Measurement of fast ion losses due to MHD modes driven by fast ions in the Large Helical Device 2009/03 Kunihiro OGAWA A, Mitsutaka ISOBE, Kazuo TOI, LHD experiment group A Nagoya University National Institute for Fusion Science (NIFS) At ASIPP

Page  2 Contents  Background & Purpose  Experimental setup –Scintillator based lost fast-ion probe  Result –Typical discharge & Scintillation image –Loss flux correlate with TAE/EPM burst –Relation of fluctuation level and increase of loss flux  Summary & Future plan

Page  3 Background & Purpose  Understanding of fast ion loss process due to fast ion driven MHD mode such as Alfvèn eigenmode (AE) is needed –fast ion losses may cause a damage of the first wall in a fusion device –the effect of AEs on fast ion loss must be clarified  example : in NSTX –fast ions which have wide range of pitch angle are lost due to AE  understanding of the effect of AE on co-going fast-ions in LHD  contribution to understanding of fast ion loss process induced by AE in tokamaks pitch D. Darrow NF (2008) pitch angle Fast ion loss due to AE in NSTX

Page  4 Scintillator based lost fast-ion probe (SLIP)  scintillator probe –it works as a magnetic spectrometer –it has a set of apertures (front/rear) it allow to enter ions having certain velocities –scintillation points it have information of velocity and pitch angle of ions  this SLIP has two set of apertures –it can be applicable to the case of CW or CCW direction of Bt  observation of co-going lost fast-ions at relatively low field (Bt < 0.75 T) model of scintillator head LHD & location of SLIP R 0 / a = 3.9 m / 0.6 m V NBacc = 180 keV picture of SLIP orbit of co-going CW-Bt orbit of co-going CCW-Bt

Page  5 Typical discharge & Scintillation image

Page  6 Observation of lost fast-ion flux using Photomultiplier (PMT) array  observation of loss flux with PMT –loss flux correlates with TAE/EPM burst  PMT array (consist of 16-PMT) –it has high-time resolution (~ 2  s) –we mainly monitor the signal of Ch. 14 it sees high luminescent point –we haven’t done calibration of image pattern At present, this image doesn’t give information of velocity and pitch angle of lost fast ions. SLIP Ch. 14 Scintillation image (t = 2.78 s) and position of PMT TAE(f~45 kHz) EPM (chirping) scintillator PMT AMP PCI CAMERA PC half mirror block diagram of data acquisition system MP spectra

Page  7 Loss flux correlate with TAE/EPM burst  Bt = 0.75 T, Rax = 3.75 m,  =1.254  when NB#2 and #3 inject  a) : filtered magnetic fluctuations  b) : PMT signal (Ch. 14)  increase in ion loss flux induced by TAE –#90048 case –mode structure : m~1, n=1 (from MP array) –frequency : 55 ~ 75 kHz  increase in ion loss flux induced by EPM –#90044 case –mode structure : m=2, n=2 (from MP array) –frequency : 10 ~ 40 kHz –frequency sharply chirping down(~ 2 ms) TAE fluc. and SLIP sig. EPM fluc. and SLIP sig. a) b)

Page  8 Relation of fluctuation level and increase in loss flux  evaluation of fluctuation level – : magnetic MP position  evaluation of increase in loss flux –ΔSLIP : I SLIP (mode exist) – I SLIP (no mode)  TAE case (m ~ 1, n = 1) –  EPM case (m=2, n=2) –ΔSLIP has threshold in, then constant –#90043 : it is due to difference of density? m/n=4/3 mode affects transport? #90043 MP spectra m/n = 4/3 EPM TAE Fluctuation level and increase of loss flux #90045 MP spectra EPM TAE

Page  9 Summary  co-going lost fast-ions are measured with a scintillator- based lost fast-ion probe –recurrent increase of lost fast-ion flux induced by TAE or EPM burst is observed –increase in loss flux due to TAE/EPM (toward Ch.14) TAE: loss flux is expressed as EPM: loss flux have a certain threshold(?), then constant but in #90043 Future plan –calibration of scintillation image scintillation pattern gives us information of velocity and pitch angle of lost ions –Are there effects of radial structure of TAE/EPM in lost fast-ion flux?