Recent optimization of the beam-optical characteristics of the 6MV van de Graaff accelerator for high brightness beams at the iThemba LABS NMP facility

• Published in: Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms Beam interactions with materials and atoms, 2005-04, Vol.231 (1-4), p.101-105
• Main Authors: Conradie, J.L., Eisa, M.E.M., Celliers, P.J., Delsink, J.L.G., Fourie, D.T., de Villiers, J.G., Maine, P.M., Springhorn, K.A., Pineda-Vargas, C.A.
• Format: Article
• Language: English
• Subjects: Beam optics; Brightness; Emittance; van de Graaff
• ISSN: 0168-583X; 1872-9584
• DOI: 10.1016/j.nimb.2005.01.041

With the aim of improving the reliability and stability of the beams delivered to the nuclear microprobe at iThemba LABS, as well as optimization of the beam characteristics along the van de Graaff accelerator beamlines in general, relevant modifications were implemented since the beginning of 2003. The design and layout of the beamlines were revised. The beam-optical characteristics through the accelerator, from the ion source up to the analysing magnet directly after the accelerator, were calculated and the design optimised, using the computer codes TRANSPORT, IGUN and TOSCA. The ion source characteristics and optimal operating conditions were determined on an ion source test bench. The measured optimal emittance for 90% of the beam intensity was about 50πmmmrad for an extraction voltage of 6kV. These changes allow operation of the Nuclear Microprobe at proton energies in the range 1MeV–4MeV with beam intensities of tenths of a pA at the target surface. The capabilities of the nuclear microprobe facility were evaluated in the improved beamline, with particular emphasis to bio-medical samples.