Demonstration of a novel phase space painting method in a coupled lattice to mitigate space charge in high-intensity hadron beams

Abstract

Multi-turn charge-exchange injection is the primary method of creating high-intensity hadron beams in circular accelerators, and phase space painting during injection enables tailoring of the accumulated phase space distribution. A technique we call eigenpainting allows injection of particles into a single mode of a coupled ring, providing full four-dimensional control of the phase space distribution. Under ideal conditions, uniform eigenpainting generates a linear-force equilibrium distribution in the transverse plane, with zero volume in four-dimensional transverse phase space, even including space charge. We have implemented eigenpainting for the first time in the Spallation Neutron Source (SNS) Accumulator Ring. Injecting 8.8 $μ$C of 800 MeV beam, we obtain a final ratio of intrinsic transverse emittances of $\approx$2.4. We analyze the effect of space charge on the final distribution through comparison of the reconstructed phase space to particle-in-cell simulations.

Figures (3)

• Figure 1: Representation of the painting trajectories in the plane of mode actions, $J_{1,2}$ corresponding to correlated (CP), anti-correlated (AP) and eigenpainting (EP) schemes (left) and time evolution of the $x$-$y$ distribution of beam produced by each scheme (right). Red points indicate the centroid position of injected beamlets; arrows indicate centroid angle if non-zero.
• Figure 2: Turn-by-turn data (black points) for three sets of injection coordiates from the BPM in the injection straight quad doublet downstream of the foil (BPM A13), showing the fit trajectory in gray and contributions from mode 1 (blue), mode 2 (red). Offsets have been removed.
• Figure 3: 2D projections of the reconstructed (top) and simulated (bottom) phase space distributions in normalized coordinates. Solid black lines in the marginal projections represent a fit to a uniform-Gaussian convolution as described in the text. Dashed lines represent a pure Gaussian distribution.