スライド 1

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かげたつしのしま
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Stephan IRLE1, Keiji MOROKUMA3 and Hiroaki NAKAMURA2 Nagoya

1 Molecular Dynamics Simulation of Chemical Sputtering of Hydrogen Atom on Layer Structured Graphite Atsushi ITO1,2, Ying WANG1, Stephan IRLE1, Keiji MOROKUMA3 and Hiroaki NAKAMURA2 Nagoya University 2) National Institute for Fusion Science 3) Kyoto University 1)

2 Plasma-Wall Interaction (PWI) Inside of LHD (Large Herical Device) Divertor plate (Graphite) Purpose of Molecular Dynamics is to clarify mechanisms of: Erosion of graphite Hydrocarbon production * A. Sagara et al, (LHD Experimental Group), J. Nucl. Mater , 1 (2003).

3 Contents 1. Difference of produced hydrocarbon on three kinds of graphite surfaces MD simulation shows that carbon chain, C2H2 and H2 are mainly produced by hydrogen atom bombardment from flat (0001), armchair, zigzag surfaces, respectively. carbon chain C2H2 H2 MD simulation of a single hydrogen atom reaction with a single graphene proves that increase of graphene temperature depends on incident energy of a hydrogen atom. This dependency agrees with that of hydrocarbon yield of chemical sputtering in experiments. yield 2. Dependence of increase of graphene temperature on incident energy Incident energy *B. V. Mech, A. A. Haasz, and J. W. Davis: J. Nucl. Mater. 255 (1998) 153.

4 Hierarchic Structure of Carbon Contents 1. Hydrogen atom bombardment on the layer structure of graphite Difference of produced hydrocarbon on three kinds of graphite surfaces 2. Hydrogen atom injection onto a single graphite Dependence of increase of graphene temperature on incident energy * H. -P. Boehm, R. Setton & E. Syumpp, Pure & Appl. Chem. 66, 1893 (1994).

Molecular Dynamics for Graphite Equation of motion of atoms is directly solved: The heart of MD is modeling of potential function U(r) Graphite needs two kinds of force: 1.

5 Molecular Dynamics for Graphite Equation of motion of atoms is directly solved: The heart of MD is modeling of potential function U(r) Graphite needs two kinds of force: 1. Covalent bond, Chemical reaction Brenner REBO potential1) & modification in parameters and functions2,3) 2. Interlayer intermolecular interaction Original potential with cone cutoff method3) [1] D.W.Brenner, et. al., J. Phys. Condens Matter 14, 783 (2002). [2] A. Ito, H. Nakamura and A. Takayama JPSJ to be published. [3] A. Ito and H. Nakamura, Commun. Comput. Phys 4 (2008)

6 1. Difference of produced hydrocarbon on three kinds of graphite surfaces MD simulation shows the following difference of produced hydrocarbon on three kinds of graphite surfaces: (a) a flat surface carbon chain (b) an armchair surface C2H2 (c) a zigzag surface H2 Three kinds of graphite surfaces Flat surface Armchair surface Zigzag surface

7 Simulation Conditions Injection side Normal injection of H atoms Injection point is at a distance from a surface Flux : 2.5x1030 atom/m2s (=10 atom/ps) Material side Periodic boundary in the x, y directions Energy conservation, i.e., no temperature control Num. of C atoms is x y Sample of Simulation Box (flat surface)

8 (a) Hydrogen atom bombardment onto a flat surface a flat surface

9 Case 1) Perfect Crystal Graphite peeling Carbon chains Case 2) with vacancies Amorphization

10 (b,c) armchair and zigzag surfaces Armchair surface Zigzag surcse

11 C2H2 and H2 production Armchair C2H2 Zigzag H2

12 Summary 1: Hydrocarbon production carbon chain C2H2 H2 Flat surface Armchair surface Zigzag surface Research is continued to 1. amorphous graphite 2. controlled temperature 3. quantitative results and so on

13 2. Increase in graphene temperature Important dependence of sputtering yield: Temperature dependence Incident flux dependence Incident energy dependence The expectation value of the increase of graphene temperature: Ep 1 Er T = ( E U ) P ( E ) + ( 1 ) E P ( E ) + ( 1 ) E P ( E ) 0 a I I r I I p I I 3Nkb EI EI EI : incident energy U0 : adsorption energy of hydrogen atom on a graphene Pa (EI), Pr (EI), Pp (EI) : adsorption, reflection, and penetration rates Er, Ep : kinetic energy of hydrogen atom after reflection or penetration Necessary values can be calculated by the MD simulation of a single hydrogen atom reaction with a single

14 Three kinds of reactions Adsorption Reflection Overhang process in adsorption Penetration

15 Adsorption, reflection and penetration rates The simulation is repeated 200 times for each incident energy where the injection point varies under the uniform distribution. reflection: EI < 1eV absorption: 1eV < EI < 7eV reflection: 7eV < EI < 30eV penetration: EI > 30eV 1 T = 3 Nkb Ep Er ) EI Pr ( EI ) + (1 ) E I Pp ( EI ) ( EI U 0 ) Pa ( EI ) + (1 EI EI

16 Incident energy dependence Yield in Experiments* The increase of graphene temperature from MD yield *B. V. Mech, A. A. Haasz, and J. W. Davis: J. Nucl. Mater. 255 (1998) 153. Incident energy A peak of the increase of graphene temperature at ev agrees with dependence of yield on the divertor in experiments. Tritium and deuterium may cause higher hydrocarbon production than hydrogen.

Summary A flat surface of layered graphite produces carbon chains with

Armchair and zigzag surfaces produce easily C2H2 and H2, respectively.

with dependence of yield on incident energy in experiments.

17 Summary A flat surface of layered graphite produces carbon chains with graphite peeling. Armchair and zigzag surfaces produce easily C2H2 and H2, respectively. The increase of graphene temperature has a peak at ev, which agrees with dependence of yield on incident energy in experiments. Problems to achieve real phenomena Large material size Low incident flux Long time simulation Temperature control Amorphous Dust & deposition chain octopus graphene/pah

20 At a peak of increase of temperature Critical point between reflection and penetration Energy barrier for penetration

21 ナノカーボンの破壊と生成の動力学破壊現象生成現象プラズマ壁相互作用星間空間の炭素ダスト水素プラズマによる炭素材の破壊材料物理炭化水素ダストの自己組織化星間物理

22 核融合研究におけるプラズマ - 壁相互作用 (PSI) 問題Herical Device) 内部 LHD (Large Divertor plate (Graphite) 1. 炭化水素発生不純物 2. 炭素材の損耗消耗 * A. Sagara et al, (LHD Experimental Group), J. Nucl. Mater , 1 (2003).

23 自作ソフトウェアによる可視化利点手軽に起動できる動作環境が幅広い欠点 1. 立体構造が判りづらい 2. 表示領域がディスプレイサイズまで

24 CompleXcope による擬似立体視大規模没入型バーチャルリアリティーシステム核融合研 1. ステレオグラスとの映像同期による擬似立体視 2. 位置センサーによる操縦者視線方向の反映 1. 3D 立体音響 2. 四面スクリーンによる視野の確保

25 CompleXcope の利点その１ステレオグラスとの映像同期による擬似立体視位置センサーによる操縦者視線方向の反映 3D 立体音響四面スクリーンによる視野の確保立体構造の把握を容易にする

26 CompleXcope の利点その２ステレオグラスとの映像同期による擬似立体視位置センサーによる操縦者視線方向の反映 3D 立体音響四面スクリーンによる視野の確保サイドスクリーンの奥行きの活用により表示範囲が制限されない

27 CompleXcope の新たな可能性粒子スケールでのエネルギー流と応力テンソル粒子間エネルギー流応力テンソル

28 局在化運動量密度と応力テンソルデルタ関数を用いて粒子ごとの物理量を場に局在させる. 運動量を局在化させて運動量密度ベクトル場を作る以後ベクトルは添字 μν のテンソル表示運動量も保存量であるので連続の式が考えられるこのとき対応する運動量流束テンソル場は 1)motion of particle particles 2)interaction between と考えられ連続の式を満たすためには次のような粒子の運動量と相互作用項の関係が要請される

29 分子動力学への応用エネルギー流応用例グラフェン表面の水素原子吸着の MD CompleXcope ではもっと立体的に流れを把握で

30 分子動力学への応用応力テンソル CompleXcope では任意の領域をワンドで選択して応力を取得できる

31 まとめ 1. カーボンの崩壊と生成の MD シミュレーション 2. 自作ソフトウェアによる可視化 3. CompleXcope による可視化の利点立体構造の把握が容易になる表示範囲が制限されない Future Work 粒子スケールのエネルギー流応力テンソルとの組み合わせによる新たな展開

32 Problems In the experiments C2Hx occurs Our simulation carbon chain(-c-c C-C-) Real structure of divertor Try There are edges Sputtering onto edge region

33 Simulation model Injection Two kinds of edge arm chair ｚ igzag C 軸 Periodic boundary 3.35Å Periodic boundary

34 グラフェンのエッジ構造 arm chair 型ｚ igzag 型

35 reflection energy Incident energy penetration energy Incident energy Resonance around?

36 If incident energy is close to potential barrier for penetration, incident energy transports to graphene.

38 Isotope effect in reaction rates

39 Hydrogen-retention in Graphite 5eV 15eV 30eV

40 2. Increase in graphite surfaces The expectation value of the increase of graphene temperature: T = 1 3Nkb Ep ' Er ' m ( E U ) P ( E ) + ( 1 ) E P ( E ) + ( 1 ) E P ( E ) + O 0 a I I r I I p I I EI EI M EI : incident energy U0 :adsorption energy of hydrogen atom on a graphene Pa (EI), Pr (EI), Pp (EI) : adsorption, reflection, and penetration rates Er, Ep : kinetic energy of hydrogen atom after reflection or penetration M, m : mass of graphene and hydrogen atom Necessary values can be calculated by the MD simulation as follows: Ep /EI Pa (EI), Pr (EI), Pp (EI) Er /EI

41 2. Increase in graphene temperature The expectation value of the increase of graphene temperature: 1 T = 3Nkb Ep Er ( E U ) P ( E ) + ( 1 ) E P ( E ) + ( 1 ) E P ( E ) 0 a I I r I I p I I E E I I EI : incident energy U0 :adsorption energy of hydrogen atom on a graphene Pa (EI), Pr (EI), Pp (EI) : adsorption, reflection, and penetration rates Er, Ep : kinetic energy of hydrogen atom after reflection or penetration Necessary values can be calculated by the MD simulation of a single hydrogen atom reaction with a single graphene MD simulation shows Increase of graphene temperature due to hydrogen atom collision has a peak around ev. This agrees with yield amount in experiments Tritium and deuterium indicate more increase of graphene temperature.

The Effect of the Circumferential Temperature Change on the Change in the Strain Energy of Carbon Steel during the Rotatory Bending Fatigue Test by Ch

The Effect of the Circumferential Temperature Change on the Change in the Strain Energy of Carbon Steel during the Rotatory Bending Fatigue Test by Chikara MINAMISAWA, Nozomu AOKI (Department of Mechanical