Biggest, most powerful, brightest: The machines used in particle physics earn their superlatives by cracking open the mysteries of the universe. By the end of 2012, experiments should confirm the existence of the Higgs boson—a theoretical particle that bestows other elementary particles with mass. The discoveries are profound, but the accelerators themselves are remarkable feats of engineering.
Just ask Lia Merminga, whose job is to keep Canada’s accelerators tuned and humming. Even as a young student in Greece, she loved the quest in physics for the answers to big questions. One of the rare women in the top echelons of physics, Merminga credits her success to hard work and attentive mentors.
Now, she heads the accelerator division at TRIUMF, Canada’s national laboratory for particle and nuclear physics. In addition to furthering physics research, the lab creates rare isotopes used in medical imaging. These short-lived elements decay in a matter of hours. The radiation they emit helps doctors find bone fractures and tumors.
Merminga spoke about cutting-edge technologies for the next generation of particle accelerators at the February 2012 meeting of the American Association for the Advancement of Science in Vancouver, Canada. Afterward, she gave SciCom’s Marissa Fessenden a peek into the inner workings of the world’s biggest machines and the life of a woman in physics.
When did you first become interested in physics?
A friend of mine gave me the biography of Madame Curie as a birthday present when I was 13. I was fascinated. Then, a superb physics teacher in high school largely influenced me. She demanded excellence from us and she gave excellence to her teaching. A woman who is so professional and who has such high standards—this was very inspiring to me.
What attracted you to accelerator physics specifically?
Initially, I didn’t have any preconceived plans. I entered the physics department at the University of Athens. In my third year, I realized it wasn’t enough. I wanted to keep going.
My current husband became a postdoctoral researcher at Fermilab and made me aware that they had a graduate program in accelerator science. I was fascinated by the fact that you are studying something quite deep. These are really very rigorous scientific questions, but you have the opportunity to make progress in relatively short time scales—compared to high-energy physics.
"I feel it is very important to be good technically. And then nothing else matters. If you know your stuff, then you are okay."
Why do these questions fascinate you?
Accelerator science touches upon many fields, and I find that very attractive. I can design and build accelerators that are used to study the most fundamental questions of our nature: the Higgs particle, or dark matter and dark energy. Here at TRIUMF, I work on nuclear physics accelerators and the cyclotron, which is used for material science and nuclear medicine. You can enable science on multiple fronts.
TRIUMF has the largest cyclotron in the world. What does it do?
There is a source of H- [hydrogen ions], and that is where everything starts. A spiral inflector takes these ions and kicks them horizontally. There is a very big magnet and structures with a gap that has an electric field, oscillating. It’s timed so that when [the beam] crosses the gap it gains energy, it gets a push. The magnetic field bends it around, it crosses the gap again and gains more energy, around and around. It circles, many times, until it reaches the desired energy. Then it hits a foil; it loses two electrons and becomes a proton beam that gets extracted out of the cyclotron.
What do you do with those protons?
We have up to four extraction ports at the cyclotron at TRIUMF. Not many cyclotrons have this capability to have several simultaneous extractions. With one of them you send [the proton beam] for materials science experiments. The second port goes out to produce medical isotopes, which we sell to a medical company housed on site. Part of the beam goes for proton therapy: We have patients with ocular melanoma, a cancer of the eye. A third port heats targets to produce rare isotope beams used for nuclear physics experiments.
A fourth port has not been used for ten years or so now. We plan to bring it online as part of phase two of the ARIEL project [a new laboratory to produce rare isotopes for nuclear physics and medicine].
You have patients come on site with ocular melanoma. What kind of treatment do they get?
They get radiation using small amounts of the proton beam. It is 95% successful. This is the only facility in Canada [that offers a] proton therapy facility for ocular melanoma. We treat about one patient every month.
The interval between treatments is more or less fixed. If for some reason the accelerator is down and they cannot conclude this treatment cycle, they would lose their eye. It is that critical.
At the meeting, you spoke about the frontiers of physics. What is the next big accelerator to be built?
It could be the International Linear Collider, but that is crucially dependent on results from the LHC [the Large Hadron Collider in Switzerland]. If the LHC sees the Higgs at a specific energy, then it is very likely that the international particle physics community will make a very strong case for an e+/e- collider with enough energy to [produce] the Higgs.
What does that mean, an e+/e- collider?
It’s a linear collider with source of electrons and a source of positrons. The beams of electrons and positrons collide. From the results of the collision, you make the Higgs. The outcomes of these collisions give very clear events. Because electrons and positrons are elementary particles, they are not believed to have any structure. That is different from colliding protons together in the LHC. Protons have parts to them—the quarks and so on—so when you collide them, all kinds of garbage comes out! You can make discoveries, but it is really hard to focus and isolate the event of interest.
Will we know about the Higgs by the end of this year?
Yes, by the end of 2012, assuming nothing will go wrong. But they have done such a spectacular job. It is awesome the way the LHC is such a manifestation of engineering and accelerator science, particularly engineering. If everything goes according to plan, we will know one way or another.
There's a big push to make the next generation of accelerators more compact. Why?
It is a practical matter. Imagine you’re a doctor at the hospital and you need to use radioisotopes to do diagnostic procedures. Imagine having them in your room next to your office where they are produced on demand [rather than mailed to you]. You can make the isotope and before it decays—even if it is very short-lived—and you would have enough time to do the procedure. It can change the way we do business right now.
What are the largest hurdles we have to overcome to make these machines more compact?
We have to find a way to accelerate these particles more efficiently, so they gain energy in a much shorter distance. The plasma wakefield goes in that direction.
Tell me about plasma wakefield accelerators.
Instead of using metallic structures to accelerate, you use plasma channels. You send a beam of electrons through the plasma. As it goes through, it creates a region of depleted electrons behind it, because it repels the electrons of the plasma. But then the ions attract those repelled electrons and the electrons snap back again. The separation of charges creates longitudinal and transverse density waves. If you now inject the particle beam, the one you really want to accelerate, it’s going to gain energy like a surfer that rides the waves as he surfs. And the fields we are talking about are tens of GeVs [a billion electronvolts] per meter. That’s a thousand times more than conventional accelerators do today.
That sounds amazing.
Yes, exactly. It is not an evolutionary way of particle acceleration; it is revolutionary. There are huge obstacles. But, there has also been huge progress. At SLAC [the SLAC National Accelerator Laboratory] they sent a beam through a plasma channel. Some of the electrons doubled their energy through this plasma, just 85 centimeters long. So this is pretty huge.
There are few women at high levels of physics and high levels of accelerator physics. Has that ever been a challenge for you?
My field is male dominated. There is no question about that. I feel that men tend to be almost too assertive. And so this has caused me some… there were times that I walked away from a meeting and cried because I perceived that somebody did not treat me respectfully. Not recently, but when I was younger and less established.
I feel it is very important to be good technically. And then nothing else matters. If you know your stuff, then you are okay. That’s my experience.
Do you think young women who are graduate students now are still facing the same kind of thing?
Overall, things aren’t equal exactly. I think it is getting better, because I think men are accepting women in the workforce and in graduate schools. But I would not be surprised if young women are facing similar problems every once in a while.
I’ve been very lucky in my whole career. On average, I don’t feel I’ve been discriminated against. If I’m invited to give a talk somewhere and I’m chosen because they want to have gender equality—by and large I want to take this opportunity. And I try to do a very good job. But I will use the opportunity to be out there and say: “Yes, women can be as good as men, and better. We are also a significant force in this field.”
Do you have any advice to give young women interested in physics?
When I was young, I heard a woman who gave a talk, and I think she was at a very high level at the National Institutes of Health at the time. She said she had two pieces of advice to young women starting up in scientific and engineering fields. One of them was, “Stay focused.” And the other was, “Don’t take no for an answer.”
I found both of them to be crucial to my success, especially “Don’t take no for an answer.” This may not have to do with my being a woman, but if you come up with an idea, somehow the tendency is that people want to turn down the idea. They say either “We tried it and it didn’t lead anywhere,” or “It’s not going to work.” Don’t stop. Don’t. Just keep pushing. Not all ideas are good, but don’t stop at the first no. To be determined and to persevere is very important.
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Marissa Fessenden, a graduate student in the Science Communication Program at UC Santa Cruz, earned her bachelor's degree in interdisciplinary studies (biology and writing) at Cornell University. At UCSC, she has worked as a reporting intern at the Santa Cruz Sentinel, the SETI Institute's "Big Picture Science" radio program, and the Stanford Medical School news office (multimedia). This summer, she'll work at Scientific American in New York as an intern for the magazine.
© 2012 Marissa Fessenden
