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Use of g -Ray-Generating Reactions for Diagnostics of Energetic Particles in Burning Plasma and Relevant Nuclear Data

Use of g -Ray-Generating Reactions for Diagnostics of Energetic Particles in Burning Plasma and Relevant Nuclear Data. Y. Nakao. Department of Applied Quantum Physics and Nuclear Engineering , Kyushu University , Japan. Diagnostics of

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Use of g -Ray-Generating Reactions for Diagnostics of Energetic Particles in Burning Plasma and Relevant Nuclear Data

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  1. Use of g-Ray-Generating Reactions for Diagnostics of Energetic Particles in Burning Plasma and Relevant Nuclear Data Y. Nakao DepartmentofAppliedQuantumPhysics and NuclearEngineering,KyushuUniversity,Japan Diagnostics of -Knock-onionsinMagnetically-confinedburning plasma -Degenerate electronsinLaser-imploded fuel Proposal & Analysisfrom theoretical side Collaborators: H. Matsuura,N. Senmyo,K. Tsukida (KyushuUniv.);M. Nakamura (Univ.ofTokyo) T. Johzaki(OsakaUniv.);V.T. Voronchev(MoscowStateUniv.) 2010 Symposium on Nuclear Data (Fukuoka, Nov.25-26, 2010) 1/20

  2. 1. Energetic Particle Diagnostics---Background Energetic particles in fusion plasmas at burning stage -Products of fusion reactions -Injected beam particles -Ions accelerated by electromagnetic waves - Knock-on ions scattered by these particles Heatbulk electron and ion fluids, and Can triggermany wave-particle interactions and instabilities Diagnosing the properties of energetic particles confined in burning plasma is one of the key issues in NF research aiming at ITER. These energetic particles should be diagnosed while they are in the plasma; Measurements inside the plasma are hardly possible. Use of reaction-produced neutrals freely escaping from the plasma core Neutrons, Gamma-rays 2/20

  3. Energetic Particle Diagnostics Based on -Ray Measurement DT fusion plasma with a small amount of6Li (9Be) 0.981(4.44)MeV -rays Informationon • energetic triton population • (α-particle confinement) • Used for energetic particle diagnostics at JET experiments • Kiptilyj et al., NF (2002), PRL (2004), NF (2005) • Use of the D(, )6Li reaction proposed by JAERI group • Ochiai et al., RSI (2006) • Use of the 6Li(t,p)8Li* reaction proposed by our group Voronchev, Kukulin, Nakao, PRE (2001). Nakamura, Nakao, Voronchev et al., JPSJ (2006), NIMA (2007), FST (2008), JPFR (2007). 3/20

  4. Gamma-Ray-Generating 6Li (t,p)8Li* Reaction 6Li + t →8Li*[0.981 MeV] + p 12fs 8Li [gr. st.] + γ 1) The reaction threshold is 181 keV in the centre-of-mass system 2) The excited state has a short lifetime of 12 fs. 181 keV E>2MeV:Experimental data available E<2MeV:Cluster folding model calculation Voronchev, Kukulin, Nakao PRE (2001) One can expect that the rate of the 0.981-MeV -ray emission is sensitive to the population of energetic tritons. 4/20

  5. Objective of the Work α 6Li (t, p) 8Li* 8Li + γ knock-ont Our early speculation Nakamura, Nakao, Voronchev et al., JPSJ (2006) One could obtain information on the energy distributions of energetic tritons and -particles by comparing the 0.981-MeV -ray measurement with kinetic model prediction incorporating the  knock-on effect. The objective Analyze theoretically diagnostic information carried bythe0.981-MeV-rays. • Teff and n eff of knock-on tritons • Confinement property of -particles 5/20

  6. Kinetic Model for Energetic Ion Populations The source of 0.981-MeV -ray • Alpha knock-on tritons • D-beam knock-on tritons • DD (burn-up) tritons • Energetic tritons Fokker-Planck equation for energetic ions Source terms • Alpha-particles & DD burn-up tritons Gaussian form • Beam-injected deuteronsdelta-function-like form • Knock-on ionsknocking-up from the background Ryutov, Phys. Scr. (1992); Helander, Lisak, Ryutov, PPCF (1993) 6/20

  7. Energetic Triton Populations --- Fokker-Planck calculationsunder conditions typical of the ITER tokamak plasma • fakt>fbkt, fDDt at MeV energy range. • Theknock-ontritons (akt) are distributed up to the energy of 4 MeV. Energy distribution functions of α knock-on tritons(akt), D-beam knock-on tritons (bkt) and DD burn-up tritons (DDt) 7/20

  8. Gamma-Ray Yield nLi /nt = 1 % • The 0.981-MeV -line reflects the presenceofthe knock-on tritons. • It may be used to infer Teff and neff of the  knock-on triton population. Comparable! • Emitted in the 9Be(,n)12C* reaction • Used in JET experiments • nBe /nt=1%,T=20keV 8/20

  9. Gamma-RayEmissionSpectrum • The spectral broadening reflects the 8Li* spectrum. 18 keV • The 8Li* spectrum is governed by the  knock-on triton population. • dY /dE can be fitted to •  increases monotonically with increasing Teff. 9/20

  10. “Analytical”Representations Fitting to the slope distribution • The fitting is successfully done especially in the energy range of 0.5-2 MeV. • Teffincreases monotonically with increasing T. 10/20

  11. Diagnostics of the  Knock-on Triton Population experimentally determined • The effective temperature Teff of the  knock-on triton could be diagnosed. • Once Teff is determined, the effective concentration neff could be assessed from experimental Y . 11/20

  12. Diagnostics of the Confinement Property of the Fusion-Born -Particles Is the experimental (T,Teff) plot placed onto the theoretical curve ? Non-classical YES. NO. Classical • The confinement property is classical. • The confinement is deteriorated. 12/20

  13. 2.Degenerate Plasma Diagnostics---Background Laser-imploded dense plasma r ≧1000rs ,kTe ≦ 1keV Electrons should be in degenerate state. Degree of degeneracy : = Fermi energy Measurements : Implosion experiment of CD targets at Osaka Univ. Consequence of electron degeneracy : Reduction in stopping power of plasma for energetic particles • Range of D-D fusion tritons • In-flight T-D reaction rate • Q, r Range lengthening 13/20

  14. Purpose of the Study g-ray generating reaction Influenceon Ignition & Burn history of compressed DT targets through D + T → a(3.52MeV) + n(14MeV) • a-particleheating • electron thermal conduction • electron-iontemperaturerelaxation • bremsstrahlung a +9Be → 12C*[2+;0] + n 12C[gr.st.]+g (4.44MeV) How to diagnose the degree of electron degeneracy in compressed DTfuel --- A matter of interest We propose a new method based on g-ray measurement. DT fuel admixed with a small amount of 9Be 14/20

  15. T D Principal reaction a n 9Be Secondary reaction 12C g n Key Idea of Degeneracy Diagnostics In-flight reaction probability Suppose the case that DT fuel admixed with a small amount of 9Be is imploded to high densities, but Not subjected to any heating laser pulse. • The fuel would not be ignited, and Most of nuclear reactions occur around the maximum compression. • Reaction products carry information • about compressed state of fuel. Experimentally, If plasma temperatures are determined in other ways, we can assessQfromPa-Be-Qcurve by measuring the g-rays and D-T neutrons. 15/20

  16. Calculated In-flight Reaction Probability ････ infinite plasma ････ infinite plasma ProbabilityPa-Behas clear dependenceson degeneracy parameterQandplasma temperaturekTe,i. 16/20

  17. g-Rays from Compressed Finite-Size DT/9Be Pellets We ignore the spatial distributions of temperature and density, and their temporal evolutions.nBe /ni=0.1. r R = 0.4 g/cm2,r = 200 g/cm3 Yield per shot : Sa =nDnT<sv>DT V=plasma volume t=timeintervalwhilethehigh densitystate is maintained ≈R/3Cs r R = 0.7 g/cm2,r = 200 g/cm3 The yield depends strongly on the plasma temperature and it seems enough for theg-raysto be detected. 17/20

  18. Summary (1) The 0.981-MeV -rays emitted in the 6Li (t,p)8Li* reaction have an important application for diagnostics of the  knock-on tritons and the -particles in burning plasmas. If the 0.981-MeV -rays are detected, we can obtain information on • Key parameters of  knock-on triton population (Teff,neff), and • Confinement property of the fusion-born -particles by comparing experimental data on the 0.981-MeV -ray yield and emission spectrum with the theoretical slowing-down calculations. 18/20

  19. Summary (2) and Future Works We have proposed use of 9Be(a,ng)12C for diagnostics of electron degeneracyin compressed DT fuel pellets. - Reaction probability Pa-Bedepends strongly on the degeneracy parameter Qand plasma temperaturekTe,i . - Experimentally,Pa-Be would be determined as the ratio of the yield of 4.44-MeV g-rays from this reaction to the D-T neutron yield. - It will be possible to diagnose the degree of degeneracy, if the 4.44-MeVg-rays and D-T neutrons can be measured. • -Temporal evolutions of density-temperature profiles, g-ray and D-T neutron generation rates should be taken into account. →Analysis including implosion dynamics 19/20

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