A diamond-detector-based system for spectrometry of fast atoms on the JET tokamak

Abstract

To study the evolution of the distribution function of fast ions with an ultimately high time resolution during both injection of neutrals and ion cyclotron plasma heating on the JET tokamak, we have developed a system for spectrometry of fast charge-exchange atoms, which consists of a spectrometric natural-diamond detector and a digital spectrometric channel. The main elements of the spectrometric system—the diamond detector, a noise-immune charge-sensitive preamplifier, and a fast analog-to-digital converter (ADC)—have been manufactured explicitly for use in spectrometry of fast charge-exchange atoms on the JET tokamak at high counting rates. The diamond detector that ensures the spectrometry of hydrogen atoms in the energy range 20–5000 keV is installed in the equatorial plane at an 18-m distance from the plasma axis at the end of the vacuum channel created for X-ray spectroscopy. A fast 14-bit ADC with 100-MHz sampling frequency and a 2-GB memory digitizes the preamplifier output signal. The developed digital spectrometric system can operate at a counting rate of up to ∼10⁷ counts/s. Laboratory tests of the developed spectrometric system have shown that its energy resolution is no worse than the resolution of a similar analog system. In the experiments on the JET, the diamond digital spectrometric system ensures recording of the energy distributions of fast charge-exchange atoms with energies >40 keV.