Positron beams and pulses for pair plasma experiments

The generation of magnetically confined electron-positron pair plasmas in the laboratory will open up an exciting frontier in plasma physics that has been eagerly anticipated for four decades. This is the goal of the APEX (A Positron Electron eXperiment) project. The limiting ingredient for accomplishing this --- i.e., for achieving 10 Debye lengths for both species in the confinement device --- is the supply of antimatter. The required number of positrons depends strongly on the parameters of the positron source, as these determine what methods can be efficiently used to transfer positrons into the trap, as well as the resulting density and temperature. Therefore, experiments have been conducted to optimize the world-class, monoenergetic NEutron-induced POsitron source MUniCh for the unique needs of APEX. The higher-flux “primary beam” has been demonstrated at low energies (5–60 eV) for the first time, which enabled drift-injection and trapping of a record number of positrons in a prototype dipole device; in situ SiC remoderation of a 400-eV beam, followed by drift injection of the remoderated positrons, has been demonstrated in the same device. Work is now underway toward adding linear non-neutral plasma traps that will be used to furnish intense, tailorable positron pulses.