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.