Bakerian Lecture: The acceleration of protons to energies above 10 GeV

Abstract

The various projects now under way to produce in the laboratory beams of protons and other elementary particles with very high energies, are often criticized as a very expensive extreme of fashion in modern physics. It is true that there has been uneconomic and unnecessary duplication of many kinds of accelerators, and that some which have been built are not being used to full advantage. However, attempts to reach in the laboratory particle energies of at least 10 GeV are essential if the frontiers of physics are to be extended. The study of the physics of particles is much concerned with the creation of both short-lived and stable particles in collisions between nucleons. In a collision between a relativistic nucleon and one which is at rest, a great concentration of energy is produced in a very small volume. This energy may be utilized, in part, to give material existence to those particles whose virtual existence is postulated by modern field theory as responsible for the nucleon interactions. Such particles are in general created in pairs—the particle and its anti-particle—as is well known in the case of the electron and its anti-particle, the positron. Energy of at least 2m 0 c 2 must be ‘compressed’ into a volume of the order of nucleon dimensions in order to create a pair of nucleons. This concentrated energy is the energy in the system moving with the centre of mass of the colliding particles, and not the energy in the laboratory system. Figure 1 shows how the energy available for the creation of pairs of particles in nucleon-nucleon collisions varies with the kinetic energy of the bombarding nucleons. Internal momentum, due to a possible structure of the nucleons, may modify these values a little, but according to Heisenberg by not more than 0⋅5 GeV.