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.

Several ideas have been proposed to “condition” an electron beam prior to the undulator of a free-electron laser (FEL) by increasing each particle’s energy in proportion to the square of its transverse betatron amplitude. This conditioning enhances FEL gain by reducing the axial velocity spread within the electron bunch. We demonstrate that for symplectic beam lines, and independent of the method, this conditioning is always accompanied by a large head-tail focusing variation which, for short-wavelength FELs, is so severe as to make conditioning completely impractical. We furthermore find that any system added to correct the head-tail focusing variation will also remove the conditioning. As an example, a new method for conditioning is presented and shown to generate exactly the same head-tail focusing problems as in previously published work.

We develop a new approach to the calculation of the synchrotron radiation in a toroidal vacuum chamber. Using a small parameter $ϵ=\sqrt{a/R}$, where $a$ is the characteristic size of the cross section of the toroid and $R$ is the bending radius, we simplify Maxwell’s equations assuming that the characteristic frequency of the modes $\omega \sim c/aϵ$ and neglect terms of higher order in $ϵ$. For a rectangular cross section of the waveguide, we find an analytical solution of the equations and analyze their asymptotics at very high frequency. We then obtain an equation which gives radiation into each synchronous mode. We demonstrate the flexibility of the new method by calculating the frequencies and the loss factors for the lowest modes in square and round waveguides.

The theory and simulation of coherent resonant coupling due to space charge in coasting or bunched anisotropic equilibrium beams is presented. Our work confirms that analytical results on coherent oscillations and instabilities of anisotropic KV (Kapchinskij-Vladimirskij) distributions are a valid tool to interpret the findings from 2D and 3D self-consistent particle-in-cell simulations for both KV and waterbag distributions. With reference to rings we discuss space charge coherent tune shifts up to fourth order and introduce a coherent coupled mode coefficient, which enables us to resolve the issue of KV anomalies by relating them to negative energy modes. The second emphasis of this study is with reference to linacs and a detailed discussion of “stability charts” describing resonant regions where approach to equipartition may occur.

An intense charged particle beam with directed kinetic energy $({\gamma }_b-1)m_b{c}^2$ propagates in the $z$ direction through an applied focusing field with transverse focusing force modeled by ${\mathbf{F}}_{\mathrm{foc}}=-{\gamma }_b{m}_b{\omega }_{\beta \perp }^2{\mathbf{x}}_{\perp }$ in the smooth-focusing approximation. This paper examines properties of the axisymmetric, truncated thermal equilibrium distribution $F_b(r,{\mathbf{p}}_{\perp })=A\exp (-H_{\perp }/{\widehat{T}}_{\perp b})\oplus (H_{\perp }-E_b)$, where $A$, ${\widehat{T}}_{\perp b}$, and $E_b$ are positive constants, and $H_{\perp }$ is the Hamiltonian for transverse particle motion. The equilibrium profiles for beam number density, $n_b(r)=\int d^{2}p{F}_b(r,{\mathbf{p}}_{\perp })$, and transverse temperature, $T_{\perp b}(r)=[n_b(r){]}^{-1}\int d^{2}p(p_{\perp }^2/2{\gamma }_b{m}_b)F_b(r,{\mathbf{p}}_{\perp })$, are calculated self-consistently including space-charge effects. Several properties of the equilibrium profiles are noteworthy. For example, the beam has a sharp outer edge radius $r_b$ with $n_b(r\ge r_b)=0$, where $r_b$ depends on the value of $E_b/{\widehat{T}}_{\perp b}$. In addition, unlike the choice of a semi-Gaussian distribution, $F_b^{\mathrm{SG}}=A\exp (-p_{\perp }^2/2{\gamma }_b{m}_b{\widehat{T}}_{\perp b})\oplus (r-r_b)$, the truncated thermal equilibrium distribution $F_b(r,\mathbf{p})$ depends on $(r,\mathbf{p})$ only through the single-particle constant of the motion $H_{\perp }$ and is therefore a true steady-state solution $(\partial /\partial t=0)$ of the nonlinear Vlasov-Maxwell equations.

We consider the impedance of a structure with rectangular, periodic corrugations on two opposing sides of a rectangular beam tube. Using the method of field matching, we find the modes in such a structure. We then limit ourselves to the case of small corrugations, but where the depth of corrugation is not small compared to the period. For such a structure we generate analytical approximate solutions for the wave number $k$, group velocity $v_g$, and loss factor $\kappa$ for the lowest (the dominant) mode which, when compared with the results of the complete numerical solution, agreed well. We find if $w\sim a$, where $w$ is the beam pipe width and $a$ is the beam pipe half-height, then one mode dominates the impedance, with $k\sim 1/\sqrt{w\delta }$ ($\delta$ is the depth of corrugation), $(1-v_g/c)\sim \delta$, and $\kappa \sim 1/(aw)$, which (when replacing $w$ by $a$) is the same scaling as was found for small corrugations in a round beam pipe. Our results disagree in an important way with a recent paper of Mostacci et al. [A. Mostacci et al., Phys. Rev. ST Accel. Beams 5, 044401 (2002)], where, for the rectangular structure, the authors obtained a synchronous mode with the same frequency $k$, but with $\kappa \sim \delta$. Finally, we find that if $w$ is large compared to $a$ then many nearby modes contribute to the impedance, resulting in a wakefield that Landau damps.

The subject of high-energy density (HED) in matter is of considerable interest to many branches of physics. Intense beams of energetic heavy ions are a promising tool for creating large samples of HED matter which can be used to study the equation-of-state properties of such exotic states of matter experimentally. The Gesellschaft für Schwerionenforschung (GSI), Darmstadt, is a unique laboratory worldwide which has a heavy ion synchrotron facility, SIS18 (with a magnetic rigidity of 18 Tm), that delivers intense heavy ion beams. Using the beams generated at this present facility, interesting experimental work has been carried out in the field of HED matter [D. H. H. Hoffmann et al., Nucl. Instrum. Methods Phys. Res., Sect. B 161–162, 9 (2000)]. The GSI is planning to significantly expand its accelerator capabilities with construction of a new synchrotron ring, SIS100, which will have a magnetic rigidity of 100 Tm. This new facility will deliver a uranium beam which will have orders of magnitude higher intensity than the existing facility and will also have the possibility of multibeam acceleration. This paper presents two-dimensional hydrodynamic simulations of different target geometries including solid as well as hollow cylinders that are irradiated with beams having different shapes of the focal spot which will be available at the SIS100 facility. These include a circular focal spot, an annular focal spot, and an elliptic focal spot, respectively. The purpose of this study is to determine the region of the physical parameters including density, temperature, and pressure that can be accessed using the SIS100 beam. This information, we hope, will be useful for designing experiments on the studies of thermophysical properties of matter including the designing of appropriate diagnostic tools.

We employ Abel’s transform to derive an analytic expression for filtering an equilibrium distribution function from its longitudinal beam profile. The result can be applied to a large class of Hamiltonians that are quadratic in the momentum coordinate.

The longitudinal dynamics and its coupling with the transverse dynamics of bunched beams with strong space charge are analyzed. We introduce a self-consistent Vlasov description for the longitudinal phase space similar to the familiar description for the transverse phase space using a Kapchinskij-Vladimirskij distribution. A longitudinal beam envelope equation is derived. An exact solution is then obtained when coupling to the transverse dynamics is ignored. This longitudinal envelope equation is coupled to the transverse envelope equation to form a set of coupled dynamical equations, which is then solved numerically. This analysis is prompted by the surprising results of recent experiments which showed that by driving an intense laser pulse into matter, which in turn creates a plasma, short bright relativistic electron bunches are produced, surprisingly narrowly focused. We find that because the space charge forces weaken with increasing transverse and longitudinal phase space, both the transverse and longitudinal emittance blowouts anticipated of bright compact bunches are mitigated by this coupling. It should be possible to capture these bunches into an rf cavity to accelerate to higher energies.