High brilliance multicusp ion source for hydrogen microscopy at SNAKE

In order to improve the lateral resolution of the 3D hydrogen microscopy by proton–proton scattering at the Munich microprobe SNAKE, we have installed a new multicusp ion source for negative hydrogen ions manufactured by HVEE at the Munich 14 MV tandem accelerator that boosts the proton beam brilliance with the potential to reduce the beam diameter at the focal plane of SNAKE. We measured a beam brilliance B = 27 A m−2 rad−2 eV−1 directly behind the ion source that is at the space charge limit for conventional ion sources. After preacceleration to in total 180 keV beam energy we measure a slightly reduced beam brilliance of B = 10 μA mm−2 mrad−2 MeV−1. For injection into the tandem accelerator, the extracted H−-current of the multicusp source of 1 mA is reduced to about 10 μA because of radiation safety regulations and heating problems at the object slits of SNAKE. Due to beam oscillations and influences of the terminal stripper of the tandem we measured a reduced beam brilliance of 0.8 μA mm−2 mrad−2 MeV−1 in front of SNAKE at 25 MeV but still being nearly 10 times larger than measured with any other ion source.