Bunch Of Particles Research Articles

Coherent Inverse Compton Scattering by Bunches in Fast Radio Bursts

Abstract The extremely high brightness temperature of fast radio bursts (FRBs) requires that their emission mechanism must be “coherent,” either through concerted particle emission by bunches or through the exponential growth of a plasma wave mode or radiation amplitude via certain maser mechanisms. The bunching mechanism has been mostly discussed within the context of curvature radiation or cyclotron/synchrotron radiation. Here we propose a family of models invoking the coherent inverse Compton scattering (ICS) of bunched particles that may operate within or just outside of the magnetosphere of a flaring magnetar. Crustal oscillations during the flaring event may excite low-frequency electromagnetic waves near the magnetar surface. The X-mode of these waves could penetrate through the magnetosphere. Bunched relativistic particles in the charge-starved region inside the magnetosphere or in the current sheet outside the magnetosphere would upscatter these low-frequency waves to produce gigahertz emission to power FRBs. The ICS mechanism has a much larger emission power for individual electrons than curvature radiation. This greatly reduces the required degree of coherence in bunches, alleviating several criticisms of the bunching mechanism raised in the context of curvature radiation. The emission is ∼100% linearly polarized (with the possibility of developing circular polarization) with a constant or varying polarization angle across each burst. The mechanism can account for a narrowband spectrum and a frequency downdrifting pattern, as commonly observed in repeating FRBs.

Properties of Particleboard from Oil Palm Biomasses Bonded with Citric Acid and Tapioca Starch.

The study investigated the effects of the addition of starch on the properties of oil palm biomass particleboard bonded with citric acid. Three kinds of oil palm biomasses were used in this study for the fabrication of particleboard, namely, oil palm frond (OPF), oil palm trunk (OPT), and empty fruit bunch (EFB) particles. Citric acid and tapioca starch at the mixing ratios of 100:0, 87.5:12.5, and 75:25 were prepared at a 60% solid content. A 30% resin content based on the oven-dried weight of the oil palm biomass particles was used. The sprayed particles were pre-dried at 80 °C for 12 h before being hot-pressed at 180 °C and 4 MPa pressure for 10 min. The physical and mechanical properties of the particleboard were evaluated. The mixtures of citric acid and tapioca starch were characterized by thermogravimetric analysis (TGA). Thermal stability of citric acid was reduced after the addition of tapioca starch. The addition of 12.5% tapioca starch improved the bending strength of the particleboard but increased the thickness swelling slightly. All UF-bonded particleboard exhibited significantly inferior performance than that of citric-acid-bonded particleboard. Citric-acid-bonded particleboard maintained its original shape after being subjected to a cyclic-aging treatment, while the UF-bonded particleboard disintegrated half way through the treatment. The performance of EFB particleboard was significantly inferior to its OPT and OPF counterparts.

Optical bunching of particles in a liquid flow.

High-speed liquid micro-jets are used to rapidly and repeatedly deliver protein microcrystals to focused and pulsed X-ray beams in the method of serial femtosecond crystallography. However, the current continuous flow of crystals is mismatched to the arrival of X-ray pulses, wasting vast amounts of an often rare and precious sample. Here, we introduce a method to address this problem by periodically trapping and releasing crystals in the liquid flow, creating locally concentrated crystal bunches, using an optical trap integrated in the microfluidic supply line. We experimentally demonstrate a 30-fold increase of particle concentration into 10 Hz bunches of 6.4 μm diameter polystyrene particles. Furthermore, using particle trajectory simulations, a comprehensive description of the optical bunching process and parameter space is presented. Adding this compact optofluidics device to existing injection systems would thereby dramatically reduce sample consumption and extend the application of serial crystallography to a greater range of protein crystal systems that cannot be produced in high abundance. Our approach is suitable for other microfluidic systems that require synchronous measurements of flowing objects.

3D numerical simulation of ribbon electron beam bending by relativistic proton bunch

Nowadays experiments in the field of high-energy physics require increasing the intensity and brightness of charged particle beams and developing new methods for their diagnosis. One of the noninvasive methods for diagnosing the parameters of an intense bunch of charged particles is based on the use of a low-energy ribbon electron beam. This paper presents a numerical model of the interaction process of the testing electron beam and the proton bunch under study. The model used to solve the problem consists of the equations of motion of the electron beam under the action of an electromagnetic field created by the relativistic proton bunch. The beam is modeled by calculating of electron trajectories passing through the 3D computational domain. The dependence of the electron beam deflection on its energy, the angle of inclination to the direction of the proton bunch, the magnitude of the space charge and the velocity of the proton bunch is investigated. It is shown that the amplitude of the electron beam deflection is proportional to the charge and gamma factor of the proton bunch and inversely proportional to the energy of the electron beam.

Radiation of a Charged Particle Bunch Moving Along a Deep Corrugated Surface with a Small Period

Radiation of a Charged Particle Bunch Moving Along a Deep Corrugated Surface with a Small Period

The radiation from ultrafast point dipoles, moving uniformly near chiral media

The article discusses the features of the radiation of ultrafast point clusters of charged particles moving uniformly near a gyrotropic medium interface. It is shown that some types of electromagnetic radiation – transient and/or Cherenkov radiation – have the characteristics of superchiral fields. Therefore, they can be effectively used to study chiral structures (for example, to detect circular dichroism, the frequency characteristics of refractive indices), various materials, including biomaterials. Ultrafast (relativistic) particles can serve as a «tool» not only for studying the structure of various materials. They can also be used as «generators» of quasiparticles that determine the «dynamic» properties of the materials under study, as well as the features of their interaction with radiation of various nature and response to external influences. In this paper, some types of circularly polarized EM waves propagating in optically active (magnetoactive, naturally active, gyrotropic, and chiral) media are considered. Using the generalized reciprocity theorem for media characterized by the Hermitian permittivity tensor, we consider the transient and Cherenkov radiation excited by a uniformly moving bunch of charged particles when it crosses (or moves along) the interface of media, one of which is an optically active gyrotropic medium. It is shown that the superchiral electromagnetic fields of the transition and Cherenkov radiation of dipoles can serve as a source of chiral collective excitations in magnetoactive and naturally active media. The investigated mechanisms of interaction of electromagnetic radiation with chiral materials (structures and media) are one of the possible physical approaches to solving the problem of the chiral purity of the biosphere and to elucidate the factor of deracemization of the organic primeval environment. A new hypothesis is presented, suggesting that ultra-high-speed clumps of charged particles of cosmic origin can cause deracemization of the prebiosphere.

Beam-based characterization of plasma density in a capillary-discharge waveguide

Next-generation plasma-based accelerators can push electron bunches to gigaelectronvolt energies within centimeter distances. In these devices, the accelerating force is provided by a driver pulse, either a laser pulse or a particle bunch, that loses its energy into the plasma generating huge electric fields up to tens of GV/m. The stability of such fields strongly depends on plasma density, whose exact value should be precisely known and controlled. However, currently available methods based on spectroscopic or interferometric techniques find it very difficult to measure plasma density lower than 1015–16 cm−3 in capillary-discharge waveguides. Here, we present a novel diagnostic tool that allows us to estimate the average density of a plasma capillary by probing it with an ultra-relativistic electron beam. The plasma density and the generated accelerating field are inferred by analyzing the beam longitudinal phase space after its interaction with the plasma. The results are validated by simulations showing excellent agreement.

Combined effect of chromaticity and feedback on transverse head-tail instability

The resonant interaction of a bunched particle beam with short-range wakefields is the cause of head-tail instability, which is a major limitation for single-bunch beam intensity in circular accelerators. There are several processes that suppress this type of instability, such as fast chromatic damping and Landau damping due to machine nonlinearity. Beam-based feedback systems (transverse dampers) provide active suppression of the beam oscillations. The combined effect of the transverse dampers and chromaticity is discussed in this article. A brief overview of theoretical and experimental studies of the head-tail instability and its mitigation is presented. Results of experimental studies of the transverse mode coupling carried out at National Synchrotron Light Source-II are compared with the theoretical model.

Physical and mechanical properties of cement board made from oil palm empty fruit bunch fibre: A review

Oil palm empty fruit bunch (OPEFB) fibre has been introduced to replace current materials mainly such as wood fibre that was not encouraged to be used as a construction sourced due to the sustainability of wood fibres and prevents the high demand of forest resources. In Malaysia, the cultivation and use of the oil palm and its products have increased because of high market demand, and this has resulted in the abundant availability of the empty fruit bunch (EFB). The EFB fibre geometry and particle size in the EFB cement bonded boards have their own mechanical and physical properties. The fibre to cement ratios are also different to boards made out of wood fibres. This experimental research work has been conducted by other researchers. The larger the particle size, the better the compaction of EFB-CB effects of cement setting by much larger surface on the board area. Short particles lead to low values of modulus of elasticity (MOE), caused by inadequate of empty fruit bunch (EFB) particles to cement substances. Nevertheless, short particles avoid large void spaces and irregularities towards cement board. Using different Cement-EFB fibre ratio has direct influence on thickness swelling (TS), modulus of rupture (MOR), and modulus of elasticity (MOE). Strength of EFB-CB depends on the bonding between fibre and cement composites. The pre-treatment fibre was indicated where the EFB fibre composite were dimensionally stable for bonding mechanisms and could be used for both interior and exterior building utilizations based on the tested physical and mechanical properties on cement-boards.

Adiabatic matching of particle bunches in a plasma-based accelerator in the presence of ion motion

Witness beam stability and preservation of its ultra-low emittance have been identified as critical challenges toward realizing a TeV-class, plasma-based linear collider. In fact, the witness bunch parameters required by a future TeV-class collider have been expected to trigger hosing instability and background ion motion, leading to emittance degradation and, potentially, to bunch loss. Recently, it has been shown that ion motion suppresses the hosing instability, and proper longitudinal bunch shaping can eliminate the ion-motion-induced emittance growth. In this paper, we propose and analyze a plasma-based method to generate the shaped bunches that enable emittance preservation in the presence of ion motion. The method is based on an adiabatic matching procedure, where a bunch with an initially untapered profile is injected in the plasma accelerator stage with an energy low enough that ion motion effects are initially small. As the bunch accelerates, it is adiabatically compressed, ion motion is gradually triggered, and the bunch slowly but continuously readjusts itself in the ion motion-perturbed wakefield acquiring the desired taper. The production of tapered witness bunch profiles that minimize energy spread and preserve emittance for collider-relevant parameters could enable the use of plasma-based accelerators for high-energy physics applications.

Transition between Instability and Seeded Self-Modulation of a Relativistic Particle Bunch in Plasma.

We use a relativistic ionization front to provide various initial transverse wakefield amplitudes for the self-modulation of a long proton bunch in plasma. We show experimentally that, with sufficient initial amplitude [≥(4.1±0.4) MV/m], the phase of the modulation along the bunch is reproducible from event to event, with 3%-7% (of 2π) rms variations all along the bunch. The phase is not reproducible for lower initial amplitudes. We observe the transition between these two regimes. Phase reproducibility is essential for deterministic external injection of particles to be accelerated.

Single shot, nondestructive monitor for longitudinal subpicosecond bunch profile measurements with femtosecond resolution

Accurate knowledge of the charged particle bunch longitudinal (time) profile is important in the context of wakefield accelerators, Compton Light sources, x-ray SASE FELs and THz radiation sources. However, it is still a challenge to obtain this information for subpicosecond long bunches and microbunched beams with the required femtosecond (fs) resolution and nondestructively. Apart from determining the profile in a nondestructive manner, the ideal bunch diagnostic would enable extraction of all required information in a single shot, have a sufficiently high repetition rate to monitor each bunch, small footprint, good cost efficiency and reliability. In this paper we present the design of a longitudinal bunch profile monitor that can determine the charged particle bunch profile with femtosecond resolution, nondestructively and in a single shot via the spectral analysis of coherent Smith-Purcell radiation (cSPr). It is based on the simultaneous deployment of three gratings with different periodicities, each with its own set of detectors. The number of the frequency sampling points is equal to the number of the optical channels and the discrimination against background radiation is based on the different polarization properties of cSPr and background radiation. The rationales for the choices made to optimize the monitor operation will be presented and the criteria for determining the number of frequency sampling points will be discussed. The possible future developments of the monitor are also presented and discussed.

Dynamical current correlations in Cooper pair splitters based on proximized quantum dots

Entanglement of electrons is studied by means of current–current correlations in two Cooper pair splitter devices: with one and two proximized quantum dots (1QD and 2QD), in presence of intra- and inter-dot Coulomb interactions, and weakly coupled with metallic electrodes. The 1QD system, where Cooper pairs can be transmitted to the same or split to different normal electrodes, is contrasted with the 2QD device, where double occupancy of a single quantum dot is forbidden and transport is only through an inter-dot singlet due to non-local crossed Andreev reflection processes deep in the superconducting energy gap. Separating the current correlation function into components for partial currents of electrons and holes through various Andreev bound states, one can see bunching and antibunching of split particles: inter-level components between electron and hole currents flowing to different electrodes are positive, while intra-level electron–electron or hole–hole components are negative, respectively. Spectral decomposition of the frequency-dependent current cross-correlation is performed to get better insight into mechanisms of entanglement and dynamics of split Cooper pairs, and to extract various charge fluctuation processes with different relaxation times, related to electron and hole currents flowing through the Andreev bound states. Only low frequency polarization fluctuations are seen in the current cross-correlations, while various negative and positive high frequency (charge fluctuations) components compensate each other in the symmetric system.

High-Temperature Superconductor Coatings for Beam Impedance Reduction in Particle Colliders: Nonlinear Effects

Coating of surfaces facing particle beams with high-temperature superconductors (HTS) for reducing the beam coupling impedance is being considered for the next generation of hadron colliders, such as the FCC-hh at CERN, where HTS would be exposed to the high-frequency wakefields generated by the particle bunches and to the strong field of the steering magnets. In this frame, we present a simple model for the calculation of the microwave response of HTS exposed to a strong external magnetic field, which takes into account the nonlinearity of the pinning potential of the vortex lattice. The equation of motion of the vortex lattice is solved in first-order approximation, and we calculate the amplitude of the third-harmonic components in the electric field produced by vortex oscillation. We deduce the time-dependent surface impedance, which could serve as a boundary condition in the simulation codes for the calculation of beam-stability phenomena in particle accelerators. Finally, time-integration of the surface impedance allows exploring the dependence of the surface impedance on surface currents, useful for analyzing the experimental results obtained using simple resonators in terms of our model.

Nanomaterials Based Nanoplasmonic Accelerators and Light-Sources Driven by Particle-Beams

Unprecedented tens of TVm−1 fields are modeled to be realizable using novel nanoplasmonic surface crunch-in modes in nanomaterials. These relativistic nonlinear surface modes are accessible due to advances in nanofabrication and quasi-solid density sub-micron particle bunch compression. Proof of principle of TVm−1 plasmonics is provided using three-dimensional computational and analytical modeling of GeV scale energy gain in sub-millimeter long tubes having nanomaterial walls with controllable free-electron densities, $n_{\mathrm t}\sim 10^{22-24}\mathrm {cm^{-3}}$ and hundreds of nanometer core radius driven by quasi-solid electron beams, $n_{\mathrm b}\sim 0.01n_{\mathrm t}$ . Besides the tens of TeVm−1 acceleration gradients, equally strong transverse fields lead to self-focusing and nanomodulation of the beam which drive extreme beam compression to ultra-solid peak densities increasing the crunch-in field strength. Apart from ultra-solid particle beams, extreme focusing also opens up a nano-wiggler like tunable coherent $\mathrm {\mathcal {O}(100MeV)}$ ultra-dense photon source.

Cherenkov radiation and emission of surface polaritons from charges moving paraxially outside a dielectric cylindrical waveguide

We investigate the radiation from a charged particle moving outside a dielectric cylinder parallel to its axis. It is assumed that the cylinder is immersed into a homogeneous medium. The expressions are given for the vector potential and for the electric and magnetic fields. The spectral distributions are studied for three types of radiation: (i) Cherenkov radiation (CR) in the exterior medium, (ii) radiation on the guided modes of the dielectric cylinder, and (iii) emission of surface polaritons. Unlike the first two types of radiation, there is no velocity threshold for the generation of surface polaritons. The corresponding radiation is present in the spectral range where the dielectric permittivities of the cylinder and surrounding medium have opposite signs. The spectral range of the emitted surface polaritons becomes narrower with decreasing energy of the particle. The general results are illustrated for a special case of the Drude model for dispersion of the dielectric permittivity of the cylinder. We show that the presence of the cylinder may lead to the appearance of strong narrow peaks in the spectral distribution of the CR in the exterior medium. The conditions are specified for the appearance of those peaks and the corresponding heights and widths are analytically estimated. The collective effects of particles in bunches are discussed.

Ultra-monochromatic far-infrared Cherenkov diffraction radiation in a super-radiant regime

Nowadays, intense electromagnetic (EM) radiation in the far-infrared (FIR) spectral range is an advanced tool for scientific research in biology, chemistry, and material science because many materials leave signatures in the radiation spectrum. Narrow-band spectral lines enable researchers to investigate the matter response in greater detail. The generation of highly monochromatic variable frequency FIR radiation has therefore become a broad area of research. High energy electron beams consisting of a long train of dense bunches of particles provide a super-radiant regime and can generate intense highly monochromatic radiation due to coherent emission in the spectral range from a few GHz to potentially a few THz. We employed novel coherent Cherenkov diffraction radiation (ChDR) as a generation mechanism. This effect occurs when a fast charged particle moves in the vicinity of and parallel to a dielectric interface. Two key features of the ChDR phenomenon are its non-invasive nature and its photon yield being proportional to the length of the radiator. The bunched structure of the very long electron beam produced spectral lines that were observed to have frequencies upto 21 GHz and with a relative bandwidth of 10–4 ~ 10–5. The line bandwidth and intensity are defined by the shape and length of the bunch train. A compact linear accelerator can be utilized to control the resonant wavelength by adjusting the bunch sequence frequency.

Loss of transverse Landau damping by noise and wakefield driven diffusion

Landau damping of coherent modes is strongly dependent on the exact shape of the particle bunches. One often assumes that the transverse distributions in high-energy hadron colliders can be approximated by Gaussian distributions, in acceptable agreement with measurements, but known to be only a first approximation. In this paper, it is investigated how a specific change of the transverse distributions can cause a loss of Landau damping. A mechanism is introduced where the coherent modes, which are excited by noise in the machine, act back on the individual particles through wakefields. The impact is modeled as a narrow diffusion in frequency space, and therefore also in action space due to amplitude dependent detuning, which leads to a local flattening of the distribution. This distribution evolution corresponds to the drilling of a borehole in the stability diagram, i.e. a local reduction of the imaginary part of the curve. Hence, initially stable regions are changed into unstable ones at the real frequencies of the coherent modes. To mitigate this instability mechanism, one must operate the machine with a stability margin of magnitude that depends on the noise amplitude and the coherent modes. In this model, the latency is defined as the time from the start of the noise excitation, on an initially Gaussian distributed bunch, to the bunch instability. The proposed model is found to agree with results in dedicated latency experiments performed in the LHC, where bunches eventually went unstable with more than twice the detuning strength required for the stabilization of a Gaussian distribution.

Quark-Novae in the outskirts of galaxies: an explanation of the fast radio burst phenomenon

ABSTRACT We show that old isolated neutron stars in groups and clusters of galaxies experiencing a Quark-Nova phase (QN: an explosive transition to a quark star) may be the source of fast radio bursts (FRBs). Each of the millions of fragments of the ultrarelativistic QN ejecta provides a collisionless plasma for which the ambient medium (galactic/halo, the intragroup/intracluster medium) acts as a relativistic plasma beam. The Buneman and the Weibel instabilities, successively induced by the beam in the fragment, generate particle bunching and observed coherent emission at GHz frequency with a corresponding fluence in the Jy ms range. The duration, frequency drift, and the rate are in agreement with observed properties of FRBs. Repeats (on time-scales of minutes to months) are due to seeing multiple fragments each beaming at a different direction and coming in at different times. Single (non-repeating) FRBs occur when only emission from the primary fragment is within the detector’s sensitivity. Key properties of FRB 121102 (its years of activity) and of FRB 180916.J0158+65 (its ∼16 d period) are recovered. The spatial and temporal coincidence between SGR 1935+2154 and FRB 200428 finds an explanation in our model. We give testable predictions.

Diffraction at the Open-Ended Dielectric-Loaded Circular Waveguide: Rigorous Approach

An elegant and convenient rigorous approach for solving circular open-ended dielectric-loaded waveguide diffraction problems is presented. It uses the solution of corresponding Wiener-Hopf-Fock equation and leads to an infinite linear system for reflection coefficients (S-parameters) of the waveguide, the latter can be efficiently solved numerically using the reducing technique. As a specific example directly applicable to beam-driven radiation sources based on dielectric-lined capillaries, diffraction of a slow TM symmetrical mode at the open end of a circular waveguide with uniform dielectric filling is considered. A series of such modes forms the wakefield (Cherenkov radiation field) generated by a charged particle bunch during its passage along the waveguide axis. Calculated S-parameters were compared with those obtained from COMSOL simulation and an excellent agreement is shown. This method is expected to be very convenient for analytical investigation of various electromagnetic interactions of Terahertz (THz) waves (both free and guided) and charged particle bunches with slow-wave structures prospective in context of modern beam-driven THz emitters, THz accererators and THz-based bunch manipulation and bunch diagnostic systems.