Ignition phase of a typical plasma scalpel

Abstract

A plasma scalpel is one of the few applications of plasma medicine widely used in the clinic, but its ignition mechanism is poorly understood. This paper investigates the ignition phase of a plasma scalpel by obtaining the electrical waveforms, vaporization dynamics, plasma production and the plasma spectrum. Additionally, equivalent circuit and physical models are proposed based on the results. Two kinds of vapor layers are formed in plasma production. One is produced by Joule heating, which occurrs at the initial stage and the other is maintained by plasma heating at the stable discharge stage. When the plasma is generated, the vapor layer will become much thinner, leading to a significant increase in the electric field. The waveforms indicate the discharge has two kinds of patterns: asymmetric and symmetric patterns. The plasma intensity in the asymmetric is much stronger than the symmetric pattern. The fitted OH spectrum reveals that the gas temperature of the plasma can reach 2600 K, which can sustain the thin vapor layer. According to the broadening of the Hα line, the electron density is estimated to be about 7.1 × 1015 cm−3. Furthermore, when the stable vapor layer is formed, the impedance of the gap increases from 70 Ω to 2000 Ω when the plasma is established. The electron density is estimated again according to the plasma impedance to be about 1015–1016 cm−3.