Bill Graham

Time resolved imaging of a pulsed plasma discharge in water

Plasma discharges inside water have been widely used for pulsed power applications such as water high voltage lines and switches. More recently underwater plasma discharges have been proved to be very efficient as an advanced oxidations process. The plasma inside water is a source of useful chemical compound such as hydrogen peroxide and hydroxyl radical that can be used for pollution control and sterilization of water [1].

Interactions of cold atmospheric pressure plasma jets with plasmid DNA

Cold atmospheric pressure plasmas offer a unique environment for treatments of soft materials, including bio-materials and living tissue. Single plasma devices can be as small as micro-meters allowing very precise treatments reducing damage to surrounding healthy living cells. It is essential to correlate direct plasma parameters with effects on bio-materials. There are various energy carrying species in the plasma such as charged particles, excited neutrals, radicals, and photons. In particular radical oxygen species ROS e.g. O, OH, have been identified as important.

Investigation of non-thermal atmospheric pressure plasma jet in contact with liquids-using ICCD camera

Summary form only given. Non-thermal atmospheric pressure plasma jets APPjs are a promising new field of research which are beneficial to many associated technologies, such as material treatment and biomedical applications [1],[2]. The use of non-thermal plasmas for the eradication and control of bacterial infection and contamination are acquired great attention in biomedical applications [3]. The effects of non-thermal plasma operating conditions on the bacterial inactivation rate have been investigated in many previous studies. In this study a kHz-driven APPj source of a structure similar to that designed by Teschke et al in 2005 [4], which has been studied recently by many research groups in different configurations [5]. The experimental setup simulates the activity of a APPj against biofilms of Bacillus cereus to investigate the influence of APPj. The method improves the understanding of the interaction mechanism between the plasma jet and the liquid biological samples.The plasma discharge is created inside a cylindrical quartz tube with inner and outer diameters 4mm, 6mm respectively and two electrodes is used to forming dielectric barrier discharge. A high voltage in kilovolt is used to ignite the plasma. A pure helium gas flows through the discharge tube at a 2 standard liters per minute and 0.5% oxygen impurities. This atmospheric pressure plasma jet is used to generate non-thermal plasma bullets away from the production region. The gas channel guides the bullets in the air space between the quartz tube and the liquid surface. In the measurements the plasma plume was allowed to interact with two different liquids, in different volumes (conductor and nonconductor). The interaction is with a dielectric container similar to the one used in the bacterial inactivation by the plasma jet. The distance between the end of the quartz tube and the liquid surface is 1.5 cm. Time-resolved images of the optical emission were measured using ICCD camera (iStar usb Andor Technology DH520) in nanoseconds time scale. The images were illustrated the evolution of the bullets in air-space and liquid surface. The spatio-temporally resolved images investigate the interaction dynamics between the plasma plume and the liquid surface.The emission intensity from only one cycle was captured and accumulated over several cycles to study the behaviour of the plume with different liquid surfaces. The absorption intensity of plasma was measured by the ICCD camera at different locations of the container. The plasma intensities and bullets velocity were measured directly. Primary results were shown that the bullets velocity depends strongly on the type and shape of the liquid surface. The images were proved that the plasma plume slightly spreads out into the liquid and absorbed inside the liquid without any penetration. The plasma remains in the liquid about 1 μs before finally extinguishing, or dissipates into the liquid. The optical emission spectroscopy of the plasma plume on different surfaces was investigated.

Atomic and nuclear physicists combine on recombination

When positive ions and negative electrons get together they naturally want to recombine. This will happen in plasmas (ionised gases) where recombination can affect the charge state distribution of the ions and produce photons. These events influence the energy balance in the plasma and the photons carry information about the constituent ions and their environment. This is why scientists studying plasmas, whether in nuclear fusion machines, the Earths ionosphere or stellar corona and gaseous nebulae, would like to have accurate measurements of reconmbination rates.