Halo formation and hollowing in relativistic electron beams

• Published in: The Physics of fluids (1958) 1988-08, Vol.31 (8), p.2349-2361
• Main Authors: Hubbard, Richard F., Lampe, Martin, Slinker, Steven P., Joyce, Glenn
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma interactions (nonlaser)
• ISSN: 0031-9171; 2163-4998
• DOI: 10.1063/1.866583

A relativistic electron beam propagating through dense gas may evolve into a variety of current density profiles J b (r) depending on the beam temperature T and plasma current profile J p (r). Four broad classes of equilibria are discernible in particle simulations: (1) Bennett‐like or compact, (2) core and halo, (3) on‐axis hollowed, and (4) off‐axis hollowed. The qualitative features of each class are reproduced in a simple analytical model that assumes an isothermal beam and a Bennett plasma current profile and iterates about an initial ansatz of a Bennett beam current profile. Bennett‐like equilibria are produced when the return current fraction f is small or when T/T B=1−f, where T B=e I b /2c is the Bennett temperature. For T/T B >1−f and moderate or high f, the equilibrium consists of a compact core surrounded by a halo, which may contain most of the beam current. In extreme cases (T/T B≫1−f and f close to unity) an off‐axis density minimum occurs. (This is also referred to as off‐axis hollowing.) For T/T B