Chijin Xiao (肖持进)
Plasma LaboratoryUniversity of Saskatchewan
ASIPP, May 26, 2011
Recent Experiments on the STOR-M Tokamak
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Outline
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STOR-M tokamak programRetarding Field Energy Analyzer for Ion
Temperature MeasurementsHelical Field Coils for MHD suppressionSXR measurements for determination of
MHD locations
PPL, Univ. of Sask.
STOR-M Tokamak
R = 46 cm, a (limiter) = 13 cm, Bt ~ 1 T, Ip ~ 50 kA
ne ~ (1-3)x1013/cm3, Te = 200 eV
PPL, Univ. of Sask.5
STOR-M Programs
Compact Torus (CT) injectionfuelling, pressure profile (bootstrap current) control in burning plasmas
Turbulent heating, heat pulse
AC operationquasi steady state tokamak operationmost efficient ohmic heating method
Diagnostics developmentPlasma flow velocity measurementsIon temperature measurement (one of the
today’s topics)
PPL, Univ. of Sask.6
STOR-M Programs (cont.)Ohmic H-modes
CT injection, plasma biasing, edge heatingMHD studies
Helical field coils suppression of m=2 mode (one of the today’s topics)
Magnetic island structures (one of the today’s topics)
Ti Measure
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Motivation for Ti measurementsRFA principlesSimulation
ModelResults
Probe designExperimental Results
Motivation for Ti Measurements
Electron temperature measurements in SOL and edge region are routinely carried out using conventional electric probes
Ion temperature measurements are scarecy and not easy
Retarding Field Analyzers (RFA) have been used in large (JET, Tore Supra) and small (ISTTOK, STOR-M) tokamaks
Precise interpretation of the data still depends on models
Technical development is still needed
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Importance of Ti Measurements in the Edge Region and SOL
H-mode (ETB)Radial force balance equation
Poloidal velocity shear calculation needs ion temperature and the parallel flow velocity
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Importance of Ti Measurements in the Edge Region and SOL
Flow measurements
Geodesic Acoustic Mode (GAM) frequency
Needs ion temperature
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What Can RFA Measure?Measures ion temperatureMeasures parallel flow Mach number
and velocity
It is relatively simple and cost effective
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Principle of the RFA
Pitts R.A. et al 2003 Rev. Sci. Instrum. 74 1112
I-V curve for the RFA
Pitts R A et al 2003 Rev. Sci. Instrum. 74 11
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eVshift (>0)=min. ion kinetic energy
Example I-V curve from JET
Pitts R A et al 2003 Rev. Sci. Instrum. 74 11
Ion side probe
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Electron side probe
Different characteristic curve
different ion temperature
Why?
What is the true temperature?
Geometry
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Bt
Vװ
Vװ
ES G1 C
Simulation – DerivationCondition 2b:
Condition 3:
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Simulation – With Plasma Flow
Probe 1 - upstream
Probe 2 - downstream
measured
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Plot of measured temperature vs actual temperature with Mach number of 0.418
Plot of measured temperature vs actual temperature for several probe dimensions19
Veco GridsNickel base
283 micron by 283 micron openings50 micron wide barsAbout 30 micron thick
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Probe design
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Probe design
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Dreval M., Rohraff D., Xiao C., Hirose A., 2009 Rev. Sci. Instrum. 80 10
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Resonance helical coil experiments
Identifications of MHD modesm/n=2/1 helical coils to supress the
dominant modeSimple model to identify required RHC
current.Experimental results
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SVD for mode analysis12 poloidally distributed coils (up to m=6
mode)4 toroidally distributed coils (up to n=2
mode)Singular value decomposition spatial
structure and temporal frequency of the dominant mode
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Resonant Helical Coils
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Mirnov coils
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SXR arrays
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Simple Simulations
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Results
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Expanded traces
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Mirnov and SXR signal amplitudes and their wavelet
spectra
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Spatial structure of modes
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Spatitial Fourier analysis and the rms amplitudes of m=1 to m=4
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Relative mode amplitudes
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Before SuppressionDuring suppressionAfter suppression
Determination of radial location of the m=2 mode
New SXR analysis techniques based on difference signals
Effectively rejects common mode noisesReliable method for dominant single modeMay be used for mode coupling cases
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Active MHD activities with dominant m=2 mode
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SXR chords and assumed magnetic islands
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Assumed emissivity profile
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Along vertical axis
Ideal integrated signal without noises
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Clear phase reversal, not much difference in amplitude
Actual measured SXR signal with noises or other small modes
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Calculated difference signals
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Clear phase reversal, and also change significantly in amplitude
Difference signal shows on the right
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More clear sinusoidal oscillations with clear phase reversalAt I4 and I10 channels
Another shot with lower discharge current
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phase reversal at I3 and I9 channels, m=2 island moved inwardsExplanations:Ip decreases q(a) increases q=2 resonance surface moves inwardM. Dreval, C. Xiao, et al, RSI (to be published)
AcknowledgementsDrs. A. Hirose, M. Dreval (SXR)Mr. Sayf Elgriw (MHD), Mr. Kurt Kreuger
(RFA)NSERC Canada科学院和科技部磁约束聚变国际合作创新团队
(ASIPP)
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Thank You!
23/4/21 03:35SWIP, ChengduPage 58
Where is Where is Univ. of Univ. of Saskatchewan ?Saskatchewan ?
Saskatoon•
23/4/21 03:35SWIP, ChengduPage 59
Research in Plasma Physics Research in Plasma Physics LaboratoryLaboratory
Fusion plasma theory (A. Hirose, A. Smolyakov)
Partially ionized plasma theory (A. Smolyakov)
Tokamak experiments (A. Hirose, C. Xiao)
CT injection (C. Xiao, A. Hirose)Plasma Processing (A. Hirose, Q.Q. Yang,
C. Xiao)Ion implantation, photonics (M. Bradley)