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Application of Advanced Nuclear Emulsion Technique to Fusion Neutron Diagnostics
Available online at www.sciencedirect.com
ScienceDirect Physics Procedia 80 (2015) 81 – 83
26th International Conference on Nuclear Tracks in Solids, 26ICNTS
Application of advanced nuclear emulsion technique to fusion neutron diagnostics Y. Nakayamaa,*, H. Tomitaa, K. Morishimab, F. Yamashitaa, S. Hayashia, MunSeong Cheonc, M. Isobed,e, K. Ogawad, T. Nakab, T. Nakanob, M. Nakamurab, J. Kawarabayashia, T. Iguchia and K. Ochiaif a
Graduate School of Eng., Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan Graduate School of Sci., Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan c Diagnostics Technology Team, ITER Korea, National Fusion Research Institute, Deajeon, 305-333, Republic of Korea d National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan e The Graduate University for AdvancedStudies, 322-6 Oroshi-cho, Toki 509-5292, Japan f Fusion Research and Development Directorate, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195, Japan b
Abstract In order to measure the 2.5 MeV neutrons produced by DD nuclear fusion reactions, we have developed a compact neutron detector based on nuclear emulsion. After optimization of development conditions, we evaluated the response of the detector to an accelerator-based DD neutron source. The absolute efficiency at an energy of 2.5 MeV was estimated to be (4.1±0.2)h10-6 tracks/neutron. © Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license © 2015 2015The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of 26ICNTS. Peer-review under responsibility of the Scientific Committee of 26ICNTS
Keywords: Nuclear emulsion, Fusion neutron measurement, Plasma diagnostics ;
1. Introduction Efficient magnetic confinement of deuterium/tritium plasma has been developed toward realization of a nuclear fusion reactor as future energy source. To obtain the required high temperature and density of the plasma, this
* Corresponding author. Tel.: +81-52-789-3790; Fax: +81-52-789-5127. E-mail address: [email protected]
1875-3892 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of 26ICNTS doi:10.1016/j.phpro.2015.11.093
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Y. Nakayama et al. / Physics Procedia 80 (2015) 81 – 83
confinement of energetic ions is important during heating. Measurement of the 2.5 MeV neutrons (DD neutron), which are one of the reaction products of the DD fusion reaction, is useful for energetic-ion diagnostics since DD neutrons are mainly produced by energetic D+ related DD reactions. We have developed a compact DD neutron detector based on a nuclear emulsion which serves as a neutron energy spectrometer and neutron camera, see references Y. Nomura (2011) and H. Tomita (2013). For DD neutron detection, we applied OPERA film and its analyzing system “S-UTS” described in K. Morishima (2010) because a large volume of the films has been successfully used in the OPERA experiment. In this paper, we show an optimization of development condition of the OPERA film for DD neutron detection and an absolute efficiency of the compact DD neutron detector. 2. Compact DD neutron detector based on nuclear emulsion system The detection principle of the compact DD neutron detector, which has been described in detail in Y. Nomura (2011), is briefly shown here. The detector consists of a nuclear emulsion plate and a pinhole collimator covering the plate as shown in Fig. 1. Using the pinhole collimator made of a tungsten alloy, most neutrons are incident into the emulsion layer after passing through the pinhole. An incident neutron interacts with a hydrogen atom in the emulsion layer by elastic scattering, transferring some recoil energy to a proton, depending on its scattering angle. After development of the emulsion, tracks of the recoiled protons caused by fast neutrons are analyzed. Because the track length of a recoiled proton in the emulsion depends on its energy, the recoiled proton energy Erp can be calculated. The scattering angle θ of a neutron can be derived from the angle between the vector directed from the pinhole to the start point of the recoiled proton track and the vector pointing along the track. Thus, the incident neutron energy En = Erp/cos2θ can be estimated. Furthermore, the combination of the pinhole collimator and nuclear emulsion may be applied as a pinhole camera for fast neutrons.
Fig. 1. Principle of fusion neutron measurement by nuclear emulsion system
3. Optimization of development conditions In a nuclear fusion experiment, intense high energy X(J)-rays are generated. Although nuclear emulsion has the capability of n-J discrimination by shape and grain density of the track, recognition of the recoiled proton tracks is difficult with a large amount of fast electron tracks caused by the high intensity X(J)-rays. Therefore, development conditions of the emulsion need to be optimized to suppress these fast electron tracks. The OPERA films were irradiated by DD neutrons and high energy X(J)-rays from deuterium plasma in the experimental fusion device Korea Superconducting Tokamak Advanced Research (KSTAR) at National Fusion Research Institute. The OPERA films were developed with an OPERA film developer with pH values 9.8 and 7.4. An adjustment of the pH level was carried out by adding acetic acid to the developer. The experimental results are shown in Fig. 2. Whereas the track density of recoiled protons was unaffected by pH and development time, development with lower pH and shorter development time lead to lower fog density. Because a development time of 40 min was sufficient to obtain the proper length of recoiled proton tracks, this duration at pH 7.4 was adopted as optimal development condition.
Fig. 2. (a)The recoiled proton density and (b) fog density in nuclear emulsion for each development condition.
Y. Nakayama et al. / Physics Procedia 80 (2015) 81 – 83
4. Response to mono-energetic DD neutron point source We evaluated the response function of the detector using an accelerator based DD neutron point source at the Fusion Neutron Source (FNS), Japan Atomic Energy Agency. The detector was set 1.5 m apart from a deuteriumstorage target at 80 degrees with respect to the direction of the beamline. Based on the angular dependence of the neutron energy, the energy at the detector position was calculated to be 2.8 MeV. After neutron irradiation, the OPERA film was developed under the conditions mentioned above and then analyzed by the S-UTS. Figure 3 shows (a) the two dimensional histogram of track density of recoiled proton on nuclear emulsion and (b) the profile of track density in the emulsion. We made a Monte Carlo simulation based on PHITS code and results are plotted in Fig. 3 (b). The experimental data is in good agreement with the calculated one. The relative efficiencies for 2.5 MeV and 2.8 MeV neutron were estimated by the Monte Carlo simulation as well. Therefore, the absolute efficiency for 2.5 MeV neutron was estimated to be (4.1±0.2)h10-6 tracks/neutron.
Fig. 3. (a) The two dimensional histogram of track density in the nuclear emulsion (5cm5cm). (b) Profiles of track density in nuclear emulsion obtained by experimental using DD neutron point source and Monte Carlo simulation based on PHITS code. The efficiencies for 2.8 MeV neutron were (4.7±0.2)h10-6 and (4.6±0.2)h10-6 tracks/neutron by the experiment and simulation, respectively.
5. Summary We have developed a compact fusion neutron detector based on nuclear emulsion in order to measure DD fusion neutrons. By development of the emulsion with a development time of 40 minutes at pH 7.4, tracks of fast electrons from the deuterium plasma could be suppressed. We evaluated the response function of the detector to a DD neutron point source. The experimental data is in good agreement with simulations and the absolute efficiency was estimated to be (4.1±0.2)h10-6 tracks/neutron at an energy of 2.5MeV. As a future work, we will analyze the emulsions to obtain the emission profile and energy spectrum of DD neutrons. Acknowledgements This work is performed with the support and under the auspices of the NIFS Collaboration Research program (NIFS12KOAH029, NIFS11KLEH011) and Cooperation between Japan and Korea in the Area of Fusion Energy Research and Related Fields. Also, this work is partly supported by the JSPS-NRF-NSFC A3 Foresight Program in the field of Plasma Physics (NSFC: No.11261140328). References K. Morishima, T. Nakano, 2010, Development of a new automatic nuclear emulsion scanning system, S-UTS, with continuous 3D tomographic image read-out, Journal of Instrumentations 5, P04011. Y. Nomura, H. Tomita, J. Kawarabayashi, T. Iguchi, M. Isobe, K. Morishima, T. Nakano, M. Nakamura, S. Ohnishi, 2011, Design Consideration on Compact Neutron Pinhole Camera with Nuclear Emulsion for Energetic-Ion Profile Diagnostics, Plasma and Fusion Research 6, 2402148. H. Tomita, F. Yamashita, Y. Yamamoto, H. Minato, K. Morishima, Y. Sakai, M. Isobe, K. Ogawa, T. Nakano, M. Nakamura, J. Kawarabayashi, T. Iguchi, K. Ochiai, M.S. Cheon, 2013, Development of Fusion Neutron Pinhole Imaging using Nuclear Emulsions for Energetic Ion Diagnostics, Plasma and Fusion Research 8, 2406095. H. Tomita, F. Yamashita, Y. Nakayama, K. Morishima, Y. Yamamoto, Y. Sakai, M. S. Cheon, M. Isobe, K. Ogawa, S. Hayashi, J. Kawarabayashi, T. Iguchi, 2014, Progress in development of neutron energy spectrometer for deuterium plasma operation in KSTAR, Review of Scientific Instruments 85, 11E120.
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ScienceDirect Physics Procedia 80 (2015) 81 – 83
26th International Conference on Nuclear Tracks in Solids, 26ICNTS
Application of advanced nuclear emulsion technique to fusion neutron diagnostics Y. Nakayamaa,*, H. Tomitaa, K. Morishimab, F. Yamashitaa, S. Hayashia, MunSeong Cheonc, M. Isobed,e, K. Ogawad, T. Nakab, T. Nakanob, M. Nakamurab, J. Kawarabayashia, T. Iguchia and K. Ochiaif a
Graduate School of Eng., Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan Graduate School of Sci., Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan c Diagnostics Technology Team, ITER Korea, National Fusion Research Institute, Deajeon, 305-333, Republic of Korea d National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan e The Graduate University for AdvancedStudies, 322-6 Oroshi-cho, Toki 509-5292, Japan f Fusion Research and Development Directorate, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195, Japan b
Abstract In order to measure the 2.5 MeV neutrons produced by DD nuclear fusion reactions, we have developed a compact neutron detector based on nuclear emulsion. After optimization of development conditions, we evaluated the response of the detector to an accelerator-based DD neutron source. The absolute efficiency at an energy of 2.5 MeV was estimated to be (4.1±0.2)h10-6 tracks/neutron. © Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license © 2015 2015The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of 26ICNTS. Peer-review under responsibility of the Scientific Committee of 26ICNTS
Keywords: Nuclear emulsion, Fusion neutron measurement, Plasma diagnostics ;
1. Introduction Efficient magnetic confinement of deuterium/tritium plasma has been developed toward realization of a nuclear fusion reactor as future energy source. To obtain the required high temperature and density of the plasma, this
* Corresponding author. Tel.: +81-52-789-3790; Fax: +81-52-789-5127. E-mail address: [email protected]
1875-3892 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of 26ICNTS doi:10.1016/j.phpro.2015.11.093
82
Y. Nakayama et al. / Physics Procedia 80 (2015) 81 – 83
confinement of energetic ions is important during heating. Measurement of the 2.5 MeV neutrons (DD neutron), which are one of the reaction products of the DD fusion reaction, is useful for energetic-ion diagnostics since DD neutrons are mainly produced by energetic D+ related DD reactions. We have developed a compact DD neutron detector based on a nuclear emulsion which serves as a neutron energy spectrometer and neutron camera, see references Y. Nomura (2011) and H. Tomita (2013). For DD neutron detection, we applied OPERA film and its analyzing system “S-UTS” described in K. Morishima (2010) because a large volume of the films has been successfully used in the OPERA experiment. In this paper, we show an optimization of development condition of the OPERA film for DD neutron detection and an absolute efficiency of the compact DD neutron detector. 2. Compact DD neutron detector based on nuclear emulsion system The detection principle of the compact DD neutron detector, which has been described in detail in Y. Nomura (2011), is briefly shown here. The detector consists of a nuclear emulsion plate and a pinhole collimator covering the plate as shown in Fig. 1. Using the pinhole collimator made of a tungsten alloy, most neutrons are incident into the emulsion layer after passing through the pinhole. An incident neutron interacts with a hydrogen atom in the emulsion layer by elastic scattering, transferring some recoil energy to a proton, depending on its scattering angle. After development of the emulsion, tracks of the recoiled protons caused by fast neutrons are analyzed. Because the track length of a recoiled proton in the emulsion depends on its energy, the recoiled proton energy Erp can be calculated. The scattering angle θ of a neutron can be derived from the angle between the vector directed from the pinhole to the start point of the recoiled proton track and the vector pointing along the track. Thus, the incident neutron energy En = Erp/cos2θ can be estimated. Furthermore, the combination of the pinhole collimator and nuclear emulsion may be applied as a pinhole camera for fast neutrons.
Fig. 1. Principle of fusion neutron measurement by nuclear emulsion system
3. Optimization of development conditions In a nuclear fusion experiment, intense high energy X(J)-rays are generated. Although nuclear emulsion has the capability of n-J discrimination by shape and grain density of the track, recognition of the recoiled proton tracks is difficult with a large amount of fast electron tracks caused by the high intensity X(J)-rays. Therefore, development conditions of the emulsion need to be optimized to suppress these fast electron tracks. The OPERA films were irradiated by DD neutrons and high energy X(J)-rays from deuterium plasma in the experimental fusion device Korea Superconducting Tokamak Advanced Research (KSTAR) at National Fusion Research Institute. The OPERA films were developed with an OPERA film developer with pH values 9.8 and 7.4. An adjustment of the pH level was carried out by adding acetic acid to the developer. The experimental results are shown in Fig. 2. Whereas the track density of recoiled protons was unaffected by pH and development time, development with lower pH and shorter development time lead to lower fog density. Because a development time of 40 min was sufficient to obtain the proper length of recoiled proton tracks, this duration at pH 7.4 was adopted as optimal development condition.
Fig. 2. (a)The recoiled proton density and (b) fog density in nuclear emulsion for each development condition.
Y. Nakayama et al. / Physics Procedia 80 (2015) 81 – 83
4. Response to mono-energetic DD neutron point source We evaluated the response function of the detector using an accelerator based DD neutron point source at the Fusion Neutron Source (FNS), Japan Atomic Energy Agency. The detector was set 1.5 m apart from a deuteriumstorage target at 80 degrees with respect to the direction of the beamline. Based on the angular dependence of the neutron energy, the energy at the detector position was calculated to be 2.8 MeV. After neutron irradiation, the OPERA film was developed under the conditions mentioned above and then analyzed by the S-UTS. Figure 3 shows (a) the two dimensional histogram of track density of recoiled proton on nuclear emulsion and (b) the profile of track density in the emulsion. We made a Monte Carlo simulation based on PHITS code and results are plotted in Fig. 3 (b). The experimental data is in good agreement with the calculated one. The relative efficiencies for 2.5 MeV and 2.8 MeV neutron were estimated by the Monte Carlo simulation as well. Therefore, the absolute efficiency for 2.5 MeV neutron was estimated to be (4.1±0.2)h10-6 tracks/neutron.
Fig. 3. (a) The two dimensional histogram of track density in the nuclear emulsion (5cm5cm). (b) Profiles of track density in nuclear emulsion obtained by experimental using DD neutron point source and Monte Carlo simulation based on PHITS code. The efficiencies for 2.8 MeV neutron were (4.7±0.2)h10-6 and (4.6±0.2)h10-6 tracks/neutron by the experiment and simulation, respectively.
5. Summary We have developed a compact fusion neutron detector based on nuclear emulsion in order to measure DD fusion neutrons. By development of the emulsion with a development time of 40 minutes at pH 7.4, tracks of fast electrons from the deuterium plasma could be suppressed. We evaluated the response function of the detector to a DD neutron point source. The experimental data is in good agreement with simulations and the absolute efficiency was estimated to be (4.1±0.2)h10-6 tracks/neutron at an energy of 2.5MeV. As a future work, we will analyze the emulsions to obtain the emission profile and energy spectrum of DD neutrons. Acknowledgements This work is performed with the support and under the auspices of the NIFS Collaboration Research program (NIFS12KOAH029, NIFS11KLEH011) and Cooperation between Japan and Korea in the Area of Fusion Energy Research and Related Fields. Also, this work is partly supported by the JSPS-NRF-NSFC A3 Foresight Program in the field of Plasma Physics (NSFC: No.11261140328). References K. Morishima, T. Nakano, 2010, Development of a new automatic nuclear emulsion scanning system, S-UTS, with continuous 3D tomographic image read-out, Journal of Instrumentations 5, P04011. Y. Nomura, H. Tomita, J. Kawarabayashi, T. Iguchi, M. Isobe, K. Morishima, T. Nakano, M. Nakamura, S. Ohnishi, 2011, Design Consideration on Compact Neutron Pinhole Camera with Nuclear Emulsion for Energetic-Ion Profile Diagnostics, Plasma and Fusion Research 6, 2402148. H. Tomita, F. Yamashita, Y. Yamamoto, H. Minato, K. Morishima, Y. Sakai, M. Isobe, K. Ogawa, T. Nakano, M. Nakamura, J. Kawarabayashi, T. Iguchi, K. Ochiai, M.S. Cheon, 2013, Development of Fusion Neutron Pinhole Imaging using Nuclear Emulsions for Energetic Ion Diagnostics, Plasma and Fusion Research 8, 2406095. H. Tomita, F. Yamashita, Y. Nakayama, K. Morishima, Y. Yamamoto, Y. Sakai, M. S. Cheon, M. Isobe, K. Ogawa, S. Hayashi, J. Kawarabayashi, T. Iguchi, 2014, Progress in development of neutron energy spectrometer for deuterium plasma operation in KSTAR, Review of Scientific Instruments 85, 11E120.
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