Parameter Dependence of Inward Diffusion on Injected Electrons in Helical Non-Neutral Plasmas

摘要

Experimental studies on an electron injection into a helical magnetic field and characteristics of non-neutral plasmas have been performed. It is found that the space potential φ_s has a weak dependence on the injection angle except for a narrow 'window' region in which φ_s significantly drops. A calculation shows that because of the electric field E_g of the electron gun (e-gun), the emitted electrons are launched quasi-parallel to the helical magnetic field B, regardless of α. This seems to agree with the observation. The 'window' seen in the data may be attributed to an current-driven instability which might result in the insufficient electron penetration or the degradation of electron confinement in the magnetic surface.