EXTREMELY COLD POSITRONS FOR ANTIHYDROGEN PRODUCTION

The storage of extremely cold (4 K) antiprotons in a Penning trap is a n important step toward the creation and study of cold antihydrogen. T he other required ingredient, the largest possible number of comparabl y cold positrons, is still lacking. These would be recombined in a hig h vacuum with the trapped antiprotons, already stored at a pressure be low 5 x 10(-17) Torr, thereby avoiding annihilation of the antihydroge n atoms before they can be used in high accuracy measurements or in co ntrolled collision experiments. In an exploratory experiment, positron s from a 18 mCi Na-22 source follow fringing field lines of a 6 T supe rconducting solenoid through tiny apertures in the electrodes of a Pen ning trap to strike a tungsten (reflection) moderator. The positron be am is chopped mechanically and a lock-in directly detects a positron c urrent of 2.5 x 10(6) e+/s on the moderator. The use of a moderator, u nlike an earlier experiment in which < 100 positrons were confined in vacuum, should greatly increase the number of positrons trapped in hig h vacuum.