Recent achievements in studies of negative beam formation and acceleration in the tandem accelerator at Budker Institute

The source for epithermal neutron production, based on vacuum insulated tandem accelerator (VITA) is under operation at the Budker Institute of Nuclear Physics since 2006. The accelerator provides a high current DС proton beam with energy up to 2 MeV. Numerous improvements to achieve stable tandem work and increase the accelerated proton current were made in more than a decade of experimental operation. These improvements include reduction of the accelerator dark current, modifications for the secondary particles suppression in the tandem gaps, vacuum improvement, upgrades of negative ion source, introduction of additional diagnostics to control and adjust the beam injection and transport. These measures provide the upgraded tandem operation with the accelerated proton current of up 9 mA. Two new schemes of negative ion injection into the tandem were designed and tested. New schemes use the upgraded version of a Penning surface-plasma negative ion source with DС H− beam current of up 15 mA and beam pre-acceleration before injection to tandem. The recent experimental results and its comparison with numerical modelling are presented and discussed.