Magnetic Fusion Power Development for Global Warming Suppression
Third PRC-US Magnetic Fusion Collaboration Workshop 18-19 May 2006
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Transcript of Third PRC-US Magnetic Fusion Collaboration Workshop 18-19 May 2006
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Third PRC-US Magnetic Fusion Collaboration Third PRC-US Magnetic Fusion Collaboration Workshop 18-19 May 2006Workshop 18-19 May 2006
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Plans and Results of the Texas
Collaboration with ASIPPLong history of collaboration between
the Fusion Research Center, Texas and the Institute of Plasma Physics, Hefei
Plans for HT-7 and EAST ECE -- Electron Cyclotron Emission radiometer for Te
CXRS -- Charge Exchange Recombination Spectroscopy for Ti and rotation
Expanded divertor
Results of Helimak project
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Spatial Coverage of ECE System on HT-7
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Schematic of the ECE diagnostic on HT-7
Lo Freq(GHz)
98.5 100.433
102.336
104.299
106.232
108.165
110.098
112.031
Hi Freq(GHz)
112 114 116 118 120 122 124 126
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ECE Data with position shift to obtain a
relative calibration.
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Te Profile (ECE)
• Relative calibration from shift is position position
• Absolute calibration form Thomson Scattering (central temperature)
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ECE Temperature Profile
• Shot 81535:
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EAST ECE System
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Proposed ECE Antenna for EAST• Diffraction limited spatial
resolution • Integrated hot calibration source
• Possible test of ITER prototype calibration source
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CXRS on HT-7 and EASTW. L. Rowan,1 Yuejiang Shi,2 June Huang,2
Huang He1, and B. N. Wan2
1Fusion Research Center, The University of Texas at Austin2Institute of Plasma Physics, Chinese Academy of Sciences
• DNB transferred to ASIPP and brought back into operation through common effort
• CXRS spectrometer and optics installed• Plans
–Develop CXRS analysis codes–Conduct transport experiments on HT-7–Transfer DNB to EAST–Transfer CXRS to EAST
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DNB, Component Mix, and
CXRS Viewing Range
€
0.25 ≤ r ≤ −0.07
0.93 ≤ ρ ≤ −0.26
CXRS view range
DNBHT-7
The beam has operated for one campaign with an useful density component mix E:E/2:E/3:E/18 = 10:26:49:15
The CXRS diagnostic is installed for the current campaign and is expected to provide Ti, v over the LFS of the plasma
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Divertor Projections
• Although ITER divertor may handle heat loads adequately, the divertor heat loads for the next-step reactor will exceed material limits: This is a show-stopper
• Other divertor configurations including radiating mantle and swept divertor will not scale to ITER or to a reactor
• Need an expanded divertor or other configuration
M. Kotschenreuther, P. M. Valanju, S. M. Mahajan, J. C. Wiley, M. Pekker Sherwood Fusion Theory Conference,
April, 2006
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Expanded Divertor for EAST
• A new configuration to reduce the heat load on the divertor plates
• Axisymmetric coils near the divertor plates expand the footprint of the intersection of the field lines with the divertor plates
• Divertor coil currents are comparable to other PF coil currents
• The first test of this idea is proposed for EAST. Use reduced plasma current and pulsed divertor coils as a proof of concept
• A concept could be presented in August at ASIPP
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An Experiment for EAST
• Energize coils in blue to yield flux expansion
• To prove the concept, use a set of coils with pulsed current just large enough to observe the expansion effect easily
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An Experiment for EAST
• Energize coils in blue to expand the green flux at the divertor plate (in the circle)
Flux Expansion Versus Divertor Coil Current
I = 0 kAexpansion = 2.2
I = 40 kAexpansion = 4.3
I = 80 kAexpansion = 10.3
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Helimak
Unique concept for a basic plasma experiment
Simple sheared cylindrical slab geometry
Device large compared with all scale lengths
Designed, engineered, and built by ASIPP
Operating successfully at Texas
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Helimak
Dimensionless test of drift-wave turbulence
Simple, but physical geometry (curvature)
Open field lines, but long ( up to ~1 km)
Test of flow shear stabilization of turbulence
Dimensionless model of SOL
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Helimak
Probe connections
Vacuum Vessel
Toroidal field coils
Vertical field coils
Microwave feed
Magnetron
Amplifiers and A/D
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Helimak
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Helimak
Helimak Dimensions and ParametersA Sheared Cylindrical Slab
<R> = 1.1 m ∆R = 1 mh = 2 mBT = 0.1 T Bv ≤ 0.01 TPulse ≤ 60 sPlasma source and heating: 6 kW ECH @ 2.45 GHzn ≤ 1011 cm-3 Te ~ 10 eVArgon, Heliumcs = 3 x 104 m/s (Argon) Vdrift = 100 m/s Vdiamagnetic = 103 m/sdrift-wave ~ 1 kHzConnection length: 10 m < L < 1000 m p (parallel loss) > 1 msProbe arrays in end plates provide vertical and full radial profilesIsolated end plates may apply radial electric fields: Vp ≤ ±100 Volts
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Helimak
0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6
Bias plate
0.77
0.82
0.87
0.92
ECH resonance radius
R (m)
Density Profiles for various ECH Resonant Radii
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Argon (shot# 402100062: 1 kW, 700 A, 15 ohms) U profile
-12
-7
-2
3
8
0 10 20 30 40 50 60 70 80 90
R - R inner [cm]
Te [eV], Vfl [V], n [10^16 m^-3] electron temperaturefloating potentialdensity
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Typical Density, Temperature, and Floating Potential Profiles
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0
0.5
1
0.6 0.8 1 1.2 1.4 1.6
Radial Profiles of Fluctuation Amplitude
∆n/n
R
(Various ECHResonant radii)
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0
20
40
60
80
100
120
0 2000 4000
Frequency Spectra
R=1.2Drift waves
in LFSgradient
R=1Coherent modeat density peak
(Hz)
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-5 -3 -1 1 3 5
Density PDF R=1.4 -- Low DensityLow median density with "blobs"
of high densityMaximum of density, coherent modeBimodal PDF typical of
harmonic oscillator
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Helimak
0
1
2
3
0 1000 2000 3000 4000
Phase
(Hz)
VPH=400 m/s
kρs~0.5
=1.2R
( - )Vertical Propagation Drift wave
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Helimak
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Helimak
Major Points
The Helimak provides a good example of a turbulence bifurcation (shear stabilization)
The stabilization is caused by j (not E)
The transition is binary, not gradual -- no intermediate states as threshold approached from either direction
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12341234BBhRiRoBRzφProbe
Helimak
Cross-section
Field lines terminate on isolated end plates
Biasing #2 plates with respect to others imposes radial electric field, current
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Helimak
Response to Negative BiasProbe n(t) across radial profile
Bias Reduced ∆n Reduced ∆n; increased <n>
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Helimak
Response to Positive BiasProbe n(t) across radial profile
Bias Reduced ∆nReduced ∆n; increased <n> Increased <n>
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Helimak
Response to Negative BiasProbe n(t) across radial profile
Bias Reduced ∆nIncreased <n>Helium
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Time History of a Bifurcation
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Negative Bias Positive Bias
Isat(t)
BiasVoltageCurrent
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Profile Changes at Bifurcation
-50 V
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
0.6 0.8 1 1.2 1.4 1.6R (m)
Profile of ∆n/n Reduction
Positive Bias
Negative Bias
Bias Plate(Various resonance radii)
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0 2000 4000 6000 8000
Γo = 1Γ- = 0.33
Γ+ = 0.53
( )Hz
Frequency-Resolved Particle Transport
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High Field Side
Low Field Side
Phase Velocity
Change with Bias
Larger changes for positive bias Equilibrium flow reversed by positive bias Negative bias adds to equilibrium flow
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Helimak
Inferred Velocity Shear Same |∂Vz/∂z| for ± bias ~104 s-1
Equilibrium V from potential profile
∆V with bias from ∆Vphase of turbulence
Rn(r)E x B equilibrium∆V for + Bias∆V for - Bias01100 700 m/s1400 1200 m/s4000 m/s200 m/sVz(-)Vz(+)
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Helimak
Velocity Shear vs.
Velocity shear ~104 s-1 comparable with shortest turbulence autocorrelation time
-0.2
0
0.2
0.4
0.6
0.8
1
0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016
Autocorrelation
Low field side c = 0.14 ms
High field side c = 0.7 msDensity
max c = 0.4 ms
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Helimak
Drive for Velocity Shear:E x B or j x B?
Plasma floating potentials and Er decrease at bifurcation,
despite large bias
Threshold voltages for positive and negative bias different
Threshold currents for positive and negative bias similar
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0
20
40
60
50 1000
5
10
15
Connection Length
Threshold Conditions -- Argon
-V
+V
-I
+I
No Transition
(V) (A)
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10
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0.75 0.8 0.85 0.9 0.95 10
5
10
+V
-V
+I
-I
Threshold Conditions -- Helium
RECH
No Transition
(V)(A)
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12341234Rzφ Flow of Bias Current , From plates j||jr across field drives sheared
vz flow
++------
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Biasing drives current from+ plates into plasma along field lines, across the field lines, and back out alongfield lines to the - plates.
For typical threshold currents,<jr> ~ 0.1 A/m2
j X B = dp/dt ~ p/p
p = mnVz
For p ~ 1 ms, Vzmax ~ 2 km/sShear, ∂vz/∂r ~ 104 s-1
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Helimak
Drive for Velocity Shear:E x B or j x B?
Plasma floating potentials and Er decrease at bifurcation
Threshold voltages for positive and negative bias different
Threshold currents for positive and negative bias similar
Symmetric current flow essential to bifurcation; if one plate isolated to stop current flow, transition absent.
Observations favor j(Shear flow driven by radial shear in j x B)
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Helimak
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Normal, Fast Bifurcation
Bias
Isat(t) at various radii
Jump between two steady states
Simultaneous at all radii
No hysteresis; bias directly controls instability
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Isat(t) at various radii
Bias
Slow Sweep Through Threshold Bias always near threshold
Jump between two steady states; sharp threshold, no graded transition
No hysteresis
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Helimak
Conclusions
• The Helimak offers a simple, controlled model of shear-flow driven turbulence bifurcations – bifurcation without hysteresis through equilibrium profile
• The shear flows are driven by current ( jxB ) ⇒ momentum transport key
• The bifurcation is a step-function in shearin g rate – no intermediate regimes near threshold