<iopmath latex="$\gamma$">γ</iopmath>-ray diagnostics of energetic ions in JET

This paper reports recent progress in the field of <iopmath latex="$\gamma$">γ</iopmath>-ray diagnosis of fast ions in the JET tokamak. The <iopmath latex="$\gamma$">γ</iopmath>-rays, born in nuclear reactions between fast ions and main plasma impurities and/or plasma fuel ions, are analysed with a new modelling tool (the GAMMOD code) that has been developed for a quantitative analysis of the measured <iopmath latex="$\gamma$">γ</iopmath>-ray energy spectra. The analysis of the <iopmath latex="$\gamma$">γ</iopmath>-ray energy spectra identifies the different fast ions giving rise to the <iopmath latex="$\gamma$">γ</iopmath>-ray emission and assesses the effective tail temperatures and relative concentrations of these fast ions. This assessment is possible, since the excitation functions for the different nuclear reactions are well established and exhibit a threshold or/and a resonant nature. The capabilities of the <iopmath latex="$\gamma$">γ</iopmath>-ray spectral analysis are illustrated with the examples from the recent <iopmath latex="$\gamma$">γ</iopmath>-ray diagnostic measurements of ⁴He, ³He, deuterium and hydrogen ions accelerated by ion-cyclotron resonance frequency heating in JET. Simultaneous measurements of several fast ion species, including highly energetic <iopmath latex="$\alpha$">α</iopmath>-particles, are demonstrated. In addition to the <iopmath latex="$\gamma$">γ</iopmath>-spectroscopy, tomographic reconstructions of the radial profile of the <iopmath latex="$\gamma$">γ</iopmath>-ray emission are performed using the JET neutron profile monitor, thus providing direct measurements of the radial profiles of fast ions in JET.