Ionization cooling

In accelerator physics, ionization cooling is a physical process for reducing the beam emittance of a charged particle beam ("cooling") by passing the particles through some material, reducing their momentum as they ionize atomic electrons in the material. Thus, the normalised beam emittance is reduced. By re-accelerating the beam, for example in an RF cavity, the longitudinal momentum may be restored without replacing transverse momentum. Thus, overall the angular spread and hence the geometric emittance in the beam will be reduced.

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