Spectral Broadening of Characteristic $\gamma$-Ray Emission Peaks from ${}^{12}\mathbf{C}({}^3\mathrm{He},p\gamma ){}^{14}\mathbf{N}$ Reactions in Fusion Plasmas

The spectral broadening of characteristic $\gamma$-ray emission peaks from the reaction ${}^{12}\mathrm{C}({}^3\mathrm{He},p\gamma ){}^{14}\mathrm{N}$ was measured in $D({}^3\mathrm{He})$ plasmas of the JET tokamak with ion cyclotron resonance heating tuned to the fundamental harmonic of ${}^3\mathrm{He}$. Intensities and detailed spectral shapes of $\gamma$-ray emission peaks were successfully reproduced using a physics model combining the kinetics of the reacting ions with a detailed description of the nuclear reaction differential cross sections for populating the $L1\mathrm{\text{−}}L8$ ${}^{14}\mathrm{N}$ excitation levels yielding the observed $\gamma$-ray emission. The results provide a paradigm, which leverages knowledge from areas of physics outside traditional plasma physics, for the development of nuclear radiation based methods for understanding and controlling fusion burning plasmas.

Figure 1

Top: experimental and fitted (solid line) peak shapes for the $E_{\gamma 1}$ (left) and $E_{\gamma 2}$ (right) $\gamma$-ray emission peaks. The unshifted $E_{\gamma 1}=2313\mathrm{keV}$ and $E_{\gamma 2}=1635\mathrm{keV}$ values are marked with vertical dashed lines. Bottom: Normalized simulated $E_{\gamma 1}$ (left) and $E_{\gamma 2}$ (right) peak shape for monoenergetic ${}^3\mathrm{He}$ ions with Gaussian pitch angle distribution centered at ${\theta }_p=90°$ and with $\mathrm{FWHM}=10°$.

Figure 2

Peak ratio (top) and width (bottom) of the simulated $E_{\gamma 1}$ and $E_{\gamma 2}$ $\gamma$-ray emission peaks for monoenergetic ${}^3\mathrm{He}$ ions of different energies (left) and Maxwellian ${}^3\mathrm{He}$ ions of different temperatures (right). The horizontal bands are the experimental values.

Figure 3

Simulated $E_{\gamma 1}$ (left) and $E_{\gamma 2}$ (right) $\gamma$-ray emission peak shapes normalized to unit height for ${}^3\mathrm{He}$ ions described by a Stix distribution with several asymptotic tail temperatures $T_{3\mathrm{He}}$. The unshifted $E_{\gamma 1}=2313\mathrm{keV}$ and $E_{\gamma 1}=1635\mathrm{keV}$ values are marked with vertical dashed lines.