P. B. Wilson

High energy electron linacs; application to storage ring RF systems and linear colliders

The theory of standing wave and travelling wave linacs is developed. Among the topics discussed are beam loading and breakup, impedances and wakes, and power sources. (AIP)

On Collinear Wake Field Acceleration

In the Voss-Weiland scheme of wake field acceleration a high current, ring-shaped driving bunch is used to accelerate a low current beam following along on axis. In such a structure, the transformer ratio, i.e. the ratio of the maximum voltage that can be gained by the on-axis beam and the voltage lost by the driving beam, can be large. In contrast, it has been observed that for an arrangement in which driving and driven bunches follow the same path, and where the current distribution of both bunches is gaussian, the transformer ratio is not normally greater than two. This paper explores some of the possibilities and limitations of a collinear acceleration scheme. In addition to its application to wake field acceleration in structures, this study is also of interest for the understanding of the plasma wake field accelerator.

A multi-moded rf delay line distribution system for the next linear collider

The Delay Line Distribution System (DLDS) is an alternative to conventional pulse compression, which enhances the peak power of rf sources while matching the long pulse of those sources to the shorter filling time of accelerator structures. We present an implementation of this scheme that combines pairs of parallel delay lines of the system into single lines. The power of several sources is combined into a single waveguide delay line using a multi-mode launcher. The output mode of the launcher is determined by the phase coding of the input signals. The combined power is extracted from the delay line using mode-selective extractors, each of which extracts a single mode. Hence, the phase coding of the sources controls the output port of the combined power. The power is then fed to the local accelerator structures. We present a detailed design of such a system, including several implementation methods for the launchers, extractors, and ancillary high power rf components. The system is designed so that it can handle the 600 MW peak power required by the NLC design while maintaining high efficiency.

The Next Linear Collider Test Accelerator

During the past several years, there has been tremendous progress on the development of the RF system and accelerating structures for a Next Linear Collider (NLC). Developments include high-power klystrons, RF pulse compression systems and damped/detuned accelerator structures to reduce wakefields. In order to integrate these separate development efforts into an actual X-band accelerator capable of accelerating the electron beams necessary for an NLC, we are building an NLC Test Accelerator (NLCTA). The goal of the NLCTA is to bring together all elements of the entire accelerating system by constructing and reliably operating an engineered model of a high-gradient linac suitable for the NLC. The NLCTA will serve as a testbed as the design of the NLC evolves. In addition to testing the RF acceleration system, the NLCTA is designed to address many questions related to the dynamics of the beam during acceleration. In this paper, we will report on the status of the design, component development, and construction of the NLC Test Accelerator.<<ETX>>

Bunch Lengthening and Related Effects in SPEAR II

In recent years, electron storage ring designers have become aware of the problems caused by the interaction of short, high current bunches with their environment. Important effects are: (1) energy loss can cause local overheating of chamber components; (2) additional rf power is required due to overall energy loss; (3) the increased energy spread requires increased aperture; (4) destructive instabilities could occur. Anomalous bunch lengthening and energy spread, the spectroscopy of longitudinal modes and the shift of synchronous phase were simultaneously measured in order to study the dynamics of the interaction. From the data obtained at SPEAR II one is led to a model of coupling impedance which should be useful in the design of any electron ring.

Low Temperature Aspects of a Cryogenic Accelerator

The object of this paper is to identify the many low temperature aspects of a cryogenic accelerator and to indicate how these are related to the operating characteristics which might ultimately be achieved.

Sheet-beam klystron RF cavities

A high-frequency sheet-beam klystron operating at a low perveance per square can produce high peak power at high efficiency. In order to provide beam stability and to maximize power extraction efficiency for a flat beam with a finite width, we have designed RF cavities in which the electric field is nearly constant across the width of the beam (on the order of several wavelengths). However, in such cavities, the electric field in the fundamental mode can couple to the TE propagating mode in the drift section if any cavity or beam asymmetry is present. The dipole field can couple between adjacent cavities even in the absence of these asymmetries as long as the frequency is above cutoff of the drift tube. The effects of coupling between RF cavities are calculated using an equivalent circuit model. Threshold parameters for onset of RF oscillation in the fundamental mode as a result of cavity coupling are obtained. We have designed choke cavities which effectively prevent such possible oscillations.<<ETX>>

Wake fields and wake field acceleration

The concepts of wake fields and wake potential are introduced, some basic properties of their functions examined and briefly a few applications are looked. (AIP)

Design of a high power sheet beam klystron

We report on theoretical studies to demonstrate the conceptual feasibility of a high‐power sheet‐beam klystron operating at 11.4 GHz. Numerical simulations are used to investigate beam dynamics and rf issues. Specific problems with the gun design, magnetic focusing, and rf coupling at the output gaps unique to the strip beam geometry of the SBK are considered. Very high efficiencies have been calculated for several values of perveance per square beam element of the SBK. We have found that a lowg‐perveance, x‐band, sheet‐beam klystron is capable of producing over 200 MW of power at 65% efficiency, using a flat electron beam with a reasonable size of 0.4 cm×16 cm, a moderate voltage of 400 Kev, a strip gun compression ratio of 10:1, a cathode loading of 124/cm2, a uniform focusing field of 3 KG, and a double‐gap standing‐wave output cavity. With only a constant longitudinal focusing field, the calculated efficiency of the SBK is among the highest of current or proposed HPM sources. (AIP)

Introduction to wakefields and wake potentials

What are wakefields and wake potentials, and why are these concepts useful in the physics of linear accelerators and storage rings? We approach this question by first reviewing the basic physical concepts which underlie the mathematical formalism. We then present a summary of the various techniques that have been developed to make detailed calculations of wake potentials. Finally, we give some applications to current problems of interest in accelerator physics. No attempt at completeness can be made in an introductory article of modest length. Rather, we try to give a broad overview and to list key references for more detailed study. It will also be apparent that the last chapter on this subject, with all the loose ends neatly tied up, has yet to be written. There are subtle points, there are controversial questions, and active calculations to resolve these questions are continuing at the time of this writing.  (AIP)