Dipole traps for non-neutral plasma and pair plasma studies

Dipole traps have demonstrated good confinement properties for non-neutral [1] and quasi-neutral plasmas [2]. We describe two such traps, one under construction and the other in the design phase that will be used to study electron-positron pair plasma and pure electron plasma confinement, respectively. The construction of the APEX (A Positron-Electron eXperiment) – levitated dipole is nearing completion. It makes use of a 15 cm diameter high-temperature superconducting (HTS) coil (I < 60 kAt) that is inductively charged using a second HTS coil (I < 164 kAt). Stable levitation is achieved with active feedback on the lifting coil current and we anticipate levitation times of order one hour with the use of a cooled radiation shield surrounding the trapping region. We present progress on construction and commissioning of system components as well as results of experiments in a prototype supported dipole trap – results that include efficient injection of positrons into a dense electron cloud [3]. A new supported dipole trap is in the design stage at Lawrence University. The design of this device is guided by emerging theory and calculations regarding the requirements for well-confined thermal equilibrium states for non-neutral plasma [4]. These states reside exclusively on the outboard midplane and are therefore likely accessible in a supported dipole trap. A primary aim is to identify a suitable target electron plasma into which to inject positrons in the APEX levitated dipole.



[1] Z. Yoshida, H. Saitoh, et al., Phys. Rev. Lett. 104, 235004 (2010).

[2] A. C. Boxer, et al., Nat. Phys. 6, 207 (2010).

[3] M. Singer, et al., Phys. Plasmas 28, 062506 (2021).

[4] P. Steinbrunner, et al., manuscript in preparation (2022).