We show that, due to inaccurate calculations with a Volterra integral equation, the results obtained in the commented paper are not true. Such an awkwardness could be avoided if the authors would retain in their calculations initial conditions for the proton bunch centroid.

The authors disagree with Dr. D. V. Pestrikov’s assertion that “the results obtained in the commented paper are not true,” based on how Volterra’s integral equations are treated in the paper. The authors would agree, for clarity, that the equal sign ($=$) in Eqs. (34), (36), and (38) in the paper be replaced by some special symbol or the approximate sign ($\approx$) to indicate the omission of initial conditions. These and similar changes together with the revision to an error found by the authors have been published in a recent erratum.

The effect of “pressing out” of a short rf powerful pulse by an electron beam from a Bragg cavity pumped by a low-power input rf signal is studied. This effect occurs as a result of the transient process from the “cold” (without the electron beam) steady state of the system to the “hot” one. It is shown that the peak power of the output pulse can be significantly higher than both the pumping rf power and the electron beam power. As for the duration of the output pulse, it is fixed by the cold characteristics of the microwave system.

Model-independent analysis of beam dynamics in circular accelerators reveals spatial-temporal modes due to beam oscillations. Although such modes have been shown to be informative, their usefulness is limited by the lack of quantitative understanding in general. Here we present a simple approach to studying the modes analytically, which results in a quantitative understanding of the modes and an algorithm to extract the physical modes by untangling the mixed singular value decomposition modes. Particularly, we focus on the coupled betatron modes that are of great interest for high-energy colliders. A simple relationship between the coupling modes and the lattice functions is established, which not only provides a quantitative understanding but also lays the foundation for using these modes to measure machine properties and beam motion in phase space.

This paper presents a survey of the present theoretical understanding of collective processes and beam-plasma interactions affecting intense heavy ion beam propagation in heavy ion fusion systems. In the acceleration and beam transport regions, the topics covered include discussion of the conditions for quiescent beam propagation over long distances; the electrostatic Harris-type instability and the transverse electromagnetic Weibel-type instability in strongly anisotropic, one-component non-neutral ion beams; and the dipole-mode, electron-ion two-stream instability driven by an (unwanted) component of background electrons. In the plasma plug and target chamber regions, collective processes associated with the interaction of the intense ion beam with a charge-neutralizing background plasma are described, including the electrostatic electron-ion two-stream instability, the electromagnetic Weibel instability, and the resistive hose instability. Operating regimes are identified where the possible deleterious effects of collective processes on beam quality are minimized.

A concept for increasing the energy of a multibunch linear collider using plasma wakefields is examined. The realization of high beam quality and high efficiency (and high luminosity) requires more complexity than the original plasma afterburner concept proposed for doubling the energy of single bunch linear colliders. This paper discusses the possibilities of using alternate bunches in the train to drive the wake and accelerate upon it or alternately a few bunches to excite the wake and a single bunch to accelerate it. Simulation results indicate that an energy of collision/energy of linac ratio of 2.8 can be obtained with 4% energy spread and 0.29 relative luminosity by utilizing five drive bunches per accelerated bunch. The concept including transverse effects is modeled with 2D linear plasma wakefield theory.

We determine the impedance of a cylindrical metal tube (resistor) of radius $a$, length $g$, and conductivity $\sigma$ attached at each end to perfect conductors of semi-infinite length. Our main interest is in the asymptotic behavior of the impedance at high frequency $(k\gg 1/a)$. In the equilibrium regime, $k{a}^2\ll g$, the impedance per unit length is accurately described by the well-known result for an infinite length tube with conductivity $\sigma$. In the transient regime, $k{a}^2\gg g$, where the contribution of transition radiation arising from the discontinuity in conductivity is important, we derive an analytic expression for the impedance and compute the short-range wakefield. The analytic results are shown to agree with numerical evaluation of the impedance.

We investigate how collective modes and colored noise conspire to produce a beam halo with much larger amplitude than could be generated by either phenomenon separately. The collective modes are lowest-order radial eigenmodes calculated self-consistently for a configuration corresponding to a direct-current, cylindrically symmetric, warm-fluid Kapchinskij-Vladimirskij equilibrium. The colored noise arises from unavoidable machine errors and influences the internal space-charge force. Its presence quickly launches statistically rare particles to ever-growing amplitudes by continually kicking them back into phase with the collective-mode oscillations. The halo amplitude is essentially the same for purely radial orbits as for orbits that are initially purely azimuthal; orbital angular momentum has no statistically significant impact. Factors that do have an impact include the amplitudes of the collective modes and the strength and autocorrelation time of the colored noise. The underlying dynamics ensues because the noise breaks the Kolmogorov-Arnol’d-Moser tori that otherwise would confine the beam. These tori are fragile; even very weak noise will eventually break them, though the time scale for their disintegration depends on the noise strength. Both collective modes and noise are therefore centrally important to the dynamics of halo formation in real beams.

A 201.5 MHz, 50 mA, 2.0 MeV deuteron radio frequency quadrupole accelerator is proposed as the neutron generator for the neutron experiment facility project at Peking University, China. Based on better understanding of beam losses, some new optimization procedures concerning both longitudinal and transverse dynamics are adopted. Accordingly, the beam transmission efficiency is improved from 91.2% to 98.3% and the electrode length is shortened from 2.91 to 2.71 m. The fundamental physical analyses are performed to look inside the new design recipe and explain why it works.

Transverse coupling impedance measurements of the Spallation Neutron Source (SNS) beam extraction system were performed and the results are here reported. The SNS beam extraction system is composed from 14 subsystems, each of which consists of a vertical kicker magnet plus a pulse forming network (PFN). Impedance bench measurements were performed on one large and one small aperture magnet, stand-alone as well as assembled with the first-article production PFN. The impedance measuring methods to cover the interesting frequency range from below 1 to 100 MHz are described in considerable detail. The upper frequency range is properly covered by the conventional twin-wire method but it had to be supplemented at the low-frequency end by a direct input impedance measurement at the magnet busbar. Required modifications of the PFN to maintain the impedance budget are discussed. The total impedance estimate was finally obtained by quadratic scaling with vertical aperture from the two tested kicker subsystems.

During heavy ion operation, large pressure rises, up to a few orders of magnitude, were observed at CERN, GSI, and BNL. The dynamic pressure rises were triggered by lost beam ions that impacted onto the vacuum chamber walls and desorbed about ${10}^4$ to ${10}^7$ molecules per ion. The deterioration of the dynamic vacuum conditions can enhance charge-exchange beam losses and can lead to beam instabilities or even to beam abortion triggered by vacuum interlocks. Consequently, a dedicated measurement of heavy-ion induced molecular desorption in the $\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{u}$ energy range is important for Large Hadron Collider (LHC) ion operation. In 2003, a desorption experiment was installed at the Super Proton Synchrotron to measure the beam-loss induced pressure rise of potential LHC collimator materials. Samples of bare graphite, sputter coated (Cu, TiZrV) graphite, and 316 LN (low carbon with nitrogen) stainless steel were irradiated under grazing angle with $158\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{u}$ indium ions. After a description of the new experimental setup, the results of the pressure rise measurements are presented, and the derived desorption yields are compared with data from other experiments.

In recent high luminosity colliders, the finite crossing angle scheme becomes popular to gain the luminosity with multibunch or long bunch operation. Success of the KEKB factory showed that the finite crossing angle scheme has no problem achieving beam-beam parameters up to 0.05. We have studied the beam-beam interactions with and without crossing angle toward higher luminosity. We discuss how the crossing angle affects the beam-beam parameter and luminosity in the present KEKB using computer simulations. The simulations showed that crab cavities, which realize the head-on collision effectively, can be expected to double the luminosity.

We compare simulations to experiments measuring electron yield from heavy ions striking metal surfaces, in particular at grazing incidence, for 1.0 MeV potassium and 182.0 MeV gold ions striking stainless steel as measured in two recent experiments. We find the electron yield is proportional to within 3% for the potassium experiments and 13% for the gold experiments to the simulated energy deposited by the ions in a thin ($\approx 20\AA$) layer at the target surface. We discuss how nonequilibrium stopping and ion wake fields may account for the larger disagreement with the gold experiments. An analytic estimate based on specular reflection predicts the peak in simulated and measured electron yield as a function of angle to within a few percent.

In the currently envisioned configurations for heavy ion fusion, it is necessary to longitudinally compress the beam bunches by a large factor after the acceleration phase. Because the space-charge force increases as the beam is compressed, the beam size in the transverse direction will increase in a periodic quadrupole lattice. If an active control of the beam size is desired, a larger focusing force is needed to confine the beam in the transverse direction, and a nonperiodic quadrupole lattice along the beam path is necessary. In this paper, we describe the design of such a focusing lattice using the transverse envelope equations. A drift compression and final focus lattice should focus the entire beam pulse onto the same focal spot on the target. This is difficult with a fixed lattice, because different slices of the beam may have different perveance and emittance. Four time-dependent magnets are introduced in the upstream of drift compression to focus the entire pulse onto the same focal spot. Drift compression and final focusing schemes are developed for a typical heavy ion fusion driver and for the integrated beam experiment being designed by the Heavy Ion Fusion Virtual National Laboratory.

The force between two moving point charges, because of its inverse square law singularity, cannot be applied directly in the numerical simulation of bunch dynamics; radiative effects make this especially true for short bunches being deflected by magnets. This paper describes a formalism circumventing this restriction in which the basic ingredient is the total force on a point charge comoving with a longitudinally aligned, uniformly charged string. Bunch evolution can then be treated using direct particle-to-particle, intrabeam scattering, with no need for an intermediate, particle-in-cell, step. Electric and magnetic fields do not appear individually in the theory. Since the basic formulas are both exact (in paraxial approximation) and fully relativistic, they are applicable to beams of all particle types and all energies. But the theory is expected to be especially useful for calculating the emittance growth of the ultrashort electron bunches of current interest for energy recovery linacs and free-electron lasers. The theory subsumes coherent synchrotron radiation and centrifugal space charge force. Renormalized, on-axis, longitudinal field components are in excellent agreement with values from Saldin et al. [DESY Report No. DESY-TESLA-FEL-96-14, 1995; Nucl. Instrum. Methods Phys. Res., Sect. A 417, 158 (1998).]

For several processes at colliding beams, macroscopically large impact parameters give an essential contribution to the standard cross section. These impact parameters may be much larger than the transverse sizes of the colliding bunches. In that case, the standard calculations have to be essentially modified. The corresponding formulas for such a beam-size effect were given 20 years ago without taking into account correlations of particle coordinates in the beams. In the present paper we derive formulas necessary to take into account quantitatively the effect of particle correlations in the spectrum of bremsstrahlung as well as in pair production. Our results are quite different from those obtained in recent papers [V. N. Baier and V. M. Katkov, Phys. Rev. D 66, 053009 (2002); V. N. Baier and V. M. Katkov, hep-ph/0305304.]. We point out the origin of this difference.

A simple scheme for field enhancement in synchrotron radiation sources such as undulators and wigglers is proposed, which is based on the fundamental nature of the superconducting loop where the magnetic flux is preserved. A superconductor ring placed to enclose the magnetic pole works as a kind of permanent magnet. The magnetization is performed by electromagnetic induction brought by the opening movement of the magnetic gap. Since neither additional external power supplies nor current leads are necessary, high-temperature bulk superconductors can easily be implemented in this scheme. Calculations to check the effectiveness of the new concept show that the critical current density of the superconductor is crucial to the performance of the synchrotron radiation sources based on this concept. Experiments were performed to verify the principle of the proposed scheme, which gave promising results to strongly support it.

A simple analytical formula is described for bunch lengthening by a linear horizontal betatron motion in an electron storage ring. An example of calculation shows that this lengthening is larger than the intrinsic bunch shortening limit for most dispersive sections, which strongly limits the wavelength region of coherent radiation.