Plasma Applications: A Dermatological View

The ability to produce cold plasma at atmospheric pressure conditions was the basis for the rapid growth of plasma related application areas in biomedicine. Plasma comprises a multitude of active components such as charged particles, electric current, UV radiation, and reactive species which can act synergistically. The antiitch, antimicrobial, and anti‐inflammatory effect was already demonstrated in in vivo and in vitro experiments and until now no resistance of pathogens against plasma treatment was observed. The combination of the different active agents and their broad range of positive effects on various diseases, especially easily accessible skin diseases, render plasma quite attractive for applications in medicine. Hence, plasma medicine as an independent and promising medical field has been emerged recently. For medical applications two different types of cold plasma are suitable; indirect (plasma jet, plasma torch) and direct plasma sources (dielectric barrier discharge ‐ DBD). So far, no standards and norms are defined for any of these plasma sources. Also, no convenient criteria for standardization of the quality rating of plasma in the view of dermatological applications exist. Although various cold plasma studies have been performed the results are hardly comparable, as physical parameters of the plasma devices, experimental conditions, and organisms used vary greatly. Therefore, standardized risk analyses are necessary for the assessment of different plasma sources. In this review two plasma sources are described and possible risk factors are discussed to estimate the safety of plasma used as a therapeutic tool in dermatology. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plasmas for medicine

Plasma medicine is an innovative and emerging field combining plasma physics, life science and clinical medicine. In a more general perspective, medical application of physical plasma can be subdivided into two principal approaches. (i) “Indirect” use of plasma-based or plasma-supplemented techniques to treat surfaces, materials or devices to realize specific qualities for subsequent special medical applications, and (ii) application of physical plasma on or in the human (or animal) body to realize therapeutic effects based on direct interaction of plasma with living tissue. The field of plasma applications for the treatment of medical materials or devices is intensively researched and partially well established for several years. However, plasma medicine in the sense of its actual definition as a new field of research focuses on the use of plasma technology in the treatment of living cells, tissues, and organs. Therefore, the aim of the new research field of plasma medicine is the exploitation of a much more differentiated interaction of specific plasma components with specific structural as well as functional elements or functionalities of living cells. This interaction can possibly lead either to stimulation or inhibition of cellular function and be finally used for therapeutic purposes. During recent years a broad spectrum of different plasma sources with various names dedicated for biomedical applications has been reported. So far, research activities were mainly focused on barrier discharges and plasma jets working at atmospheric pressure.     

Microwave Plasmas at Atmospheric Pressure

Microwave plasmas at atmospheric pressure are used for surface treatments like for example cleaning, sterilization or decontamination purposes, for a pre‐treatment to increase the adhesion of lacquer, paint, or glue, and for the deposition of different kind of layers and coatings. Micro plasma jets can also be applied for biomedical applications and for treatment of small and complex geometries like for example the inside of capillaries. Larger plasma torches which exhibit higher gas temperatures can also be used for chemical syntheses like waste gas decomposition, methane pyrolysis, or carbon dioxide dissociation and for plasma spraying purposes. In the present publication an overview on the development and the investigation of the operating principle of two atmospheric pressure microwave plasma torches at frequencies of 2.45 GHz and 915 MHz will be presented. The plasma sources are based on a cylindrical resonator combined with coaxial structures. To explain how these plasma sources work, simulations of the electric field distribution will be discussed. Furthermore, some physical characteristics of an air and an Ar/H2 atmospheric plasma like gas temperatures, excitation temperatures and densities as well as the heating of the plasma by the microwave will be investigated. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microstructured Plasma Sources

Dielectric barrier discharges generated in microcavities or by the use of microstructures have gained increasing interest in research and industry in recent years. This is due to the advantages of small dimensions of microstructured plasma sources and particularly their ability to generate plasmas at atmospheric pressure. In the scope of this work the design and fabrication of two different microplasma sources is presented. First, microplasma reactors based on microstructured electrode arrays which have detailed dimensions in the range of some tens of micrometers and have been successfully applied for the decomposition of waste gases are presented. Subsequently microplasma stamps, which allow the generation of microplasmas in closed cavities and which are powerful process tools for area‐selective modification of various surfaces at atmospheric pressure, are presented. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Discharge Plasma Potential on Diffusion Plasma Parameters Controlled by a Mesh Grid in a Double Plasma Device

The plasma region under investigation is separated from the discharge region by a mesh grid. Plasma potential and electron number densities and electron temperatures under bi‐Maxwellian approximation for electron distribution function of the multi‐dipole argon plasma are measured. The cold electrons in the diffusion region are produced by local ionization. The hot electrons are the ionizing electrons behaving as Maxwellian. The electron trapping process in the discharge region is produced by potential well due to positive plasma potential with respect to the anode and by a repulsive grid. The dependence of ratios of the density of the hot to the cold electrons N_E (=N_eh/N_ec) and hot to cold electron temperature T(=T_eh/T_ec) in the diffusion region on the depth of the potential well has been investigated. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

常压介质阻挡放电等离子体发射光谱的检测分析

以常压介质阻挡放电等离子体作为研究对象,在常温常压条件下使用介质阻挡放电光谱诊断装置,得到N2第二正系跃迁和Ar原子发射谱线。通过对放电光谱的检测分析,可以察知常压介质阻挡放电等离子体的特性,并可运用同一元素谱线的相对强度来诊断电子激发温度等物理参量,以达到对材料表面改性过程的实时监控,工作的结果对常压介质阻挡放电及其在材料改性的应用中具有重要的意义。     

Effect of nonthermal atmospheric pressure plasma on plasma coagulation in healthy persons and patients under treatment with Warfarin

Recently, nonthermal atmospheric pressure plasma has been used in medical devices for sterilization, blood coagulation, induction of apoptosis in cancer cells, etc. The purpose of this study is to evaluate the impact of cold atmospheric plasma on coagulation time in patients under treatment with warfarin as an anticoagulant agent (group A) and to compare this impact in healthy persons (group B). To measure the coagulation time, Clotting Time (CT) is used. After obtaining informed consent from each subject, two venous blood samples are taken to check CT. One sample is processed with plasma (case sample) and the other sample is not processed with plasma. CT in both samples is measured by a physician and recorded in a form in addition to demographic characteristics and drug history. The data are analysed using Statistical Package for the Social Sciences (SPSS) software. The Mann–Whitney test is used for comparison between groups and the Wilcoxon signed‐ranks test is used to compare the difference between CT before and after plasma processing. The results show the significant effect of plasma on the reduction of plasma coagulation time, and this reduction is higher in the warfarin‐treated group.     

微等离子体及其应用

微等离子体已成为近年来国际上低温等离子体研究的热点课题之一。微等离子体是被限制在一个有限的空间范围内(尺度为毫米量级甚至更低)的等离子体,它通常能够运行在大气压条件下,它的低功耗、高密度、高稳定等特性以及其小巧、经济、便携等优势,为其在紫外光源的获得、微化学分析系统、生物医学、材料表面改性和加工、环境污染物的处理等领域提供了广泛的应用空间。文章对微等离子体及其应用进行了综述,介绍了各种微等离子体源的产生方法,以及它们在不同领域的研究和应用情况。     

Atmospheric Pressure Plasma Application for Pollution Control in Industrial Processes

Economic application of atmospheric pressure plasma technology for industrial pollution control requires fulfilling two propositions: First application of pollution control technologies needs to result in clear environmental, health, or safety benefits motivating political measures. Second plasma technology needs to be competitive as compared to other available pollution control technologies. Thus in this article methods for the evaluation of atmospheric plasma application for industrial pollution control are reviewed: Examples of emission regulations and emission control technologies are given. Requirements of industrial scale emission control and of thermal and non‐thermal exhaust gas treatment technologies are described. The potential of various non‐thermal plasma reactor concepts for cost effective treatment of industrial scale gas flows is analyzed, and methods for the evaluation of plasma energy balance and plasma chemical kinetics are given for them. How to deal with shortcomings of atmospheric pressure plasmas such as lack of plasma‐chemical selectivity is addressed in a section about plasma‐catalytic hybrid processes. Further the progress made recently in electrostatic precipitation is reviewed, and the importance of electro‐hydrodynamic effects for the reactor design both for electrostatic precipitation and for plasma chemical pollution control is considered. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterisation of a Simple Non‐Thermal Atmospheric Pressure Plasma Source for Biomedical Research Applications

The recent progress in plasma medicine as well as biomedical aspects of plasma physics over the last years have enhanced the need for experimental plasma devices which are capable of producing non‐thermal atmospheric pressure plasmas. These plasma sources are used for studying the effect of non‐thermal plasmas on biological samples of different nature. In this paper we present such an easy to build low cost apparatus that can be used for scientific as well as for educational purposes. Directions for the construction of the device are given and the basic plasma parameters are investigated. The characterisation of the experiment was done by electrical diagnostics for the measurements of the plasma potential in combination with optical emission spectroscopy. The latter is used for the determination of the excitation temperature of the plasma and the electron density. Furthermore the influence of the produced plasma on yeast cells is demonstrated. The produced plasma is characterised in different ways and it was found that the feeding gas has also a considerable impact on the radio frequency wave form of the source. It is also demonstrated that the constructed plasma source is capable of producing non‐thermal plasma that hinder cell growth of yeast colonies on a agar substrate. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

针板型大气压氦气冷等离子体射流的二维模拟

大气压冷等离子体射流的传播机理一直是人们研究的一个热点. 本文采用自洽的二维等离子体流体模型, 研究了大气压氦气冷等离子体射流在自身环境气体中以及在介质管中的传播问题. 得到了电子密度、电离速率、空间电场以及电子温度等参量的时空分布规律, 分析了介质管大小以及介质管介电常数对射流放电性质的影响, 得到了一种提高电子密度和射流尺寸的新方法. 关键词： 大气压冷等离子体射流 等离子体子弹 数值模拟 流体模型     

一种新型微空阴极结构的大气压射频冷等离子体源

介绍微空阴极的结构和物理机理，着重介绍一种新型大气压下射频激励的大面积冷等离子体源——融合空心阴极(fused hollow cathodes，FHC).结合应用和与之有关的研究，简单介绍空心阴极的放电特性，以及影响其放电特性的因素，如阴极材料、气体种类、频率、气体流速、气压、阴极内径等.另外提到了其他两种相关的微空阴极系统. 关键词： 微空阴极 大气压 冷等离子体 射频     

Impact of Electrode Design,Supply Voltage and Interelectrode Distance on Safety Aspects and Characteristics of a Medical DBD Plasma Source

In the frame of plasma source development for dermatological applications in the field of plasma medicine, operational safety of the devices is of superior priority. For sources based on the concept of dielectric barrier discharges (DBD), electric potentials with amplitudes in the range of some kV are arranged in close proximity to the skin of patients, wherein dielectric strength of the electrodes and leakage currents are crucial for electrical applicability. In this work, ceramic electrodes of 10 mm in diameter and varying ceramic thickness are operated at input powers up to 300 mW against non‐biological counter electrodes. In a combined experimental and numerical approach, electric fields inside the ceramic are determined, whereas values are well below the dielectric strength of the material. The spectrally weighted plasma emission is within limit values of exposure to human skin as long as daily treatment does not exceeded 7 h. Neutral gas temperatures of up to 310 K are determined which underline the minor thermal impact of the plasma exposure. In contrast, values for reduced electric fields are of the order of some hundred Townsend and thus the electrons can initiate various secondary effects such as chemical reaction chains. Consequently, ozone concentrations in the discharges are quantified between 230 ppm and 1140 ppm in close proximity to the actual discharge volume and the results are discussed in the frame of risk assessment for therapeutic applications in dermatology. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Development and Application of Low Temperature Plasma Technology

The development and applications of low temperature plasma technology used in surface modification of materials are presented in this paper. Based on plasma sources and ion sources technology, multi-functions ion implantation and deposition technologies were developed and the related processes are also used to treat different products. The related technologies were translated into industrial productions supported by national research projects. Following the last development of international plasma researches, the standardization and internationalization processes of plasma technologies are executed in our center.     

Generation of Large‐Area Highly‐Nonequlibrium Plasma in Pure Hydrogen at Atmospheric Pressure

Diffuse Coplanar Surface Barrier Discharge (DCSBD) is a novel type of atmospheric‐pressure plasma source developed for high‐speed large‐area surface plasma treatments. Basic characteristics of DCSBD operated in pure atmospheric‐pressure hydrogen were measured using optical and emission spectroscopy methods, and its potential for the surface treatment application was demonstrated by hydrogen plasma reduction of Cu₂O thin layers. The discharge generates a thin layer of diffuse non‐equilibrium plasma with a high power density of 70 Wcm^–3. The mean electron density and electron temperature derived from spectroscopic data were 1.3 x 10¹⁶cm^–3 and 19 x 10³K, and the surface Cu₂O layers forming a weak boundary were reduced to metallic copper within several seconds. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Pinch Plasma Radiation Sources for the Extreme Ultraviolet

Extreme ultraviolet lithography (EUVL) is under discussion to be implemented in the production of chips as early as 2005 to 2007 for reducing structures in semiconductor devices to below 70 nm. The challenging task of developing optical components and radiation sources within this short period of time is pushing technology. As discharge produced and laser produced plasmas are the main candidates for EUV‐sources, plasma technology is forced to leap forward significantly. Progress in EUV‐sources is expected to open EUV‐technology for other applications in science and technology with increased need for spatial resolution, elemental contrast or sensitivity. Various technical concepts for realising high power sources for EUV lithography are under investigation world‐wide. Laser produced and discharge produced plasmas are the most promising schemes. Discharge produced pinch plasmas in general are of special interest, because their prospected costs (esp. cost of ownership) for the demanded throughput is expected to be much lower than with laser produced plasmas. However, the discharge plasmas are of high risk, because many crucial tasks have to be solved before reaching the required power levels. Beside the optimisation of the EUV‐generation ‐ which is the key to build the most reliable device with demanded EUV power ‐ the success will depend on the individual technical aspects of each source concept. Currently investigated pinch plasma concepts are evaluated based on their potential to be upgraded to fulfil the challenging demands of EUV‐lithography.     

Plasma Photocathodes

Plasma wakefield accelerators offer accelerating and focusing electric fields three to four orders of magnitude larger than state-of-the-art radiofrequency cavity-based accelerators. Plasma photocathodes can release ultracold electron populations within such plasma waves and thus open a path toward tunable production of well-defined, compact electron beams with normalized emittance and brightness many orders of magnitude better than state-of-the-art. Such beams will have far-reaching impact for applications such as light sources, but also open up new vistas on high energy and high field physics. This paper reviews the innovation of plasma photocathodes, and reports on the experimental progress, challenges, and future prospects of the approach. Details of the proof-of-concept demonstration of a plasma photocathode in 90° geometry at SLAC FACET within the E-210: Trojan Horse program are described. Using this experience, alongside theoretical and simulation-supported advances, an outlook is given on future realizations of plasma photocathodes such as the upcoming E-310: Trojan Horse-II program at FACET-II with prospects toward excellent witness beam parameter quality, tunability, and stability. Future installations of plasma photocathodes also at compact, hybrid plasma wakefield accelerators, will then boost capacities and open up novel capabilities for experiments at the forefront of interaction of high brightness electron and photon beams.     

Plasma Diagnostics Using K‐Line Emission Profiles of Silicon

Modifications of K‐line profiles due to a warm dense plasma environment are a suitable tool for plasma diagnostics. We focus on Si K_α emissions due to an electron transfer from 2P to 1S shell. Besides 2P fine structure effects we also consider the influence of excited and higher ionized emitters. Generally spoken, a plasma of medium temperature and high density (warm dense matter) is created from bulk Si the greater part of atoms is ionized. The high energy of K_α x‐rays is necessary to penetrate and investigate the Si sample. The plasma effect influences the many‐particle system resulting in an energy shift due to electron‐ion and electron‐electron interaction. In our work we focus on pure Si using LS coupling. Non‐perturbative wave functions are calculated as well as ionization energies, binding energies and relevant emission energies using the chemical ab initio code Gaussian 03. The plasma effect is considered within a perturbative approach to the Hamiltonian. Using Roothaan‐Hartree‐Fock wave functions we calculate the screening effect within an ion‐sphere model. The different excitation and ionization probabilities of the electronic L‐shell and M‐shell lead to a charge state distribution. Using this distribution and a Lorentz profile convolution with a Gaussian instrument function we calculate spectral line profiles depending on the plasma parameters. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigations of Droplet‐Plasma Interaction using Multi‐Dimensional Coupled Model

Recently developed multi‐dimensional coupled fluid‐droplet model is used to investigate the behavior of complex interaction between the liquid precursor droplets and atmospheric pressure plasma (APP). The significance of this droplet‐plasma interaction is not well understood under diverse realm of working conditions in two‐phase flow. In this study, we explain the implication of vaporization of liquid droplets in APP which are subsequently responsible to control major characteristics of surface coating depositions. Coalescence of water droplets is more dominant than Hexamethyldisiloxane (HMDSO) droplets because of its sluggish rate of evaporation. A disparity in the performance of evaporation is identified in two independent mediums, such as gas mixture and discharge plasma using HMDSO precursor. The length of evaporation of droplets is amplified by an increment of gas flow rate indicating with a reduction in the gas temperature and electron mean energy. In particular, the spatio‐temporal density distributions of charged particles show a clear pattern in which the typical nitrogen impurity ions are primarily effective as compared to other helium ionic species along the pulse of droplets in APP. Finally, we contrast the behavior of discharge species in the pure helium and He‐N2 gas mixtures revealing the importance of stepwise and Penning ionization processes. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

大气压氩气射流等离子体的光谱特性研究

等离子体喷枪是一种重要的等离子体源,已成为近几年低温等离子体研究的一个重要课题。本文利用钨针-钨丝网电极制作了直流喷枪装置,在大气压空气中产生了稳定的等离子体羽,并采用发射光谱的方法,对等离子体羽的等离子体参数进行了研究。在钨针电极与钨丝网电极之间放出耀眼的白光,钨丝网电极出口的气流下游有火苗形状的等离子体羽喷出。在电压保持不变的条件下(13.5 kV),等离子体羽长度随气体流量增加而增大;在气体流量保持不变的条件下(10 L·min-1),羽长度随外加电压的增大而增大。在气体流量一定的条件下,放电电压和放电电流呈反比例关系,即电压随着电流的增大而减小,说明放电属于辉光放电。采集了该喷枪在300～800 nm范围内的放电发射光谱,通过玻尔兹曼方法对放电等离子体电子激发温度进行了测量。结果表明,电子的激发温度随外加电压的增大而降低,随着工作气体流量的减小而升高。利用放电的基本理论对上述现象做了解释。这些研究结果对大气压均匀放电等离子体源的研制和工业应用具有重要意义。