There are a family of stable solutions for putting a crystalline beam in Brookhaven National Laboratory's Booster accelerator, because angular momentum about the vertical axis can be freely chosen within a range.   The videos below show this for several different values, the top six of which stay at a low temperature (<20mK).   Changing how fast the bunch spins actually changes its shape as shown in the vertical plots afterwards.
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<br />It would have been nice to make the angular momentum in the drift sections zero, as in the bottom-right plot, as this would make laser cooling easier to achieve, but this is right at the edge of the stable parameters and heats (as well as being such a flat bunch it is almost two dimensional).   You can also see particle diffusion over many turns, since this is still slightly in the liquid state.   Needs to be roughly half the temperature to be fully solid.   But still an ultra-cold beam by most definitions!
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<br />#physics #accelerators<p><video src='posts/202605/post-20260513-153644-a.mp4' loading='lazy' preload='metadata' controls></video></p>