Lawrence’s Cyclotron

I’ll be posting some cool nerdy stuff tech from the past on this blog during the research phase for the new novel SITE Z. The story takes place during World War II and revolves around super-weapon development, including the uranium bomb. One of the early problems to overcome was efficiently separating U235 from U238. Ernest O. Lawrence patented (although Leo Slizard invented) a cyclotron in 1934. Lawrence was a physicist at the Berkley Radiation Laboratory at the University of California.

A cyclotron accelerates charged particles from the center outward in a spiral trajectory, held within the cyclotron by a magnetic field. The particles are accelerated by a pulsed electric field. Check out the figure below from Lawrence’s 1934 patent to see how it works.

Looking at Fig. 1, components 1 and 2 are electrodes and are ‘semicylindrical hollow plates’ closed on the outer diameter but open facing each other. Component 4 is a high frequency oscillator that produces a pulsating electric field to accelerate the ions. Ions or electrically charged particles are inserted into the space between the two electrodes 1 and 2. this is where the pulsating electric field is concentrated. The ions accelerate and spiral outward and are held in check by the magnetic field provided by magnets (Fig 2, component 3), unless they are allowed to eject from the cyclotron. Look at the bottom left of Fig. 1 where there’s an arrow pointing out of electrode 2 and labeled High Speed Ions.

One of the cool things about cyclotrons are relativistic considerations. As ions approach the speed of light their mass increases. In the early cyclotron shown here the frequency of the  pulsating electric field is held constant.

This is a clever machine and Lawrence was convinced that a device based on its principles could separate U235 from U238 and provide fissionable material for a bomb.