Charles W. Carlson – known as Chuck by his legion of friends and colleagues — passed away peacefully on November 12, 2020. Chuck lived with Alzheimer’s disease and he was fortunate to have his loving family by his side during his more than15 years of decline. Chuck was born on December 31, 1942, in Cambridge, Minnesota, the son of the county recorder and a one-room teacher. He was and is still remembered in his hometown as the precocious child that he was. His early experiments included a rocket that misfired horizontally and damaged a clothesline full of sheets. Chuck was the youngest of five children. During his 51-year marriage, he and Gretchen raised three children and they have two grandchildren. It is comforting to know that he maintained his sense of humor and love of music to the end, humming along with his children to Dire Straits, a few days before he died. Chuck was reserved, understated, unassuming, and disinterested in status indicators. That, along with his major impact on auroral and magnetospheric physics as well as space instrumentation, is how he is remembered.
Chuck received a Bachelor of Arts degree in physics from the University of Minnesota, came to Berkeley in 1964, and earned a Ph.D. in physics under the supervision of Kinsey Anderson in 1977. The reason for his long, 13-year graduate student career was the opposite of inattention. It was because he was involved in and led 10 sounding rocket experiments during those 13 years. These rockets flew from worldwide bases, including Canada, India, Brazil, Alaska, Greenland and Norway, and they included a host of collaborators from all over the world. After completion of his thesis work, Chuck built and flew instruments on a further dozen sounding rockets and on nine satellites. The tradition of flying Chuck’s instrument designs has continued to this day with variations of his detectors on the Van Alan Probes, THEMIS, MAVEN, MMS and Parker Solar Probe satellites.
Chuck designed and built the plasma instruments for all his missions. He was meticulous and single minded in this work. For example, Chuck designed the electronics, laid-out the circuit boards, and calibrated the detectors in laboratory vacuum systems for all his instruments. The best lab engineers often came to Chuck to discuss their design concepts and many have noted his quick and incisive comments and improvements to their designs.
The most spectacular example of Chuck’s ingenuity was his invention of the “top-hat” electrostatic analyzer, designed in 1979, while he was on a sabbatical at the Max Planck Institute in Garching, Germany. Until then, measurements of charged particle velocity distributions had been severely hampered by the limited coverage and non-uniform response in the incoming aperture angle of the particle detectors. The top-hat solved this problem in an elegant way. Starting with a hemispherical analyzer (consisting of two concentric spherical plates), Chuck’s idea was to cut off the top of the outer hemisphere, and raise the cut-off piece (the “top-hat”) a short distance above the hole to create an entrance for the particles from all directions within a 360 degree circular entrance aperture. This design was quickly proven in the lab in Garching, with the help of Goetz Paschmann, and its first satellite flight was on the AMPTE/IRM in 1984. It improved the time resolution of detailed charged particle measurements by more than two orders-of-magnitude,measuring in seconds what the prior art, exemplified by the instruments on ISEE, took minutes to measure.
An equally magnificent achievement was realized when Chuck proposed and built the FAST satellite, the second NASA Small Explorer mission. This was one of the first NASA missions that was led entirely by an external Principal Investigator rather than a NASA agency or civil servant. The FAST mission, launched in 1996, was a complete game changer in understanding auroral physics, because of its high time resolution top-hat particle detectors and state-of-the-art fields instruments. It established the cause of the aurora by providing unequivocal and quantitative proof that that the auroral electron and ion beams are the result of electric potential drops along geomagnetic field lines. The data thus revolutionized our understanding of auroral particle acceleration, including Chuck’s discovery of beams of upward going energetic electrons that have no visual analog and are sometimes referred to as the invisible or inverse aurora. FAST data opened the door to a whole range of new phenomena that lie at the core of acceleration physics and forced a revision of existing models to ones that are far richer and more comprehensive.
Through his strong involvement in the sounding rocket program and leadership of the FAST mission, Chuck mentored more than a dozen graduate students in the art of instrument building and unraveling the complex processes of auroral plasma physics. It is a tribute to Chuck that many of his students have gone on to become leaders in their fields of research.
Chuck achieved enormous success with his research, instrumentation development, and leadership. He participated in nearly 300 publications that received more than 26,000 citations and that earned him an H-index of 88. He was the recipient of many honors including the Alfven Medal of the European Geophysical Union. An appropriate way to summarize Chuck’s career is to quote from the Alfven award as follows: “The 2007 Hannes Alfvén Medal of the European Geophysical Union was awarded to Charles W. Carlson for his pioneering work in developing novel diagnostic instruments and whole payloads leading to a major increase in our knowledge of the complexities of space and, in particular, auroral plasmas.”