Recent Results from the Heliotron J Experiment

Hangzhou International Stellarator Workshop March 26th-28th, 2018, Zhejiang University, Hangzhou, China

Recent Results from The Heliotron J Experiment

Presented by K. Nagasaki

Institute of Advanced Energy, Kyoto University The Heliotron J Group and Collaborators

T. Mizuuchi, K. Nagasaki, H. Okada, T. Minami, S. Kado, S. Kobayashi, S. Yamamoto, S. Ohshima, S. Konoshima, T. Senju, K. Yaguchi, M. Shibano, K. Toshi, K. Sakamoto, K. Nakagai, T. Takahashi (IAE, Kyoto University) Y. Kishimoto, Y. Nakamura, A. Ishizawa, K. Imadera (GSES, Kyoto Univ.) S. Murakami, T. Shikama (Graduate School of Engineering, Kyoto Univ.) Y. Takeiri, M. Osakabe, K. Y. Watanabe, S. Okamura, M. Yokoyama, K. Nagaoka, Y. Suzuki, Y. Narushima, S. Nishimura, S. Sakakibara, K. Tanaka, H. Takahashi, G. Motojima, Y. Yoshimura, H. Igami, K. Ogawa, K. Mukai, T. Oishi, N. Tamura (National Institute for Fusion Science) N. Nishino (Hiroshima Univ.), T. Fukuda (Osaka Univ.), Y. Nakashima (Univ. Tsukuba) , S. Kitajima (Tohoku Univ.) , N. Kenmochi (U. Tokyo) D. Anderson, K. Likin, C. Deng (Univ. Wisconsin, USA) N. B. Marushchenko, G. Weir (IPP, Germany)) E. Ascasibar, A. Cappa, T. Estrada, F. Castejon (CIEMAT. Spain) B. Blackwell (ANU, Australia) D. Yu, L. Zang (SWIP, China), J. Zhu (Zhejiang Univ.) B. Liu (Southwest Jiaotong Univ., China) Outline

1. History of Heliotron Research and Heliotron J 2. Magnetic configuration control ̶ Neoclassical transport ̶ Anomalous transport ̶ Energetic particle confinement

3. Recent experimental results ̶ High-density H-mode triggered by high intense gas puffing ̶ Isotope effect on edge turbulence ̶ Electron ITB ̶ Suppression of energetic-particle-driven MHD modes by ECH/ECCD

4. Summary Outline

1. History of Heliotron Research and Heliotron J 2. Magnetic configuration control ̶ Neoclassical transport ̶ Anomalous transport ̶ Energetic particle confinement

4. Summary Heliotron Fusion Research in Kyoto University

1958 1966 1976 1996 超高温プラズマエネルギー理工学研究所 “Cradle” ヘリオトロン研究施設（工学部）核融合研究センター IAE, Kyoto Univ. Project Helicon PPL, Dep. Eng. PPL, Kyoto Univ. エネルギー科学研究科 Kyoto Univ. Kyoto Univ. GSE, Kyoto Univ.

1980 1959 1960 1965 1970 1975

Heliotron A Advanced Heliotron B Heliotron C Heliotron D Heliotron DM Heliotron E Helical Concept R=0.47m R=1.085m R=0.45m R=2.2m a=0.075m a=0.1m a=0.04m a=0.2m B=0.6T B=0.3T B=1T B=2T 2000

1998 LHD (NIFS)

Heliotron J Helical-Axis Heliotron Configuration

M. Wakatani, Y. Nakamura et al., Nucl. Fusion 40 (1999) 569 Keywords： High-level compatibility between good particle confinement & MHD stability Currentless steady state Potential for built-in divertor Compact & high-b Simple helical coil system

1. Omnigeneity for drift optimization and magnetic well for MHD stability are combined with a helical magnetic axis  High-b  Control of neoclassical and turbulent transport

2. Bumpy component as the third knob of configuration control  s-optimization  Control of BS current  Er effect Heliotron J Device

 Specification  Single helical coil (l=1), two kinds of toroidal coil and three pairs of poloidal coil  Flexibility of magnetic configuration  R=1.2 m, < 0.2 m

 Bt < 1.5 T, 0.4 < i/2p < 0.65  Nf = 4, helical-axis Heliotron  Heating systems  ECH: P < 0.4 MW, f = 70 GHz  NBI: P < 1.6 MW, E < 30 keV (H) [co and counter injection]  ICRF: P < 0.8 MW  Achieved plasma parameters   Te(0) <3 keV  Ti < 0.4keV Characteristics of Heliotron J Configuration

 The straight structure is designed where quasi-omgeneity is formed

Straight section (f=45) Straight section Corner section (f=45) (f=0) Corner section (f=45)

Iota well depth

 The magnetic field strength is flat in the straight section, making the magnetic field gradient gentle.  The B contour shape is tokamak-like at corner section Role of Bumpiness

• Bumpiness provides control of Bmin contour for deeply trapped particles • Inward shift of magnetic axis is not necessary for optimization of neoclassical transport

Fourier Spectra of B

• Field configuration of Heliotron J is mainly composed of toroidicity, helicity and bumpiness • Helical coil winding law M M  p f  sin  f  L L 

• The negative  produces magnetic well in the whole plasma region

 Reduction of neoclassical ripple transport  Control of bootstrap current  MHD stabilization and good energetic particle confinement Three Bumpiness Configurations

Bumpiness (eb=B04/B00) can be changed with Toroidicity toroidicity and helicity fixed

・ eb = 0.15 (high bumpiness)

・ eb = 0.06 (medium bumpiness, STD)

・ eb = 0.01 (low bumpiness) at r~2/3a Helicity Bumpiness Outline

1. History of Heliotron Research and Heliotron J 2. Magnetic configuration control ̶ Neoclassical transport ̶ Anomalous transport ̶ Energetic particle confinement

4. Summary Experimental BS current Agrees with Neoclassical SPBSC Code Results

Experimental bootstrap current agrees with neoclassical prediction 19 -3 within a factor of 2 at ne = 0.4-1.0  10 m

(off-axis deposition) 19 -3 19 -3 ne = 0.4x10 m ne = 1.0x10 m

 BS current is dominant at this resonance condition  Three kind of pressure profiles are assumed G. Motojima, Fus. Sci. Tech (2007) Role of Trapped Electrons on ECCD

1.7

B /B • Experiments on scanning magnetic field str cor 1.6 0.78 (e = 0.17) b 0.82 (e = 0.15) configuration in Heliotron J show importance b 0.89 (e = 0.13) 1.5 b 0.95e = 0.06) b 0.99 (e = 0.05) of trapped electrons for ECCD 1.4 b 1.06 (e = 0.01) b

• The experimental results quantitatively (T) |B| 1.3 agree with a theoretical calculation using the 1.2 ECH injection port TRAVIS code which includes parallel 1.1 1.0 momentum conservation -45 -30 -15 0 15 30 45 Toroidal Angle f (deg)

High bumpiness Medium bumpiness Low bumpiness 4 4 4

h=0.95 I (exp) h=1.06 h=0.82 EC I (exp) P =260kW P =260kW P =260kW EC ECH I (theory) ECH 3 ECH 3 EC 3 I (theory)  /=0.478  /=0.499  /=0.490 EC 0 0 0 19 -3 19 -3 19 -3 n ~0.5x10 m n ~0.5x10 m n ~0.5x10 m e e 2 e 2 2 (kA) (kA) (kA)

EC EC EC I I 1 I 1 1

0 0 0 IEC (exp)

IEC (theory)

-1 -1 -1 0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6 N N N || || || K. Nagasaki, Nucl. Fusion (2011) Effect of Bumpiness on Parallel Plasma Flow

Lee, PPCF (2013) Nishioka, PoP (2016)

The measured C6+ parallel flow is consistent with the neoclassical prediction with the Sugama- Nishimura method including the edge spontaneous flow

Medium bumpiness (STD) High bumpiness Global Confinement Depends on Bumpiness Component

• Good global energy confinement is obtained at the magnetic configuration with medium bumpiness (ECH) and high bumpiness (NBI) Power scan experiments Density scan experiments

T. Mizuuchi, FST 50 (2006) 352 S. Kobayashi , FEC (2008) EX/P5-13 GKV Code Results Show That Zonal Flow in High Bumpiness Suppresses Turbulence Transport

• GKV code is applied to HJ NBI plasmas.  ITG mode is unstable  Elongated mode structure in B direction due to weak shear  Large amplitude of ZF is expected

 Growth-rate in high eb case is smaller than standard one  Nonlinear calculation shows same tendency  due to stronger |B| at bad-curvature region  Consistent to the experimental result

Config standard High eb

g(vTi/R0) 0.4 0.26

2 ci(vTir Ti/R0) 5.9 4.2 Electrostatic potential profile of the ITG mode

2 ce(vTir Ti/R0) 2.4 1.7 A. Ishizawa et al 2017 Nucl. Fusion 57 066010 High Bumpiness Is Favorable for Energetic Minority Proton Confinement and Bulk Heating

Bulk Heating vs. Bumpiness • ICRF pulse of 23.2 MHz or 19 MHz with 250-290kW 0.25 B04/B00 = 0.15 was injected into an ECH target plasma where Ti(0) 0.20 19 -3

= 0.2 keV, Te(0) = 0.8 keV and ne = 0.4 x 10 m )

V 0.15

(

• High energy ion-flux up to 34 keV is observed at the i

T B /B = 0.01 0.10 04 00 pitch angle of 120 deg only in the high bumpy case 

0.05 • The bulk ion heating efficiency in the high B04/B00 = 0.06 0.00 bumpiness is highest among three configurations 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 PICRF (MW)

6 Low Bumpiness 6 Medium Bumpiness High Bumpiness 10 10 106 19 MHz 19 MHz 128 deg 127 deg 23.2 Mhz 128 deg 5 125 deg 5 10 10 125 deg 105 123 deg 121 deg 121 deg 120 deg 117 deg 118 deg 118 deg 104 104 4 113 deg 112 deg 10 114 deg 108 deg 108 deg 111 deg

3 3 3 (E) (E) (arb.) (E) (arb.) 10 Pitch Angle 10 Pitch Angle (E) (arb.) 10 Pitch Angle H H H f f f

102 102 102

101 101 101 0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35 Energy (keV) Energy (keV) Energy (keV) Outline

1. History of Heliotron Research and Heliotron J 2. Magnetic configuration control ̶ Neoclassical transport ̶ Anomalous transport ̶ Energetic particle confinement

4. Summary H-Mode Transition Triggered by High-Intensity Gas Puffing in NBI Plasmas Low e config |B|=1.3T, P =1MW 6 t NBI #60553-60559 t W (kJ) #60553(H) ,I DIA ) 5 245ms n

-3 e DIA #60514(L) I (kA) m

W t

0 19 235ms

5 (x1019m-3) (x10 FIR e

e 210ms n n 0 -1 -0.5 0 0.5 1

0 -2 2 )

BES(r/a=0.9) #60553 BE 40 ~ 0.4 T (I e

20 -4 10 f (kHz)f 0 Log (keV) 0.15 (A.U.) e T  /D 

H 0 I 0 -1 -0.5 0 0.5 1 200 210 220 230 240 250 r/a time (ms)  A short-pulsed high intensity gas puffing (HIGP) was applied from inboard side.  H-mode transition has been observed with formation of steep density gradient at peripheral.  Before transition, an n = 2 bursting mode (4-30kHz) and low-f fluctuation (<3kHz), which causes particle exhaust, have been observed. Kobayashi, IAEA FEC 2016 Relation between Bursting Mode and H-mode Transition

• A bursting n=2 mode with f=5-30kHz has been observed in density and magnetic fluctuations before L-H transition

0.4 • Reduction in the particle exhaust #60553, Low config. et at transition may trigger (A.U.)  0.2 /D formation of the steep density  H I 237 238 239 240 241 242 gradient in the peripheral region 0.3 f =33.3deg Mirnov TOR 0 -0.3 303.3deg #60520-#61868

dB/dt (A.U.) dB/dt -70 Bursting frequency (0.8-3kHz) BES Filtered 1 ) HIGP width 10-15ms -4

m P =1MW 0.95 0 (A.U.) NB 19 -60 r/a BE I -1 ~ 0.85 -80 -50 noise

r/a=0.94 r/a=0.88 (x10 /dr IBE -IBE e level r/a=0.98 r/a=0.94 w/ H-mode r(A.U.) IBE -IBE dn -40 

/ Low-pass filtered transition -40 -3 BE I (<3kHz) BES 0 0.8-3kHz 5 10

 I / 237 238 239 240 241 242 BE BE time (ms)

Kobayashi, IAEA FEC 2016 Isotope Effect and Its Configuration Dependence of Zonal Flow

A hypothesis/ ZFs contribute to isotope effect？

Coherence  Standard  Low bumpiness 5 to 3 0.1 0.1 [a.u.] [a.u.] <4kHz D <4kHz <4kHz

0.05 Coherence 0.05 H

H D

Fluc.Amplitude 0

Fluc.Amplitude 0 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 Coherence Coherence  Larger amplitude  Smaller amplitude  Stronger correlation  Weaker correlation  Isotope effect on long range on D plasmas on D plasmas correlation (ZF) were investigated in Tokamaks  Opposite dependence of isotope effect, weaker (TEXTOR, ISTTOK) and helical correlation and amplitude of ZF on D plasma, is devices(TJ-II, Heliotron J). observed in low bumpiness configuration. →Configuration optimization might be necessary from the viewpoint of turbulence & isotope effect.

S. Ohshima, ISHW2017, Invited Talk Expansion of Enhanced Confinement Region in Electron ITB During Plasma Current Ramp-up

ECH Conditions  Heating position：magnetic axis  Injection power: 270 kW  absorption rate(X-mode, single path): ~90%

 The rapid increase of the Te at r/a~0.1 is observed at the plasma current ~0.6 kA.  The eITB foot points moves to the outer region as the current increase. e-ITB Foot Point Moves As The n/m=4/7 Rational Surface Appears and Shifts Outward

Rotational transform profiles after eITB foot point after the formation of n/m=4/7 rational surface the formation of n/m=4/7 rational surface

 When the plasma current exceeds the threshold (Ip ∼ 0.9 kA), the ι(r/a)/2π exceeds 4/7 and the rational surface i/2π= 4/7 appears  As the plasma current increases, the ι(r/a)/2π around r/a ∼ 0.2 increases, causing the movement of the position of rational surface. According to the movement of the rational surface, the eITB foot point moves to the outside region. Both Co and Counter ECCD Stabilize EPM and GAE in Heliotron J

No ECCD (N||=0.0) Ctr-ECCD (N||= -0.3) Co-ECCD (N||= +0.4) 2011.12.21 5to3 (HV+86TA+60TB+98AV+19IV-15) 2012.07.12 #46118 #46128 #48104 1.0 1.0 1.0 19 -3 19 -3 n (1019 m-3) n (10 m ) ne (10 m ) e e

0.5 0.5 0.5

0.0 0.0 0.0 2 2 2 I (kA) 1 I (kA) 1 I (kA) 1 p p p

0 0 0

-1 -1 -1 0.5 dB/dt (a.u.) 0.5 dB/dt (a.u.) 0.5 dB/dt (a.u.)

0.0 0.0 0.0

-0.5 -0.5 -0.5 1.0 0.4 0.4 NBI NBI

0.5

0.2 0.2 NBI(BL1) 70GHz ECH (N =0.0) 70GHz ECH (N =0.3) || || 70GHz ECH (N =0.4) 0.0 0.0 0.0 || 200 250 300 200 250 300 200 250 300 TIme (msec) TIme (msec) #48104, 5to3 configurationTIme (msec) N||=0.4 500

400

300

200 Frequency (kHz) 100

0 150 200 250 300 Time (msec) Nagasaki, Nucl. Fusion (2013) Yamamoto, Nucl. Fusion (2017) Stabilization Effect Depends on Magnetic Shear Intensity • EC-driven current enhances magnetic shear (s ~ 0 in vacuum) • Amplitude of EPMs is obviously suppressed by increasing Ip regardless of its sign

0.06 #48085-48115 #46107-46132 5to3 config 0.3 iota=0.525 B=1.21T (HV+86%) B=1.25T co-ECCD 0.26 MW ECH 0.3MW

NBI BL1 0.5MW ) NBI 0.6+0.8MW )

0.04 -5 -5 0.2

(x10 (x10 t t /B ECH-only phase /B Stabilized

rms 0.02 rms

b 0.1 b ECH-only phase

0.00 0.0 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.0 0.1 0.2 r/i(di/dr) at r/a=0.6 r/i(di/dr) at r/a=0.6 • EPMs suffer from strong continuum damping whose rate is proportional to magnetic shear • Increase in absolute magnetic shear leads to suppression of EPMs A Low-Frequency Alfvén Eigenmode (LF-AE) Is Observed in Co-NBI Plasmas

• LF-AE is steadily observed in NBI heated, co-current flowing plasmas in standard configuration.

• Real frequency linearly depends on . • Real frequency is near the boundary of BAE gap. • Nonlinear interaction exists among bands of LF-AE and a very low frequency (<10kHz) m=0,n=0 mode.

TAE

EPM DATA rho0.71 BAE f* = 41 kHz Near-Future Plans

We will carry out next experimental campaign from July, 2018 • Understanding of MHD and Turbulence ̶ Isotope effect (H/D ratio control) ̶ Turbulence measurement with fast CXRS, reflectometer, CECE, Langmuir probes, fast digitizer oscilloscope • Optimization of particle fueling and operation scenario ̶ HIGP, SMBI, pellet injection ̶ Resonant magnetic perturbation coils • Control and measurement of plasma profiles and flow ̶ Iota (q) control for e-ITB ̶ Toroidal and poloidal flow measurement with CXRS ̶ Multi-pass Nd:YAG TS system and multi-channel 320GHz FIR system • Energetic particles and related MHD instabilities ̶ Scintillator type lost ion probe, Si FNA, Fast camera • Impurity transport ̶ Laser blow-off method Summary

• The 3D magnetic configuration scan in Heliotron J has demonstrated - The parallel transport such as BS and EC current and toroidal rotation agrees with neoclassical theory - The bumpiness affects the global energy confinement and the energetic particles • Recent experimental results show - The high-density H-mode triggered by HIGP is closely related to a bursting mode, forming steep density gradient in the peripheral region - Long range correlation is enhanced at D-dominant plasmas - Electron ITB formation is linked with a rational surface - AEs are effectively stabilized by ECH/ECCD

• We have been carrying out the Heliotron J experiments for 18 years • We have started discussion about next generation machine