Grad student applies intuitive 'fuzzy logic' to plasma physics
By Trevor Pritchard
Jordan Morelli is applying philosophy to physics, with results that could change the way North American engineers tackle plasma confinement in fusion reactors.
Morelli, a recent PhD graduate from the Department of Physics, developed a plasma controller that uses 'fuzzy logic' to make adjustments in the reactor. It's a perspective, explains Morelli, that allows for more flexibility than the traditional Boolean logic on which most current controllers are based.
"Fuzzy logic is a concept that's been around for 50 years or so," he says. "It's something that's intuitive, something that we use all the time as people. Fuzzy logic allows us to have degrees of truth, [unlike] Boolean logic where things are either true or false."
Nevertheless, it's still an approach which the North American scientific community has yet to adopt wholeheartedly, preferring time-tested Boolean systems to the innovative solutions offered by fuzzy logic devices.
For his thesis, Morelli worked with the donut-shaped Saskatchewan Torus Modified (STOR-M) Tokamak, a "prototype of a fusion reactor" at the University of Saskatchewan. The STOR-M Tokamak allows physicists like Morelli to study some of the plasma confinement issues that would be relevant if a commercial fusion reactor were one day to be built.
Plasma is a superheated state of matter consisting of negatively-charged electrons and positively-charged ions. Because of its electrical charge, ionized plasma is especially receptive to the forces of magnetism, and its position can be controlled and manipulated through the creation of magnetic fields.
The more stable the flow of plasma through the reactor, the more easily it can be studied. This is where Morelli's controller comes in.
"In our particular device," explains Morelli, "the quality of plasma is strongly related to its horizontal position."
"We want to keep the plasma in the centre of the hollow donut. Vertically, we're already able to do that quite well. Horizontally, however, we're not so set."
Keeping the plasma away from the outer walls of the reactor was one of Morelli's chief concerns. If the plasma comes into contact with the reactor walls, safeguards ensure that it cools rapidly. That's beneficial for Morelli's personal health, as temperatures generated by the reactor can reach up to 20,000 degrees Celsius, but not for the analysis of the plasma.
And compounding the problem of confinement is the fact that the entire process - creating the plasma discharge, observing it, and losing it - takes approximately 50 milliseconds, occurring literally in the blink of an eye. Thus Morelli had to develop a program that not only would ensure the plasma would remain relatively stable, but also one that could perform the required computations at an extremely rapid pace.
Traditional control systems based on Boolean logic are fully capable of accomplishing this task, Morelli admits. Fuzzy logic controllers, however, would be able to make more "intelligent decisions" than their traditional counterparts, beneficial in a highly dynamic environment like the STOR-M Tokamak.
Looking to the future, Morelli hopes the scientific community will continue to embrace novel approaches to existing problems. "I've shown that a fuzzy logic controller is suitable for the Tokamak," he says with satisfaction. "Now [that] the international effort to create a fusion reactor can't be limited to traditional control techniques, maybe they'll be more willing to apply new approaches."
Resting on his laurels, however, is not part of Morelli's plan. "I'm interested in a research career," he says, "and academia provides the best opportunity for that." Morelli is currently teaching with the Department of Physics, and is seeking a full-time faculty position in the future.