Modeling of very high frequency large-electrode capacitively coupled plasmas with a fully electromagnetic particle-in-cell code

Phenomena taking place in capacitively coupled plasmas with large electrodes and driven at very high frequencies are studied numerically utilizing a novel energy- and charge-conserving implicit fully electromagnetic particle-in-cell / Monte Carlo code ECCOPIC2M. The code shows a good agreement with different cases having various collisionality and absorbed power. Although some aspects of the underlying physics were demonstrated in the previous literature with other models, the particle-in-cell method is advantageous for the predictive modeling due to a complex interplay between the surface mode excitations and the nonlocal physics of the corresponding type of plasma discharges operated at low pressures, which is hard to reproduce in other models realistically

Modelling of a miniature microwave driven nitrogen plasma jet and comparison to measurements

The MMWICP (miniature microwave ICP) is a new plasma source using the induction principle. Recently Klute et al presented a mathematical model for the electromagnetic fields and power balance of the new device. In this work the electromagnetic model is coupled with a global chemistry model for nitrogen, based on the chemical reaction set of Thorsteinsson and Gudmundsson and customized for the geometry of the MMWICP. The combined model delivers a quantitative description for a non-thermal plasma at a pressure of p = 1000 Pa and a gas temperature of Tg = 650–1600 K. Comparison with published experimental data shows a good agreement for the volume averaged plasma parameters at high power, for the spatial distribution of the discharge and for the microwave measurements. Furthermore, the balance of capacitive and inductive coupling in the absorbed power is analyzed. This leads to the interpretation of the discharge regime at an electron density of ne ≈ 6.4 × 1018 m−3 as E/H-hybridmode with an capacitive and inductive component

3-dimensional semi-analytic model of a microwave driven miniature plasma jet

Microwave or Radio frequency driven plasma jets play an important role in various technical applications and are usually operated in a capacitive mode. The MiniatureMicroWaveICP (MMWICP) is a new promising plasma source and successfully transfers the induction principle to a miniature plasma jet. This work presents a 3-dimensional semi-analytic model of the electron density of the MMWICP. The model is based on a drift-diffusion equation which is coupled to the electromagnetic model of the MMWICP presented by Klute et al in Plasma Sources Sci. Technol. 29 065018 (2020). An analytic solution is found by expanding the expression of the electron density into a series of eigenfunctions. The 3-dimensional profile of the electron density is simulated for characteristic values of the power absorbed by the plasma. The results show that the spatial distribution of the electron density is highly depended on the absorbed power. The results are found to be in good agreement with experimental measurements.74th Annual Gaseous Electronics Conferenc

Controlling plasma properties under differing degrees of electronegativity using odd harmonic dual frequency excitation

International audienceThe charged particle dynamics in low-pressure oxygen plasmas excited by odd harmonic dual frequency waveforms (low frequency of 13.56 MHz and high frequency of 40.68 MHz) are investigated using a one-dimensional numerical simulation in regimes of both low and high electronegativity. In the low electronegativity regime, the time and space averaged electron and negative ion densities are approximately equal and plasma sustainment is dominated by ionisation at the sheath expansion for all combinations of low and high frequency and the phase shift between them. In the high electronegativity regime, the negative ion density is a factor of 15--20 greater than the low electronegativity cases. In these cases, plasma sustainment is dominated by ionisation inside the bulk plasma and at the collapsing sheath edge when the contribution of the high frequency to the overall voltage waveform is low. As the high frequency component contribution to the waveform increases, sheath expansion ionisation begins to dominate. It is found that the control of the average voltage drop across the plasma sheath and the average ion flux to the powered electrode are similar in both regimes of electronegativity, despite the differing electron dynamics using the considered dual frequency approach. This offers potential for similar control of ion dynamics under a range of process conditions, independent of the electronegativity. This is in contrast to ion control offered by electrically asymmetric waveforms where the relationship between the ion flux and ion bombardment energy is dependent upon the electronegativity

Concepts, Capabilities, and Limitations of Global Models : A Review

International audienceFor researchers wishing to generate an understanding of complex plasma systems, global models often present an attractive first step, mainly due to their ease of development and use. These volume averaged models are able to give descriptions of plasmas with complex chemical kinetics, and without the computationally intensive numerical methods required for spatially resolved models. This paper gives a tutorial on global modeling, including development and techniques, and provides a discussion on the issues and pitfalls that researchers should be aware of. Further discussion is provided in the form of two reviews on methods of extending global modeling techniques to encompass variations in either time or space

Searching for the image of scientists from the point of view of gifted students

Bilim ve teknolojinin devamlı gelişim gösterdiği şu çağda ülkelerin de kendisini yenileyip eğitim olanaklarını gözden geçirmesi gereklidir. Fen ve teknoloji dersi, öğrencilerin amaçlı ve planlı bilgilerle ilk kez karşılaştığı ilköğretim yıllarında, öğrencinin doğal dünyayı daha anlamlı bir şekilde yorumlaması, neden-sonuç ilişkileriyle muhakeme yeteneğinin gelişmesi, bilimi ve bilim insanlarını sevme ve örnek alma yönünde tutumlar geliştirmesi açısından önemlidir. Fen ve teknoloji eğitiminde bilim ve bilim insanına yönelik olumsuz düşünceler ve kullanılan yanlış kavramlar tespit edilerek, öğrencilerin bilime ve bilim insanına karşı doğru imajlar geliştirmeleri sağlanmalıdır. Yapılan bu çalışmanın amacı, üstün yetenekli öğrencilerin bilim insanı hakkındaki imaj ve görüşlerini ortaya koymaktır. Bu araştırmanın çalışma evrenini 2011 2012 öğretim yılında Ankara, Adana ve İstanbul illerindeki Bilim ve Sanat Merkezlerinde eğitim gören üstün yetenekli öğrenciler oluşturmaktadır. Ankara ilinde Yasemin Karakaya bilim sanat merkezinden 94, Ankara bilim sanat merkezinden 60, İstanbul Bilim Sanat merkezinden 29 ve Adana bilim sanat merkezinden 77 öğrenci olmak üzere toplamda 260 öğrenci araştırmaya katılmıştır. Araştırmada 3 bölümden oluşan bir ölçek kullanılmıştır. İlk bölüm öğrencilerin demoğrafik özelliklerini belirlemeye yönelik sorulardan oluşmaktadır. İkinci bölümde öğrencilerin bilim insanı hakkındaki düşüncelerini ve imajlarını belirlemeye yönelik 34 maddeden oluşan likert tipi ölçektir. Son bölümde de öğrencilerin bilim insanı hakkındaki imajlarını belirleyebilmek amacıyla Chambers tarafından geliştirilen DAST ( Bir Bilim İnsanı Çiz ) testi kullanılmıştır. Araştırmanın sonucunda öğrenciler genel olarak laboratuar önlüklü, gözlüklü, laboratuarda deney yapan bilim insanı çizmişlerdir. Anket sonuçlarında bayanların bilim insanı olma konusunda olumlu düşünceler besleyen öğrencilerin, çizimlerinde çoğunluk olarak erkek bilim insanı çizdikleri görülmüştür. Öğrencilerin bilim insanı hakkındaki düşünceleri öğrencilerin cinsiyetine göre, farklı bilim sanat merkezlerine göre ve ilk öğretim kademelerine göre farklılık göstermemektedir.In this era during which the science and technology develop continuously the countries also need to update their education potentials and renew themselves. The science and technology class is very important in primary education where the students meet the first time with the purposive and planned information. Because it ensures the students interpret natural world correctly, develops the student's ability of understanding cause and effect relations, ensures them love the science and scienctists and behave within this framework. In the science and technology class negative opinions regarding the science ad scientist should be determined and the students should gain correct image as regards the science and the scientist. The purpose of this study is to present the images and opinions of the gifted students regarding scientists. The target population of this study consists of the gifted students who have education in the Science and Art Centers in Ankara, Adana and Istanbul during the 2011-2012 education season. 94 students who attend yasemin karakaya science and art center, 60 students who attend Ankara science and art center, 29 students who attends to İstanbul science and art center and 77 students who attends to adana science and art center participate to this study. Totaly, 260 students are participated in this study. A scale which is compose of tree section is used in this study. The first section of the scale contains questions to determine the demographic characteristics of the students. In the second Section there is 34-element likert scale for knowledge about students' attitudes towards scientists. In the last part of the study, DAST ((Draw A Scientist Test) improved by Chambers is used get knowledge about students' attitudes towards scientists. Statistically significant result showed that students generally draw in their drawing scientists with laboratory dress, glasses and works in loboratory. Although, there were some students who is optimistic for being woman scientists in drawings, according to the resut of questionarys, man scientists were seen extencievely in their drawings. Student's thoughts about the scientists isn't seem to different from the primary school grades according to student's sex and location of science and art center

Numerical investigation of a DC glow discharge in an Argon gas : two-component plasma model

Abstract only