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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, Japan1National Institute for Fusion Science, Toki, Japan2Department of Nuclear Engineering, Kyoto University, Kyoto, Japan
3Troitsk Institute for Innovation and Fusion Research, Troitsk, Russia
1. Motivation 2. Diagnosis system3. Measurement results4. Numerical analyses5. 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 Rax 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
Rax=3.53m Rax=3.6m Rax=3.75m
It is predicted that the magnetic configuration at Raxof 3.53m gives the improved confinement of energetic trapped particles.
Drift surface of trapped particle
Vacuum magnetic flux surfaces
r/a=0.5 r/a=0.5 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
Rtan~3.75m
Rtan~3.6-3.65m
NBI#1
Hydrogen neutral (H0) beams with 180keVTangential 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
Rtan~3.75m
Rtan~3.6-3.65m
Do NB depositions have the influence to the particle confinement?
CX neutral flux and spectra at three different configurations
50-200keV
1.7-2.1sec
3.6 0.88 2.66 0.35 13.1 2.9 2.4
Rax[m] ne [1019m-3] Te [keV] τs [s] Teff [keV] NBI1 3 [MW]
3.53 1.01 2.20 0.25 11.3 2.9 2.4
3.75 0.77 2.26 0.34 8.9 2.9 2.4
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 ne
Low ne
50-200keV
High ne
Low ne
1.7-2.1secLow ne
High ne
Effective temperature Teff
•Saturation value of Teff at 3.75m is the smallest in all cases.
Plot effective temperature Teff as a function of slowing down time s
by taken into account of NB deposition positionsRtan~3.75m Rtan~3.6-3.65m
•In the NBI#1 and 3 case, saturation value of Teff 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 90-130 deg.
Calculation condition•Magnetic configurations at Rax of 3.53, 3.6 and 3.75m with Bt 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 Rax of 3.53 and 3.6m•The confinement at Rax 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 Teff
Summary
•Investigate energetic particle confinement among three configurations experimentally
Poor confinementNo significant difference
Rax=3.53m Rax=3.6m Rax=3.75m
Poor confinement
Experimental results
(Saturation value of Teff at 3.6m is the largest)
No significant difference on NB deposition is observed.
The largest confinement region (in the case of LHD)
Orbit analysesNo significant difference