Radial compression of antiproton cloud for production of ultraslow antiproton beams

Cooling and manipulation of a large number of antiprotons held in an electro-magnetic trap are key techniques for the synthesizing antihydrogen atoms and antiprotonic atoms [1]. We, MUSASHI sub-group in ASACUSA collaboration, achieved accumulation and cooling of antiprotons with at least 50 times higher efficiency than has been achieved by conventional methods [2]. Extracting these antiprotons from the trap and transporting them efficiently in the form of a beam is the next step not only towards synthesizing antihydrogen atoms for use in CPT symmetry test, but also for studying atomic collision dynamics. Since charged particles tend to follow magnetic field lines, a cloud of antiprotons should have a small radius in the trap for better focusing of extracted beams. We report the radial compression of antiprotons (5 × 10) under ultrahigh vacuum conditions (< 10−11 Torr) by applying a rotating electric field. Compression without any resonant structures like strong drive compression [3] was achieved without electrons as coolant [4]. Recently compression together with electrons was also tried reported by ALPHA collaboration [5]. Also our running and planned experiments with such produced ultraslow antiproton beams at CERN will be discussed, which including atomic collision experiments and antiproton confinement in a cusp trap designed for antihydrogen synthesis.