Numerical study of Penning-Malmberg-Surko positron trap efficiency

Efficiency of a gas filled positron trap can be improved in two ways: by shortening the operation time required to thermalize the particles in the trap, and by increasing the percentage of particles trapped. We examine both techniques by a well tested Monte Carlo code, and give an overview of the loss processes involved. Temporal and spatial evolution of the energy distribution of particles allows us to show gradual transition of a beam into a swarm of particles. The model trap is a classic three stage potential well design using N$_{2}$ as a buffer gas in the first two stages and a N$_{2}$/CF$_{4}$ mixture in the third. It was found that including cross sections for rotational e$^{+}$-N$_{2}$ excitation is essential to achieve final stages of thermalization. Various trap implementations use different sources and moderators, and depending on the properties of the incoming beam, the trap itself can be optimized by changing its attributes (buffer gas pressures, dimensions of the chamber, electric potential shape, duration of different operation stages, etc.)