Mitigation of Space-Charge Driven Fourth-Order Resonance by Beam Spinning

Recently discovered $4\sigma=360^{\circ}$ fourth-order particle resonance sets one of the fundamental operational limits for high-intensity linear accelerators. To mitigate this nonlinear space-charge driven resonance and subsequent envelope instabilities, we propose a novel approach of using spinning beams with finite average canonical angular momentum. From the analytical and numerical simulation studies, we found that the spinning beams have an intrinsic characteristic that can suppress the impact of the fourth-order resonance on emittance growth and associated envelope instability. We use initially well-matched Gaussian beams in a periodic solenoidal lattice, and consider stripping of $\rm H^-(or~ D^-)$ beams by a thin foil inside a pair of solenoids placed before the main linac to inject the spinning beams.