In this paper we discuss the self-stabilization of the so-called fast ion instability of an electron beam in the case when coherent oscillations of bunches can be described in the linear approximation. Such a possibility occurs due to an increase in the number of ions along the electron beam and a proportional increase in the betatron tune shifts of electrons in subsequent bunches. The tune variation along the beam results in the BNS damping of the coherent oscillations of electron bunches.

We have studied the beam dynamics in a high field separated-sector cyclotron to establish conditions required to achieve single-turn extraction. Extraction efficiency above 99% is aimed to avoid beam-induced damages. A sufficient last-turn separation and a preservation of beam quality throughout the acceleration are the prerequisites. The last-turn separation can be enhanced with the orbital precession induced by an off-centering injection as in existent lower field separated-sector cyclotrons. The beam qualities, on the other hand, are affected by the resonances traversed or approached during the acceleration. Acceleration of light nuclei to the energies of 300–400 MeV/u was especially disturbing because of the broadening of radial beamwidth upon crossing the ${\nu }_r=3\mathrm{}/2$ resonance. Tolerance to the third harmonic gradient field, which causes the resonance in lowest order, is set to be 0.1 G/cm. The integer resonance ${\nu }_z=1\mathrm{}$ can be avoided with a proper design of the yoke. The longitudinal space charge forces were also investigated to estimate the intensity limits determined by the energy spreads of beam assuming simplified charge distributions. Moreover, beam preparations for injection matching are described in view of reducing the beam losses into the extraction elements.

An essential feature of third generation storage ring based light sources is the magnetic lattice is designed with a high degree of periodicity. Tracking simulations show that if the periodicity is perturbed (by focusing errors, for example), nonlinear resonances become excited, which causes a reduction in the dynamic aperture. Therefore it is important to have a method to measure and correct perturbed periodicity. In this paper we study the effect of broken and restored periodicity at an actual third generation light source: the Advanced Light Source at Lawrence Berkeley National Laboratory. First, we show that it is possible to accurately determine the storage ring optic and thus the perturbation of the periodicity by fitting measured orbit response matrices. This method allows us to determine individual field gradient errors in quadrupoles and closed orbit errors in sextupoles. By varying individual quadrupole field strengths it is possible to correct the optic, largely restoring the lattice periodicity. A comparison is made of the performance of the storage ring before and after the optic is corrected. Measurements of the electron beam tails and the synchrotron light image reveal a large suppression in resonance excitation after the optic is corrected. Correcting the optic also improves the injection efficiency.

We study single bunch stability with respect to monopole longitudinal oscillations in electron storage rings. Our analysis is different from the standard approach based on the linearized Vlasov equation. Rather, we reduce the full nonlinear Fokker-Planck equation to a Schrödinger-like equation which is subsequently analyzed by perturbation theory. We show that the Haissinski solution [Nuovo Cimento Soc. Ital. Fis. 18B, 72 (1973)] may become unstable with respect to monopole oscillations and derive a stability criterion in terms of the ring impedance. We then discuss this criterion and apply it to a broadband resonator impedance model.

In future linear collider schemes, energy loss, as well as deterioration of the beam due to long-range wakefields, is a severe problem to be overcome. The wakefield effects in accelerator sections for these colliders are thought to be reduced either by damping, by detuning, or by a combination of both. While, in principle, damping is possible by selective coupling to dangerous higher order modes (HOMs), an alternative way is to prevent coherent excitation of these wakes by modifying a constant gradient accelerator tube in such a way that each following cell is progressively detuned in relation to the preceding ones (“detuned” or “stagger-tuned” structure). This should result in low transit time factors for the higher order modes. However, the disturbed longitudinal symmetry of the structure induces trapped modes especially in the lower dipole bands, which are again dangerous for the beam. The process of detuning suppresses the synchronous dipole modes with their extreme high loss factors, but it also produces many other HOMs with significant loss factors. Experimental results were compared with the predictions of MAFIA field calculations.

This paper deals with the evaluation of the longitudinal coupling impedance due to a charged particle traveling along the axis of an iris in a circular waveguide. The solution of the electromagnetic problem is given in terms of a dual series expansion, and some interesting developments of this technique are presented in this paper.

This work deals with the design of the Institute of Physics of the University of São Paulo (IFUSP) main racetrack microtron accelerator end magnets. This is the last stage of acceleration, comprised of an accelerating section (1.04 m) and two end magnets (0.1585 T), in which a 5.10 MeV beam, produced by a racetrack microtron booster has its energy raised up to 31.15 MeV after 28 accelerations. Poisson code was used to give the final configuration that includes auxiliary pole pieces (clamps) and auxiliary homogenizing gaps. The clamps create a reverse fringe field region and avoid the vertical defocusing and the horizontal displacement of the beam produced by extended fringe fields; Ptrace code was used to perform the trajectory calculations in the fringe field region. The auxiliary homogenizing gaps improve the field uniformity as they create a “magnetic shower” that provides uniformity of $\pm 0.3\%$, before the introduction of the correcting coils that will be attached to the pole faces. This method of correction, used in the IFUSP racetrack microtron booster magnets, enabled uniformity of $\pm 0.001\%$ in an average field of 0.1 T and will also be employed for these end magnets.

Measured angular and energetic distributions of neutrons obtained by bombarding Be, C, and U thick targets with ${}^2\mathrm{H}$ at 17, 20, and 28 MeV incident energies are reported. The data were obtained using the time-of-flight method. The energetic distributions of neutrons were determined at 0°, 5°, 10°, and 20°. The data are compared with a modelization based on stripping formalism extended for thick targets.

Beam energy loss in a cavity can be easily computed for a relativistic bunch using time-domain codes like MAFIA or ABCI. However, for nonrelativistic beams the problem is more complicated because of difficulties with its numerical formulation in the time domain. We calculate the cavity loss factors for a bunch in frequency domain as a function of its velocity and compare results with the relativistic case.

The KEK Accelerator Test Facility (KEK-ATF) was constructed to develop technologies for producing a low-emittance beam which will be required by future linear colliders. The KEK-ATF consists of an injector linac, a damping ring, and a beam extraction line. The basic optical structure of the damping ring is a FOBO lattice, which reduces the horizontal dispersion at the center of the bending magnets and, as a consequence, can produce an extremely small emittance beam. To verify the performance of such a unique, low-emittance lattice, it is crucial to measure the horizontal emittance. The horizontal emittance was measured using wire scanners in the beam extraction line. Since the horizontal beam position was not stable, we established a method to correct the measured beam size for position fluctuation (“jitter”) and we succeeded in the observation of the so far smallest horizontal emittance in any accelerator. The measured horizontal emittance was $1.37\pm 0.03\mathrm{nm}$ at a beam energy of 1.285 GeV and a bunch population of $\backslash (3–5\backslash )\times {10}^9$, in agreement with the design value of 1.27–1.34 nm at the beam energy and the bunch population.

A six-dimensional symplectic beam-beam interaction map using finite discrete slices of a strong beam is extended to infinitesimal slices. The new map is calculated under the assumption of a longitudinal Gaussian distribution with approximations. A round Gaussian beam is simulated to demonstrate accuracies of the approximations.

Experimental results are presented from the first free electron maser experiment to use a pseudospark electron source. A pulsed, 70–80 kV, 10 A electron beam of normalized brightness ${10}^{11}\mathrm{A}\mathrm{m}{}^{-2\mathrm{}}{\mathrm{rad}}^{-2\mathrm{}}$ and current density $1\mathrm{kA}\mathrm{cm}{}^{-2\mathrm{}}$ from a pseudospark electron cathode was used to produce coherent microwave radiation via a Cherenkov interaction between the electron beam and the ${\mathrm{TM}}_{01}$ mode of a 60-cm-long alumina-lined waveguide. A gain of 29 dB was measured with an output power of 2 kW in the frequency range 25.5–28.6 GHz. The experimental results were found to be consistent with numerical simulations of Cherenkov amplification.

A realistic treatment of halo formation must take into account 3D beam bunches and 6D phase space distributions. We recently constructed, analytically and numerically, a new class of self-consistent 6D phase space stationary distributions, which allowed us to study the halo development mechanism without being obscured by the effect of beam redistribution. In this paper we consider nonstationary distributions and study how the halo characteristics compare with those obtained using the stationary distribution. We then discuss the effect of redistribution on the halo development mechanism. In contrast to bunches with a large aspect ratio, we find that the effect of coupling between the $r$ and $z$ planes is especially important as the bunch shape becomes more spherical.

We derive the exact specification that a two-stage betatronic collimation insertion must satisfy to cut the halo of a proton beam down to its ultimate limit which is the aperture of the secondary collimators. Our result is a set of correlated phase advances between primary and secondary collimators. We then determine the number of jaws needed to reach a given level of performance. We also specify the optic of a momentum collimation insertion.

Starting from the Vlasov equation for the single-particle phase-space distribution of beam particles in hadron storage rings, the angle-averaged distribution function of the action variables is studied by means of projection operator. It is shown that the angle-averaged distribution function is governed by a kinetic equation similar to the Fokker-Planck equation but with a memory integral. For localized nonlinear perturbations, this kinetic equation can be further reduced to a moment map which can be iterated numerically for studying the beam-size growth in hadron storage rings. To examine the validity of this treatment, the evolution of beam size is studied with examples of integrable and nonintegrable systems. It is found that the result from the moment map agrees very well with the exact solution for the integrable example or that from multiparticle tracking for the nonintegrable example when the system is not very close to low-order resonances. The angle-averaged distribution function is a promising tool to study the effect of the space charge and beam-beam interaction on high-intensity hadron beams.

The transverse motion of beam halo particles is described by a particle-core model which uses the space-charge field of a continuous cylindrical oscillating beam core in a uniform linear focusing channel to provide the force that drives particles to large amplitudes. The model predicts a maximum amplitude for the resonantly-driven particles as a function of the initial mismatch. We have calculated these amplitude limits and have estimated the growth times for extended-halo formation as a function of both the space-charge tune-depression ratio and a mismatch parameter. We also present formulas for the scaling of the maximum amplitudes as a function of the beam parameters. The model results are compared with multiparticle simulations and we find very good agreement for a variety of initial particle distributions.

Measuring a synchronous phase shift as a function of beam current is commonly done in accelerator physics to estimate the longitudinal impedance of a storage ring vacuum chamber. This measurement is normally done with RF techniques that do not have enough accuracy to detect small phase shifts typical to the newer storage rings. In this paper we report results from a new method for precise measurement of a synchronous phase shift. Our method involves downmixing from the RF frequency to a kHz range and then using an audio DSP lock-in amplifier for the actual phase detection. This paper describes the idea and the advantages of a new method as well as its practical implementation in the apparatus we build for precise synchronous phase measurements in the Stanford Linear Collider damping rings. The results of those measurements are also presented.

Several pairs of Siberian snakes are usually required to preserve the beam polarization in a high energy proton ring. It is found that installing additional type-3 snakes in the arcs of a high energy accelerator could significantly reduce local spin perturbation between snakes and thus improve overall spin stability in the ring. The best results could be obtained when a type-3 snake is installed $1/4$ of the way into each arc.

We calculate the longitudinal impedance for small obstacles of arbitrary shape located on the surface of a round perfectly conducting pipe. Calculations are carried out in a small-angle approximation that assumes a smallness of the angle between the surface of the obstacle and the unperturbed surface of the pipe. As an illustration of the accuracy of this approach, we compare the impedance of the triangular mask and an ellipsoidal protrusion in small-angle approximation with a more general result known from the literature. We also apply our theory to the calculation of the impedance due to the roughness of the wall surface in terms of the spectral function characterizing statistical properties of the microscopic surface landscape.

An evaluation of the optical transition radiation (OTR) single particle image dimension is obtained using diffraction theory based on a realistic description of the radiation source. This approach allows the analysis of the effect of the finite size of the emitting screen and of the imaging system. The role of practical experimental conditions in treating the intensity tail problem is estimated. It is shown that, by exploiting the polarization properties of OTR, a considerable enhancement in the spatial resolution can be achieved, which becomes very similar to that of a standard point source.