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On energetic particle diagnostics based on gamma-ray measurement

11 th ITPA Topical Group Meeting on Diagnostics, Sep. 4, 2006, Tohoku Univ., Sendai, Japan. On energetic particle diagnostics based on gamma-ray measurement. M. Nakamura (for Y. Nakao). Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, 812-8581, Japan

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On energetic particle diagnostics based on gamma-ray measurement

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  1. 11th ITPA Topical Group Meeting on Diagnostics, Sep. 4, 2006, Tohoku Univ., Sendai, Japan On energetic particle diagnostics based on gamma-ray measurement M. Nakamura (forY. Nakao) Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, 812-8581, Japan E-mail: nakamura@nucl.kyushu-u.ac.jp • Contents • Introduction ― what process is employed ? • Estimations ― what can be diagnosed ? • Concluding Remarks

  2. Introduction ― what process is employed ? • Estimations ― what can be diagnosed ? • Concluding Remarks

  3. 1.1 Introduction: gamma-ray measurement Gamma-ray measurement Vigorously used for energetic particle diagnostics especially at JET experiments What kinds of reactions are especially important ? Resonant reactions Threshold reactions D(,γ)6Li*proposed by Ochiai et al. 6Li (t, p)8Li*proposed by our group Voronchev, Kukulin, JPG (2000); Voronchev, Kukulin, Nakao, PRE (2001); Nakamura, Voronchev, Nakao et al., JPSJ (2006)

  4. 1.2 Introduction: properties of the 6Li(t,p)8Li* reaction • The reaction threshold is 181 keV in the centre-of-mass system • The excited state has a short lifetime of 12 fs. 181 keV Voronchev, Kukulin JPG (2000); Voronchev, Kukulin, Nakao PRE (2001) The rate of the 0.981-MeV gamma-ray emission is sensitive to the population of energetic tritons.

  5. 1.3 Introduction: the preliminary estimation The reaction probability function Pt (Et ) In order to briefly estimate the 6Li(t,p)8Li* reaction rate, we introduce the function Pt(Et). Occurrence of the 6Li(t,p)8Li* reaction is sensitive to the presence of energetic tritons above the energy of 1 MeV.

  6. 1.4 Introduction: the objective of the present work Speculation One could obtain information on the energy distributions of energetic tritons and alpha-particles by comparing the 0.981-MeV gamma-ray measurement with kinetic model prediction incorporating the alpha knock-on effect. Nakamura, Voronchev, Nakao et al., JPSJ (2006) The present objective To develop such an early qualitative discussion We analyze diagnostic information carried by the 0.981-MeV gamma-rays.

  7. Introduction ― what process is employed ? • Estimations ― what can be diagnosed ? • Concluding Remarks

  8. 2.1 Energetic tritons and the gamma-rays The source of the gamma-rays Energetic tritons Alpha knock-on tritons D-beam knock-on tritons DD (burn-up) tritons 181 keV These populations can be evaluated by solving the Fokker-Planck equation for energetic ions.

  9. 2.2 The energetic triton population Conditions T = 20 keV, nd = nt = ne/2 = 0.5×1020 m-3, ENBI = 1 MeV, PNBI = 73 MW, Vplasma = 730 m-3 Assumption • Ignoring the DT fusion reaction induced by knock-on deuterons and tritons. • Considering that Energetic ions slow down only through Coulomb scattering. • Ignoring losses of energetic ions during slowing-down (that is, their confinement is good). (6Li’s are assumed to be at rest.) • The gamma-ray emission from the 6Li(t,p)8Li* reaction would be determined by the alpha-knock-on tritons.

  10. 2.3 The gamma-ray yield and energy spectrum The yield The energy spectrum T = 20 keV, nd = nt = ne/2 = 0.5×1020 m-3 ENBI = 1 MeV nd = nt = ne/2 = 0.5×1020 m-3 ENBI = 1 MeV • The yield and energy spectrum of 0.981-MeV gamma-rays • aresolely governed by the energetic triton population, especially the alpha knock-on tritons.

  11. 2.5 Comparison with the 4.44-MeV gamma-ray yield The 4.44-MeV gamma-rays Emitted in the 9Be(α,n)12C* reaction The sizable cross section Vigorously used for alpha-particle diagnostics at JET experiments Kiptily et al., NF (2002) Comparison between the 0.981- and 4.44-MeV gamma-yields Under the plasma conditions typical of ITER: T = 20 keV, nd = nt = ne/2 = 0.5×1020 m-3, nLi/nd = nBe/nd = 0.01, Comparable!

  12. 2.6 The diagnostic information on the alpha-knock-on tritons The physical meaning of : the gamma-ray yield due to knock-on tritons with energy • The emission of the 0.981-MeV gamma-rays reflects the presence of alpha-knock-on tritons with energy of 0.6-1.6 MeV.

  13. 2.7 The diagnostic information on the alpha-particles The physical meaning of Yα, g : the gamma-ray yield due to alpha-particles with energy Eα, g< Eα<Eα, g-1 • The emission of the 0.981-MeV gamma-rays reflects the presence of alpha-particles with energy of 2.0-3.5 MeV.

  14. 2.8 Information on the confinement property • The presentstudy ….. Assumed that the confinement of energetic particles is good. The emission of the 0.981-MeV gamma-rays reflects the presence of alpha-knock-on tritons with energy of 0.6-1.6 MeV, and alpha-particles with energy of 2.0-3.5 MeV. • When the confinement of energetic particles is affected by • specific loss mechanisms ….. Detection of the gamma-rays Kinetic model prediction Diagnosing the confinement property of alpha-knock-on tritons and alpha-particles

  15. Introduction ― what process is employed ? • Estimations ― what can be diagnosed ? • Concluding Remarks

  16. 3 Concluding Remarks The 6Li(t,p)8Li* reaction may have an important applicability to energetic ion diagnostics in DT fusion plasmas. The yield and energy spectrum of 0.981-MeV gamma-rays is solely governed by the energetic (especially alpha-knock-on) triton population. The emission of the 0.981-MeV gamma-rays reflects the presence of alpha-knock-on tritons with energy of 0.6-1.6MeV, and alpha-particles with energy of 2.0-3.5 MeV. The confinement property of these ions could be diagnosed by comparison of the 0.981-MeV gamma-ray detection with kinetic model predictions. If the 0.981-MeV gamma-rays are detected, one can diagnose not only the presence of alpha-knock-on tritons andalpha-particles, but also the confinement properties of these ions.

  17. On energetic particle diagnostics based on gamma-ray measurement K. Ochiai Directorates of Fusion Energy Research, Japan Atomic Energy Agency

  18. Measurement of 2.186MeV gamma-ray from D(,)6Li Kobe university Tandem Van de Graaffaccelerator, Pelletron 5SDH-2, +15 line For diagnostics of high energetic a-particle, JAEA-FNS and Kobe University has carried out measurements emitted 2.186 MeV gamma ray from D(a,g)6Li reaction. Target C2D2

  19. Gamma spectra and emission rate From our results, the emission rate of the 2.186-MeV gamma from the D(a,g)6Li reaction in typical burning plasma can estimate 104 /cm3/sec So, in case of ITER, the emission rate is about 1012-13 sec-1 and it is thought that the intensity is sufficient for the measurement for alpha particle diagnostics. Emission rate 104 /cm3/sec on typical plasma 1012-13 sec-1 in case of ITER Dependency of yields of measured photo peak in 2234 < Eg < 2254 keV on 2.0, 2.25, 3.0 and 4.0 MeV He ion beam ,Ea, implantation (Open circle: present data and Closed circle: past experimental data). Measured gamma spectra from used C2D4, carbon and TiDx samples under 3.5-MeV He++ irradiation.

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