Low temperature high current ion beams and laminar flows⋆
INFN-Laboratori Nazionali di Legnaro, Viale dell’Universitá N. 2, 35020
Legnaro ( PD), Italy
Received in final form: 14 April 2014
Published online: 24 July 2014
Self-consistent Vlasov-Poisson equilibria for the extraction of ions with low temperature Ti are discussed, with comparison to the laminar flow case Ti = 0, in two dimensional diodes. Curvilinear coordinates aligned with laminar beam flow lines are extended to the low ion temperature case, with a reduced current density jd, expressed with cathode integrals. This generalizes one-dimensional interpolation between rays along the cathode coordinate to multidimensional integrations, including also the momentum components, so that jd is free from the granularity defect and noise, typical of standard ray tracing approach. A robust numerical solution procedure is developed, which allows studying current saturated extraction and drift tube effects. A discussion of particle initial conditions determines the emission angles and shows that temperature effect at beam edge is partly balanced by the focus electrode inclination. Results for a typical diode are described, with detail about normalized emittance, here taken strictly proportional to the x − px phase space area, for a beam with non uniform velocities.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2014