Ion source antenna development for the Spallation Neutron Source

Abstract

The operational lifetime of a radio-frequency (rf) ion source is generally governed by the length of time the insulating structure protecting the antenna survives during exposure to the plasma. Coating the antenna with a thin layer of insulating material is a common means of extending the life of such antennas. When low-power/low-duty factor rf excitation is employed, antenna lifetimes of several hundred hours are typical. When high-power, >30 kW, and high-duty cycles, ∼6%, are employed, as is the case of the Spallation Neutron Source (SNS) ion source, antenna lifetime becomes unacceptably short. This work addresses this problem by first showing the results of microanalysis of failed antennas from the SNS ion source, developing a model of the damage mechanism based on plasma-insulator interaction, using the model to determine the dimensional and material properties of an ideal coating, and describing several approaches currently under way to develop a long-lived antenna for the SNS accelerator. These approaches include thermal spray coatings, optimized porcelain enamel coatings, refractory enamel coatings, and novel antenna geometries designed to operate with low rf electric fields.