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

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

Third harmonic ICRF heating of Deuterium beam ions on ASDEX Upgrade

We report on recent experiments on the ASDEX Upgrade (AUG) tokamak (major radius R ≈1.65 m, minor radius a ≈ 0.5 m) with third harmonic ICRF heating of deuterium beam ions. Prior to this work, the scheme has been developed and applied on the JET tokamak, the largest currently operating tokamak (R ≈ 3 m, a ≈ 1 m), for fusion product studies and for testing alpha particle diagnostics in preparation of ITER [1]. The experiments reported here demonstrate that this scheme can also be used in medium size tokamaks such as AUG despite their reduced fast ion confinement.This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.Postprint (published version

Design and optimization of an advanced time-of-flight neutron spectrometer for deuterium plasmas of the large helical device

A time-of-flight neutron spectrometer based on the Time-Of-Flight Enhanced Diagnostic (TOFED) concept has been designed and is under development for the Large Helical Device (LHD). It will be the first advanced neutron spectrometer to measure the 2.45 MeV D–D neutrons (DDNs) from helical/stellarator plasmas. The main mission of the new TOFED is to study the supra-thermal deuterons generated from the auxiliary heating systems in helical plasmas by measuring the time-of-flight spectra of DDN. It will also measure the triton burnup neutrons (TBNs) from the d+t reactions, unlike the original TOFED in the EAST tokamak. Its capability of diagnosing the TBN ratios is evaluated in this work. This new TOFED is expected to be installed in the basement under the LHD hall and shares the collimator with one channel of the vertical neutron camera to define its line of sight. The distance from its primary scintillators to the equatorial plane of LHD plasmas is about 15.5 m. Based on Monte Carlo simulation by a GEANT4 model, the resolution of the DDN energy spectra is 6.6%. When projected onto the neutron rates that are typically obtained in LHD deuterium plasmas (an order of 1015 n/s with neutral beam injection), we expect to obtain the DDN and TBN counting rates of about 2.5 · 105 counts/s and 250 counts/s, respectively. This will allow us to analyze the DDN time-of-flight spectra on time scales of 0.1 s and diagnose the TBN emission rates in several seconds with one instrument, for the first time in helical/stellarator plasmas

Improvements in physics models of AFSI-ASCOT-based synthetic neutron diagnostics at JET

\u3cp\u3eNew development steps of AFSI-ASCOT based synthetic neutron diagnostics and validation at JET are reported in this contribution. Synthetic neutron diagnostics are important not only in existing tokamaks, where they are used to interpret experimental data, but also in the design of future reactors including DEMO and beyond, where neutron detectors are one of the few diagnostics available. Thus, development and validation of realistic synthetic diagnostics is necessary for increasing confidence in existing models and future diagnostic designs. Recent development in AFSI includes physical corrections such as implementation of plasma rotation and reduction of the fast particle contribution in thermal reactant distribution. The rotation typically changes the beam-thermal reaction rates by 1–5%, while accounting for the fast particle density consistently reduces the neutron deficit (widely known inequality of the measured and calculated neutron rates) by up to 15% depending on the discharge. Further developments include implementation of angular dependence of DD differential fusion cross sections and accounting for finite Larmor radius effect, which is important for high-energy particles such as ICRH. Additionally, the role of data based analysis in synthetic diagnostics development with the help of JETPEAK database is discussed.\u3c/p\u3

Improvements in physics models of AFSI-ASCOT-based synthetic neutron diagnostics at JET

| openaire: EC/H2020/633053/EU//EUROfusionNew development steps of AFSI-ASCOT based synthetic neutron diagnostics and validation at JET are reported in this contribution. Synthetic neutron diagnostics are important not only in existing tokamaks, where they are used to interpret experimental data, but also in the design of future reactors including DEMO and beyond, where neutron detectors are one of the few diagnostics available. Thus, development and validation of realistic synthetic diagnostics is necessary for increasing confidence in existing models and future diagnostic designs. Recent development in AFSI includes physical corrections such as implementation of plasma rotation and reduction of the fast particle contribution in thermal reactant distribution. The rotation typically changes the beam-thermal reaction rates by 1–5%, while accounting for the fast particle density consistently reduces the neutron deficit (widely known inequality of the measured and calculated neutron rates) by up to 15% depending on the discharge. Further developments include implementation of angular dependence of DD differential fusion cross sections and accounting for finite Larmor radius effect, which is important for high-energy particles such as ICRH. Additionally, the role of data based analysis in synthetic diagnostics development with the help of JETPEAK database is discussed.Peer reviewe

Exploring New Frontiers of the Ion-Scale Turbulence Suppression by Fast Ions

Understanding and controlling the turbulent transport developing at the ion-scale, which strongly limits the thermal confinement in tokamaks, is crucial in view of the steady-state ITER operations. As ITER will be mainly heated by the fusion-born alpha particles, the development of ITER-relevant scenarios, together with complex numerical analyses, is crucial in order to study the possible effects of the alpha particles on turbulence regimes to date not explored in detail. Therefore, the present work aims at unveiling further steps towards the complete understanding of the impact of fast ions on the microturbulence, by extending the frontiers of our knowledge towards MeV-range of fast ion energy and turbulence patterns different to the well-established ITG, by means of very demanding gyrokinetic numerical analyses.5th Asia Pacific Conference on Plasma Physic

First measurement in a magnetic confinement fusion experiment of the T + T -> 5He + n intermediate two-body resonant reaction

We report on the first experimental measurements made at a magnetic confinement fusion device of the T + T → α + 2n reaction indicating the presence of the intermediate two-body resonant reaction T + T → ⁵He + n. During the second deuterium-tritium campaign (DTE2) at the Joint European Torus, measurements of fusion plasmas with high tritium concentrations, n_T/(n_T + n_D) ≈ 0.99, heated with T neutral beam injection (NBI), were performed using the neutron time-of-flight (TOF) spectrometer TOFOR. We detect a peak in the neutron emission TOF spectrum consistent with the two-body resonant reaction. The TT neutron emission energy spectrum is modeled using an R-matrix framework where the distributions of the most likely model parameters given our experimental TOF data are determined utilizing a Markov chain Monte Carlo approach. We compare our best estimate of the TT neutron emission energy spectrum with results obtained at inertial confinement fusion experiments at the OMEGA facility and find a spectral shape that is consistent with the energy dependency in the neutron spectrum observed at OMEGA