OBSERVATION OF ULTRACOLD HEAVY ION BEAMS WITH MICROMETER SIZE BY SCRAPING

A method to measure the horizontal beam size of electron cooled ion beams with micrometer resolution has been developed. It exploits small variations of the beam momentum for micrometer displacement in a dispersive section of the storage ring. The method has been applied to low intensity beams which are supposed to undergo a phase transition to an ordered state. The measurements evidenced that the low intensity beam does not only collapse to small momentum spread, but also shrinks abruptly in the transverse degree of freedom. This confirms the hypothesis that a one-dimensional ordered structure is formed.