Positron plasma control techniques for the production of cold antihydrogen

An observation of a clear dependence of antihydrogen production on positron plasma shapes is reported. For this purpose a plasma control method has been developed combining the plasma rotating-wall technique with a mode diagnostic system. With the help of real-time and nondestructive observations, the rotating-wall parameters have been optimized. The positron plasma can be manipulated into a wide range of shapes aspect ratio 6.5<=alfa<=80 and densities (1.5 10^8<=n<= 7 10^9 cm−3) within a short duration (25 s) compatible with the ATHENA antihydrogen production cycle.