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"Manas, P."
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Understanding data analytics and predictive modelling in the oil and gas industry
Covers aspects of data science and predictive analytics used in oil and gas industry by looking into the challenges of data processing and data modelling unique to this industry. It includes upstream management, intelligent/digital well, value chain integration, crude basket forecasting and so forth.
BOOK
Maximizing the ion temperature in an electron heated plasma: from WEST towards larger devices
In electron heated plasmas, as the power increases, it is experimentally reported that the ion temperature (Ti ) saturates while the electron temperature (Te ) increases [Beurskens NF 2022]. As on AUG, W7X and elsewhere, Ti saturates around 1.5 keV in WEST L-mode electron heated plasmas while Te reaches 4 keV. Simulations within the integrated model METIS have been compared against a whole WEST campaign consisting mostly of L-mode plasmas with Lower Hybrid heating ranging from 1 to 5.5 MW. In METIS, the collisional equipartition is modeled as well as the turbulent heat transport using the neural network regression of the quasilinear gyrokinetic code QuaLiKiz. The observed Ti saturation is well captured by the modeling framework. The saturation correlates with a low ratio of the energy confinement time to the volume averaged electron-ion collisional heat exchange time. It is then shown that Ti saturation in electron heated plasma is due to an equipartition time higher than the energy confinement time. In larger devices, no Ti saturation is expected nor predicted by physics based integrated modeling used in this work, thanks to equipartition times sufficiently shorter than the energy confinement time.
Journal Article
Operational space for lower hybrid heating scenarios in the full tungsten environment of WEST
In tungsten—W—Environment in Steady-state Tokamak (WEST), the lower hybrid current drive (LHCD) system is key for achieving long pulse operation by providing most of the non-inductive plasma current, as well as a crucial source of electron heating. Therefore, determining the operational space for its application is fundamental. In the present study, the LHCD operational space is deeply analyzed for 0.5 MA pulses. This space is bounded by three limits: (i) the ratio of the LHCD power over density must be above a threshold to compensate tungsten radiation with enough core heating, (ii) the line-averaged density must be high enough to allow good coupling of the hybrid wave with the plasma, and (iii) fast electron ripple losses must be below a limit to avoid reaching a thermal threshold on plasma-facing components. If the tungsten radiation peak or burn-through phase is not safely overcome, a maximum electron temperature of 1.5 keV is obtained, confinement is degraded, and magnetohydrodynamic activity is frequently triggered, potentially causing a disruption. From experimental measurements and interpretative simulations, we highlight the main mechanisms that prevent the plasma from heating up during LHCD power ramp-up. Three parameters play a major role: plasma density, tungsten concentration and LHCD power deposition. A strategy to overcome this limitation is found: a precise density ramp-up performed simultaneously with the increase in LHCD power. Additionally, we show that boronization greatly facilitates the burn-through of tungsten by lowering its content during the heating phase. Finally, taking into account the three constraints given above, the LHCD operational space is determined at power ramp-up and during constant heating phases.
Journal Article
WEST L-mode record long pulses guided by predictions using Integrated Modeling
A new record was set on the WEST Tokamak, designed to operate long duration plasmas in a tungsten (W) environment, with an injected energy of 1.15GJ and a plasma duration 364s. Scenario development was supported by integrated modeling using the High Fidelity Plasma Simulator (HFPS), the European IMAS-coupled version of JETTO/JINTRAC, which integrates physics-driven modules into a unified framework. In particular, a reduced model for Lower-Hybrid heating and Current-Drive (LHCD) and the quasi-linear turbulent transport model TGLF are crucial for long pulses predictions up to the Last Closed Flux Surface (LCFS). Using this workflow, a 100 s reference discharge was modeled and plasma kinetic profiles and loop voltage were quantitatively well matched. In preparation for the recent long duration experiments, non-inductive current-drive actuators (IP,ne,PLHCD) were varied to determine the operational domain going towards fully non-inductive discharges. In particular, decreasing the plasma current is shown to ease the access to such conditions, with a careful monitoring of (ne,PLHCD) to avoid machine limitations. In addition, post-prediction experiments conducted within the investigated parameter range validated the predicted dependencies and were shown to be in quantitative agreement. Exploratory work on the use of ECCD for MHD stability purpose is also introduced.
Journal Article
Full radius integrated modelling of ohmic ramp-up at TCV including self consistent density prediction
The ramp-up is a critical phase in the operations of a Tokamak, during which engineering and physics aspects must be taken into account to ensure stability, minimize flux consumption and avoid disruptions. Predicting ramp-up phases faces challenges such as nonlinearity, uncertainty on boundary and initial conditions and changes in the magnetic equilibrium. Our work uses the High-Fidelity Pulse Simulator (HFPS), a Python workflow based on JINTRAC. The input and output are in machine and code generic IMAS data format. The HFPS predicts the evolution of the current, temperature, main ion density and impurity density up to the separatrix. The self-consistent prediction of the density during the ramp-up represents the main element of novelty in this work. To this end, a closed feedback loop is set to match experimental line averaged density. QuaLiKiz (Citrin et al 2017 Plasma Phys. Control. Fusion 59 124005), TGLF (Staebler et al 2016 Phys. Plasmas 23 062518) and FRANTIC (Tamor 1981 J. Comput. Phys. 40 104119) are used to calculate turbulent fluxes and the source of neutrals respectively. QuaLiKiz and TGLF predict a transition from Trapped Electron Mode early in the discharge to Ion Temperature Gradient dominated turbulence. The results are compared to higher fidelity simulations with GKW, which show qualitative agreement. Good general agreement is reached between integrated modelling and experimental data, quantified by proposed measures of agreement. A large set of sensitivities to modelling choices and initial and boundary conditions is performed on four different discharges, to assess the robustness of the approach.
Journal Article