Mass spectroscopy and ICCD analysis of coupled and uncoupled mode in a Gatling-gun like plasma source

Summary form only given. A novel type of plasma source, composed of an array of seven plasma jets arranged adjacent to one another similar in shape to a Gatling machine gun, has been recently developed to take advantage of the jet-to-jet coupling phenomenon and generate atmospheric pressure cold plasmas with higher intensity and energy with respect to singular plasma jets¹. This source can be operated either in “uncoupled” mode, where seven plasma jets are independently produced, or in the “coupled” mode, where plasma jets merge in a single combined very intense jet. Previous experiments demonstrated a higher antibacterial potential and surface activation efficacy of this source when operated in the coupled mode than in uncoupled one².In the present study, the coupling phenomenon occurring in a Gatling plasma source driven by high voltage sinusoidal waveforms (80 KHz, up to 6.3 kVpeak-peak) was investigated using mass spectrometry, iCCD imaging and electric measurements. Different modes of operation were achieved by varying the feeding gas (He) flow between 2 slm (coupled mode) and 7 slm (uncoupled mode). A molecular beam mass spectrometer (HIDEN HPR60) was used to detect mass spectra of plasmas. Residual gas analyses (RGA) mode and secondary ion mass spectrometry mode (SIMS+/-) were used to investigate the mass spectra of neutral species and of positive and negative ions respectively, for different sets of operating conditions in both coupled and uncoupled mode. ICCD analysis and electrical characterization were also performed to investigate the temporal evolution of the plasma structure in the two modes. Results shows that in the coupled mode ion concentrations are at least one order of magnitude higher as compared to the uncoupled mode for similar operating conditions. Consistently, ICCD acquisitions shows higher emission intensity in coupled than uncoupled mode and differences in plasma front propagation.