Life’s turns are as interesting and complex as the twists in a stellarator’s magnetic loops.
Just ask DOE Princeton Plasma Physics Laboratory (PPPL) physicist David Gates, the Stellarator Physics Leader at PPPL and a visiting professor last summer at the National Institute for Fusion Science (NIFS) in Japan.
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.
and stellarators are types of experimental fusion energy machines in
which plasma 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
Gates, who received a Ph.D. from Columbia Univ.
in 1993, had worked on tokamaks since graduate school. “Tokamaks are
the most successful fusion concept in the sense that they have come
closest to achieving fusion conditions,” he says.
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, an expert in
plasma controls who had previously worked on PPPL’s National Spherical Torus Experiment.
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. “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.”
stellarators—which are three-dimensional (3D)—lacked good
confinement because researchers did not know how to handle 3D systems.
Theoretical and computer advances during the past two decades
transformed the picture, making stellarators an attractive option.
interest in stellarators was piqued indirectly. While conducting tours
for PPPL, 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.”
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.” Gates 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. Along the stellarator path, Gates was
offered the prestigious professorship in Japan, where he spent three
months working on the Large Helical Device (LHD), a type of stellarator
called a heliotron.
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?