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In atmospheric pressure capacitively coupled microplasma jets, VoltageWaveform Tailoring (VWT) was demonstrated to provide ultimate control of theElectron Energy Distribution Function (EEDF), which allows to enhance andadjust the generation of selected neutral species by controlling the electronpower absorption dynamics. However, at the fundamental level, the physicalorigin of these effects of VWT remained unclear. Therefore, in this work, theelectron power absorption dynamics is investigated in a He/N$_2$ jet with anitrogen concentration of 0.05\% driven by a valleys waveform at a basefrequency of 13.56 MHz for different numbers of harmonics using aself-consistent Particle in Cell simulation coupled with a spatio-temporallyresolved analysis of the electron power absorption based on the momentumbalance equation. Due to the local nature of the transport at atmosphericpressure, ohmic power absorption is dominant. Increasing the number ofharmonics, due to the peculiar shape of the excitation waveform the sheathcollapse at the grounded electrode is shortened relative to the one at thepowered electrode. As a consequence, and in order to ensure flux compensationof electrons and positive ions at this electrode, a high current is driventhrough the discharge at the time of this short sheath collapse. This currentis driven by a high ohmic electric field. Close to the grounded electrode,where the electron density is low and the electric field is high, electrons areaccelerated to high energies and strong ionization as well as the formation ofa local electron density maximum are observed. This electron density maximumleads to a local ambipolar electric field that acts as an electric fieldreversal and accelerates electrons to even higher energies. These effects areunderstood in detail to fundamentally explain the unique potential of VWT forEEDF control in such plasmas.

Electron power absorption in micro atmospheric pressure plasma jets driven by tailored voltage waveforms in He/N$_2$