Speaker
Description
See full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1097.pdf
The analysis of turbulent flows in the edge region of tokamak plasmas requires the measurement of time-averaged turbulent stresses and fluxes such as the Reynolds stress (RS), which has been identified in recent models and experiments [1] as a likely driver of poloidal zonal flows expected to play a key role in the L-H transition. However, the common method of using floating potential fluctuations measured by Langmuir probes (LP) V^(LP)(fl) suffers from being contaminated by electron temperature fluctuations T_e[2, 3]. For the interpretation of such experiments it is worth-while to seek a correction of V^(LP)(fl) statistics by the exploitation of additional knowledge of T_e statistics offered by e.g. the combination of LP with ball-pen probes (BPP) [4].
A proof-of-principle correction scheme for the RS measured by LP was found for experimental data measured in the COMPASS tokamak with the modified Reynolds stress probe head [5]. The correction scheme is based on the decomposition of RS into statistical moments such as variance and poloidal and radial covariances of V^(LP)_(fl) measured by LP with statistical moments of T_e from BPP measurements. The correction scheme was further compared with the relationships between the associated statistical moments in comparable turbulent HESEL [6] simulations.
The correction scheme was further tested for the time-evolving phenomena of Limit Cycle Oscillations (LCO) observed in the vicinity of the L-H transition in the COMPASS tokamak [5]. The LCO typically have a frequency of 3-5 kHz. Their frequency is observed to scale inversely with the plasma density as well as with other global parameters.
References
[1] G. R. Tynan, I. Cziegler, P. H. Diamond, et al., Plasma Physics and Controlled Fusion 58, 044003 (2016)
[2] B Nold, et al., New J. Phys. 14 063022, (2012)
[3] O. Grover, J. Adamek, J. Seidl, et al., Review of Scientific Instruments 88, 063501 (2017)
[4] J. Adamek, H. W. M¸ller, C. Silva, et al., Review of Scientific Instruments 87, 043510 (2016)
[5] O. Grover, J. Seidl, J. Adamek, et al., Nuclear Fusion 58, 112010 (2018)
[6] A.H.Nielsen, G.S.Xu, J.Madsen, et al., Physics Letters A 379, 3097-3101 (2015)
