Magnetic dipole traps for pair plasma experiments

Magnetized pair plasmas (comprising positively and negatively charged particles with the same mass) have been the topic of theoretical and computational work for decades, and the goal of the APEX (A Positron Electron eXperiment) collaboration is to confine them in the laboratory. A levitated dipole trap is an ideal device for this purpose, for reasons including the facts that the confining field requires no plasma current and that dipolar fields are relevant to astrophysical systems (in which pair plasmas naturally arise). Compared to existing levitated dipole experiments, the APEX device will be smaller and lighter and have less heat load.In parallel with the design and construction of the levitated dipole, a number of key questions have been investigated in a prototype trap based on a supported permanent magnet; these include the demonstration of lossless injection (by means of the ExB drift), the manipulation of positrons once they are in the trap (by means of oscillating wall biases), and the observation of confinement times exceeding 1 s (despite system asymmetries). Efforts are now underway to upgrade the prototype trap first to a supported and then to a levitated high-temperature super conducting (HTSC) coil.