Instead of slip stacking, an alternate method of doubling the linear intensity of the Fermilab Main Injector is discussed. This method makes use of rf barriers to transfer 12 booster batches from the Fermilab Booster to the Main Injector in 12 consecutive booster cycles, totaling 800 ms. After that, adiabatic capture of the beam into 53 MHz buckets can be accomplished in about 10 ms. Because the beam is debunched during the injection process and no rf voltage is required, the beam loading voltages in the rf cavities are small and can be eliminated by a combination of counterphasing and mechanical shorts.

The appearance of rings of charge observed near the edge of beams from high-perveance guns is described with a simple ray tracing technique inspired by the particle-core model. We illustrate the technique, which has no analog in light optics, with examples from experiments employing solenoid focusing of an electron beam. The rings of charge result from the combined effects of external focusing and space-charge forces acting on paraxial fringe particles with relatively large initial transverse velocities. The model is independent of the physical mechanisms responsible for the fringe particles. Furthermore, the focal length for edge imaging in a uniform focusing channel is derived using a linearized trajectory equation for the motion of fringe particles. Counterintuitively, the focal length decreases as the beam current increases.

We discuss the choice of bunch length and crossing angle near the beam-beam limit in a storage-ring collider. First, we derive expressions for the tune shifts of either bunched or continuous round beams which are induced by a single collision with arbitrary crossing angle and bunch length and for the associated luminosities. Then, considering two collision points with alternating planes of crossing, we demonstrate that, if the total beam-beam tune shift is held constant, the collider luminosity increases as a function of bunch length and crossing angle. This implies a corresponding increase in the bunch intensity. As an illustration, we present numerical examples for a Large Hadron Collider upgrade and for the Very Large Hadron Collider.

This paper investigates the identification and correction of antisymmetric field components in combined function magnets. A measurement procedure is developed to identify small field components on the order of ${10}^{-3\mathrm{}}$ in the plane of the reference path. Furthermore, a method is proposed to compensate them by surface correction coils on the poles of the magnet. As an example, the measurement and compensation of antisymmetric field components in a $90°$ bending magnet of the double sided microtron HDSM at the MAMI-C electron scattering facility is simulated with the help of the electromagnetic design code TOSCA.

In this paper, a perturbation theory is developed for calculating the 6D transfer matrix of a combined function magnet. Starting from the linear part of the Hamiltonian, the transfer matrix $M$ is decomposed into an infinite sum over matrices $M_n$, which represent an $n$-fold interaction of the beam with the quadrupole content of the magnet. Given the magnetic field in the vicinity of the reference path, each matrix $M_n$ can be calculated either analytically or by numerical integration. As an example, the transfer matrix is calculated of the $90°$ bending magnet of the double sided microtron HDSM at the MAMI-C electron scattering facility, which so far has been possible only by means of particle tracking.

Macroparticle simulation plays an important role in modern accelerator design and operation. Most linear rf accelerators have been designed based on macroparticle simulations using longitudinal position as the independent variable. In this paper, we have done a systematic comparison between using longitudinal position as the independent variable and using time as the independent variable in macroparticle simulations. We have found that, for an rms-matched beam, the maximum relative moment difference for second, fourth moments and beam maximum amplitudes between these two types of simulations is $0.25\%$ in a 10 m reference transport system with physical parameters similar to the Spallation Neutron Source linac design. The maximum $z$-to- $t$ transform error in the space-charge force calculation of the position dependent simulation is about $0.1\%$ in such a system. This might cause a several percent error in a complete simulation of a linac with a length of hundreds of meters. Furthermore, the error may be several times larger in simulations of mismatched beams. However, if such errors are acceptable to the linac designer, then one is justified in using position dependent macroparticle simulations in this type of linac design application.

Field quality in superconducting magnets strongly depends on the geometry of the coil. Fiberglass spacers (shims) placed between the coil and the collars have been used to optimize magnetic and mechanical performances of superconducting magnets in large accelerators. A change in the shim thickness affects both the geometry of the coil and its state of compression (prestress) under operational conditions. In this paper we develop a coupled magnetomechanical model of the main Large Hadron Collider dipole. This model allows us to evaluate the prestress dependence on the shim thickness and the map of deformations of the coil and the collars. Results of the model are compared to experimental measurements carried out in a dedicated experiment, where a magnet model has been reassembled 5 times with different shims. A good agreement is found between simulations and experimental data both on the mechanical behavior and on the field quality. We show that this approach allows us to improve this agreement with respect to models previously used in the literature. We finally evaluate the range of tunability that will be provided by shims during the production of the Large Hadron Collider main dipoles.

The coherent synchrotron radiation of a bunch in a bunch compressor may lead to the microwave instability producing longitudinal modulation of the bunch with wavelengths small compared to the bunch length. It can also be a source of an undesirable emittance growth in the compressor. We derive and analyze the equation that describes linear evolution of the microwave modulation taking into account incoherent energy spread and finite emittance of the beam. Numerical solution of this equation for the Linac Coherent Light Source bunch compressor gives the amplification factor for different wavelengths of the beam microbunching.

We present the results of a detailed study on the acceleration of intense ion beams by relativistic laser plasmas. The experiments were performed at the 100 TW laser at the Laboratoire pour L’Utilisation des Lasers Intenses. We investigated the dependence of the ion beams on the target conditions based on theoretical predictions by the target normal sheath acceleration mechanism. A strong dependence of the ion beam parameters on the conditions on the target rear surface was found. We succeeded in shaping the ion beam by the appropriate tailoring of the target geometry and we performed a characterization of the ion beam quality. The production of a heavy ion beam could be achieved by suppressing the amount of protons at the target surfaces. Finally, we demonstrated the use of short pulse laser driven ion beams for radiography of thick samples with high resolution.

The nuclear science community considers the construction of the Rare Isotope Accelerator (RIA) facility as a top priority. The RIA includes a 1.4 GV superconducting linac for production of 400 kW cw heavy ion beams. The initial acceleration of heavy ions delivered from an electron cyclotron resonance ion source can be effectively performed by a 57.5 MHz 4-m long room temperature RFQ. The principal specifications of the RFQ are (i) formation of extremely low longitudinal emittance, (ii) stable operation over a wide range of voltage for acceleration of various ion species needed for RIA operation, and (iii) simultaneous acceleration of two-charge states of uranium ions. cw operation of an accelerating structure leads to a number of requirements for the resonators such as high shunt impedance, efficient water cooling of all parts of the resonant cavity, mechanical stability together with precise alignment, reliable rf contacts, a stable operating mode, and fine tuning of the resonant frequency during operation. To satisfy these requirements a new resonant structure has been developed. This paper discusses the beam dynamics and electrodynamics design of the RFQ cavity, as well as some aspects of the mechanical design of the low-frequency cw RFQ.

Electron bunches produced in self-modulated laser wakefield experiments usually have a broad energy distribution, with most electrons at low energy (1–3 MeV) and only a small fraction at high energy. We propose and investigate further acceleration of such bunches in a channel-guided resonant laser wakefield accelerator. Two-dimensional simulations with and without the effects of self-consistent beam loading are performed and compared. These results indicate that it is possible to trap about $40\%$ of the injected bunch charge and accelerate this fraction to an average energy of about 50 MeV in a plasma channel of a few mm.

ac dipoles in accelerators are used to excite coherent betatron oscillations at a drive frequency close to the tune. These beam oscillations may last arbitrarily long and, in principle, there is no significant emittance growth if the ac dipole is adiabatically turned on and off. Therefore the ac dipole seems to be an adequate tool for nonlinear diagnostics provided the particle motion is well described in the presence of the ac dipole and nonlinearities. Normal forms and Lie algebra are powerful tools to study the nonlinear content of an accelerator lattice. In this article a way to obtain the normal form of the Hamiltonian of an accelerator with an ac dipole is described. The particle motion to first order in the nonlinearities is derived using Lie algebra techniques. The dependence of the Hamiltonian terms on the longitudinal coordinate is studied showing that they vary differently depending on the ac dipole parameters. The relation is given between the lines of the Fourier spectrum of the turn-by-turn motion and the Hamiltonian terms.

An analytical formula for the wake potential of a closed spherical resonator with perfectly conducting walls is presented. Mode analysis is used for the calculation. For every rotationally symmetric TM mode the loss parameter is calculated and the formula for the determination of the corresponding frequency is given. The final wake potential is an infinite sum over all modes mentioned above.

In the presence of rf focusing and a purely inductive impedance bunch, equilibria in the form of Haïssinski distributions—when they exist—are linearly stable. This is the case whether the potential well distortion associated with the impedance causes bunch lengthening or shortening. We provide a general proof of this fact using Hamiltonian methods and energy principles. In the presence of bunch shortening our analysis indicates that there is a critical current for linear stability. However, this threshold is identical to the critical current defining the condition for the very existence of a Haïssinski equilibrium.

A relativistic electron beam moving in a circular orbit in free space can radiate coherently if the wavelength of the synchrotron radiation exceeds the length of the bunch. In accelerators coherent synchrotron radiation of the bunch is usually suppressed by the shielding effect of the conducting walls of the vacuum chamber. However an initial density fluctuation with a characteristic length much shorter than the bunch length can radiate coherently. If the radiation reaction force results in the growth of the initial fluctuation, one can expect an instability which leads to microbunching of the beam and an increased coherent radiation at short wavelengths. Such an instability is studied theoretically in this paper.

In the past, a longitudinal dipole-coupled bunch instability had limited high current operation at the Cornell Electron-Positron Storage Ring (CESR) and resulted in a degradation of luminosity performance. A longitudinal feedback system successfully damps this instability, and the exchange of superconducting rf cavities for normal conducting rf cavities in CESR has further reduced the instability's strength. A description of the longitudinal dynamics with the instability present are described in this paper along with detailed measurements of the instability using a dual-axis synchroscan streak camera. The measurements were made on single trains of bunches, multiple trains, and colliding beams. These measurements give a characterization of the instability's degradation of luminosity, modes of oscillation, and bunch distribution changes.

Luminosity-driven channeling extraction has been observed for the first time in a 900 GeV study at the Fermilab Tevatron. This experiment, Fermilab E853, demonstrated that useful TeV level beams can be extracted from a superconducting accelerator during high luminosity collider operations without unduly affecting the background at the collider detectors. Multipass extraction was found to increase the efficiency of the process significantly. The beam extraction efficiency was about 25%. Studies of time dependent effects found that the turn-to-turn structure was governed mainly by accelerator beam dynamics. Based on the results of this experiment, it is feasible to construct a parasitic 5–10 MHz proton beam from the Tevatron collider.

A novel, single shot, nondestructive scheme to measure the bunch length of submillimeter relativistic electron bunches using the electro-optical method is described. In this scheme, the birefringence induced by the electric field of the electrons converts the temporal characteristics of the bunch to a spatial intensity distribution of an optical pulse. Electric field characteristics, induced birefringence, and retardation are calculated for a few typical electron beam parameters and criteria limiting the resolution are established.

We report in this paper on full scale 2D particle-in-cell simulations investigating laser wakefield acceleration. First we describe our findings of electron beam generation by a laser propagating through a single gas jet. Using realistic parameters which are relevant for the experimental setup in our laboratory we find that the electron beam resulting after the propagation of a $0.8\mu \mathrm{m}$, 50 fs laser through a 1.5 mm gas jet has properties that would make it useful for further acceleration. Our simulations show that the electron beam is generated when the laser exits the gas jet, and the properties of the generated beam, especially its energy, depend only weakly on most properties of the gas jet. We therefore propose to use the first gas jet as a plasma cathode and then use a second gas jet placed immediately behind the first to provide additional acceleration. Our simulations of this proposed setup indicate the feasibility of this idea and also suggest ways to optimize the quality of the resulting beam.