Originally developed in 1921 and used in radar technology during World War II, magnetrons are now the focus of physicists and engineers at the U.S. Department of Energy's Jefferson Lab. They aim to use these compact devices to drive high-performance particle accelerators, potentially reducing their carbon footprint and broadening their applications beyond scientific research.
Particle accelerators have numerous applications, from cancer therapy to food sterilization, water treatment, and security. However, making these energy-intensive machines more efficient and affordable is essential for their wider adoption. To this end, the DOE's Office of Science is funding various projects under initiatives such as "Research Opportunities in Accelerator Stewardship and Accelerator Development" and "Accelerate Innovations in Emerging Technologies." These projects focus on utilizing novel superconducting materials, standard cooling equipment, machine learning, and magnetrons as sources of radiofrequency (RF) fields to develop more compact and efficient accelerators.
"Industry wants the compactness, the high efficiency, and the low cost," said Haipeng Wang, a senior accelerator physicist at Jefferson Lab and the lead investigator on the magnetron study. His team collaborates with private-sector firms and universities to create scalable, low-cost magnetron systems for compact and potentially portable superconducting RF accelerators.
A magnetron, unlike its fictional counterparts from popular culture, is a type of vacuum tube that generates microwaves by crossing a stream of electrons with a magnetic field. The most common type, the cavity magnetron, features a copper cylinder with a central hole and several surrounding chambers. When electrons are introduced into this setup, they spiral in the magnetic field, causing the electric current to oscillate and produce RF waves.
"When magnetrons are saturated, they reach the desired power at the defined frequency," Wang said. "But to lock that frequency in, you have to act fast."
Magnetrons have been used in various applications since World War II, including radar systems and microwave ovens. The latter was famously discovered by physicist Percy Spencer when he noticed that a candy bar in his pocket melted while he was testing a magnetron-based radar system. This led to the development of the first commercial microwave oven in 1947.
Today, magnetrons could revolutionize particle accelerators by offering efficiency levels surpassing 70%. In comparison, the klystrons currently used in accelerators like Jefferson Lab's Continuous Electron Beam Accelerator Facility (CEBAF) offer high output power but with lower efficiency.
Wang's team, supported by DOE grants, is exploring the use of magnetrons as RF sources for compact, industrial accelerators. This research could eventually lead to significant cost savings and improved efficiency for facilities like CEBAF.
"Ultimately, the goal is driving CEBAF," Wang said. Magnetrons not only promise higher efficiency but also utilize many commercially available components, making them cost-effective.
However, challenges remain. Magnetrons can be unstable at varying power levels, and the Jefferson Lab team is working on solutions, such as using extra wire coils to stabilize the frequency. They are also investigating power combining techniques to scale up magnetron systems without losing efficiency.
"The frequency of the tube has to match that of the cavity very well," said Kevin Jordan, a senior engineer at Jefferson Lab. "We can use an amplifier to push and pull a little, coaxing it along, but everything is about having the field in the cavity match the electrons."
Future research will focus on improving control systems, reducing noise, and enhancing operational stability. The aim is to achieve a cost-effective and efficient magnetron system that could reduce energy costs significantly.
"This is a wonderful story of collaborative R and D from fundamental research that we started some 15 years ago," Wang said. "There are so many good people on the team, from industry to research institutions, to universities. We are glad to be a part of that."
Related Links
Thomas Jefferson National Accelerator Facility
Understanding Time and Space
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