The ‘neutron deficit’ in the JET tokamak

Weisen, H.; Kim, Hyun Tae; Strachan, J.; Scott, S.D.; Baranov, Y.; Buchanan, J.; Fitzgerald, Michael L.; Keeling, D.; King, D.; Giacomelli, L.; Koskela, T.; Weisen, M. J.; Giroud, C.; Maslov, M.; Core, W.G.F.; Zastrow, K.‐D.; Syme, Don; Popovichev, S.; Conroy, S.; Lengar, Igor; Snoj, Luka; Batistoni, P.; Santala, M.; Contributors, Jet

doi:10.1088/1741-4326/aa6dcc

Cited by 29 publications

(57 citation statements)

References 24 publications

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“…These results provide further evidence that the T i profile from JETTO + QuaLiKiz is underpredicted, as the neutron rates using the simulated profiles consistently fall under the measured neutron rate, though still within the ± 2σ uncertainty ranges for pure Ni. These results are consistent with previous works on this matter [29] and accentuate the importance of reliable impurity composition and profile estimations for any extrapolation exercises, due to the impact of fuel dilution on the total fusion rate.…”

Section: Validation Of the Nominal Settingssupporting

confidence: 92%

Application of Gaussian process regression to plasma turbulent transport model validation via integrated modelling

Citrin

Auriemma

et al. 2019

Nucl. Fusion

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This paper outlines an approach towards improved rigour in tokamak turbulence transport model validation within integrated modelling. Gaussian process regression (GPR) techniques were applied for profile fitting during the preparation of integrated modelling simulations allowing for rigourous sensitivity tests of prescribed initial and boundary conditions as both fit and derivative uncertainties are provided. This was demonstrated by a JETTO integrated modelling simulation of the JET ITER-like-wall H-mode baseline discharge #92436 with the QuaLiKiz quasilinear turbulent transport model, which is the subject of extrapolation towards a deuterium-tritium plasma. The simulation simultaneously evaluates the time evolution of heat, particle, and momentum fluxes over ∼ 10 confinement times, with a simulation boundary condition at ρ tor = 0.85. Routine inclusion of momentum transport prediction in multi-channel fluxdriven transport modelling is not standard and is facilitated here by recent developments within the Qua-LiKiz model. Excellent agreement was achieved between the fitted and simulated profiles for n e , T e , T i , and Ω tor within 2σ, but the simulation underpredicts the mid-radius T i and overpredicts the core n e and T e profiles for this discharge. Despite this, it was shown that this approach is capable of deriving reasonable inputs, including derivative quantities, to tokamak models from experimental data. Furthermore, multiple figures-of-merit were defined to quantitatively assess the agreement of integrated modelling predictions to experimental data within the GPR profile fitting framework.

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Section: Validation Of the Nominal Settingssupporting

confidence: 92%

Application of Gaussian process regression to plasma turbulent transport model validation via integrated modelling

Citrin

Auriemma

et al. 2019

Nucl. Fusion

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“…Simulations were repeated using the EFIT equilibrium to quantify errors due to profile fitting, this only changed the modelled neutron rate by ∼ 3%. These neutron discrepancies are small compared to those reported in [19] but it should be noted that the diagnostics used to produce the total neutron rate on JET have recently been recalibrated resulting in an increase in the measured neutron rate and, typically, a decrease in the discrepancy with respect to simulations.…”

Section: Isotope Ratio Measurementsmentioning

confidence: 56%

Mixed hydrogen-deuterium plasmas on JET ILW

et al. 2020

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A study of mixed hydrogen-deuterium H-mode plasmas has been carried out in JET-ILW to strengthen the physics basis for extrapolations to JET D-T operation and to support the development of strategies for isotope ratio control in future experiments. Variations of input power, gas fuelling and isotopic mixture were performed in H-mode plasmas of the same magnetic field, plasma current and divertor configuration. The analysis of the energy confinement as a function of isotope mixture reveals that the biggest change is seen in plasmas with small fractions of H or D, in particular when including pure isotope plasmas. To interpret the results correctly, the dependence of the power threshold for access to type-I ELMing H-modes on the isotope mixture must be taken into account. For plasmas with effective mass between 1.2 and 1.8 the plasma thermal stored energy () scales as , which is weaker than that in the ITER physics basis, IPB98 scaling. At fixed stored energy, deuterium-rich plasmas feature higher density pedestals, while the temperature at the pedestal top is lower, showing that at the same gas fuelling rate and power level, the pedestal pressure remains constant with an exchange of density and temperature as the isotope ratio is varied. Isotope control was successfully tested in JET-ILW by changing the isotope ratio throughout a discharge, switching from D to H gas puffing. Several energy confinement times (300 ms) are needed to fully change the isotope ratio during a discharge.

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“…The answer is given in table 2. Note that although this calculation is rough, it does not rely on the absolute neutron calibration and should be insensitive to the "neutron deficit" -mismatch between predicted by TRANSP and measured neutrons sometimes observed in JET plasma simulations [15] Pulse number 91232 91227 nD/(nD+nH) edge -measured 0.14 0.67 nH/(nD+nH) edge -measured 0.86 0.33 nD/(nD+nH) core -derived 0.157 0.676 nH/(nD+nH) core -derived 0.843 0.324 Table 2: measured and calculated edge and core D/H isotope concentrations.…”

Section: Figure 2 Illustration Of Possible H/d Isotope Profiles Withmentioning

confidence: 99%

Observation of enhanced ion particle transport in mixed H/D isotope plasmas on JET

et al. 2018

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Particle transport in tokamak plasmas was intensively studied in the past, particularly in relation to density peaking and presence of anomalous inward particle convection in Land H-mode. While in the L-mode case the presence of the anomalous inward pinch has previously been unambiguously demonstrated, particle transport in H-mode was unclear. The main difficulty of such studies is that particle diffusion and convection could not be measured independently in steady-state conditions in the presence of a core particle flux. Therefore, it is usually not possible to separate the transport effect-inward convection, from the source effect-slow diffusion of particles introduced to the plasma core by NBI heating. In this work we describe experiments done on JET with mixtures of two hydrogenic isotopes: H and D. It is demonstrated that in the case of several ion species, convection and diffusion can be separated in a steady plasma without implementation of perturbative techniques such as gas puff modulation. Previous H-mode density peaking studies suggested that for this relatively high electron collisionality plasma scenario, the observed density gradient is mostly driven by particle source and low particle diffusivity D<0.5* χeff. Transport coefficients derived from observation of the isotope profiles in the new experiments far exceed that value-ion particle diffusion found to be as high as D≥2*χeff, combined with a strong inward convection. Apparent disagreement with previous findings was explained by significantly faster transport of ion components with respect to the electrons, which could not be observed in a single main ion specie plasma. This conclusion is confirmed by quasilinear gyrokinetic simulations.

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The ‘neutron deficit’ in the JET tokamak

Cited by 29 publications

References 24 publications

Application of Gaussian process regression to plasma turbulent transport model validation via integrated modelling

Application of Gaussian process regression to plasma turbulent transport model validation via integrated modelling

Mixed hydrogen-deuterium plasmas on JET ILW

Observation of enhanced ion particle transport in mixed H/D isotope plasmas on JET

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