Limits of space charge mitigation with self-consistent beams

A major challenge for the operation of high-intensity hadron accelerators is the effect of Coulomb repulsion of charged particles, or space charge, on the beam dynamics. Space charge effects can lead to a reduction in beam quality and uncontrolled beam loss. Shaping the beam distribution through phase space painting is one path to mitigating space charge effects in hadron accumulator rings.

We will conduct an experimental comparison of three painted non-planar beam distributions in the Spallation Neutron Source (SNS) accumulator ring, including a Gaussian, hollow, and uniform distribution. We will explore a range of space charge intensities to investigate the potential of each distribution to mitigate space charge effects. We will also attempt to reproduce the experimental data with the PyORBIT code, a particle-in-cell (PIC) accelerator simulation program developed at the SNS.

The objectives of this project will be to experimentally compare three types of non-planar painted beam distributions over a range of intensities near the nominal working point of the SNS; to compare the distributions near resonance bands; to explore the use of a novel technique for characterizing space charge effects based on core-particle simulation techniques; to reproduce experimental results in simulation; and to predict the mitigation potential of non-planar beam distributions in future high-power accelerators.

We will use standard diagnostics available at the SNS, including beam loss monitors, beam position monitors, and wire scanners. We will used demonstrated analysis techniques, such as four-dimensional phase space tomography and transverse tune scans. We will also use electron scanner data for online optimization of the injection processes, leveraging AI/ML techniques. Finally, we will explore a new technique based on time-delay injection to investigate core-particle models of halo formation in the ring.

Non-planar painted beams are a cost-effective space charge mitigation strategy based on well-understood linear dynamics, requiring standard hardware. Non-planar painted beams could push the intensity limits in existing accelerators, reduce the cost of future high-power accelerators, or improve beam quality with minimal development effort. Experimental demonstration could introduce non-planar beams as a realistic, cost-effective alternative to increasing linac energies as a solution for mitigating space charge in the first stage of hadron complexes. A demonstration of the robustness of such beams could also have profound impact on the operation of colliders where the implications of non-planar beams go beyond space charge mitigation, providing increased luminosity.