Fast ion synergistic effects in JET high performance pulses

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The evolution of the JET high performance hybrid scenario, including central accumulation of the tungsten (W) impurity, is reproduced with predictive multi-channel integrated modelling over multiple confinement times using first-principle based core transport models. 8 transport channels (𝑇 𝑖 , 𝑇 𝑒 , 𝑗, 𝑛 𝐷 , 𝑛 𝐵𝑒 , 𝑛 𝑁𝑖 , 𝑛 𝑊 , 𝜔) are modelled predictively, with self-consistent sources, radiation and magnetic equilibrium, yielding a system with multiple non-linearities: This system can reproduce the observed radiative temperature collapse after several confinement times. W is transported inward by neoclassical convection driven by the main ion density gradients and enhanced by poloidal asymmetries due to centrifugal acceleration. The slow evolution of the bulk density profile sets the timescale for W accumulation. Modelling this phenomenon requires a turbulent transport model capable of accurately predicting particle and momentum transport (QuaLiKiz) and a neoclassical transport model including the effects of poloidal asymmetries (NEO) coupled to an integrated plasma simulator (JINTRAC). The modelling capability is applied to optimise the available actuators to prevent W accumulation, and to extrapolate in power and pulse length. Central NBI heating is preferred for high performance, but gives central deposition of particles and torque which increase the risk of W accumulation by increasing density peaking and poloidal asymmetry. The primary mechanism for ICRH to control W in JET is via its impact through turbulence in reducing main ion density peaking (which drives inward neoclassical convection), increased temperature screening and turbulent W diffusion. The anisotropy from ICRH also reduces poloidal asymmetry, but this effect is negligible in high rotation JET discharges. High power ICRH near the axis can sensitively mitigate against W accumulation, and dominant ion heating (e.g. He-3 minority) is predicted to provide more resilience to W accumulation than dominant electron heating (e.g. H minority) in the JET hybrid scenario. Extrapolation to DT plasmas finds 17.5MW of fusion power and improved confinement compared to DD, due to reduced ion-electron energy exchange, and increased Ti/Te stabilisation of ITG instabilities. The turbulence reduction in DT increases density peaking and accelerates the arrival of W on axis; this may be mitigated by reducing the penetration of the beam particle source with an increased pedestal density.

Section: Validation Of Predictive Capability Of Scenario Evolutionmentioning

confidence: 73%

Section: Validation Of Predictive Capability Of Scenario Evolutionmentioning

confidence: 73%

Predictive multi-channel flux-driven modelling to optimise ICRH tungsten control and fusion performance in JET

Casson¹,

Patten²,

Bourdelle³

et al. 2020

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“…The NBI + RF synergistic effects, important for example in discharges with 2nd harmonic RF acceleration of fast NBI ions, were modelled with the quasi-linear RF kick operator [43,44]. The operator communicates TORIC computed RF electric field components and perpendicular wave vectors for each toroidal mode to NUBEAM [45].…”

Section: Transp Databasementioning

confidence: 99%

Overview of interpretive modelling of fusion performance in JET DTE2 discharges with TRANSP

Štancar,

Kirov,

Auriemma

et al. 2023

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In the paper we present an overview of interpretive modelling of a database of JET-ILW 2021 D-T discharges using the TRANSP code. The main aim is to assess our capability of computationally reproducing the fusion performance of various D-T plasma scenarios using different external heating and D-T mixtures, and to understand the performance driving mechanisms. We find that interpretive simulations confirm a general power-law relationship between increasing external heating power and fusion output, which is supported by absolutely calibrated neutron yield measurements. A comparison of measured and computed D-T neutron rates shows that the calculations’ discrepancy depends on the absolute neutron yield. The calculations are found to agree well with measurements for higher performing discharges with external heating power above ∼20 M W , while low-neutron shots display an average discrepancy of around +40% compared to measured neutron yields. A similar trend is found for the ratio between thermal and beam-target fusion, where larger discrepancies are seen in shots with dominant beam-driven performance. We compare the observations to studies of JET-ILW D discharges, to find that on average the fusion performance is well modelled over a range of heating power, although an increased unsystematic deviation for lower-performing shots is observed. The ratio between thermal and beam-induced D-T fusion is found to be increasing weakly with growing external heating power, with a maximum value of ≳ 1 achieved in a baseline scenario experiment. An evaluation of the fusion power computational uncertainty shows a strong dependence on the plasma scenario type and fusion drive characteristics, varying between ±25% and 35%. D-T fusion alpha simulations show that the ratio between volume-integrated electron and ion heating from alphas is ≲ 10 for the majority of analysed discharges. Alphas are computed to contribute between ∼15% and 40% to the total electron heating in the core of highest performing D-T discharges. An alternative workflow to TRANSP was employed to model JET D-T plasmas with the highest fusion yield and dominant non-thermal fusion component because of the use of fundamental radio-frequency heating of a large minority in the scenario, which is calculated to have provided ∼10% to the total fusion power.

“…It was assumed that the plasma only contains a single impurity, which is nickel. The Ni concentration was imposed to fit the experimental averaged value of Z eff = 1.4-1.5, as measured by visible spectroscopy between 48.5-49 s and as used in the TRANSP simulations published in [13]. For the prescribed magnetic field (2.88 T), fixing the frequency of the ICRF antennas at 42.5 MHz ensures the reigning wave heating mechanisms are core fundamental cyclotron heating of the H minority and second harmonic heating of the D majority and D beam population.…”

Section: Predictive Simulations For Jet Shot 92436 (Code Validation)mentioning

confidence: 99%

“…Some recent work on extrapolated DT plasma scenarios and using TRANSP [11] highlighted the synergistic effects observed when simultaneously exploiting ICRH and NBI heating. This description hinges on temperatures being prescribed-making use of profiles provided by another code, such as JINTRAC-rather than predicted [12][13][14][15]. Confidence is gained in making predictions for future experiments by adopting a wide range of tools, each having advantages and drawbacks.…”

Section: Introductionmentioning

confidence: 99%

European transport simulator modeling of JET-ILW baseline plasmas: predictive code validation and DTE2 predictions

Huynh¹,

Lerche²,

Eester³

et al. 2021

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The European transport simulator is a fusion machine simulator useful for making predictions of high-performance fusion plasmas, in particular for DT reactors. Recent developments introducing self-consistent simulations of combined RF + NBI heating schemes in which majority, minority and beam ions are simultaneously heated is documented. The predictive simulations are first validated by comparison with the experimental data on a DD JET baseline plasma. In order to prepare the next JET DTE2 experimental campaign, extrapolations of fusion performance on DT plasma from DD plasma are made with a particular focus on ion cyclotron resonance heating (ICRH) computation. Traditional ion cyclotron range of frequency heating models do not permit the study of Coulomb collisional interaction of various ion species simultaneously including neutral beam injection ions, and generally forces one to consider only minority populations. Accounting for multi-population interaction is made possible here by solving coupled sets of Fokker–Planck equations for all ion species adopting the non-linear collision operator for arbitrary distribution functions, accounting for effects, such as the self-collisions of majority (or large minority) populations. To answer the question whether H minority scheme or 3He minority ICRH scheme is better for boosting the DT fusion performance, minority concentration scans are produced.