Wide dynamic range neutron flux monitor having fast time response for the Large Helical Device

Isobe, M.; Ogawa, K.; Miyake, Hideaki; Hayashi, Hiroshi; Kobuchi, T.; Nakano, Yuji; Watanabe, K.; Uritani, Akira; Misawa, Tsuyoshi; Nishitani, T.; Tomitaka, Makoto; Kumagai, T.; Mashiyama, Y.; Ito, Daiki; Kono, Shigehiro; Yamauchi, M.; Takeiri, Y.

doi:10.1063/1.4891049

Cited by 58 publications

(49 citation statements)

References 13 publications

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“…The neutron flux monitor, the neutron activation system, the vertical neutron camera, and scintillating-fiber detectors are used for obtaining Sn, total DD and secondary DT neutron emission amount, neutron emission profiles, and time evolution of the DT neutron emission rate, respectively. The time evolution of Sn is obtained by the absolutely-calibrated neutron flux monitor consisting of fission chambers and 3 He/ 10 B proportional counters [21]. The digital signal 5 processing unit is developed for the fission chamber equipped with the field programmable logic circuit realizing the wide dynamic range up to 5×10 9 cps and finer temporal resolution of 2 ms. Study of global confinement of beam ions will be enhanced by means of the neutron flux monitor.…”

Section: Neutron Diagnostics In the Large Helical Devicementioning

confidence: 99%

Energetic ion confinement studies using comprehensive neutron diagnostics in the Large Helical Device

et al. 2019

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Understanding of energetic particle (EP) confinement is one of the critical issues in realizing fusion reactor. In stellarator/helical devices, the research on EP confinement is one of the key topics to obtain better confinement by utilizing the flexibility of three-dimensional magnetic field. Study of EP transport in the Large Helical Device (LHD) has been performed by means of escaping EP diagnostics in hydrogen plasma operation. By starting deuterium operation of the LHD, confinement study of EPs has progressed remarkably by using newly developed comprehensive neutron diagnostics providing the information of EPs confined in the core region. The total neutron emission rate (Sn) increases due to the relatively low deviation of beam ion orbit from the flux surface with the inward shift of the magnetic axis. Sn has the peak around the electron density of 2×10 19 m -3 to 3×10 19 m -3 , as predicted. It is found that the fraction of beam-beam components in Sn is evaluated to be approximately 20% by the Fokker-Planck models TASK/FP in the plasma with both co-and counter-neutral beam injections. The equivalent fusion gain in DT plasma achieved 0.11 in a negative-ion-based neutral beam heated 2 plasma. Time evolution of Sn following the short pulse neutral beam injection into the electroncyclotron-heated low-beta plasma is reproduced by drift kinetic simulation, indicating that transport of beam ion injected by short pulse neutral beam can be described with neoclassical models in magnetohydrodynamic quiescent low-beta plasmas. The vertical neutron camera works successfully, demonstrating that in the co-neutral beam injected plasma, neutron emission profile shifts according to magnetic axis position. The shift of the neutron emission profile is reproduced by orbit-following models. The triton burnup study is performed for the first time in stellarator/heliotron so as to understand the alpha particle confinement. It is found that the triton burnup ratio, which largely increases at inward shifted configurations due to the better triton orbit and better plasma performance in inward shifted configuration is similar to that measured in tokamak having a similar minor radius with the LHD. We study the confinement capability of EPs toward a helical reactor in magnetohydrodynamic -quiescent region and expansion of the energetic-ion physics study in toroidal fusion plasmas.

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Section: Neutron Diagnostics In the Large Helical Devicementioning

confidence: 99%

Energetic ion confinement studies using comprehensive neutron diagnostics in the Large Helical Device

et al. 2019

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“…In the following experiments, the toroidal magnetic field strength is |B| = 2.75 T, whose direction is counter-clockwise from the top view and the preset of the magnetic axis position is R axis = 3.6 m. Therefore, NB#1 and NB#3 are co-direction of the magnetic field and NB#2 is counter-direction. The averaged plasma minor radius is approximately 0.6 m. The plasma temperature and density profiles have been measured by the Thomson scattering diagnostics and the neutron emission rate has been measured by Neutron Flux Monitor [9].…”

Section: Scenariomentioning

confidence: 99%

Analysis of Energetic Particle Confinement in LHD Using Neutron Measurement and Simulation Codes

Nuga

Seki

Ogawa

et al. 2019

Plasma and Fusion Research

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The fast ion confinement time in the Large Helical Device (LHD) is investigated by using the neutron measurement and simulations. To estimate the fast ion confinement time, a series of short pulse neutral beam (NB) injection experiments have been performed. Additionally, the NB heating simulation code, CONV_FIT3D, has been extended to estimate the neutron emission rate in LHD. We estimate the fast ion confinement time from the differences between the measured and the simulated neutron decay times after the NB is turned off. It is found that the fast ion confinement time of three tangential NBs have similar values τ c ∼ 0.5 sec and the confinement time of the perpendicular NB is approximately τ c ∼ 0.06 sec. Additionally, by using the confinement time and the ion ratio data estimated from the simulation result, we can obtain a simulation result similar to the measured data.

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“…The experiments were performed in a relatively low-electron temperature condition in order to maintain the low total neutron emission rate (S n ) so to avoid the counting loss of the CNES. The neutron counting rate obtained by CNES in each NB phase is compared to S n obtained by a neutron flux monitor (NFM) [7,20], as shown in Fig. 5a).…”

Section: Measurement Of Neutron Energy In Nb Heated Lhd Plasmamentioning

confidence: 99%

Observation of significant Doppler shift in deuterium-deuterium neutron energy caused by neutral beam injection in the large helical device

et al. 2022

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The compact neutron emission spectrometer (CNES) having a tangential sightline was installed to observe a significant Doppler shift of the neutron energy due to the high-energy tangential neutral beam (NB) injections in the Large Helical Device (LHD) for understanding of the energy distribution of fast-ion. The CNES is based on a 1-inch diameter and 1-inch height EJ301 liquid scintillator coupled with a conventional 1-inch photomultiplier tube. The histogram of the integrated pulse signal (Qtotal) during different NBs heating phases measured by the CNES shows that the edge of Qtotal changes depending on NB directions. Using the simple derivative unfolding technique, the neutron energy spectra were unfolded from the measured Qtotal histogram. Peaks of the neutron energy shift to 2.0 MeV, 2.42 MeV, and 3.0 MeV according to the injection direction of NBs. The obtained neutron energy is almost consistent with the virgin deuterium-deuterium neutron energy evaluated by the simple two-body kinematics considering the sightline of CNES, NB injection angle, and NB injection energy.

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Wide dynamic range neutron flux monitor having fast time response for the Large Helical Device

Cited by 58 publications

References 13 publications

Energetic ion confinement studies using comprehensive neutron diagnostics in the Large Helical Device

Energetic ion confinement studies using comprehensive neutron diagnostics in the Large Helical Device

Analysis of Energetic Particle Confinement in LHD Using Neutron Measurement and Simulation Codes

Observation of significant Doppler shift in deuterium-deuterium neutron energy caused by neutral beam injection in the large helical device

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