Abstract: We present a technology for diagnosing the D－T fusion process by detecting capture $\gamma$-rays. This technology provides an alternative route to diagnosing the D－T reaction process when a great deal of heavy Z materials surrounds the D－T region. A very important aspect of this paper is to focus on the methods of shielding low-energy $\gamma$-rays whose radiation intensity is 10⁶ times higher than that of the capture $\gamma$-rays. Another aspect is about how to distinguish signal from noise. The result of a 50/1 signal-to-noise ratio indicates that the designed double-magnetic spectrograph is very successful for diagnosing the D－T fusion reaction process.

Key words: prompt physical process diagnostic, D－T fusion, capture $\gamma$-rays, strong pulsed radiation field