The extraction of the proton beam circulating in a ring accelerator using a bent single crystal  was carried out in a number of research centers (JINR, IHEP, CERN, FNAL). The proton beam  was directed strictly perpendicular to the surface of the single crystal at a small angle  (smaller than the Lindhard angle) relative to the curved crystallographic planes. This geometry  of particle capture in the planar channeling mode is called end‑face capture. This paper presents the results of extracting a proton beam from an accelerator using the phenomenon of volume particle capture in the channeling mode. In this case, the proton beam is directed at the crystal at an angle many times greater than the Lindhard angle. As the proton moves in the bent crystal, the angle between the particle veloсity and the plane decreases over a short distance, and the particle moves almost parallel to the plane.In this region, due to multiple scattering on atoms, a particle has a probability of being captured into the channeling mode (i.e., transitioning from an over‑barrier state to an under‑barrier one). The figure illustrates both types of particle capture into channeling.

The extraction of a proton beam using particle capture into channeling was implemented for the first time in the world’s accelerator practice at the SPASCHARM facility at the Institute for High Energy Physics. When pointing a primary beam with an intensity of $3\times 10^{11}$ protons/cycle at a crystal in the ring of the U-70 accelerator  at the SPASCHARM installation, an intensity of up to $6\times 10^6$ protons/cycle was observed. Despite the lower intensity of the output beam compared to the traditional output based on the face-end capture of particles, the output using the phenomenon of volume capture provides more stable parameters of the output beams.

Figure 1: Scheme of particle extraction at volume capture

S.F.Reshetnikov et al.
JETP Letters 124, issue 5 (2026)