Resonant slow extraction in synchrotrons using anti-symmetric sextupole fields

Abstract

This paper proposes a novel method for resonant slow extraction in synchrotrons by using special anti-symmetric sextupole fields, which can be produced by a special magnet structure. The method has the potential in applications demanding for very stable slow extraction from synchrotrons. Our studies show that the slow extraction at the half-integer resonance by using anti-symmetric sextupole field has some advantages compared to the normal sextupole field, and the latter is widely used in the slow extraction method. One of them is that it can work at a more distant tune from the resonance, so that it can reduce significantly the intensity variation of the extracted beam which is mainly caused by the ripples of magnet power supplies. The studies by both the Hamiltonian theory and numerical simulations show that the stable region at the proximity of the half-integer resonance by anti-symmetric sextupole field is much smaller and flatter than the one by standard sextupole field at the third-order resonance. The particles outside the region will be driven out in two possible directions in quite short transit time but with spiral steps similar as in the third-order resonant extraction. By gradually increasing the field strength, the beam can be extracted with intensity more homogeneous than by the usual third-order resonant method, in the means of both smaller intensity variation and spike in the beginning spill. Similar to the case with a normal sextupole, we derive an empirical formula for the area of the stable region with an anti-symmetric sextupole. One can find that with the same field strength and the same tune distance to the resonance, the area of stable region or the change of the area due to the working point variation in the case of anti-symmetric sextupole is about 1/14 of the one in the case of standard sextupole. The detailed studies including beam dynamic behaviors at the proximity of other resonances, influence of 2-D field error, half-integer stop-band, and resonant slow extraction by using quadrupole field have also been presented.

Concept for a Future Super Proton-Proton Collider

“…Fig. 4: Schematic for the multi-stage collimation system at SPPC Besides the method used at LHC, other novel methods will be considered, including the one studied in CERN and FNAL with bent crystals [34][35], and the one employing nonlinear magnets to enhance the collimation efficiency [36][37] 3 Key technical systems 3.1 High-field superconducting magnets…”

Design Concept for a Future Super Proton-Proton Collider

“…Besides the conventional method used at the LHC with primary scattering collimators and absorbers, other novel methods will be considered, including the one studied in CERN and FNAL with bent crystals [42,43], and the one employing nonlinear magnets to enhance the collimation efficiency [44,45].…”