Halo Formation and Hollowing in Relativistic Electron Beams
Abstract
A relativistic electron beam propagating through dense gas may evolve to a variety of current density profiles J sub b (r) depending on the beam temperature T and plasma current profile J sup P (r). Four broad classes of equilibria are identified 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 which 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 sub B = 1-f, where T sub 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 sub 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 sub B < 1-f and moderate or high f, the beam core is broader than the plasma current profile, and on-axis hollowing results. Simulations with the ultrarelativistic SARLAC simulation code exhibit all of these types of equilibria. SARLAC also treats transverse beam distortion arising from the resistive hose instability. Hose instability growth appears to be strongly enhanced when halos are generated. Keywords: Relativistic electron beam; Return current; Resistive instability; Hollowing; Hose instability.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 10, 1988
- Accession Number
- ADA199734
Entities
People
- Glenn Joyce
- Mártin Lampe
- Richard F. Hubbard
- Steven P. Slinker
Organizations
- United States Naval Research Laboratory