-
Transport and fluctuations in LHD and comparisons with tokamaks
ITPA CDBM and Transport meetings - Spring 2007 at EPFL Lausanne K.
Tanaka1), C. Michael1), L.N. Vyacheslavov4), H.Yamada1), M.
Yokoyama1) O.Yamagishi1), H. Takenaga2), K. Muraoka3), H.Urano2),
S. Murakami5), A. Wakasa6) and LHD Experimental group1) National
Institute for Fusion Science, 322-6 Oroshi, Toki, 509-5292, Japan2)
Japan Atomic Energy Agency 801-1 Mukouyama Naka Ibaraki, 311-0193,
Japan3) School of Engineering, Chubu University, 1200 Matsumoto,
Kasugai, Aichi 487-8501 4) Budker Institute of Nuclear Physics,
630090, Novosibirsk, Russia5) Department of Nuclear Engineering,
Kyoto University, Kyoto 606-8501, Japan6) Graduate School of
Engineering, Hokkaido University, Sapporo, 060-8628, Japan
-
There is a similarity and dissimilarity between
helical/stellarator and tokamakSimilarityBoth global energy
confinements scaling (IPB98(y2) for tokamak and ISS04 for
helical/stellarator) are similar and are Gyro Bohm like
.Dissimilarity Shape of density profile.
The motivation of comparison study between helical/stellarator
and tokamak is to understand common underlined physics of
transport.
-
Outline of talk Comparison of global energy confinement scaling
between tokamak and helical/stellaratorRole of neoclassical
optimization on anomalous transport.Particle transport of
LHDExperimental turbulence study in LHD
-
International sterraltor scaliing 04 (ISS04) is dimensionally
similar to IPB98(y,2) on r*. Both are weak Gyro Bohm (H.Yamada
N.F.1684 (2005))In Gyro Bohm like transport, transport is
turbulence driven, of which wave length is order of ion Larmor
radius.H. Yamada, Nucl. Fusion 45 (2005) 1684Tokamak Ip are treated
through q2/3 into stellarator scaling.
-
In LHD, edge (r=0.7~1.1) fluctuation level measured by phase
contrast imaging (PCI) increases with increase of edge diffusion
coefficient. This is similar to tokamak observation.kperp ri~0.5.
This is expected by linear calculation of GOBLIN code. In tokamak,
smaller peak wavenumber kperp ri~0.1 was reported anywhere.Edge
transport influence global confinement. Similar fluctuation
character may results in similar r* scaling K.Tanaka Fusion Sci.
Tech. (2007)97
-
The particularity of helical/stellarator is enhanced
neoclassical transport in low collision regime Neoclassical
Transport coefficientBanana regimeneiPlateau regime1/n regimeFuture
operation regime of reactorAround one orderExperimental De,ceAround
one orderhelical/stellaratortokamakFuture operation regime of
reactor Neoclassical Transport coefficientPlateau
regimeneiExperimental De,ceS. Murakami Nucl. Fusion 42 (2002)
L19L22Axis PositionAxis PositionDneo/Dtokamak plateuDneo/Dtokamak
plateu1/n regimePlateau regimeIn 1/n, neoclassical transport is
minimum at Rax=3.53mIn Plateau, neoclassical transport is smaller
at more inward axis.Inward shiftedOutward shiftedInward
shiftedOutward shifted
-
Magnetic axis position change magnetic helical ripple and higher
ripple results in larger neoclassical transportFlux SurfaceOrbit of
guiding centerHC-IPlasmaHelical coilShifts by external vertical
field and Shafranov shiftsB contour
-
Energy confinement is improved by shift of magnetic axis
positionInward shift of Rax Optimization in terms of drift
optimizationEffect of neoclassical transport is pronounced in
collisionless regime
Confinement improvement by the inward shift of Rax still exists
in collisional regimeNeoclassical optimization is successful !Much
more than neoclassical theory !?0.60.03Smaller helical
rippleSmaller helical ripple
-
One of the key parameter to determine global energy is eh_eff,
which is representative amplitude of magnetic helical rippleH.
Yamada, Nucl. Fusion 45 (2005) 1684Representative helical ripple
amplitude at r=2/3
-
Global energy confinements are gyro Bohm character and edge
particle diffusion (~edge thermal conductivity ~ global energy and
particle transport) are dominated by turbulence (kperpri~0.5)
driven transport.With smaller magnetic ripple (inward shifted
configuration and smaller neoclassical transport), energy transport
is reduced.Reduced neoclassical configuration introduce smaller
anomalous transport.Recent non linear gyro kinetic simulation
support this. At reduced neoclassical configuration with smaller
magnetic helical ripple, zonal flow can be more induced, then
turbulence is supressed. (Sugama, Watanabe P.R.L. 94,115001,(2005),
Watanabe, Sugama, 21st FEC IAEA-CN-149/EX/5-4)
Summary of global energy confinement in LHD
-
60U Elmy H modeLHD Rax=3.6m Density scan at PNBI=8-10MW PNBI
scan at similar averaged densityDifferent character of density
profiles are observed in JT60U and LHD
-
Magnetic axis position changes density profile as well.Inward
shiftedSmall magnetic helical ripple and reduced neoclassical
transportOutward shiftedLarge magnetic helical ripple and enhanced
neoclassical transport
-
NBI 11.4MWNBI 1.7MWExample of transport analysisD is
anomalous.Vout is comparable Vneo.Impurity may not account for ne
profileHigher Te gradient induce outward convection
-
Density modulation experiments shows Dcore is anomalous, outward
Vcore is comparable with neoclassical oneBlank; Experiment,
Colored; Neoclassical At lower collisionality Dcore is close
toDneo.Dneon*hInward Vcore is not neoclassical.Plateau1/n
- Core particle flux is zero. In core region of hollow density
profile, outward neoclassical pinch is balanced with inward
anomalous diffusion.Outward neoclassical convectionInward anomalous
diffusion.Total flux~0-D grad neneVInward directed anomalous flux
is predicted by linear theory (O.Yamagishi 14. 012505 (2007) ) G~0
in core (r
-
Summary of particle transport in LHDOne of the particularity of
the helical/stellarator is particle transport. Hollow density
profiles are often observed. This is clear contrast that density
profile is always peaked in tokamak.Enhanced neoclassical transport
introduces hollow density profile.Peaked density profile is
obtained at reduced neoclassical configuration and is likely to be
driven by anomalous process.Particle diffusion is anomalous,
outward convection is comparable with neoclassical value. Inward
pinch is against neoclassical prediction.Linear gyro kinetic
calculation suggests the balance of turbulence driven flux and
neoclassical flux produce hollow density profile.
-
Top view of integrated fluctuationTop view of upper
fluctuationTop view of lower fluctuationPrinciple of 2D PCIUpper
fieldLower fieldLaser BeamPropagation direction tells spatial
points of fluctuation.
-
Integrated 2D picture with 8x6=48ch 2D array6.1mm17.5mmSpatial
2D Fourier TransformFluctuation of lower partFluctuation of upper
part
Present resolution is a/3~a/5. Signal suffers from cancellation
effectsExample signal of 2D PCIA.Sanin et al., Rev. Sci. Instrum.,
Vol. 75, No.10, (2004) pp.3439-3441C. Michael et al., , Rev. Sci.
Instrum. 77, 10E923 (2006) L.N.Vyacheslavov et al.,IEEE special
issue of plasma image Vol.33 (2005) pp.464-465
-
Movie of Fluctuation
-
Velocity spectrum shows ExB branch and i-diamag branch Core low
k and egde e-diamg. high k propagate ExB rotation speed.Edge
i-diamg components propagates in i-diamag direction in plasma
frameVExBStrong velocity shear in edge may reduce transport.
-
Edge Ion diamag. components show possible correlation with edge
diffusion. Fluctuation level becomes larger at outward shifted
configuration
- New attempts to measure direct contribution of fluctuation to
transportFluctuation induced energy and particle flux is given
bySignal is line integrated, but radially dominatedwe tried to
estimate fluctuation induced flux from edge PCI signal around
r=1.0.2.5
-
Outward FluxInward FluxWhen NBI power reduced ( transport should
have reduced as well), fluctuation induced flux reduced at outside
of LCFS1.767sec1.933seckrs~0.2Outside of LCFS, Inside of LCFS
-
Large amplitude burst take 20% of all time but make 80% of
averaged fluxDetail consideration is necessary about integration
effects of signal.Bursting signal contributes flux a
lot.AmplitudeMean~0
-
Summary of fluctuation Study2D phase contrast is working to
measure fluctuation profile using magnetic shear technique.The
results shows different k branch in core and edge.Edge ion
diamagnetic components play role on edge particle transport
(~global particle transport)Edge velocity shear may play important
role on reduced transport Core fluctuation is likely play role on
density profile.Preliminary data was obtained to estimate
fluctuation induced flux. Fluctuation induced flux is reduced when
beam power is reduced and total transport is reduced.
-
Summary of achieved parameter of LHDAchieved ValueTarget]
Central ion temperature13.5keV at 0.3x1019m-3 Ar plasma) 5keV at
1.2x1019m-3 (H plasma) 10keV at 2x1019m-3 Central electron
temperature 10keV at 0.5x1019m-3 10keV at 2x1019m-3 Volume Averaged
beta % at 0.425T 5 % at 1~2T Central electron density1x1021m-3 at
Te(0)= 0.4keV 40x1019m-3 Stored Energy1.44MJ 4MJ Steady State
operation 31min. 45sec 700 kW 1.3GJ 54 min 28sec 500 kW1.6GJ hour
(3,000W)]High density and stable operation are advantage
-
Core fluctuation may play role on density profile shaping.Most
of fluctuation components exists in ITG/TEM unstable regionTokamak
like. Turbulence transport produce peaked profileHelical
particular. Inward turbulence driven flux can be balanced with
outward neoclassical
-
Analysis of fluctuation profiles and phase velocityWhich
direction in the plasma frame do fluctuations propagate?Analyze
fluctuation phase velocity profileCompare with +NBI CVI CX
measurement of vExBCompare with drift velocity
Appear to be 3 fluctuation peaks
Peaks 1 and 2 propagate close to electron drift velocity.
Possibly electron drift waves?
Fluctuation amplitude is peaked in regions where Er shear is
zero. More than coincidence?
Compare radial profiles of fluctuation amplitude with parameter
profiles
Characteristics can vary widely among discharges. This is one
example.123#60334 t=2.22sRax=3.6m, B=-2.75T
-
Spatial profile of k spectrum shows three different branchHigh k
(k~0.7mm-1) electron diamag.Low k (~0.3mm-1)High k (k~0.7mm-1) ion
diamag.
-
Rax=3.9m, 1.54T, Dedge=0.57m2/secRax=3.75m, 1.5T,
Dedge=0.42m2/secRax=3.6m, 1.49T, Dedge=0.18m2/sec
-
Turbulence spectrumReal plasma is turbulent. And its spectrum is
two dimensionally broad in the cross section perpendicular to B.We
measures Fourier components perpendicular to beam axis in broad
spectrum Does the measured signal represent local fluctuation?
-
One of the key parameter to determine global energy and particle
confinements is eh_eff, which is representative amplitude of
magnetic helical rippleScatter of data suggests there are other
hidden parameter.H. Yamada, Nucl. Fusion 45 (2005)
1684helical/stellarator database
-
The value at r=2/3 is a good approximationof the volume averaged
value.Tokamak Ip are treated through q2/3 into stellarator
scaling.
-
Experimental values are compared with neoclassical ones.In the
following equation, D1,D2,Er were calculated by GSRAKE and DCOM
code. Neoclassical convection term was defined as following.The
thermo diffusion term (the second and third term) dominates for
electron particle transport in the present experiment regime.
-
Blank; Experiment, Colored; Neoclassical Dneon*h1/n
-
The volume averaged value of rotational transform is more
appropriate than the surface value.Limiter insertion in
LHDJT-60UY.Kamada et al. NF (1993)li dependence in tokamaksJT-60U,
TFTRThe value at r=2/3 is a good approximationof the volume
averaged value.
-
Comparison with Tokamak Database : ProvisionalDifferent
definition of aReasonable reconsideration ofprofile effect is
allowed.Translation of Ip to iTake the value of the rotational
transform at r=2/3
-
Scaling investigations ISS04: renormalizationRef.: H. Yamada et
al. NF 45 (2005)
-
HDLIDHelical Diverter (HD)Local Island Diverter
(LID)TemperatureDensityRadial Electric Field By GSRAKE codeClear
difference of density profiles are observed between LID and
HDHOLLOWFLAT
-
Enhanced particle transport is observed on LID This is good
material to study role of turbulence on particle
confinementsLID,HD
-
Electromagnetic GK mode equation[1] J.B.Taylor, et al., Plasma
Physics 10, 479 (1968)[2] G.Rewoldt, et al., Phys. Fluids 25, 480
(1982) Collisionless F0=FM E0=0
-
(kthi=0.5)ITG results in HD/LID
configurationsRelativetemperaturegradientRelativedensitygradient
ITG growth rate is larger in LID than in HD, and unstable range is
also broader in LID. This is reasonable just because 1/LT is larger
in LID. - The value of growth rate can be related to the value of
T. - But, the unstable range should be only related to 1/LT, i.e.,
large f() of T=T0f(), not large T0, is relevant. The effects of
1/Ln or on ITG growth rate seems weak compared to 1/LT.LIDHDa
- Neoclassical Er shearing rate is insufficient to suppress the
ITG growth rate.Linear growth rate .vs. Er shearing
rateHeuristically the condition, lin(Er=0)
-
Comparison of i-dia branch amplitude and ITG growth
rateAmplitude in i-dia branch (edge) scales with calculated ITG
growth rate.Profiles of growth rate and observed amplitude are
similar.HDLIDLarge particle transportsmall particle transport
-
Calculation procedure7/15
-
Dynamics of raw signals of 1-D PCI system5/15