Stellarator Man

(Photo by Elle Starkman, PPPL)

 
By Patti Wieser

Life's turns are as interesting and complex as the twists in a stellarator's magnetic loops.

Just ask PPPL physicist David Gates, the new Stellarator Physics Leader at PPPL and a visiting professor this summer at the National Institute for Fusion Science (NIFS) in Japan.

The longtime tokamak researcher has turned his eye from the toroidal symmetry of tokamaks to the curvy, complicated magnets — and the promise of steady-state operations — of stellarators.

Tokamaks and stellarators are types of experimental fusion energy machines in which plasma — a hot, electrically charged gas that is the fuel for fusion energy production — is confined by magnetic fields inside a vacuum chamber. In stellarators, external magnetic coils generate twisted field lines around the inside of the vacuum chamber to contain the plasma; in tokamaks, there are two sets of magnets, an external set surrounding the vacuum chamber and an internal transformer that drives current in the plasma through pulses, creating twisted magnetic field lines.

Gates's shift to stellarators was a long time coming. He'd worked on tokamaks since graduate school. "I went into tokamak research because most fusion research is on tokamaks," says the physicist, who received a Ph.D. from Columbia University in 1993. "They are the most successful fusion concept in the sense that they have come closest to achieving fusion conditions."

That said, he admits to being "fairly skeptical" that a tokamak can lead to a reactor. Generally, tokamaks operate in a pulsed mode and are subject to disruptions. A practical fusion reactor will require continuous operation and control over plasma disruptions. "Stellarators offer the best possibility for steady-state operation," says Gates, who believes stellarators may very well be the configuration when fusion is on the grid.

Gates, an expert in plasma controls, notes that researchers have not been able to operate tokamaks in steady state without getting plasma instabilities that lead to disruptions. Once plasma disrupts, the fusion reaction ends. "I'm concerned about plasma control," he says.

"The upside of a stellarator is that the helical (twisted) field is now imposed by external coils so you don't need a current — you don't need to drive a current anymore. That whole requirement goes away," says the stellarator convert. "That makes it easy to imagine a steady-state device."

Historically stellarators — which are three-dimensional (3-D) — lacked good confinement because researchers did not know how to handle 3-D systems. Theoretical and computer advances during the past two decades transformed the picture, making stellarators an attractive option.

Gates's interest in stellarators was piqued indirectly. "I wasn't actually looking for another project," he says, noting he was quite happy working on the National Spherical Torus Experiment (NSTX). But while conducting tours for the Laboratory, he brushed up on his stellarator knowledge to better answer visitors' questions about the National Compact Stellarator Experiment (NCSX), now mothballed.

"I wanted to answer their questions so I read about the stellarator and the more I read about it the more fascinated I became," says Gates, who joined PPPL's research staff nearly 13 years ago after working as a research associate for four years at Culham Laboratory in the U.K. "[Today's modern] stellarators are potentially a break-through for fusion."

Gates was ready for something new since he had reached his professional goals on the spherical torus, and the idea of building a stellarator program at PPPL was just the ticket. "The goal is to advance the idea of optimized stellarators," he says.

He admits there are complexities associated with stellarator research, "but, of course, it's the kind of complexity that looks like a good challenge to me."

He is now responsible for leading PPPL's experimental stellarator physics activities, including collaboration on off-site stellarator experiments and providing physics input to stellarator engineering tasks. "He will have a key role in shaping PPPL's stellarator program and exploring the important scientific connections between stellarators and tokamaks," notes Advanced Projects Head Hutch Neilson.

At PPPL, Gates — most often seen wearing a signature sports coat and open-collar shirt and carrying a mug — was a common feature of the NSTX Control before moving to a third floor office to take up his stellarator responsibilities. His droll sense of humor pierces through conversations about fusion research, the latest movie he's seen (Iron Man II at interview time) and the joys of parenting two teenage sons.

Along the stellarator path, Gates was offered the prestigious professorship in Japan, where he is spending three months this summer working on the Large Helical Device (LHD), a type of stellarator called a heliotron. His research this summer focuses on an experimental computer modeling code that will reconstruct the LHD plasma based on measurements, and on high-pressure instabilities and fast-particle physics. The professorship (one each summer) was created as part of the Lab's participation in the world stellarator program.

In Japan, where his wife, Karen, and their two sons, James and Robert, are joining him for a portion of the visit, Gates also will be managing two post-docs who are making a diagnostic operational on the LHD. Last year, PPPL's Manfred Bitter developed and built the diagnostic, an X-ray crystal spectrometer. The spectrometer measures intensities of soft X-rays emitted by a plasma and uses these intensities to determine plasma temperatures.

The stellarator advocate notes that both Europe and Japan have billion-dollar stellarators, and he hopes the place where preeminent astrophysicist Lyman Spitzer first developed the stellarator concept — PPPL — will one day be home to a new stellarator. His dream is for NCSX to be completed.

Gates takes a breather from physics by jogging, doing the New York Times crossword puzzle, playing guitar, and participating in Tae Kwon Do — and cheering his sons in their Tae Kwon Do adventures, as well as their academic activities. "James took the silver medal in both sparring and weapons in the American Tae Kwon Do Association World championships in Little Rock and Robert got a 700 on the math SAT in 7th grade," he beams.

Gates says altruism motivates him to devote his life to fusion energy research.

"I read about fusion and it was apparent that it would be the solution to energy," says the Wisconsin native, who saw the energy crisis peak while in high school. "I wanted to solve the world's problems.

The fusion program has taken him to projects and meetings around the globe. And ten years from now, he intends to be conducting and leading fusion research. "Hopefully I will be at PPPL with the domestic stellarator program."

It's no surprise Gates identifies with the flexible Mr. Fantastic. Asked what superhero he would be if given the chance, he pauses and says, "The rubber guy in the Fantastic Four — Mr. Fantastic. He was smart and he thought his way out of situations. If he was stuck, he was flexible."

Maybe it pays to be flexible in life, just as it does in fiction for the genius scientist superhero from Marvel Comics.

Otherwise, how else would a lifetime tokamak man end up in stellarators?