Martin Singer

• For the creation of a positron-electron (pair) plasma the A Positron Electron eXperiment (APEX) collaboration needs large quantities of positrons. Accumulating many positrons is an experimentally challenging task. To achieve this task, a new prototype multi cell Penning-Malmberg trap (MCT) was designed and constructed. The accumulation of large charged-particle ensembles with one charge sign dominating, so-called non-neutral plasmas, in Penning-Malmberg traps is limited by the plasma space charge. The MCT avoids this limitation by separating the plasma space charge into multiple storage traps in the same magnetic field. This MCT includes a master-cell, and three storage cells (one on-axis, and two off-axis). With this device plasma transfer to the off-axis cells was tested and improved. The goal was to transfer multiple plasmas off-axis while avoiding particle losses during the process. The dissertation introduces the vacuum setup, diagnostics, and the MCT, and explores its operation. The plasma creation process, cyclotron cooling, and the plasma confinement is detailly described. Different schemes for the autoresonant excitation of the diocotron mode are discussed as well as the dynamics during the transport to the off-axis cells. These dynamics are dominated by competing diocotron drift modes that can lead to significant particle losses. New techniques are presented which allow to suppress these modes. These techniques mitigate losses and centre the plasma in the off-axis cells during the transfer process, significantly improving it. In addition, the dissertation demonstrates the first consecutive transfer and confinement in two different off-axis cells. The confinement in multiple off-axis traps is a milestone for the future use of a MCT at the NEPOMUC positron source in Munich.