Nuclear astrophysics studies at LENA: The accelerators

摘要

The accelerators of the Laboratory for Experimental Nuclear Astrophysics (LENA) are described. These include a modified 1 MV Van de Graaff accelerator, a new electron cyclotron resonance (ECR) ion source with its 200 kV acceleration system, and the associated beam transport system. The new ECR ion source utilizes an array of permanent magnets to provide the 87.5 mT solenoidal magnetic field needed for ECR at 2.45 GHz. With 300 W of input radio frequency (RF) power and an extraction voltage of 15 kV, a beam current of 7 mA has been extracted from the source within a measured normalized emittance of O.197t-mm - mrad. Proton currents in excess of 1 mA can be accelerated to target from the ECR source over the energy range of 90-200 keV. Beam properties have been measured using low-energy resonances in ~(18)O(p,y)~(19)F and ~(27)Al(p,y)~(28)Si. The Van de Graaff accelerator can produce 250 uA over the energy range 0.3-1 MeV (and somewhat lower currents at lower energies). This new capability will be crucial in the direct search for low-energy resonances in nuclear reactions of astrophysical significance.