High-resolution gamma ray spectroscopy measurements of the fast ion energy distribution in JET ⁴He plasmas

Abstract

High-resolution γ -ray measurements were carried out on the Joint European Torus (JET) in an experiment aimed at accelerating 4 He ions in the MeV range by coupling third harmonic radio frequency heating to an injected 4 He beam. For the first time, Doppler broadening of γ -ray peaks from the 12 C(d, pγ ) 13 C and 9 Be(α, nγ ) 12 C reactions was observed and interpreted with dedicated Monte Carlo codes based on the detailed nuclear physics of the processes. Information on the confined 4 He and deuteron energy distribution was inferred, and confined 4 He ions with energies as high as 6 MeV were assessed. A signature of MHD activity in γ -ray traces was also detected. The reported results have a bearing on diagnostics for fast ions in the MeV range in next step fusion devices.

Fast ion energy distribution from third harmonic radio frequency heating measured with a single crystal diamond detector at the Joint European Torus

“…23 This scenario, which is particularly effective at accelerating deuterium ions to the MeV range as previously demonstrated, 5,24,25 is of relevance for fast ion physics studies in a deuterium plasma. Here, we show, in particular, that SDD data can be used to extract parameters of the highly non-Maxwellian fast ion energy distribution generated in the experiment by detailed modeling of the instrument response function and the emission spectrum of the fusion neutrons born in the plasma.…”

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

“…Further work needs to be addressed to the design of neutron attenuators that can reduce the overall detector load at an acceptable level to enable measurements. A promising candidate is 6 LiH, as both 6 Li and H, being light nuclei, are good neutron moderators. Besides, 6 Li is also a neutron absorber, with a capture cross section of 3·10 3 b for thermalized neutrons.…”

“…A promising candidate is 6 LiH, as both 6 Li and H, being light nuclei, are good neutron moderators. Besides, 6 Li is also a neutron absorber, with a capture cross section of 3·10 3 b for thermalized neutrons. Clearly, a deeper understanding of the LaBr 3 response to 14 MeV neutrons is a preliminary requirement for the attenuator design.…”

“…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]. A review on neutron and gamma-ray measurements in tokamak plasmas for fast ion studies has been recently published in [3].…”

Data pre-processing using an FPGA by binning gamma ray energies and forwarding consolidated spectra data

“…Several gamma-ray diagnostics were installed at JET, the only present machine capable to confine fast ions (MeV range) produced by external sources (ICRF and NBI auxiliary heating sources) [6]. One of the diagnostics is the JET 2D gamma-ray profile monitor, composed by 19 lines-of-sight to view the plasma through CsI(Tl) detectors.…”