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An international team of fusion experts working at the DIII-D National Fusion Facility in San Diego, California, has discovered a way to minimize the effects of a phenomenon that can decrease the performance of fusion reactors and even possibly cause damage to the device. This work shows that localized electron heating by microwaves is an effective tool for modifying Alfvén eigenmode activity in DIII-D and other devices worldwide.

Alfvén waves can cause redistribution or loss of the injected neutral beam ions that are needed to heat fusion devices and of the helium nuclei (alpha particles) produced by the fusion reaction that also contribute to the continued heating of the plasma. If left to grow unabated, the Alfvén waves can result in reduced performance and potentially damage vessel components.

Powerful microwave beams deposited near the location of so-called reversed shear Alfvén eigenmodes (RSAEs) are found to modify the wave activity significantly—in some cases completely removing the modes. Based on experiments run at the DIII-D tokamak, the team has arrived at a simple model that determines how to predictably minimize RSAEs by using microwaves to heat the electrons at particular points in the plasma.

Read the full report here.

-- Spectrograms showing the change in wave activity with and without microwave heating. With no heating (top), upward frequency sweeping RSAEs are observed. With heating near the wave location (bottom), no RSAEs are expected or observed. Adapted from: M.A. Van Zeeland, W.W. Heidbrink , S.E. Sharapov , D. Spong , A. Cappa, et.al., Nucl. Fusion 56, 112007 (2016).

An update on ITER has been published in the Autumn 2017 issue of Energy Focus, the flagship magazine of the UK-based Energy Industries Council.

Titled "Is Fusion the Fuel of the Future?" the article describes recent project performance, concerns about the effect of Brexit, and why it's all worth it.

You can read the article on line at Energy Focus (pp 46-47).