With a Bayesian approach, the linear optics correction algorithm for storage rings is revisited. Starting from the Bayes’ theorem, a complete linear optics model is simplified as “likelihood functions” and “prior probability distributions.” Under some assumptions, the least square algorithm and then the Jacobian matrix approach can be rederived. The coherence of the correction algorithm is ensured through specifying a self-consistent regularization coefficient to prevent overfitting. Optimal weights for different correction objectives are obtained based on their measurement noise level. A new technique has been developed to resolve degenerated quadrupole errors when observed at a few select beam position monitors (BPMs). A necessary condition of being distinguishable is that their optics response vectors seen at these specific BPMs should be near orthogonal.

We report on our latest transverse focusing results of subnanosecond proton bunches achieved with a laser-driven multi-MeV ion beamline. In the frame of the LIGHT collaboration, a target normal sheath acceleration (TNSA) source based 6 m long beamline was installed. In the past years, the laser-driven proton beam was transported and shaped by this beamline. The particle beam is collimated with a pulsed high-field solenoid and rotated in longitudinal phase space with a radio-frequency cavity which leads to an energy compression with an energy spread of $(2.7\pm 1.7)\%$ ($\mathrm{\Delta }\mathrm{E}/{\mathrm{E}}_0$ at FWHM) or a time compression to the subnanosecond regime. Highest peak intensities in the subnanosecond regime open up an interesting field for several applications, e.g., proton imaging, as injectors in conventional accelerators or precise stopping power measurements in a plasma. We report on achieving highest peak intensities using an installed second solenoid as a final focusing system in our beamline to achieve small focal spot sizes. We measured a focal spot size of $1.1\times 1.2\mathrm{mm}$ leading to $5.8\times {10}^{19}\mathrm{protons}\mathrm{per}\mathrm{s}{\mathrm{cm}}^2$ at a central energy bin of $(9.55\pm 0.25)\mathrm{MeV}$, which can be combined with a bunch duration below 500 ps at FWHM.

We suggest a new on-axis injection scheme that uses a transverse deflecting rf cavity to kick the incoming beam into an already populated bucket but with a timing offset from the synchronous phase. In a new on-axis injection scheme, two deflecting rf cavities are required: one upstream of the injection point that crabs the stored beam and the other downstream of the injection point that both uncrabs the stored beam and kicks the incoming beam onto the axis of the orbital plane. We present a theoretical analysis and numerical simulations of the stored beam and injected beam with the new injection scheme.

High-frequency modulations appearing in the kinetic energy distribution of laser-accelerated ions are proposed for retrieving the acceleration field dynamics at the femtosecond timescale. Such an approach becomes possible if the laser-cycling field modulates the particle density in the ion spectra and produces quasitime stamps for analysis. We investigate target and laser parameters determining this effect and discuss the dependencies of the observed modulation. Our findings refine a basic mechanism, the target normal sheath acceleration, where an intense and ultrafast laser pulse produces a very strong electrical field at a plasma-vacuum interface. The field decays rapidly due to energy dissipation and forms a characteristic spectrum of fast ions streaming away from the interface. We show that the derived decay function of the field is in accordance with model predictions of the accelerating field structure. Our findings are supported by two-dimensional particle-in-cell simulations. The knowledge of the femtosecond field dynamics helps to rerate optimization strategies for laser ion acceleration.

We demonstrate single-shot temporal characterization of relativistic electron bunches using single-cycle terahertz (THz) field streaking. A transverse deflecting structure consisting of a metal slit enables efficient coupling of the THz field and electron bunch. The intrinsically stable carrier envelope phase and strong gradient of the THz pulses allow simultaneous, self-calibrated determination of the time-of-arrival with subfemtosecond precision and bunch duration with single-femtosecond precision, respectively, opening up new opportunities for ultrafast electron diffraction as well as accelerator technologies in general.

The HRMT27-RodTarg experiment employed the HiRadMat facility at CERN to impact intense 440 GeV proton beams onto thin rods 8 mm in diameter, 140 mm in length, and made of high-density materials such as Ir, W, Ta, Mo, and alloys. The purpose of the experiment was to reduce uncertainties on the CERN antiproton target material response and assess the material selection for its future redesign. The experiment was designed to recreate the extreme conditions reached in the production target, estimated in an increase of temperature above $2000°\mathrm{C}$ in less than $0.5\mu \mathrm{s}$ and a subsequent compressive-to-tensile pressure wave of several gigapascals. The goals of the experiment were (i) to validate the hydrocode calculations used for the prediction of the antiproton target response and (ii) to identify limits and failure mechanisms of the materials of interest. In order to accomplish these objectives, the experiment relied on extensive instrumentation (pointing at the target rod surfaces). This paper presents a detailed description of the experiment as well as the recorded online results which showed that most of the investigated materials suffered internal damage from conditions 5–7 times below the ones present in the AD target. Tantalum, on the other hand, apparently withstood the most extreme conditions without presenting internal cracking.

Collective effects such as wakefields affect the dynamics of high brightness electron beams in linear accelerators (linacs) and can degrade the performance of short wavelength free-electron lasers (FELs). If a reliable model of wakefields is made available, the accelerator can be designed and configured with parameters that minimize their disrupting effect. In this paper, the simulated effect of geometric (diffractive) wakefields and of coherent synchrotron radiation on the electron beam energy distribution at the FERMI FEL is benchmarked with measurements, so quantifying the accuracy of the model. Wakefield modeling is then extended to the undulator line, where particle tracking confirms the limited impact of the resistive wall wakefield on the lasing process. The study reveals an overall good understanding of collective effects in the facility.

In the following years, the Fermilab Muon Campus will deliver highly polarized muon beams to the Muon $g-2$ experiment. The Muon Campus contains a target section wherein secondaries are produced, the delivery ring which separates the muons from the rest of the beam, and a sequence of beam lines that transports them to the Muon $g-2$ storage ring. Here, we report the first results of beam measurements at the Muon Campus with an emphasis on the key achievements that have contributed to the successful beam delivery to the Muon $g-2$ experiment. These achievements include the production of an intense secondary beam from the target, its transport over 2 km, the successful monitoring of muons from the available diagnostics, and the development of techniques for measuring the transverse optics. We also present detailed comparisons between the experimental data and simulation and discuss the similarities and differences observed.

We consider a semi-infinite open-ended cylindrical waveguide with uniform dielectric filling placed into collinear infinite vacuum waveguide with larger radius. Electromagnetic field produced by a point charge or Gaussian bunch moving along structure’s axis from the dielectric waveguide into the vacuum one is investigated. We utilize the modified residue-calculus technique and obtain rigorous analytical solution of the problem by determining coefficients of mode excitation in each subarea of the structure. The main attention is paid to analysis of penetration of Cherenkov radiation into vacuum regions of the outer waveguide. Numerical simulations in cst Particle Studio are also performed (for long enough bunch exciting the first Cherenkov mode only) and an excellent agreement between analytical and simulated results is shown. The discussed structure can be used for generation of Terahertz radiation by modulated bunches (bunch trains) by means of high-order Cherenkov modes. In this case, due to high frequencies numerical simulations become extremely difficult while the developed analytical technique still remains the efficient approach for calculation of the radiation characteristics.

Radiation generated by a charge moving along one of the prism borders is analyzed. The size of the object is assumed to be much larger than the wavelengths under consideration. We calculate the wave field outside the target using the “aperture method” which is applicable for any distances from the prism. We obtain the particular form of Stratton-Chu formulas for the case of the prism and develop an algorithm for the calculation of the radiation field outside the prism. Typical numerical results are demonstrated and discussed.

Large distributed control systems typically can be modeled by a hierarchical structure with two physical layers: console level computers (CLCs) layer and front end computers (FECs) layer. The control system of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) consists of more than 500 FECs, each acting as a server providing services to a large number of clients. Hence the interactions between the server and its clients become crucial to the overall system performance. There are different scenarios of the interactions. For instance, there are cases where the server has a limited processing ability and is queried by a large number of clients. Such cases can put a bottleneck in the system, as heavy traffic can slow down or even crash a system, making it momentarily unresponsive. Also, there are cases where the server has adequate ability to process all the traffic from its clients. We pursue different goals in those cases. For the first case, we would like to manage clients’ activities so that their requests are processed by the server as much as possible and the server remains operational. For the second case, we would like to explore an operation point at which the server’s resources get utilized efficiently. Moreover, we consider a real-world time constraint to the above case. The time constraint states that clients expect the responses from the server within a time window. In this work, we analyze those cases from a game theory perspective. We model the underlying interactions as a repeated game between clients, which is carried out in discrete time slots. For clients’ activity management, we apply a reinforcement learning procedure as a baseline to regulate clients’ behaviors. Then we propose a memory scheme to improve its performance. Next, depending on different scenarios, we design corresponding reward functions to stimulate clients in a proper way so that they can learn to optimize different goals. Through extensive simulations, we show that first, the memory structure improves the learning ability of the baseline procedure significantly. Second, by applying appropriate reward functions, clients’ activities can be effectively managed to achieve different optimization goals.

We propose a scheme that can generate attosecond x-ray pulses through an angular dispersion enhanced self-amplified spontaneous emission (ESASE) free electron laser (FEL). In this scheme, an angular dispersion section is implemented into a conventional ESASE set-up, together with a few cycle laser pulse to manipulate the electron beam effectively. During the procedure, the transverse-longitudinal phase space coupling is introduced into the electron beam in addition to the energy modulation and momentum compaction processes. As a result, the peak current of the electron beam will be strengthened significantly within a narrow width of the electron bunch, which can be used to generate ultrashort FEL pulses. Comparing to a conventional ESASE scheme, the proposed scheme can reduce the required modulation laser power by at least one order of magnitude. The signal-to-noise ratio of the final FEL radiation pulses can also be improved. In addition, we discuss the possibility of using this scheme to generate two-pulse two-color x-ray FEL with tunable central wavelengths and time delays for a conceivable x-ray pump/x-ray probe experiment.

In our previous study on a normal-conducting 508.9-MHz continuous-wave accelerating cavity, it was discovered that most breakdown events were accompanied by the explosion of a stable bright spot on one of the two end plates of the cavity (Breakdown Type I) or by a spot-type explosion not originating from a stable bright spot (Breakdown Type II); both of these explosions can be understood as breakdown triggers. In the present study, the light emitters of stable bright spots in Breakdown Type I and the dynamics of spot-type explosions in Breakdown Type II were investigated using hyperspectral and high-speed cameras, respectively, during high-power test.

Magnets to be used for the internal quadrupoles of an interdigital $H$-mode drift tube linear accelerator (IH-DTL) using KONUS beam dynamics should be both compact in size and high in focusing field gradient. Permanent magnets are an attractive solution, but then the ability to adjust the field strength is lost. We investigated two different solutions to this problem: the first using external adjustable electromagnets; the second using internal adjustable permanent magnets. The first method moves the variability out of the resonant cavity, using adjustable electromagnet quadrupole doublets before entry into the IH-DTL to compensate for the lack of internal variability. We carried out optimization simulations with custom code that ran many instances of the lorasr beam dynamics simulation software, using different values of field strength for the external doublets. By optimizing the magnet settings for different values of input current, we were able to compensate for the space-charge forces involved in accelerating a high-intensity continuous-wave (CW) deuteron beam. Second, we designed some novel adjustable permanent-magnet quadrupoles to be used inside the cavity, which combine the advantages of small cross-section and variable field gradient. This allows much more control over the beam, and even other ion species with differing charge-to-mass ratios can be accommodated within the same accelerator design. We developed two adjustable permanent-magnet designs: one with an electromagnetic component, and the other with two concentric moving rings of Halbach-array quadrupoles.

The solenoid scan is a widely used method for the in-situ measurement of the thermal emittance in a photocathode gun. The popularity of this method is due to its simplicity and convenience since all rf photocathode guns are equipped with an emittance compensation solenoid. This paper shows that the solenoid scan measurement overestimates the thermal emittance in the ordinary measurement configuration due to a weak quadrupole field (present in either the rf gun or gun solenoid) followed by a rotation in the solenoid. This coupled transverse dynamics aberration introduces a correlation between the beam’s horizontal and vertical motion leading to an increase in the measured 2D transverse emittance, thus the overestimation of the thermal emittance. This effect was systematically studied using both analytic expressions and numerical simulations. These studies were experimentally verified using an L-band 1.6-cell rf photocathode gun with a cesium telluride cathode, which shows a thermal emittance overestimation of 35% with a rms laser spot size of 2.7 mm. The paper concludes by showing that the accuracy of the solenoid scan can be improved by using a quadrupole magnet corrector, consisting of a pair of normal and skew quadrupole magnets.

The suppression of transverse wakefield effects using transversely elliptical drive beams in a planar structure is studied with a simple analytical model that unveils the geometric nature of this phenomenon. By analyzing the suggested model we derive scaling laws for the amplitude of the longitudinal and transverse wake potentials as a function of the Gaussian beam ellipticity—${\sigma }_x/a$. We explicitly show that in a wakefield accelerator application it is beneficial to use highly elliptical beams for mitigating transverse forces while maintaining the accelerating field. We consider two scaling strategies: (1) aperture scaling, where we keep a constant charge to have the same accelerating gradient as in a cylindrical structure and (2) charge scaling, where aperture is the same as in the cylindrical structure and charge is increased to match the gradient.

A high-resolution, intratrain position feedback system has been developed to achieve and maintain collisions at the proposed future electron-positron International Linear Collider (ILC). A prototype has been commissioned and tested with a beam in the extraction line of the Accelerator Test Facility at the High Energy Accelerator Research Organization in Japan. It consists of a stripline beam position monitor (BPM) with analogue signal-processing electronics, a custom digital board to perform the feedback calculation, and a stripline kicker driven by a high-current amplifier. The closed-loop feedback latency is 148 ns. For a three-bunch train with 154 ns bunch spacing, the feedback system has been used to stabilize the third bunch to 450 nm. The kicker response is linear, and the feedback performance is maintained, over a correction range of over $\pm 60\mu \mathrm{m}$. The propagation of the correction has been confirmed by using an independent stripline BPM located downstream of the feedback system. The system has been demonstrated to meet the BPM resolution, beam kick, and latency requirements for the ILC.

One major concern in the design and operation of high-intensity rings is beam loss due to beam halo. Another issue of importance in applications involving fixed targets is the uniformity of the beam energy deposition on the target. Both of these issues could be favorably addressed by a hard-edged beam with uniform transverse density. This paper presents a detailed feasibility study for painting such a beam into a high-intensity proton ring. For the purposes of this paper, we define self-consistent beams to be ellipsoidal, or elliptical in 2D, distributions that have uniform density and linear space charge force and that retain these properties under all linear transformations. Because of their linear space charge forces and linear transport properties, self-consistent distributions may undergo very little halo formation if realized in practice. Because of their uniform density, they would have smaller maximum space charge tune shifts than peaked density distributions, and they would be attractive for high-intensity fixed target applications. Self-consistent distributions involve very special relationships between the phase space coordinates, making them singular in some respects and difficult to realize experimentally. The most famous self-consistent distribution is the Kapchinsky-Vladimirsky distribution, but now many other self-consistent distributions have been discovered. One such, the 2D rotating distribution, can be painted as a coasting beam into a ring having an appropriately designed and tuned lattice. For bunched beams, if the bunch length is sufficiently long, it is expected that the coasting beam assumption will be a good approximation during painting. However, it is unknown how robust self-consistent distributions will be under real world transport in the presence of nonlinearities and collective effects. This paper studies these issues for a particular case of interest by applying realistic detailed computational models to the simulation of painting a self-consistent rotating beam into the Spallation Neutron Source (SNS) ring. As a result, we propose a case that can be carried out with only a minor modification of the SNS hardware.