Streamer inception and imaging in various atmospheres

Streamers are the first stage of many discharges involving high voltages.They consist of a propagating ionization front leaving behind atrail of conductive, quasi-neutral plasma. In this contribution we willshow experiments on streamers revealing some of their most importantproperties: their inception and their propagation and branchingbehaviour.We study streamer inception by applying repetitive high voltagepulses and studying the statistics of inception delay. By means of smallbias pulses between the high voltage pulses, we are able to manipulatethese statistics, which reveals a lot on the processes governing theinception.Secondly, we study the propagation and branching of streamers bya combination of stereoscopic and stroboscopic measurements of ’lowcomplexity’ streamer discharges. We have developed automated routineswhich can determine propagation velocities, branching angles andmuch more from these and can directly compare these against numericalresults, thereby also giving unprecedented insights into the fundamentalsof such discharges

Measuring electron density, electric field and temperature of a micro-discharge air plasma jet using optical emission spectroscopy

A micro-discharge air plasma jet was developed operated at low frequency (50 Hz) ac high voltage (kV). The micro-discharge plasma jet was generated by feeding air through a dielectric installed between two disk-shaped electrodes with a hole of 1 mm diameter in the center. Both of the electrodes were made of copper. The micro-discharge in the dielectric is evolved as a plasma jet from the outer electrode through its hole. The ac power supply was a neon light transformer. Optical emission spectroscopy was employed to study the plasma discharge characteristics. Specair software was used to analyze the collected spectrum. The reduced electric field and electron density of plasma as well as rotational and vibrational temperatures, referring to ion or gas and electron temperature respectively were measured by processing emission spectrum

Effects of a negative corona discharge on subsequent positive streamers

Positive streamers can be affected significantly by preceding discharges such as earlier streamers or a corona discharge. In this paper, we primarily discuss the effect of such a corona discharge on subsequent positive streamers with different intervals between them (0/500/990 ms) in air and pure nitrogen at 80 mbar with a repetition frequency of 1 Hz. We found that in air, when the interval time is 500 or 990 ms, a preceding discharge leads to shorter and weaker streamers or even prevents streamer inception altogether. This is likely due to negative ions which have converted to species that are harder to detach. The weaker streamers are also caused by more stable inception clouds which branch out later. When a corona discharge immediately precedes a streamer discharge in air, the streamers become longer, brighter while some branches develop from the side of the electrode instead of its tip. These effects are likely all related to plasma shielding caused by the corona discharge. In nitrogen, inception is primarily caused by electrons instead of negative ions. When the interval time is 500 or 990 ms in this gas, there is nearly no difference between streamers with and without a preceding corona discharge, because the inception time in nitrogen is the formative time that is not sensitive to the initial electron density. For near-zero intervals between corona and streamer discharges in nitrogen, streamers become smoother and thicker which can be attributed to a higher background ionization left by the corona discharge

Cold atmospheric plasma as an effective method to treat diabetic foot ulcers: A randomized clinical trial

Cold atmospheric plasma (CAP) was shown to decrease bacterial load in chronic wounds. It was also presented as a novel approach to healing wounds in both in vitro and in vivo experiments. We aimed to examine the first randomized clinical trial for the use of CAP in diabetic foot ulcers. Patients (n = 44) were randomly double-blinded, and assigned to receive standard care (SC, n = 22) without or with CAP, to be applied three times a week for three consecutive weeks (SC + CAP, n = 22), using block randomization with mixing block sizes of four. The trial was conducted at the Diabetes Research Center in Tehran, Iran. CAP was generated from ionized helium gas in ambient air, and driven by a high voltage (10 kV) and high frequency (6 kHz) power supply. Primary outcomes were wound size, number of cases reaching wound size of <0.5, and a bacterial load after over three weeks of treatment. CAP treatment effectively reduced the fraction of wound size (p = 0.02). After three weeks, the wounds to reach fraction wound size of ≤0.5 was significantly greater in the SC + CAP group (77.3%) compared to the SC group (36.4%) (p = 0.006). The mean fraction of bacterial load counted in each session ‘after CAP exposure’ was significantly less than ‘before exposure’ measures. CAP can be an efficient method to accelerate wound healing in diabetic foot ulcers, with immediate antiseptic effects that do not seem to last long

Beneficial effects of cold atmospheric plasma on inflammatory phase of diabetic foot ulcers; a randomized clinical trial

Purpose: The healing process is impaired in diabetic wounds like the other types of chronic wounds. Cytokines, and growth factors are valuable candidates for determination of wound vitality or duration. The aim of this study is to introduce a beneficial method to stop the inflammatory phase and infection in the wound healing process for accelerating the treatment of diabetic foot ulcers. Methods: As a randomized controlled trial, 44 patients with diabetic foot ulcers were selected and randomized. Twenty-two patients received standard care and rest of them received SC (standard care) + CAP (cold atmospheric plasma), n = 22). Clinical examination was performed to assess the status of peripheral nerves and arteries for all patients. Cold plasma jet was used as a source of helium gas plasma generator. Plasma was irradiated on the wound 5 min, 3 times a week for 3 consecutive weeks. Results: Applying a plasma jet was effective in wound healing. The level of inflammatory cytokines was changed. Moreover, after applying plasma the mean expression of these variables was significantly decreased (P = 0.001). Following the plasma treatment, the level of cytokines such as IL-1 (39.44 ± 7.67), IL-8 (368.30 ± 82.43), INF-γ (17.03 ± 2.62), TNFα (22.75 ± 4.02) has decreased, inflammatory factors have ameliorated over three weeks, and accelerate wound healing. After CAP exposure, the mean of the mean fraction of bacterial load counts was significantly decreased. Conclusion: The effect of plasma irradiation on infectious diabetic foot ulcer was decreased bacterial load then accelerated wound healing by effecting on inflammatory phase in diabetic foot ulcers