Princeton graduate student creates program that helps stabilize fusion plasma

Princeton graduate student creates program that helps stabilize fusion plasma
Imène Goumiri led the design of a controller. Credit: Elle Starkman/PPPL Office of Communications

Imène Goumiri, a Princeton University graduate student, has worked with physicists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) to simulate a method for limiting instabilities that reduce the performance of fusion plasmas. The more instabilities there are, the less efficiently doughnut-shaped fusion facilities called tokamaks operate. The journal Nuclear Fusion published results of this research in February 2016. The research was supported by the DOE's Office of Science.

The new method uses feedback from sensors for real-time control of the rotation of plasma that swirls within a tokamak and fuels fusion reactions. Goumiri, a student in the Princeton Department of Mechanical and Aerospace Engineering, led the design of a controller that employs two different kinds of actuators. The first provides a torque—or twisting force that causes rotation—by injecting high-energy neutral particles into the plasma. The second uses a tokamak's three-dimensional coils to create a magnetic field that generates a torque by acting as a drag on the rotation and slowing it down.

Goumiri built a model of plasma rotation from data collected from PPPL's National Spherical Torus Experiment (NSTX) before it was upgraded, and used it to construct the program in MATLAB software. She then translated the program into a predictive model based on PPPL's TRANSP code, the global standard for analyzing plasma performance. The TRANSP model found the new approach to be effective at controlling rotation.

"This confirmed the validity of our model and the efficacy of the controller," said Goumiri, the lead author of the paper. Coauthors included Clarence Rowley, Princeton professor of mechanical and , and David Gates, principal research physicist at PPPL and stellarator physics leader, who served as her academic advisors; and Steve Sabbagh, senior research scientist and adjunct professor of applied physics at Columbia University on long-term assignment to PPPL, a member of her doctoral committee who served as a scientific advisor.

"Shear" lessens instabilities

The new program, which adapts quickly to feedback from the plasma, draws on the fact that rotating different sections of a plasma at different speeds creates a force called "shear" that lessens instabilities. Rotation can also disrupt transport, a process that leaks heat from the plasma and interferes with fusion reactions.

A unique aspect of the new model is its use of three-dimensional magnetic fields to manipulate the torque produced by the neutral beam injector. The drag created by these magnetic fields, technically known as "neoclassical toroidal viscosity," gives researchers more precise and continuous control of the plasma rotation.

Looking ahead, researchers noted that the upgraded NSTX, called the National Spherical Torus Experiment-Upgrade (NSTX-U), has a second neutral beam injector that can affect a broader region toward the edge of the plasma. This broadened region could alter the shear and enable greater control of plasma instabilities.

Researchers also noted that this new class of controllers can be developed from simulations based on experimental data, with no need for additional experiments for calibration. The new method could replace classical controllers like proportional-integral-derivative (PID) systems, which use experiments to tune their parameters. The new method would necessitate fewer experiments and would provide a way to predict requirements for adjusting rotation in future fusion facilities.

Explore further

Identifying new sources of turbulence in spherical tokamaks

More information: I.R. Goumiri et al. Modeling and control of plasma rotation for NSTX using neoclassical toroidal viscosity and neutral beam injection, Nuclear Fusion (2016). DOI: 10.1088/0029-5515/56/3/036023
Citation: Princeton graduate student creates program that helps stabilize fusion plasma (2016, April 15) retrieved 22 September 2019 from
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Apr 15, 2016
Perhaps we should put Ms. Goumiri in charge of ITER, maybe something useful would happen before 2035.

The DOE should develop a Plan B to ITER and lay it out for public inspection and comment. This technology is too important to leave to the folks at ITER who have wasted an entire decade and want to waste another decade or two before useful science on D-T plasma is performed.

Apr 15, 2016
Sounds like great theoretical work: Get it into a tokamak ASAP.
It also sounds like multiple / steerable / aim-able neutral beam injection could produce even better results by precisely targeting particular layers of rotating plasma.

If experiment doesn't fully match theory:(As it may not in such a randomised turbulent system ) A fuzzy logic layer to fine tweak or limit or boost the applied corrections based on multiple results of past corrections could help.

Apr 18, 2016
Now that the LHC is a proven success, maybe some of those LHC folks could take over ITER and make some real science happen. Looking at the two projects, one might guess that it would be harder to build LHC because of the sheer size of the thing. If nothing else, let's try to understand why LHC has been a tremendous success and ITER has been a tremendous failure.

Apr 18, 2016
Don't underestimate the scale and complexity of the ITER project see Youtube:-

Of course it has its flaws, but it was designed a few years back and its too big a project to update easily.
Hopefully the folk at PPPL will get them to add lithium coated limiters before it melts the beryllium off its blankets and so poisons the plasma.
The sustained burns, ITER will be capable of, will certainly teach us a lot about plasma containment. instability control, and diverter and blanket design.

Apr 18, 2016
"The sustained burns, ITER will be capable of, will certainly teach us a lot about plasma containment. instability control, and diverter and blanket design."

True, but only if: 1. the project is actually built; and 2. the D-T experiments occur first at ITER and not elsewhere years before, both of which are in serious doubt at this point. Some of the folks from PPPL are brilliant, maybe put them in charge of ITER. Same for the folks at General Atomics. We need somebody who can drive ITER to completion the way we need it to be driven. Maybe Elon Musk would be willing to provide some oversight and a kick in the pants. Somebody needs to get this project back on track or kill it.

Apr 19, 2016
D-T experiments HAVE been done elsewhere. If we didn't have that tested confidence in ignition we probably wouldn't be building ITER at all.
But ITER has to handle D-T and the helium "ash" semi-continually (eventually as the first campaigns will have no tritium for several years).

Radically new and exciting tokamak concepts like MIT's ARC don't include Tritium or ash handling.

ITER is an overly conservative design and could indeed have listened to more input from the wizards at MIT and PPPL before pouring the concrete and ordering the coils, but it is what it is: A research reactor with many years of carefully planned escalating tests ahead of it: With more elements of research and committee control than suits the urgency of our need for 'Uranium-free' power sources.

I hope others will find the funding for high temp coils and high field tokamaks (like ARC)
DEMO certainly shouldn't look like an online oversized over-managed over-priced version of ITER.

Apr 19, 2016
EyeNStein, it is the excruciatingly slow pace of ITER that is the most troubling. Obviously, I realize D-T experiments have been done elsewhere, included at JET, where a record 16 MW was produced way back in 1997 for 24 MW input. I applaud the MIT ARC design and it uses D-T fusion just like ITER. The key feature of ARC is the use of more modern higher magnetic field superconductors to shrink the overall design.

The biggest problem with ITER is not so much the technology, although it is becoming dated, it is the lack of progress. Can anyone justify the delay from 2006 to 2035 until the first D-T experiments begin? How is it that the buildings are not even finished yet? Something is clearly wrong. Turn control over to MIT, PPPL, General Atomics, LHC, or any reputable scientific institution or agency. I recently discovered the U.S. has required an independent committee to investigate and I sincerely hope they can figure out what is going on over there.

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