Schweickhard “Schwick” von Goeler, inventor of groundbreaking diagnostics used to analyze fusion experiments worldwide, dies at 84
Schweickhard “Schwick” von Goeler, an award-winning physicist at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) for more than 35 years and the inventor of numerous X-ray diagnostics used in fusion experiments worldwide, died of leukemia on Dec. 6 in Springfield, Massachusetts. He was 84.
Von Goeler invented the X-ray crystal spectrometer whose modern version, developed by PPPL physicists Ken Hill and Manfred Bitter, can be found on the new Wendelstein 7-X stellarator in Germany, the Large Helical Device in Japan, the KSTAR and EAST superconducting tokamaks in Korea and China. It is also in use on, as well as the Alcator C-Mod tokamak at MIT and will be installed on PPPL’s recently completed National Spherical Torus Experiment-Upgrade and on the international fusion experiment ITER that is under construction in France.
“Schwick led the X-ray diagnostics branch at PPPL for very many years,” said Hill, who collaborated with von Goeler and Bitter on many of the devices. “He personally pioneered the use of many of the X-ray measurement techniques of the plasmas in tokamaks to determine what was happening inside. PPPL’s world leadership in the use of X-rays continues to this day.”
Von Goeler was a physicist at PPPL from 1964 to 1999 and a lecturer in Princeton University’s graduate program in plasma physics during most of that time. Starting in the 1970s, he pioneered the use of X-rays in diagnostics to get a clear picture of the inner workings of the super-heated ionized gas called plasma during fusion experiments. He invented diagnostics for most of PPPL’s major experiments, including the Symmetric Tokamak (ST), the Princeton Large Torus (PLT), the Poloidal Diverstor Experiment (PDX), the Tokamak Fusion Test Reactor (TFTR), and the National Spherical Torus Experiment (NSTX).
Father of X-ray diagnostics
“He was not only the father of a lot of the X-ray diagnostics that are now universally used, but also a lot of the physics that went with it,” said physicist Brent Stratton, who worked with von Goeler on diagnostics for the NSTX. “He was not just an inventor but a strong physicist.”
Ned Sauthoff, the director of the U.S. ITER Project Office, recalls working with Von Goeler and physicist Wolfgang Stodiek during Sauthoff’s first year of graduate school at Princeton University in 1971. Von Goeler was developing an X-ray pulse height analyzer (PHA) to measure the electron temperature and metallic impurity content in a tokamak called the ST that had been converted from the C-Stellarator.
“I remember sitting in that darkened control room, with the green glows from the screens of the oscilloscopes that were photographed following each shot to provide the data record, and the doorbell announcing the next shot,” he said in an email message. “It took very little time for me to realize that Schwick was truly exceptional, particularly in his ability to observe and to question. Schwick was meticulous in his design and analysis of instruments.”
Von Goeler and his colleagues used the PHA to analyze the level of metal impurities in the plasma, which can cool the plasma and halt fusion reactions. They found that the amount of impurities in the plasma from the walls of the tokamak was 10 times higher than expected.
With von Goeler, Sauthoff developed an X-ray imaging system for the ST that the physicists used to discover the formation of magnetic islands and related instabilities in tokamak plasmas.
Detecting sawtooth oscillations
The X-ray imaging system also allowed von Goeler, Wolfgang Stodiek and Sauthoff to detect for the first time a phenomenon called “sawtooth oscillations,” which signal internal plasma disruptions. The discovery led to a 1974 paper by von Goeler and his collaborators in Physical Review Letters. “Nobody had done a measurement like that – nobody,” said Bitter, who was recruited by von Goeler to PPPL and became a lifelong colleague and friend. “He had brilliant ideas.”
Building on his earlier PHA invention, von Goeler and Hill introduced the X-ray crystal spectrometer, which allowed physicists to identify the spectra of metal impurity ions in the plasma. They next developed an improved X-ray crystal spectrometer with a very high spectral resolution, which also allowed researchers to measure the ion temperature of the hot core of the plasma through Doppler measurements — a feat that only a high-resolution device could achieve. The results led to another paper in Physical Review Letters by Bitter and von Goeler in 1979.
The spectra of highly charged ions that the physicists obtained from tokamak plasmas were also of great interest for astrophysicists, who observed those spectra in solar flares and used them to derive the electron temperature and other parameters of the flares.
In 1984, von Goeler was awarded the Prize for Excellence in Plasma Physics (now the John Dawson award) by the American Physical Society’s Division of Plasma Physics. He was honored for his invention of an X-ray camera to analyze the high-energy X-rays that were emitted in experiments that injected radio frequency waves into the plasma to drive a current that could maintain the plasma without ohmic heating, and that raised the temperature high enough to create the conditions necessary for fusion.
With engineer Lane Roquemore, physicist Larry Johson and Bitter, von Goeler invented a scintillator detector for a neutron collimator for TFTR that could accurately measure neutrons from deuterium-tritium fusion events. This detector led to the discovery of sawtooth oscillations. “They gave a real sense of the structure of plasma that the theorists could work with,” said Ken Young, a retired PPPL physicist who worked with von Goeler when Young was head of the Diagnostics Division on TFTR.
“He had a very quiet manner but at the same time he was very engaging and very patient in explaining things to you,” said David Johnson, former head of the ITER Fabrication Department at PPPL, who started his career in 1975 and worked with van Goeler.
X-ray camera for NSTX
Even after his retirement in 1999, von Goeler continued inventing. Russ Feder, now the U.S. ITER diagnostics team leader, recalls working on his first diagnostic job with von Goeler and Brent Stratton on a very fast X-ray camera with microsecond time resolution for NSTX. “He was very mild-mannered, very classy very respectful,” Feder said. “It’s very clear that my job path at PPPL was very much helped by working with Schwick.”
Von Goeler was born in 1931 in Berlin to Margaret and Karl Friedrich Goeler von Ravensburg. His father was a metal physicist and technical director of the Mettalgesellschaft, one of Germany’s largest industrial conglomerates based in Frankfurt. He was killed in 1944 in World War II.
Von Goeler grew up during wartime Germany and after high school won a scholarship to study gardening at Kent State University in Ohio as part of a post-war “reeducation” project. As an undergraduate in physics at the University of Marburg in Germany he became interested in fusion energy and went on to get a Ph.D. in plasma physics from that school. He first came to PPPL when he received an offer of a postdoctoral fellowship. He remained at the Laboratory for the rest of his career, with the exception of a sabbatical in Italy in the late 1960s and in Germany in the late 1970s, and an Alexander von Humboldt fellowship in 1987 to do research at the Max Planck Institute in Germany.
“I think he really found a home at PPPL and felt like he had a lot of wonderful colleagues and was able to explore interesting questions and do important work,” said his daughter Dorothea von Goeler.
A violinist who played chamber music and in orchestras throughout his life, von Goeler met his wife Adelheid when his quartet needed a cello player. The couple married in 1963 and had three daughters, Ruth and Dorothea, of Northampton, Massachusetts and Hanna, of Montclair, New Jersey, and five grandchildren.
The von Goelers lived in Princeton until 2004 when they moved to Haydenville, Massachusetts, to be closer to two of their daughters. They moved to nearby Florence last year. An avid gardener, von Goeler continued to use his early skills to grow beautiful and abundant gardens throughout his life. He was a member of the Pioneer Valley Symphony Orchestra and was active in the Adult Forum at the Immanuel Lutheran Church where he was a member.
“Schwick’s legacy lives on, sustained by those who worked with him, by those who were inspired by him, and by those who seek to gain a deeper understanding the physics of tokamak plasmas,” Sauthoff said. “His passion for detailed observation and questioning is a model for all of us.”
Services will be held on Dec. 19 at 1 p.m. at Immanuel Lutheran Church in Amherst, Massachusetts.
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