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Magnetic fields can calm plasma instabilities, simulations suggest

Date:
August 15, 2016
Source:
DOE/Princeton Plasma Physics Laboratory
Summary:
Physicists have conducted simulations that suggest that applying magnetic fields to fusion plasmas can control instabilities known as Alfven waves that can reduce the efficiency of fusion reactions.
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Magnetic perturbations in a fusion plasma are shown.
Credit: Gerrit Kramer

Physicists led by Gerrit Kramer at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have conducted simulations that suggest that applying magnetic fields to fusion plasmas can control instabilities known as Alfvén waves that can reduce the efficiency of fusion reactions. Such instabilities can cause quickly moving charged particles called "fast ions" to escape from the core of the plasma, which is corralled within machines known as tokamaks.

Controlling these instabilities leads to higher temperatures within tokamaks and thus more efficient fusion processes. The research was published in the August issue of Plasma Physics and Controlled Fusion and funded by the DOE Office of Science (Fusion Energy Sciences).

"Controlling and suppressing the instabilities helps improve the fast-ion confinement and plasma performance," said Kramer, a research physicist at the Laboratory. "You want to suppress the Alfvén waves as much as possible so the fast ions stay in the plasma and help heat it."

The team gathered data from experiments conducted on the National Spherical Torus Experiment (NSTX) at PPPL before the tokamak was recently upgraded. Then they conducted plasma simulations on a PPPL computer cluster.

The simulations showed that externally applied magnetic perturbations can block the growth of Alfvén waves. The perturbations reduce the gradient, or difference in velocity, of the ions as they zoom around the tokamak. This process calms disturbances within the plasma. "If you reduce the velocity gradient, you can prevent the waves from getting excited," notes Kramer.

The simulations also showed that magnetic perturbations can calm Alfvén waves that have already formed. The perturbations alter the frequency of the plasma vibration so that it matches the frequency of the wave. "The plasma absorbs all the energy of the wave, and the wave stops vibrating," said Kramer.

In addition, the simulations indicated that when applied to tokamaks with relatively weak magnetic fields, the external magnetic perturbations could dislodge fast ions from the plasma directly, causing the plasma to cool.


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Materials provided by DOE/Princeton Plasma Physics Laboratory. Note: Content may be edited for style and length.


Journal Reference:

  1. G J Kramer, A Bortolon, N M Ferraro, D A Spong, N A Crocker, D S Darrow, E D Fredrickson, S Kubota, J-K Park, M Podestà, W W Heidbrink. Mitigation of Alfvénic activity by 3D magnetic perturbations on NSTX. Plasma Physics and Controlled Fusion, 2016; 58 (8): 085003 DOI: 10.1088/0741-3335/58/8/085003

Cite This Page:

DOE/Princeton Plasma Physics Laboratory. "Magnetic fields can calm plasma instabilities, simulations suggest." ScienceDaily. ScienceDaily, 15 August 2016. <www.sciencedaily.com/releases/2016/08/160815185824.htm>.
DOE/Princeton Plasma Physics Laboratory. (2016, August 15). Magnetic fields can calm plasma instabilities, simulations suggest. ScienceDaily. Retrieved May 24, 2017 from www.sciencedaily.com/releases/2016/08/160815185824.htm
DOE/Princeton Plasma Physics Laboratory. "Magnetic fields can calm plasma instabilities, simulations suggest." ScienceDaily. www.sciencedaily.com/releases/2016/08/160815185824.htm (accessed May 24, 2017).

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