Emilio Martines

In 1996, when the danger of sideways forces was first recognised, the operational window of the JET tokamak was significantly restricted. Limits were placed on the maximum magnetic field and plasma current to prevent excessive stresses on the vacuum vessel. Despite three decades of research, predictions for the sideways force on the ITER wall remain highly uncertain, ranging from 2 to 60 MN with the upper estimate exceeding the design value of 48 MN, which would result in operational restrictions (operation with I_p<15 MA potentially affecting ITER's ultimate fusion performance). To address this issue, the ITPA community launched the dedicated joint experiment MDC-25 in 2018. While substantial progress has been made, recent findings highlight the need for complementary studies on a specialised linear device to investigate plasma-wall currents, key contributors to sideways forces. Here, we propose the first linear device specifically designed to investigate plasma-wall interactions in the presence of kink modes, with the aim of resolving uncertainties related to plasma-wall currents and associated sideways forces. It is expected that the findings obtained with the new device will guide the design of vacuum vessels and plasma facing components for future tokamaks.

The detection and quantification of reactive oxygen and nitrogen species (RONS) in plasma-treated water (PTW) are essential for advancing plasma applications in biomedical and agricultural fields. However, RONS characterization remains challenging, as conventional techniques often require chemical reagents that can alter the sample. Electrochemical impedance spectroscopy (EIS) offers a non-destructive alternative by probing the electrical response of aqueous systems and providing information on ionic concentration, charge transfer, and diffusion processes. This study investigates the feasibility of EIS as a diagnostic tool for characterizing physicochemical changes in PTW. Calibration experiments were performed using saline solutions with different ionic concentrations to evaluate the sensitivity of impedance measurements. Impedance spectra were recorded over a frequency range of 0.1 Hz to 10 kHz and analyzed using Nyquist and Bode plots with equivalent circuit modeling. Deionized water was treated with cold atmospheric plasma at different discharge powers (3.53–10.15 W) and treatment times (5–30 min) to generate RONS. The results show that EIS can monitor plasma-induced changes in conductivity and interfacial properties associated with variations in ionic content. In particular, systematic changes in solution resistance and admittance were observed and were correlated with plasma-induced changes in ionic composition. These findings demonstrate that EIS is a sensitive and non-invasive diagnostic method for PTW analysis.

Cold atmospheric plasma (CAP) has demonstrated promising antimicrobial activity and potential to promote tissue regeneration. However, most existing research has focused on its effects on soft tissue cells, such as fibroblasts, while its influence on osteoblasts, the main cells responsible for alveolar bone formation, is rather limited. As a first step towards addressing this gap, the present study assessed the biological effects of a newly custom-designed CAP source on the pre-osteoblastic MC3T3-E1 cell line, with a primary focus on the cellular survival and osteogenic differentiation. Through the use of diverse in vitro methods, the cytotoxicity (e.g. Live&Dead and CCK-8 assays; morphological characterisation) and osteogenic differentiation potential (e.g. alkaline phosphates activity and Alizarin Red S staining) of a helium-based CAP were assessed. The cytotoxicity results indicated a treatment duration- and exposure number-dependent response, i.e. repeated CAP exposures within the 30 s–60 s range yielded the highest cell survival and metabolic activity, while extended exposures (180 s–240 s) significantly reduced cell viability by approx. 30%. On the contrary, an opposite trend was observed in terms of osteogenic differentiation, where repeated, prolonged exposures (90 s−120 s), resulted in an enhanced matrix mineralisation, suggesting an increased level of late-stage osteogenic differentiation. Overall, these findings indicate that CAP treatment can modulate the MC3T3-E1 pre-osteoblasts’ behaviour in a dose-dependent manner, suggesting a potential relevance for bone regeneration applications, and possibly for alveolar bone regeneration. Importantly, this study represents an initial effort towards the exploration of the effects of CAP exposure on osteoblasts using a pre-osteoblastic cell line and highlights the need for further research through more in-depth studies (e.g. periodontal-specific cell models and in vivo studies) prior to clinical translation.

While atmospheric pressure plasma sources are emerging as potentially innovative instruments in medicine, some aspects of the interaction between plasma and biological substrates remain unclear. The high diversity in both sources and applications in the literature, and the lack of a systematic testing protocol, has resulted in a wide variety of devices that cannot be efficiently compared with one another. In this work, an integrated benchmark involving physical, chemical, and biological diagnostics is proposed. The setup is designed to be stable and fixed, while remaining adaptable to different sources. Three different sources, for a total of five configurations, are compared, demonstrating the possibility of obtaining multimodal data. Comparing the biological effects in terms of E. coli abatement between direct and indirect treatments allowed for the exclusion of short-timescale species and phenomena to have a key role in the abatement. The chemical characterisation describes the equilibrium of reactive oxygen and nitrogen species in treated samples, whose presence in the water has been found to be coherent with the plasma operating gas and the nitrogen vibrational temperatures. Nitrate, nitrite and peroxide are excluded from having an autonomous role in the inactivation biochemistry, suggesting the presence of a synergistic effect.

Due to the great increase in the non-thermal plasma (NTP) bio-applications, especially thanks to its antimicrobial properties, many types of NTP generating devices have been developed recently. However, a comparison of these devices is difficult due to the differences in the setup of studies testing them, e.g., in species of microorganisms used and sample preparations. In this study, we optimized a robust and reproducible standard protocol using Bacillus subtilis spores and applied it to compare seven different NTP generating devices in terms of technical parameters and sporicidal properties. Inhibition zones determined using the Aurora software and the complete inhibition of bacteria growth induced by the NTP treatment were analyzed to determine both local and overall effects, respectively. The highest sporicidal efficacy of the tested devices was achieved by the volume dielectric barrier discharge from Wroclaw, which inhibited 99.9% of colony forming units after 30 min of exposure. To our knowledge, a comparative study of this extent has not been published to date. The presented protocol is based on an established bacterial method and can therefore serve as a general standard for an effective comparison of NTP sources across laboratories worldwide.

To achieve a uniform argon plasma in an atmospheric pressure jet, we explored the possibility of using dual-frequency excitation in a coaxial dielectric barrier discharge device. Two separate ring-shaped electrodes outside an alumina tube generate the two frequencies. The upstream electrode is powered at low frequency (LF, 17 kHz ), while the downstream electrode is powered at radio frequency (RF, 27 MHz ). To assess the interaction with the substrate, a grounded electrode, covered by a glass substrate, is placed 5 mm from the outlet of the alumina tube. We analyze the device with a fluid model and compare the results with experimental electrical and optical characterization. As the plasma is ignited by the LF, positive streamers develop from the LF electrode and reach the substrate in a few hundred nanoseconds. At this stage, the substrate is charged and a surface discharge propagates on the glass; however, no additional ionization occurs in the jet. As RF is added, the plasma is sustained by modulation in the Ω regime. At the same time, the LF polarization propagates through the plasma, influencing the sheaths on the facing dielectric walls. When the voltage drop in the sheaths exceeds a threshold level, an additional γ mode originates due to the secondary electrons emitted by the surfaces, leading to an increase in power dissipation. This coexistence of the two regimes is observed in the simulation, and it is validated experimentally by time-resolved photoemission measurements. As a result, the dual-frequency plasma exhibits a filamentary structure similar to that of an LF-driven jet. However, RF excitation caused diffused pre-ionization of the gas, which reduced the charge density gradients, resulting in wider microdischarge channels and a lower average electric field. Streamers propagation is therefore limited, while an ion flow to the substrate is maintained and controlled by the LF polarization.

Due to its antimicrobial, anti-inflammatory and pro-healing properties, the application of cold atmospheric plasma (CAP) has emerged as a new and promising therapeutic strategy in various fields of medicine, including general medicine and dentistry. In this light, the aim of the present study was to investigate the effects of a homemade plasma jet on the cellular behaviour of two important cell types involved in gingivitis, namely gingival fibroblasts (HGF-1 cell line) and macrophages (RAW 264.7 cell line), by the direct application of CAP in different experimental conditions. The cellular behaviour of the HGF-1 cells was investigated in terms of viability/proliferation (LIVE/DEAD and CCK-8 assays), morphological features (immunofluorescent staining of the actin cytoskeleton) and fibronectin expression (immunocytochemical staining of the fibronectin network), while the macrophages’ response was evaluated through the assessment of the cellular survival/proliferation rate (LIVE/DEAD and CCK-8 assays), morphological behaviour (immunofluorescent staining of the actin cytoskeleton) and inflammatory activity (pro-inflammatory cytokine secretion profile (ELISA assay) and foreign body giant cells (FBGCs) formation (immunofluorescent staining of the actin cytoskeleton and multinuclearity index determination)). The in vitro biological assessment revealed an upward trend dependent on treatment time and number of CAP applications, in terms of fibroblasts proliferation (p < 0.0001) and fibronectin expression (p < 0.0001). On the other hand, the macrophages exposed to five consecutive CAP applications for longer treatment times (over 120 s) exhibited a strong pro-inflammatory activity, as evinced by their altered morphology, pro-inflammatory cytokine profile (p < 0.0001) and FBGCs formation. Overall, our results demonstrate that CAP exposure, when used with appropriate operating parameters, has a beneficial effect on the cellular response of HGF-1 and RAW 264.7 cells, thus paving the way for further in vitro and in vivo investigations that will allow the translation of CAP treatment from research to clinic as an alternative therapy for gingivitis.

The High Voltage Padova Test Facility (HVPTF) is an experimental device for investigating high voltage (HV) Direct Current insulation in a vacuum, in support of the development of the prototype of a neutral beam injector for ITER, named MITICA. Inside a high vacuum environment, two stainless steel electrodes, spaced by a few centimeters gap, can achieve a voltage difference of up to 800 kV. During the electrode conditioning process, small current bursts, known as micro-discharges (MDs) occur, accompanied by the emission of X-rays, and of an overall increase in gas emission measurement. This study focuses on the fine dynamics of the MD phenomenon measured by the current signal and by the X-ray detectors, in an attempt to provide a possible physical interpretation of this mechanism. In particular, it appears that the MD fine dynamics are related to the growing asymmetry between the MD current values collected by the anode and cathode, observed during the electrode conditioning. The role of the vacuum chamber, acting as a third electrode, is investigated by an updated toy model, which evaluates the different current contributions collected from the two polarized electrodes, particularly those generated by secondary electron (SE) emission. The ratio of anode to cathode currents computed by the toy model closely matches the experimental one. Further experimental observations supporting the hypothesis of anode gas emission and expansion are discussed. Finally, a first study about the statistical distribution of the time intervals between successive MD suggests the occurrence of almost two different trigger mechanisms, evolving during the electrode conditioning process.