CKM and the Beginning of a Partnership with Helen Edwards — 1998
Tim Koeth’s first experience at Fermilab came in 1998, when, as a young aspiring physicist, he headed west to work on Gordon Thomson’s proposed CKM (Charged Kaons at the Main Injector) experiment. The project required a specialized radio-frequency device—a TM110 transverse deflecting cavity—and Tim was given the opportunity to develop it. He packed up his life and moved to the cornfields west of Chicago, where he would spend roughly a year working in the laboratory of Helen Edwards, one of Fermilab’s legendary accelerator physicists. For Tim, it was exactly the sort of scientific adventure he had been looking for.
At the time, however, he had little appreciation for the stature of the people he was about to encounter. Before meeting Helen, colleagues warned the young physicist about her formidable intensity and suggested that he might be “chewed up” by the experience. He therefore approached their first meeting with considerable trepidation. The reality made a very different impression.
Helen Edwards receives the 1989 National Medal of Technology from President George H. W. Bush at the White House, October 18, 1989. The photograph is personally inscribed to Edwards by President Bush.
Who was Helen Edwards? She is often referred to as the Architect of the Tevatron. Helen T. Edwards was one of the preeminent accelerator physicists of her generation and a central figure in the creation of Fermilab’s Tevatron, the world’s first large superconducting particle accelerator. As Deputy Project Manager, Edwards helped lead its design, construction, commissioning, and operation, directing work spanning accelerator optics, radio-frequency systems, controls, diagnostics, and beam extraction. In 1989, President George H. W. Bush presented Edwards and three of her Fermilab colleagues with the National Medal of Technology, the nation’s highest honor for technological achievement, for their contributions to the Tevatron.
In early 1998, when Helen entered the room, Tim saw a person with enormous determination which seemed almost at odds with her appearance. She was intense, direct and utterly focused on getting difficult things accomplished. Tim later described the encounter by saying that he was “scientifically bewitched by Helen Edwards.” Whatever impression her physical stature might initially have given, he quickly understood that there was nothing frail about her. That first meeting began a professional relationship that would profoundly influence Tim’s development as an experimental physicist.
Learning by Building
Tim’s assignment was substantial for a young scientist: develop a TM110 RF deflecting cavity for CKM. He first had to gather and understand the proposed experiment’s operational requirements, acquire the necessary electromagnetic design tools, learn the principles of RF cavity design, and then turn those requirements into hardware. Under Helen’s mentorship, Tim rapidly came up to speed. Her approach suited him particularly well: understand the physics, find the people and resources necessary to solve the problem, and then “get it done.”
Tim also discovered that working for Helen provided an unexpected advantage. Around Fermilab, mentioning that something was “for Helen” had a remarkable tendency to make obstacles disappear and doors open. Tim jokingly came to call this his “Helen Card.” As his work took him into different Fermilab divisions—and eventually into other Department of Energy laboratories—he discovered that the Helen Card seemed to work there as well. It was an early indication to Tim of just how extensive Helen Edwards’ reputation and legacy had become throughout the accelerator community.
The cavity moved from concept to hardware remarkably quickly. The elliptical copper half-cells were formed with assistance from the Rutgers University machine shop, and the pieces were joined using precision electron-beam welding. Several copper prototypes would ultimately be produced as Tim refined the design and fabrication process.
One of those first prototypes produced a particularly memorable moment.
Only about five weeks after beginning the project, Tim returned from an electron-beam-welding operation carrying a newly completed, gleaming copper cavity. He arrived at Helen’s group meeting about ten minutes late—but with the finished prototype in his hands. Helen looked at the cavity, broke into an enormous smile, gave her characteristic laugh, and began applauding. The room joined her. Tim would later remember that moment as important for both of them. Until then, Helen had been discovering what this young physicist could do. The finished cavity demonstrated something that would become characteristic of Tim’s work with her: he was comfortable moving between physics, engineering, machine shops and laboratories, and he could take an experimental idea all the way from requirements and calculations to an actual piece of accelerator hardware. Tim believed that this was the moment Helen began to understand his particular strengths and abilities as an experimentalist.
A Project That Refused to Disappear
The larger CKM experiment ultimately did not come to fruition in its originally envisioned form, and Tim’s approximately year-long assignment came to an end. Yet the cavity work proved anything but a scientific dead end. The TM110 deflecting-cavity concept continued to develop at Fermilab. More importantly for Tim, the physics and technology he had first encountered under Helen would unexpectedly return to his life years later. When Tim subsequently pursued his Ph.D. at Rutgers and again worked under Helen Edwards at Fermilab’s A0 Photoinjector Laboratory, a descendant of the CKM deflecting-cavity concept became the heart of an ambitious accelerator experiment: transverse-to-longitudinal emittance exchange (EEX).
The idea was to manipulate the phase space of an electron beam so that characteristics normally associated with its transverse dimensions could be exchanged with those in its longitudinal dimension. Tim designed the EEX beamline and its TM110 deflecting-cavity system, oversaw construction and commissioning, and ultimately performed the first experimental demonstration of transverse-to-longitudinal emittance exchange—the work that became the centerpiece of his Ph.D. dissertation.
In retrospect, the continuity is striking. The young physicist who arrived at Fermilab in 1998 not knowing Helen Edwards—or even fully appreciating who she was—was handed the problem of designing a TM110 cavity. He learned the physics, learned the design tools, worked with machinists and welders, crossed institutional boundaries to get hardware fabricated, and within weeks walked into Helen’s meeting carrying a finished copper cavity. Roughly a decade later, Tim and Helen would return to essentially the same class of RF technology, this time as advisor and doctoral student, and use it to accomplish a new accelerator-physics experiment.
The CKM project therefore occupies a special place in Tim’s career. It was his first Fermilab experiment, his introduction to accelerator RF, and, most importantly, the beginning of his relationship with Helen Edwards. The cavity itself was only a prototype for an experiment that was never ultimately built. But the knowledge, mentorship and mutual recognition that grew around it endured—and became the foundation for some of Tim’s most important later work.