Progress report storage of slow positron beam

Storage of slow positron beam is becoming important from various reasons. For example stored intense positrons may be irradiated to matter synchronous with low frequency intense laser beams. In plasma physics intense positrons are necessary to study positron-electron plasma. Another important field is the synthesis of anti-hydrogen atoms from anti-protons and positrons, where 1010 positrons are required within about 1 μs. Furthermore positron storage consists of fundamental techniques that will be applied to various aspects of the positron beam technology, such as construction of ultra-short positron pulses. An idea of accumulating slow positrons was proposed based on the principle of spiral orbit spectrometer. In a model experiment using electrons the accumulation time was found to be about 30 μs. A linear storage method using the Penning trap was initiated by Ito et al. and Akahane et al. for the purpose of time-stretching pulsed positron beams produced using an electron Linac. In these cases positrons could be accumulated several hundred μs to several ms. Accumulation of several ms is tolerable if the time-stretching is the purpose of the accumulation, because the repetition of the positron pulses are 50-200 Hz. However an accumulation of positrons of the order of seconds to hundred seconds was reportedly successful. If this is really possible it is not a dream to obtain 1010 positrons when an intense positron source is used. For example, an electron Linac of moderate power can produce 107 - 108 slow e+/s and with this the total intensity may reach 1010 in 100 seconds. We started to develop a method to accumulate positrons and did some experiments from April to June, 1995. In this report, the result of these experiments are presented. (J.P.N.)