Three case studies on beams with continuous, twofold, and threefold rotational symmetries are conducted. We prove that, regardless of their triangulation, beams with threefold rotational symmetry (e.g., from electron cyclotron resonance ion source) always have the same rms properties as beams with cylindrical symmetry. These counterintuitive results derived purely from symmetry considerations have clarified beam dynamics at the Facility for Rare Isotope Beams.

Experiments were performed at the Fermilab Accelerator Science and Technology facility to elucidate the effects of long-range wakefields in TESLA-type superconducting rf cavities. In particular, we investigated the higher-order modes (HOMs) generated in the eight, nine-cell cavities of a cryomodule (CM) due to off-axis steering with correctors located $\sim 4\mathrm{m}$ upstream of the CM. We have observed correlated submacropulse centroid slews of a few hundred microns and centroid oscillations at $\sim 240\mathrm{kHz}$ in the rf beam-position-monitor data after the CM. The entrance energy into the CM was 25 MeV, and the exit energy was 100 MeV with $125\mathrm{pC}/\mathrm{bunch}$ and $400\mathrm{pC}/\mathrm{bunch}$ in 50-bunch pulse trains. These experimental results were evaluated for machine learning training aspects which will be used to inform the commissioning plan for the Linac Coherent Light Source-II injector CM. With an entrance beam energy of $<1\mathrm{MeV}$ in this case (or for $\sim 6\mathrm{MeV}$ at the European X-ray Free-electron Laser injector), the HOM-effect mitigation would be particularly critical.

The generation of highly coherent radiation in a high repetition rate free electron laser driven by a superconducting linear accelerator has become a topic of growing interest. External seeding schemes like high-gain harmonic generation (HGHG) and echo-enabled harmonic generation are proven to be able to generate coherent radiation in the extreme ultraviolet and x-ray range. However, the repetition rate of current laser systems with sufficient power to modulate the electron beam is limited to the kilohertz range. Recently, to achieve seeding at a high repetition rate, an optical resonator scheme has been introduced to recirculate the radiation in the modulator to seed the electron bunches. In this paper, two harmonic optical klystron resonator configurations either starting with a seed laser or starting from shot noise are studied. With the harmonic optical klystron as the seeding source, the efficiency of harmonic radiation generation at a comparatively high harmonic can be significantly enhanced when compared with a standard single-stage HGHG. Simulation results show that highly coherent, stable, and high repetition rate pulses in the water window range could be generated by the proposed seeding schemes. Some practical considerations including beam energy chirp effects and the power density effects on mirrors are discussed.

An experimental study of the afterglow mode was performed with a third generation electron cyclotron resonance ion source, SECRAL-II (Superconducting ECR ion source with Advanced design in Lanzhou No. II), under double frequency heating. The experimental results show that intense pulsed beams of highly charged ions (e.g., $266\mathrm{e}\mu \mathrm{A}$ of ${{}^{129}\mathrm{Xe}}^{34+}$ and $169\mathrm{e}\mu \mathrm{A}$ of ${{}^{129}\mathrm{Xe}}^{38+}$) could be produced at high frequency ($24+18\mathrm{GHz}$) and high power ($\sim 8\mathrm{kW}$), even compared with the beam intensity records of SECRAL-II obtained in continuous wave (cw) mode at higher microwave frequency ($28+18\mathrm{GHz}$) and higher power ($\sim 10\mathrm{kW}$), the gain factor is also up to $\sim 3$. Meanwhile, it is found that the afterglow decay time in our study is much longer than that obtained with the second generation ECR ion sources typically operating at 10–18 GHz, and the corresponding peak duration is greater than 2 ms. This study provides a viable solution for heavy ion synchrotron accelerator complex such as High Intensity Heavy Ion Accelerator Facility project that requires intense pulsed beams of highly charged ions with long peak duration.

The evolution of two intense pulsed electron beams for an x-ray flash radiography application is characterized in a coupling of experimental and simulation studies. For this purpose, experiments were performed at Commissariat à l’Energie Atomique et aux Energies Alternatives with a new dual-pulse inductive voltage adder named “Mi2.” This experimental setup has been designed and built to produce two intense pulsed electron beams of 2 kA, 700 keV, and 80 ns full width at half maximum from a velvet cold cathode. The delay between the pulses ranges from tens of nanoseconds to a few microseconds. This study quantifies the effect of the plasma dynamics on the beam current of the second pulse, which represents an important parameter from the beam transport point of view. A multidimensional particle-in-cell simulation model is used to provide a numerical analysis in order to determine the influence of velvet plasma dynamics on the second pulse. Analysis of the experimental results indicates that the motion of the electron extraction zone within the expanding plasma remains lower than 1 mm for $3\mu \mathrm{s}$ delay, inducing a minor impact on the beam current extracted from the velvet cathode. Based on the developed model, this plasma expansion induces an increase of 5% for the current extracted from the second pulse with a delay of $1\mu \mathrm{s}$ for two pulses having the same voltage, which is consistent with linear induction accelerator injector parameters for multiple pulse use.

Brookhaven National Laboratory (BNL) and Thomas Jefferson National Accelerator Facility are collaborating on the design and construction of the next Electron Ion Collider (EIC) to be built at BNL. The EIC is a unique high-energy, high-luminosity, polarized electron-proton/ion collider. The EIC accelerator complex needs about 10 new rf and SRF systems with frequencies spanning 24 MHz to 1773 MHz, requiring more than 60 new high-power fundamental power couplers (FPCs). These couplers will operate in either pulsed mode or continuous wave mode with peak traveling wave power ranging from 10 s to 380 kW. Here we present our design for a 1-MW broadband rf window suitable for EIC rf and SRF systems with operating frequencies up to 591 MHz. This design takes advantage of the numerous synergies between the various rf and SRF systems to make it broadly applicable. The rf window design criteria are based on the requirement for the 591-MHz electron storage ring (ESR) SRF cavities, as it will operate at both the highest traveling wave power and the highest peak power over the EIC $\mathrm{rf}/\mathrm{SRF}$ complex. The results presented will detail the FPC power requirement, rf window choices, design criteria, and multiphysics performance in the most critical application, the ESR SRF cavity, and how the rf window design applies to other EIC $\mathrm{rf}/\mathrm{SRF}$ systems.

There has been a renewed interest in applying multiobjective (MO) optimization methods to a number of problems in the physical sciences, including to rf structure design. The results of these optimizations generate large datasets, which makes visualizing the data and selecting individual solutions difficult. Using the generated results, Pareto fronts can be found giving the trade-off between different objectives, allowing one to utilize this key information in design decisions. Although various visualization techniques exist, it can be difficult to know which technique is appropriate and how to apply them successfully to the problem at hand. First, we present the setup and execution of MO optimizations of one standing wave and one traveling wave accelerating cavity, including constraint handling and an algorithm comparison. In order to understand the generated Pareto frontiers, we discuss several visualization techniques, applying them to the problem, and give the benefits and drawbacks of each. We found that the best techniques involve clustering the resulting data first to narrow down the possible choices and then using multidimensional visualization methods such as parallel coordinate plots and decision maps to view the clustered results and select individual solutions. Finally, we give some examples of the application of these methods and the cavities selected based on arbitrary design requirements.

The study of collective beam instabilities has long been an important and active research topic in particle accelerators. The collective effects are typically divided into two categories: the short-range single-bunch instabilities and the long-range multibunch or multiturn instabilities. Robinson instability can be the mostly encountered long-range multiturn instability. We recently explored a collective multiturn instability driven by the short-range coherent undulator radiation in the laser cavity modulator of a steady-state microbunching (SSMB) storage ring. In this paper, we formulate and compare such an instability with the Robinson instability. Considering the radiation slippage effect and the finite duration, the functional form of the radiation wakes is essentially different from that of the Robinson case. We also relate a special case of the newly explored instability to the high-gain free-electron laser process and find that a similar cubic dispersion equation can be obtained. The discussions and comparisons presented in this paper may shed light on the underlying physical mechanisms of the collective beam dynamics in the laser cavity modulator of an SSMB storage ring.

Radio-frequency cavities used in modern particle accelerators operate in ${\mathrm{TM}}_{m10}$-like modes composed of a single, dominant multipole of order $m$; $m=0$ modes are used for the longitudinal acceleration of a particle beam and $m\ne 0$ modes for controlling transverse beam dynamics. The practical design of the latter, however, can be complex and require extensive analysis through the iteration of both approximate mathematical models and computationally expensive simulations to optimize the performance of the structure. In this paper we present a new, systematic method for designing azimuthally modulated rf cavities that support modes composed of any number and magnitude of user-specified transverse multipoles, either with or without a longitudinally accelerating component. Two case studies are presented of rf cavity designs that support modes composed of a longitudinally accelerating field in addition to a single transverse multipole, and designs that support modes composed of two transverse multipoles. We discuss generalizing the discoveries and conclusions from the two case studies to designing cavities that support modes composed of any number of multipoles. The theoretical work is verified with analysis of 3D simulations and experimental measurements are presented of a cavity operating in a 3 GHz mode that simultaneously longitudinally accelerates and transversely focuses a beam.

Several proposals to measure a possible small electric dipole moment (EDM) of charged particles aligned with the spin and the well-known magnetic dipole moment (MDM) are based on the concept to circulate bunches with an initial polarization in the horizontal plane and to observe the buildup of a vertical spin component caused by the EDM. Most proposals aim at operating the ring with “frozen spin,” such that, with an MDM only, the spin remains aligned with the trajectory. The signature of a finite EDM is the buildup of a vertical spin component. Machine imperfections may lead as well to a vertical spin buildup, which can be misinterpreted as an EDM and thus limit the sensitivity of the experiment. For that reason, a good understanding of spin dynamics is mandatory to estimate and limit such systematic errors in the measurement. In this paper, a coordinate system attached to the trajectory is introduced to expand the spin. This is of particular interest for fully electric EDM rings operated at the “magic energy” to satisfy the frozen spin condition. The procedure is used for a straightforward analysis of geometric phase and other second order effects, which limit the possible sensitivity, i.e., the smallest EDM which can be detected in presence of systematic effects.

The aim of this study is to make the parameter space of zero-current phase advance greater than 90° available to the high-intensity linear accelerator (linac) design and operation, which has been excluded to avoid the envelope instabilities and particle resonances. The earlier study of Cheon et al. [Nucl. Instrum. Methods Phys. Res., Sect. A 1013, 165647 (2021)] reported that the spinning of ion beams can mitigate the fourth-order particle resonance and the associated envelope instability in high-intensity linacs. In the present work, we further investigate the effects of beam spinning on the fourth-order particle resonance in the case of 3D bunched beams with fast acceleration. We also explore the space-charge-driven resonance in the longitudinal plane and confirm that the fourth-order particle resonance can be manifested when the longitudinal zero-current phase advance ${\sigma }_{z0}$ is larger than 90° and the depressed phase advance ${\sigma }_z$ is less than 90°, similar to the transverse case. The beam spinning effects are examined in both transverse and longitudinal planes during beam acceleration through periodic solenoid and quadrupole-doublet focusing channels.

A two-dimensional boundary element method for calculating the impedance of infinitely long cryogenic vacuum chambers of general cross section is presented. The formulation is based on combining Kirchhoff’s boundary integral representation of an electromagnetic field with the surface impedance boundary condition for the anomalous skin effect, which can occur in metals at cryogenic temperature. As a result, the electromagnetic field in the chamber is expressed as a superposition of the direct and indirect space charge fields and resistive-wall wakefield. This feature allows us to compute the corresponding three impedance contributions separately. This method does not assume a specific transverse charge density such as uniform and Gaussian distributions as well as the ultrarelativistic approximation. A technique for computing the impedances and the form factors in the method is also described. The presented method is applied to circular, rectangular, elliptical, and racetrack-type vacuum chambers. The geometric effect of the cryogenic vacuum chamber cross section on the resistive-wall impedance is shown. The effect of beam velocity is demonstrated for the racetrack-type cryogenic vacuum chamber.

In this paper, we discuss different approaches for the estimation of transverse bunch characteristics, namely, tune and chromaticity, using Schottky-based diagnostics. In particular, we show how, depending on the signal quality and the availability of other instruments or information sources, we can choose appropriate strategies combining both spectrum fitting procedures and explicit parameter calculations. In addition, we revisit and formally derive the expression that relates the chromaticity with the width of the Schottky spectral sidebands, discussing the rigorous meaning of this width and in which conditions it can be applied. Results obtained using the proposed approaches are compared with the standard techniques for different fills in the LHC.

The Hadron Experimental Facility at the Japan Proton Accelerator Research Complex is used for various nuclear and elementary particle physics experiments that use secondary particle beams. The secondary-particle production target is a key element for the generation of particles such as kaons and pions. To increase beam power, a new target was developed and installed. The target, which is made of gold and indirectly cooled with water, was designed so that the maximum stresses do not exceed the allowable stresses determined based on the pressure vessel standard. 95 kW is considered to be the maximum power of the primary proton beam for a 5.2-s beam duration. The new target was stably operated up to a power of 65 kW. In addition, beam position estimation based on multipoint temperature measurements of the target was demonstrated.

The production of high spectral brilliance radiation from electron beam sources depends critically on the electron beam qualities. One must obtain very high electron beam brightness, implying simultaneous high peak current and low emittance. These attributes are enabled through the use of very high field acceleration in a radio-frequency (rf) photoinjector source. Despite the high fields currently utilized, there is a limit on the achievable peak current in high brightness operation, in the range of tens of Ampere. This limitation can be overcome by the use of a hybrid standing wave/traveling wave structure; the standing wave portion provides acceleration at a high field from the photocathode, while the traveling wave part yields strong velocity bunching. This approach is explored here in a C-band scenario, at field strengths ($>100\mathrm{MV}/\mathrm{m}$) at the current state-of-the-art. It is found that one may arrive at an electron beam with many hundreds of Amperes with well-sub-micron normalized emittance. This extremely compact injector system also possesses attractive simplification of the rf distribution system by eliminating the need for an rf circulator. We explore the use of this device in a compact 400 MeV-class source, driving both inverse Compton scattering and free-electron laser radiation sources with unique, attractive properties.

Because of the inherent value of high-energy particle beams for the study of quantum electrodynamics effects, it is of great importance to accurately model the physics in numerical simulations. Numerical effects may alter the dynamics of a simulation and may change the physics of energy losses on account of the radiation reaction (RR) force. In this work, the numerical Cherenkov effect in combination with the RR force are analyzed in the vacuum propagation of an ultrarelativistic electron bunch. It is revisited that the use of the standard Yee solver in the present setup triggers the numerical Cherenkov instability. With the instability at hand, the simulation results of the Yee solver are compared to data obtained by the $X$-dispersionless Maxwell solver, also known as the rhombi-in-plane (RIP) solver. There, the numerical instability is suppressed by several orders of magnitude. Afterward, the impact of radiation reaction on the dynamics is studied for both cases. It is shown that the combination of the Yee solver and the RR force enhances the error significantly and the electron bunch loses about 90% of its energy as a result. These huge energy losses can be observed only if both the Lorentz force and the RR force are enabled in the code. In contrast, the RIP Maxwell solver is not plagued by these issues and accurately calculates the dynamics of the electron bunch.

Accurate numerical modeling of normal-conducting accelerator magnets requires a reliable characterization of the iron saturation and hysteresis as well as a precise knowledge of the magnet geometry as built. Computations of the field quality are not easily achieving the accuracy required by the accelerator operation, particularly for eddy-current effects in fast-ramping magnets. This paper proposes a (measurement) data-driven model for the nonlinear magnetization of normal-conducting magnets. The model adopts a volume integral formulation compatible with eddy-current simulations. A two-step updating procedure is applied. The first step is the fitting of material parameters directly in the magnet model. The second step is the updating of the magnetization by measurements of the integral field harmonics. The result is a full-order updated model that can be employed in static or dynamic simulations. Finally, the procedure is validated on an iron-dominated, normal-conducting magnet.