Suppressing electron-beam shot noise below the random level
In plain words
Electrons arrive at random, which seeds noisy x-ray output and harmful instabilities; collective forces can make them more evenly spaced than random, but only at long wavelengths so far.
Precise statement
Coulomb repulsion acting over a quarter plasma period in a drift can reduce beam density fluctuations below the Poisson shot-noise level. Determine whether suppression by more than 10 dB can be produced and kept through acceleration and compression at wavelengths below 1e-5 cm, which would reduce SASE start-up noise and microbunching gain.
What would settle it
Measured coherent radiation from a beam below the shot-noise level at the stated wavelength after acceleration and compression.
Status in the literature
Sub-shot-noise density fluctuations were reported at optical wavelengths in the 2010s; suppression at XUV and x-ray wavelengths is undemonstrated.