Dependence of the turbulent particle flux on hydrogen isotopes induced by collisionality

Angioni, C.; Fable, E.; Manas, P.; Mantica, P.; Schneider, P. A.

doi:10.1063/1.5045545

Cited by 16 publications

(21 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Density peaking due to core sources and transport has been the subject of many studies and the relative contribution remains uncertain, requiring further investigation and more experiments [27], [28], [29] . Modelling has shown that there is a weak effect of isotope mass on density peaking but this was in plasmas without NBI heating, so there was no central source of particles [30]. The effect of isotope mass on density peaking is subject to future work and should be considered for JET DT plasmas.…”

Section: Isotope Exchangementioning

confidence: 99%

Mixed hydrogen-deuterium plasmas on JET ILW

et al. 2020

View full text Add to dashboard Cite

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.

show abstract

Section: Isotope Exchangementioning

confidence: 99%

Mixed hydrogen-deuterium plasmas on JET ILW

et al. 2020

View full text Add to dashboard Cite

show abstract

“…In all cases, 𝑇 𝑒 is similar due the stiffness of the ETG scale transport. In heavier isotopes, the transfer of energy from ions to electrons is less efficient, allowing to a larger 𝑇 𝑖 /𝑇 𝑒 to be sustained, known to suppress the ITG instability (the collisional detrapping of trapped electrons (∼ ν 𝑖𝑒 /ω) is also more effective at larger mass, reducing trapped electron mode drive [49,53,54]). The resulting enhancement in fusion performance in DT is 37%: At 9.5s, the DD case has a DT equivalent fusion power [55] of 10.8 MW (computed using the DDeq ratios defined in Fig.…”

Section: Extrapolation To Dtmentioning

confidence: 99%

“…The isotope extrapolation with a fixed pedestal (figures 9 and 10) shows a positive effect on confinement with heavier isotope, due to the inverse ion mass scaling of the ionelectron energy exchange [52] and its interaction with the turbulent transport: In all cases, T e is similar due the stiffness of the ETG scale transport. In heavier isotopes, the transfer of energy from ions to electrons is less efficient, allowing to a larger T i /T e to be sustained, known to suppress the ITG instability (the collisional detrapping of trapped electrons (∼ ν ie /ω) is also more effective at larger mass, reducing trapped electron mode drive [49,53,54]). The resulting enhancement in fusion performance in DT is 37%: At 9.5 s, the DD case has a DT equivalent fusion power [55] of 10.8 MW (computed using the DD eq ratios defined in figure 10, at 9.5 s), while the DT case has a predicted fusion power of 14.8 MW (before limiting W accumulation in either case), with ~50% thermonuclear reactions and ~50% beam-target.…”

Section: Extrapolation To Dtmentioning

confidence: 99%

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

Casson¹,

Patten²,

Bourdelle³

et al. 2020

Nucl. Fusion

Self Cite

View full text Add to dashboard Cite

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.

show abstract

“…This effects adds to the linear stabilisation of TEM by collisions which scales as , where γ 0 is the collisionless growth and is therefore stronger at high isotope mass (Angioni et al . 2018). Nonlinear GENE (Jenko et al .…”

Section: Effects Depending On Working Gas Isotopementioning

confidence: 99%

Isotope dependence of energy, momentum and particle confinement in tokamaks

Weisen

Maggi²,

Oberparleiter³

et al. 2020

J. Plasma Phys.

Self Cite

View full text Add to dashboard Cite

The isotope dependence of plasma transport will have a significant impact on the performance of future D-T experiments in JET and ITER and eventually on the fusion gain and economics of future reactors. In preparation for future D-T operation on JET, dedicated experiments and comprehensive transport analyses were performed in H, D and H-D mixed plasmas. The analysis of the data has demonstrated an unexpectedly strong and favourable dependence of the global confinement of energy, momentum and particles in ELMy H-mode plasmas on the atomic mass of the main ion species, the energy confinement time scaling as ${\tau _E}\sim {A^{0.5}}$ (Maggi et al., Plasma Phys. Control. Fusion, vol. 60, 2018, 014045; JET Team, Nucl. Fusion, vol. 39, 1999, pp. 1227–1244), i.e. opposite to the expectations based only on local gyro-Bohm (GB) scaling, ${\tau _E}\sim {A^{ - 0.5}}$ , and stronger than in the commonly used H-mode scaling for the energy confinement (Saibene et al., Nucl. Fusion, vol. 39, 1999, 1133; ITER Physics Basis, Nucl. Fusion, vol. 39, 1999, 2175). The scaling of momentum transport and particle confinement with isotope mass is very similar to that of energy transport. Nonlinear local GENE gyrokinetic analysis shows that the observed anti-GB heat flux is accounted for if collisions, E × B shear and plasma dilution with low-Z impurities (9Be) are included in the analysis (E and B are, respectively the electric and magnetic fields). For L-mode plasmas a weaker positive isotope scaling ${\tau _E}\sim {A^{0.14}}$ has been found in JET (Maggi et al., Plasma Phys. Control. Fusion, vol. 60, 2018, 014045), similar to ITER97-L scaling (Kaye et al., Nucl. Fusion, vol. 37, 1997, 1303). Flux-driven quasi-linear gyrofluid calculations using JETTO-TGLF in L-mode show that local GB scaling is not followed when stiff transport (as is generally the case for ion temperature gradient modes) is combined with an imposed boundary condition taken from the experiment, in this case predicting no isotope dependence. A dimensionless identity plasma pair in hydrogen and deuterium L-mode plasmas has demonstrated scale invariance, confirming that core transport physics is governed, as expected, by the 4 dimensionless parameters ρ*, ν*, β, q (normalised ion Larmor radius, collisionality, plasma pressure and safety factor) consistently with global quasi-linear gyrokinetic TGLF calculations (Maggi et al., Nucl. Fusion, vol. 59, 2019, 076028). We compare findings in JET with those in different devices and discuss the possible reasons for the different isotope scalings reported from different devices. The diversity of observations suggests that the differences may result not only from differences affecting the core, e.g. heating schemes, but are to a large part due to differences in device-specific edge and wall conditions, pointing to the importance of better understanding and controlling pedestal and edge processes.

show abstract

Dependence of the turbulent particle flux on hydrogen isotopes induced by collisionality

Cited by 16 publications

References 30 publications

Mixed hydrogen-deuterium plasmas on JET ILW

Mixed hydrogen-deuterium plasmas on JET ILW

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

Isotope dependence of energy, momentum and particle confinement in tokamaks

Contact Info

Product

Resources

About