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Modification of Toroidal Flow Velocities in the STOR-M Tokamak *

This study investigates the modification of toroidal flow velocities in the STOR-M Tokamak through resonant magnetic perturbations (RMPs) and compact torus (CT) injection. Results show the suppression of MHD fluctuations and changes in flow velocities with different RMP amplitudes and CT injection. Implications for plasma confinement and disruption control are discussed.

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Modification of Toroidal Flow Velocities in the STOR-M Tokamak *

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  1. Modification of Toroidal Flow Velocities in the STOR-M Tokamak* C. Xiao, S. Elgriw, A. Rohollahi, D. Basu, G. Tomney, M. Nakajima, J. Adegun, A. Hirose and STOR-M Team Plasma Laboratory, University of Saskatchewan *Supported by CRC, NSERC and Sylvia Fedoruk Center

  2. Outline • Motivations • Experimental setup (RMP, CT, diagnostics) • Modification of flow velocities by Resonant Magnetic Perturbations (RMPs) • Modification of flow velocities by Compact Torus (CT) injection • Future work IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  3. Motivations IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  4. Motivations • MHD instabilities (tearing mode or magnetic islands) interacts with the resistive wall or error field from coils. • If the plasma (or mode) does not rotate, those modes could be “locked’ and grow quickly causing minor or major disruptions IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  5. Motivations • MHD instabilities degrade confinement • Major disruptions in a fusion reactor • Huge thermal load on the first wall • Induces high voltages/current on coils and structures • Control of plasma rotation is desired • by unbalanced neutral beam injection. IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  6. Motivations • We present results of plasma velocity control by two other means on STOR-M • by resonant magnetic perturbations (RMP) • By compact torus (CT) injection IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  7. Experimental setup IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  8. Experimental Setup IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  9. 20-30 kA IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  10. Experimental setup -RMP 2nd bank 1st bank m/n=2/1 helical coils to suppress the dominant mode IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  11. Experimental setup -CT ρ CT injection mainly for studies of direct deep fuelling Tangential CT injection may inject momentum IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  12. Experimental setup -CT Typical parameters： CT vel.: 150-200 km/s CT mass ~ 0.5 micro grams STOR-M pl. mass: 1 micro gram ρ CT injection mainly for studies of direct deep fuelling Tangential CT injection may also inject momentum IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  13. Mirnovcoil arrays Mirnov coil arrays used to detect the mode structure and frequencies. SVD algorithm is used to analyze the MHD modes IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  14. Ion Doppler Spectroscopy PMT array: Time resolved flow measurement Normal view: Wavelength calibration Bt Choices of impurities  spatial resolution: CIII: r=7cm OV: r= 4cm CVI: r=0cm Tangential view: Doppler shift Ip IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  15. Flow modification by RMP IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  16. Model Predictions Simulation: 1. TOSCA: equilibrium field 2. Instability: 3. Vacuum field by RMP , IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  17. Model Predictions Simulation: 1. TOSCA: equilibrium field 2. Instability: 3. Vacuum field by RMP , IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  18. Results -suppression IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  19. MHD fluctuations RMP IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  20. Spatial Fourier analysis and the rms amplitudes of m=1 to m=4 modes IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  21. Spatial structures of modes obtained using SVD algorithm During RMP (m=3) After RMP (m=2) Before RMP (m=2) Before and after RMP, m=2 mode, during RMP: m=3 mode IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  22. Relative mode amplitudes Before Suppression During suppression After suppression IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  23. Intrinsic plasma toroidal flow (normal current direction) r~7 cm r~4 cm r~0 cm • Co-current flow （CCW） at outer region • Counter-current flow （CW）at inner region IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  24. Modification of flow velocities by RMP r~0 cm r~4 cm RMP OV and CVI flow measurements at different RMP current RMP was fired at 20ms for 8ms ( +ve: co-current direction, -ve: counter-current direction) IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  25. Effects of RMP Current Amplitude • Increasing IRMP • Change in velocity increases • MHD fluctuation amplitude decreases IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  26. Modification of flow velocities by two RMP pulses RMP IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  27. Modification of flow velocities by NRMP NRMP NRMP r=4 cm r=0 cm Reverse plasma current  non-resonant magnetic perturbations (NRMP) Flow is still in the counter-current direction OV and CVI flow velocities do not change much in magnitude IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  28. Flow modification by CT injection IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  29. Suppression of MHD oscillations as also seen in RMP experiments IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  30. Flow modification by CT injection Injected CT momentum is approximately 10 times the plasma rotation IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  31. Questions Is the flow modification by CT injection caused by • suppression of MHD fluctuations? • by momentum injection? IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  32. Flow modification by CT injection (Reversed Ip direction) IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  33. Reverse plasma current direction  Reverse flow direction (along CT inj. direction in the core plasma) • Momentum injection  speed up • MHD suppression  slow down IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  34. Flow modification by CT injection(Reversed Ip direction (CCW)) Injected CT momentum is approximately 10 times the momentum due to plasma rotation IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  35. Future work • Quantitatively separate the contributions from MHD and momentum injection to flow velocity modification • Simultaneously measure MHD and CT velocity and density Suppress MHD by RMP and then inject CT • Study the mechanism of momentum deposition and transport in STOR-M IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  36. Conclusions • RMP effectively modifies the toroidal flow velocity and suppresses the MHD fluctuations in STOR-M • Compact torus injection appears to inject momentum into the STOR-M discharge and modifies to toroidal flow velocities. IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  37. Thank you! IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  38. Additional Slides IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  39. 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) IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  40. Relative mode amplitudes Before Suppression During suppression After suppression IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  41. CT formation principle IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  42. CT formation principle (cont’d) IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  43. IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  44. CT formation principle (cont.) IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  45. CT Acceleration IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  46. III. CT penetration and fuelling IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  47. Model Predictions The q=2 surface is closer to the edge and RMP is more effective IEA International RFP workshop, Hefei, Oct. 26-29, 2015

  48. Model Predictions Simulation: 1. TOSCA: equilibrium field 2. Instability: 3. Vacuum field by RMP , IEA International RFP workshop, Hefei, Oct. 26-29, 2015

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