Development of Net-Current Free Heliotron Plasmas in the Large Helical Device

Transcription

1 Development of Net-Current Free Heliotron Plasmas in the Large Helical Device A. Komori for the LHD Experimental Group National Institute for Fusion Science Toki, Japan 22nd IAEA Fusion Energy Conference Geneva, October,1/17 28

2 Reactor relevant net-current free plasmas in LHD ASDEX MAST Unique test bed for high-performance steady state plasmas & 3-D study Large commonality with tokamaks 2/17

3 Outline _ 1. High ion temperature 6.8 kev at ne = 2 119m-3 with confinement improvement similar to ITB accompanied by Impurity hole 2. High beta <β> = 5 %, <β> > 4.5 % for > 1τE 3. High density ne () = m-3 at B = 2.5 T with Internal Diffusion Barrier (IDB) in Helical Divertor 4. Steady state 5. Summary EX: 22 papers, TH: 8 papers, FT: 4 papers in this conference Please visit these studies for details on transport, MHD stability, fast Ions, AE, heating physics, divertor, PSI, dust and reactor design 3/17

4 New perpendicular NBI much improves ion transport study - High-power NBI of 23 MW in total 4 beam lines of NBI = 3 tangential + 1 perpendicular ( + 1 perpendicular in 21) Tangential beams 18keV-tangential NB injector Perpendicular beam NBI 7 MW, E = 4kV with positive-ion sources i 4keV-perpendicular NB injector Ion heating (T () = 6.8 kev) works as a diagnostic beam for 4/17

5 Improvement of ion heat transport realized by upgrade of ion heating power _ 8 8 Pi=6.5~1MW 6 Ti (kev) Ti() (kev) Pi=2.5~5MW 1 3 _2 ne (119 m-3) ρ Above Pi / ni > MW m3 (Fri) EX/8-2Ra by Nagaoka 5/17

6 Ion thermal transport is improved significantly in ITB phase χ i_exp(w/o ITB) 1 1 χ i (m2/s) i 2 χ (m /s) χ i_exp(itb) χ i_nc(itb) 1 ρ =.3 ρ =.8 χ i_nc(w/o ITB).2.4 ρ Pi/ni (MW/119m-3) Anomalous transport is suppressed in the ITB phase NC analysis suggests large negative Er (Ion root) (Fri) EX/8-2Ra by Nagaoka 6/17

7 Carbon impurity is expelled due to outward convection in ITB phase : Impurity Hole t=1.25s 1..3 ncvi (119 m-3) 1.5 t=1.65s R (m) t=1.25s t=1.65s ncvi (119 m-3) ne (119m-3) R (m) More hollow as the ion temperature gradient is increased Steep Ti gradient Extremely hollow carbon profile impurity hole, which is quite different from electron density profile. Contradicting NC prediction suggests anomalous convection (Fri) EX/8-2Rb by Ida 7/17

8 β of 5 % has been achieved and β of 4.5 % has been maintained in steady state 3-D equilibrium calculated by HINT 5 <β > (%) <β > > 3.5 % 5 τ duration 1 /τ 15 E Beta limit Transport in the ergodic layer Change of magnetic topology, e.g., magnetic island dynamics Effect of stochasticity has been investigated in detail (Wed) EX/P5-9 by Weller, (Fri) EX/8-1Rb by Ohdachi, TH/P9-19 by Suzuki 8/17

9 High-β Operational Regime Standard Scenario IDB Scenario Sa (Fri) EX/8-1Rb by Ohdachi Co ll th o o wt ap se Ap = 6.6 (25~) Ap = 6.3 (24) Ap = 5.8 (~23) Magnetic axis position is a key parameter for high-beta Standard Scenario (broad pressure profile) - restrict the plasma outward shift to maintain good heating efficiency at low-field increase plasma aspect ratio <β> = 5 %, β ~ 1 % IDB Scenario (peaked pressure profile) - overcome the core density collapse <β> = 2 %, β ~ 1 % 9/17

10 Interaction between Alfvén eigenmodes and energetic-particles in LHD TAE-induced fast-ion loss measurement with scintillator probe (SLIP) Analysis in collaboration (Fri) EX/P8-5 by Nishiura with AE3D code (Thu) TH/3-4 by Spong (ORNL) Impact of Alfvén eigemodes on GAM (Fri) EX/P8-4 by Toi Understanding of RSAE freq. sweeping with MHD theory (Fri) EX/P8-4 by Toi Phase space structure analysis of TAE-induced fast-ion transport (Tue) TH/P3-9 by Todo 1/17

11 Achievements of High Density, High Pressure Discharges with Internal Diffusion Barrier e 21-3 Maximum n () exceeds 1 1 m Maximum P() =13 kpa Pressure is limited (Fri)rise EX/8-1Rb byby Ohdachi Core Density Collapse (CDC) CDC mitigated by elongation P() = 15 kpa IDB widens as the preset magnetic axis is moved outward and IDB foot extends to LCFS with Rax= 4. m LCFS IDB foot shifted axis max. ne() κ optimized max. P() IDB formation 11/17

12 Diffusion Coefficient kept at tolerable level under large density gradient due to IDB Relationship between time evolution and gradient of density profiles Core plasma a (pressure rise): dne/dρ increases with IDB formation, D.5 m2/s b (maximum pressure): flux increase without dne/dρ change c (pressure decline): dne/dρ decrease with density decay, D.5 m2/s Mantle plasma A (IDB formation period): Can not reach large dne/dρduring high flux IDB phase, D.43 m2/s (after IDB disappearance): merge into c, D.5 m2/s Thermal transport is unaffected by particle transport (Fri) EX/8-1Ra by Sakamoto 12/17

13 Transport in ergodic layer is a key to high-performance high density plasmas reff (m) LC/m Te/eV 1 Core plasma is surrounded by ergodic layer due to stretching and folding of magnetic islands Edge surface layers.65 Outboard Inboard 3-D edge transport code : EMC3-EIRENE Impurity screening in stochastic region by friction with bulk plasma flow Retention of impurities via short flux tube in edge surface layer Remarkable reduction of impurity contamination in high density operation CIII/ne exp. CV/ne exp. CIII /ne Sim. CV /ne Sim _ ne (1 m ) (Wed) EX/P4-26 by Burhenn, TH/P4-4 by Feng, (Fri) EX/9-4 by Kobayashi 8 Emission Sim. (1-19 W m3) Inboard Emission Exp. (a.u.).6 Stochastic region 13/17

14 Control of heat load on divertor plate is a major key for steady state operation Critical PRF=.65 MW : Penetration of metal impurities from deposited layer on divertor plate can be simulated by small Fe pellet 2 Te (kev) PRF (MW) ne Divertor Temp. (K) pl Tdiv (K) (119 m-3) before replacing 4 Pulse length (s) 1 τ =-τ log(1-p 3 1 ht RFcr /P ) RF Before After after replacing Time (sec) Averaged RF Power (MW) Divertor plates with significant temperature increase replaced by ones with better heat conductivity critical PRF is mitigated Mode-conversion heating to avoid the production of energetic ions (Thu) EX/P6-29 by Kumazawa 14/17

15 Nearest Future Plan 1. Upgrade of heating capability NBI ICH ECH 5th beam line 7 MW, 6 kev 3 MW steady state 1 MW steady state 2. Closed helical divertor 3. Deuterium Identification and documentation of isotope effect Upgrade of NBI (32 MW in total) 4. Reactor design study FFHR : Force-Free Helical Reactor 15/17

16 Summary 1. High ion temperature 6.8 kev at ne = 2 119m-3 with confinement improvement similar to ITB 2. High beta <β> = 5 %, <β> > 4.5 % for > 1τE 3. High density ne () = m-3 at B = 2.5 T with Internal Diffusion Barrier (IDB) 4. Steady state 1MW for 8 s 5. Near-term upgrade package closed helical divertor, heating capability, deuterium 6. 3-D effect inspiring new advanced physics model and theory which are to be validated in LHD experiment 16/17

17 Contributions from LHD Ion Transport (ITB) EX/8-2Ra (K.Nagaoka), Rb (K.Ida), EX/P5-1 (M.Yoshinuma) High β / MHD EX/8-1Rb (S. Ohdachi), TH/P3-9 (Y.Todo), EX/P5-9 (A.Weller), EX/P8-4 (K.Toi), TH/P9-19 (Y.Suzuki) High Density (IDB) EX/8-1Ra (R.Sakamoto), EX/9-4 (M.Kobayashi), EX/P4-26 (R.Burhenn) Steady State EX/P6-29 (R.Kumazawa) Transport MHD Stability Fast Ion & AE Heating physics Divertor PSI & Dust Reactor TH/6-1 (S.Toda), EX/P5-6 (K.Tanaka), EX/P5-1 (S.Inagaki), EX/P5-11 (T.Fukuda), EX/P6-2 (Y.Nakamura), TH/P8-2 (T.H.Watanabe) TH/P9-16 (H.Miura), TH/P9-17 (N.Mizuguchi), TH/P9-18 (M.Sato) EX/P8-3 (S.Murakami), EX/P8-5 (M.Nishiura) EX/P6-13 (H.Igami), EX/P6-14 (S.Kubo), EX/P6-3 (H.Kasahara) EX/P4-24 (S.Masuzaki), TH/P4-4 (Y.Feng) FT/2-1 (N.Yoshida), EX/P4-7 (N.Ashikawa), EX/P4-8 (T.Hino) FT/P3-17 (S.Imagawa), FT/P3-18 (K.Kozaki), FT/P3-19 (O.Mitarai) 17/17