Design

Our ion source is an electron bombardment source, in particular, a PIG source. The operating principle is that neutral hydrogen can be ionized when bombarded with fast electrons. These electrons are sourced from a hot filament via field-assisted thermionic emission. Here, a hot filament (tungsten) is placed in an electric field such that the combination of the thermal energy of the free electrons in the filament and the potential gradient across the filament-vacuum barrier allows electrons to escape the filament and be accelerated by the electric field in the source. In addition, the magnetic field of the cyclotron coils the electron trajectories increasing their time of flight and increasing the chance of an ionization occurring.

Construction

ISource

As with all components of the cyclotron, the goal was to produce as inexpensive a prototype as possible. Thus, we tried to manufacture the whole ion source from readily available copper plumbing components. The gas and electrical feeds are made from 1/8” refrigeration tube, the remainder of the source is constructed from 1/2” copper tubing and fittings. The electrical insulators and standoffs were made from PFTE due to its vacuum compatibility.