Effects of the tube diameter on the propagation of helium plasma plume via electric field measurement

Abstract

In this work, the dependence of the length of plasma plume, propagation velocity, electric field in the streamer head, and propagation mode transition on the tube diameter varied in the range of 0.07–4 mm is investigated for the first time. The atmospheric-pressure helium plasma plume, ignited by a positive pulsed direct current voltage with a pulse rising time of 60 ns, is confined inside a long glass tube. First, the decreased tube diameter results in the reduction of the length of plasma plume but the growth of aspect ratio of plasma plume. Second, as the tube diameter decreases, the average velocity of the propagation of plasma plume increases first, then reaches a maximum value at tube diameter of 1 mm, and finally decreases for the tube diameter decreasing further. Third, the electric field in the streamer head, determined by the method based on Stark polarization spectroscopy of He 447 nm line, increases monotonically from 9 kV/cm to 20 kV/cm with the tube diameter decreasing from 4 mm to 0.6 mm. Finally, when the tube diameter is further reduced to 0.07 mm, high-speed photography reveals that the propagation mode of the plasma plume transits from the plasma bullet to the continuous plasma column.

The effects of the tube diameter on the discharge ignition and the plasma properties of atmospheric‐pressure microplasma confined inside capillary

“…They observed that the streamer velocity increases first and then decreases after reaching a peak at the tube diameter of 200 µm . In our previous work, for a He streamer propagating inside a tube, as the tube diameter decreases from 4 to 0.6 mm, the streamer velocity increases first and then decreases after reaching a peak at the tube diameter of 1 mm . These results are similar to our case.…”

“…This also agrees well with the observation of the corona‐like air plasma for smaller capillaries in Figure . Similar behavior has been observed in our previous work, where the electric field strength in the head of the ionization front increases from 9 to 20 kV cm −1 for the tube diameter decreasing from 4 to 0.6 mm. The electric field in front of the ionization wave is composed of the external electric field and the local electric field induced by the charges.…”

“…To understand the effects of the tube diameter, several research groups have made great efforts in previous works . As the tube diameter decreases from several mm to 80 µm, the significant increase of the ignition voltage, the current density, the electric field, and the electron density is observed . Meanwhile, the gas temperature is weakly dependent on the tube diameter .…”

“…The numerical simulation results reveal that the increase of the ignition voltage with the reduction of the tube diameter is caused by the decrease of the seed electron density . Moreover, using a high‐speed imaging technique, as the tube diameter is further reduced to 70 µm, the propagation of the helium (He) microplasma plume converts from a discrete “plasma bullet” mode to a continuous plasma column mode . In the front view of the plasma volume, when the tube diameter decreases, the discharge transits from a donut‐shaped mode to a contracted mode .…”

Time Behaviour of Helium Atmospheric Pressure Plasma Jet Electrical and Optical Parameters

“…We were able to point in this way that, for constant flow rate conditions and fixed electrode arrangement, the length of the outside jet depends on the frequency and amplitude of the driving high voltage pulses ( Figure 6). Supplementary, it has been demonstrated in a number of recent studies, that this characteristic dimension of the outside plasma jets in helium is also influenced by the electrodes dimensions and constructive details [40,41], gas flow rate [38,[42][43][44], dielectric tube diameter [45][46][47].…”