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!

23/4/22 00:34SWIP, ChengduPage 58

Where is Where is Univ. of Univ. of Saskatchewan ?Saskatchewan ?

Saskatoon•

23/4/22 00:34SWIP, 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)