Edge and SOL turbulence on HFS/LFS at ASDEX Upgrade by Microwave Reflectometry V.E. Nikolaeva1,2, M. E. Manso1, L. Guimarais1, U.Stroth3, G. D. Conway3, C. Silva1, and the ASDEX Upgrade team Associação Euratom/IST, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisboa, Portugal 2Technische Universität München, James-Franck-Str. 1, D-85748 Garching, Germany 3 Max Planck Institut für Plasmaphysik, EURATOM Association, Garching, Germany 1
Outlook Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop. Lewis Carroll, Alice in Wonderland Motivation Experimental set up Methodology HFS/LFS SOL/edge density fluctuations in L-mode Radial profile dn/n RMP effect Asymmetry dn/n in USN, DN, LSN Triangularity/power effect at LFS Summary
Turbulence is widely spread phenomena Hi-C, NASA Photo by Marc Mawson
Why do we investigate turbulence?
Why do we investigate turbulence?
Why do we investigate turbulence in fusion? Motivation Plasma turbulence greatly enhances energy and particles transport across magnetic field lines Anomalous transport processes degrade plasma confinement Investigation of turbulence properties is important to improve efficiency/reliability of a fusion reactor
Principles of reflectometry diagnostic O-Mode: Ewave B0: solely depend on ne 2 1 nc e F c= 2 π ϵ0 m e A(t)cos[2πF0 + φ(t)] to get φ(t) Hilbert transform relation between phase φ(t) and the density fluctuation level δne/ne determined from (O mode): 1D model by C.Fanack: 2/3 1/3 Large wavenumbers 2ka< kf < 2k0: k A =0.63 k 0 L δn 0 Δϕmax k f / k 0 = ncr π 2 L/ λ 0 1/ 2 ( ) Ln = nc ne
ASDEX Upgrade tokamak (Axially Symmetric Divertor EXperiment) major radius (R) 1.65 m minor radius (a) 0.5 m 1.6 ma max plasma current (Ip) max toroidal magnetic field (Bt) 3.1 T max pulse duration max electron density (ne) 10 s 1020 m-3
ASDEX Upgrade tokamak (Axially Symmetric Divertor EXperiment) major radius (R) 1.65 m minor radius (a) 0.5 m 1.6 ma max plasma current (Ip) max toroidal magnetic field (Bt) 3.1 T max pulse duration max electron density (ne) 10 s 1020 m-3
HFS&LFS FMCW reflectometer Density [x1019m-3] V 3.0-7.0 Q 1.5-3.0 Ka 0.8-1.5 K 0.3-0.8 Fluctuation Data: 8s @2MHz LFS Z=0.14 HFS Z=0.07
HFS/LFS radial profile of density fluctuations ne = 0.71*1019 m-3 SOL decrease of δn/n inside of LCFS LFS HFS Thesis of E. Viezzer, 2012
RMP effect RMP effect on HFS/LFS on HFS/LFS SOL density SOL density fluctuation fluctuation ne = 0.36*1019 m-3 SOL without RMP with RMP HFS Ref without RMP with RMP Magnetics LFS Ref HFS Ref RMP
Turbulence asymmetries HFS/LFS in USN, DN, LSN USN LSN USN Ka ne=1*1019 m-3 edge LFS HFS LFS K ne=0.4*1019 m-3 SOL HFS
Strong poloidal asymmetry in fluctuation amplitudes measured with LFS/HFS reflectometer LSN DN RMP USN RMP USN DN LSN USN LFS HFS LFS DN LFS HFS HFS LSN Edge stronger asymmetry in USN, not such a strong asymmetry like at SOL SOL - strongest asymmetry in DN; USN DN LSN USN dn/n higher both at LFS/HFS LSN DN RMP USN RMP not clear DN, dn/n high at HFS
Turbulencechanges changeswith withtriangularity, triangularity,lfs LFS Turbulence H-mode, ELM suppression density shoulder steep region density shoulder steep region Changes are observed only at low power and at the shoulder region where turbulence seems to increase with δ (from #30728 to #30718)
Turbulencechanges changeswith withnbi NBIpower, power,lfs LFS Turbulence density shoulder density shoulder steep region steep region Changes are observed mainly at the shoulder region, in case of medium δ effect is more pronounced, turbulence decreases with increase of NBI power
Summary HFS/LFS SOL/edge assymmetries Drop of density fluctuations inside close to LCFS Effect of RMP coils is mainly pronounced on HFS SOL HFS/LFS SOL/edge density fluctuations asymmetry observed in L-mode in USN, DN, LSN configurations Triangularity and power effect, LFS At higher power effect of triangularity on density turbulence from separatrix to pedestal area is not pronounced At low power effect of triangularity is seen at density profile shoulder, turbulence is higher for higher triangularity
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Experimental set up, HFS/LFS reflectometers O-Mode: Ewave B0: Independent of magnetic field. WKB approximation. Multi-channel reflectometer diagnostics Hopping LFS reflectometer RFL LFS 2 channels [FLQ, FLV] FF or hopping density fluctuation measurements heterodyne: in-phase & quadrature (IQ) detector: I(t) = A(t)cos(φ(t)) & Q(t) = A(t)sin(φ(t)) separation phase φ(t) & amplitude A(t) fluctuations FMCW LFS&HFS reflectometer RTR LFS: 5 channels [K, Ka, Q, V, W] HFS: 4 channels [K, Ka, Q, V] swept frequency profiles measurements or FF density fluctuation measurements homodyne: single ended detector A(t)cos[2πF0 + φ(t)] F0 microwave source frequency toroidal section of AUG tokamak