title: A 2D Particle in Cell model for ion extraction and focusing in electrostatic accelerators.
abstract: Negative ions are fundamental to produce intense and high energy neutral beams used to heat the plasma in fusion devices. The processes regulating the ion extraction involve the formation of a sheath on a scale comparable to the Debye length of the plasma. On the other hand, the ion acceleration as a beam is obtained on distances greater than λD. The paper presents a model for both the phases of ion extraction and acceleration of the ions and its implementation in a numerical code. The space charge of particles is deposited following usual Particle in Cell codes technique, while the field is solved with finite element methods. Some hypotheses on the beam plasma transition are described, allowing to model both regions at the same time. The code was tested with the geometry of the NIO1 negative ions source, and the results are compared with existing ray tracing codes and discussed.
authors.affiliation: Consorzio RFX, C.so Stati Uniti 4, 35127 Padova, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Veltri
authors.affiliation: INFN-LNL, Viale dell' Università 2, 35020 Legnaro (PD), Italy.
authors.forename: M
authors.initials: M
authors.lastname: Cavenago
authors.affiliation: Consorzio RFX, C.so Stati Uniti 4, 35127 Padova, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Serianni