Electrosurgical Plasma Discharges

Electrosurgical instruments employing plasmas to volumetrically ablate tissue are now enjoying widespread use in medical applications. We have studied several commercially available instruments in which luminous plasma discharges are formed near electrodes immersed in saline solutions when sufficiently large amplitude bipolar voltage waveforms are applied. Different aqueous salt solutions have been investigated, including isotonic NaCl solution as well as solutions of KCl, and BaCl_2. With strong driving voltage applied, a vapor layer is formed as well as visible and UV optical emissions. Spectroscopic measurements reveal the predominant emissions are from the low ionization potential salt species, but significant emissions from electron impact dissociated water fragments such as OH and H-atoms also are observed. The emissions also coincide with negative bias on the active electrode. These optical emissions are consistent with an electron density of about 10^12cm^-3 and an electron temperature of about 4 eV. Experimental results and model calculations of the vapor layer formation process and plasma formation in the high-field region will be discussed.