at asipp 2014/10/20

Effect of Energetic-Ion/Bulk-Plasma-driven MHD Instabilities on Energetic Ion Loss in the Large Helical Device

Kunihiro OGAWA, Mitsutaka ISOBE, Kazuo TOI, Masaki OSAKABE,Kunihiro OGAWA, Mitsutaka ISOBE, Kazuo TOI, Masaki OSAKABE,Fumitake WATANABE, Akihiro SHIMIZU, Fumitake WATANABE, Akihiro SHIMIZU, DD onaldonald A. SpongA. Spong33, , Douglass S DarrowDouglass S Darrow44

, Satoshi OHDACHI, Satoru SAKAKIBARA, LHD Group. , Satoshi OHDACHI, Satoru SAKAKIBARA, LHD Group.

National Institute for Fusion Science, Nagoya Univ.National Institute for Fusion Science, Nagoya Univ.11, Kyoto Univ., Kyoto Univ.22, ORNL, ORNL33, PPPL, PPPL44

At ASIPP04/20/23

Contents of my presentationBackground and purpose

– The meaning of study

Experimental setups

– scintillator-based lost ion probe

Experimental result

– Increase of lost ion flux due to TAE

Calculation setups

– DELTA5D code (guiding-centre orbit code)

The result of calculation

– Compare with experimental result

Summary

BackgroundAnomalous loss of fast ion in

fusion device

– It might cause localized damage of first wall

Understanding of loss process of fast ion is needed

– Alfvén eigenmode (AE)-induced loss is observed on many tokamaks

– Low frequency MHD modes such as NTM also cause fast-ion losses

Contribution from the 3D plasma is needed to confirm the theory

[1] D.DARROW et al., NF (1997)

GAE induced loss in TFTR [1]

m/n=2/1 NTM induced loss in AUG [2]

Fast Ion Loss NTM mode

[2] M. Garíca-Muñoz et.al, NF (2007)

Experimental setups

The structure of Helical system

plasma shape and magnetic field

– Tokamak : poloidal cross sections at any toroidal angle are the same

• Magnetic surface is created w/ plasma current.

– Helical : poloidal cross section have certain cycle

• Magnetic surface exist w/o plasma current.

Safety factor

– Increase toward the outside (normally, q = ~1 to ~3)

– decrease toward the outside (normally, q = ~3 to ~ 0.6)

Flux surface of EAST

Flux surface of LHD

Profile of safety factor

Scintillator-Based Lost-Fast Ion Probe (SLIP)

Double aperture structure allows fast ions having certain velocities to enter

Scintillation points has information of velocity and pitch angle () of fast ions

This SLIP has two sets of double apertures :“Bi-directional lost-fast ion probe”

– It can be applicable to both cases of CW or CCW direction of Bt

Observation of co-going lost fast ions at relatively low field (Bt < 0.75 T)

Experimental Result

TAE discharge

TAE (m~1/n=1)

– f = 40 ~ 80 kHz (TAE1, TAE2)

(Amplitude: TAE1 <<TAE2)

RIC (dominant: m/n = 1/1)

– Dominant: f = 2 kHz

– Excited by bulk plasma

TAE: toroidal Alfvén eigenmode　 RIC: resistive interchange mode

<bulk> ~ 1.5 % 　 <fast> ~ 1.0 %

Energy and pitch angle of lost ion due to TAE

Three domains are observed. (D1 ~ D3)

D1: E~130 keV, χ=35º D2: E~100 keV, χ=40º D3: E~150 keV,χ=55º

D1: mainly RIC loss, D2: mainly TAE loss, D3: mainly collisional loss

Increase of loss flux coming D2 region due to TAE2 are observed

Image of scintillator plate Time trace of TAE2, RIC and SLIP(#90091)

Mirnov

Mirnov

SLIP

SLIP

SLIP

Initial Study on the Effect of TAE on Energetic Particle Confinement

The method to simulate the energetic ion confinement VMEC

– Reconstruction of equilibrium

HFREYA

– birth profile of energetic ion

DELTA5D (guiding centre)

– Orbit of energetic ion in plasma region

– The model of fluctuation

– Follow the orbit to the LCFS

– Scattering/collision by bulk plasma is concerned

Lorentz orbit

– Orbit of energetic ion outside of the plasma with vacuum field.

– follw the orbit to SLIP from LCFS

– E = 0 is assumed

b B α: f(place, amplitude)

flow of the calculation

Beam of TAE

Lost Ion

Condition of the Calculation

Te and ne are measured with Thomson scattering

Ti = Te, ni = ne is assumed in the calculation

Model of TAE : magnetic fluctuation having m/n=1+2/1 TAE2 structure

Profiles of Te, ne, Alfvén spectraEigenfunction of TAE2

Effect of TAE model fluctuation on energetic ion orbit

– Normalized amplitude of fluctuation is b/b0 =0, 4.5x10-4, 1.0x10-3

– Energetic ion

• E ~ 180 keV, χ~ 15º

– Topology of passing orbit drift toward outside is as same as the drift of banana orbit

Orbit of energetic ion in presence of TAE model fluctuation.

w/o TAE w/ TAE w/ TAE

Effect of TAE model fluctuation on energetic ion loss

We follow the energetic ion orbit within 1 ms– TAE exist but profile of energetic ion

seems not to be changed.

– Energetic ion :E=160 ~ 200 keV

– b/b0=1.0x10-3 assumed Increase of loss in χ~25º , 40º ,50 re

gion is gotten from the calc..– Three loss region correspond to the

D1 ~ D3 region?

although there are some degrees difference.

However, only D2 flux increases in the experiment.– Effect of RIC or interaction of TAE an

d ion should be included?

– Amplitude of TAE2 should be measured?

#90091 t = 2.82 s　

Exp. Res.

RIC loss

TAE loss

Collisional loss

Effect of TAE on lost ion flux

Summary

Lost energetic ion due to energetic particle/bulk plasma pressure excite MHD is observed

– TAE cause energetic ion loss comes to D2 region.

Calculation of orbit in presence of TAE model fluctuation using DELTA5D was held

– three domains of loss are identified though they have some degrees difference.

– Loss coming to D1 ~ D3 regions increase due to TAE model fluctuation in calculation

Interaction between TAE and energetic particle and effect of RIC should be included in future calculation.

at asipp 2014/10/20

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