The atmospheric pressure plasma generated using a quartz tube, helium gas, and foil electrode by applying AC high voltage is investigated. A plasma plume is formed with a small bullet-like volume of plasma that travels at high speed inside of the quartz tube filled with a helium gas. The average movement velocity of the plasma bullet and the emitted light from helium plasma are observed inside the quartz tube. Both the average plasma bullet velocity and the power spectrum density (PSD) of the helium ion (He I) tend to decrease towards the tip of the plasma plume. The average plasma bullet velocity is linearly proportional to the PSD of He I. Therefore, the movement velocity of the plasma bullet is available to estimate from the PSD of He I at one measurement point. Published by AIP Publishing.