Recent Experiments on the STOR-M Tokamak Chijin Xiao （肖持进） Plasma Laboratory University of Saskatchewan ASIPP, May 26, 2011 number slides

Outline STOR-M tokamak program Retarding Field Energy Analyzer for Ion Temperature Measurements Helical Field Coils for MHD suppression SXR measurements for determination of MHD locations

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.

STOR-M Programs Turbulent heating, heat pulse Compact Torus (CT) injection fuelling, pressure profile (bootstrap current) control in burning plasmas Turbulent heating, heat pulse AC operation quasi steady state tokamak operation most efficient ohmic heating method Diagnostics development Plasma flow velocity measurements Ion temperature measurement (one of the today’s topics) PPL, Univ. of Sask.

STOR-M Programs (cont.) Ohmic H-modes CT injection, plasma biasing, edge heating MHD studies Helical field coils  suppression of m=2 mode (one of the today’s topics) Magnetic island structures (one of the today’s topics) PPL, Univ. of Sask.

Ti Measure Motivation for Ti measurements RFA principles Simulation Model Results Probe design Experimental 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 Importance of global or core temperature. Some values. Some measuring techniques.

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 Importance of Edge region measurements. Some measuring techniques. Sentence describing main point.

Importance of Ti Measurements in the Edge Region and SOL Flow measurements Geodesic Acoustic Mode (GAM) frequency Needs ion temperature Importance of Edge region measurements. Some measuring techniques. Sentence describing main point.

What Can RFA Measure? Measures ion temperature Measures parallel flow Mach number and velocity It is relatively simple and cost effective Importance of Edge region measurements. Some measuring techniques. Sentence describing main point.

Principle of the RFA Pitts R.A. et al 2003 Rev. Sci. Instrum. 74 11

I-V curve for the RFA eVshift (>0)=min. ion kinetic energy Pitts R A et al 2003 Rev. Sci. Instrum. 74 11

Example I-V curve from JET Different characteristic curve different ion temperature Why? What is the true temperature? Ion side probe Electron side probe Pitts R A et al 2003 Rev. Sci. Instrum. 74 11

Geometry Vװ ES G1 C Bt Vװ Give more description of the function for flux. Derivation for Gamma?

Simulation – Derivation Condition 2b: Condition 3: Fix bound in Gamma2 to g(v)

Simulation – With Plasma Flow Probe 1 - upstream Probe 2 - downstream measured

As RFA currently being used on STOR-M a = 1.30mm l1 = 6.94mm l2 = 4.40mm Plot of measured temperature vs actual temperature with Mach number of 0.4

T_i routinely measured higher than T_e T_i routinely measured higher than T_e. No complete explanation is available for this. Plot of measured temperature vs actual temperature for several probe dimensions

Veco Grids Nickel base 283 micron by 283 micron openings 50 micron wide bars About 30 micron thick - these don’t cover plate thickness 3 basic designs outlined in report Thickness introduces a opacity. Transmission is not 100%. Calculate same conditions as in model to determine if these need to be taken into account during the design.

Probe design - these don’t cover plate thickness 3 basic designs outlined in report Thickness introduces a opacity. Transmission is not 100%. Calculate same conditions as in model to determine if these need to be taken into account during the design.

Probe design - these don’t cover plate thickness 3 basic designs outlined in report Thickness introduces a opacity. Transmission is not 100%. Calculate same conditions as in model to determine if these need to be taken into account during the design. Dreval M., Rohraff D., Xiao C., Hirose A., 2009 Rev. Sci. Instrum. 80 10

Resonance helical coil experiments Identifications of MHD modes m/n=2/1 helical coils to supress the dominant mode Simple model to identify required RHC current. Experimental results

SVD for mode analysis 12 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

Resonant Helical Coils

Mirnov coils

SXR arrays

Simple Simulations

Results

Expanded traces

Mirnov and SXR signal amplitudes and their wavelet spectra

Spatial structure of modes

Spatitial Fourier analysis and the rms amplitudes of m=1 to m=4

Relative mode amplitudes Before Suppression During suppression After suppression

Determination of radial location of the m=2 mode New SXR analysis techniques based on difference signals Effectively rejects common mode noises Reliable method for dominant single mode May be used for mode coupling cases

Active MHD activities with dominant m=2 mode

SXR chords and assumed magnetic islands

Assumed emissivity profile Along vertical axis

Ideal integrated signal without noises Clear phase reversal, not much difference in amplitude

Actual measured SXR signal with noises or other small modes

Calculated difference signals Clear phase reversal, and also change significantly in amplitude

Difference signal shows on the right More clear sinusoidal oscillations with clear phase reversal At I4 and I10 channels

Another shot with lower discharge current phase reversal at I3 and I9 channels, m=2 island moved inwards Explanations: Ip decreases  q(a) increases  q=2 resonance surface moves inward M. Dreval, C. Xiao, et al, RSI (to be published)

Acknowledgements Drs. 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)

Thank You!

Where is Univ. of Saskatchewan ? C. Xiao, Institute of Physics, Beijing, June 25, 2001 Where is Univ. of Saskatchewan ? Saskatoon • SWIP, Chengdu 2017年4月22日4时4分

Research in Plasma Physics Laboratory 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) SWIP, Chengdu 2017年4月22日4时4分