A non-thermal plasma source ('plasma needle') generated under atmospheric pressure by means of radio-frequency excitation has been characterized. Plasma appears as a small (sub-mm) glow at the tip of a metal pin. It operates in helium, argon, nitrogen and mixtures of He with air. Electrical measurements show that plasma needle operates at relatively low voltages (200-500 V peak-to-peak) and the power consumption ranges from tens of milliwatts to at most a few watts. Electron-excitation, vibrational and rotational temperatures have been determined using optical emission spectroscopy. Excitation and vibration temperatures are close to each other, in the range 0.2-0.3 eV, rotational gas temperature is at most a few hundred K. At lowest power input the source has the highest excitation temperature while the gas remains at room temperature. We have demonstrated the non-aggressive nature of the plasma: it can be applied on organic materials, also in watery environment, without causing thermal/electric damage to the surface. Plasma needle will be used in the study of plasma interactions with living cells and tissues. At later stages, this research aims at performing fine, high-precision plasma surgery, like removal of (cancer) cells or cleaning of dental cavities.

The Advanced Oxidation Process pulsed corona discharges have been utilized for the degradation of phenol in aqueous solution. The pulsed positive corona discharges are struck in the ambient gas phase over the solution. Experiments have been performed using both an air and argon atmosphere. Phenol conversion and the production of major oxidation products in the solution have been determined, using ion-exclusion chromatography with UV absorbance and conductivity detectors in series. The corona pulse energy has been measured from voltage and current waveforms using capacitive current correction. Oxidation products are polyhydroxybenzenes and carboxylic acids. Even though phenol conversion efficiencies by pulsed positive corona discharges in air and argon are similar, the degradation pathways are different.

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In this work we present Thomson scattering measurements on a nanosecond pulsed high voltage dielectric barrier discharge (DBD)-like helium plasma jet, operated in ambient air. With the low detection limit offered by a triple grating spectrograph equipped with a high quantum efficiency intensified charge-coupled device (ICCD) camera, temporally and spatially resolved electron densities and mean energies have been mapped. 7 kV peak with 250 ns width pulses at 20 kHz are applied to the inner cylindrical shaped electrode of a DBD. This results in a peculiar hollow electron density profile in the vicinity of the jet nozzle with maximum values of n e = 5 × 10 18 m −3 and mean energies of up to 2.5 eV. Further downstream, the profile collapses radially and contracts. A much higher electron density is found (2 × 10 19 m −3) while the mean energy is lower (0.5 eV).

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