Progress of the Felsenkeller shallow-underground 5 MV accelerator for nuclear astrophysics

In the case of astrophysically important reactions, cross section measurements at or near the Gamow energy require high-intensity accelerators, long running times of typically one year per experiment, and ultra low background [1]. The highly successful LUNA 0.4MV accelerator in Gran Sasso, Italy, has pioneered this field with data on several nuclear reactions of stellar hydrogen burning and of Big Bang nucleosynthesis. As a result, there is a call for one or more new underground accelerators with higher beam energy, able to address also helium and carbon burning and the neutron sources for the astrophysical s-process [2].
Such an accelerator is being installed at the Felsenkeller underground site in Dresden, Ger- many. It is shielded from cosmic radiation by 45 m of rock, reducing the muon flux by a factor of 40. An intercomparison exercise has shown that at Felsenkeller, the background in a typical nuclear astrophysics γ-ray detector is competitive to the deep-underground case in the crucial 6-8 MeV γ-ray energy range, if an additional muon veto is used.
A high-current 5MV Pelletron accelerator that was previously used in York, UK, has been bought for this purpose. It is being fitted with an internal ion source to provide intensive H+ and He+ beams in addition to the existing external sputter ion source. The site construction progress will be shown. The laboratory will be open to outside users, who are invited to form a user consortium.