• Abstract and Figures
• Public Full-text

An in-situ accelerator-based diagnostic for plasma-material interactions science in magnetic fusion devices by Zachary Seth Hartwig B.A. in Physics, Boston University (2005) Submitted to the Department of Nuclear Science and Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY February 2014 c Massachusetts Institute of Technology 2014. All rights reserved. Author............................................. ................. Department of Nuclear Science and Engineering 21 November 2013 Certified by......................................... ................. Dennis G. Whyte Professor Thesis Supervisor Certified by......................................... ................. Richard C. Lanza Senior Research Scientist Thesis Reader Accepted by......................................... ................ Mujid S. Kazimi TEPCO Professor of Nuclear Engineering Chair, Department Committee on Graduate Students 2 An in-situ accelerator-based diagnostic for plasma-material interactions science in magnetic fusion devices by Zachary Seth Hartwig Submitted to the Department of Nuclear Science and Engineering on 21 November 2013, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Abstract Plasma-material interactions (PMI) in magnetic fusion devices such as fuel retention, ma- terial erosion and redeposition, and material mixing present significant scientific and engi- neering challenges, particularly for the next generation of devices that will move towards reactor-relevant conditions. Achieving an integrated understanding of PMI, however, is severely hindered by a dearth of in-situ diagnosis of the plasma-facing component (PFC) surfaces. To address this critical need, this thesis presents an accelerator-based diagnostic that nondestructively measures the evolution of PFC surfaces in-situ. The diagnostic aims to remotely generate isotopic concentration maps that cover a large fraction of the PFC surfaces on a plasma shot-to-shot timescale. The diagnostic uses a compact, high-current radio-frequency quadrupole accelerator to in- ject 0.9 MeV deuterons into the Alcator C-Mod tokamak. The tokamak magnetic fields – in between plasma shots – are used to steer the deuterons to PFCs where the deuterons cause high-Q nuclear reactions with low-Z isotopes ∼5 µm into the material. Scintillation detectors measure the induced neutrons and gammas; energy spectra analysis provides quan- titative reconstruction of surface concentrations. An overview of the diagnostic technique, known as accelerator-based in-situ materials surveillance (AIMS), and the first AIMS diag- nostic on the Alcator C-Mod is given; a description of the complementary simulation tools is also provided. Experimental validation is shown to demonstrate the optimized beam in- jection into the tokamak, the quantification of PFC surfaces isotopes, and the measurement localization provided by magnetic beam steering. Finally, the first AIMS measurements of fusion fuel retention are presented, demonstrating the local erosion and codeposition of deuterium-saturated boron surface films. The finding confirms that deuterium codeposition with boron is insufficient to account for the net fuel retention in Alcator C-Mod. Thesis Supervisor: Dennis G. Whyte Title: Professor Thesis Reader: Richard C. Lanza Title: Senior Research Scientist 3 4 Fear is the mindkiller. — Paul Maud’Dib 5 6 Acknowledgments In many ways, this section was the most difficult for me to write. When one has received so much from so many it becomes a challenge to convey to each of them the depth of gratitude that they are owed; I have made my best effort here. As such, I discarded the possibility of a standard single acknowledgments page long ago and make no apology for my lack of brevity. I have decided to split my acknowledgments into personal and professional categories since I owe the achievement of this thesis not only to my scientific colleagues but also to my family and friends outside of MIT. These categories are somewhat arbitrary, however, as I am extremely fortunate to count many of those who have contributed to my scientific development as personal friends. Professional Because I consider this thesis to be the culminating destination in the long adventure of training to be a scientist, I find it most appropriate to start at the very beginning of the journey. I am grateful to Paul Baudendistel, whose passion for science and excellence in teaching first kindled my interest in physics in his high school classroom; I recall clearly to this day his brave demonstration of conservation of energy with a bowling ball and a pendulum! I am next indebted to Martin Schmaltz, who taught me electromagnetism as an undergraduate biomedical engineer. Conversations with him outside of the classroom opened my mind to the beauty and challenge of physics; I switched majors and haven’t looked back. My first opportunity to do physics in the laboratory I owe to Lee Roberts, who of- fered me a research position at Boston University. During my time there, I had the privilege of working with two of the most generous and gifted physicists. I owe the majority of my development as an experimental physicist to Kevin Lynch, whose pa- tient teaching, hilarious cynicism, high expectations, and tolerance for practical jokes helped me flourish as a younger student. Rob Carey complemented that education in the laboratory, classroom, and adviser’s office; in my own interactions with students and colleagues I continuously strive to emulate his example. During my thesis work at MIT, I had the privilege of working with an extraordinary 7 set of individuals. I am foremost indebted to Dennis Whyte for his constant presence during this thesis. I can pay no higher compliment than to say that it was the scientific environment he created for me - the freedom to explore and execute my own ideas with his complete confidence and eager collaboration - that enabled my success. I could not have found a better supervisor. I extend sincere thanks to Dick Lanza, from whom I received much of my knowledge of particle detectors and who has been a source of wisdom on a number of projects including this thesis. Bruce Lipschultz also played a crucial role during my time at MIT, providing continuous encouragement and insightful discussion on scientific matters for which I am grateful. I met Bruce before coming to MIT - at a bike shop nonetheless - and I hope that this thesis is just the beginning of a long and fruitful collaboration. Ian Hutchinson graciously agreed to serve as my committee chair and has probably, as my neighbor at the PSFC, put up with more loud music than he would care to recall; I thank him for his guidance, generosity and tolerance. I am indebted to Harold Barnard and Brandon Sorbom, with whom I toiled side- by-side in the trenches of experimental science during this project. The success of this thesis is the product, in large part, of the many late nights, frustrations, and achievements that we have shared together. I am also grateful to Pete Stahle, for his long-term engineering support with the RFQ accelerator and excellent conversation on the ice rink. That the RFQ was successfully refurbished - and not thrown out the window in a fit of rage - is a testament to their incredible skill and patience with physical hardware that laid the foundations for our project. I am extremely grateful to Dave Terry, who, in a phrase that will appeal to his Texan roots, really grabbed the bull by the horns to ensure the successful execution of our experiment. He was instrumental in guiding us through the tortuous path of implementing a major diagnostic on Alcator C-Mod. I am also grateful to Rui Vieira and Henry Savelli who provided outstanding engineering support; Rui’s constant use of the phrase “we can do anything” to refer to C-Mod engineering was quite reassuring during times of panic. I also want to extend my thanks to Gary Dekow, Jim Irby, Ron Rosati, Tom Toland, and the rest of the technical and machine shop staff at the PSFC who provided constant technical support during our experiments. I am also grateful to all the students, scientists, faculty, and staff who I have had the privilege of working with during my time at MIT. Finally, none of this thesis would have been accomplished without incredible admin- istrative support. If the scientific enterprise were a professional cycling team, the administrators are the mechanics who toil away in the background to ensure that the riders wake up everyday to a perfectly running machine. My success owes much to the efforts Heather Barry and Jessica Coco, for their professional support as much as their refreshing source of nonscientist friendship. I grateful to Claire Egan, Valerie Censabella, and the rest of the excellent staff at the MIT Plasma Science and Fusion Center and Department of Nuclear Science and Engineering. 8 Personal As I thought about these acknowledgments to preface my thesis on advanced mea- surement instrumentation, it is amusing but entirely expected to discover that the debt I owe to my immediate family is beyond measure. My parents, Paul and Kitty, probably deserve the accolades that accompany this thesis more than I do. It was their parenting skill, constant support, and enduring patience (sometimes severely tested!) that molded me into the person I am today. I also owe much to my brothers, Matt and Fitz. While I am now a physicist, Matt was the reason I ended up in science and engineering, due to his pursuit of engineering and willingness to share his Legos. Fitz’s tremendous accomplishments continue to impress and inspire me, and parts of this thesis were written to his outstanding recent EP. I am very much indebted to Emily Jump. She not only agreed to marry me during an extremely stressful and busy time in our lives but provided unending, uncomplaining support that made all the difference during the last few years of fairly nonstop work. She has brought a tremendous amount of levity and joy into my life that has provided a much needed sense of balance and perspective.

Load more

  162

Copy Link