Abstract
The properties of L-mode confinement have been investigated with a set of dedicated experiments in ASDEX Upgrade and with a related modelling activity with the transport code ASTRA and the quasi-linear turbulent transport model TGLF-SAT2, with boundary conditions at the separatrix. The values at the boundary have been set by the two-point model for the electron temperature, with the ion temperature proportional to the electron temperature by a constant factor, and the electron density set by a constant fraction of the volume averaged density. The influx of neutrals has been set through a feedback procedure which ensures that in the simulation the same particle content as in the experiment is obtained. The sensitivity of the results under considerable variations in the choice of the boundary conditions has been investigated and found to be limited. The predictions of this full-radius modelling set-up have been compared to experimental results covering a scan in electron cyclotron resonance heating (ECRH) power in both hydrogen and deuterium plasmas, a plasma current scan with fixed magnetic field, under both ECRH and neutral beam injection heating, an increase in plasma density with constant ECRH power in hydrogen plasmas, as well as variations of the fraction of electron and ion heating at approximately constant total heating power, as well as a change of main ion from deuterium to hydrogen. The ASTRA-TGLF predictions have been found to reproduce all of the experimentally explored dependences with relatively good accuracy, providing evidence, for the first time to our knowledge, that the main properties of L-mode confinement can be reproduced by conventional full-radius transport modelling with a quasi-linear turbulent transport model. Evidences of largest disagreement, although usually not exceeding the 20%, have been found at high electron heating power, where TGLF underpredicts the electron and particularly the ion thermal stored energies, and in the current dependence of confinement, which, in electron heated conditions, is predicted to be weaker than in the experiment.
| Original language | English |
|---|---|
| Article number | 066015 |
| Journal | Nuclear Fusion |
| Volume | 62 |
| Issue number | 6 |
| DOIs | |
| State | Published - Jun 2022 |
Funding
The authors are grateful to F. Ryter, T. Pütterich and P.A. Schneider for very fruitful discussions and for their help in the design and the performance of the experimental discharges at ASDEX Upgrade. The authors also gratefully acknowledge the contribution from R. Fischer, for the profiles with the integrated data analysis suite, and from R.M. McDermott, for the charge exchange recombination spectroscopy measurements, which have been used in this work. The excellent support from the ECRH and NBI heating groups at ASDEX Upgrade is also warmly acknowledged. C.A. would also like to thank the colleagues of the ITPA Topical Group Transport and Confinement, Joint Activity 31, and of the EUROfusion task TSVV11 for fruitful and motivating discussions, in particular C. Bourdelle, Y. Camenen, J. Citrin, L. Garzotti, A. Ho, P. Mantica and G. Snoep. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training program 2014–2018 and 2019–2020 under Grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commision.
Keywords
- confinement
- integrated modelling
- tokamak
- turbulent transport