Synergetic RF and NB heating effects in JET DT plasmas studied with neutron emission spectroscopy

Abstract

The MPR neutron emission spectroscopy diagnostic has been used to study plasmas produced at JET during the main deuterium-tritium experimental campaign (DTE1). The plasmas were subjected to Radio Frequency (RF) and Neutral Beam (NB) heating in different combinations during periods of individual discharges. Similar discharges with different heating combinations were also compared. This paper deals, in particular, with the synergetic coupling of the ion cyclotron resonance frequency of the RF power to the fast ions from the NB injection. The key observable in this study is the high-energy tail that can be detected in the neutron spectrum as evidence of the RF acceleration of fuel ions. The synergy effect was observed both in deuterium and tritium heated discharges, with RF coupled to the second harmonic resonance of the heating species. It was seen that the NB power is enhanced and that the effect demonstrated a correlation with the total injected RF and NB power.This coupling effect was quantified in terms of the measured spectral amplitude and the derived temperature of the supra-thermal high-energy tail of the fuel ion populations. Bulk heating effects were also studied in discharges with favourable conditions for NES measurements.

Fuel ion ratio determination in NBI heated deuterium tritium fusion plasmas at JET using neutron emission spectrometry

“…This ensures that no other neutron emission components than thermonuclear and beam-thermal will contribute to the MPR data, besides a low energy component from scattered neutrons (see figure 3). For example if ICRF heating was used it could give rise to a high-energy suprathermal component in the MPR data, which would complicate the analysis [11]. Discharges with strong MHD activity were also avoided, since this is not accurately modelled by TRANSP/NUBEAM.…”

Evaluation of neutron spectrometer techniques for ITER using synthetic data

“…It should be noted that in the 3 He free ICRH plasmas, the GDOS technique has a better time resolution than the MPR technique. This can be understood from the restricted range of detected proton recoil energies of the present implementation of the MPRu hodoscope.…”

“…The studied ICRH scenario has the frequency tuned to the second harmonic of the tritium ions (which coincides with the first harmonic of 3 He) at 53 MHz, with a fuel mix of n d =n t ≈n e /2 and a seeded 3 He population of 0-3% relative concentration. Without 3 He, the ICRH couples to the tritium to produce pronounced tails of high energy ions and, consequently, a signature of high-energy neutrons originating from ICRH ions reacting with the thermal ion population is present in the neutron spectrum, as illustrated in Figure 11a.…”

“…Without 3 He, the ICRH couples to the tritium to produce pronounced tails of high energy ions and, consequently, a signature of high-energy neutrons originating from ICRH ions reacting with the thermal ion population is present in the neutron spectrum, as illustrated in Figure 11a. Introducing a small fraction of 3 He has the effect to reduce this high energy component as shown in Figure 11b, where 3% of the ions in the plasma are 3 He. This can be understood by the more efficient coupling of the ICRH to the first harmonic of 3 He than to the second harmonic of tritium.…”

Reaction analysis of neutron emission from D and DT plasmas with/without3He

“…Results of the latter types were presented in [4][5][6] for a neutral particle analyser (NPA) and in [7][8][9] for γ -ray measurements, respectively. Regarding fast ion physics from neutron emission spectra, the studies included neutral beam (NB)-injected ions [10][11][12][13] and ion response to various types of RF power injection [10-12, 14, 15] as well as the information on fusion products of t and α ions through their fusion burn-up and KO scattering. The behaviour of fusion t and α in the plasma was studied through the emission of triton burn-up neutrons (TBN) and alpha knock-on neutrons (AKN) in comparison with emission of neutrons directly from the unperturbed thermal equilibrium state referred to as DDN and DTN for d + d → n + 3 He and d + t → n + α reactions [16,17].…”