Plasma diagnostic system improved to ensure safe nuclear fusion

BEIJING - Chinese researchers have improved a diagnostics system for nuclear fusion devices, paving the way for producing controlled thermonuclear fusion power in the future.

At the temperatures required for fusion reactions, the matter can only exist in the plasma state, free negative electrons and positive nuclei. Some fusion reactors use a magnetic field to confine hot plasma for fusion actions to take place.

Plasma is hard to control and contain and is subject to sudden termination, usually with very little warning. When a disruption occurs, the considerable thermal and magnetic energy contained within the plasma is suddenly released very quickly, which can lead to damages.

Scattering of laser light from the electrons in plasma is known as Thomson scattering. It has been used as an established method to measure the electron temperature and density in fusion devices, assisting in the identification of critical points of the fusion plasmas.

Researchers from Aerospace Information Research Institute, Chinese Academy of Sciences and University of Science and Technology of China (USTC) tested their new Thomson scattering diagnostic system in the Keda Torus eXperiment, a fusion device at the USTC.

The new system used laser beams of 200 Hz repetition rate and 1.5 J pulse energy each as the source of intense radiation for scattering and achieved the accurate detection of the electron temperature under 5 electron volts, the energy unit that electron temperature is often expressed in terms of.

The time response of the diagnostic system using a single laser unit is two times faster than that of a conventional one.

According to the researchers, the frequency of laser beam decides how often the diagnostic system measure the electron temperature. In a hot magnetically confined plasma, the laser system thus can record fast changes and measure turbulence and electron fluctuations so as to ensure safe operation of the fusion reactor.

In future studies, the researchers plan to develop Thomson scattering diagnostic system based on laser beams with much higher frequency.

Nuclear fusion has the potential to revolutionize energy production, with virtually endless power available from common elements like hydrogen and helium and no dangerous waste products produced.