Effects of deep fueling on the performance of CFETR hybrid scenario

The BOUT++ six-field turbulence code is used to simulate the ITER 11.5 MA hybrid scenario and a brief comparison is made among ITER baseline, hybrid and steady-state operation (SSO) scenarios. Peeling–ballooning instabilities with different toroidal mode numbers dominate in different scenarios and consequently yield different types of ELMs. The energy loss fractions (ΔW ped/W ped) caused by unmitigated ELMs in the baseline and hybrid scenarios are large (∼2%) while the one in the SSO scenario is dramatically smaller (<1%), which are consistent with the features of type-I ELMs and grassy ELMs respectively. The intra ELM divertor heat flux width in the three scenarios given by the simulations is larger than the estimations for inter-ELM phase based on Goldston’s heuristic drift model. The toroidal gap edge melting limit of tungsten monoblocks of divertor targets imposes constraints on ELM energy loss, giving that the ELM energy loss fraction should be smaller than 0.4%, 1.0%, and 1.2% for ITER baseline, hybrid and SSO scenarios, correspondingly. The simulation shows that only the SSO scenario with grassy ELMs may satisfy the constraint.

Results are presented from the JET Trace Tritium Experimental (TTE) campaign using minority tritium (T) plasmas (nT/nD < 3%). Thermal tritium particle transport coefficients (DT, vT) are found to exceed neo-classical values in all regimes, except in ELMy H-modes at high densities and in the region of internal transport barriers (ITBs) in reversed shear plasmas. In ELMy H-mode dimensionless parameter scans, at q95 ∼ 2.8 and triangularity δ = 0.2, the T particle transport scales in a gyro-Bohm manner in the inner plasma (r/a < 0.4), whilst the outer plasma particle transport scaling is more Bohm-like. Dimensionless parameter scans show contrasting behaviour for the trace particle confinement (increases with collisionality, ν* and β) and bulk energy confinement (decreases with ν* and is independent of β). In an extended ELMy H-mode data set, with ρ*, ν*, β and q varied but with neo-classical tearing modes (NTMs) either absent or limited to weak, benign core modes (4/3 or above), the multiparameter fit to the normalized diffusion coefficient in the outer plasma (0.65 < r/a < 0.8) gives DT/Bϕ ∼ ρ*2.46ν*−0.23β−1.01q2.03. In hybrid scenarios (qmin ∼ 1, low positive shear, no sawteeth), the T particle confinement is found to scale with increasing triangularity and plasma current. Comparing regimes (ELMy H-mode, ITB plasma and hybrid scenarios) in the outer plasma region, a correlation of high values of DT with high values of vT is seen. The normalized diffusion coefficients for the hybrid and ITB scenarios do not fit the scaling derived for ELMy H-modes. The normalized tritium diffusion scales with normalized poloidal Larmor radius in a manner close to gyro-Bohm , with an added inverse β dependence. The effects of ELMs, sawteeth and NTMs on the T particle transport are described. Fast-ion confinement in current-hole (CH) plasmas was tested in TTE by tritium neutral beam injection into JET CH plasmas. γ-rays from the reactions of fusion alpha and beryllium impurities (9Be(α, nγ)12C) characterized the fast fusion-alpha population evolution. The γ-decay times are consistent with classical alpha plus parent fast triton slowing down times (τTs + ταs) for high plasma currents (Ip > 2 MA) and monotonic q-profiles. In CH discharges the γ-ray emission decay times are much lower than classical (τTs+ταs), indicating alpha confinement degradation, due to the orbit losses and particle orbit drift predicted by a 3-D Fokker–Planck numerical code and modelled using TRANSP.

Turbulent transport in tokamak advanced scenarios

The hybrid scenario is thought to be an important mode of operation for the ITER tokamak. Analytic and numerical calculations demonstrate that toroidal effects at finite β have a strong influence on tearing mode stability of hybrid modes. Indeed, they persist in the large aspect ratio limit, R/a → ∞. A similar strong coupling effect is found between the m = 1, n = 1 harmonic and the m = 2, n = 1 harmonic if the minimum safety factor is less than unity. In both cases the tearing stability index, Δ′ increases rapidly as β approaches ideal marginal stability, providing a potential explanation for the onset of linearly unstable tearing modes. The numerical calculations have used an improved version of the T7 code (Fitzpatrick et al 1993 Nucl. Fusion 33 1533), and complete agreement is obtained with the analytic theory for this demanding test of the code.

In this article, we construct a portfolio of commodity futures which mimics the Dow Jones Commodity Index and perform an extensive stress testing exercise with a focus on hybrid scenarios. The increased volume of investments in commodities as financial instruments over the last decades underline the importance of a more thorough framework for stress testing of related portfolios. Our study is the first to show comparatively the marginal impact of the model choice for portfolio components versus the marginal role of tail dependence on the portfolio profit and loss in stress testing exercises. We model the distribution of returns of portfolio components with an asymmetric AR-GARCH model combined with Extreme Value Theory for extreme tails, and employ multivariate copula functions to model the time-varying joint dependence structure. Our study reveals that indeed, for a realistic stress test, a special attention should be given to the tail risk in individual commodity returns as well as to tail correlations. We also draw conclusions about parameter risk persistent in stress testing exercises. Finally yet importantly, in line with Basel IIIb, the study highlights the importance of using forward-looking hybrid and hypothetical scenarios over historical scenarios.

A review of the development of advanced tokamak scenarios at the Joint European Torus (JET) is presented. It has been established that the current profile plays an important role in these regimes, and the presentation of the experimental achievement has been organized with this in mind. The main achievements are discussed: from high beta plasmas starting with a fully diffused plasma current; from hybrid scenarios with a flat current profile and central q around unity; from pellet-enhanced modes where the role of reversed magnetic shear (transiently) was first established; from optimized shear configurations with weakly reversed shear allowing the establishment of internal transport barriers in D-T plasmas for the first time, including the production of 8.2 MW of fusion power; and from strongly reversed shear and steady-state scenarios. The required development of the control techniques for these advanced scenarios is also described. The results obtained have significantly contributed to the development of advanced scenarios for ITER operation. The prospects for further development of hybrid and steady-state scenarios for ITER are indicated in view of the ongoing upgrades to additional heating systems in JET.

ITER hybrid and target steady-state fusion burn scenarios are simulated using the PTRANSP integrated modelling code together with input from the TSC code. In the hybrid scenarios, the majority of the current is driven inductively; whereas, for the target steady-state scenarios, approximately 22% of the current (at 1000 s) is driven inductively with the remaining current driven by the bootstrap, neutral beam and radio frequency sources. Predictive simulations are carried out using either the new Multi-Mode or the GLF23 anomalous transport model. Momentum transport is used to compute the toroidal angular frequency profile which, in turn, is used to compute the self-consistent flow shear suppression of anomalous transport. The simulations of the hybrid scenario indicate that the fusion power production at 1000 s will be approximately 500 MW corresponding to a fusion Q = 9.4. The fusion power predicted in the simulations of the target steady-state scenarios is found to depend on the time dependence of the input heating and associated current drive. It is found that turning off some components of auxiliary heating causes the fusion power production to increase. The fusion power obtained in the target steady-state scenarios, depending on the transport model and input injected power, ranges from 168 MW up to 226 MW, corresponding to a fusion Q ranging from 2.0 to 6.8.

In this article, we construct a portfolio of commodity futures which mimics the Dow Jones Commodity Index and perform an extensive stress testing exercise with a focus on hybrid scenarios. The increased volume of investments in commodities as financial instruments over the last decades underline the importance of a more thorough framework for stress testing of related portfolios. Our study is the first to show comparatively the marginal impact of the model choice for portfolio components versus the marginal role of tail dependence on the portfolio profit and loss in stress testing exercises. We model the distribution of returns of portfolio components with an asymmetric AR-GARCH model combined with Extreme Value Theory for extreme tails, and employ multivariate copula functions to model the time-varying joint dependence structure. Our study reveals that indeed, for a realistic stress test, a special attention should be given to the tail risk in individual commodity returns as well as to tail correlations. We also draw conclusions about parameter risk persistent in stress testing exercises. Finally yet importantly, in line with Basel IIIb, the study highlights the importance of using forward-looking hybrid and hypothetical scenarios over historical scenarios.

In this paper, we performed a stress-testing for a portfolio of commodity futures, which mimics the dynamics of the DJ-UBS index. We identified extreme events that impacted commodity prices over time, and looked at correlation structures in a dynamic way, with copula functions. In line with Basel III financial regulations, we derived baseline, historical, and hybrid scenarios and discussed their advantages and shortfalls. We found that the financialization of commodity markets led to an increase in correlations and in the probability for joint extremes. However, we identified structural breaks in commodity markets that temporarily led to a breakdown of expected statistical patterns and of traditional dependence structures among commodities. This fact shows the need for forward-looking stress testing techniques, like hybrid and hypothetical scenarios, as encouraged by financial regulators.

Stress-testing for portfolios of commodity futures

A typology of scenarios for the organization of spatial restoration of economic systems with their unique adaptation to the needs of Ukraine and the development of a hybrid scenario format as the main strategy for substantiating a multi-level toolkit for its effective implementation by 2030 have been developed. An integrated eight-stage system was formed (analysis of initial conditions and risks (2024-2025); determination of priority areas of development (2025-2026); development of a hybrid scenario model (2026-2027); implementation of innovative and technological solutions (2027-2028); modernization of institutional infrastructure (2028-2029); integration of ecological and social components (2029); monitoring and adaptation of the hybrid strategy (2029-2030); ensuring the continuity of development and sustainability (2030) of the implementation of the hybrid scenario of the reconstruction of economic systems it is put into practice taking into account national imperatives, economic stability and predictive adaptability, which makes it a universal tool for comprehensive spatial reconstruction of the country in the post-war period. The predictive format of the hybrid scenario until 2030 has been built, which gradually ensures the implementation of the strategy, which: a) takes into account the dynamic multifactorial nature of recovery processes in the post-crisis period, where each stage covers specific risks, priorities and resources; b) integrates innovative-technological, cognitive-informational, institutional, ecological and social components into a single architecture of a hybrid format, which ensures high flexibility and sustainability of the approach to spatial development; c) offers monitoring and adaptation of the strategy at the final stages, allowing to adjust implementation mechanisms depending on external and internal changes, in particular in the economic, environmental and social spheres; d) focuses on ensuring the continuity and long-term sustainability of development until 2030, which for the first time combines forecasting, resource provision and adaptation mechanisms within a single conceptual platform for the spatial restoration of economic systems of Ukraine.

Higher-dimensional models of neutrino physics with one or more right-handed neutrinos in the bulk have attracted considerable attention in recent years. However, a critical issue for such models is to find a way of introducing the required flavor dependence needed for generating neutrino oscillations. In this paper, we point out that a natural minimal framework that accomplishes this can be constructed by combining the bulk-neutrino hypothesis for right-handed neutrinos with the split-fermion scenario for left-handed neutrinos. This combination leads to a unique flavor signature for neutrino phenomenology which easily incorporates large flavor mixing angles. This hybrid scenario also has a number of additional important features. For example, one previous difficulty of the split-fermion scenario applied to neutrinos has been that the mass matrix is exponentially sensitive to neutrino displacements within the brane. However, in our hybrid scenario, the interactions between the brane and bulk naturally convert this dependence from exponential to linear. Another important feature is that our hybrid scenario provides its own natural regulator for Kaluza-Klein sums. Thus, in our scenario, all Kaluza-Klein summations are manifestly finite, even in cases with multiple extra dimensions. But most importantly, our mechanism completely decouples the effective neutrino flavor mixing angles from the sizes of the overlaps between the neutrino wave functions within the brane. Thus, we are able to obtain large neutrino mixing angles even when these neutrinos have significant spatial separations and their overlaps vanish.

In peptide receptor radionuclide therapy (PRRT) of patients with neuroendocrine neoplasias (NENs), intratherapeutic dosimetry is mandatory for organs at risk (e.g. kidneys) and tumours. We evaluated commercial dosimetry software (Dosimetry Toolkit) using varying imaging scenarios, based on planar and/or tomographic data, regarding the differences in calculated organ/tumour doses and the use for clinical routines. A total of 16 consecutive patients with NENs treated by PRRT with 177Lu-DOTATATE were retrospectively analysed. Single-photon emission computed tomography (SPECT)/low-dose computed tomography (CT) of the thorax and abdomen and whole body (WB) scintigraphy were acquired up to 7 days p.i. (at a maximum of five imaging time points). Different dosimetric scenarios were evaluated: (1) a multi-SPECT-CT scenario using SPECT/CT only; (2) a planar scenario using WB scintigraphy only; and (3) a hybrid scenario using WB scintigraphy in combination with a single SPECT/low-dose CT. Absorbed doses for the kidneys, liver, spleen, lungs, bladder wall and tumours were calculated and compared for the three different scenarios. The mean absorbed dose for the kidneys estimated by the multi-SPECT-CT, the planar and the hybrid scenario was 0.5 ± 0.2 Sv GBq-1, 0.8 ± 0.4 Sv GBq-1 and 0.6 ± 0.3 Sv GBq-1, respectively. The absorbed dose for the residual organs was estimated higher by the planar scenario compared to the multi-SPECT-CT or hybrid scenario. The mean absorbed tumour doses were 2.6 ± 1.5 Gy GBq-1 for the multi-SPECT-CT, 3.1 ± 2.2 Gy GBq-1 for the hybrid scenario and 5.3 ± 6.3 Gy GBq-1 for the planar scenario. SPECT-based dosimetry methods determined significantly lower kidney doses than the WB scintigraphy-based method. Dosimetry based completely on SPECT data is time-consuming and tedious. Approaches combining SPECT/CT and WB scintigraphy have the potential to ensure compromise between accuracy and user-friendliness.

Interspecific hybridization is an important evolutionary phenomenon that generates genetic variability in a population and fosters species diversity in nature. The availability of large genome scale datasets has revolutionized hybridization studies to shift from the observation of the presence or absence of hybrids to the investigation of the genomic constitution of hybrids and their genome-specific evolutionary dynamics. Although a handful of methods have been proposed in an attempt to identify hybrids, accurate detection of hybridization from genomic data remains a challenging task. In addition to methods that infer phylogenetic networks or that utilize pairwise divergence, site pattern frequency based and population genetic clustering approaches are popularly used in practice, though the performance of these methods under different hybridization scenarios has not been extensively examined. Here, we use simulated data to comparatively evaluate the performance of four tools that are commonly used to infer hybridization events: the site pattern frequency based methods HyDe and the D-statistic (i.e., the ABBA-BABA test) and the population clustering approaches structure and ADMIXTURE. We consider single hybridization scenarios that vary in the time of hybridization and the amount of incomplete lineage sorting (ILS) for different proportions of parental contributions (γ); introgressive hybridization; multiple hybridization scenarios; and a mixture of ancestral and recent hybridization scenarios. We focus on the statistical power to detect hybridization and the false discovery rate (FDR) for comparisons of the D-statistic and HyDe, and the accuracy of the estimates of γ as measured by the mean squared error for HyDe, structure, and ADMIXTURE. Both HyDe and the D-statistic are powerful for detecting hybridization in all scenarios except those with high ILS, although the D-statistic often has an unacceptably high FDR. The estimates of γ in HyDe are impressively robust and accurate whereas structure and ADMIXTURE sometimes fail to identify hybrids, particularly when the proportional parental contributions are asymmetric (i.e., when γ is close to 0). Moreover, the posterior distribution estimated using structure exhibits multimodality in many scenarios, making interpretation difficult. Our results provide guidance in selecting appropriate methods for identifying hybrid populations from genomic data.

Combined ICRF and NBI heating played a key role in achieving the world-record fusion yield in the first deuterium-tritium campaign at the JET tokamak in 1997. The current plans for JET include new experiments with deuterium-tritium (D-T) plasmas with more ITER-like conditions given the recently installed ITER-like wall (ILW). In the 2015-2016 campaigns, significant efforts have been devoted to the development of high-performance plasma scenarios compatible with ILW in preparation of the forthcoming D-T campaign. Good progress was made in both the inductive (baseline) and the hybrid scenario: a new record JET ILW fusion yield with a significantly extended duration of the high-performance phase was achieved. This paper reports on the progress with the hybrid scenario which is a candidate for ITER longpulse operation (∼1000 s) thanks to its improved normalized confinement, reduced plasma current and higher plasma beta with respect to the ITER reference baseline scenario. The combined NBI+ICRF power in the hybrid scenario was increased to 33 MW and the record fusion yield, averaged over 100 ms, to 2.9x1016 neutrons/s from the 2014 ILW fusion record of 2.3x1016 neutrons/s. Impurity control with ICRF waves was one of the key means for extending the duration of the high-performance phase. The main results are reviewed covering both key core and edge plasma issues.