ELECTRODE DESIGN OF THE ESS-BILBAO ACCELERATOR PROTON EXTRACTION SYSTEM ∗

The goal of extracting high proton currents from the ECR source of the ESS-Bilbao Accelerator has required comprehensive and systematic studies to find the appropriate geometric parameters for the electrode extraction system. Electrostatic and beam dynamics simulations are used to achieve a complete optimization of the accelerating electrode shapes, gap distances, and extraction electrode apertures, in order to ensure the extraction of a 70 mA proton beam from a 3.75 mm aperture radius. For the accelerating electrode shapes two different designs were mainly analyzed; the first is based on a Pierce geometry; and the second on a spherically convergent layout. Both designs consist of a tetrode system comprising a plasma electrode fed at 75 kV, followed by a puller system formed by a grounded extraction electrode separated to a certain distance from the plasma chamber, an electron repeller electrode fed at -3 kV; and finally, a fourth electrode at ground potential.