This paper introduces a new type of high-frequency (HF) sustained discharge where the HF field applicator is a planar transmission line that allows us to fill with plasma a long chamber of rectangular cross-section (typically 1 m × 15 cm × 5 cm). Peculiar interesting features of this plasma source are a low gas temperature (typically below 40 °C in the 1 Torr range in argon), broadband impedance matching with no need for retuning, stability and reproducibility of the discharge (non-resonant behaviour). This type of plasma source could be useful for web processing; nonetheless, it is applied here to plasma sterilization, taking advantage of its low gas temperature to inactivate microorganisms on polymer-made medical devices to avoid damaging them. The predominant biocide species are the UV photons emitted by the discharge whereas most plasma sterilization techniques call for reactive species such as O atoms and OH molecules, which induce significant erosion damage on polymers. Polystyrene microspheres are actually observed to be erosion-free under the current plasma sterilization conditions (scanning electron micrographs have been examined). Moreover, inactivation is quite fast: 106 B. atrophaeus spores deposited on a Petri dish are inactivated in less than 1 min. Correlation of the UV radiation with the spore inactivation rate is examined by (i) considering the emitted light intensity integrated over the 112–180 nm vacuum UV (VUV) range with a photomultiplier; (ii) looking with an optical spectrometer at the emission spectrum over the 200–400 nm UV range; (iii) using absorption spectroscopy to determine the role of the VUV argon resonant lines (105 and 107 nm) on spore inactivation. It is found that the test-reference spores are mainly inactivated by VUV photons (112–180 nm) that are primarily emitted by impurities present in the argon plasma.

The surfaguide is a waveguide-based electromagnetic-surface-wave launcher that allows sustaining long plasma columns using microwaves. Its electrodynamic characteristics are examined experimentally and theoretically in the perspective of achieving an efficient plasma source without any need for impedance matching retuning as operating conditions are varied over a broad range. The plasma source design and its modelling using equivalent-circuit theory are described and a simple procedure is provided to determine the optimum dimensions of the surfaguide that maximize the transfer of microwave power to plasma. As an example, with an optimized surfaguide, the reflected power in an N 2 discharge at atmospheric pressure stays below 3% for powers in the 2-6 kW range and gas flow rates in the 30-150 l min −1 domain under varying concentrations (<2%) of admixed gases such as SF 6 , O 2 and argon.

Long plasma columns generated by high-frequency (HF) fields and extending over distances longer than the free-space wavelength of the applied electromagnetic (EM) field are of interest in various applications. A commonly used method to achieve such long plasma columns calls for the propagation of EM surface waves that use the plasma as their propagating medium. In such a case, the HF field applicator, called a wave launcher, is much shorter than the actual length of the plasma column. Long plasma columns can also be sustained by using field applicators that run along the full length of the discharge tube. Most such linear applicators rely on waveguide components. However, it is possible to use transverse electric magnetic planar-transmission-lines based on stripline technology to design efficient linear field applicators. Using such an approach, we have developed a new type of HF linear field applicator that operates on a relatively wide frequency range (typically, 200-2450 MHz). Comparison of the discharge that it generates with a surface-wave discharge (SWD) sustained under similar operating conditions shows that the discharge volume is larger than that obtained with a SWD at the same power level, hence a lower gas temperature and a plasma column more axially uniform, two valuable features for some applications. The contraction of these plasma columns is shown to occur at higher gas pressures than with SWDs. All these measurements are carried out in argon as the discharge gas.

Catheters, which comprise small diameter (≤4 mm), long (typically more than a meter), thermosensitive polymer tubings, are generally used only once. This is because conventional low temperature sterilisation techniques are considered inadequate for used catheters. The plasma sterilisation method proposed in the current paper should allow for the achievement of re‐sterilisation of catheters according to accepted regulations. The plasma process described enables one to sterilise, in less than 10 min, the inner part of a long 4 mm i.d. Teflon tube contaminated initially with 106 Bacillus atrophaeus spores. This result was obtained by achieving an argon discharge at reduced pressure (750 mTorr) within the hollow (dielectric) tube itself. The discharge was sustained using a microwave field‐applicator called a stripline, fully enclosing the tube to be treated. This linear field‐applicator yields a uniform plasma all along the tube, hence the uniform biocide action. The biocide agents are the vacuum ultra‐violet (VUV) photons, which include oxygen and nitrogen atomic lines, the N2 Lyman‐Birge‐Hopfield (LBH) bands, the UV photons emitted by the NOβ and NOγ molecular systems resulting from the contamination, even though at a very low‐level, of the argon gas (high purity argon is used) by air. Scanning electron microscopy (SEM) revealed no apparent damage to the external structure of the spores and to polystyrene microspheres exposed to plasma during the time required for reaching sterility. To check for sterility in such narrow bore tubes without having to cut them into two pieces, a procedure was developed to introduce and afterwards collect the bacterial spores used as bio‐indicators. This diagnostic procedure allowed, at the same time, the imaging of the microorganisms relatively efficiently with SEM, showing the eventual stacking of bacterial spores, a possible source of sterilisation failure.

Cover: The cover presents two SEM micrographs showing stacks of bacterial spores on the inner surface of a Teflon tube (i.d./o.d. 4/6 mm). Low‐damage sterilization is achieved using a glow‐discharge in flowing argon at reduced pressure, directly within the thermally‐sensitive dielectric tube. Further details can be found in the article by J. Pollak, M. Moisan,* D. Kéroack, J. Séguin, and J. Barbeau on page 14.