Diagnosis of physical parameters of fast particles in high power fusion plasmas with high resolution neutron and gamma-ray spectroscopy

Abstract

High resolution neutron emission spectroscopy (NES) and gamma-ray spectroscopy (GRS) measurements of fast ions in high power fusion plasmas are reviewed. NES is a well established diagnostics of the velocity distribution of fast fuel ions and was recently used to investigate the interaction of energetic ions with MHD instabilities. High energy resolution GRS on fusion plasmas is a more recent application and was shown to provide information on the distribution function of fast minority ions accelerated by ICRH, such as 4 He and 3 He. Starting from measurements on today's high power D plasmas, fast ion measurements with NES and GRS in a DT burning plasma of next step tokamaks, such as ITER, are discussed. The enhanced neutron and gamma-ray fluxes expected on ITER will allow for time-resolved measurements of the fast fuel and minority ion dynamics in the ms time scale. The intensity of the alpha knock-on component in the 14 MeV neutron spectrum and of the 4.44 and 3.21 MeV gamma-ray peaks from the 9 Be(α,nγ ) 12 C reaction is studied as a diagnostics for the α particle slowing down distribution in a DT plasma. The results show that the two techniques are sensitive to different regions of the α particle phase space and thus provide complementary information.

Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating

“…Since three-ion scenarios allow minimizing the number of resonant particles down to ‰ levels, rather high-energy ions can be generated. An independent confirmation of accelerating 3 He ions to high energies is provided by gamma-ray emission spectroscopy on JET 21,22 . Figure 3a displays the gamma-ray advantage of increasing the absorbed RF power per ion.…”

“…Low-temperature plasmas offer an even larger variety of scenarios since light ion species are not necessarily fully ionized. Ion species T 9 Be, 7 Li, 22 Ne D, 4 He, 12 31 . Their study resembles closely the ( 3 He)-H minority heating in tokamaks.…”

Response of LaBr3(Ce) scintillators to 2.5 MeV fusion neutrons

“…γ-ray spectroscopy is one of the few diagnostic techniques proposed for this scope [2]. Gamma-ray emission results from interactions between the energetic ions and impurities that are naturally found in the plasma [2][3][4]. Recently, γ-ray measurements at low counting rates and high energy resolution in present tokamak devices [5,6] have shown that added parameters of the fast ion energy distribution can be obtained by combining information on the intensity and shape of characteristic peaks of γ-ray reactions occurring in the plasma [7][8][9][10].…”

“…Recently, γ-ray measurements at low counting rates and high energy resolution in present tokamak devices [5,6] have shown that added parameters of the fast ion energy distribution can be obtained by combining information on the intensity and shape of characteristic peaks of γ-ray reactions occurring in the plasma [7][8][9][10]. A review on neutron and gamma-ray measurements in tokamak plasmas for fast ion studies has been recently published in [3]. Unlike present devices, γ-ray measurements in next step tokamaks, such as ITER, will have to be performed at MHz counting rates, still with high energy resolution, and under significant irradiation from 2.5 and 14 MeV neutrons produced by the main fusion reactions, d+d → n+ 3 He in deuterium plasmas and d+t → n+α in deuterium-tritium.…”

“…A review on neutron and gamma-ray measurements in tokamak plasmas for fast ion studies has been recently published in [3]. Unlike present devices, γ-ray measurements in next step tokamaks, such as ITER, will have to be performed at MHz counting rates, still with high energy resolution, and under significant irradiation from 2.5 and 14 MeV neutrons produced by the main fusion reactions, d+d → n+ 3 He in deuterium plasmas and d+t → n+α in deuterium-tritium. Dedicated solutions therefore need to be developed.…”