The Kingman Lecture Series

On Oct. 23, Michael C. Downer came to the annual Andrews University celebration of Research Week, presenting a talk entitled “Small Particle Accelerators for Big 21st Century Science.” The presentation was held in the Howard Performing Arts Center (HPAC) and the formal talk began at 7:30 p.m. in the auditorium after some light refreshments in the HPAC lobby. With different classes offering extra credit for attendance at the presentation, the university giving out elusive chapel co-curricular credit and much interest in the topic being presented, nearly 90 people gathered to attend the lecture. Sponsored by Robert and Lillis Kingman, the Kingman lectures provide funds to invite researchers on the front lines of modern science and share their results at Andrews University. The topic presented was scientifically relevant yet comprehensible for those without a solid scientific background.

Downer began his presentation with the great leap in scientific technology that allowed a centimeters-long accelerator to bring electrons to the speed of 6 GeV (giga electron volts), as opposed to the older Jefferson lab small particle accelerator that has a 1.4 km loop along which the particles are accelerated. The new and smaller accelerators are based on recent scientific discoveries. They are made to complement older techniques, not completely replace them, so they are likely to be used along with older and larger accelerators. The use of particle accelerators is widespread, with nearly 9,000 medical accelerators (used to generate X-rays for medical scans) and 2,000 industrial accelerators, with others used by security services (for cargo scanning) and laboratory accelerators for scientific research (the search for particles that make up protons and neutrons). 

Currently, femtosecond X-ray free-electron lasers, the name of smaller accelerators achieving GeV speeds, are being made more affordable and accessible. Free-electron lasers have already been used in laser proton cancer therapy, a treatment where laser targets the cancer cells to eradicate them. Making them smaller and more portable will allow more people to take advantage of such treatments.

Downer continued the story of miniaturizing small particle accelerators. Physicists have a history of miniaturizing technology, such as computers or transistors. However, instead of attempting to do the same with accelerators, physicists have made them bigger. This is because of the way particle accelerators usually work. Benjamin Franklin observed that because a neutral object has both positive and negative charges when faced with a charged object, the charges rearrange so that the opposite charges are on different sides. Scientists realized that they could use this property to gradually add charge to an object, causing it to propel forward at greater and greater speeds. However, because accelerators are made of atoms, anything over the ratio of 10×E⁷ volts per meter will experience electrical overload (too much charge for that small area). Downer explained that physicists make accelerators large because high voltages in too small an area will fry the scientific instrument. So, to achieve greater speeds, physicists need accelerators to be bigger to accommodate the higher energy levels without damaging the accelerator.

Thus, to shrink accelerators, they must be made of something other than atoms. 

“I have one word for you,” said Downer. “One word, just one word, plasma! There is a great future in plasma. Think about it.”

Plasma is a state of matter in which electrons and protons are free to flow in a fluid-like manner. Because of their fluid, ionized nature, very little further damage can be done to it. Accelerators built of plasma make it possible to bring particles to incredible speeds without the threat of damaging the plasma. (Due to its nature, no further damage can be done to plasma, which is not the case for solids.) Because plasma is fluid, the difficulty of shaping it can be resolved with the generation of a plasma wave, illustrated by a boat (laser pulse) driving the plasma wave, allowing the particles to “surf” on it, generating speeds higher than any previous accelerators could at that size. Plasma accelerators do work, slowly working up from MeV (1996 studies conducted by the University of Michigan) to 1 GeV (2006), adding charge along a few centimeters long plasma strip, with the laser pulse charging the particles to get to the GeVs. Scientists must find a way to snapshot the plasma waves to measure the data. Further research conducted by Downer’s lab revealed that energy spread over an area shrunk, leading to a greater concentration of power (2013). The speed of 8 GeV was further achieved in other laboratories. 

Small particle accelerators have great applications in generating X-rays through machines called synchrotrons. An X-ray free-electron laser creates the most coherent, energetic, and short-pulsed technology that will be exceedingly useful in scientific research. Using short X-ray free-electron lasers, biologists have found more information on how photosynthesis works, specifically the role of Photosystems 1 and 2 in the process. This is just one example of potential discoveries made possible using small particle accelerators. Moving forward, the X-ray analysis of biomolecules would allow scientists to get further information about biomolecules. The swiftness of a laser pulse allows scientists to achieve a scanned image of the biomolecule before it is destroyed by the plasma and laser. Another area of further research includes spectroscopy, or using light to gather information about a substance. Multi-dimensional X-ray spectroscopy allows for gathering even more information regarding objects of interest.

Future applications of this technology will enable scientists to discover more about life and matter. Downer concludes that although more research is needed, the scientific possibilities of using small particle accelerators are nearly endless.