BEAMS
In the literature: open
Predicting halo population and fractional loss in megawatt proton linacs
In plain words
Simulations cannot yet predict the tiny fraction of protons that escape the core of an intense linac beam, which is what matters for radiation damage.
Precise statement
In MW-class proton and H- linacs (SNS, J-PARC, ESS, PIP-II) losses must stay below about 1e-6 to 1e-4 of the beam per unit length. Predict, blind and to within a factor 2, the halo population beyond 5 rms beam sizes from the measured initial distribution, lattice errors and space charge, and identify which mechanisms (envelope mismatch, particle-core resonances, intrabeam stripping of H- ions) dominate the measured loss pattern.
What would settle it
Blind prediction of halo profiles measured with high-dynamic-range diagnostics in an operating MW linac.