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The influence of nitrogen impurities on the atmospheric pressure helium discharge in Townsend mode is investigated based on a 1D fluid model. The level of nitrogen impurities was varied in the range 0.1–10 000 ppm, in which the discharge exhibits three notable discharge modes, namely multipulse Townsend discharge, single-pulse Townsend discharge, and multipulse glow discharge with the increase in the impurity level. It is found that the influence of nitrogen impurities on helium discharge in the Townsend mode is entirely different from that in the glow mode; the discharge characteristics are different under different nitrogen contents. Under 1 ppm nitrogen content, both the breakdown voltage and discharge current remain unchanged. As the N2 content increases, the breakdown voltage still remains unchanged but the discharge current decreases. As the N2 content exceeds 350 ppm, the discharge transits from the Townsend mode into the glow mode, and the breakdown voltage decreases dramatically while the current density increases.

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