Study of the discharge mode transition in a Ne-flexible micro-tube plasma (FμTP)

Not only Helium and Argon but also Neon, Krypton, and Xenon can be used as plasma gas for a discharge applied for soft ionization with similar ionization efficiency, although it is clear that each of the excited and even ionized states of Xe is lower than the ion energy of N 2 + or H 3 O + . In this work, the discharge behavior of these plasmas both inside and outside of the capillary were investigated to study the mechanisms of soft ionization. Two discharge modes were found. In He- and Ne 2.0 kV -FμTP, the ionization wave of N 2 + is mainly responsible for the propagation of excitation and ionization inside the capillary while the ionization wave of noble gas ions plays the role in Ar-, Kr- and Xe-FμTP. With an increase of the applied voltage, Ne 2.5 kV -FμTP fulfils characteristics of both categories. All the measured ionization waves stop in the vicinity of the capillary outlet. For all plasmas, the propagation of excitation wave is tracked in ambient surrounding, which hints that an ionization wave is propagating outside the capillary. It is assumed that ions species of air components such as N 2 + , O 2 + and H 3 O + are generated in the ambient surrounding. The ionization wave of these ions continue supporting the propagation of the excitation wave. • Two discharge categories are found in FμTPs. • The propagation of Ne-FμTP at low voltage depends on the potential created by N 2 + . • Ne + ions are identified in Ne-FμTP operated at high voltage. • Potentials created by N 2 + and Ne + guide the propagation of Ne-FμTP at high voltage.