Edge and Internal Transport Barrier Formations in CHS. Identification of Zonal Flows in CHS and JIPPT-IIU

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1 Edge and Internal Transport Barrier Formations in CHS S. Okamura, T. Minami, T. Akiyama, T. Oishi, A. Fujisawa, K. Ida, H. Iguchi, M. Isobe, S. Kado, K. Nagaoka, K. Nakamura, S. Nishimura, K. Matsuoka, H. Matsushita, H. Nakano, M. Nishiura, S. Ohshima, A. Shimizu, C. Suzuki, C. Takahashi, K. Toi, Y. Yoshimura and M. Yoshinuma National Institute for Fusion Science, Oroshi 3-6, Toki 59-59, Japan ) Graduate School of Engineering, The University of Tokyo, Tokyo , Japan ) High Temperature Plasma Center, The University of Tokyo, Tokyo , Japan Rapported paper Identification of Zonal Flows in CHS and JIPPT-IIU

2 Transport Studies in CHS (Compact Helical System) First Talk Confinement Improvement Transport Barrier Formations Edge Transport Barrier (ETB) Transport Barriers for higher-density Plasmas Internal Transport Barrier (ITB) FEC(Lyon) Density Threshold N e <.4 x 9 m -3 NBI Plasmas Second Talk Turbulence and Plasma Flow Structure (E r ) Measurement Zonal Flow Measurement by HIBP ECH Plasmas without beam driven instabilities

3 Edge Transport Barriers (ETB) in CHS Experiment 99 IAEA conference at Würzburg K. Toi, S. Okamura, H. Iguchi, et al. " Formation of H-mode like transport barrier in the CHS heliotron/torsatron " 5 CHS (Compact Helical System) R = m, Bt < T, Ap = 5. with Ohmic current control Ip ~ 3-4 ka for Bt ~. -.4 T Iota() :.5.8 Iota(a) :.9. -dv/dψ (%) Magnetic Well Magnetic Hill Rotational Transform Iota [/q(r)] Present Experiment Normalized Radius (r/a). Use standard configuration Rax = 9. cm. No ohmic current drive (< ka bootstrap and beam driven current) 3. Two NBIs both in co-injection

4 H-mode Transition in NBI Heated Hydrogen Discharge Magnetic Configuration : Rax= 9. cm, κ=. Bt=.95 T, P NBI =.6 MW P.rad (kw) Wdia(kJ) Ne (x 9 m -3 ) ECH Ne.63a Radiation(kW) NBI.# NBI.# Time(sec) Transition to ETB H α Energy Back Transition Edge Density Radiation Density Profile Temperature Profile YAG Thomson Measurement Ne ( 9 m -3 ) Te (kev) msec 8 msec (r/a) Edge Transport Barrier 75 msec 8 msec (r/a)

5 Beam Emission Spectroscopy (BES) for Local Density Measurement (a) ECH NBI.# NBI.# Expanded View Pre-phase of transition (b) H α H α BES Emission 3 (c) R=.53 m BES Emission R=.53 m BES Emission 5 5 (d) R=.64 m R=.64 m BES Emission (e) R=.75 m LCMS R=.75 m Time(sec) Time(sec)

6 Heating Power Dependence of Transition Magnetic Configuration : Rax= 9. cm, κ=. Bt=.95 T <nl>.center H.alpha <nl>.edge DT3 #457 Time delay from NBI start to transition ECH NBI# NBI# Puff Delay Time (msec) DT DT Time (sec) Power threshold for Ne = x 9 m -3 5 DT3 DT DT Heating Power (MW) Twice larger than tokamak scaling

7 ETB Formation with Improved Electron Confinement When the density profile shape is hollow during the transition phase, improved electron confinement is simultaneously obtained with ETB for NBI plasma without ECH ECH NBI.# NBI.# Density Profile Ne ( 9 m -3 ) YAG Thomson Measurement 65 msec 7 msec (r/a) Edge Transport Barrier (x 9 m -3 ) Wdia(kJ) 4 3 Ne-av Radiation(kW) Time(sec) Temperature Profile Te (kev) msec 7 msec (r/a) Internal Transport Barrier

8 SUMMARY. Formation of transport barrier at plasma edge for particle flow was observed in CHS and dynamics of edge density profile was studied.. Heating power threshold exists for the transition. It is roughly two times larger than tokamak scaling. 3. When the density profile is hollow shape during the transition, the improvement of electron heat transport was simultaneously observed (without ECH) for middle density plasma (Ne ~ 3 x 9 m -3 ) which is above density threshold of previous ITB experiments in CHS.

9 Identification of Zonal Flows in CHS and JIPPT-IIU A. Fujisawa, K. Itoh, H. Iguchi, K. Matsuoka, S. Okamura, A. Shimizu, T. Minami, Y. Yoshimura, K. Nagaoka, C. Takahashi, M. Kojima, H. Nakano, S. Ohshima, S. Nishimura, M. Isobe, C. Suzuki, T Akiyama, K. Ida, S.-I. Itoh and P. H. Diamond Y. Hamada, A. Nishizawa, T. Ido, T. Watari, K. Toi, Y. Kawasumi and JIPPT-IIU group National Institute for Fusion Science Kyushu University, RIAM University of California, San Diego

10 Zonal Flows Is that really present in toroidal plasma? ITER zonal flows: regulating turbulence and transport m=n=, k r =finite Two branches ) Zonal flow nearly zero frequency This finding! Poloidal Crosssection ExB flows ) Geodesic acoustic mode Oscillatory (f~ C s /R) -DIII-D(BES) -ASDEX-U(Reflectometor) -H-heliac (probes) -JFT-M (HIBP) The zonal flow appears in E-field fluctuation in toroidal plasma HIBP is a strong candidate for identification of zonal flows

11 HIBP in JIPPT-IIU Tokamak Z (cm) Observation points 6 45 kv 45 kv 3 kev kev Potential fluctuation 6 P (V /khz) f (khz) ρ. Frequency vs. radius φ&φ4 - - φ&φ M= symmetry C()=.79 τ=58.6 µs f=46 khz C()=.8 τ=53.7 µs f=46 khz - - τ (µs) Amplitude vs. radius 9 R(cm) Multi-channel measurements up to 6 f (khz) 4 Amplitude (V) 4 r (cm) r (cm) Coherent oscillation was found to show GAM characteristics

12 Dual HIBPs in CHS Electric field measurement φ = E r r = φ out φ cen HIBP# observation points φ out E r φ ctrφ in ExB flow HIBP System 9 degree apart HIBP# observation points φ out ECR-heated plasma n e =5x cm -3 T e =.5 kev T i =. kev Spectrum of electric field fluctuation P E (V /khz ). r ~ cm (r/a~/3) Zonal flows GAM Coherence.5 φ ctr Poloidal Crosssection R=m, a=.m R=m, a=.m φ in ExB flow Poloidal Crosssection E r Low frequency fluctuation (f<khz) shows a long-range correlation Zonal flow is identified. noise level. f (khz)

13 Dynamics and Structure of Zonal Flows A numerical filter is used to remove high frequency (f> khz) δe (V) - on slightly different magnetic flux surfaces δe (V) t (ms) r =cm - on a magnetic flux surface θ E in E in θ π r =r =cm E in E in r =.5cm t (ms) ~ Vpp C crs (r,r ) = E (r )E (r ) / E (r ) E (r ) C (r,r ) r =cm r (cm) 3 4 Radial wavelength ~.5 cm Dynamics and radial structure of zonal flows are measured.

14 Confinement & Zonal Flow Bifurcated states in CHS Time evolution of turbulence &zonal flow.5 φ (kv) ITB HIBP# HIBP# φ(kv).3. Potential HIBP# no ITB.5 ρ Dual HIBPs caught the exact moment of spontaneous transition in a discharge. Density fluctuation HIBP# Zonal flow HIBP# with ITB without ITB Zonal flow amplitude is reduced after back-transition δn/n φ(v) t (ms)

15 Summary JIPPT-IIU. Coherent oscillation with GAM characteristics was found in the HIBP measurements on JIPPT-IIU tokamak. CHS. Heavy ion beam probe successfully measured the local electric field fluctuation spectrum.. Dual HIBPs confirm the presence of zonal flows (f<~khz) by showing a long-distance correlation with toroidal symmetry in electric field fluctuation 3. The amplitude of zonal flow is about V. The radial wavelength is ~.5 cm. 4. The amplitude of the zonal flows is found to be reduced in the barrier location after the transport barrier decayed.

16 GAM in CHS Power (V /khz). P~f Coherence GAM in potential & electric field.8 E r. Noise level. f (khz) Power (V /khz). P~f -.6 Noise level for power.. f (khz).5 Coherence Power (V /khz).4.5 φ f (khz).5 Coherence

17 Lithium Beam Probe Measurement of Edge Density Profile 8 ECH NBI.# NBI.# Density(A.U.) 6 4 T T T3 T4 T5 T6 T7 T8 LCMS for.% beta H-alpha(A.U.) T T T3 T5 T7 T4 T6 T Time(sec) # Position (r/a) [for.8% beta]

18 Confinement Improvement in Comparison with Scaling New International Stellarator Scaling H. Yamada, et al. : This conference EX/-5 ISS 4v τ =.48a R P n B ι E for CHS/ATF/Heliotron-E renormalization factor =.4 abs e /3 Maximum energy of each discharge is plotted as a function of average density Confinement improvement of about 4% is given by ETB formation Normalized Wp/(P.39 ) (A.U.) with ETB ISS4 Scaling No ETB Average Density ( 9 m -3 )