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.

This article is devoted to electron beam distortions in the “electron compressor” setup for beam-beam compensation in the Tevatron collider. The effects of electron space charge force and the interaction of the electron beam with the impacting elliptical antiproton beam are studied. We make an estimate of the longitudinal magnetic field necessary to keep the electron beam distortions low.

We study the dynamics of transverse oscillations near the linear coupling resonance excited by a pair of skew quadrupoles at the Laboratório Nacional de Luz Síncrotron UVX electron storage ring through the analysis of the beam profile. Transverse coherent oscillations were excited with a fast kicker and the profile of the oscillating beam was observed by focusing visible synchrotron radiation from a bending magnet onto a fast charge-coupled device camera. Using a single resonance approximation, we calculated the border of the time-averaged transverse beam profile as a function of the complex coupling coefficient $\kappa$, which characterizes the distribution of coupling fields along the storage ring. A least-squares fit of the calculated beam profile border to the experimentally obtained isointensity contours provided a new method to determine both the modulus and the phase of $\kappa$. The values obtained for the modulus are in good agreement with those from the conventional normal mode tune separation technique, and the values obtained for the phase of $\kappa$ agree with calculations based on the model lattice and the known skew quadrupole distribution.

A new scheme of ${\mathrm{H}}^{-}$ charge-exchange injection without stripping foils is proposed. It is composed of a neutralizer of the ${\mathrm{H}}^{-}$ beam using Lorentz stripping, the colliding system of a high power laser and the ${\mathrm{H}}^0$ beam to excite ${\mathrm{H}}^0$ atoms to the $3P$ state using the Rabi oscillation, and a magnet to strip the ${\mathrm{H}}^0\left(3P\right)$ to a proton beam by Lorentz stripping. The necessary laser wavelength, laser power, magnetic-field gradient, and maximum magnetic field are estimated for a beam energy from 1.0 to 3.0 GeV. The result shows that such a scheme is sufficiently feasible for ${\mathrm{H}}^{-}$ beams with an energy discussed here.

We have studied the autophasing conditions in long linear accelerators for a phase advance scaling along the machine instead of the usual beta scaling. A new lattice scaling provides the damping of the resonant enlargement of bunches in transverse wakefields with small required correlated energy spread in the bunch. In addition, such an approach allows one to keep the amplitude of coherent betatron oscillations small by a proper choice of the phase advance at the first cell. It is shown that the scaling of the phase advance per cell gives significant advantages with respect to singlebunch and multibunch instabilities.

Results are presented for electron beam transport experiments in a 1-m-long straight section consisting of a solenoid and five short printed-circuit quadrupoles. A linear computer code for rms envelope matching, SPOT, is used for channel design, while final simulations with more realistic elements are obtained with a $2\frac{1}{2}\mathrm{D}$ version of WARP, a particle-in-cell code. Reasonable agreement is found between calculations and the effective beam envelope obtained from pictures of the beam on a movable phosphor screen. The results validate, within experimental errors, the use of short magnetic quadrupoles for the transport of space-charge dominated beams. The straight section constitutes the prototype matching section for an electron recirculator to be built at the University of Maryland.

We report experimental results on the high peak current electron beam generated at the Argonne Wakefield Accelerator facility for wakefield applications. The facility produces bunch charges in the range 15–100 nC by using a photocathode based RF electron gun. The energy of the beam is 14 MeV. Our measurements show that for bunches of 100 nC, the pulse length can be as short as 30 ps. A detailed systematic study of pulse length versus charge is reported, as well as comparisons with numerical simulations. Dark current beam loading in the high field RF gun is also discussed.

Transverse mode coupling instability is one of the major limitations of a single bunch current in storage rings. Until now it has appeared in large electron-positron machines, while its presence in proton colliders has not been observed. This paper describes a theoretical analysis of the effect of longitudinal variation of the betatron tune on the transverse mode coupling instability. This variation can be introduced by an RF quadrupole. In the result, the instability threshold could be significantly increased when a modulation of the betatron frequency is comparable with the synchrotron tune.

The fast head-tail instability with space charge is studied using series expansion techniques, numerical simulations, and a new formulation which allows for precise estimates of growth rates and thresholds. In regimes where they are reliable, all three techniques predict that space charge suppresses the fast head-tail instability. It is found that the series expansion techniques are unreliable for parameter regimes commonly employed in hadron accelerators. The numerical techniques are less prone to error, but the computational requirements become severe as space charge tune shifts increase. The new model has neither of these problems, but it underestimates the benefits of chromaticity, at least in its simplest form.

The exact solution of the classical nonlinear equation of motion for a relativistic electron in the field of two electromagnetic (EM) waves is obtained. For the particular case of the linearly polarized standing EM wave in the planar optical cavity, intensity of the nonlinear Compton scattering, the time of flight, and the momentum variation after the relativistic electron passes along the cavity axis are calculated in weak and strong field limits. These effects depend on the initial phase of the EM wave at the electron entrance into the cavity and can be used for producing, diagnostics, and acceleration of relativistic electron (positron) microbunches.

The proton driver for the muon collider must produce short pulses of protons in order to facilitate muon cooling and operation with polarized beams. In order to test methods of producing these bunches, we have operated the alternating-gradient synchrotron near transition and studied procedures which involved moving the transition energy ${\gamma }_t$ to the beam energy. We were able to produce stable bunches of $3–5\times {10}^{12}$ protons with rms widths of $\sigma =2.0\mathrm{}–2.7\mathrm{ns}$ for longitudinal bunch areas of $1.5\mathrm{eV}\mathrm{s}$, in addition to making measurements of the lowest two orders of the momentum compaction factor.

This article presents results of wideband seismic measurements at the Fermilab site, namely, in the tunnel of the Tevatron and on the surface nearby, as well as in two deep tunnels in the Illinois dolomite, thought to be a possible geological environment of the Fermilab future accelerators.