An investigation of collisionless plasma beam interaction with a nonhomogeneous magnetic field

• Main Author: Lee, Peter Hoong-Yee
• Format: Others
• Published: 1973
• Online Access: https://thesis.library.caltech.edu/6009/3/Lee__phy_1973.pdf; Lee, Peter Hoong-Yee (1973) An investigation of collisionless plasma beam interaction with a nonhomogeneous magnetic field. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/XNF6-9D90. https://resolver.caltech.edu/CaltechTHESIS:08262010-104719284 <https://resolver.caltech.edu/CaltechTHESIS:08262010-104719284>

The interaction between a rarefied flowing plasma and an externally imposed nonhomogeneous magnetic field is studied experimentally in a collisionless plasma wind tunnel, where a collisionless plasma beam is directed through a current loop. The collisionless plasma is generated by an electron bombardment engine. Nominal values of ion flow speed, number density, electron temperature and magnetic induction of the loop are U ~10^4 m/s, N ~5 x 10^7/cc, kT_e ~0.2 eV and B ~10 Gauss, respectively. Due to lack of probe theories in the presence of nonhomogeneous magnetic fields and failure of conventional Langmuir probe methods, a new, simple method of diagnostics is developed. This method employs two probes of different geometry and obtains information on the ion density and flow speed from the ion-saturation region of the probe characteristic. Radial density profiles in the wake of the current loop mapped by the "two-probe" method indicate annular density "peaks" at certain radial positions. In order to understand this non-uniform "pinching" process, a theoretical analysis is attempted. It is found that the experimentally observed phenomenon can be qualitatively described by the collision-less two-fluid equations, but turbulent "friction" is required to improve the two-fluid model. A heuristic turbulent model is used, and evidence of turbulence in the flow field is also obtained through measurements of the fluctuating probe currents.