The S-DALINAC (Superconducting-DArmstadt-LINear-ACcelerator) is a superconducting electron accelerator at TU Darmstadt, running since 1991. It was initially constructed as a twice-recirculating accelerator with a maximum energy of 130 MeV in continuous wave (cw) operation. In 2016 it has been converted into a thrice-recirculating accelerator. A floorplan of the accelerator hall and the experimental section is given in Figure 1.
The beam is either produced in a thermionic gun with an electrostatic pre-acceleration of 250 keV or in SPIN (S-DALINAC Polarized INjector) – a source for polarized electrons with a pre-acceleration of up to 125 keV. Following both sources the beam is prepared for an acceleration with a time-structure of 3 GHz in a chopper-prebuncher section. The beam is than guided through the superconducting injector accelerator (consisting of a 5-cell and two 20-cell niobium cavities) which is able to accelerate the beam up to 10 MeV with beam currents of up to 60 µA. The injector beam can be used for the research of nuclear resonance fluorescence or it can be deflected into the main accelerator (consisting of eight 20-cell niobium cavities) for further acceleration and recirculation. In case of a recirculating set-up the injector accelerator is operated with an energy gain of up to 7.5 MeV. The main LINAC accelerates the beam up to 30 MeV per pass. Recirculating the beam up to three times leads to a final energy of up to roughly 130 MeV with a beam current of up to 20 µA. The beam is than guided into an experimental area. In this area exclusive (e,e'x) experiments can be conducted at the QCLAM spectrometer. The 169°-Lintott spectrometer is capable of high resolution inclusive (e,e’) electron scattering experiments. The low energy photon tagger NEPTUN complements the experimental capabilities.