Plasma Diffusion Along a Fine Tube Positive Column

The propagation velocity of light emission is observed to be u_p ~0.92 times10⁺⁵ m/s along a tube of an inner diameter r_o ~1.5 times10^-3 m with an external electrode fluorescent lamp filled with 97% Ne and 3% Ar at a total pressure of 30 torr, a mercury-free lamp without phosphor coating the inside glass wall. The origin of this propagation is shown to be ambipolar diffusion with a plasma diffusion speed of u_p ~ (4.8/r_o)D_a for diffusion coefficient D_a along the positive column. When a high voltage magnitude is applied at the external electrode, a high-density plasma is generated inside the hollow electrode, and the plasma diffuses along the positive column toward the ground electrode.