Linear Accelerators

DOE-HDBK-1108-97

Radiological Training for Accelerator Facilities

Student's Guide

The Cockcroft-Walton accelerator and the van de Graaff generator have since been refined and

replaced as sources of very high-energy particles; however, they retain their importance in two

respects:

N They provide injection systems for higher-energy circular accelerators, and

N They have been improved and extended to provide higher-energy linear accelerators.

From the laboratory-sized generator of Cockcroft and Walton, the linear accelerators have grown

to the 2-mile length of the Stanford Linear Accelerator (SLAC).

Linear Accelerators

In its simplest form, a linear accelerator consists of a series of electrodes. Alternate electrodes

are connected electrically to each other, and holes bored through them permit the passage of the

beam.

The electric field created by the electrodes exerts a force on the charged particles and accelerates

them.

Linear accelerators have a number of significant advantages. Chief among them is the ease with

which particles may be introduced at one end and extracted at the other. But to achieve very

high energies, accelerators must be of great length and very high voltages because the particles

must be pushed by large forces for long periods of time.

At Stanford University, a 1 billion volt (1-GeV) linear electron accelerator was completed in

1951. In a series of experiments over a period of years, the charge distributions on the nuclei

were measured for many elements. In recognition of the importance of this series of

experiments, Professor Hofstadter was awarded the Nobel Prize in Physics in 1961.