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

Real-time feedback control of the impurity emission front in tokamak divertor plasmas

Long-pulse operation of a self-sustained fusion reactor using toroidal magnetic containment requires control over the content of alpha particles produced by D-T fusion reactions. On the one hand, MeV-class alpha particles must stay confined to heat the plasma. On the other hand, decelerated helium ash must be expelled before diluting the fusion fuel. Our kinetic-magnetohydrodynamic hybrid simulations of a large tokamak plasma confirm the existence of a parameter window where such energy-selective confinement can be accomplished by exploiting internal relaxation events known as `sawtooth crashes'. The physical picture -- consisting of a synergy between magnetic geometry, optimal crash duration and rapid particle motion -- is completed by clarifying the role played by magnetic drifts. Besides causing asymmetry between co- and counter-going particle populations, magnetic drifts determine the size of the confinement window by dictating where and how much `reconnection' occurs in particle orbit topology.Comment: Main article: 9 pages, 7 figures. Supplementary material: 9 pages, 15 figures. References: 3 pages. 2021 IAEA TCM EPPI Conferenc

Numerical study of helium ash and fast particle dynamics in a sawtoothing tokamak plasma

A relaxation even known as “sawtooth crash” is simulated in a large tokamak plasma with monotonic safety factor close to unity. The domain and the time scale of the event are set to match observations. The simulation follows passive alpha particles with energies 35 keV-3.5 MeV, whose initial density peak is localized in the relaxing domain. While the 35 keV profile flattens, a synergy of multiple physical factors allows the 3.5 MeV profile to remain peaked, facilitating the use of benign sawtooth activity in a fusion reactor to expel helium ash while preserving good confinement of fast alphas.17th Technical Meeting on Energetic Particles and Theory of Plasma Instabilities in Magnetic Confinement Fusion (EPPI