Design study for the KOBRA (KOrea Broad acceptance Recoil spectrometer and Apparatus) at RAON

The KOBRA (KOrea Broad acceptance Recoil spectrometer and Apparatus) is a multi-purpose recoil spectrometer for low-energy nuclear experiments at the RAON accelerator complex. It is divided into two stages based on the operational function: the first stage (F0–F3) is an in-flight separator or beam transport line, and the second stage (F3–F5) is a large acceptance spectrometer. For spectrometers using radioactive ion (RI) beams, high performance, such as high resolution and large acceptance, are especially required due to the limit of quality of RI beams. In this respect, a dispersion-matching technique and a movable magnet system were employed for high resolution and large acceptance, respectively. Reaction spectra at the focal plane for the dispersion matching mode were obtained and analyzed using a Monte Carlo simulation code. In addition, the geometrical angular acceptances with respect to the distance between the reaction target and the first Q-pole doublet of the second stage were calculated, and the expected maximum solid angle of the spectrometer was estimated.