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EicC is a highly polarized electron-ion collider proposed by the Institute of Modern Physics, Chinese Academy of Sciences. The center of mass collision energy is between 15-20 GeV. EicC aims at a peak luminosity of 2×1033 cm-2·s-1 for electron-proton collision. In the electron-proton collision mode, the electron ring (eRing) and proton ring (pRing) of EicC have 256 and 448 bunches, respectively. Since the number of bunches in the two rings is different, when some bunches in one beam are missing, the effect of the missing bunches will be transmitted to multiple electron and proton bunches through beam-beam interactions, which may cause instability. In order to investigate the effect of missing bunches on the beam stability, self-consistent beam-beam effect simulations were performed using the AthenaGPU program, and the dipole instability was analyzed under linear approximation using the AthenaMatrix program. In the case of missing electron bunches, the simulation results show that missing any number of bunches does not cause beam instability but only affects the luminosity at equilibrium and the luminosity degradation rate. After scanning the electron beam-beam parameter using the matrix method, the results show that the instability growth rate in the horizontal direction is the same as that without missing electron bunches, regardless of the number of missing bunches. The vertical instability growth rate decreases as the number of missing bunches increases. Under the current beam parameters and only considering the effect of missing bunches on beam instability, EicC allows any number of electron bunches to be missing. The dipole instability occurs in the vertical direction when one proton bunch is missing. When two proton bunches are missing, quadrupole instability occurs in the horizontal direction, and after the amplitude of the quadrupole oscillation increases to a large value, the bunch centroid also starts to oscillate. When three proton bunches are missing, the beams show dipole instability in the vertical direction, similar to the case in which one proton bunch is missing, and quadrupole instability in the horizontal direction, similar to the case in which two proton bunches are missing. When more proton bunches are missing, no instability is observed in the simulation, but the luminosity is lower than expected. The above instabilities that appear in the horizontal and vertical directions can be avoided by adjusting the electron beam’s horizontal and vertical nominal tunes to 0.60 and 0.58, respectively. Although the dipole or quadrupole instability can be avoided by adjusting the nominal tunes to move the beams out of the instability region, it does not necessarily suppress the negative effect of missing bunches on bunch size.

Investigation of instabilities that emerge in the interaction of a charged-particle beam with elements of the chamber of state-of-the-art synchrotron radiation sources and colliders is an important task, since the beam parameters required in such facilities can only be attained if such effects are taken into account. Conditions for the development of a microwave instability in the USSR, a fourth-generation 6-GeV synchrotron radiation source with an emittance of 70 pm under design, are analyzed. The options to reduce its effect on the parameters of the beam accumulated in the accelerator ring and, as a result, on the output parameters of the facility are investigated. [ABSTRACT FROM AUTHOR]

In this article we aim to investigate the kinetic turbulence in a reconnecting current sheet (RCS) with X- and O-nullpoints and to explore its link to the features of accelerated particles. We carry out simulations of magnetic reconnection in a thin current sheet with 3D magnetic field topology affected by tearing instability until the formation of two large magnetic islands using particle-in-cell (PIC) approach. The model utilizes a strong guiding field that leads to the separation of the particles of opposite charges, the generation of a strong polarization electric field across the RCS, and suppression of kink instability in the “out-of-plane” direction. The accelerated particles of the same charge entering an RCS from the opposite edges are shown accelerated to different energies forming the “bump-in-tail” velocity distributions that, in turn, can generate plasma turbulence in different locations. The turbulence-generated waves produced by either electron or proton beams can be identified from the energy spectra of electromagnetic field fluctuations in the phase and frequency domains. From the phase space analysis we gather that the kinetic turbulence may be generated by accelerated particle beams, which are later found to evolve into a phase-space hole indicating the beam breakage. This happens at some distance from the particle entrance into an RCS, e.g. about 7di (ion inertial depth) for the electron beam and 12di for the proton beam. In a wavenumber space the spectral index of the power spectrum of the turbulent magnetic field near the ion inertial length is found to be −2.7 that is consistent with other estimations. The collective turbulence power spectra are consistent with the high-frequency fluctuations of perpendicular electric field, or upper hybrid waves, to occur in a vicinity of X-nullpoints, where the Langmuir (LW) can be generated by accelerated electrons with high growth rates, while further from X-nullponts or on the edges of magnetic islands, where electrons become ejected and start moving across the magnetic field lines, Bernstein waves can be generated. The frequency spectra of high- and low-frequency waves are explored in the kinetic turbulence in the parallel and perpendicular directions to the local magnetic field, showing noticeable lower hybrid turbulence occurring between the electron’s gyro- and plasma frequencies seen also in the wavelet spectra. Fluctuation of the perpendicular electric field component of turbulence can be consistent with the oblique whistler waves generated on the ambient density fluctuations by intense electron beams. This study brings attention to a key role of particle acceleration in generation kinetic turbulence inside current sheets.

Subject and purpose. Investigation of the generation mechanisms of electromagnetic waves by the motion of charged particles in various electrodynamic systems is an actual problem of modern radiophysics and electronics. Recently, much attention has been paid to the interaction between the streams of charged particles and solid-state structures that have dispersive properties. As a rule, such structures contain plasma-like media. The basis for the generation of electromagnetic waves is the system instabilities caused by perturbations in the streams of charged particles. The stationary mode of wave generation is provided by nonlinear interactions of a charged particle beam with eigenmodes of solid-state structure. In this paper, a theoretical study of the nonlinear stabilization effect of instability of an infinitesimally thin tubular electron beam propagated along the surface of solid-state plasma cylinder has been carried out. Methods and methodology. Using Maxwell's equations and motion equation of plasma electrons based on an integrated approach (analytical and numerical) the nonlinear theory of instability of a tubular electron beam flying over a plasma cylinder has been constructed. The plasma of the cylinder was assumed collisionless. The calculations have been performed in electrostatic approximation due to the nonrelativistic velocity of the beam electrons. Results. It is shown that the nonlinear stabilization of the wave amplitude increase is realized due to the bunching of the beam electrons into bunches and their subsequent capture by the wave field. The law of the instability rise time and the wave maximum amplitude from the plasma cylinder radius has been revealed. It is established that the nonlinear stage of instability begins earlier in an electrodynamic system with a smaller radius of the plasma cylinder. In this system, the maximum value of the slow amplitude has greater value. Conclusions. The research results broaden our understanding about the physical properties of systems with plasma-like media and systematize knowledge about the excitation mechanisms of potential surface waves in electrodynamic systems that form the basis of microwave oscillators.

Nowadays a good deal of attention is focused on problems of generating electromagnetic oscillations on the basis of the interaction of charged particles with the structures containing dielectric and plasma-like media. This is due to the sufficiently high efficiency of conversion of the electron beam kinetic energy into electromagnetic radiation. The currently available theoretical results give only qualitative descriptions of experiments. Therefore, it is important to give a detailed description of such effects maximally close to the real conditions of the experiment. In this connection the detailed theoretical study of the instability of the non-relativistic infinitely thin tubular beam of electrons moving in a vacuum above a dielectric cylinder has been performed. It has been shown that either Cherenkov effect or anomalous Doppler effect occurs in relation to the distance (the impact parameter) between the beam and the dielectric.

Abstract The fast beam ion instability (FBII) in electron storage ring is widely studied by solving two coupled equations of motion for electrons and ions. The instability growth rate was estimated from the analytical method and also from the numerical method using strong–weak and strong–strong interactions among the electrons and ions. In a storage ring, several ion species exists, and each of them have different ion frequencies at different locations along the circumference, due to strong focusing lattice. This creates a spread in ion frequencies, and that helps in damping the instability effect via Landau damping. In essence, ions couple the electron beam with different oscillating frequencies. The combined contributions of multi-gas species and optics variation in the lattice are taken care by solving the fast ion instability in the wake function formalism. Here, the wake field produced by the ions is estimated following a similar procedure, which is being used for the cavity like structure inside the vacuum chamber. Since the associated wake function due to ions last for duration more than the bunch to bunch separation duration, it drives multi-bunch instability. We investigate the possibility of FBII for the Indus-2 storage ring using the growth rate formulation of conventional multi-bunch instability, and the results are presented. Also a suitable bunch filling pattern is mooted for suppression of the FBII. [ABSTRACT FROM AUTHOR]

Nowadays a good deal of attention is focused on problems of generation of millimeter and submillimeter electromagnetic waves under the interaction of fluxes of charged particles with solids. However, today there is no consistent theoretical description of this type of effects. In this connection we present the detailed theoretical research on the instability effect of non-relativistic infinitely thin hollow electron beam which moves in vacuum above a dielectric (plasma) cylinder. The calculations have been performed in electrostatic approximation due to the non-relativistic velocity of the beam electrons. The cases where the dielectric permittivity is constant and depends on the frequency have been considered. The dispersion curves of exited modes have been constructed. The dependences of the increments (decrements) of the modes on the value of the bunch radius and on the azimuth mode index have been studied. It has been shown that for both the dielectric and plasma media the largest values of the increments (decrements) of the excited modes occur for zero value of the azimuth mode index. The maximum values of the increments (decrements) decrease with increasing the azimuth mode index. It has been established that the frequency dependence of the dielectric permittivity leads to the absolute instability. This instability exists in the corresponding finite interval of the longitudinal wave number.

It is well known that electron beams accelerated in solar flares can drive two-stream instability and produce radio bursts in the solar corona as well as in the interplanetary medium. Recent observations show that the solar wind likely originates from nanoflare-like events near the surface of the Sun where locally heated plasma escapes along open field lines into space. Recent numerical simulations and theoretical studies show that electron two-stream instability (ETSI) driven by nanoflare-accelerated electron beams can produce the observed nanoflare-type radio bursts, the non-Maxwellian electron velocity distribution function of the solar wind, and the kinetic scale turbulence in solar wind. This brief review focus on the basic theoretical framework and recent progress in the nonlinear evolution of ETSI driven by electron beams, including the formation of electron holes, Langmuir wave generation in warm plasma, and the nonlinear modulation instability and Langmuir collapse. Potential applications in heliophysics and astrophysics are discussed. [ABSTRACT FROM AUTHOR]

The stability properties of transverse envelopes of mismatched intense continuous charge particle beam propagating in a general quadrupole focusing channel have been investigated in the presence of image charge effect due to a cylindrical conducting pipe. Phase shifts and growth factors of the envelope oscillations in the case of instability are calculated by numerical evaluation of the eigenvalues of linearly perturbed envelope equations for small deviations from the matched beam conditions. A detailed study on the region of instability and its dependence on the system parameters like occupancy of the quadrupole focusing field, syncopation factor, zero current phase advance, beam intensity etc. have been carried out. It has been found that the strength and regions of envelope instability due to the lattice and confluent resonances in the parametric space are affected by the presence of image charge. [ABSTRACT FROM AUTHOR]

This paper gives an overview of collective effects that are likely to appear and possibly limit the performance in a diffraction-limited storage ring (DLSR) that stores a high-intensity ultra-low-emittance beam. Beam instabilities and other intensity-dependent effects that may significantly impact the machine performance are covered. The latter include beam-induced machine heating, Touschek scattering, intra-beam scattering, as well as incoherent tune shifts. The general trend that the efforts to achieve ultra-low emittance result in increasing the machine coupling impedance and the beam sensitivity to instability is reviewed. The nature of coupling impedance in a DLSR is described, followed by a series of potentially dangerous beam instabilities driven by the former, such as resistive-wall, TMCI (transverse mode coupling instability), head-tail and microwave instabilities. In addition, beam-ion and CSR (coherent synchrotron radiation) instabilities are also treated. Means to fight against collective effects such as lengthening of the bunch with passive harmonic cavities and bunch-bybunch transverse feedback are introduced. Numerical codes developed and used to evaluate the machine coupling impedance, as well as to simulate beam instability using the former as inputs are described. [ABSTRACT FROM AUTHOR]

Abstract: The flexible behaviors in the aerospace structures can lead to undesired performance and degradation of their control and guidance system. The aims of the current work are to analyze the bending vibration of a Two Stage to Orbit (TSTO) Launch Vehicle (LV) with propulsion force modeled as a free–free jointed bipartite beam under a follower force, study its effects on oscillation of the actuators, and finally develop a solution to reduce these oscillations. The vibration analysis of the beam model is carried out using Ritz method. The rigid dynamics of a TSTO LV in the pitch channel was then modeled and modified using the vibrational model of the device for the same channel. A new dynamic model with an adaptive control system for a TSTO LV has been developed, allowing the aerospace structure to run on its maximum bearable propulsion force with the optimum effects on the oscillation of its actuators. Simulation results show that such a control model provides an effective way to reduce the undesirable oscillations of the actuators. [Copyright &y& Elsevier]

Abstract: Beam instability caused by the electron cloud has been observed in positron and proton storage rings and it is expected to be a limiting factor in the performance of the positron damping ring (DR) of future linear colliders (LC) such as ILC and CLIC . To test a series of promising possible electron cloud mitigation techniques as surface coatings and grooves, in the Positron low-energy ring (LER) of the PEP-II accelerator, we have installed several test vacuum chambers including (i) a special chamber to monitor the variation in the secondary electron yield of technical surface materials and coatings under the effect of ion, electron and photon conditioning in situ in the beam line (ii) chambers with grooves in a straight magnetic-free section and (iii) coated chambers in a dedicated newly installed 4-magnet chicane to study mitigations in a magnetic field region. In this paper, we describe the ongoing R&D effort to mitigate the electron cloud effect for the LC damping ring, focusing on the first experimental area and on results of the reduction in the secondary electron yield due to in situ conditioning. [ABSTRACT FROM AUTHOR]

In this paper a free-free uniform beam with damping effects subjected to follower and transversal forces at its end is considered as a model for a space structure. The effect of damping on the stability of the system is first investigated and the effects of the follower and transversal forces on the vibration of the beam are shown next. Proportional damping model is used in this work, hence, the effects of both internal (material) and external (viscous fluid) damping on the system are noted. In order to derive the frequency of the system, the Ritz method has been used. The mode shapes of the system must therefore be extracted. The Newmark method is utilized in the study of the system vibration. The results show that an increase in the follower and transversal forces leads to an increase of the vibrational motion of the beam which is not desirable. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of the instability regions of a free-free flexible jointed bipartite beam under the follower and transversal forces as a realistic simulation of a two-stage aerospace structure. The aim of this study is to analyze the effects of the characteristics of a flexible joint on the beam instability to use maximum bearable propulsion force. A parametric study is conducted to investigate the effects of the stiffness and the location of the joint on the critical follower force by the Ritz method and the Newmark method, then to research the vibrational properties of the structure. It has been shown that the nature of instability is quite unpredictable and dependent on the stiffness and the location of the joint. The increase of the follower force or the transversal force will increase the vibration of the model and consequently cause a destructive phenomenon in the control system of the aerospace structure. Furthermore, this paper introduces a new concept of the parametric approach to analyze the characteristics effects of a flexible two-stage aerospace structure joint design. [ABSTRACT FROM AUTHOR]

Abstract: Beam instability caused by an electron cloud is one of the limiting factors in the performance of future advanced positron and proton storage rings. At a wiggler section in the positron ring of the KEK B-factory (KEKB), we installed a test beam chamber with a replaceable insertion and investigated different techniques for the mitigation of electron-cloud effect in a high magnetic field. All techniques were investigated under identical conditions. In this study, the insertions with an isosceles-triangular groove surface and a flat surface were investigated and compared. The groove insertion was composed of grooves running longitudinally along the beam orbit in order to reduce the beam impedance. In this experiment, a large reduction of almost one order of magnitude in the measured electron-cloud current was observed when the groove surface was used instead of the flat one. This is the first experimental demonstration of the concept of the groove surface in a magnetic field. The results are also compared with those obtained in a previous experiment in which a clearing electrode insertion was used. [Copyright &y& Elsevier]

Abstract: In the beam pipe of high-intensity positron/proton storage rings, undesired electron clouds may be first produced by photoelectrons and the ionization of residual gases; then the clouds increase by the secondary electron emission. In this study, a strip-line clearing electrode has been developed to mitigate the electron-cloud effect in high-intensity positron/proton storage rings. The electrode is composed of a thin tungsten layer with a thickness of 0.1mm formed on a thin alumina ceramic layer with a thickness of 0.2mm. The narrow alumina gap between the electrode and the beam pipe decreases the beam impedance and also enhances the heat transfer from the electrode to the beam pipe. A test model has been installed in the KEK B-factory (KEKB) positron ring, along with an electron monitor with a retarding grid. The electron density in a field free region decreased by one order of magnitude was observed on the application of ±500V to the electrode at a beam current of 1.6A with 1585 bunches. The reduction in the electron density was more drastic in a vertical magnetic field of 0.77T, that is, the electron density decreased by several orders by applying +500V to the electrode at the same beam current. This experiment is the first experiment demonstrating the principle of the clearing electrode that is used to mitigate the electron-cloud effect in a positron ring. [Copyright &y& Elsevier]

Stability properties of the resistive hose instability is investigated for a rounded current-density profile of a charged particle beam propagating through a background plasma where the electron collision time (1/vc) is comparable to or longer than the magnetic decay time (Td). The eigenvalue equation is derived based on the energy group model, including the stabilizing influence of a finite magnetic decay time. The dispersion relation of the resistive hose instability in a charged particle beam with an arbitrary current density profile is derived, assuming that the eigenfunctions can be represented by the rigid displacement of the self magnetic field in the plasma. Stability analysis for perturbations propagating through the beam pulse, from its head to tail is carried out for an arbitrary current profile of the beam. It is shown from the stability analysis that the width of the range Ω² corresponding to instability decreases drastically as the value of parameter VcTd decreases from infinity to zero, thereby being a very narrow bandwidth of instability. It is also shown for arbitrary current profile that any perturbation with frequency Ω higher than the maximum betatron frequency ωβm is stable. Here, Ω is the Doppler-shifted frequency seen by beam particles. [ABSTRACT FROM AUTHOR]

Laser gain of the NIJI-IV compact storage-ring-based Free Electron Laser (FEL) system at AIST reached ∼9% at 200 nm for an average beam current of 16.3 mA. In addition to such a drastic gain enhancement, improvement of the laser-cavity performance has led to successful FEL lasing in the vacuum ultraviolet below 200 nm even in a compact system. Temporal and spectral characteristics of the NIJI-IV FEL were examined around 200 nm. FEL performance will be briefly discussed from the application point of view. [Copyright &y& Elsevier]

The stability of the electron beams and maximum share of the electrons oscillatory energy, i.e. finally efficiency, power, and pulse duration of the gyrotron to a considerable extent depend on the velocity and the energy spread (VESP) of the HEB. The basic factors determining VESP in the helical beams are discussed. Among these factors static (initial velocities, cathode heterogeneities, space charge fields) and dynamic (negative mass and diochotron instabilities and a global instability connected with the capture of the electrons in the gyrotron adiabatic trap) factors are considered. Qualitative models of the excitation of the space charge oscillation as well the parasite electromagnetic radiation of the HEB are developed. Some experimental data of the investigation of the parasitic electromagnetic radiation spectrum in one gyrotron are discussed. The methods of the experimental investigation of the VESP are described. [ABSTRACT FROM AUTHOR]