<p>An ion source has an arc chamber with an electron-emitting element and a repeller. A manifold assembly defines a cavity and a gas outlet configured to allow gas flow to the arc chamber. This gas outlet is closer to the repeller than the electron-emitting element. In one embodiment, the ion source has a first crucible and a second crucible. The first crucible and the second crucible are connected to the manifold assembly. In one instance, the crucibles have tamper-resistant features.</p>
