Fusion neutron production with deuterium neutral beam injection and enhancement of energetic-particle physics study in the Large Helical Device

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1 15 th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems, 5-8 September, PPPL Session 8 : Diagnostic Development : O-14 Fusion neutron production with deuterium neutral beam injection and enhancement of energetic-particle physics study in the Large Helical Device M. Isobe 1,2, K. Ogawa 1,2, T. Nishitani 1, N. Pu 2, H. Kawase 2, R. Seki 1,2, H. Nuga 1,E. Takada 3, S. Murakami 4, Y. Suzuki 1,2, M. Yokoyama 1,2, M. Osakabe 1,2, and LHD experiment group 1 1 National Institute for Fusion Science, National Institutes of Natural Sciences Toki , Japan 2 SOKENDAI (The Graduate University for Advanced Studies), Toki , Japan 3 National Institute of Technology, Toyama College, Toyama , Japan 4 Kyoto University, Kyoto , Japan 1/18

2 Outline of talk 1) Deuterium operation of LHD 2) Neutron diagnostics prepared for LHD Neutron flux monitor (NFM) Neutron activation system (NAS) Vertical neutron camera (VNC) Scintillating fiber (Sci-Fi) detector 3) Representative results from 1 st deuterium campaign of LHD 4) Summary 2/18

3 LHD deuterium operation began in March 7, 2017 after long-term preparation First deuterium plasma (#133301) Group photo after the ceremony (VIPs version) 3/18

4 Deuterium operation of LHD and expected neutron emission rate Deuterium plasma experiment began in LHD to explore higher-performance helical plasmas and to gain a positive prospect toward an LHD-type fusion reactor. Neutron yield measurement is essential in the LHD operation, since neutron yield has to be managed in compliance with neutron budgets approved by NRA of JA. Total neutron emission rate (n/s) 2x x Expected neutron rate Max. neutron rate is expected to be over 1x10 16 (n/s) when full power NB heating is performed. In LHD, generated neutrons are dominated by neutrons coming from beam-plasma reactions. Neutron diagnostics play an important role to accelerate understanding of EP physics in LHD plasmas. Line-averaged density (x m -3 ) 4/18

5 A comprehensive set of neutron and gamma-ray diagnostics prepared for the LHD deuterium campaign Diagnostics Measurement target Role Status (1) Neutron flux monitor Total neutron rate, yield Neutron yield management Fusion output Global fast-ion confinement Working (2) Neutron activation system Total neutron yield Secondary DT neutron yield Neutron yield management Triton burnup Working (3) Vertical neutron camera Neutron emission profile Beam ion profile Beam-ion transport by EPM/AE Working (4) Fast-neutron scintillation detector Neutron fluctuation Beam-ion transport by EPM/AE Working (5) Sci-Fi detector Secondary DT neutron rate Triton burnup Working (6) g-ray scintillation detector Prompt g-ray flux Confinement of MeV ion D- 3 He reaction rate in the future Working Development of DD neutron spectrometer will be initiated in FY2017 to measure fast-ion velocity distribution in a plasma core in the collaboration with Peking Univ. 5/18

6 LHD is equipped with three ex-vessel NFMs characterized by fast-response and wide dynamic range capabilities 235 U fission chamber (FC) Thermal neutron sensitivity : 0.1 (cps/nv) 10 B counter Thermal neutron sensitivity : 6.5 (cps/nv) 3 He counter Thermal neutron sensitivity : 39 (cps/nv) FC up to 5x10 9 (cps) 235 U FC can work in a high-neutron yield shot, playing an important role in neutron yield management and energetic-particle physics study. 10 B and 3 He counters are used for a low-neutron yield shot, e.g. ECRH plasma w/o NB.

7 In situ NFM calibration on LHD in Nov., 2016 (1) In situ NFM calibration was performed to evaluate total neutron emission rate. The calibration was carried out along the method standardized in the WS on the neutron calibration held at PPPL in (J.D. Strachan et al., Rev. Sci. Instrum. 61(1990)3501.) Relation between neutron rate S n and pulse counting rate C rate is expressed as S n (n/s) = a C rate (cps) Coefficient a is obtained by using a neutron source whose neutron rate is known. Activation foil Track placed at R ax of 3.74 m Neutron detectors ( 235 U, 10 B, 3 He) 252 Cf source intensity : 800 MBq (~10 8 (n/s)) M. Isobe et al., Rev. Sci. Instrum. 81 (2010)10D310. 7/18

8 Y X W E V U T K In situ NFM calibration on LHD in Nov., 2016 (2) The train loaded with 252 Cf ran continuously inside the VV. J Calibrations with continuous run were performed seven times with different discrimination levels of FC. F G H I L M B N O Point-by-point measurements were also carried out. D C B A S R Q P 線源容器クレーンで搬入のため 近辺の機器とある程度間隔が必要 Train 作業位置 Station 人が入るため通路が必要 作業領域を右側にとることも可 3m の棒により 線源を容器から 列車に移すため 4m ほど必要 DD ファーストプラズマ前の較正実験まで使用 現在の予定では 平成 26 年 12 月まで それ以降は 大きな装置の改造がない限り使用しないが 再び行 う場合に 作業領域が確保できるようにお願いします 8/18

9 Neutron pulse counts during in situ calibration 235 U fission chambers Dependence of detection efficiency on source toroidal angle 10 B and 3 He counters S n (n/s) = a C rate (cps) Coefficient a for primary FC(TOP) : 1.46x10 8 9/18

10 Neutron emission rate measured with NFM in LHD (1) Systematic survey of neutron emission rate for beam-heated plasmas Highest neutron rate shot in 1 st D campaign S n in R ax of 3.6 m is the highest. It tends to decrease as R ax is shifted outwardly as expected. 3.3x10 15 (n/s) Time (s) 10/18

11 Neutron emission rate measured with NFM in LHD (2) Perpendicular beam blip injection into an ECRH plasma Peak value of S n increases as n e increases as expected according to increase of beam deposition. Neutron decay time tends to be shorter (longer) as n e increases (decreases). This tendency is consistent with that predicted by classical slowing-down theory 11/18

12 Central fuel ion temperature evaluated from neutron emission rate in an ECRH deuterium plasma of LHD Waveforms of ECRH discharge Time evolutions of T d (0) and T imp T d (0) 10 B counter Time (s) K. Ogawa, M. Isobe et al., accepted for publication in Plasma and Fusion Research. Total neutron emission rate, profile deduced from TS, and H/D ratio are used. Z eff is assumed to be 2. T d (0) evaluated by neutron emission rate is consistent with T imp (Ar) measured with X- ray crystal spectroscopy diagnostic. 12/18

13 Neutron activation system on LHD The NAS on LHD has two irradiation ends, which perform important roles in crosschecking neutron yield evaluated by the NFM. Pneumatic tubes Measurement room Pneumatic control system HPGe 2.5-L port Station Neutron yield per shot evaluated by NAS In(n,n ) 115m In Neutron yield per shot evaluated by NFM Neutron yield evaluated by NAS agrees well with that measured with NFM. Also, NAS has been used to measure secondary 14 MeV neutron fluxes by using 28 Si(n, p) 28 Al reaction to study 1 MeV triton s behavior. 13/18

14 Vertical neutron camera on LHD Arrangement of VNC 11 channel Collimator was made of heavy concrete. Detector can be stably operated up to 10 6 (cps) with online + offline n-g discrimination capability. The peak of line-integrated neutron emission profile shifts outward with an increase of R ax.

15 Significant change of neutron emission profile due to recurrent fast-ion-driven MHD bursts Shot# R ax =3.62 m B t =2.83 T (CCW) Magnetic fluctuation amplitude Intermittent decreases of neutron emission rate are observed associated with MHD bursts. Line-integrated neutron profile suggest that beam ions confined in plasma core region are lost due to MHD modes. 15/18

16 Study of 1 MeV triton s behavior by measuring secondary D-T neutron Time-resolved 14 MeV neutron flux is measured by using scintillating-fiber detectors. Reactions in a deuterium plasma D+D -> 3 He (0.8 MeV) + n (2.5 MeV) D+D -> T (1 MeV) + p (3 MeV) Secondary reaction T+D -> 4 He (3.5 MeV) + n (14 MeV) Neutron emission rate (n/s) Time evolutions of total and 14 MeV neutron rates NBI Total neutrons 14MeV neutrons Shot #: MeV n Recoil proton Scintillation light Time (s) Build-up rate of 14 MeV neutron flux is slower than that of total neutron rate. It comes from cross section curve for D-T reaction. 16/18

17 Triton burnup ratio significantly depends on magnetic field configuration The Sci.-Fi. detector is calibrated by using results measured with calibrated NAS. Helically trapped orbits Triton burnup ratio can be evaluated in every shots. R ax =3.6 m R ax =3.75 m R ax =3.9 m Maximum triton burnup ratio is ~0.45% in R ax /B t of 3.55 m/2.89 T. Triton burnup ratio decreases as a plasma column is shifted outwardly as expected from orbit calculations. 17/18

18 Summary 1) The LHD project stepped into a new stage. The deuterium experiment began in March 7 th, 2017 after long-term preparation. 2) A comprehensive set of neutron diagnostics has been installed. 3) Total neutron yield Y n has been measured with a fast response, wide dynamic range NFM, and NAS. Y n management is essential in the operation of LHD. Max. counting rate capability of NFM goes up to ~5x10 9 (cps). In situ calibration by using 252 Cf (800 MBq) was performed in Nov Neutron rate has reached ~3.3 x10 15 (n/s) in the inwardly shifted configuration at R ax of 3.55 m. 4) DD neutron profile has been measured with VNC. Neutron emission profile have changed according to Rax. Significant change of neutron profile was observed due to recurrent fast-ion-driven MHD events. 5) In addition to NFM, VNC, and NAS, scintillating fiber detectors have been used to study confinement property of 1 MeV tritons. Triton burnup ratio decreases as a plasma column is shifted outwardly as expected. 18/18