turbulence characterization in the outer region of fusion plasmas: flow measurements in the edge...
TRANSCRIPT
Turbulence characterization in the outer region of fusion plasmas:
Flow measurements in the edge region of the RFX-mod experiment
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Gianluca De Masi
Outline:Outline:
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Experimental setupExperimental setup
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Gundestrup (=217° 30’)
U-probe (=247° 30’)
r (mm)
0 a = 459
z
Plasma radius= 0.459 m
Major radius = 2 m
Plasma current= 2 MA
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8
2
76
5
43
B≈Bθ
r
φ
δ
Gundestrup probeGundestrup probe
protruding electrode flush electrode
23
mm
graphite electrodes
boron nitride case 4
0 m
m
Electrode n°Electrode n° δ δ angle w.r.t. equatorial plane angle w.r.t. equatorial plane
1 22,5°
2 67,5°
3 112,5°
4 157,5°
5 202,5°
6 247,5°
7 292,5°
8 337,5°
The 8 external electrodes radius is about 2 mm (comparable with ion Larmor radius) with 4.8 mm2 area
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U-probeU-probe
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•Measurements of n, Te, Vp at 6 radial positions (Δr=6mm)•17 measurements of floating potential Vf at several radial positions (Δr=6 mm) e toroidal positions (Δφ=24 mm and 72 mm) •10 triaxial magnetic probes (Δrmin=6 mm, Δφ=95 mm )
Interpretation Models (1)Interpretation Models (1)
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Interpretation Models (2)Interpretation Models (2)
MacLatchy et al (1992)
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Interpretation Models (3)Interpretation Models (3)
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Interpretation Models (4)Interpretation Models (4)
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Main plasma parameters in several experimental campaigns considered (insertion probe range [409,479] mm)
Plasma current < 400 kA
Electron density (1.5-2.8) x 1019 m-3
Electron temperature(that we assume equal to Ti)
30 eV (at the deepest radial insertion, r = 409 mm)
Ion Larmor radius 4 mm (at r = 409 mm)
Ion thermal velocity 5.4 x 104 m/s (at r = 409 mm)
Ion sound velocity 7.6 x 104 m/s (at r = 409 mm)
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Flow measurements results (1)Flow measurements results (1)
Ion saturation current configuration
Time behaviour of a typical ion saturation current signal,
collected by a probe electrode during one of considered
discharges[Shot = 22920; Probe= 5 (δ = 202,5°); r = 449 mm]
Angular behaviour of i(δ) in 3 different shots
corresponding to different radial positions
Shots=[22368, 22369, 22373];F= -0.05
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Flow measurements results (2)Flow measurements results (2)Radial Profiles
In both cases the profiles are comparableThe parallel drift velocity inside the plasma reaches values of 0.5 cS (corresponding to (3-4) x 104 m/s)
The perpendicular drift velocity is of the order of 0.1 cS (corresponding to 3 x 103 m/s) in the tile shadow, and it reaches values of –0.2 cS (corrisponding to 1.5 x 104 m/s) inside
the plasma11/04/23 12
Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Ion saturation current configuration
Flow measurements results (3)Flow measurements results (3)Floating Potential configuration
Time behaviour of a floating potential signal,
collected by a probe electrode during one of considered discharges
[Shot = 22326; Probe= 3 (δ =112,5°); r = 439 mm]
Angular behaviour of V(δ) in 3 different shots
corresponding to different radial positions
Shots=[22413, 22345, 22411]; F= -0.2
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
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8
2
76
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43
Electron flux effect
B
Flow measurements results (4)Flow measurements results (4)
Radial profiles
Velocity profiles based on floating potential measurements are comparable with the ones based on ion saturation current measurements
Parallel drift velocity reaches values of 0.4 cS (corresponding to 3 x 104 m/s) inside the plasma
Perpendicular drift velocity is of the order of 0.3 cS (corresponding to (0.8-0.9) x 104 m/s) in tile shadow, up to -0.2 cS (corresponding to (1-2) x 104 m/s) inside the plasma
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Floating Potential configurationFloating Potential configuration Ion saturation current configuration
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Flow measurements results (5)Flow measurements results (5)Gundestrup and U-probe
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Several plasma parameters have been investigated during different experimental campaigns at different radial positions, in order to create a database and study the edge plasma flow variations w.r.t. global discharges parameters
Flow measurements results (6)Flow measurements results (6)
Reversal parameterReversal parameterF = Btor (a)/<Btor>
Greenwald densityGreenwald densitynG= IP / πa2
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Flow measurements results (7)Flow measurements results (7)Flow profiles comparison w.r.t. several plasma parameters Flow profiles comparison w.r.t. several plasma parameters
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Flow measurements results (8)Flow measurements results (8)
Velocity radial profilesVelocity radial profiles
In the region of strong gradient, fluctuations coupling between flow contributions <vradM┴> and <vradM││> could be transfer momentum to the perpendicular drift
Work in progressWork in progress
Plasma dynamics fluctuations
F-Crashes:
Correlation between fast variations of reversal parameter F and drift velocity fluctuations?
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Work in progressWork in progress
Plasma dynamics fluctuations (2)
Coherence and phase of parallel and perpendicular drift velocity fluctuations
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
Work in progressWork in progress
Parallel drift velocity transient due to pressure gradient?
Pellet injectionSome tokamak results link the L-H mode transition to an edge flow gradient.
O.D.Gurcan et al.,’Intrinsic rotation and electric field shear’,Physics of Plasmas,14 (2007)
SummarySummary
-For the ion saturation current measurements we found that the two applied interpretation models give comparable estimates of the parallel and perpendicular drifts
-We have verified the reliability of floating potential measurements in order to evaluate the Mach number. A good agreement exists between the plasma flow and the ExB drift flow
-The perpendicular velocity comparison between Gundestrup and U-probe reveals a double shear (across the r=a surface and deeper into the plasma)
-Very important informations about mechanisms that regulate the transport in the RFP edge could be obtained by studying plasma dynamic fluctuations and further research is now in progress
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
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Centro Ricerche Fusione Consorzio RFXUniversità degli studi di Padova
International Doctorate in Fusion Science and Engineering
ReferencesReferences-G. Serianni, ‘Struttura della regione esterna di un plasma confinato in una configurazione Reversed Field Pinch’, Tesi di dottorato in Fisica, Università degli studi di Padova, Anno Accademico 1994/1995;
-V. Antoni, et al., Nuclear Fusion, 36 (1996) 435;
-P.C. Stangeby, G.M. McCracken, Nucl. Fusion, 30 (1990) 1225
-S. Jachmich, et al.,’Influence of plasma flow on the floating potential and anensuing novel technique for measuring parallel flows’, (27th EPS Conference on Contr. Fusion and Plasma Phys. Budapest), ECA vol. 24B (2000) 832
-I.H. Hutchinson, ‘A fluid theory of ion collection by probes in strong magnetic fields with plasma flow’, Phys. Fluids 30 (1987) 3777
-C.S. MacLatchy, et al., ‘Gundestrup: a Langmuir/Mach probe for measuring flows in the scrape off layer of TdeV’, Rev. Sci. Instrum. 63 (1992), 3923
-M. Hudis, L.M. Lidsky, ‘Directional Langmuir probe’, J. Appl. Phys. 41 (1970) 5011
-M. Zuin, et al., ‘Fast dynamics of relaxation events in RFX-mod’, (2006)
-O.D.Gurcan et al.,’Intrinsic rotation and electric field shear’,Physics of Plasmas,14 (2007)