Russell M. Kulsrud
Russell M. Kulsrud, 97, a pioneering theoretical physicist whose work helped define the modern fields of plasma physics and astrophysics — connecting the physics of fusion reactors to the forces that shape the cosmos — died on September 23, 2025, after a short illness.
In a career spanning more than six and a half decades at Princeton University, Dr. Kulsrud helped lay the theoretical foundations for understanding plasmas — the ionized gases that make up stars, solar winds, and much of the visible universe. His insights ranged from the behavior of charged particles in fusion reactors to the origins of magnetic fields in galaxies.
“He possessed exceptional physical intuition,” said the late astrophysicist John Bahcall, his longtime colleague at Princeton University and the Institute for Advanced Study. “He could see to the heart of a problem and help the rest of us see it, too.”
Dr. Kulsrud’s research advanced both fusion energy and astrophysics, fields that prior to his work rarely intersected. At the Princeton Plasma Physics Laboratory (PPPL), he explored the stability of magnetically confined plasmas — the key to achieving controlled fusion, the process that powers the sun. Indeed, he and his colleagues at PPPL pioneered much of modern stability theory. In astrophysics, he investigated cosmic rays, black holes, magnetic turbulence, and galactic dynamos — the mechanisms that generate magnetic fields across the universe.
His blend of mathematical rigor and physical intuition made him a natural teacher. Over his career, he advised 19 doctoral students who then spawned over 54 “grand-students.” “He made complex phenomena understandable,” said a former student. “He taught us to think about the universe as a single, connected system.” Steven Cowley, Director of PPPL and a former student of Kulsrud said, “He was extraordinarily generous with his time. During countless hours together at the blackboard, he showed me that, when viewed from the right perspective, everything becomes simple.”
In 1993, the American Physical Society awarded Dr. Kulsrud its highest honor in the field, the James Clerk Maxwell Prize for Plasma Physics, recognizing his “pioneering contributions to basic plasma theory, to the physics of magnetically confined plasmas, and to plasma astrophysics.”
He later distilled his lifetime of knowledge in the 2005 textbook Plasma Physics for Astrophysics, praised for its rare combination of accessibility and intellectual depth. It remains a staple in graduate programs around the world.
From Kansas to the Cosmos
Russell Marion Kulsrud was born on April 10, 1928, in Lindsborg, Kansas, a small town founded by Swedish immigrants, to Carl J. Kulsrud, a Norwegian immigrant and Harvard educated historian, and Mary Hughell Kulsrud, an English teacher and grammarian, whose pioneer family traveled to Iowa by covered wagon to stake a farm. Kulsrud showed an early fascination with both music and mathematics — twin passions that would stay with him throughout his life.
He earned a bachelor’s degree in physics and astronomy from the University of Maryland in 1949 and completed his master’s and doctorate degrees in physics at the University of Chicago in 1952 and 1954, respectively. His doctoral thesis committee included four Physics Nobel Laureates: Enrico Fermi, Murray Gell-Mann, Hannes Alfvén, and Subrahmanyan Chandrasekhar, who served as his adviser.
Studying at University of Chicago’s Yerkes Observatory, where he met his future wife, aspiring astrophysicist Helene he was mentored by celebrated Danish astronomer Bengt Strömgren. Dr. Kulsrud joined a young, secret government effort at Princeton known as Project Matterhorn. Founded by astrophysicist Lyman Spitzer, under the auspices of the Atomic Energy Commission, the project was dedicated to exploring controlled nuclear fusion — a potential source of clean and limitless energy.
Dr. Kulsrud was among its earliest and most influential theorists, tasked with describing how magnetism could hold ultra-hot plasma in place long enough to release fusion energy. His elegant theoretical work helped form the basis for modern plasma confinement research.
He later became head of the Princeton Plasma Physics Laboratory’s Theory Division and, in 1967, joined Princeton’s Department of Astrophysical Sciences, where he taught and conducted research as a tenured professor until his retirement in 2004.
A Life of Science and Music
Outside the laboratory, Dr. Kulsrud was a devoted pianist who gave public recitals well into his eighties. He and his wife, Laney, were ardent supporters of The Princeton Festival. In Helene, Dr. Kulsrud found a partner who shared his drive to make the world a better place.
“He was always wise, kind, patient and always humble about his accomplishments,” his daughter, Pamela Corey, said. “He had a deep gentleness — a curiosity about everything, and a love of music and nature that balanced his scientific brilliance. His sense of humor was his calling card.”
Dr. Kulsrud continued to pursue research after retirement, focusing on magnetic reconnection — the process by which magnetic field lines break and reconnect, releasing massive amounts of energy, both in laboratory plasmas and in solar flares. Since 2006, he served as one of the science advisors to TAE Technologies, a fusion power company co-founded by Microsoft’s Paul Allen’s Vulcan Energy Group, that is developing sustainable and economically competitive alternative energy solutions.
Dr. Kulsrud is survived by his daughter, Pamela Corey, and son-in-law, Troy Corey, of Westchester, N.Y. Recently, he was predeceased by his wife of nearly 70 years, Helene Kulsrud (March 2025); a daughter, Suzanne Allison Gammon; and a son, Peter Clifford Kulsrud.
A memorial service and endowed lecture series in his honor will be announced by Princeton University’s Department of Astrophysical Sciences. Flags at the university were lowered to half-staff in his memory.
A funeral service will be held at the Kimble Funeral Home, 1 Hamilton Avenue, Princeton, NJ on October 25, 2025 at 11 a.m. Donations in his name may be made to the Princeton Public Library or to the Michael J. Fox Foundation for Parkinson’s Research.
In the words of a former colleague, “Russell Kulsrud spent his life illuminating the hidden order of the universe — and did so with grace, patience, and music in his heart.”
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Estelle Kuhn
October 3, 1926 – September 8, 2025
Estelle Kuhn died peacefully in her Manhattan apartment on September 8, 2025, less than a month before her 99th birthday.
Born in New York City into a close-knit family of Russian Jewish immigrants, Estelle Ruth Henkin grew up living in both Brooklyn and Manhattan. Her father, an accountant, imbued in his two children a lifelong concern for social justice and human rights. From an early age, she was a voracious reader, often secretly reading books ‘off topic’ during school. As a teenager, Estelle fell in love with the art museums of the city — she knew the Frick Collection backwards and forwards — and she attended New York’s High School of Music & Art.
After receiving her undergraduate degree in sociology from NYU in 1947, she worked for two years as a NYC social worker. During that time she met Princeton mathematics graduate student Harold Kuhn, a good friend of her brother Leon Henkin, then a Princeton mathematics postdoctoral researcher. Estelle and Harold married on Christmas Eve, 1949, six months before Harold finished his Ph.D.
The 1950-51 academic year took the couple to Paris, where Harold had a fellowship. They returned to Princeton, where their son Clifford was born, and then moved to Secane, PA. In 1959, the family, now including sons Nicholas and Jonathan, moved back to Princeton more permanently.
The year in Paris was the first of a number of sabbatical years lived abroad, in locations chosen with an eye towards art and culture: London in 1958-59, Rome in 1965-66, London in 1971-72. Estelle and Harold both learned French and Italian well enough to read modern novels in those languages, and Estelle mastered the culinary arts of both countries with élan.
In the 1960s, while minding a family with three young children, Estelle was an active member of the League of Women Voters and the Princeton Association for Human Rights (PAHR). She was one of the leaders of PAHR’s Housing Group, which was focused on exposing discriminatory redlining and promoting affordable housing. In the 1970s, she began a two decade stint working for the American Civil Liberties Union, running an ACLU office in Trenton. In retirement, Estelle served for many years as a volunteer in New Jersey’s program of Court Appointed Special Advocates for Children.
The family house in Princeton reflected Estelle’s sense of style: designed by architect Thaddeus Longstreth, filled with classic mid-20th-century furniture, and decorated with modern art.
Later in life, Estelle and Harold settled into a routine of taking a midwinter holiday on the island of Bequia, with a suitcase filled with books. The purchase of an apartment in Manhattan made it easier for them to go to art galleries and the theater, and eventually they moved there permanently.
She was predeceased by her husband Harold and oldest son Clifford. She is survived by her sons Nicholas and Jonathan; daughters-in-law Kathie Klein, Beth Kuhn, and Michele Herman; her grandchildren Michael, Joshua, Jeremy, Gabriel, Lee, Emily, and Jeffrey and their partners; and great-grandson Elliot.
Donations in Estelle’s memory may be made to the American Civil Liberties Union.
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Rekha Arapurakal
Rekha Arapurakal, beloved wife, mother, grandmother, sister, aunt, and friend, passed away peacefully at her home in Princeton, New Jersey, on August 29, 2025. She was 76 years old.
Born on January 5, 1949, in Trivandrum, India, Rekha’s life was marked by brilliance and warmth. After completing her BA in Math with Honors at Lady Shri Ram College in New Delhi, she joined the Indian Space Research Organization, where she literally reached for the stars, working in rocket science.
In 1973 she married Ravi Arapurakal and moved to Frankfurt am Main, Germany, before moving to Vienna, Austria for the next four years, where she resumed her studies, preparing for her doctorate in Econometrics and returning to Frankfurt for the next couple of years.
In 1981, Rekha moved with her family to Princeton, where she embraced a new chapter of life with characteristic courage and creativity. In 1984, she founded Personal Travel, an agency that served the community for decades and reflected her adventurous spirit. Rekha was also deeply engaged in her neighborhood, contributing to the Dempsey Neighborhood Association, and she cultivated a stunning garden that became a source of joy for her family and friends.
Rekha will be remembered for her sharp wit, her infectious laughter, and her extraordinary gift for bringing people together. A consummate hostess, she filled her home with warmth, food, music, and generosity. At Christmastime, she led lively caroling tours through Princeton, a tradition that touched countless lives and spread joy throughout the community. She was a fashion icon who rarely left the house without an impeccably draped sari.
She is survived by her devoted husband, Ravi; her loving sons, Rajiv and Ranjit; her daughter-in-law, Elora; and her cherished grandchildren, Nayan and Nusa. She is also mourned by her sister, Renu, and brother-in-law, Paul; her brother-in-law, Pravin; her nieces Shruti, Shona, Miria, Leela, and Leanne; her nephews Sachin, Joey, Brandon, and George; as well as many cousins, extended family members, and dear friends.
Rekha’s legacy is one of brilliance, laughter, love, and community. She will be deeply missed and lovingly remembered.
Rekha’s life will be celebrated in a future event which will be announced later.
In lieu of flowers, please make a donation to The Trenton Children’s Chorus.