High efficiency positron moderation a feasibility study of the slow beam confinement extraction

A method which reduces the energy of positrons emitted from a radioisotope source to values of only a few keV (premoderation), by trapping them in high magnetic and electric fields and by passing them through an absorber many times, was tested and presented in a previous publication. In this paper we have analyzed a possible solution for the necessary follow-up operations of extracting the positrons from the premoderation stage and guiding them onto a final moderator, by using a system of four drifting E × B electrodes. Moreover it is shown how the moderated positrons can finally be transported out of the high field confinement to a low field region. A careful analysis and simulation of the motion of the particles in the used electric and magnetic field distribution was performed, respecting the condition of adiabatic motion and minimizing the distortions on the beam cross section introduced by the electrodes. In such a way, we maximized the overall efficiency of the beam extraction from the confinement (the estimated value is 90%), and we reduced the final cross section of the moderated positron beam in the low field region, acceptable for the subsequent beam extraction from the magnetic field.