An intense positron pulse source at NEPOMUC

• Applicants: Professor Dr. Christoph Hugenschmidt; Professor Dr. Lutz Schweikhard; Professor Dr. Thomas Sunn Pedersen
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 326943750

Experiments with positrons have so far used continuous beams or pulsed beams of low density and high repetition rate. Here we suggest to use recently developed techniques for efficient storage of positrons to build a positron trap of unprecedented capacity. It will enable to store the primary beam of the NEPOMUC beamline, and produce short, very intense positron pulses from this IPPS (Intense Positron Pulse Source).Positrons will be stored in a system of cylindrical traps in which positrons are travelling along the field lines of a superconducting electromagnet, and are additionally confined by electrostatic potentials (Penning- Malmberg trap). The project aims for a storage capacity of 10^12 particles. In order to achieve this figure, a system of several Penning-Malmberg traps will be used, that are radially arranged around the central axis of the magnet. To fill the traps, positrons will be transported radially (perpendicular to the fieldlines) in a so-called Master cell, spanning the whole diameter of the magnet.Equally important, we will develop techniques to inject the primary NEPOMUC beam, currently guided by a field of 5 mT, into the field of the storage cells (5 T). In order to do so, positrons can either be decelerated and cooled down by inelastic collisions with a neutral background gas ('buffer gas trap'). Very cold positrons produced such can then be accelerated electrostatically into the stronger magnetic field. Alternatively, we will explore the route of direct injection of very energetic positrons into the 5 T field, where they will be slowed down by collisions in a metallic remoderator. We will develop both techniques initially, in order to decide for the more efficient one, which will eventually be realized in our system.Applications for intense, extremely short positron pulses produced in our device are in particular for the investigation of positron-matter interaction. The project is an apparative pre-requisite for future research on charged, trapped nano-particles using positron pulses using a dedicated set-up at NEPOMUC. A second aim is the production of the first cold, magnetically enclosed pair plasma composed of electrons and positrons. This project, which is equally important for fundamental plasma physics as well as for astrophysics, will be the first application for the planned device. Further research aims are in condensed matter physics: For the first time, it will be possible to investigate bulk solids, in which positrons are occupying not only ground, but - because of their higher density - also excited states.

• DFG Programme: Research Grants
• Co-Investigator: Eve V. Stenson, Ph.D.