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10:30 AM

ARC Bldg. Room 231/233

Fermilab

Self-interacting, nonequilibrium, very-many-body systems such as elliptical
galaxies and charged-particle beams seem generically to exhibit rapid
evolution to a quasi-equilibrium state. Such systems comprise some
1010-12 particles. The associated collisional relaxation time of elliptical
galaxies is ~1015-16 years, several orders of magnitude larger than the age
of the universe. For a nonrelativistic charged-particle beam it is ~1-10 µs,
i.e., "1-10 km", typically much longer than, e.g., the length of a linac.
Yet, elliptical galaxies appear to be "relaxed" to a smooth density distribution,
and charged-particle beams have likewise been seen to "relax" to a smooth
density distribution, and also to equipartition in a few meters, depending
on details of the space charge. How so? In this talk I will describe
an "elementary" mechanism, one that is based on the behavior of the orbits
comprising the system and how these orbits mix through their accessible
phase space. I will then use it as the foundation for estimating time
scales for relaxation to quasi-equilibria and show that they are in
reasonable agreement with the true values computed in numerical simulations
and seen in the (few) beam experiments done to date.

Talk Slides:
PDF

(Coffee & Cookies before the seminar starting 10:00 am)