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Effect of Helical Magnetic Field Ripples on Energetic Particle Confinement in LHD Plasmas

Effect of Helical Magnetic Field Ripples on Energetic Particle Confinement in LHD Plasmas. T.Saida , M.Sasao, M.Isobe 1 , M.Nishiura 1 , S.Murakami 2 , K.Matsuoka 1 , A.V.Krasilnikov 3 , M.Osakabe 1 and LHD experimental group

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Effect of Helical Magnetic Field Ripples on Energetic Particle Confinement in LHD Plasmas

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  1. Effect of Helical Magnetic Field Ripples on Energetic Particle Confinement in LHD Plasmas T.Saida, M.Sasao, M.Isobe1, M.Nishiura1, S.Murakami2, K.Matsuoka1, A.V.Krasilnikov3, M.Osakabe1 and LHD experimental group Department of Quantum Science and Energy Engineering, Tohoku University, Sendai, Japan 1National Institute for Fusion Science, Toki, Japan 2Department of Nuclear Engineering, Kyoto University, Kyoto, Japan 3Troitsk Institute for Innovation and Fusion Research, Troitsk, Russia

  2. Outline of talk • Motivation • 2. Diagnosis system • 3. Measurement results • 4. Numerical analyses • 5. Summary

  3. Tokamak Heliotron Energetic ion orbits in Tokamak & Heliotron • Passing particle • Trapped particle • Passing particle • Locally trapped particle • Helically trapped particle • Transition particle

  4. Motivation The improved performance for confinement of energetic trapped particles is expected to be obtained by optimization of magnetic configurations in heliotron. • Need to demonstrate the expected confinement of the energetic trapped particleexperimentally Compare to the energetic particle confinement at three different magnetic axes Raxof 3.53, 3.6 and 3.75m in LHD How about other particle orbits? Inject neutral beam ions tangentially Measure ions with perpendicular pitch angle Pitch angle scatterings The confinement of the other particle orbits can be investigated.

  5. Magnetic structure and energetic trapped particle orbit Rax=3.53m Rax=3.6m Rax=3.75m Drift surface of trapped particle Vacuum magnetic flux surfaces r/a=0.5 r/a=0.5 r/a=0.5 It is predicted that the magnetic configuration at Raxof 3.53m gives the improved confinement of energetic trapped particles.

  6. NBI#3 Hydrogen neutral (H0) beams with 180keV Tangential counter injection Two NBs have different depositions Diagnosis systemfast neutral measurement NBI#1 Rtan~3.75m No significant differences in NDD line-of-sight at R ax of 3.53, 3.6, 3.75m Rtan~3.6-3.65m • NBI systems R=3.68m Natural Diamond Detector (NDD) PHA mode

  7. Initial pitch angle of energetic beam ions and pitch angle of measured ions Pitch angle at ionization points of tangentially ctr.-injected NB Pitch angles of particles reaching NDD Rtan~3.75m Slowing down deflection NDD measures partially slowed down, the pitch angle scattered perpendicular ions. Rtan~3.6-3.65m Do NB depositions have the influence to the particle confinement?

  8. 1.7-2.1sec 50-200keV Rax[m] ne [1019m-3]Te [keV]τs[s]Teff [keV] NBI1 3 [MW] 3.53 1.012.200.2511.32.9 2.4 3.6 0.882.660.3513.1 2.9 2.4 3.75 0.772.260.348.9 2.92.4 CX neutral flux and spectra at three different configurations

  9. High ne 1.7-2.1sec Low ne Low ne High ne Low ne 50-200keV High ne Electron density dependence of CX neutral spectra Estimate the effective temperature as a function of slowing down time by taken into account of NB deposition.

  10. Rtan~3.75m Rtan~3.6-3.65m Effective temperatureTeff Plot effective temperature Teff as a function of slowing down time ts by taken into account of NB deposition positions • Saturation value of Teff at 3.75m is the smallest in all cases. • In the NBI#1 and 3 case, saturation value of Teffat 3.6m is the largest. • No significant difference between 3.53 and 3.6m is observed. • There are no significant difference on NB depositions.

  11. Numerical approach(Lorentz orbit code) Calculation condition • Magnetic configurations at Raxof 3.53, 3.6 and 3.75m with Btof 2.5T • Proton with energy of 75keV and pitch angles of 90-130 deg. • Calculate without collisions time-backwardly from starting points • Classify orbit types of energetic particles from the topology Regard particle crossing over last closed flux surface (r=1) as lost particle • Estimate the confinement region

  12. Orbit topology of confined particle • Passing particle • Transition particle • Locally trapped particle • Helically trapped particle

  13. Orbit classification • No significant difference between Rax of 3.53 and 3.6m • The confinement at Rax of 3.75m is not improved.

  14. Confinement region • Confinement region at 3.6m is the largest among three configurations. • Magnetic configuration at 3.6m has the largest plasma volume. The tendency is consistent with that of saturation value ofTeff

  15. Orbit analyses Summary • Investigate energetic particle confinement among three configurations experimentally Rax=3.53m Rax=3.6m Rax=3.75m Experimental results No significant difference Poor confinement (Saturation value of Teff at 3.6m is the largest) No significant difference on NB deposition is observed. No significant difference Poor confinement The largest confinement region (in the case of LHD)

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