Deuterium experiment project on LHD and impact of plasma ion species on confinement M. Osakabe a, Y.Yokoyama a, K.Nagaoka a, H.Takahashi a, R.Seki a, S.Murakami b, M.Yoshinuma a, K.Tanaka a, K.Ida a, K.Nagasaki c, T.Fujita d, Y.Ohya e, M.Isobe a, T. Morisaki a, S.Sakakibara a, Y.Takeiri a, and LHDproject a National Institue for Fusion Science, Toki, Gifu 509-5292, Japan b Kyoto University, Nishikyo, Kyoto 615-8540, Japan c Kyoto University, Uji, Kyoto 615-8540, Japan d Nagoya University, Nagoya, Aichi 466-8550, Japan e Shizuoka Univeristy, Shizuoka, Shizuoka 422-8017, Japan 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 1
CONTENTS 1. Deuterium experiment on LHD Objective & Main subjects Schedule & Constraints 2. Isotope Effect Brief description Possible candidate Direct /Indirect effect by isotopes 3. Summary 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 2
DEUTERIUM EXPERIMENTS ON LHD 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 3
Objectives of the LHD deuterium experiment are; 1. To realize high-performance plasmas by confinement improvement and by the improved heating devices. This will provide a wide operational range in plasma parameter space relevant to the reactor plasmas. As a consequence, scientific research area will be expanded and the variety of experiments will also be available. 2. To study the isotope effect in the plasma confinement. The information of isotope effect in Helical system will provide the configuration dependence such as iota(safety factor) and shear of the effect. 3. To demonstrate that the confinement capability of highenergy ions is relevant to the burning plasmas in helical systems. Better understanding of energetic particle confinement in 3D magnetic field configuration. 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 4
Annual Plan for LHD Deuterium Experiment First 6 years Second 3 years FY 1st year 2nd 6th year 7th 9th year Experiments Maximum Annual Yield of Tritium Maximum Annual Discharge of Tritium Maximum Annual Yield of Neutron Preliminary Exp. (Commissioning) 3.7x10 10 Bq (1 Ci) (Integrated yield) Plasma Exp. For Target Parameters 3.7x10 9 Bq (0.1 Ci) (Integrated yield) 2.1x10 19 (Integrated yield) Integrated High- Performance Exp. 5.55x10 10 Bq (1.5 Ci) (Integrated yield) 3.2x10 19 (Integrated yield) 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 5/21
ISOTOPE EFFECT 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 6
Isotope effect on the confinement is widely observed in Tokamak plasmas, but its physical mechanism is not clear. Empirical Scaling of isotope by ττ EE ~AA αα is often mentioned. The α is different in the discharge scinarios and machine. Favorable dependence on mass is usually observed,i.e., α>0. ITER89-P: α=0.5[1], ITERH93-P:α=0.4, DD/DT: TFTR(supershot): α=0.85[3], JET(H-mode): α=0.03(total) (α=-0.17(core), α=0.5(pedestal))[4, 5] Theoretical prediction contradicts to the empirical scaling laws: Gyro-Bohm scaling indicates negative dependence on mass [5]: α=-0.2 (Engineering). (Physics Scaling: α=-0.5) [1] P.N.Yushmanov, et.al., NF 30(1990)1999 [2] M. Bessenrodt-weberpals, et.al., NF22(1993)1205 [3] S.D.Scott, et.al., POP 2(1995)2299 [4] J.Jacquinot, et.al., PPCF 41(1999)A13 [5] J.G.Cordy, et.al., NF 39(1999)301 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 7
Possible candidates of mechanism for Isotope effect Direct effect: The mass (and/or charge) of bulk-ion species has some influence on confinement: v th, r L is different : e.g., Mach number => Zonal flow generation [1] Indirect effect [2]: Neutrals [2] Impurity => Er formation [1] T.H. Watanabe et al., NF 51 (2011) 12300 [2] K.Itoh and S-I. Itoh, PPCF 37(1995)491 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 8
Decrease of long range correlation was observed at TEXTOR, but not in TJ-II. Direct Effect TEXTOR: Y.Xu, et al., PRL 110(2013)265005 TJ-II: B. Liu et al., EPS-2014, submitted PRL LRC C xy (τ=0) C xy (τ=0) Experimental findings show a systematic increasing in the amplitude of zonal flows during the transition from H to D dominated plasmas in TEXTOR tokamak but NOT in the TJ-II stellarator. 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 9
On FT-2, turbulence level modulation at GAM frequency was observed. Anti-correlation between the GAM amplitude and the effective electron thermal diffusivity was also observed on the experiment. GAM ampl χ eff (m 2 /s) 30 20 10 0 6 H 3 H D D 4 5 6 r (cm) noise IAEA-FEC 2014, EX/11-2Ra, A. Gurchenko 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 10
Indirect Effect (I) ITER like wall experiments gave us some useful information: H-mode confinement degraded to 70% (All-C =>ILW) The confinement recovered by adjustment of diverter strike point [1]. <= Neutral effect N2-seeding to diverter region recovers the H-mode performance[2]. <= Impurity effect V/H C/C C/V Low δ [1] C.F.Magi, et.al., IAEA-FEC 2014 EX3-3 [2] G.P. Maddison, et.al., NF54(2014)073016 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 11
It is widely recognized that the reduction of recycling of hydrogen isotope from wall improves the confinement Supershot in TFTR[1], High- Ti discharge in LHD[2] were achieved with low recycling condition. Neutral penetration length and reflection coefficient can be different between D and H. Isotope effect of confinement can be appeared through neutral distribution. E.W. Thomas,et.al., NIM B69(1992)427 [1] J.D.Strachen,et.al., PRL58(1987)1004 [2] H.Takahshi, et.al., PFR9(2014)1402050 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 12
Indirect Effect (II) The sputtering yield at carbon plate by H/D are different. The amount of carbon impurity in plasmas is different: Higher Z eff in D-plasmas[1,2] J.B. Roberto et al., ORNL/TM-8593 (1983) Target: Carbon D H [1] H. Urano, et.al., NF52(2012)114021 [2] M. Besserodt-weberpals, et.al., NF33(1993)1205 Ion Energy [ev] 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 13
Impurity effect H-mode confinement degraded to 70% (All-C =>ILW) The confinement recovered by N 2 -seeding [1]. N2-seeding (all-c) [1] G.P. Maddison, et.al., NF54(2014)073016 All-C w/o N 2 ILW w. N 2 N2-seeding (ILW) Correlation between impurity accumulation and turbulence/confinement property must be investigated in D-experiments. 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 14
Carbon impurity affects the confinement property of plasmas [1] 4 different-size C pellets were injected into in high-ti plasmas. Carbon impurity was quickly expelled by Impurity Hole formation. Degradation confinement was observed at low carbon density. Indicating the existence of threshold of C density for ion heat confinement improvement n e =~1.5x10 19 [m -3 ] Zeff=~2 [1] M.Osakabe, et.al., PPCF 56(2014)095011 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 15
SUMMARY Objectives and schedules in the deuterium experiment are described. Possible candidate of isotope effect are shown. Direct Effect 1 Mass (/Charge) of ion species influences to the confinement property. Indirect effect 2 Neutral distribution/amount 3 Impurity amount Different sputtering yield of diverter/1 st wall by hydrogen isotopes might affect the confinement. To explore the physics of isotope effects, these three candidates must be considered. 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 16
On LHD, we are starting to build up confinement database of mass and charges by using impurities, i.e., He, N, C, and Ne, etc, at this moment as a preparation to explore the isotope effect. Questions to KSTAR colleagues; Is there anybody who are interested on this issue in KSTAR? Can KSTAR be operated in Hydrogen? (NB might have problem?). Do you have enough tools to investigate those effects separately? I would like to have some collaboration (may be starting from information exchange on this WS) on this issue with KSTAR team!! 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015
BACK UP SLIDES 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 18
Mass dependence in GB scaling Assuming the characteristic wave length l and the frequency w as: Characteristic wave length: ll~ 1 kk ρρ ii, and Characteristic frequency: ωω 1 ττ vv TTTT LL where L is a characteristic scale length of the equilibria., Gyro-Bohm diffusivity is expressed as: χχ ii GGGG ll 2 ττ ρρ 2 ii vv TTTT LL ρρ ii TT ii eeeeee TT ii 3 2 1 2 mm ii eebb 2 LL The energy confinement time will be: ττ GGGG EE aa 2 χχ GGGG 1 ii mm ii (Physics scaling) In the case of the engineering scaling, Ti is expressed by P(heating power) and n(density) as: PPττ EE = WW ttt = 3 2 nnnn = 3nn iitt ii with an assumption of nn ii = nn ee and TT ii =TT ee. PPττ Thus, TT ii = EE 3nn. Substituting this into the physics scaling, one can obtain the following relationship (ττ EE ττ GGGG EE ): ττ EE GGGG aa2 eebb 2 LL aa 2 eebb 2 LL 3 2 mm 1 2 ii TT ii PPττ EE GGGG 3nn 3 2 3 2 5 2 aa2 eebb 2 LLnn ee GGGG ττ EE PP 3 2 mm 1 2 ii ττ GGGG 1 EE mm 5 ii. mm ii mm 1 2 ii J.G.Cordy, et.al., NF 39(1999)301 2015/3/6 KSTAR Conference 2015, Feb.25-27, 2015 19