Order number: 4612 THESIS submitted to UNIVERSITÉBORDEAUX 1 ÉCOLE DOCTORALE DES SCIENCES PHYSIQUES ET DE L’INGÉNIEUR and UNIVERSIDADPOLITÉCNICADEMADRID E. T. S. DE INGENIEROS AERONÁUTICOS by CARLOSYÁÑEZVICO for the degree of DOCTOR in ASTROPHYSICS, PLASMAS AND CORPUSCLES at Université Bordeaux 1 and in AEROSPACE ENGINEERING at Universidad Politécnica de Madrid HYDRODYNAMICSTABILITYTHEORYOFDOUBLE ABLATIONFRONTSTRUCTURESININERTIAL CONFINEMENTFUSION Defended on November 19, 2012 at Talence (France) Board of examiners: Mr BETTI Riccardo Professor, University of Rocherster Reviewer Mr BOUQUET Serge Professor, CEA/INSTN Reviewer Mr SANZ RECIO Francisco Javier Professor, Polytechnical University of Madrid Supervisor Mr TIKHONCHUK Vladimir Professor, University of Bordeaux Supervisor Ms OLAZABAL-LOUME Marina Research engineer, CEA Supervisor Mr PELAEZ ALVAREZ Jesus Professor, Polytechnical University of Madrid Examiner Mr KELLAY Hamid Professor, University of Bordeaux Examiner Carlos Yáñez Vico: Hydrodynamic stability theory of double ablation front struc- tures in inertial confinement fusion, © November 2012 ¡Intelijencia, dame el nombre exacto, y tuyo y suyo, y mío, de las cosas! Juan Ramón Jiménez Dedicated to my lovin’ wife Cécile and my lil’ Lou-Andréa, am the eternal witness of your beauty CURRICULUMVITAE The author was born in Madrid, Spain on June 22, 1984. He attended the School of Aeronautics in the Polytechnical University of Madrid from 2002 to 2008, and received a degree in Aeronautical Engineering in 2008. He com- pleted the graduate studies with a Diploma Thesis defended in 2008 at the Institute for Hydromechanics of Karlsruhe Institute of Technology, where he conducted a research in the field of stability theory in stratified turbulent shear flows under the supervision of Dr. Manuel García-Villaba. After a first experience working as aeronautical engineer in the helicopter industry, he came to the University of Bordeaux in the fall 2009 as a graduate student at CELIA laboratory. He received a three-year funding from the CEA/Aquitaine Region to carry out doctorate studies under an international joint supervision between the University of Bordeaux and Polytechnical University of Madrid. He pursued his research in the hydrodynamic instabilities in inertial con- finement fusion under the directions of Professor Javier Sanz and Professor Vladimir Tikhonchuk. v PUBLICATIONSRELATEDTOTHISTHESIS Some results from this PhD research work have given rise to the following publications: 1. C. Yañez, J. Sanz, M. Olazabal-Loumé and L. F. Ibañez. Linear stability analysis of double ablation fronts in direct-drive inertial confinement fusion. Phys. Plasmas 18, 052701 (2011) doi; 2. C. Yañez, J. Sanz and M. Olazabal-Loumé. Self-consistent numerical dis- persion relation of the ablative Rayleigh-Taylor instability of double ablation fronts in inertial confinement fusion. Phys. Plasmas 19, 062705 (2012) doi 3. C. Yañez, J. Sanz, M. Olazabal-Loumé and L. F. Ibañez. Modeling hydro- dynamic instabilities of double ablation fronts in inertial confinement fusion. EPJ Web of Conference (submitted) and have been partially presented in the following conferences: 1. EPS 2010, 37th Conference on Plasma Physics (Dublin, 2010), 2. 4th Forum ILP: Lasers and Plasmas (Praz-sur-Arly, 2011), 3. EPS 2011, 38th Conference on Plasma Physics (Strassbourg, 2011), and 4. IFSA 2011, 7th International Conference on Inertial Fusion Sciences and Applications (Bordeaux, 2011); 5. EPS 2012, 39th Conference on Plasma Physics (Stockholm, 2012) and in the following graduate summer schools: 1. Erasmus Intensive Programme: Applications of Electronics in Plasma Physics (Crete, 2010), and 2. High Energy Density Physics Summer School (San Diego, 2011). vii ACKNOWLEDGMENTS This PhD thesis has been an amazing three-year trip with people in every station that I would like to thank now. The itch for research does not come alone but someone should introduce you to this awesome world. In my case, I have to go back some years in time to find that person in my German experience in the Karlsruhe Institute of Technology. There, Manuel Garcia-Villalba showed me the path to research. Going back to Spain, I went to the industry. In the farewell he told me: “I bet you’ll come back. I did”. He was right. I came back and I began this PhD thesis. Beginnings are usually hard, plenty of changes, especially when they are abroad. I would like to thank those persons who make first steps in Cheeseland easier for me. In a pro- fessional frame, much was the help that Virginie Saavedra gave to me. In a personal frame, I will never forget the warm welcome of Maurice, Edith and Corinne. From the very first day, I was already part of the family. I continued with happiness the son-in-law tradition. I would like to express my deep gratitude to Javier Sanz. Javier has trans- mitted to me the passion for research, the shrewdness to look for the fun- damentals, to decompose inaccessible problems in complex but pure ones, to non-stopping search elegant and analytic insights. He loves science and physics. And now, me too. I would also like to thank my French supervisors, Vladimir and Marina, who have always been there for all my questions, who have always been patient to explain me the tricky points of fusion physics. I continue to list (sorry if I forget anyone) all the persons in CELIA lab that has contributed to make this three years nicer; the permanents Jerome, Jean- Luc, Xavier, Edouard, Guillaume, Gerard, Philippe, Loic, Rachel..., the PhD students Jessy, Céline, Marion, Candice, Cyril, François, Benjamin, Mickael, Remi, Alexandra..., my office mates Igor, Marie and Thibault and the secre- taries Céline, Fabienne and Emmanuelle, always ready to help me with any paper stuff. I sincerely thank all the members of the Applied Physics department of the School of Aeronautics in Madrid for their kind welcome to my stays there and the fruitful coffee break discussions. A special thanks to the secretary Maricarmen that has helped me so much with the administration stuff. viii ix I would also like to thank the reviewers, Riccardo Betti and Serge Bouquet, for their time dedicated to careful reading this manuscript and all their valu- able comments and suggestions that have definitely improved the text. Friends are always there, sharing all the moments, joyful and sorrowful ones. Thank you, Gerardo. Thank you, David. We will continue redoing the world. In all my life steps, there are always some constant references of love and af- fection, of hard-working and peaceful enjoyment. They come from my mom, dad and sister. Simply, thank you. I am what I am because of you. And last but not least (not at all), some words to my sweetheart, my beloved wife. You know you are the core of my life. Thanks for supporting me and staying at my side... And there is a new arrival while preparing this text, my new born daughter Lou-Andréa. What to say about her? You are now the sun of our days (and the storm of our nights!). ABSTRACT The Rayleigh-Taylor instability is a major issue in inertial confinement fu- sion capable to prevent appropriate target implosions [20]. In the direct-drive approach, the energy deposited by directed laser irradiation ablates off the ex- ternal shell of the capsule (ablator) into a low-density expanding plasma. This induces a high pressure around the ablating target surface (ablation region) that accelerates the capsule radially inwards. This situation, a low density fluid pushing and accelerating a higher density one, is the standard situation for the development of the Rayleigh-Taylor instability, and therefore a poten- tial source of target compression degradation. Actual target capsule designs comprise a core of thermonuclear fuel (mix- ture deuterium and tritium), which is enclosed by a thin layer that behaves as ablator. The choice of the ablator material that provides the best performances to achieve succesful implosions has been the object of intense reasearch in re- cent years. First experiences were performed using hydrogenic ablators, i.e., cryogenic deuterium and tritium with a thin plastic overcoat. The use of hy- drogenic ablators is motivated by their relatively low density that permits them to achieve high ablation velocities with low in-flight aspect ratio and, therefore, exhibit good hydrodynamic stability [25, 35]. However, direct-drive cryogenic implosion experiments on the OMEGA laser facility have shown that this type of ablators presents a low threshold for the two-plasmon de- cay instability leading to elevated levels of hot electron preheat for ignition- relevant laser intensities [38, 30]. This excessive preheat is another source of compression degradation and implies not achieving the onset of ignition re- quirements on high total area densities and high hot spot temperatures. If hydrogenic ablators (low-Z material) are excluded as viable ablators, other concepts of target design need to be explored. One of these alternative target designs involves the use of moderate-Z ablators such as SiO2 or doped plastic. Recently, the performance of this concept was tested on direct-drive implo- sion experiments on OMEGA [40]. In that study, the use of glass ablators (SiO2 ) suggested a mitigation of target preheat for ignition-relevant laser in- tensities. Thus, moderate-Z materials are less affected by the TPD instability, and hence they are a potential candidate for ICF target ablators. Furthermore, experiments carried out in GEKKO XII laser facility indicated that the use of brominated plastic foils significantly reduces the growth of the RT instability x xi compared to an undoped plastic targets [11, 12]. This improvement in the hydrodynamic stability properties seems to be explained by the increasing importance of radiative energy transport in the ablated moderate-Z material. For moderate-Z materials, the hydrodynamic structure of the ablation re- gion formed by the irradiation of high intensity laser beams differs from that of low-Z materials (hydrogenic ablators). In particular, the role played by the radiative energy flux becomes non-negligible for increasing atomic number material and ended up forming a second ablation front.