A theoretical approach for describing the electromagnetic radiation produced by a prolonged electron bunch propagating in the lattice of metallic wires of finite length is presented. This approach is based on the vibrator antenna theory and involves the approximate solving of Hallen’s integral equation. For a single wire, it is also supposed that a wire is sufficiently thin and charge motion is relativistic. For many-wire structures, the approximation similar to the kinematic approach of the parametric x-ray radiation theory is additionally applied. The validity of the method is verified by numerical simulations with comsol Multiphysics. Possible applications of the interaction between charged particle bunches and artificial wire structures are discussed.

The Large Hadron Collider (LHC) at CERN is being prepared for its full energy exploitation during run III, i.e., an increase of the beam energy beyond the present 6.5 TeV, targeting the maximum discovery potential attainable. This requires an increase of the operating field of the superconducting dipole and quadrupole magnets, which in turn will result in more demanding working conditions due to a reduction of the operating margin while the energy deposited by particle loss will increase. Beam-induced magnet quenches, i.e., the transition to normal conducting state, will become an increasing concern, because they could affect the availability of the LHC. It is hence very important to understand and be able to predict the quench levels of the main LHC magnets for the required values of current and generated magnetic fields. This information will be used to set accurate operating limits of beam loss, with sufficient but not excessive margin, so to achieve maximal beam delivery to the experiments. In this study we used a one-dimensional, multistrand thermal-electric model to analyze the maximum beam losses that can be sustained by the LHC magnets, still remaining superconducting. The heat deposition distribution due to the beam losses is given as an input for the stability analysis. Critical elements of the model are the ability to capture heat and current distribution among strands, and heat transfer to the superfluid helium bath. The computational model has been benchmarked against energy densities reconstructed from beam-induced main dipole quenches during LHC operation at 6.5 TeV. The model was then used to evaluate the stability margin of both main dipole and main quadrupole magnets at different beam energies, up to the expected ultimate operating energy of the LHC, 7.5 TeV. The comparison between the quench levels underlines how the increase of beam energy implies a substantial reduction of magnets stability and will require much stricter setting on the allowable beam losses to avoid resistive transitions during operation.

A compact Thomson parabola spectrometer for diagnostics of laser-generated plasma, projected in Messina University, has been employed in different experiments concerning diagnostics of laser-generated plasmas. It allows to detect charged particles emitted from hot laser plasma and fast analyzing of their charge state, kinetic energy and mass-to-charge ratio. Moreover, it is possible to detect electrons emitted from laser-generated plasma. The spectrometer consists of a double pinhole input for alignment direction, a permanent magnet (0.004-4 kG) and an electric field ($0.05–5\mathrm{kV}/\mathrm{cm}$) both orthogonal to the direction of the incident particles, and different type of planar detectors (multichannel plates, phosphorous screen, gafchromic, CR39 and PM 355 track detectors). Measurements have been acquired at MIFT in Messina observing electrons up to 10 keV kinetic energy, at INFN-LNS of Catania using ions emitted from plasma submitted to a postacceleration up to 30 kV per charge state and at PALS Laboratory in Prague detecting energetic ions above 1 MeV per charge state. The particles recognition using the Thomson spectrometer has been obtained comparing the experimental parabola curves with the theoretical simulations obtained using COMSOL software. Results will be presented and discussed.

Beam dynamics of the racetrack-shape fixed field induction accelerator for giant cluster ions were established. Linear optics theory and Runge-Kutta particle tracking approaches were developed, and the consistency between two approaches was confirmed. Use of gradient field bending magnets with a reverse field strip and ramping quadrupole doublets were crucial to achieve the orbit stability. A physically limited size of the huge bending magnet in the longitudinal direction generated the inherent closed-orbit distortion that substantially affected the orbit stability. In addition, the inherent field component $B_s$ along the orbit coordinate “$s$” induced horizontal-vertical (H-V) couplings. A possible correction method of this closed-orbit distortion was proposed. A net effect of the H-V coupling was evaluated. Longitudinal motion with a time-varying transition energy, which is one of characteristic features in the racetrack-shape fixed field induction accelerator, was studied with the help of computer simulations.

Short-period crystalline undulators have the potential to enable intense and monochromatic sources of hard X and $\gamma$ radiation. Three crystalline undulators were manufactured and their structural properties were characterized at the ESRF x-ray light source. In particular, a crystalline undulator consists in a periodically bent crystal in which channeled electrons or positrons follow the bending of the crystalline planes, thus generating electromagnetic radiation in analogy with standard magnetic undulators. State-of-the-art magnetic undulators can be built with a period of no less than a few cm. On the other hand, a crystalline undulator could be built with a period down to the sub-mm range. Thus, a crystalline undulator would allow generating harder photons. Since the radiator consists of a small crystal, a crystalline undulator is a valid and low-cost alternative for intense hard radiation production at electron accelerator facilities. The three samples were realized at the INFN laboratory of Ferrara, Italy, through the grooving method, namely a method developed to induce a self-standing and adjustable deformation to a crystal. The samples showed a uniform and sinusoidal curvature, thus proving that the grooving method is suitable for building crystalline undulators.

Progress in the development of a neutron detector employing the ${}^9\mathrm{Be}{(n,\alpha )}^6\mathrm{He}({\beta }^{-},{\tau }_{1/2}=807\mathrm{ms})$ reaction is reported. This detector’s intended use is to estimate 2.45-MeV, deuterium-deuterium (DD) neutron yields from magnetized liner fusion (MagLIF) targets and proposed future gas-puff experiments at Sandia National Laboratory’s $Z$ facility, Albuquerque, NM. This unique detector employs a simple stacked-component construction: 23 flat beryllium plates (99% pure, 0.318 cm thick) sandwiched between 22 plastic scintillator sheets (BC-404, 1-mm-thick). Each Be plate and scintillator sheet is a planar square (10 cm on a side) and the assembly is enclosed in a cubical, sealed, 1.5-mm-thick, Al-walled box. Scintillation light due to deposited energy from the ${}^6\mathrm{He}$ betas is emitted and transmitted edgewise to ultraviolet-transmitting Lucite light guides optically coupled to two, independent, high-gain photomultiplier tubes. Reported here are details of the characterization of the neutron detection sensitivity (beta decay counts per incident neutron) of each photomultiplier tube side. These measurements were conducted at the Sandia National Laboratories ion beam facility, which provided beams of pulsed 175-keV deuterons focused onto a 2.6-micron thick deuterated erbium target ($\mathrm{Er}{D}_2$). Neutrons were produced via the $D(d,n){}^3\mathrm{He}$ reaction. The neutron flux ($\text{incident}\mathrm{neutrons}/{\mathrm{cm}}^2/\sec$) on the Be detector was inferred by the measurement of the protons from the equally branched $D(d,p)T$ reaction. Steady-state neutron pulses incident on the Be detector induced the ${}^6\mathrm{He}$ beta decay activity necessary to determine the detector’s neutron sensitivity referred to as the $F$-factor. The rational, methodology, and experimental details behind this approach and the results with uncertainties of the subsequently determined $F$-factor of the Be detector are detailed. Additional comments regarding improvements to the calibration methodology plus future studies and the use of this detector in $Z$ experiments will be discussed briefly.

As the development of nuclear physics and atomic sciences progresses, monochromatic and high-flux gamma-ray light sources are highly demanded by many experiments in these fields. We have designed a compact storage ring for gamma-ray source generation based on the Compton backscattering technique. The energy range of the electron beam stored in the ring will be from 500 to 800 MeV, with the capability of generating a gamma ray with an energy range from about 4 to 10 MeV. The maximum energy loss for an electron could be more than 1% for one scattering event, which could have a significant impact on electron beam dynamics. To study this impact, a 6D macroparticle tracking code has been developed by including the Compton scattering, damping, quantum excitation, and synchrotron radiation in the storage ring. The equilibrium states have been studied with this code, and the results show good agreement with theoretical predictions. The electron beam loss rate induced by Compton scattering has also been investigated by varying the input laser beam parameters. This study allows us to optimize the storage ring operation for a stable, high-flux, and narrow-bandwidth gamma-ray beam generation.

The electrostatic cumulation of current density in relativistic vacuum diodes with ring-type cathodes is described theoretically and confirmed experimentally. The distinctive feature of the suggested cumulation mechanism is a very low energy spread of electrons. As a result of electrostatic cumulation, a thin relativistic electron beam with a current density of $1\mathrm{kA}/{\mathrm{mm}}^2$ can be formed. This quantity exceeds typical current density values in high-current Cherenkov sources by an order of magnitude. Such a beam can be used as an active medium in high-power terahertz sources.

Resonance surfaces for a 2.45 GHz electron cyclotron resonance ion source are investigated. In addition to the typical flat-B and minimum-B profiles, we have investigated on two new magnetic field structures, namely the torus zone and the double zone configurations. The impacts of such surfaces on the microwave power absorption are discussed. Furthermore, the uniformity of the ion emissive surfaces in connection with the resonance surfaces is examined. Different configurations for absorbing microwave power and simultaneously for producing uniform ion density distribution near the extraction wall of the source are discussed.

We investigate the radiation of surface polaritons by a charged particle rotating around a dielectric waveguide. The general case is considered when the waveguide is immersed in a homogeneous medium. For the evaluation of the corresponding electromagnetic fields the electromagnetic Green tensor is used. A formula is derived for the spectral distribution of the radiation intensity for surface-type modes. It is shown that the corresponding waves are radiated on the eigenmodes of the dielectric cylinder. We demonstrate that the number of radiated quanta for surface polaritons of a given harmonic can be essentially larger than that for guiding modes of the cylinder. The geometry under consideration is of interest from the point of view of generation and transmitting of waves in waveguides, a subject which is of considerable practical importance in microwave engineering and optical fiber communications.

A superconducting (SC) linac allows a few orders of magnitude larger average beam current than a normal conducting linac, therefore the powerful beam is expected to lead to outstanding discoveries in various scientific fields, such as high luminosity accelerators and high brilliance light source. However, the high construction and operation costs of the SC linac is a critical issue for realizing large scale facilities. To resolve this problem, we propose a continuous wave (cw) operation of an SC linac shared by electron/positron beams for effective multipurpose utilization. A high current positron source is required for high-energy physics projects: a linear electron-positron collider and a muon collider, while high-current and high-quality electron beams are expected to realize the high brilliant x-ray light sources. As an example, we discuss the injector of the International Linear Collider, an x-ray free-electron laser, and an energy-recovery linac light source. We found a feasible solution of a basic design for the proposed multibeam operation despite the high-quality beam requirements and complicated operation: control of mixed beams without pulsed magnets, and heat load in the cavity, high stability of beam energy, and operation at high average current.

We analyze the electromagnetic field (EMF) of a small bunch that moves uniformly in a circular metal waveguide and crosses the boundary between two areas: a vacuum area and an area loaded with an anisotropic homogeneous nondispersive dielectric characterized by a diagonal permittivity tensor. Two cases are studied in detail: the bunch flies from a vacuum into the dielectric and, inversely, from the dielectric into a vacuum. In the second case, so-called Cherenkov-transition radiation (CTR) can be generated in the vacuum area of the waveguide. Exact expressions for the EMF components are obtained and investigated. A comparison between the present problems and the analogous problems in the case of an isotropic dielectric is performed. We discuss some benefits occurring from using the anisotropic dielectric. For example, anisotropic dielectric allows more efficient generation of radiation compared to the isotropic dielectric for the same bunch and geometry parameters.

We demonstrate optical guiding of high-intensity laser pulses in long, low-density hydrodynamic optical-field-ionized (HOFI) plasma channels. An axicon lens is used to generate HOFI plasma channels with on-axis electron densities as low as $n_e(0)=1.5\times {10}^{17}{\mathrm{cm}}^{-3}$ and matched spot sizes in the range $20\mu \mathrm{m}\lesssim W_M\lesssim 40\mu \mathrm{m}$. Control of these channel parameters via adjustment of the initial cell pressure and the delay after the arrival of the channel-forming pulse is demonstrated. For laser pulses with a peak axial intensity of $4\times {10}^{17}{\mathrm{W}\mathrm{cm}}^{-2}$, highly reproducible, high-quality guiding over more than 14 Rayleigh ranges is achieved at a pulse repetition rate of 5 Hz, limited by the available channel-forming laser and vacuum pumping system. Plasma channels of this type would seem to be well suited to multi-GeV laser wakefield accelerators operating in the quasilinear regime.

The NT-02 neutrino physics target made of the isotropic graphite grade produced neutrinos for the MINOS and MINERVA high-energy physics experiments. The segmented, 95-cm-long NT-02 target was bombarded with a 340 kW, Gaussian 1.1 mm sigma beam of 120 GeV protons reaching $6.516\times {10}^{20}$ protons on target and a peak fluence of $8.6\times {10}^{21}\mathrm{protons}/{\mathrm{cm}}^2$. Reductions in detected neutrino events during the experiment were attributed to radiation-induced damage on the target material leading to the NT-02 target replacement. With future neutrino physics targets aiming at the multimegawatt power regime, identifying life expectancy or fluence thresholds of target materials is of paramount importance, and, therefore, pinpointing the exact cause and target failure mode triggering the neutrino yield reduction is critical. To help unravel the effects of the 120 GeV beam on the isotropic graphite structure at the microstructural or lattice level, x-ray beams from National Synchrotron Light Source II were utilized to study failed in-beam as well as intact NT-02 target segments. The primary objective was to arrive at a scientifically sound explanation of the processes responsible for the target failure by correlating macroscopic observations with microstructural analyses. Results from transmission electron microscopy studies were integrated in assessing the microstructural evolution. The x-ray diffraction study revealed (a) the diffused state reached by the graphite microstructure within the $1\sigma$ of the beam where the graphite lattice structure transforms into a nanocrystalline structure, a finding supported by electron microscopy examination, thus providing an indication of the fluence threshold, and (b) the dominant role of the irradiation temperature profile exhibiting a high gradient from the beam center to the heat sink and aggravating the damage induced in the microstructure by the high proton fluence. The effects of the 120 GeV protons on the isotropic graphite target structure are corroborated by observed damage induced by 160-MeV protons and by fast neutrons to comparative doses on similar graphite, an assessment that will aid the design of next-generation megawatt-class neutrino targets.

The Facility for Rare Isotope Beams (FRIB) being constructed at Michigan State University [J. Wei et al., The FRIB superconducting linac—status and plans, LINAC’16, Lansing, MI, p. 1, http://accelconf.web.cern.ch/AccelConf/linac2016/papers/mo1a01.pdf] is based on a cw superconducting linear accelerator which is designed to deliver unprecedented 400 kW heavy ion beam power to the fragmentation target. The installation of the accelerator equipment is approaching completion and multistage beam commissioning activities started in the summer of 2017 with expected completion in 2021. A room-temperature test electron cyclotron resonance ion source, ARTEMIS, provided argon and krypton beams for the commissioning of the low energy beam transport, a radio frequency quadrupole (RFQ), the medium energy beam transport (MEBT) and the first three accelerating cryomodules. The commissioning of the first linac segment (LS1), composed of 15 cryomodules, is planned in the spring of 2019. This paper describes the first results of experimental beam dynamics studies in the LEBT, RFQ, MEBT and the first three cryomodules with comparison to the numerical simulations.

Ion acceleration in electrostatic collisionless shocks is driven by the interaction of the high-power laser with specially tailored near-relativistic critical density plasma. 2D EPOCH particle-in-cell simulations show that the ion acceleration is dependent on the target material used. In materials with low charge-to-mass ratio $⟨Z/A⟩$, proton beams with high flux and low energy spread are generated. In multi-ion plasmas the ions with different $⟨Z/A⟩$ acquire different velocities under a non-oscillating component of electrostatic field in the upstream region. This relative drift between the protons ($⟨Z/A⟩=1$) and the lower $⟨Z/A⟩$ ions leads to the excitation of electrostatic ion two-stream instability. This in turn generates a low-velocity component in the upstream expanding protons. The velocity distribution of the upstream expanding protons is further broadened toward the higher velocity by the electrostatic ion two-stream instability between reflected protons, which results in large number of protons being accelerated by the shock.

The slow resonant extraction of a beam in a storage ring is a very well-established technique. Several high-energy physics accelerator facilities around the world are currently using this technique for high-intensity beam operations. As the demand for beam power is constantly growing, extraction efficiency in many cases is becoming a limiting factor. In this report, we discuss a new effective approach to improving the slow extraction efficiency by using configurations of higher multipoles. We will describe this approach, determine optimal multipole configurations, and present the results of simulations to support the proposed recipe. We found that, with the use of higher multipole field content, the extraction efficiency can be improved, and, therefore, the level of prompt and residual radioactivity in the accelerator components and surrounding buildings can be reduced by as much as 40% or more. We also explored manipulating the higher-order effects produced in the pure sextupole configurations for the same purpose and demonstrated that similar results can be achieved by only rearranging the sextupole magnets in the lattice.

Beryllium is a material extensively used in various particle accelerator beam lines and target facilities, as beam windows and, to a lesser extent, as secondary particle production targets. With increasing beam intensities of future multimegawatt accelerator facilities, these components will have to withstand even greater thermal and mechanical loads during operation. As a result, it is critical to understand the beam-induced thermal shock limit of beryllium to help reliably operate these components without having to compromise particle production efficiency by limiting beam parameters. As part of the RaDIATE (radiation damage in accelerator target environments) Collaboration, an exploratory experiment to probe and investigate the thermomechanical response of several candidate beryllium grades was carried out at CERN’s HiRadMat facility, a user facility capable of delivering very-high-intensity proton beams to test accelerator components. Multiple arrays of thin beryllium disks of varying thicknesses and grades, as well as thicker cylinders, were exposed to increasing beam intensities to help identify any thermal shock failure threshold. Real-time experimental measurements and postirradiation examination studies provided data to compare the response of the various beryllium grades, as well as benchmark a recently developed beryllium Johnson-Cook strength model.

This paper describes the design and simulation of a proof-of-concept octupole lattice at the University of Maryland Electron Ring (UMER). This experiment tests the feasibility of nonlinear integrable optics, a novel technique that is expected to mitigate resonant beam loss and enable low-loss high-intensity beam transport in rings. Integrable lattices with large amplitude-dependent tune spreads, created by nonlinear focusing elements, are proposed to damp beam response to resonant driving perturbations while maintaining large dynamic aperture. At UMER, a lattice with a single octupole insert is designed to test the predictions of this theory. The planned experiment employs a low-current high-emittance beam with low space charge tune shift ($\sim 0.005$) to probe the dynamics of a lattice with large externally-induced tune spread. Design studies show that a lattice composed of a 25-cm octupole insert and existing UMER optics can induce a tune spread of $\sim 0.13$. Stable transport is observed in PIC simulation for many turns at space charge tune spread 0.008. A maximum spread of $\mathrm{\Delta }\nu =0.11$ (rms 0.015) is observed for modest octupole strength (peak $50\mathrm{T}/{\mathrm{m}}^3$). A simplified model of the system explores beam sensitivity to steering and focusing errors. Results suggest that control of orbit distortion to $<0.2\mathrm{mm}$ within the insert region is essential. However, we see only weak dependence on deviations of lattice phase advance ($\le 0.1\mathrm{rad}$.) from the invariant-conserving condition.