transport-driven scrape-off layer flows, the role of the...
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Transport-driven scrape-off layer flows,the role of the X-point
J.E. Rice, A.E. Hubbard, J.W. Hughes, M. Greenwald, R. Granetz, I. Hutchinson, J. Irby, Y. Lin, B. Lipschultz, E.S. Marmar,K. Marr, D. Mossessian, R. Parker, W. Rowan, N. Smick, J.A. Snipes,
J.L. Terry, S.M. Wolfe, S.J. Wukitch and the Alcator C-Mod Team
AlcatorC-Mod
and connections to the L-H power thresholdin Alcator C-Mod
Presented by B. LaBombard
Key contributors:
Presented at the 32nd EPS Plasma Physics Conference Tarragona, Spain
27 June - 1 July, 2005
AlcatorC-Mod
A leading paradigm for L-H transition physics involves plasma flow shear...yet, a compelling explanation for x-point sensitivity has been elusive
Motivation: The input power required to attain a High confinement mode in a tokamak (H-mode) depends on magnetic topology...
...a factor of ~2 higher power is typically required when Bx—B points away versus toward the active x-point (dating back to ASDEX)
†Nucl. Fusion 44 (2004) 1047, Phys. Plasmas 12 (2005) 056111.
AlcatorC-Mod
A leading paradigm for L-H transition physics involves plasma flow shear...yet, a compelling explanation for x-point sensitivity has been elusive
Recent results from Alcator C-Mod suggest an (unexpected) explanationfor the topology-dependence of the L-H power threshold†:
Motivation: The input power required to attain a High confinement mode in a tokamak (H-mode) depends on magnetic topology...
...a factor of ~2 higher power is typically required when Bx—B points away versus toward the active x-point (dating back to ASDEX)
transport-driven plasma flows in the scrape-off-layer...
...and the flow boundary conditions that they impose (X-point dependent) on the confined plasma
†Nucl. Fusion 44 (2004) 1047, Phys. Plasmas 12 (2005) 056111.
AlcatorC-Mod
Focus of this talk:
Key experimental observations...
A leading paradigm for L-H transition physics involves plasma flow shear...yet, a compelling explanation for x-point sensitivity has been elusive
Recent results from Alcator C-Mod suggest an (unexpected) explanationfor the topology-dependence of the L-H power threshold†:
Motivation: The input power required to attain a High confinement mode in a tokamak (H-mode) depends on magnetic topology...
...a factor of ~2 higher power is typically required when Bx—B points away versus toward the active x-point (dating back to ASDEX)
transport-driven plasma flows in the scrape-off-layer...
...and the flow boundary conditions that they impose (X-point dependent) on the confined plasma
transport-driven flows in the SOL connection to magnetic X-point topology, toroidal plasma rotation
...and the L-H threshold
†Nucl. Fusion 44 (2004) 1047, Phys. Plasmas 12 (2005) 056111.
Transport-DrivenScrape-off Layer Flows
Outline of Talk
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
L-H Thresholds & Flowsin other topologies
near-sonic// flows ballooning-like
transportballooning-like transport drive G^
Transport-DrivenScrape-off Layer Flows
Outline of Talk
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
L-H Thresholds & Flowsin other topologies
Transport-DrivenScrape-off Layer Flows
G^
Flow Boundary Condition on Confined Plasma
=> x-point dependent toroidal rotation of confined plasma
DVf DVfIp
BT
co-currentrotation drive
counter-currentrotation drive
DVf DVfIp
BT
co-currentrotation drive
counter-currentrotation drive
Outline of Talk
Connection to X-point Sensitivity of L-H Threshold
L-H Thresholds & Flowsin other topologies
...via topology-dependent toroidal plasma rotation
Transport-DrivenScrape-off Layer Flows
G^
Flow Boundary Condition on Confined Plasma
DVf DVfIp
BT
co-currentrotation drive
counter-currentrotation drive
DVf DVfIp
BT
co-currentrotation drive
counter-currentrotation drive
Connection to X-point Sensitivity of L-H Threshold
Outline of Talk
L-H Thresholds & Flowsin other topologies
=
Lower-limited and lower-null dischargeshave same L-H power thresholds=> SOL flow pattern may play role
Transport-DrivenScrape-off Layer Flows
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
L-H Thresholds & Flowsin other topologies
Outline of Talk
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
OuterScanningProbeInner
ScanningProbe
VerticalScanningProbe
Diagnostics:
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
Lower Single Null
IpBT
Bx—B
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
Upper Single Null
IpBT
Bx—B
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
Double Null
IpBT
Bx—B
0510 0
0510 0
AlcatorC-Mod
Evidence for Cross-field Transport Asymmetries.... ...Driving Near-Sonic Flows in Inner SOL
0 5 1000.1
1.0
10.0
100.0
0 5 1000.0
0.1
0.2
0.3
0.4
0 5 100-50
-25
0
25
50
0
-25
0
25
Outer SOL
1020
eV
m-3
Distance from Separatrix (mm)
10
100
ElectronPressure
RMS Jsat/<Jsat>
1
10
100
0
0.1
0.2
0.3
510 0
-50
-25
0
25
50
Inner SOL
Parallel FlowVelocity (km/s)
Fluctuations
0510 0
0510 0
AlcatorC-Mod
Evidence for Cross-field Transport Asymmetries.... ...Driving Near-Sonic Flows in Inner SOL
0 5 1000.1
1.0
10.0
100.0
0 5 1000.0
0.1
0.2
0.3
0.4
0 5 100-50
-25
0
25
50
0
-25
0
25
Outer SOL
1020
eV
m-3
Distance from Separatrix (mm)
10
100
ElectronPressure
RMS Jsat/<Jsat>
1
10
100
0
0.1
0.2
0.3
510 0
-50
-25
0
25
50
Inner SOL
Parallel FlowVelocity (km/s)
Inner SOL plasma 'disappears' in Double Null LnT reduced by factor of 4
Fluctuations
0510 0
0510 0
AlcatorC-Mod
Evidence for Cross-field Transport Asymmetries.... ...Driving Near-Sonic Flows in Inner SOL
Fluctuation levels persistentlylower on Inner SOL
0 5 1000.1
1.0
10.0
100.0
0 5 1000.0
0.1
0.2
0.3
0.4
0 5 100-50
-25
0
25
50
0
-25
0
25
Outer SOL
1020
eV
m-3
Distance from Separatrix (mm)
10
100
ElectronPressure
RMS Jsat/<Jsat>
1
10
100
0
0.1
0.2
0.3
510 0
-50
-25
0
25
50
Inner SOL
Parallel FlowVelocity (km/s)
Consistent with low ^ transportin inner SOL
Inner SOL plasma 'disappears' in Double Null LnT reduced by factor of 4
Fluctuations
0510 0
0510 0
AlcatorC-Mod
Evidence for Cross-field Transport Asymmetries.... ...Driving Near-Sonic Flows in Inner SOL
Fluctuation levels persistentlylower on Inner SOL
0 5 1000.1
1.0
10.0
100.0
0 5 1000.0
0.1
0.2
0.3
0.4
0 5 100-50
-25
0
25
50
0
-25
0
25
Outer SOL
1020
eV
m-3
Distance from Separatrix (mm)
10
100
ElectronPressure
RMS Jsat/<Jsat>
1
10
100
0
0.1
0.2
0.3
510 0
-50
-25
0
25
50
Inner SOL
Parallel FlowVelocity (km/s)
Consistent with low ^ transportin inner SOL
Near-sonic // flows on Inner SOL
Inner SOL plasma 'disappears' in Double Null LnT reduced by factor of 4
Fluctuations
Always directed from outer to inner SOL in upper and lower-null, but ~stagnant in double-null
0510 0
0510 0
AlcatorC-Mod
Evidence for Cross-field Transport Asymmetries.... ...Driving Near-Sonic Flows in Inner SOL
Fluctuation levels persistentlylower on Inner SOL
Plasma exists on inner SOL because it flows along field lines from outer SOL
0 5 1000.1
1.0
10.0
100.0
0 5 1000.0
0.1
0.2
0.3
0.4
0 5 100-50
-25
0
25
50
0
-25
0
25
Outer SOL
1020
eV
m-3
Distance from Separatrix (mm)
10
100
ElectronPressure
RMS Jsat/<Jsat>
1
10
100
0
0.1
0.2
0.3
510 0
-50
-25
0
25
50
Inner SOL
Parallel FlowVelocity (km/s)
Consistent with low ^ transportin inner SOL
Near-sonic // flows on Inner SOL
Inner SOL plasma 'disappears' in Double Null LnT reduced by factor of 4
Fluctuations
Always directed from outer to inner SOL in upper and lower-null, but ~stagnant in double-null
0510 0
0510 0
AlcatorC-Mod
Evidence for Cross-field Transport Asymmetries.... ...Driving Near-Sonic Flows in Inner SOL
Fluctuation levels persistentlylower on Inner SOL
Plasma exists on inner SOL because it flows along field lines from outer SOL
0 5 1000.1
1.0
10.0
100.0
0 5 1000.0
0.1
0.2
0.3
0.4
0 5 100-50
-25
0
25
50
0
-25
0
25
Outer SOL
1020
eV
m-3
Distance from Separatrix (mm)
10
100
ElectronPressure
RMS Jsat/<Jsat>
1
10
100
0
0.1
0.2
0.3
510 0
-50
-25
0
25
50
Inner SOL
Parallel FlowVelocity (km/s)
Outer SOL flows weaker, co-current, appear modulated by topology...
Consistent with low ^ transportin inner SOL
Near-sonic // flows on Inner SOL
Inner SOL plasma 'disappears' in Double Null LnT reduced by factor of 4
Fluctuations
Always directed from outer to inner SOL in upper and lower-null, but ~stagnant in double-null
Toroidal Distance (cm)
Ver
tica
l (cm
)
-10 0 10 20-20-6
6
0
Upper Null Discharge
Toroidal Distance (cm)
Ver
tica
l (cm
)-10 0 10 20-20
-6
6
0
Lower Null Discharge
Magnetic Field Line
Direction of Flow
Magnetic Field Line
Direction of Flow
AlcatorC-Mod
CH4 Puff Camera
Plasma flow direction depends on Upper/Lower Null topology,identical to that seen by Inner Scanning Probe
Similar patterns of strong Inner SOL flows are evident in other devices:
Data from C+1 "plumes"at inner midplane location†
C+1 light,515 nm
†D. Jablonski, et al., J. Nucl Mater. 241-243 (1997) 782.
Gas Injection Experiments: Also Reveal Strong Inner SOL Flows, Closely Aligned with Magnetic Field Lines
JET: Mach probe data, inner div. carbon flakes, 13C transport experimentsDIII-D: 13C transport experiments
AlcatorC-Mod
Probe Data can be Mapped onto a "Flux-Tube Coordinate", S,Revealing Transport-Driven Component of Parallel Flow
IpBT0
0.250.75
0.5
1 S
0
0.25
0.5
0.75
1 S
Lower Null Upper Null
Definition of flux-tube coordinate, S
AlcatorC-Mod
Probe Data can be Mapped onto a "Flux-Tube Coordinate", S,Revealing Transport-Driven Component of Parallel Flow
r = 4 mm
0
10
20
1020
eV
m-3
Electron Pressure, nTe
0.0 0.5 1.0
0
1
Mac
h#
Mach Number, M//
Normalized distance along field line, S0.25 0.75
Outer SOL Inner SOL
Data from matched Lower-Nulland Upper-Null discharges
0
10
20 nTe(1+ M//2/2)
1020
eV
m-3
IpBT0
0.250.75
0.5
1 S
0
0.25
0.5
0.75
1 S
Lower Null Upper Null
Definition of flux-tube coordinate, S
AlcatorC-Mod
Probe Data can be Mapped onto a "Flux-Tube Coordinate", S,Revealing Transport-Driven Component of Parallel Flow
r = 4 mm
0
10
20
1020
eV
m-3
Electron Pressure, nTe
0.0 0.5 1.0
0
1
Mac
h#
Mach Number, M//
Normalized distance along field line, S0.25 0.75
Outer SOL Inner SOL
Data from matched Lower-Nulland Upper-Null discharges
Lower nTe on Inner SOL
0
10
20 nTe(1+ M//2/2)
1020
eV
m-3
IpBT0
0.250.75
0.5
1 S
0
0.25
0.5
0.75
1 S
Lower Null Upper Null
Definition of flux-tube coordinate, S
AlcatorC-Mod
Probe Data can be Mapped onto a "Flux-Tube Coordinate", S,Revealing Transport-Driven Component of Parallel Flow
r = 4 mm
0
10
20
1020
eV
m-3
Electron Pressure, nTe
0.0 0.5 1.0
0
1
Mac
h#
Mach Number, M//
Normalized distance along field line, S0.25 0.75
Outer SOL Inner SOL
Data from matched Lower-Nulland Upper-Null discharges
Lower nTe on Inner SOL
Toroidal rotation, Pfirsch-Schlüter flows, ... ...appear as offsets to average of +
0
10
20 nTe(1+ M//2/2)
1020
eV
m-3
~ transport-driven// flow component
Transport-driven parallel flow from Outer to Inner SOL
IpBT0
0.250.75
0.5
1 S
0
0.25
0.5
0.75
1 S
Lower Null Upper Null
Definition of flux-tube coordinate, S
AlcatorC-Mod
Probe Data can be Mapped onto a "Flux-Tube Coordinate", S,Revealing Transport-Driven Component of Parallel Flow
r = 4 mm
0
10
20
1020
eV
m-3
Electron Pressure, nTe
0.0 0.5 1.0
0
1
Mac
h#
Mach Number, M//
Normalized distance along field line, S0.25 0.75
Outer SOL Inner SOL
Data from matched Lower-Nulland Upper-Null discharges
Lower nTe on Inner SOL
Toroidal rotation, Pfirsch-Schlüter flows, ... ...appear as offsets to average of +
0
10
20 nTe(1+ M//2/2)
1020
eV
m-3
Thermal + flow energy ~constant
~ transport-driven// flow component
Transport-driven parallel flow from Outer to Inner SOL
=> implies a free-streaming flow response
IpBT0
0.250.75
0.5
1 S
0
0.25
0.5
0.75
1 S
Lower Null Upper Null
Definition of flux-tube coordinate, S
AlcatorC-Mod
Probe Data can be Mapped onto a "Flux-Tube Coordinate", S,Revealing Transport-Driven Component of Parallel Flow
r = 4 mm
0
10
20
1020
eV
m-3
Electron Pressure, nTe
0.0 0.5 1.0
0
1
Mac
h#
Mach Number, M//
Normalized distance along field line, S0.25 0.75
Outer SOL Inner SOL
Data from matched Lower-Nulland Upper-Null discharges
Lower nTe on Inner SOL
Toroidal rotation, Pfirsch-Schlüter flows, ... ...appear as offsets to average of +
0
10
20 nTe(1+ M//2/2)
1020
eV
m-3
Thermal + flow energy ~constant
~ transport-driven// flow component
Transport-driven parallel flow from Outer to Inner SOL
=> implies a free-streaming flow response
IpBT
Lower Null Upper Null
Implied transport-driven flow pattern
co-currentV//f G^ G^
counter-current V//f
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
Lower Single Null
Toroidal RotationInferred from Ar17+
X-ray Doppler
OuterScanningProbeInner
ScanningProbe
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
Double Null
Toroidal RotationInferred from Ar17+
X-ray Doppler
OuterScanningProbeInner
ScanningProbe
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
Upper Single Null
Toroidal RotationInferred from Ar17+
X-ray Doppler
OuterScanningProbeInner
ScanningProbe
-15 -10 -5 0 5 10 150
-60
-30
0
30
-15 -10 -5 0 5 10 150-10
0
10
20
-15 -10 -5 0 5 10 150
Distance Between Primary andSecondary Separatrices (mm)
-40
-30
-20
r = 2 mm
r = 1 mm
Inner Probe
Outer Probe
Core Ar17+Doppler
To
roid
al V
elo
city
(km
s-1
)AlcatorC-Mod
X-point Topology Sets Magnitude and Direction of Transport-Driven SOL Flows => Core Plasma Rotation is Affected
-15 -10 -5 0 5 10 150
-60
-30
0
30
-15 -10 -5 0 5 10 150-10
0
10
20
-15 -10 -5 0 5 10 150
Distance Between Primary andSecondary Separatrices (mm)
-40
-30
-20
r = 2 mm
r = 1 mm
Inner Probe
Outer Probe
Core Ar17+Doppler
To
roid
al V
elo
city
(km
s-1
)AlcatorC-Mod
X-point Topology Sets Magnitude and Direction of Transport-Driven SOL Flows => Core Plasma Rotation is Affected
Toroidal projections of flows nearseparatrix shift toward counter-currentin sequence:lower => double => upper-null
-15 -10 -5 0 5 10 150
-60
-30
0
30
-15 -10 -5 0 5 10 150-10
0
10
20
-15 -10 -5 0 5 10 150
Distance Between Primary andSecondary Separatrices (mm)
-40
-30
-20
r = 2 mm
r = 1 mm
Inner Probe
Outer Probe
Core Ar17+Doppler
To
roid
al V
elo
city
(km
s-1
)AlcatorC-Mod
X-point Topology Sets Magnitude and Direction of Transport-Driven SOL Flows => Core Plasma Rotation is Affected
Toroidal projections of flows nearseparatrix shift toward counter-currentin sequence:lower => double => upper-null
Central plasma toroidal rotationcorrespondingly shifts more towardcounter-current direction
-15 -10 -5 0 5 10 150
-60
-30
0
30
-15 -10 -5 0 5 10 150-10
0
10
20
-15 -10 -5 0 5 10 150
Distance Between Primary andSecondary Separatrices (mm)
-40
-30
-20
r = 2 mm
r = 1 mm
Inner Probe
Outer Probe
Core Ar17+Doppler
To
roid
al V
elo
city
(km
s-1
)AlcatorC-Mod
X-point Topology Sets Magnitude and Direction of Transport-Driven SOL Flows => Core Plasma Rotation is Affected
Toroidal projections of flows nearseparatrix shift toward counter-currentin sequence:lower => double => upper-null
Central plasma toroidal rotationcorrespondingly shifts more towardcounter-current direction
Toroidal velocity change is largest oninner SOL=> suggests inner SOL flow is responsible for change in rotation of confined plasma
18 km/s
12 km/s
50 km/s
DV
-15 -10 -5 0 5 10 150
-60
-30
0
30
-15 -10 -5 0 5 10 150-10
0
10
20
-15 -10 -5 0 5 10 150
Distance Between Primary andSecondary Separatrices (mm)
-40
-30
-20
r = 2 mm
r = 1 mm
Inner Probe
Outer Probe
Core Ar17+Doppler
To
roid
al V
elo
city
(km
s-1
)AlcatorC-Mod
X-point Topology Sets Magnitude and Direction of Transport-Driven SOL Flows => Core Plasma Rotation is Affected
Toroidal projections of flows nearseparatrix shift toward counter-currentin sequence:lower => double => upper-null
Central plasma toroidal rotationcorrespondingly shifts more towardcounter-current direction
Toroidal velocity change is largest oninner SOL=> suggests inner SOL flow is responsible for change in rotation of confined plasma
18 km/s
12 km/s
50 km/s
DV
~5 mm change in x-point balanceis sufficient to reverse flows=> consistent with scale length of pressure gradients near separatrix
-15 -10 -5 0 5 10 150
-60
-30
0
30
-15 -10 -5 0 5 10 150-10
0
10
20
-15 -10 -5 0 5 10 150
Distance Between Primary andSecondary Separatrices (mm)
-40
-30
-20
r = 2 mm
r = 1 mm
Inner Probe
Outer Probe
Core Ar17+Doppler
To
roid
al V
elo
city
(km
s-1
)AlcatorC-Mod
X-point Topology Sets Magnitude and Direction of Transport-Driven SOL Flows => Core Plasma Rotation is Affected
Toroidal projections of flows nearseparatrix shift toward counter-currentin sequence:lower => double => upper-null
Central plasma toroidal rotationcorrespondingly shifts more towardcounter-current direction
\Transport-driven SOL flows impose boundary conditions on confined plasma
Toroidal velocity change is largest oninner SOL=> suggests inner SOL flow is responsible for change in rotation of confined plasma
18 km/s
12 km/s
50 km/s
DV
~5 mm change in x-point balanceis sufficient to reverse flows=> consistent with scale length of pressure gradients near separatrix
IpBT
V//f V//f
^ transport-driven parallel SOL flows
AlcatorC-Mod
If Transport-Driven SOL Flow/Rotation Paradigm is Correct,Radial Electric Fields in SOL Should Depend on X-point Topology
Ballooning-like transport leads to a helical flowcomponent in the SOL with net volume-averagedtoroidal momentum: co-current for lower null, counter-current for upper null
IpBT
V//f V//f
^ transport-driven parallel SOL flows
DVfDVf
IpBT
Influence on plasma rotation
AlcatorC-Mod
If Transport-Driven SOL Flow/Rotation Paradigm is Correct,Radial Electric Fields in SOL Should Depend on X-point Topology
Ballooning-like transport leads to a helical flowcomponent in the SOL with net volume-averagedtoroidal momentum: co-current for lower null, counter-current for upper null
Being free to rotate only in the toroidal direction,the confined plasma acquires a correspondingco-current or counter-current rotation increment
IpBT
V//f V//f
^ transport-driven parallel SOL flows
DVfDVfEr
DErxBq
IpBT
Influence on plasma rotation
Erweaker
DErxBq
stronger
AlcatorC-Mod
If Transport-Driven SOL Flow/Rotation Paradigm is Correct,Radial Electric Fields in SOL Should Depend on X-point Topology
Ballooning-like transport leads to a helical flowcomponent in the SOL with net volume-averagedtoroidal momentum: co-current for lower null, counter-current for upper null
Being free to rotate only in the toroidal direction,the confined plasma acquires a correspondingco-current or counter-current rotation increment
Via momentum coupling across separatrix,a topology-dependent toroidal rotationcomponent, Er/Bq, should appear in the SOL
=> Stronger Er in SOL for lower null=> Weaker Er in SOL for upper null
AlcatorC-Mod
Plasma Potentials Near Separatrix Systematically Increasein the Sequence: Upper, Double, Lower-Null
0 5 1000
20
40
60
0 5 100
30
50
70
0 5 10030
50
70
r (mm)
Inner Probe
Est
imat
ed P
lasm
a P
ote
nti
al (
volt
s)
Vertical Probe
Outer Probe
Double NullLower Null
Upper Null
More positive Er in SOL near separatrix in Lower-Null
Caution: Accuracy of potential profile shape is uncertain!Plasma potential profiles estimated from sheath potential drop
DEr/Bq ~ 8 km/s, ~consistent with measured change in parallel (toroidal) flow in SOL
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
IpBT
DVfEr
DErxBq
strongerDVf
DErxBq
Erweaker
stronger weaker
Bx—B
SOL flows => topology-dependent rotation (and Er) near separatrix
SOL widths same; Rotation fi 0 near wall => Implies toroidal velocity shear (ErxB shear) near separatrix is:
=> Lower L-H power threshold when Bx—B points toward x-point!
L-H transition is thought to involvevelocity shear suppression of plasma turbulence
Novel Hypothesis:
1
2
1020
m-3
-40
0
40
km s
-1
Ar17+ Toroidal Velocity
eV
400
200
0
0123
MW
ICRF Power
Line Averaged Density
Electron Temperature
Max|—pe/ne| from TS100
10
keV
m-1
-0.2 -0.1 0.0 0.1L-H transition time (s)
in region 0.95 < y < 1
ECE:TS:y=0.95
AlcatorC-Mod
L-H Transition Coincides with Plasma Rotation AttainingRoughly the Same Value, Independent of Topology
Input power level to attain L Hdepends on x-point topology
Bx—B
Ohmic+ICRF => no momentum input
1
2
1020
m-3
-40
0
40
km s
-1
Ar17+ Toroidal Velocity
eV
400
200
0
0123
MW
ICRF Power
Line Averaged Density
Electron Temperature
Max|—pe/ne| from TS100
10
keV
m-1
-0.2 -0.1 0.0 0.1L-H transition time (s)
in region 0.95 < y < 1
ECE:TS:y=0.95
AlcatorC-Mod
L-H Transition Coincides with Plasma Rotation AttainingRoughly the Same Value, Independent of Topology
Input power level to attain L Hdepends on x-point topology
Edge Te and electron pressure gradientsat L H transition also different
Bx—B
Ohmic+ICRF => no momentum input
1
2
1020
m-3
-40
0
40
km s
-1
Ar17+ Toroidal Velocity
eV
400
200
0
0123
MW
ICRF Power
Line Averaged Density
Electron Temperature
Max|—pe/ne| from TS100
10
keV
m-1
-0.2 -0.1 0.0 0.1L-H transition time (s)
in region 0.95 < y < 1
ECE:TS:y=0.95
AlcatorC-Mod
L-H Transition Coincides with Plasma Rotation AttainingRoughly the Same Value, Independent of Topology
Input power level to attain L Hdepends on x-point topology
Edge Te and electron pressure gradientsat L H transition also different
Plasma rotation during ohmic phasestarts out counter-current in USN....
Bx—B
Ohmic+ICRF => no momentum input
---- SOL flow boundary condition!
1
2
1020
m-3
-40
0
40
km s
-1
Ar17+ Toroidal Velocity
eV
400
200
0
0123
MW
ICRF Power
Line Averaged Density
Electron Temperature
Max|—pe/ne| from TS100
10
keV
m-1
-0.2 -0.1 0.0 0.1L-H transition time (s)
in region 0.95 < y < 1
ECE:TS:y=0.95
AlcatorC-Mod
L-H Transition Coincides with Plasma Rotation AttainingRoughly the Same Value, Independent of Topology
Input power level to attain L Hdepends on x-point topology
Edge Te and electron pressure gradientsat L H transition also different
Plasma rotation during ohmic phasestarts out counter-current in USN....
Bx—B
....but ramps toward co-current aspressure gradients build up
similar rotation at the L H transition!
Ohmic+ICRF => no momentum input
---- SOL flow boundary condition!
1 2 3 4
-40
0
40
0
20 r = 2 mm
1 4
1 2 3 4
0
20
Total Input Power (MW)
r = 2 mm
Lower NullUpper Null
L H(at transition)
AlcatorC-Mod
Two Elements Combine to Affect Toroidal Rotation: SOL Flows (~Topology) + Plasma Pressure (~Power)
Vertical Probe
Outer Probe
Core Ar17+ Doppler
Toroidal Velocities
km s
-1
DV
Transport-driven SOL flows impose acounter-current toroidal rotation offset in Upper Null
1 2 3 4
-40
0
40
0
20 r = 2 mm
1 4
1 2 3 4
0
20
Total Input Power (MW)
r = 2 mm
Lower NullUpper Null
L H(at transition)
AlcatorC-Mod
Two Elements Combine to Affect Toroidal Rotation: SOL Flows (~Topology) + Plasma Pressure (~Power)
Vertical Probe
Outer Probe
Core Ar17+ Doppler
Toroidal Velocities
km s
-1
Transport-driven SOL flows impose acounter-current toroidal rotation offset in Upper Null
Toroidal rotation also depends on~plasma pressure, ramping towardsco-current direction as input powerincreases
Slope:~14 km s-1 MW-1
Slope:~8 km s-1 MW-1
Slope:~8 km s-1 MW-1
- Effect extends to separatrix; seen by probes in SOL 1 2 3 4
-40
0
40
0
20 r = 2 mm
1 4
1 2 3 4
0
20
Total Input Power (MW)
r = 2 mm
Lower NullUpper Null
L H(at transition)
AlcatorC-Mod
Two Elements Combine to Affect Toroidal Rotation: SOL Flows (~Topology) + Plasma Pressure (~Power)
Vertical Probe
Outer Probe
Core Ar17+ Doppler
Toroidal Velocities
km s
-1
Transport-driven SOL flows impose acounter-current toroidal rotation offset in Upper Null
Toroidal rotation also depends on~plasma pressure, ramping towardsco-current direction as input powerincreases
Slope:~14 km s-1 MW-1
Slope:~8 km s-1 MW-1
Slope:~8 km s-1 MW-1
- Effect extends to separatrix; seen by probes in SOL 1 2 3 4
-40
0
40
0
20 r = 2 mm
1 4
1 2 3 4
0
20
Total Input Power (MW)
r = 2 mm
Lower NullUpper Null
L H(at transition)
AlcatorC-Mod
Two Elements Combine to Affect Toroidal Rotation: SOL Flows (~Topology) + Plasma Pressure (~Power)
Vertical Probe
Outer Probe
Core Ar17+ Doppler
Toroidal Velocities
km s
-1
But, a similar relationship between co-current core rotation and plasma pressureis seen during the H-mode phase...
Theories:
- sub-neoclassical transport
- turbulence
B. Coppi, Nucl. Fusion 42, 1 (2002).
A.L. Rogister, et al., Nucl. Fusion 42, 1144 (2002).
K.C. Shaing, Phys. Rev. Lett. 86, 640 (2001)
=> Mechanism for this not resolved
... J. Rice, et al., Nucl. Fusion 41, 277 (2001)
L-H Transition occurs at nominally thesame toroidal rotation speed
=> Upper Null requires more input power
Transport-driven SOL flows impose acounter-current toroidal rotation offset in Upper Null
Toroidal rotation also depends on~plasma pressure, ramping towardsco-current direction as input powerincreases
- Effect extends to separatrix; seen by probes in SOL 1 2 3 4
-40
0
40
0
20 r = 2 mm
1 4
1 2 3 4
0
20
Total Input Power (MW)
r = 2 mm
Lower NullUpper Null
L H(at transition)
AlcatorC-Mod
Two Elements Combine to Affect Toroidal Rotation: SOL Flows (~Topology) + Plasma Pressure (~Power)
Vertical Probe
Outer Probe
Core Ar17+ Doppler
Toroidal Velocities
km s
-1
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
Lower Single Null
IpBT
Bx—B
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
Inner Divertor 'Nose' Grazing
IpBT
Bx—B
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
Inner Divertor 'Nose' Limited
IpBT
Bx—B
Outline of Talk
Transport-DrivenScrape-off Layer Flows
L-H Thresholds & Flowsin other topologies
Flow Boundary Condition on Confined Plasma
Connection to X-point Sensitivity of L-H Threshold
Inner Wall Limited
IpBT
Bx—B
0
1
2
1020
m-3
0
1
2
MW
3
5
7
a.u
.
Da
0.6 0.8 1.0 1.2 1.4 1.6Time (s)
Line AveragedDensity
ICRF Power0.6 0.8 1.0 1.2 1.4 1.6
0.6 0.8 1.0 1.2 1.4 1.6
AlcatorC-Mod
Lower Limited discharges have L-H power thresholds that are virtually identical to Lower Single Null discharges!
Does not matter if lower X-point is centered in divertor, grazing the wall,or buried inside the vacuum vessel structure
What common element causes L-H threshold to be identical?
0510 00.1
1.0
10.0
100. 0
0510 00.0
0.1
0.2
0.3
0.4
-50
-25
0
25
50
0
10
100
10
00
0.1
0.2
-50
1
10
100
0
0.1
0.2
0.3
-50
-25
0
25
50
Inner SOL
1020
eV
m-3
0510
AlcatorC-Mod
Lower-Limited and Lower X-point discharges have identical SOL flow patterns....perhaps a key commonality
ElectronPressure
Fluctuations
Distance from Separatrix (mm)
-25
0
25
Outer SOL
0 5 100
0 5 100
10
10
0 5 100
RMS Jsat/<Jsat>
Parallel FlowVelocity (km/s)
0510 00.1
1.0
10.0
100. 0
0510 00.0
0.1
0.2
0.3
0.4
-50
-25
0
25
50
0
10
100
10
00
0.1
0.2
-50
1
10
100
0
0.1
0.2
0.3
-50
-25
0
25
50
Inner SOL
1020
eV
m-3
0510
AlcatorC-Mod
Lower-Limited and Lower X-point discharges have identical SOL flow patterns....perhaps a key commonality
ElectronPressure
Fluctuations
Distance from Separatrix (mm)
-25
0
25
Outer SOL
0 5 100
0 5 100
10
10
0 5 100
RMS Jsat/<Jsat>
Parallel FlowVelocity (km/s)
Pressure profiles near separatrix& fluctuation asymmetries are similar in all topologies
0510 00.1
1.0
10.0
100. 0
0510 00.0
0.1
0.2
0.3
0.4
-50
-25
0
25
50
0
10
100
10
00
0.1
0.2
-50
1
10
100
0
0.1
0.2
0.3
-50
-25
0
25
50
Inner SOL
1020
eV
m-3
0510
AlcatorC-Mod
Lower-Limited and Lower X-point discharges have identical SOL flow patterns....perhaps a key commonality
ElectronPressure
Fluctuations
Distance from Separatrix (mm)
-25
0
25
Outer SOL
0 5 100
0 5 100
10
10
0 5 100
RMS Jsat/<Jsat>
Parallel FlowVelocity (km/s)
Pressure profiles near separatrix& fluctuation asymmetries are similar in all topologies
Lower-Limited, Grazing, Lower X-pointhave co-current inner SOL flows...Upper X-point => counter-current
0510 00.1
1.0
10.0
100. 0
0510 00.0
0.1
0.2
0.3
0.4
-50
-25
0
25
50
0
10
100
10
00
0.1
0.2
-50
1
10
100
0
0.1
0.2
0.3
-50
-25
0
25
50
Inner SOL
1020
eV
m-3
0510
AlcatorC-Mod
Lower-Limited and Lower X-point discharges have identical SOL flow patterns....perhaps a key commonality
ElectronPressure
Fluctuations
Distance from Separatrix (mm)
-25
0
25
Outer SOL
0 5 100
0 5 100
10
10
0 5 100
RMS Jsat/<Jsat>
Parallel FlowVelocity (km/s)
Pressure profiles near separatrix& fluctuation asymmetries are similar in all topologies
Lower-Limited, Grazing, Lower X-pointhave co-current inner SOL flows...Upper X-point => counter-current
IpBT
SOL flow pattern defined by X-points and/or Limiter contact
co-currentV//f G^
Key commonality for L-H sensitivity?
=> same LH threshold
co-currentV//f G^
†Normalized to threshold scaling from Int. H-mode Threshold Database, J. Snipes, et al., PPCF 42, A299 (2000).
†
-20 -10 0 10 200.5
1.0
1.5
2.0
No
rmal
ized
inp
ut
po
wer
Normalized L-H Power Thresholdsfor Various Magnetic Topologies
D, Distance between primary and secondary separatrices or inner wall gap (mm)
AlcatorC-Mod
New Insight: Connection between magnetic topology and L-H threshold may be recast in terms of control of Inner SOL flows
-20 -10 0 10 200.5
1.0
1.5
2.0
No
rmal
ized
inp
ut
po
wer
Normalized L-H Power Thresholdsfor Various Magnetic Topologies
D, Distance between primary and secondary separatrices or inner wall gap (mm)
AlcatorC-Mod
New Insight: Connection between magnetic topology and L-H threshold may be recast in terms of control of Inner SOL flows
D parameterizes:
Lower x-point or Lower-Limited
Upper x-point or Upper-Limited
(2) Width of Inner SOL available for these flows
(1) Direction of transport-driven SOL flows in Inner SOL (negative = co-current)
-20 -10 0 10 200.5
1.0
1.5
2.0
No
rmal
ized
inp
ut
po
wer
Normalized L-H Power Thresholdsfor Various Magnetic Topologies
D, Distance between primary and secondary separatrices or inner wall gap (mm)
AlcatorC-Mod
New Insight: Connection between magnetic topology and L-H threshold may be recast in terms of control of Inner SOL flows
D parameterizes:
Lower x-point or Lower-Limited
Upper x-point or Upper-Limited
(2) Width of Inner SOL available for these flows
(1) Direction of transport-driven SOL flows in Inner SOL (negative = co-current)
Lower X-pt, Lower Grazing, Lower LimitedFavorable (co-current) Inner SOL flow => Lowest L-H thresholds
-20 -10 0 10 200.5
1.0
1.5
2.0
No
rmal
ized
inp
ut
po
wer
Normalized L-H Power Thresholdsfor Various Magnetic Topologies
D, Distance between primary and secondary separatrices or inner wall gap (mm)
AlcatorC-Mod
New Insight: Connection between magnetic topology and L-H threshold may be recast in terms of control of Inner SOL flows
D parameterizes:
Lower x-point or Lower-Limited
Upper x-point or Upper-Limited
(2) Width of Inner SOL available for these flows
(1) Direction of transport-driven SOL flows in Inner SOL (negative = co-current)
Lower X-pt, Lower Grazing, Lower LimitedFavorable (co-current) Inner SOL flow => Lowest L-H thresholds
Reduced Inner Gap, Double NullInner SOL flow blocked or balanced => Increased L-H thresholds|D| < ~5 mm, corresponds to flow change
-20 -10 0 10 200.5
1.0
1.5
2.0
No
rmal
ized
inp
ut
po
wer
Normalized L-H Power Thresholdsfor Various Magnetic Topologies
D, Distance between primary and secondary separatrices or inner wall gap (mm)
AlcatorC-Mod
New Insight: Connection between magnetic topology and L-H threshold may be recast in terms of control of Inner SOL flows
D parameterizes:
Lower x-point or Lower-Limited
Upper x-point or Upper-Limited
(2) Width of Inner SOL available for these flows
(1) Direction of transport-driven SOL flows in Inner SOL (negative = co-current)
Lower X-pt, Lower Grazing, Lower LimitedFavorable (co-current) Inner SOL flow => Lowest L-H thresholds
Reduced Inner Gap, Double NullInner SOL flow blocked or balanced => Increased L-H thresholds|D| < ~5 mm, corresponds to flow change
Upper NullUnfavorable (counter) Inner SOL flow => Highest L-H thresholds
-20 -10 0 10 200.5
1.0
1.5
2.0
No
rmal
ized
inp
ut
po
wer
Normalized L-H Power Thresholdsfor Various Magnetic Topologies
D, Distance between primary and secondary separatrices or inner wall gap (mm)
AlcatorC-Mod
New Insight: Connection between magnetic topology and L-H threshold may be recast in terms of control of Inner SOL flows
D parameterizes:
Lower x-point or Lower-Limited
Upper x-point or Upper-Limited
(2) Width of Inner SOL available for these flows
(1) Direction of transport-driven SOL flows in Inner SOL (negative = co-current)
Lower X-pt, Lower Grazing, Lower LimitedFavorable (co-current) Inner SOL flow => Lowest L-H thresholds
Reduced Inner Gap, Double NullInner SOL flow blocked or balanced => Increased L-H thresholds|D| < ~5 mm, corresponds to flow change
Upper NullUnfavorable (counter) Inner SOL flow => Highest L-H thresholds
Inner Wall-Limited - worst of all worlds?no Inner SOL flow, impurity susceptible => Highest L-H thresholds
AlcatorC-ModSummary
A cross field transport-driven plasmacirculation loop is evident in C-Mod
X-points and/or limiter contact points set the // flow direction
SOL flows impose a toroidal rotation boundary condition for confined plasmaX-point/limiter topology and toroidal rotation at boundary are linked!
IpBT
V//f V//f DVfDVf
Bx—B
ErDErxBq
Erweaker
DErxBq
stronger
near-sonic// flows ballooning-like
transportG^
=> Potential explanation for the topology dependence of the L-H power threshold
AlcatorC-ModSummary
L-H threshold studies with different x-point topologies support hypothesisthat SOL flows have a controlling influence
SOL flows impede co-current rotation with upper x-pointCorrespondingly, more input power (which promotes co-rotation) is required
L-H transition is coincident with toroidal rotation achieving similar level,independent of x-point topology
The role of magnetic topology in affecting L-H thresholds can be formulated in terms of the resultant flows in the Inner SOL
L-H Power Thresholds
Co-Current Inner SOL flows
1.0
1.5
2.0
-20 -10 0 10 20D (mm)
Counter-Current Inner SOL flows
No
rmal
ized
Po
wer
Same L-H power threshold
=
top related