HT-7
description
Transcript of HT-7
HT-7HT-7ASIPPASIPP
Turbulence and coherent structuresTurbulence and coherent structuresin the HT-7 Tokamakin the HT-7 Tokamak
Guo Sheng Xu (Guo Sheng Xu (徐国盛徐国盛 ))
B.N. Wan, W. Zhang, S.Y. Ding, J.F. Chang, Y.D. LiB.N. Wan, W. Zhang, S.Y. Ding, J.F. Chang, Y.D. Li
Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, ChinaInstitute of Plasma Physics, Chinese Academy of Sciences, Hefei, China
[email protected]@ipp.ac.cn
Hang Zhou meeting Sept. 25, 2007Hang Zhou meeting Sept. 25, 2007
systemssystems
Plasma edge region:Langmuir probe arrays
Questions presented for discussion
1. Evidence for ballooning structures of plasma turbulence in HT-7
2. Zonal flows measurements in HT-7
3. Electrostatic coherent mode in HT-7
4. Multi-scale coherent structure in plasma turbulence
5. Open questions
toroidallinearmodecoupling
实验中测量到的湍流,显然是充分发展的非线性饱和状态的结果。我们看到的不是一个线性的单模,而是多模叠加并充分演化的最终状态。非线性湍流模拟提供了一个和实验比较以及理解实验结果的平台。
Ballooningstructures
Zonal flows break the global eigenmode structure in ITG turbulence more isotropic in direction
In a torus linear mode couplingballooning structuresToroidal global eigenmode
kr
02
0
sk
qnkr
tirqintr n 0expˆ,,,~
k
single mode structure
Li
qR
mnqk
//
qnd
1
At plasma edge turbulence propagate in theelectron diamagnetic direction and alsopropagate in the radial direction
02
0
sk
qnkr
dr
dq
q
rs
r
A movie shows the intermittently occurring coherent structure in HT-7
r
r
HT-7上发现湍流的实频依赖于当地参数。Turbulence frequency was found increase with TePropagate in the electron diamagnetic direction
In plasma core measured byCO2 collective scattering
0 250 500 750 1000 1250 1500 1750 20000.0
0.2
0.4
0.6
0.8
1.0
No
rma
lize
d P
ow
er
Sp
ect
ra
Frequency ( kHz )
CO2 laser scattering
HT-7 Shot 81705200 ~ 750 ms
k = 11.4 cm-1
k = 20 cm-1
0 200 400 600 800 10000.0
0.2
0.4
0.6
0.8
1.0
No
rma
lize
d P
ow
er
Sp
ect
ra
Frequency ( kHz )
Measured byLangmuir probe
= 0.6 = 0.78 = 0.9
In plasma edge measured byLangmuir probe
ks = 1 ~ 5
In plasma core frequency band10 kHz ~ 1 MHz/ci = 0 ~ 6%
ks = 0 ~ 1
In plasma edge frequency band10 kHz ~ 300 kHz/ci = 0 ~ 2%
ee
e Tdr
dn
eBn
Tk~*
020406080
01020304050
010203040
0 20 40 60 80 1000
10
20
0 20 40 60 80 1000 20 40 60 80 100
ne
f
( 2 )r = 0.5 cm
( 3 )r = 0 cm
( 4 )r = -0.5 cm
( 5 )r = -1 cm
( 6 )r = -1.5 cm
( 7 )r = -2 cm
( 8 )r = -2.5 cm
( 9 )r = -3 cm
( 10 )r = -3.5 cm
( 1 )r = 1 cm
( 11 )r = -4 cm
( 12 )r = -4.5 cm
Aut
o p
ower
spe
ctra
S(f
)
f ( kHz )
In plasma edge measured by Langmuir probe
ne0 ~ 1.51019m-3
ee
e Tdr
dn
eBn
Tk~*
Questions presented for discussion
1. Evidence for ballooning structures of plasma turbulence in HT-7
2. Zonal flows measurements in HT-7
3. Electrostatic coherent mode in HT-7
4. Multi-scale coherent structure in plasma turbulence
5. Open questions
ks = 0 ~ 1
/ci = 0 ~ 2%
Zonal flowsspectrumThere are generally three components in
the measured fluctuation spectra:1. broad band turbulence2. zero-mean-frequency zonal flows3. low frequency coherent mode
Zero-mean-frequency zonal-flow modeStudy on the HT-7 tokamak
Zonal flows pattern
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0 20 40 60 80 100-3-2-10123
0 20 40 60 80 1000 20 40 60 80 100
( 2 )r = 0.5 cm
( 3 )r = 0 cm
( 4 )r = -0.5 cm
( 5 )r = -1 cm
( 6 )r = -1.5 cm
( 7 )r = -2 cm
k (f
) (
ra
d/c
m )
( 8 )r = -2.5 cm
( 9 )r = -3 cm
( 10 )r = -3.5 cm
( 1 )r = 1 cm
( 11 )r = -4 cm
f ( kHz )
( 12 )r = -4.5 cm
ion
ele
Poloidal dispersion relations measured at 12 radial locationsPoloidal dispersion relations measured at 12 radial locations
Ed
ge
SOL
Questions presented for discussion
1. Evidence for ballooning structures of plasma turbulence in HT-7
2. Zonal flows measurements in HT-7
3. Electrostatic coherent mode in HT-7
4. Multi-scale coherent structure in plasma turbulence
5. Open questions
Langmuir probe
magnetic coils
Low frequency coherent mode in HT-7
10~20 kHz electrostatic coherent mode was frequently observed in the plasma edge region of the HT-7 tokamak. Our special designed new experiments clearly demonstrated that this coherent mode is strongly correlated with tearing mode activity in the plasma core region.
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Tearing mode
10 kHz
17 kHz
P2
P1
Mirnov coils
Cross section
MHD spectrumMeasured byMirnov coils
9 kHz 18 kHz
MHD spectrumMeasured byMirnov coils
Potential fluctuation spectrameasured by Langmuir probeat plasma edge
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Correlation between two potential signals toroidally separated by about 90°Turbulence is almost completely decorrelated, while MHD perturbations have strong correlation in long distance.
tnmim
mnmn
rer
rbB
1
1
tnmim
mnmnr
rer
ribB
1
1
0
1
0
1
**
**
*
0~
02
3
2
3
0
n
n
T
e
mnpenmnmn
pnTTnnTTn
nn
e
gt
RBtt
t
uuBBuEuuuu
uuuuuu
uu
Global magnetic field perturbations induced by rotating islands of tearing mode
Coupling of the global magnetic field perturbations with the local electron drift mode large-scale electrostatic perturbations
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Poloidal rake probe
MHD spectrumMeasured byMirnov coils
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Questions presented for discussion
1. Evidence for ballooning structures of plasma turbulence in HT-7
2. Zonal flows measurements in HT-7
3. Electrostatic coherent mode in HT-7
4. Multi-scale coherent structure in plasma turbulence
5. Open questions
m
immrnqtinirt expˆexp,,,~
Different mode number overlapping
4 cm inside the LCFS, averaged lifetime of turbulence eddies is around 25 s.lifetime of the largest turbulence eddy is about 100 s, beyond this time scale the fluctuation is completely decorrelated.
long correlation tailfrom 12.5 to 100 s
Turbulence structureat plasma edge
Intermittently occurring large-scale coherent structuresmainly in low frequency region
a
tts
attsaW as
1
,, ,
Two dimension FFTDispersion relation Vph = 2 km/s
Typical drift-wave dispersion relation
Turbulence propagates in the electron diamagnetic direction with phase velocityVph ~ 2 km/s.
Turbulence concentrates in low frequency and long wavelength region.Decay towards high frequency and short wavelength region.
Large-scale coherent structure : poloidal scale > 6 cm, time scale > 50 sSmall-scale coherent structure : poloidal scale < 1 cm, time scale < 10 sCoiflet wavelets (a biorthogonal wavelet) are used to extract these structures
Structures self-similarity Intermittency
Use singular value decomposition method to seethe multi-scale structures of plasma turbulence
Sort according tosignal magnitude
Large-scale
Large-scale structures have long lifetime up to 100 s
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1. Which mode is responsible for plasma turbulence at tokamak edge? Particular instability at plasma edge or spreading from the core region?
2. Plasma turbulence structure in tokamaks is ballooning or not?
3. Besides zonal flows, local parameters (n, T, p) changing (with r) is also a possible reason for breaking the global enginemode structure and the presence of mesoscale ballooning structures.
4. Big eddy not necessarily implies big contribution to transport. The traditional fluid picture of convection transport need to be reconsidered. Particles scattering by wave diffusive transport
Open questions
Li
Thanks for your attention.
Filamentary structures or blob structures in plasma turbulence were observed in some tokamaks recently by imaging: TFTR, ASDEX, Alcator C-Mod, DIII-D, NSTX. // >> 1 m (qR~10 m), = 1~10 cm. beam emission spectroscopy (BES)gas-puff imaging (GPI)
NSTXMaqueda, Wurden, ZwebenRev. Sci. Instrum. 72, 931 (2001)
Alcator C-ModGrulke, Terry, LaBombard, ZwebenPhys. Plasmas 13, 012306 (2006)
Not ELMy !
Alcator C-ModTerry, LaBombard, Zweben, http://www.pppl.gov/~szweben/index.html
Tangential view
Side view
Top view