Fig. 2-4 Experimental arrangement for studying the behavior of high energy ions in a high temperature JT-60 plasma The range of gamma-ray measurement was 0.5 - 20 MeV.

Fig. 2-5 Time variation of magnetic fluctuations (TAE mode) and the gamma-ray intensity Gamma-ray intensities decrease because of unstable magnetic fluctuations caused by high energy protons, showing a loss of protons themselves. The gamma-ray intensities of the 2.1 MeV and 4.4 MeV indicate the behavior of the protons with energies greater than 2.5 MeV and 5 MeV, respectively.

Gamma (gamma)-rays are generated in a high temperature plasma in large tokamaks by various nuclear reactions. A diagnostic method for high energy ions in the plasma using gamma-rays has recently been developed as an alternative to a more well-known diagnostic, which measures ions with lower energies via the measurement of neutral particles produced by charge exchange. There is some concern that a future fusion reactor may have an extra flux of fusion-produced high energy alpha (alpha) particles (3.5 MeV) due to unstable fluctuations of the confining magnetic field, induced by the alpha particles themselves. Such an instability is referred to as a TAE-mode. We are investigating this anticipated instability by simulation experiments on JT-60 : protons (simulated alpha particles) are accelerated to an MeV-level by the ion cyclotron resonance frequency (ICRF) heating method, and gamma-rays generated by high energy nuclear reactions in the plasma are measured (Fig. 2-4). Fig. 2-5 shows measured fluctuations in the magnetic field and the time variations of the gamma-ray intensities. The decrease in the gamma-ray intensity is correlated with the growth of the magnetic fluctuations, indicating a decrease in density of the high energy protons. This is the first result obtained by a gamma-ray measurement that shows a clear correlation between the TAE mode and the behavior of MeV-level high energy particles.

Reference T. Kondo et al., Gamma-Ray Measurements in JT-60U ICRF Heated Plasma, Purazuma Kaku Yugo Gakkai-Shi, 72 (12), 1397 (1996).

Select a topic in left column