Capillaritron: A new, versatile ion source

The Capillaritron is an ion source consisting of a very fine bore capillary and a concentric accelerating electrode. When a gas flows through the capillary and a potential difference of several kilovolts is maintained between the capillary and an accelerating electrode, current densities exceeding 100 A/cm2 with angular current densities greater than 6 mA/steradian are obtained from a source aperture only 2.5 × 10−3 cm in diameter. The source has been tested with hydrogen, helium, and argon and appears capable of operating with any gas. A tentative theory based on the existence of a plasma inside the capillary, which is sustained by a small flow of electrons to the capillary from the beam, and a relatively large current released from the walls by excited atoms, appears consistent with observations.