As the inaugural Hermann Grunder Fellow, John Vennekate is developing a compact superconducting radiofrequency accelerator that could remove contaminants from wastewater
NEWPORT NEWS – Hermann Grunder is the founding director of the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility. In addition to helping shape the lab into its current form, Grunder transformed the vision of the lab’s premier particle accelerator in the late 1980s, changing it to one that featured a new superconducting technology and recirculating design. The result was the design-specification-surpassing Continuous Electron Beam Accelerator Facility (CEBAF) that we know today.
In honor of Grunder’s contributions to accelerator science, Jefferson Lab recently established a fellowship in his name: the Hermann Grunder Postdoctoral Fellowship in Accelerator Science.
“We are very happy to welcome John as the first recipient of the Grunder Fellowship. It’s fitting that he will be pushing the boundaries of superconducting technologies with the goal of applying them in new ways to benefit society, something that was a high priority for Jefferson Lab’s founding director,” said Jefferson Lab Director Stuart Henderson.
Now, the first Hermann Grunder fellow, John Vennekate, has started work at Jefferson Lab. He said he hopes to follow in the footsteps of his fellowship’s namesake to continue blazing a new trail for practical applications of superconducting accelerators.
“I feel quite honored,” he said. “I’m happy to be here.”
The ultimate goal of Vennekate’s fellowship project is to develop a compact accelerator based on superconducting radiofrequency (SRF) technology for environmental remediation applications, such as cleaning wastewater at a water treatment plant.
The concept of using accelerators for wastewater remediation isn’t new. Irradiating water with an accelerator’s electron beam safely removes contaminants. Past accelerators for this purpose were based on normal conducting technology, which left researchers struggling to maintain cost efficiency while scaling up small prototypes to build machines powerful enough for big wastewater plants, while being able to compete with traditional and less expensive water treatment methods.
“The gap that so far people were not able to bridge was the power,” Vennekate said. “Our idea is to use SRF technology to bridge that gap.”
New Technologies for SRF Accelerators
He explained that, in the past, it was difficult to build SRF accelerators suitable for industrial applications, because the cavities that actually accelerate the electron beam must be extremely cold. Usually, cooling these cavities requires liquid helium. The refrigerators needed to keep liquid helium cold are big, expensive and require experts to operate them – requirements that are difficult and costly in an industrial setting.
But recent progress in three technologies has made it possible to cool SRF cavities without liquid helium: niobium-tin (Nb3Sn) coatings, cryocoolers and copper cladding.
SRF radiofrequency cavities are made of niobium, which is a superconductor at very low temperatures. Nb3Sn cavities are niobium cavities that have been coated with Nb3Sn, and they superconduct just as well, and sometimes even better, as plain niobium cavities but at higher temperatures, meaning they don’t have to be cooled down as much.
Another recent step forward in the field is the progress made in the field of cryocoolers, which are standalone machines that can cool accelerators to superconducting temperatures without liquid helium. These cryocoolers are far more compact units about the size of a regular refrigerator that can be plugged into the wall and operated by anyone with appropriate training.
Further, additive manufacturing techniques were applied to add a thick, high-purity copper layer onto the outer surface of SRF radiofrequency cavities. This cladding more efficiently conducts heat to the cryocooler, helping it cool the cavities to optimum operating temperatures.
Combining the new Nb3Sn cavities with the cryocooler and copper cladding technologies should enable a machine to produce an electron beam with enough energy at high enough power for a range of industrial and environmental applications, including treating municipal wastewater. While many components of the machine are already known, Vennekate will need to bring them together and finesse them into a single system.
“My task, and what matches quite well with my experience, is the system integration,” he said. “We have the heart of the whole thing already, but need a cryostat, a whole module around it, an injector, an RF source, a power supply, cryogenics, electronics, and more.”
He will combine all of these components to “build the house” around the Nb3Sn SRF cavities.
“It’s all in the details, and you have to get all these things together and get them to work,” he said.
At the end of the three years, he wants to have a detailed plan for the accelerator, and maybe even build a prototype of a machine that could be used in a water treatment plant.
The Road to Research
Vennekate did similar work while earning his Ph.D. at Helmholtz-Zentrum Dresden Rossendorf, where he helped build a small injector for an SRF accelerator. During his Ph.D., he also came to Jefferson Lab to work on cavities with Gianluigi “Gigi” Ciovati, an accelerator scientist at Jefferson Lab.
“That was really amazing and actually part of the reason that I found Jefferson Lab attractive,” Vennekate said. “I’ve rarely worked with someone that had so much joy. He has a professional but also very relaxed and patient style of working I have rarely seen anywhere else.”
Ciovati will be Vennekate’s fellowship supervisor.
“I had told him to join Jefferson Lab to help us make the world a better place with SRF, in reference to the possibility of future compact SRF accelerators for environmental remediation,” said Ciovati, who himself has developed SRF technology for wastewater-remediation accelerators.
Vennekate brings to this fellowship two and half years of experience building SRF accelerators for industrial applications at a company in Germany called Research Instruments.
“This new fellowship at Jefferson Lab perfectly meshes with my previous work at RI,” he said.
When Vennekate discovered a picture of Hermann Grunder in CEBAF Center, he wanted to learn more about him.
“He is Swiss American,” Vennekate said. “And it’s funny that the first guy to fill that fellowship is a native German. Germany is not too far away from Switzerland, and I spent some time in Switzerland doing my master’s at CERN back in the day. It’s sort of an interesting loop.”
Hermann Grunder was also an advocate for promoting applications of nuclear physics and its technologies beyond the realm of basic research, particularly when those developments could benefit society. Jefferson Lab has emphasized proactive transfer of its unique technologies to the marketplace since its founding, resulting in a wide range of applications in fields as diverse as industrial safety, cryogenics and medicine.
Knowing he’s the first Hermann Grunder fellow stressed Vennekate a little at first, but he’s optimistic.
“Once I heard that I was the first, there was a bit of pressure on my shoulders,” he said. “I’m probably not arrogant enough to hope to set a legacy right now, but I hope I don’t fail. I just feel fortunate and grateful for this opportunity.”
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Hermann Grunder Biography
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By Chris Patrick
Contact: Kandice Carter, Jefferson Lab Communications Office, firstname.lastname@example.org