High intensity capillary gas ion source for accelerator applications

An ion source based on the field ionization of a gas flowing out from a small capillary was developed and investigated. The source consists of a metallic nozzle with a small hole of 5-20 µm in diameter and the tip radius of about 20-50 µm, a tungsten needle inside the nozzle, and an extractor. If the nozzle is sharp enough the ion source can also operate without a tungsten tip. The gas was introduced into the nozzle under the pressure of 0.1-1 bar leading to the rest gas pressure near the source in the vacuum chamber in the range of 10^-4 - 10 ^-5 mbar. Also liquids can be ionized in the ion source. Argon, helium, nitrogen and organic liquids like alcohol and acetone were used for measurements. I-V characteristics of the source, energy distributions and mass spectra of the emitted ions were investigated in a test stage. An emission current up to several hundreds of µA could be emitted, corresponding to current densities up to 20-50 A/cm ².
The ion source shows a long term stable operation with noble gases (several days) in the vacuum test stage. This source can be used for high and low energy micro-beams as well as in focused ion beam systems. In combination with a charge-exchange canal it can be also applied in tandem accelerators.