There are three requirements in making a traveling wave accelerator: longitudinal electric field, synchronization, and confinement. We present and analyze a conceptually new kind of charged particle accelerator, making use of a photonic band gap lattice for field confinement near the beam axis, and employing dielectric material to produce a speed of light synchronous longitudinal electric field. An example structure design is presented. We also discuss nonlinear effect and other configurations without higher order dipole modes. Parallel scheme and fabrication are presented.

Strong evidence for self-excited emission of coherent synchrotron radiation in the microwave spectral region was observed at the Synchrotron Ultraviolet Radiation Facility (SURF III) electron storage ring at the NIST. The microwave emission between 25 and 35 mm was dominated by intense bursts of radiation. The intensity enhancement during these bursts was on the order of 10 000 to 50 000 over the incoherent value. The shape, width, and period of the bursts depend strongly on the operational parameters of the storage ring. Coherent microwave emission was observed only when the beam was unstable, namely, during bunch-length relaxation oscillations. We report on the measurements of the microwave bursts, and correlate the data with signals from a beam monitor electrode and photodiode detector. The coherent enhancement of the radiation intensity is ascribed to spontaneous self-induced microbunching of the electrons within the bunch.

The strong-strong interactions of two colliding beams are simulated by tracking the motion of a set of macroparticles. The field generated by each distribution is evaluated using the fast multipole method together with some elements of particle-mesh methods. This technique allows us to check the exact frequencies of the coherent modes and the frequencies of oscillations of individual particles in the beam. The agreement between the simulations and analytical calculations is largely improved. Furthermore, it is an efficient method to study the coherent modes in the case of separated beams.

Diffusion bonding and brazing of high purity copper were investigated to develop procedures for joining precision machined copper components for the Next Linear Collider (NLC). Diffusion bonds were made over a range of temperatures from 400 °C to 1000 °C, under two different loading conditions [3.45 kPa (0.5 psi) and 3.45 MPa (500 psi)], and on two different diamond machined surface finishes. Brazes were made using pure silver, pure gold, and gold-nickel alloys, and different heating rates produced by both radiation and induction heating. Braze materials were applied by both physical vapor deposition (PVD) and conventional braze alloy shims. Results of the diffusion bonding experiments showed that bond strengths very near that of the copper base metal could be made at bonding temperatures of 700 °C or higher at 3.45 MPa bonding pressure. At lower temperatures, only partial strength diffusion bonds could be made. At low bonding pressures (3.45 kPa), full strength bonds were made at temperatures of 800 °C and higher, while no bonding (zero strength) was observed at temperatures of 700 °C and lower. Observations of the fracture surfaces of the diffusion bonded samples showed the effects of surface finish on the bonding mechanism. These observations clearly indicate that bonding began by point asperity contact, and flatter surfaces resulted in a higher percentage of bonded area under similar bonding conditions. Results of the brazing experiments indicated that pure silver worked very well for brazing under both conventional and high heating rate scenarios. Similarly, pure silver brazed well for both the PVD layers and the braze alloy shims. The gold and gold-containing brazes had problems, mainly due to the high diffusivity of gold in copper. These problems led to the necessity of overdriving the temperature to ensure melting, the presence of porosity in the joint, and very wide braze joints. Based on the overall findings of this study, a two-step joining method is proposed for fabricating the NLC structures. The structure would be assembled with pure silver braze inserts using a self-aligning step joint design, then the assembly would be vacuum diffusion bonded at 700 °C and 3.45 MPa pressure to seal the critical inner portion of the assembly. Finally, during the same furnace cycle, the temperature would be increased to 800 °C in order to react the silver with the copper to form a liquid braze alloy that would join and seal the outer portion of the cells together.

We present a method to generate a flat (large horizontal to vertical emittance ratio) electron beam suitable for linear colliders. The concept is based on a round-beam rf photoinjector with finite solenoid field at the cathode together with a special beam optics adapter. Computer simulations of this new type of beam source show that the beam quality required for a linear collider may be obtainable without the need for an electron damping ring.

Traditional photocathode rf gun design is based around the use of ${\mathrm{TM}}_{0,1,0}$-mode cavities. This is typically done in the interest of obtaining the highest possible gradient per unit supplied rf power and for historical reasons. In a multicell, aperture-coupled photoinjector, however, the gun as a whole is produced from strongly coupled cavities oscillating in a $\pi$ mode. This design requires very careful preparation and tuning, as the field balance and resonant frequencies are easily disturbed. Side-coupled designs are often avoided because of the dipole modes introduced into the cavity fields. This paper proposes the use of a single higher-order mode rf cavity in order to generate the desired on-axis fields. It is shown that the field experienced by a beam in a higher-order mode rf gun is initially very similar to traditional 1.5- or 2.5-cell $\pi$-mode gun fields, and projected performance in terms of beam quality is also comparable. The new design has the advantages of much greater ease of fabrication, immunity from coupled-cell effects, and simpler tuning procedures. Because of the gun geometry, the possibility also exists for improved temperature stabilization and cooling for high duty-cycle applications.

We discuss the feasibility of a digital feedback system to cure self-bunching of the electron-cooled coasting ion beam in ion-storage rings such as CELSIUS [S. Holm, A. Johansson, S. Kullander, and D. Reistad, Phys. Scr. 34, 513–532 (1986)]. Such a system is based on a fast digital filter that acts as a tunable artificial wake potential. It may also aid stable operation of accumulator rings for future spallation neutron sources or heavy ion rings used for inertial fusion energy production.

The two rings of the Relativistic Heavy Ion Collider are equipped with superconducting dipole magnets. At injection, induced persistent currents in these magnets lead to a sextupole component. As the persistent currents decay with time, the horizontal and vertical chromaticities change. From magnet measurements of persistent current decays, chromaticity changes in the machine are estimated and compared with chromaticity measurements.

This paper deals with a nonstandard method for calculating the magnetic field of planar wigglers and undulators consisting of pure permanent magnets. This method of calculation is based on certain properties of the Fourier transform. It allows the analytical expression of the Fourier transform for the planar magnetic fields through the wiggler's geometry and magnetization of its blocks. The upper theoretical limit for the amplitude of the magnetic field is derived and matched with the field amplitude of planar wigglers with standard designs. The property of universality for planar wigglers is also taken into consideration as it may greatly simplify the analysis of magnetic fields for wigglers with different designs.

We present the theoretical design and cold test of a 17 GHz photonic band gap (PBG) cavity with improved coupling from an external rectangular waveguide. The PBG cavity is made of a triangular lattice of metal rods with a defect (missing rod) in the center. The ${\mathrm{TM}}_{010}$-like defect mode was chosen as the operating mode. Experimental results are presented demonstrating that critical coupling into the cavity can be achieved by partial withdrawal or removal of some rods from the lattice, a result that agrees with simulations. A detailed design of the PBG accelerator structure is compared with a conventional (pillbox) cavity. One advantage of the PBG cavity is that its resonance frequency is much less perturbed by the input/output coupling structure than in a comparable pillbox cavity. The PBG structure is attractive for future accelerator applications.

In the past few years, the concept of a high intensity muon storage ring has been pursued as an option for the next generation neutrino source. To produce the high intensity muon beam needed for the successful operation of a neutrino source, on the order of ${10}^{20}$ muon decays per year, the phase space occupied by the muon beam must be significantly reduced before the beam is accelerated. The initial transverse emittance of the muon beam before acceleration is assumed to be $9\pi \mathrm{mm}\mathrm{rad}$. Because of the time limitation imposed by the muon lifetime, the technique employed to accomplish the desired emittance reduction is ionization cooling. In this paper we present two ionization cooling lattice designs, which use solenoidal focusing elements and liquid hydrogen absorbers to reduce the muon beam phase space. We discuss the design concepts and engineering constraints for these lattices and present simulation results obtained using a detailed tracing code with a complete model of muon-matter interactions. The reduction in transverse emittance is approximately a factor of 5. This result is within a factor of 2 of the total cooling requirements for a successful neutrino factory design and within a factor of 1.4 of the requirements for the main cooling section specified in the conceptual design of this machine.

Transverse stability with nonlinear space charge is studied within the context of coasting beams. For bare tune spreads originating from chromaticity or frequency slip, the space charge tune spread has a fairly small effect and the incoherent space charge force is well modeled by a transverse capacitance. For tune spreads due to octupoles or fringe fields, beams are more stable when the bare tune increases with betatron amplitude.

Two-beam accelerators (TBAs) have been proposed as efficient power sources for next generation high-energy linear colliders. Studies have demonstrated the possibility of building TBAs from $X$-band $\backslash (\sim 8–12\mathrm{GHz}\backslash )$ through Ka-band $\backslash (\sim 30–35\mathrm{GHz}\backslash )$ frequency regions. The relativistic klystron two-beam accelerator project, whose aim is to study TBAs based upon extended relativistic klystrons, is described, and a new simulation code is used to design the latter portions of the experiment. Detailed, self-consistent calculations of the beam dynamics and of the rf cavity output are presented and discussed together with a beam line design that will generate nearly 1.2 GW of power from 40 rf cavities over a 10 m distance. The simulations show that beam current losses are acceptable and that longitudinal and transverse focusing techniques are sufficiently capable of maintaining a high degree of beam quality along the entire beam line.

The nonlinear regime of the beam-beam instability for flat beams is considered. Excitation of coherent modes and mode interaction is studied above the threshold of instability. It is shown that the exponential growth of the linear approximation may saturate, leading to a finite growth of transverse emittance.

Stationary, self-consistent, and localized longitudinal density perturbations on an unbunched charged-particle beam, which are solutions of the nonlinearized Vlasov-Poisson equation, have recently received some attention. In particular, we address the case that space charge is the dominant longitudinal impedance and the storage ring operates below transition energy so that the negative mass instability is not an explanation for persistent beam structure. Under the customary assumption of a bell-shaped steady-state distribution, about which the expansion is made, the usual wave theory of Keil and Schnell for perturbations on unbunched beams predicts that self-sustaining perturbations are possible only (below transition) if the impedance is inductive (or resistive) or if the bell shape is inverted. Space charge gives a capacitive impedance. Nevertheless, we report numerous experimental measurements made at the CERN Proton Synchrotron Booster that plainly show the longevity of holelike structures in coasting beams. We shall also report on computer simulations of boosterlike beams that provide compelling evidence that it is space-charge force which perpetuates the holes. We shall show that the localized solitonlike structures, i.e., holes, decouple from the steady-state distribution and that they are simple solutions of the nonlinearized time-independent Vlasov equation. We have derived conditions for stationarity of holes that satisfy the requirement of self-consistency; essentially, the relation between the momentum spread and depth of the holes is given by the Hamiltonian—with the constraint that the phase-space density be high enough to support the solitons. The stationarity conditions have scaling laws similar to the Keil-Schnell criteria except that the charge and momentum spread of the hole replaces that of the beam.

Harmonic cavities have been used in storage rings to increase beam lifetime and Landau damping by lengthening the bunch. The need for lifetime increase is particularly great in the present generation of low to medium energy synchrotron light sources where the small transverse beam sizes lead to relatively short lifetimes from large-angle intrabeam (Touschek) scattering. We review the beam dynamics of harmonic radio-frequency systems and discuss optimization of the beam lifetime using passive harmonic cavities.

A draft scenario of optical stochastic cooling of muons is considered. Difficult places of this scenario are highlighted and constraints are explained. The parameters of a $2\mathrm{TeV}\times 2\mathrm{TeV}$ muon collider utilizing muons after optical stochastic cooling are presented.

We investigate algorithms for computing steady state electromagnetic waves in cavities. The Maxwell equations for the strength of the electric field are solved by a mixed method with quadratic finite edge (Nédélec) elements for the field values and corresponding node-based finite elements for the Lagrange multiplier. This approach avoids so-called spurious modes which are introduced if the divergence-free condition for the electric field is not treated properly. To compute a few of the smallest positive eigenvalues and corresponding eigenmodes of the resulting large sparse matrix eigenvalue problems, two algorithms have been used: the implicitly restarted Lanczos algorithm and the Jacobi-Davidson algorithm, both with shift-and-invert spectral transformation. Two-level hierarchical basis preconditioners have been employed for the iterative solution of the resulting systems of equations.

A vertical instability of the KEK-Photon Factory electron storage ring was observed in a multibunch mode with empty buckets (bunch gap) using a bunch-by-bunch beam diagnostic system that consisted of a high-speed light shutter and an optical betatron oscillation detector. It was clearly seen that vertical betatron frequencies of individual bunches varied along a bunch train. The dependence of the betatron frequencies on the bunch positions in the train was explained by modulation of trapped-ion density caused by passage of the beam. Agreement between experimental results and the theoretical prediction was quite good.