Since joining the Plasma Fusion Center, Dr. Greenwald has conducted physics research on the Alcator A, C, and C-Mod tokamaks, including studies of energy and particle transport, pellet fueling and density limits. His recent work has focused on the role of critical gradients in determining plasma temperature profiles, on the EDA H-mode regime, and on the role of turbulent transport in determining the tokamak density limit. This latter work is aimed toward defining a "first principals" theory for the limit with the long term goal of obtaining reliable predictions and extrapolations to future machines.

Dr. Greenwald's work in pellet fueling on Alcator C included the discovery of a new regime of enhanced energy and particle confinement. This was the first attainment of an internal transport barrier in a tokamak which is recognized as one of two generic approaches (along with H-Mode) to improving tokamak confinement. Because of the correlation with peaked density profile, the work spurred interest in the Ion Thermal Gradient driven (ITG) mode, now believed to be the principal mechanism for anomalous transport in tokamaks.

Dr. Greenwald served for a time as chair of the Department of Energy Fusion Energy Sciences Advisory Committee (FESAC) was a recipient of Fusion Power Associates 2014 Leadership Award.

PSFC Director Dennis Whyte issued the following statement:

Dear PSFC colleagues,

It is with an array of emotions that I announce that Senior Scientist Martin Greenwald, Deputy Director of PSFC, will be retiring on February 1, 2022 after 43 years of extraordinary service and contributions to PSFC, MIT and the worldwide magnetic fusion effort.

While I am thrilled to know that he will be starting a new adventure, I also know that we will all sorely miss his sound leadership, his scientific insight, and his dedicated personality. Luckily he will not be going far, and he will continue to serve as a visiting scientist at PSFC for the foreseeable future. We will continue to enjoy his company, his advice, and his immense experience. Many of his day-to-day obligations will shift to others, and plans are already coming in place for much of that. It comes as no surprise that "replacing" Martin simply is not possible, and instead a group of people will be called upon to take on the myriad of responsibilities he held. Personally, Martin has been invaluable as Deputy Director of PSFC. I learned so much from him about leadership.

This announcement has made me stop to reflect on everything we have accomplished during Martin's time and due to his leadership. His accomplishments are too many to describe in detail. Martin led pellet fueling experiments on Alcator-C that provided the first experimental proof of achieving the necessary Lawson breakeven n*tauE product. His discovery of the tokamak density limit, which carries his name, will be studied and known by many generations of fusion scientists, and continues to be one of the most important reasons for pursuing the high-field compact fusion pathway, embodied by the Alcator experiments and now SPARC. And to the latter, Martin was one of the chief architects of SPARC's science and energy mission.

And Martin has been a recognized and thoughtful leader to the entire fusion community, including his chairing of FESAC and the "Greenwald report" on gaps to fusion energy systems --- a blueprint that continues to guide the fusion community.

It is difficult to give credit to just one person for the PSFC's successes, yet it is hard to imagine our success without Martin. Perhaps most important, Martin has helped us attract a talented workforce who will carry on our mission, and for that I am thankful - and these teams will remain as a legacy to Martin's thoughtful and dedicated mentorship. I look forward to working with new people who will pick up where Martin leaves off, and I am confident that PSFC will continue to be a leader in the scientific community.

Please join me in extending the warmest wishes for Martin in his retirement.

He can be reached at g@psfc.mit.edu