Filamentary plasma discharge inside water : initiation and propagation of a plasma in a dense medium Paul Ceccato To cite this version: Paul Ceccato. Filamentary plasma discharge inside water : initiation and propagation of a plasma in a dense medium. Engineering Sciences [physics]. Ecole Polytechnique X, 2009. English. pastel- 00005680 HAL Id: pastel-00005680 https://pastel.archives-ouvertes.fr/pastel-00005680 Submitted on 11 Jan 2010 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. PhD report of Paul CECCATO « Pour le titre de docteur en physique de l’Ecole Polytechnique Mention physique et applications Ecole doctorale EDX MICROPLASMAS DE CAVITATION EN MILIEU FLUIDE CONDENSE : APPLICATION A LA PURIFICATION DE L’EAU » Filamentary plasma discharge inside water : initiation and propagation of a plasma in a dense medium Jury members: Anne Bourdon EM2C Ecole Centrale France Bill Graham Queen’s University Belfast UK Svetlana Starikovskaya LPP Ecole Polytechnique France Referee members: Peter Bruggeman Eindhoven University of Technology Netherlands Olivier Lesaint G2E Université Grenoble France Achieved at the LPP laboratory in Ecole Polytechnique Palaiseau (Paris) France 2006-2009 supervisor: Antoine Rousseau Page | 1 Thanks Thanks first to all to the cold plasma team Thanks Antoine Rousseau for the PhD thesis funding Thanks Olivier Guaitella for the experimental and moral support Thanks Joseph Youssef for sharing the experimental room Thanks Philippe Auvray for help Thanks Jean Larour for multiple technical solutions and discussions Thanks Pierre Ledelliou for dedicated experimental work Thanks Mikael Baudier for reactor design and realisation Thanks all laboratory personnel in a general way Thanks Lucas Shaper for a challenging experimental campaign Thanks to Svetlana Starikovskaya, Olivier Lesaint, Peter Bruggeman to have read this report and made useful comments, Thanks to the other members of the jury Thanks Bill Graham for you enthousiasm Thanks to Dr Bruggeman, Dr Locke, Dr Lukes, Dr Graham, Dr Babaeva, Dr Lesaint, Dr Beroual, Dr Koslov for interest and usefull discussions in internationnal scientific conferences. Did I missed someone? Page | 2 Summary: This thesis presents an experimental study of a filamentary microplasma discharge inside liquid water. Such plasmas are used for liquid electrical insulations tests and for pollution control of water. Plasmas inside dense media are less understood than discharge inside gases. The purpose of the present thesis is to understand the physical mechanisms responsible for initiation and propagation of the discharge. A point to plane electrode configuration submerged in water has been constructed and was submitted to a high voltage pulse. Filaments inception and propagation and several discharges modes have been characterized with electrical measurements and time resolved nanosecond imaging. A Shadow diagnostic using 2 iCCDs was implemented to study the gas content and the shock wave emission from the discharge. The influence of the applied voltage polarity and the water conductivity was investigated. Spectroscopic measurements were performed on the OH emission band and the hydrogen emission lines. At positive high voltage the growth of the discharge begins by the nucleation of a microbubble at the needle electrode within a few microseconds at an applied voltage of 40kV, a hemispheric tree like filamentary structure grows at 3km/s during 100ns and is followed by the propagation of second filamentary structure ten time faster. This continuous propagation on a nanosecond time scale is followed by a stepwise propagation in case of distilled water. When the filaments reach the opposite electrode electrical breakdown occurs. At negative polarity the discharge is much slower 600m/s. The morphology of the gas cavity is driven by interface instability. Curiously, water conductivity has no influence at positive voltage polarity and even inhibits the propagation of the plasma filaments at negative voltage polarity. This thesis made possible to achieve a better understanding of the detailed phenomenology of electrical discharges in water. Résumé: Il s’agit de l’étude expérimentale d’un microplasma dans l’eau liquide. Ce type de plasma est rencontré dans les domaines de l’isolation électrique par liquides diélectrique ou la dépollution de l’eau. Les plasmas en milieu liquide sont bien moins connus et maitrisés qu’en milieux gazeux. L’objectif de cette thèse est de comprendre les mécanismes physiques sous jacents à l’initiation et à la propagation de la décharge. Un réacteur pointe/plan a été réalisé et soumis à un pulse de haute tension. L’initiation et la propagation des différents modes de décharge plasma à travers le milieu liquide ont été caractérisés par des diagnostiques électrique et d’imagerie rapide nanoseconde. Un diagnostic d’ombroscopie à deux iCCD a également été réalisé afin d’observer le contenu gazeux non lumineux de la décharge et l’émission d’ondes de choc. Nous avons principalement testé l’influence de la polarité de la tension appliquée ainsi que l’influence de la conductivité de l’eau. Des mesures spectroscopiques ont été réalisées sur la bande d’émission de OH et les lignes de l’hydrogène. En polarité positive, une bulle micrométrique est nucléé à la pointe en quelques microsecondes puis une décharge filamentaire se propage à 3km/s durant typiquement 100ns, suivie par une décharge dix fois plus rapide. A basse conductivité, cette propagation continue est suivie par une propagation par bonds. Le claquage de l’intervalle de liquide est obtenu quand les filaments parviennent à la contre-électrode. La décharge en polarité négative est beaucoup plus lente à 600m/s. Curieusement la conductivité de l’eau n’a aucune influence sur la décharge en polarité positive et inhibe la propagation en polarité négative. Cette étude apporte une meilleure compréhension de la phénoménologie détaillée de la décharge plasma dans l’eau. Page | 3 Filamentary plasma discharge inside water : initiation and propagation of a plasma in a dense medium 1 General introduction 1.1 The plasma state ................................................................................................... 6 1.2 Cold plasmas in industry ...................................................................................... 7 1.3 Filamentary plasmas ............................................................................................ 7 1.4 Pollution control by plasma processes in gases .................................................. 7 1.5 Plasmas in water .................................................................................................. 8 1.6 Purpose of the present thesis .............................................................................. 12 1.7 Brief overview of this report .............................................................................. 12 2 Discharges inside water, state of the art, synthesis and discussion 2.1 Electrode configurations: homogeneous field, inhomogeneous fields, small gaps and large gaps, streamer, spark, arcs.............................................................................. 15 2.2 Chemical yield of plasma inside water .............................................................. 20 2.3 Discharges modes and classification ................................................................. 26 2.4 Influence of experimental parameters: parametric experimental studies performed in literature ................................................................................................... 35 2.5 Electrostatic considerations ............................................................................... 45 2.6 The liquid state and its ability to withstand electron avalanches: from gases to liquids and vice versa ..................................................................................................... 48 2.7 Bubble processes ................................................................................................ 63 2.8 Interface processes ............................................................................................. 72 2.9 Summary on the mechanisms for initiation and propagation ............................ 77 2.10 Purpose of this work: a fine time resolved study of the case of water............... 80 3 experimental setup and experimental procedures 3.1 Reactors.............................................................................................................. 82 3.2 Electrical ............................................................................................................ 88 3.3 Emission imaging............................................................................................... 93 3.4 Transmission imaging ........................................................................................ 98 3.5 Spectroscopy .................................................................................................... 103 4 The positive polarity 4.1 General description of the positive mode: