Accelerator Update

About the Fermilab Accelerators

The Fermilab chain of accelerators begins with an electrostatic pre-accelerator based on the Cockcroft-Walton design. It produces H- ions with an energy of 750 keV (1 eV = one electron volt). The H- means that an extra ion has been added to the proton, giving it an overall negative charge.

The history of the Nobel-Prize-winning Cockcroft-Walton design
In May of 1928, Ernest Walton had been trying to produce "fast electrons," realized his method of producing these particles wasn't going to work - his problem was that the lighter the particle (ions have very little mass) the higher the voltage requirements. He proposed to Sir Ernest Rutherford, then head of Cambridge University's Cavendish Laboratory, Britain, a method of accelerating positively charged particles. The proton's high mass eased the need for high voltages at high frequencies.

John Cockcroft had also proposed using protons as a means of disintegration. Walton built most of the high voltage and accelerator apparatus while Cockcroft solved many of Walton's engineering problems.

The final Cockcroft-Walton machine, completed at Cavendish in 1932, was the first linear accelerator. Their work on the transmutation of lithium not only corroborated Gamow's theory of tunneling, but it was the initial verification of Einstein's law concerning the equivalence of mass and Energy, E=mc².

The larger machines of the 1950s and 60s and high-energy physics as we know it are a direct result of the fundamental research performed by John Cockcroft and Ernest Walton. As Rutherford said, "it's the first step that counts."

The figure is a diagram of the original Cockcroft-Walton accelerator at the Cavendish Laboratory, Cambridge, c. 1932. In 1951, during Professor I. Waller's presentation of the Nobel Prize in Physics to Sir John Cockcroft, Waller said:

"The work Cockcroft and Walton was a bold thrust forward into a new domain of research. Great difficulties had to be overcome before they were able to achieve their first successful experiments at the beginning of 1932. By then, they had constructed an apparatus which, by multiplication and rectification of the voltage from a transformer, could produce a nearly constant voltage of about six hundred thousand volts. They had also constructed a discharge tube in which hydrogen nuclei were accelerated. Causing these particles to strike a lithium layer, Cockcroft and Walton observed that helium nuclei were emitted from lithium. Their interpretation of this phenomenon was that a lithium nucleus into which a hydrogen nucleus has penetrated breaks up into two helium nuclei, which are emitted with high energy, in nearly opposite directions. This interpretation was later fully confirmed.

Thus, for the first time, a nuclear transmutation was produced by means entirely under human control."