Progress toward laboratory quasi-neutral pair plasmas (in the "NNP regime")

The APEX (A Positron Electron eXperiment) Collaboration’s efforts to create and study low-temperature, magnetized, electron-positron pair plasma are rooted in physics understanding and experimental techniques from the field of non-neutral plasmas (NNPs). They are also inspired by the field’s exemplary interplay between reproducible experiments, tractable simulations and testable theory. The overall experimental plan for e+e- plasmas involves installing several small plasma devices –- all also well-suited for NNPs -- together at the world-class NEPOMUC positron source (operated at the FRM II research neutron source). Positrons will be accumulated and stored in a series of linear NNP traps (PAX: Positron Accumula­tion Experiment); these will then feed e+ pulses to either of two table­top-sized, toroidal confinement devices with complementary magnetic topologies. These are the levitating dipole APEX-LD (Levitating Dipole) and the stellarator EPOS (Electrons and Positrons in an Optimized Stellarator) – both based on HTS coils – in which the positrons will be combined with electrons and their collective plasma properties characterized. Recent highlights from the collaboration have included studies of pure e- plasmas in APEX-LD; optimization and engineering design reviews for EPOS; gamma-detector-array-based measurements of e+ transport and cooling in a prototype (supported) dipole trap; e- plasma manipulations in a linear, “multi-cell” trap; and accompanying numerical/theoretical modeling. Next year, when FRM II is scheduled to return to user operation, APEX-LD and the first two stages of PAX (a Surko trap plus accumulator) will be installed on NEPOMUC, allowing us to combine significant numbers of positrons and electrons (N > 10^8) and take our first measurements of the resulting interacting ensembles.