1. Present Status and Future Plan of Helical Research in NIFS
Fusion Power Associates 39th Annual Meeting, Dec. 4-5, 2018, Washington, DC, USA
Present Status and Future Plan of Helical Research in NIFS
Tomohiro Morisaki
National Institute for Fusion Science

2. Contents Introduction status of stellarator/heliotron research
Summary of experimental result of LHD
brief summary of hydrogen experiment for 18 years
preliminary results from first deuterium experiment
Future plan toward 2020s
LHD
magnetic fusion research in NIFS and Universities (under discussion)
Summary
Tomohiro Morisaki, 39th FPA 2018

3. Status of stellarator/heliotron research
ITER/tokamak
 First fusion reactor of human being
 2025 first plasma
 2035 DT burning
Stellarator/heliotron
 currentless operation
=> disruption free
 steady-state operation
Stellarator/heliotron as an alternative concept to ITER/tokamak line
W7-X
 start operation (2015)
LHD
 start deuterium experiment (2017)
Tomohiro Morisaki, 39th FPA 2018

4. Stellarator/heliotron family: Evolution of helical system research
1950
1960
1970
1980
1990
2000
2010
C-Stellarator (1961) L.Spitzer U-bent, Helical windings
Medium-size Stellarators
W7-A Low shear and magnetic well
Reduction of PS current
(1981)
Heliotron J
Quasi-isodynamic with simple helical winding
W7-X (2015-)
Quasi-isodynamic
Heliac(1982)
TJ-II, H-1NF
Figure 8
Stellarator
figure 8 shape axis
L=1 High beta
CHS
Heliotron D
Helical winding
High shear
Built in divertor
Heliotron E
High or Medium shear
Large Helical Device (LHD)
Optimized Heliotron (1998)
Concept (1951)
Heliotron
Concept (1958)　
Helias
Quasi-symmetric, Quasi-isodynamic
W7-AS
HSX
ATF
Uragan- 2M/3M
Torsatron
TJ-IU
TJ-K
CAT
TU-Heliac
Lyman Spitzer
Tomohiro Morisaki, 39th FPA 2018

5. Stellarator/heliotron research in the world
TJ-II
TJ-K
W7-X
URAGAN
CFQS
LHD
H-J
SCR-1
CTH
HIDRA
CNT
HSX
H1-N
Tomohiro Morisaki, 39th FPA 2018

6. LHD, the 20 years old stellarator/heliotron
2018
Te = ~20eV
First plasma
10keV
present
deuterium Ti
10 keV (ne = 1.3 1019 m-3) Te
20 keV (2.0 1018 m-3)
10 keV (1.6 1019 m-3) ne
1.21021m-3 (Te = 0.25 keV) 
5.1 % (BT = T)
4.1 % (1.000 T)
Tomohiro Morisaki, 39th FPA 2018

7. LHD - a superconducting heliotron -
Specifications
 Helical mode numbers: l/m=2/10
 All superconducting coil system
 Plasma major radius: m
 Plasma minor radius: m
 Plasma volume: m3
 Toroidal field strength: 3 T
 20 RMP coils
Heating Systems
 negative-NBI x 3 ( keV), H16MW, D8MW
 positive-NBI x 2 (40-80keV), H6MW, D18MW
 ICH (20 – 100MHz) x MW
-> tentatively removed
 ECH (77GHz x 3, 154 x 2, 82.7, 84) MW
Tomohiro Morisaki, 39th FPA 2018

8. Physics and engineering, progressed in hydrogen exp.
LHD has demonstrated potential of heliotron
 thermal transport in LHD presents gyro-Bohm nature
 observation of non-local transport
 operational regime and path to achieve high beta plasma
 3-d effect on
- transport (viscosity) => neoclassical, turbulent (zonal flow)
- MHD stability (magnetic topology) => island
- edge (stochastic region) => detachment, ELM control
 edge heat and particle control with divertor
- etc.
(Yamada, PPCF2004)
(Komori, Ohdachi NF2009)
Helical Divertor
Local Island Divertor
Tomohiro Morisaki, 39th FPA 2018

9. First results from LHD deuterium experiment
LHD extended its operational regime with D plasma
Ti = 10 keV was first achieved in stellarator/heliotron
Tomohiro Morisaki, 39th FPA 2018

10. What is changed in deuterium plasma ?
Global energy confinement is clearly improved in D from H in gyro-Bohm nature
Energy confinement time in NBI plasma
𝜏 𝐸,𝑡ℎ,𝑁𝐵𝐼 𝑠𝑐𝑙 ∝ 𝐴 −0.01±0.02 𝐵 0.85± 𝑛 𝑒 0.78±0.01 𝑃 𝑎𝑏𝑠 −0.87±0.01   
(AD/AH)-0.01 = = 0.99
0.71 in gyro-Bohm prediction
 No significant mass dependence, which indicates clear discrepancy from gyro-Bohm model (isotope effect)
 Comparison between dimensionally similar plasmas also indicates clear isotope effect
Energy confinement time in ECH plasma
𝜏 𝐸,𝑡ℎ,𝐸𝐶𝐻 ∝ 𝐴 0.24± 𝑛 𝑒 0.58±0.01 𝑃 𝑎𝑏𝑠 −0.52±0.01
(AD/AH)0.24 = = 1.18
 Obvious mass dependence (isotope effect) identified
Each experiment was performed with purity of H and D > 80%
Tomohiro Morisaki, 39th FPA 2018

11. Confinement properties of energetic ions
Triton burnup experiment can examine behavior of high energy fusion products
Inward-shifted configuration provides
“better” EP confinement but worse MHD stability
D + D => p + T(1 MeV)
D + D => 3He + n(2.5MeV)
T + D => n(14MeV) + 4He (3.5 MeV)
tokamaks:
- TFTR~0.7%
- KSTAR~0.45%
EP confinement in LHD is comparable to tokamaks with similar plasma cross section
Triton burn-up ratios quantitatively agree with theoretical predictions
Tomohiro Morisaki, 39th FPA 2018

12. What to do, toward 2020s
LHD should demonstrate potential for the helical reactor
Achievement of high-performance plasmas through confinement improvement
scientific research in more reactor-relevant conditions with
- high fusion triple product of > 1020m-3keVs,
- high beta value of > 5 %
Clarification of isotope effect on confinement
long-standing mystery in world fusion research
Needs to be understood towards burning plasma
Demonstration of confinement capability of energetic ions in helical systems
perspectives towards helical reactor
Achievement of steady-state operation
Global particle balance
Tomohiro Morisaki, 39th FPA 2018

13. What to do next, concretely
Realization of steady-state operation with
P > 1MW
duration > 1h
high nT
=> realizes reactor relevant conditions of
high recycling (R ~ 1) operation
furthermore with divertor simulator
high heat/particle flux on divertor target plates (ITER relevant)
high heat/particle fluence (ITER relevant)
Metalization with W (and Mo, SS) can investigate
impurity behavior (effect of W on core plasma prior to long-pulse operation in tokamak (JT-60SA, ITER)
Tomohiro Morisaki, 39th FPA 2018

14. Domestic strategy of magnetic fusion research – under discussion –
ITER
QST
Commercial reactor
DEMO
R & D
JT-60SA
Conduct complementary study to tokamak and deepen comprehensive understanding of toroidal plasmas.
NIFS, Universities
LHD-Upgrade
(long pulse, W-wall)
next-step
(optimized, HTC, steady-state)
LHD
scientific research
innovative fusion research
spin-off to fundamental science and appication
Tomohiro Morisaki, 39th FPA 2018

15. Summary
LHD has progressed as a large-scale superconducting device since 1998, having demonstrated its advantage of steady-state operation, and now entering advanced deuterium experiment phase.
Operational regime was extended to Ti = 10 keV with D plasma, and clear isotope effect was identified in ion channel.
Behavior of energetic particles was investigated with newly installed neutron diagnostics.
For the realization of fusion power, stellarator/heliotron community should conduct complementary study to tokamak, and deepen comprehensive understanding of toroidal plasmas.
Tomohiro Morisaki, 39th FPA 2018

16. Tomohiro Morisaki, IAEA-FEC2018

17. LHD - a superconducting heliotron -
Characteristics
 thick stochastic layers (3D)
 built-in divertor (helical divertor)
reff (m)
 high shear in edge
LHD
W7-X
Tomohiro Morisaki, IAEA-FEC2018

18. Diagnostics and facilities newly installed or upgraded for D-exp.
exhaust detritiation system, installed
NBI, ECH, optimized for D-beam
Stack
neutron diagnostics, installed
Closed divertor, improved
upgraded to bulk CX to separately measure H/D ion profile with high resolution
Tanaka M, FIP/P1-7
CXRS, upgraded
Ida, EX/10-1
Ikeda, FIP/P1-54
Keywords:
- neutron
- isotope
- high energy particle
- profile measurement
Ogawa, EX/P3-20
Motojima, EX/P3-27
Tomohiro Morisaki, IAEA-FEC2018

19. Strategy to evaluate isotope effect in LHD
𝜒 GB ~ 𝜌 2 𝑉 th 𝑅 ~ 𝒎 𝟎.𝟓 𝑇 1.5 𝑅 𝑞 2 𝐵 2
Isotope effect is a long-standing mystery
But clear discrepancy from gyro-Bohm model is identified in many tokamaks
indicates confinement of heavier ions should be worse
Gyro-Bohm model
What about in stellarator/heliotrons ?
Thomson scattering
- 30Hz (144ch, continuous)
- 1kHz (42ch, 50ms)
- 15kHz (42ch, 15ms)
Two approaches to identify mass effect
confinement
Global
Scaling of global confinement time
CXRS (toroidal/poloidal)
- 50Hz (120ch)
- 200Hz (50ch)
- 1kHz (36ch)
with quite small error bar
𝜏~ 𝐴 𝑥 1 ∙𝜌 ∗ 𝑥 2 ∙ 𝜈 ∗ 𝑥 3 ∙ 𝛽 𝑥 4
Local transport
Local
<= enabled by excellent profile measurements
Dependence on local parameters, their gradients
𝜒~ 𝐴 𝑥 1 ∙𝜌 ∗ 𝑥 2 ∙ 𝜈 ∗ 𝑥 3 ∙ 𝛽 𝑥 4 ∙ 𝑇 𝑒 𝑇 𝑖 𝑥 5 ∙ 𝑅 𝐿 𝑇 𝑥 6 ∙ 𝑅 𝐿 𝑛 𝑥 7 ∙∙∙∙
Tomohiro Morisaki, IAEA-FEC2018

20. What is changed in deuterium plasma ?
Global
Particle confinement degrades in deuterium discharges
Particle confinement time in NBI plasma
Yamada
EX/P3-5
𝜏 𝐸,𝑡ℎ,𝑁𝐵𝐼 𝑠𝑐𝑙 ∝ 𝐴 −0.26±0.04 𝐵 1.11± 𝑛 𝑒 0.25±0.03 𝑃 𝑎𝑏𝑠 −0.89±0.03   
(AD/AH)-0.26 = = 0.84
Particle confinement time in ECH plasma
K.Tanaka
EX/P3-6
𝜏 𝑃 𝐸𝐶𝐻 ∝ 𝐴 −0.33± 𝑛 𝑒 0.52±0.02 𝑃 𝑎𝑏𝑠 −0.69±0.02
(AD/AH)-0.33 = = 0.80
Further accumulation of database and analyses are necessary to reach conclusion for particle confinement
Tomohiro Morisaki, IAEA-FEC2018

21. Precise profile measurements enable advanced analyses
Local
Significant isotope effect was observed both in ion and electron heat transports
Nagaoka
EX/5-1
ci/cGB in GKV
ce/cGB in GKV
Zonal flow enhancement was also confirmed in GKV simulation
Reduction of i/GB and e/GB in D plasma were reproduced with the nonlinear GKV simulations
Tomohiro Morisaki, IAEA-FEC2018

22. What about the impurity transport ?
Local
Isotope effect on impurity transport was found to have two steps
Ida
EX/10-1
H- plasma
Ti(0) ~ 7 keV
nC is hollow inside ITB (outward convection)
D- plasma
Ti(0) ~ 9 keV
nC is peaked inside ITB (inward convection)
Primary effect
Peaked nC stabilizes ITG turbulence (K.Kim, PoP (2017)
Ti(D) > Ti(H)
Secondary effect
Tomohiro Morisaki, IAEA-FEC2018

23. Confinement properties of energetic ions
EP confinement was investigated by neutron flux decay after short pulse NB injection (NB blip)
Ogawa, EX/P3-20
GNET
 Time evolution of Sn obtained in experiment is compared with GNET calculation
 Beam ion transport can be described with neoclassical model
Tomohiro Morisaki, IAEA-FEC2018

24. Interactions between EPs and MHD modes
Neutron diagnostics contribute to quantitative research on energetic particle (EP) confinement, and on interaction between MHD modes and EPs
Ohdachi
EX/1-3Rb
Precession motion
Mode Rotation
helically trapped EP orbit
Resistive interchange mode is destabilized when the precession motion of helically trapped EPs resonates with pressure driven interchange modes
Velocity modulation caused by toroidicity of the magnetic field produces the resonance.
ECH and RMP application can suppress EIC without reducing EP pressure
Tomohiro Morisaki, IAEA-FEC2018