A novel spectrometer concept for exotic nuclear structure research at the elec- tron/ion collider ELISe at FAIR*

Electron scattering on stable target nuclei has been the most reliable tool to study nuclear structure. This tool will be available for the investigation of exotic nuclei at the electron-ion collider ELISe at FAIR. The ELISe facility is based on the colliding storage rings EAR and NESR for electrons and ions, respectively. The main instrument of ELISe will be an electron spectrometer that accepts a large fraction of scattering angles. The spectrometer consists of a Pre-Deflector (PD), a Quadrupole (Q), a Hexapole (H) and a vertically bending Dipole (D) magnets [1,2]. This spectrometer allows to measure scattering angles as small as 10 ̊ all the way to backward angles of approximately 60 .̊ The conceptual design study with a vertically opening gap but constant field PD [1] was completed. The next task is the optimization of the final lay-out for the ELISe spectrometer. In order to verify the conceptual design and to establish design parameters, ion-optical calculations have been performed with the code COSY INFINITY. An example of the ion optical calculation is shown in Fig. 1. The incident electron energy is at 517.6 MeV and the electron scattering angle is at 22.7̊. The radii of the bore of Q and H are 17.0 cm and the (horizontal) gap of D is 15.5 cm. The (vertical) good-field region of D is 25.0 cm. The polar and azimuthal angle acceptances of the spe-