This award recognizes doctoral thesis research of outstanding quality and achievement in beam physics and engineering. Minghao Song received his PhD in 2022 from the Illinois Institute of Technology, with his dissertation titled, “Advanced methods for storage ring nonlinear beam dynamics design and implementation.”
Let’s start with your thesis research: Can you give a brief description of the work, and its impact on the field?
My thesis research is focused on developing advanced methods for low-emittance storage ring nonlinear beam dynamics design and implementation. The storage ring light source has experienced a rapid development in the past decades. To meet the increasing demand of scientific users for synchrotron radiation with higher brightness photon beam, the storage ring emittance is further reduced to ultra-low level. At the same time, it becomes more challenging to achieve good performance of nonlinear beam dynamics for the low-emitting storage ring, although it is essential.
A highly efficient optimization algorithm is needed to simultaneously maximize the dynamic aperture and momentum aperture. The thesis work was done to apply a machine learning-based algorithm, called Multi-Generation Gaussian Process Optimizer (MG-GPO), to storage ring lattice design and online optimization. The MG-GPO algorithm builds a Gaussian process (GP) model to pre-select solutions that have higher probabilities of yielding good results, and iteratively updates the best solutions. It has been demonstrated with a faster convergence rate compared to traditional algorithms PSO/MOPSO and NSGA-II. This algorithm serves as a strong candidate for nonlinear lattice design and online optimization for future generation ultra-low emittance storage rings.
Correction of nonlinear beam dynamics is also important for low-emittance storage rings because unplanned errors cause the actual machine performance to deviate from the design. An effective method is needed to excite sustained large beam oscillation amplitude to accurately measure and correct features related to nonlinear beam dynamics. The advanced method of autoresonant excitation was proposed by exciting nonlinear beam motion with swept driving frequency. The autoresonance threshold theory was derived for the storage ring nonlinear optics system and demonstrated to be in good agreement with simulation and experiment. The agreement of simulated measurements of detuning coefficients and resonance driving terms with the model verifies its high measurement accuracy and shows its capability in commissioning and operation for future machines.
How did you become involved in accelerator research?
I have been involved in accelerator research since my master's degree. Before that, I never thought I would go into the accelerator field. Before going to graduate school, I went to a summer camp and visited a synchrotron radiation facility. It was the first time I had seen such a large scientific facility, and I later learned that it was a particle accelerator. Since then, I have been very interested in this sophisticated machine and was fascinated to know how it works. So, I started my master's thesis on accelerator research, focusing on the study of the wakefields of free-electron lasers. My Ph.D. thesis is a continuation of accelerator research, but focused on nonlinear beam dynamics design and implementation of storage ring accelerators. These are different experiences in accelerator research, but I have enjoyed exploring new discoveries in different research directions.
What did you find most challenging during your Ph.D., technical or otherwise?
I had some research experience during my master's time. But I found that there are more requirements for a Ph.D. As a Ph.D. student, you have to learn a lot more to solve a problem, and most of the time you should learn by yourself. I once spent almost a year on an R&D problem. After trying many methods, the result was still far from our expectations. Later, I had some new ideas and wanted to try them again. This is the charm and fun of science. You never know what the results will be when you tackle a problem that no one has answered before. It is probably right to stop when you get stuck and go back when you have new inspirations.
What advice do you have for graduate students in the field of accelerator physics?
I would like to share my experience and what I have learned from senior scientists in the field of accelerator physics. Accelerator physics involves many physics concepts in electromagnetism, classical mechanics, quantum mechanics, general relativity and so on. The first and essential step is to have a solid understanding of these physics concepts. In addition, many concepts of accelerator physics are modeled by mathematics and can be simulated with computational tools. Therefore, improving your skills in mathematics and computation can enhance your understanding of accelerator physics. To ensure that we stay at the forefront of the field, reading papers regularly is one way to track the latest developments. Finally, collaborating or discussing with peers and seniors can inspire you with new ideas and advance your career.
What are you working on now? Will you continue your earlier research, or start something new?
I’m currently working at the Brookhaven National Laboratory, NSLS-II. NSLS-II is a 3GeV storage ring light source with a circumference of 792m. In addition, the accelerator physicists and engineers at NSLS-II are planning to upgrade NSLS-II to produce a brighter photon beam for scientific users. One of my primary works is to design the storage ring lattice for the NSLS-II upgrade. The goal is to provide a reliable storage ring lattice that meets several performance metrics. Another of my main works is to develop and apply machine learning methods to improve the stability and reliability of the existing NSLS-II light source. These works are not quite the same as or a continuation of my Ph.D. thesis research, but they still have some relationships with my earlier work.
Tell us something interesting about yourself outside of work!
I am a sports fan of football and basketball. Sometimes I like to watch games with the teams I follow. In my spare time, I sometimes play badminton or table tennis with my colleagues. In addition to sports, I also like to travel and watch series.