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 Department of Quantum Science and Energy Engineering, Tohoku University, Sendai, Japan 1 National Institute for Fusion Science, Toki, Japan 2 Department of Nuclear Engineering, Kyoto University, Kyoto, Japan 3 Troitsk Institute for Innovation and Fusion Research, Troitsk, Russia

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

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

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

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

Diagnosis system fast neutral measurement R=3.68m Natural Diamond Detector (NDD) No significant differences in NDD line-of-sight at R ax of 3.53, 3.6, 3.75m PHA mode NBI#3 R tan ~3.75m R tan ~ m NBI#1 Hydrogen neutral (H 0 ) beams with 180keV Tangential counter injection Two NBs have different depositions NBI systems

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

CX neutral flux and spectra at three different configurations keV sec R ax [m] n e [10 19 m -3 ] T e [keV] τ s [s] T eff [keV] NBI1 3 [MW]

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. High n e Low n e keV High n e Low n e sec Low n e High n e

Effective temperature T eff Saturation value of T eff at 3.75m is the smallest in all cases. Plot effective temperature T eff as a function of slowing down time  s by taken into account of NB deposition positions R tan ~3.75m R tan ~ m In the NBI#1 and 3 case, saturation value of T eff at 3.6m is the largest. No significant difference between 3.53 and 3.6m is observed. There are no significant difference on NB depositions.

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

Orbit topology of confined particle Helically trapped particle Transition particle Passing particle Locally trapped particle

Orbit classification No significant difference between R ax of 3.53 and 3.6m The confinement at R ax of 3.75m is not improved.

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

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