Validation of a full-plasma integrated modeling approach on ASDEX Upgrade

In this work we present the extensive validation of a refined version of the integrated model based on engineering parameters (IMEP) introduced in reference (Luda et al 2020 Nucl. Fusion 60 036023). The modeling workflow is now fully automated, computationally faster thanks to the reduced radial resolution of the TGLF calculation, and it includes the modeling of the toroidal rotation, which was still taken from experimental measurements in our previous work. The updated model maintains the same accuracy as its previous version when tested on the cases presented in the initial publication. The confined plasma, from the magnetic axis to the separatrix, is simulated without using any experimental information from profiles measurements, and the inputs of IMEP are the same engineering parameters used when programming a plasma discharge. The model validation database consists of 50 ASDEX Upgrade (AUG) stationary (over a few energy confinement time) H-mode phases, which largely cover the entire AUG operational domain. The prediction of IMEP is compared with experimental measurements and with scaling laws, such as the IPB98(y,2), the ITPA20-IL, and AUG specific regressions. This modeling framework has proven to be very accurate over the entire set of 50 cases, with a significantly lower mean relative error with respect to each of the scaling laws considered, accurately reproducing the change in pedestal and core confinement caused by a change in plasma current, heating power, fueling rate, triangularity, magnetic field, NBI voltage (i.e. the effect of a change in the core particle source), and heating mix (e.g. correctly predicting the effect on confinement caused by a change in T e/T i). Plasma confinement is correctly described by IMEP also for two particular operating regimes, such as the ITER baseline scenario, and the QCE regime (quasi continuous exhaust, also referred as type-II and small ELMs). This work clearly demonstrates the power of this approach in pulling out physics mechanisms to interpret subtle interdependencies and that a 1D integrated model can reproduce experimental results over very large parameter variations with a higher accuracy than any statistical regression. This approach has therefore the potential to improve the prediction of the fusion performance in future tokamak reactors.

Energy confinement in the spherical tokamak Globus-M2 with a toroidal magnetic field reaching 0.8 T

The work presents the results of the energy confinement study carried out on the compact spherical tokamak (ST) Globus-M2 with toroidal magnetic field (BT) as high as 0.8 T. A reproducible and stable discharge was obtained with the average plasma density (5-10) 1019 m-3. Despite the increase in the magnetic field, the neutral beam injection (NBI) led to clear and reproducible transition to the H-mode accompanied by a decrease in the turbulence level at the plasma edge. NBI allowed effectively heat the plasma: electron and ion temperatures in the plasma core exceeded 1 keV. In comparison with the previous experiments carried out with BT=0.4 T plasma total stored energy was increased by a factor of 4. The main reason of this phenomenon is a strong dependence of the energy confinement time (τE) on the toroidal magnetic field in the spherical tokamak. It was experimentally confirmed that such kind of dependence is valid for ST with magnetic field up to 0.8 T. It also has been shown that the enhancement of the energy confinement in the Globus-M2 with collisionality decrease is associated with an improvement of both electron and ion heat transport.

Optimization of HF- injection at the 2nd harmonic of ECRH on T-10 tokamak in order to obtain high energy content in plasma

Non-traditional scheme of HF-injection has been used in T-10 tokamak for ECRH at the 2nd harmonic of ECR in X-mode. Two HF-launcher systems, with focusing beams, injected power in opposite directions under toroidal angles +/-20˚. Input power from each launcher was about the same (Phf =0.8 ÷ 0.85MWt). Absorbed energy was deposed in central area of plasma column. The new phenomenon has been found in some shots with W-limiter and Li-coating in the regime mentioned above. The spontaneous rise of the electron density nearly in the all plasma column occurs simultaneously with the rise of Te in the wide region (0<r/a<0.8) at the steady-state of ECRH. The value of the energy confinement time abruptly rises by ~15%. The absolute value of the electron heat and density fluxes reduces abruptly in the whole plasma column similarly to that of at non-local (or global) L-H transitions found earlier in JET and JT-60U. The accumulation of tungsten and light impurities is absent. In a series of shots, without L-H transitions, measurements of X-ray spectra (PHA data) showed a significant difference in comparison with the ECCD co-injection by two gyrotrons.

Recent ECRH/ECCD experiments aiming for higher density and temperature operations in the LHD

In LHD, real-time control of the incident EC wave polarization and quick response microwave bolometer for monitoring the stray radiations have been developed for efficient and safe operation of the high power and long pulse ECRH/ECCD. As a high power ECRH/ECCD application aiming for high density, ECRH has been demonstrated up to 85% of the cutoff density by the fundamental X-mode excitation in HFS with use of a horizontal port antenna located in LFS. As another application aiming for high temperature, the effect of the control of the rotational transform with use of the ECCD on the sustainment of the e-ITB is investigated. It has been suggested that higher local electron energy confinement time is obtained inside the e-ITB with placing the m/n = 2/1 magnetic island near the edge of the e-ITB compared to the case when the 2/1 island is vanished in the plasma.