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, Fumitake WATANABE, Akihiro SHIMIZU, Donald A. Spong 3, Douglass S Darrow 4, Satoshi OHDACHI, Satoru SAKAKIBARA, LHD Group. National Institute for Fusion Science, Nagoya Univ. 1, Kyoto Univ. 2, ORNL 3, PPPL 4 At ASIPP 2016/3/11

Page  2 Contents of my presentation  Background 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

Page  3 Background  Anomalous 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

Page  5 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

Page  6 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 B t  Observation of co-going lost fast ions at relatively low field (B t < 0.75 T)

Experimental Result

Page  8 TAE discharge  TAE (m~1/n=1) –f = 40 ~ 80 kHz (TAE 1, TAE 2 ) (Amplitude: TAE 1 <<TAE 2 )  RIC (dominant: m/n = 1/1) –Dominant: f = 2 kHz –Excited by bulk plasma TAE: toroidal Alfvén eigenmode RIC: resistive interchange mode ~ 1.5 % ~ 1.0 %

Page  9 Energy and pitch angle of lost ion due to TAE  Three domains are observed. (D 1 ~ D 3 )  D 1 : E~130 keV, χ =35º D 2 : E~100 keV, χ =40º D 3 : E~150 keV, χ =55º  D 1 : mainly RIC loss, D 2 : mainly TAE loss, D 3 : mainly collisional loss  Increase of loss flux coming D 2 region due to TAE 2 are observed Image of scintillator plate Time trace of TAE 2, RIC and  SLIP (#90091) Mirnov SLIP

Initial Study on the Effect of TAE on Energetic Particle Confinement

Page  11 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 α: f(place, amplitude) flow of the calculation Beam  of TAE Lost Ion

Page  12 Condition of the Calculation  T e and n e are measured with Thomson scattering  T i = T e, n i = n e is assumed in the calculation  Model of TAE : magnetic fluctuation having m/n=1+2/1 TAE 2 structure Profiles of T e, n e, Alfvén spectra Eigenfunction of TAE 2

Page  13 Effect of TAE model fluctuation on energetic ion orbit –Normalized amplitude of fluctuation is b/b 0 =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

Page  14 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/b 0 =1.0x10 -3 assumed  Increase of loss in χ ~25º, 40º,50 region is gotten from the calc.. –Three loss region correspond to the D 1 ~ D 3 region? although there are some degrees difference.  However, only D 2 flux increases in the experiment. –Effect of RIC or interaction of TAE and ion should be included? –Amplitude of TAE 2 should be measured? #90091 t = 2.82 s Exp. Res. RIC loss TAE loss Collisional loss Effect of TAE on lost ion flux

Page  15 Summary  Lost energetic ion due to energetic particle/bulk plasma pressure excite MHD is observed –TAE cause energetic ion loss comes to D 2 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 D 1 ~ D 3 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.