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Events on Monday, November 12th, 2018

Plasma Physics (Physics/ECE/NE 922) Seminar
Advances and discoveries en route to magnetically confined electron-positron plasmas
Time: 12:05 pm
Place: 2241 chamberlin hall
Speaker: Dr. Eve Stenson, IPP Garching
Abstract: The large mass imbalance between ions and electrons produces a
separation of the two species' length and time scales that is a
cornerstone of traditional plasma physics. To consider the behavior of a
"pair plasma", comprising particles with opposite charge but equal mass,
is to revisit much of plasma physics from the ground up. Since the idea
was first introduced four decades ago, on the order of 1000 papers have
explored this topic via a variety of analytical and computational
treatments, but the experimental side of the investigation is still in
its nascence. Laboratory studies of matter-antimatter plasmas will
enable new tests of simulation and theory predictions, with implications
for our understanding of fundamental plasma science, astrophysical
phenomena in which pair plasmas play a role, and also traditional
electron-ion plasmas.

Toward these ends, the goal of the APEX (A Positron Electron eXperiment)
collaboration is to create and study electron-positron plasmas confined
in the magnetic field of a levitated dipole. A key milestone that was
recently achieved is the demonstration of lossless injection of
low-energy (e.g., 5-eV) positrons into a prototype dipole trap, in which
the positrons can then be confined for several seconds (corresponding to
hundreds of thousands of toroidal transits). Another recent result of
note is the discovery that phosphor screens (long used to diagnose both
matter and antimatter) produce significantly more luminescence from
incident positrons than incident electrons. This has potential to be a
new means of investigating luminescent materials, in addition being of
significant utility for nonperturbatively diagnosing low-energy positron
beams and plasmas.

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