R. B. Neal

Design of Linear Electron Accelerators with Beam Loading

The optimum design of linear electron accelerators depends upon the degree of beam loading, i.e., the fraction of the radio‐frequency power which is converted into beam power. With very light loading, the product of the radio‐frequency attenuation constant I, and the accelerator length L should be approximately 1.26 for maximum beam energy in a given length. For heavier loading the product IL must be reduced to produce maximum electron energy and maximum conversion efficiency from radio‐frequency power to electron beam power. The attenuation constant I can be chosen by the proper selection of the dimensions of the accelerating structure. Expressions and design curves are given for the optimum values of IL to maximize electron beam energy and electron beam power as a function of beam loading.

Recent Beam Performance and Developments at SLAC

The purpose of this paper is to describe recent developments at SLAC which have contributed to improvements in beam operation. The paper will be divided into two parts. The first will summarize overall beam performance and operational efficiency in delivering beams to various experiments. The second will be devoted to specific developments such as the achievement of higher energies, increasingly narrow energy spectra, higher beam breakup current thresholds, chopped beams and improvements in pulse-to-pulse operation. The discussion will include a description of various new pulsed devices such as pulsed quadrupoles, improvements in the positron source and new beam loading measurements obtained for very short pulses.

SLAC: The accelerator

LAST MAY, APPROXIMATELY four years after construction started at the Stanford Linear Accelerator Center, a beam traveled the entire two‐mile length of the accelerator from an injector at the west end to a beam dump at the east end. This machine is distinguished not only by its length and high energy (20 GeV); it also produces high current (30 microamperes), exceeding by a factor of 100 that of any other machine operating with an energy greater than 10 GeV. Moreover the design permits future expansion (from stage I to stage II) that will double both energy and current by adding radiofrequency sources along the length. Details of the design evolution appear in references 1–5.

Feasibility Study of a Two-Mile Superconducting Linac

Assuming that investigations now underway will result in superconducting accelerator structures capable of withstanding gradients of 33 MeV/m, a feasibility study of a two-mile 100 GeV superconducting electron linac with 6% duty cycle has been made at frequencies of 1428 and 2856 MHz. Tentative machine parameters and the preliminary design of components and systems have been examined. These studies are based upon a traveling-wave accelerator structure with RF feedback in each 20-ft section.