**Figure 8.**

*A long arc chamber with a 3 mm slot can generate a broad ribbon beam; the uniformity and efficiency of ionization along the arc chamber is crucial.*

and by Eq. (2) this gives very high upper limits to beam current, well over 1 amp of ions at keV energies. We require the ion source to be efficient, which means trapping 60–140 eV electrons in a tight efficient zone behind the extraction slit, and then introducing a uniform distribution of gas or vapor to be ionized.

We also want an analyzing device to separate ion species with modest resolving power, useful for a number of light ions, which also has a breadth essentially unlimited by scaling laws.
