Plasma Physics (Physics/ECE/NE 922) Seminars |
Events on Monday, October 24th, 2022
- Exploring the new electron-positron plasma frontier: the annihilation signature of cold magnetically-confined pairs and accessing the relativistic and magnetized regime
- Time: 12:00 pm
- Place: 1610 Engineering Hall
- Speaker: Jens von der Linden, IPP Garching
- Abstract: Advances in positron production, accumulation, and trapping are enabling a new plasma physics frontier: electron-positron pair plasma. I will report on two parallel efforts.
One line of research aims to accumulate and magnetically confine moderated positrons with electrons in sufficient numbers to produce a pair plasma with a small Debye length (but with a skin depth exceeding the plasma size). The mass symmetry of pair plasma has led to many predictions with regard to their stability to electrostatic modes and (absence of) turbulence. Yet, it is unclear how to diagnose the behaviour of these electromagnetically transparent plasmas without terminating them. Here, I show that direct annihilation in the bulk of the plasma, positronium formation and subsequent annihilation, as well as transport to the wall and magnets will produce various volumetric and localized sources of gamma emission with rates related to the plasma parameters. Methods for diagnosing and differentiating between volumetric and localized gamma sources are developed.
The other effort aims to magnetize the large numbers (up to 10^12) of pairs produced through laser-target interactions at intense short-pulse laser facilities. The energy of these pair beams can be controlled by manipulating the sheath on the backside of the target. The charge ratio of the pair beam can be made unitary with magnetic collimation. The lifetime of these pair beams can be extended with magnetic mirror trapping. Together, these experimental techniques could make the relativistic and magnetized plasma regime, prevalent around massive astrophysical objects such as magnetars, accessible.