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