This paper presents the first experimental results of the transverse profile measurements using a vibrating wire scanner at the Yerevan synchrotron injector electron beam (6 nA after collimation). The advantage of this novel technique is that there is no need for secondary radiation or particle detectors. The local beam intensity is measured using the natural oscillation frequency of the wire, which is a function of the wire temperature.

Most studies of coherent synchrotron radiation (CSR) have considered only the radiation from independent dipole magnets. However, in the damping rings of future linear colliders, a large fraction of the radiation power will be emitted in damping wigglers. In this paper, the longitudinal wakefield and impedance due to CSR in a wiggler are derived in the limit of a large wiggler parameter $K$. After an appropriate scaling, the results can be expressed in terms of universal functions, which are independent of $K$. Analytical asymptotic results are obtained for the wakefield in the limit of large and small distances, and for the impedance in the limit of small and high frequencies.

A large-scale Vlasov simulation study of the microwave instability below transition energy in a beam confined between two barrier pulses is performed. Starting from a matched distribution function for the confined ion beam including the space charge impedance the stability threshold in the longitudinal impedance plane is obtained. A simple stability criterium is found to be in good agreement with the simulation results.

A nondestructive beam energy-spread monitor using multi-strip-line electrodes has been newly developed in order to measure and control the energy spread of a single-bunch electron beam at an $180°$ arc with a beam energy of 1.7 GeV in the KEKB injector linac. The detection principle is described based on a multipole-moment analysis of an electromagnetic field generated by a charged beam. A proof-of-principle experiment was performed to verify the analysis. The result shows that taking into account the second-order moment derived from the multipole-moment analysis, the analyzed transverse beamwidths are consistent with those measured by a screen monitor, and the energy spreads are estimated to be $0.150\%\pm 0.007\%$ and $0.264\%\pm 0.004\%$ for electron beams with charges of 0.9 and $8\mathrm{nC}/\mathrm{bunch}$ at the rf phase of the energy-spread minimum, respectively. In this report we describe in detail the experimental result using the beam energy-spread monitor along with a theoretical multipole-moment analysis.

The formation of the beam halo in charged particle accelerators is studied in the framework of a stochastic-hydrodynamic model for the collective motion of the particle beam. In such a stochastic-hydrodynamic theory the density and the phase of the charged beam obey a set of coupled nonlinear hydrodynamic equations with explicit time-reversal invariance. This leads to a linearized theory that describes the collective dynamics of the beam in terms of a classical Schrödinger equation. Taking into account space-charge effects, we derive a set of coupled nonlinear hydrodynamic equations. These equations define a collective dynamics of self-interacting systems much in the same spirit as in the Gross-Pitaevskii and Landau-Ginzburg theories of the collective dynamics for interacting quantum many-body systems. Self-consistent solutions of the dynamical equations lead to quasistationary beam configurations with enhanced transverse dispersion and transverse emittance growth. In the limit of a frozen space-charge core it is then possible to determine and study the properties of stationary, stable core-plus-halo beam distributions. In this scheme the possible reproduction of the halo after its elimination is a consequence of the stationarity of the transverse distribution which plays the role of an attractor for every other distribution.

In the design of the vacuum chamber of a storage ring, special care has to be taken to keep the impedance as low as possible, in order to not degrade the quality of the circulating beam. Since the start of the commissioning of the Italian synchrotron light source ELETTRA in 1993, several low gap insertion vacuum chambers with internal aperture of 14 mm have been installed into the storage ring. Monitoring of their individual impedances and effects has been carried out with measurements on the electron beam after each new installation. The subsequent evolutions of the total longitudinal and transverse impedances are presented in this paper. Furthermore, in contradiction with the foreseen single-bunch effect, noticeable excitations of particular narrow band longitudinal coupled multibunch instabilities as a function of the position of the blades of the vertical scraper have been observed. In order to achieve a deeper insight of the phenomenon, an exhaustive characterization of both the longitudinal and transverse impedances of the scraper has been carried out.

We present a particle core model study of the space charge effect on high intensity synchrotron beams, with specific emphasis on the Proton Storage Ring (PSR) at Los Alamos National Laboratory. Our particle core model formulation includes realistic lattice focusing and dispersion. We transport both matched and mismatched beams through real lattice structure and compare the results with those of an equivalent uniform-focusing approximation. The effects of lattice structure and finite momentum spread on the resonance behavior are specifically targeted. Stroboscopic maps of the mismatched envelope are constructed and show high-order resonances and stochastic effects that dominate at high mismatch or high intensity. We observe the evolution of the envelope phase-space structure during a high intensity PSR beam accumulation. Finally, we examine the envelope-particle parametric resonance condition and discuss the possibility for halo growth in synchrotron beams due to this mechanism.

The dispersion relation for the resistive hose instability in a charged particle beam with a flattop density profile is derived from the linearized Vlasov-Maxwell equations. Stability properties of the resistive hose instability where the perturbations are initiated at the beam entrance are investigated. In particular, the complex eigenfrequency $\Omega$ in the dispersion relation is expressed as a function of the real oscillation frequency $\omega$ of the excitation at the beam entrance. As expected, the growth rate $\mathrm{Im}\Omega ={\Omega }_i$ decreases rapidly as the conducting wall approaches the beam ($r_w/r_b\to 1$). The growth rate also decreases substantially as the frequency ratio $\omega /{\nu }_c$ increases, where ${\nu }_c$ is the electron collision frequency. Stability properties for perturbations propagating through the beam pulse from its head to tail are also investigated. In this case, the growth rate $\mathrm{Im}\omega$ is calculated in terms of the real oscillation frequency $\Omega$ of each beam segment. It is shown that the resonance frequency $\Omega ={\Omega }_r$ corresponding to the infinite growth rate detunes considerably from the betatron frequency ${\omega }_{\beta }$ of the beam particles. It is also found that the bandwidth corresponding to instability is narrow when the plasma electron collision time ($1/{\nu }_c$) is long compared with the magnetic decay time (${\tau }_d$).

Low-energy, background electrons are ubiquitous in high-energy particle accelerators. Under certain conditions, interactions between this electron cloud and the high-energy beam can give rise to numerous effects that can seriously degrade the accelerator performance. These effects range from vacuum degradation to collective beam instabilities and emittance blowup. Although electron-cloud effects were first observed two decades ago in a few proton storage rings, they have in recent years been widely observed and intensely studied in positron and proton rings. Electron-cloud diagnostics developed at the Advanced Photon Source enabled for the first time detailed, direct characterization of the electron-cloud properties in a positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron-cloud production mechanisms and details of the beam-cloud interaction can be inferred. A significant longitudinal variation of the electron cloud is also observed, due primarily to geometrical details of the vacuum chamber. Such experimental data can be used to provide realistic limits on key input parameters in modeling efforts, leading ultimately to greater confidence in predicting electron-cloud effects in future accelerators.

The ion-hose instability is a transverse electrostatic instability which occurs on electron beams in the presence of a low-density ion channel. It is a phenomenon quite similar to the interaction between electron clouds and proton or positron beams in high-energy accelerators and storage rings. In the DARHT-2 accelerator, the 2-kA, $2\mathrm{\text{−}}\mu \mathrm{s}$ beam pulse produces an ion channel through impact ionization of the residual background gas (${10}^{-7}–{10}^{-6}\mathrm{torr}$). A calculation of the linear growth by Briggs indicates that the instability could be strong enough to affect the radiographic application of DARHT, which requires that transverse oscillations be small compared to the beam radius. We present semianalytical theory and 3D particle-in-cell simulations (using the Lsp code) of the linear and nonlinear growth of the instability, including the effects of the temporal change in the ion density and spatially decreasing beam radius. We find that the number of $e$-foldings experienced by a given beam slice is given approximately by an analytic expression using the local channel density at the beam slice. Hence, in the linear regime, the number of $e$-foldings increases linearly from head to tail of the beam pulse since it is proportional to the ion density. We also find that growth is strongly suppressed by nonlinear effects at relatively small oscillation amplitudes of the electron beam. This is because the ion oscillation amplitude is several times larger than that of the beam, allowing nonlinear effects to come into play. An analogous effect has recently been noted in electron-proton instabilities in high-energy accelerators and storage rings. For DARHT-2 parameters, we find that a pressure of $\le 1.5\times {10}^{-7}\mathrm{torr}$ is needed to keep the transverse beam oscillation amplitude less than about 20% of the rms beam radius.

Energy recovering an electron beam after it has participated in a free-electron laser (FEL) interaction can be quite challenging because of the substantial FEL-induced energy spread and the energy antidamping that occurs during deceleration. In the Jefferson Lab infrared FEL driver accelerator, such an energy recovery scheme was implemented by properly matching the longitudinal phase space throughout the recirculation transport by employing the so-called energy compression scheme. In the present paper, after presenting a single-particle dynamics approach of the method used to energy recover the electron beam, we report on experimental validation of the method obtained by measurements of the so-called “compression efficiency” and “momentum compaction” lattice transfer maps at different locations in the recirculation transport line. We also compare these measurements with numerical tracking simulations.

We present an experimental evidence of a bunch compression scheme that uses a traveling wave accelerating structure as a compressor. The bunch length issued from a laser-driven radio-frequency electron source was compressed by a factor $>3$ using an $S$-band traveling wave structure located immediately downstream from the electron source. Experimental data are found to be in good agreement with particle tracking simulations.

A particle beam of very small cross section is useful in many accelerator applications including biological and medical ones. We show the capability of the channeling technique using a micron-sized structure on a surface of a single crystal, or using a nanotube, to produce a beam of a cross section down to one square micrometer (or nanometer). The channeled beam can be deflected and thus well separated in angle and space from the primary and scattered particles. Monte Carlo simulation is done to evaluate the characteristics of a channeled microbeam. Emittances down to 0.001 nm rad, and flux up to ${10}^6\mu {\mathrm{m}}^{\mathrm{2}}$ per second, can be achieved for protons and ions.

Phase mixing of chaotic orbits exponentially distributes these orbits through their accessible phase space. This phenomenon, commonly called “chaotic mixing,” stands in marked contrast to phase mixing of regular orbits which proceeds as a power law in time. It is operationally irreversible; hence, its associated $e$-folding time scale sets a condition on any process envisioned for emittance compensation. A key question is whether beams can support chaotic orbits, and if so, under what conditions? We numerically investigate the parameter space of three-dimensional thermal-equilibrium beams with space charge, confined by linear external focusing forces, to determine whether the associated potentials support chaotic orbits. We find that a large subset of the parameter space does support chaos and, in turn, chaotic mixing. Details and implications are enumerated.

The VINCY Cyclotron (VINča CYclotron) is a multipurpose machine intended to accelerate light as well as heavy ions. To extract heavy ions with low energy and light ions an extraction system with stripping foil is used. Heavy ions with high energy will be extracted by means of an electrostatic deflector. The former extraction system will be manufactured and used first. The proposed unidirectional stripping extraction system is the optimal balance between the placement of the extraction line and the required diversity and quality of the extracted beam. The available range of extraction directions is set by geometry limitations.

Some general features of the beam emittance are discussed. The significance of rms values for the emittance calculation and emittance measurements is emphasized and it is shown that the emittance of a beam is not necessarily constant in a drift space.

Two-beam accelerators based upon relativistic klystron’s (RK’s) have been proposed as power sources for future generation linear electron-positron colliders. These drivers are susceptible to several transverse beam breakup (BBU) instabilities. An experiment to study a particular technique (the “betatron node scheme”) for ameliorating the high-frequency BBU has been performed at LBNL on a 1 MeV, 500 A induction accelerator beam. The results of this experiment are particularly important for RK, but apply to any system where the betatron phase advance between perturbing structures is an integral multiple of 180°. This phase advance is beneficial in linear accelerators as the instability growth changes from exponential to linear. In the experiment described below, the beam is contained in a solenoidal focusing channel, rf cavities are spaced every 60 cm, and growth in the transverse motion was measured as a function of phase advance. Details of the experiment and results are presented.

We have applied our simulation code POSINST to evaluate the contribution to the growth rate of the electron cloud instability in proton storage rings. In particular, we present here recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source at Oak Ridge, and updated results for the Proton Storage Ring at Los Alamos. A key ingredient in our model is a detailed description of the secondary electron emission process, including a refined model for the emitted energy spectrum, and for the three main components of the secondary yield, namely, the true secondary, rediffused and backscattered components.