Extraction of intense beams from ECR ion sources and electrostatic acceleration

Abstract

High-space charge effects and problems related to beam transport are discussed in the context of an electron cyclotron-resonance ion sources extraction and pre-acceleration low emittance line (which works as the injector of a new superconducting Radio Frequency Quadruple (RFQ) under commissioning at Laboratori Nazionali di Legnaro (LNL)) at several values of the extracted beam current. In the extractor, both the cases of short-range magnetic fringe field (virtual source approximation) and large-range fringe field are simulated. Analytical expression of ion flow and plasma sheaths are easily incorporated in the charged fluid approach and in numerical modeling with three-dimensional simulation programs, which can treat several coupled field variables and lower space dimension (known as multiphysics codes). Advantages of flexibility and of representation of finer details are remarked. Effects of plasma potential and extraction hole thickness (0.5 mm) on the plasma meniscus can be resolved, even in the context of a simulation including 1 m long objects. An example of beam injection into an acceleration tube is also given; results are consistent with the tube-design goals and with the experimentally observed parameters.