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

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

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

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

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

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 = 0.425 T) 4.1 % (1.000 T) Tomohiro Morisaki, 39th FPA 2018

LHD - a superconducting heliotron - Specifications  Helical mode numbers: l/m=2/10  All superconducting coil system  Plasma major radius: 3.42-4.1 m  Plasma minor radius: 0.63 m  Plasma volume: 30 m3  Toroidal field strength: 3 T  20 RMP coils Heating Systems  negative-NBI x 3 (180-190keV), H16MW, D8MW  positive-NBI x 2 (40-80keV), H6MW, D18MW  ICH (20 – 100MHz) x 6 3 MW -> tentatively removed  ECH (77GHz x 3, 154 x 2, 82.7, 84) 5.5MW Tomohiro Morisaki, 39th FPA 2018

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

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

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±0.02 𝑛 𝑒 0.78±0.01 𝑃 𝑎𝑏𝑠 −0.87±0.01    (AD/AH)-0.01 = 2-0.01 = 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±0.01 𝑛 𝑒 0.58±0.01 𝑃 𝑎𝑏𝑠 −0.52±0.01 (AD/AH)0.24 = 20.24 = 1.18  Obvious mass dependence (isotope effect) identified Each experiment was performed with purity of H and D > 80% Tomohiro Morisaki, 39th FPA 2018

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

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

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

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

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

Tomohiro Morisaki, IAEA-FEC2018

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

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

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

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±0.04 𝑛 𝑒 0.25±0.03 𝑃 𝑎𝑏𝑠 −0.89±0.03    (AD/AH)-0.26 = 2-0.26 = 0.84 Particle confinement time in ECH plasma K.Tanaka EX/P3-6 𝜏 𝑃 𝐸𝐶𝐻 ∝ 𝐴 −0.33±0.02 𝑛 𝑒 0.52±0.02 𝑃 𝑎𝑏𝑠 −0.69±0.02 (AD/AH)-0.33 = 2-0.33 = 0.80 Further accumulation of database and analyses are necessary to reach conclusion for particle confinement Tomohiro Morisaki, IAEA-FEC2018

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

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

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

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