Measurement of fast ion losses due to MHD modes driven by fast ions in the Large Helical Device

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

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

3. Background & Purpose Fast ion loss due to AE in NSTX • 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 angle D. Darrow NF (2008) pitch

4. model of scintillator head picture of SLIP orbit of co-going ion @ CW-Bt orbit of co-going ion @ CCW-Bt 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) LHD & location of SLIP R0 / a = 3.9 m / 0.6 m VNBacc = 180 keV

5. Typical discharge & Scintillation image

6. SLIP Ch. 14 Observation of lost fast-ion flux using Photomultiplier (PMT) array Scintillation image (t = 2.78 s) and position of PMT • 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 ms) • 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. TAE(f~45 kHz) MP spectra block diagram of data acquisition system half mirror PMT scintillator CAMERA AMP EPM (chirping) PCI PC

7. Loss flux correlate with TAE/EPM burst TAE fluc. and SLIP sig. • Bt = 0.75 T, Rax = 3.75 m, g=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) a) b) EPM fluc. and SLIP sig.

8. Relation of fluctuation level and increase in loss flux Fluctuation level and increase of loss flux • evaluation of fluctuation level • : magnetic fluctuation @ MP position • evaluation of increase in loss flux • ΔSLIP : ISLIP (mode exist) – ISLIP (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? EPM #90043 MP spectra #90045 MP spectra TAE TAE EPM m/n = 4/3

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?