Abstract
TGLF transport model predictions have been assessed in the vicinity of a theoretical high ß burning plasma spherical tokamak at Q=10. Linear micro-stability calculations from TGLF have been compared on a surface at mid-radius with the gyrokinetic code GS2. Differences between TGLF and GS2 spectra can be characterised by the RMS difference in growth rates, s?. We find considerable improvement in the quality of TGLF growth rate spectrum can be achieved by increasing the number of parallel basis functions and by tuning the TGLF parameter used in the model for trapped particles, ?trap.
| Original language | English |
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| State | Published - 2019 |
| Externally published | Yes |
| Event | 46th European Physical Society Conference on Plasma Physics, EPS 2019 - Milan, Italy Duration: Jul 8 2019 → Jul 12 2019 |
Conference
| Conference | 46th European Physical Society Conference on Plasma Physics, EPS 2019 |
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| Country/Territory | Italy |
| City | Milan |
| Period | 07/8/19 → 07/12/19 |
Funding
The TGLF linear electrostatic micro-instability predictions have been compared with local gyrokinetic calculations using GS2 for highly shaped equilibria at R/a = 3.0 and R/a = 1.9, where the other local parameters are taken from a SCENE equilibrium for BurST. We have explored the sensitivity of the TGLF results to the number of basis functions and the value of θtrap. For the local equilibrium with R/a = 3.0, the default TGLF settings resulted in a σγ = 58%. Increasing the number of basis functions to 8 reduced this to σγ = 45%. Similarly at R/a = 1.9 increasing the number of basis functions to 8 and reducing the value of θtrap = 0.4 dropped σγ from 77% to 29%. This indicates that the default TGLF parameters can be adjusted to improve the model’s description of electrostatic micro-instabilities in STs. Note that the parameters found here may not be suitable for all flux surfaces, and other surfaces must be studied to assess the optimal values. A more self-consistent approach, with a modest additional computational cost, may be to update θtrap using the k|| after a first iteration, and use this to recalculate the impact on trapped particles. Future work will compare TGLF with local gyrokinetics for high β equilibria, where fluctuations in the magnetic field are more important; this will be the regime necessary to optimise the efficiency of fusion power production. This work was supported by the Engineering and Physical Sciences Research Council [EP/L01663X/1]. This work has been carried out within the framework of the EURO-fusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
| Funders | Funder number |
|---|---|
| H2020 Euratom | 2014-2018, 633053, 2019-2020 |
| Engineering and Physical Sciences Research Council | EP/L01663X/1 |
