激光等离子体中高能电子各向异性压强的粒子模拟
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摘要
直接驱动惯性约束聚变(ICF)的实现需要对靶丸进行严格的对称压缩,以达到自持热核反应(点火)所需的条件.快点火方案的应用降低了对靶丸压缩对称性以及驱动能量的要求,但压缩及核反应过程中良好的靶丸对称性无疑有助于核反应增益的提高.本文研究了快点火方案中高能电子注入高密等离子体后导致的各向异性电子的压强张量.这一现象存在于ICF快点火方案中的高能电子束"点火"及核反应阶段.鉴于高能电子加热离子过程以及靶丸核反应自持燃烧过程的时间较长,高密靶核会由于超高的各向异性压强的作用破坏高密靶丸的对称性,降低核燃料密度,进而降低了核燃料燃烧效率以及核反应增益.
Direct-drive inertial confinement fusion(ICF) requires a symmetric compression of the fuel target to achieve physical conditions for the ignition. The fast ignition scheme reduces the symmetry requirements for the target compression and the necessary driving energy, but symmetrically compressed target will certainly help improve the efficiency of the nuclear fuel burning. In this paper, with the particle-in-cell(PIC) simulation method, characteristics of the anisotropic pressure tensor of hot electrons are reported for the ultra intense laser pulse interaction with over dense plasmas, which mimics the scenario of the last stage when hot electrons are utilized to ignite the compressed fuel core in the ICF fast ignition scheme. A large number of hot electrons can stimulate pressure oscillations in the high density plasma. As the component parallel to the electron velocity dominates the pressure tensor, the electron density distribution perturbation propagates rapidly in this direction. In order to keep those hot electrons in the high density fuel plasma core for a period long enough for them to deposit energy and momentum, a magnetic field perpendicular to the electron velocity is used. The PIC simulation results indicate that the hot electrons can be trapped by the magnetic field, and the components of the anisotropic pressure tensor related to the parallel direction are significantly affected, thereby producing a high peak near the incidence surface. Since it is a relatively long process for the energy transfer from electrons to fuel ions and the nuclear interaction to be completed, the fluid effects take their roles in the fuel target evolution. The anisotropic electron pressure will deteriorate the fuel core symmetry, reduce the density, and achieve a lower efficiency of nuclear fuel burning and a lower gain of nuclear reaction than expected. The effects of the hot electron anisotropic pressure tensor in the fast ignition scheme should be considered as a factor in experiments where the nuclear reaction gain is measured to be much lower than the theoretical prediction.
Direct-drive inertial confinement fusion(ICF) requires a symmetric compression of the fuel target to achieve physical conditions for the ignition. The fast ignition scheme reduces the symmetry requirements for the target compression and the necessary driving energy, but symmetrically compressed target will certainly help improve the efficiency of the nuclear fuel burning. In this paper, with the particle-in-cell(PIC) simulation method, characteristics of the anisotropic pressure tensor of hot electrons are reported for the ultra intense laser pulse interaction with over dense plasmas, which mimics the scenario of the last stage when hot electrons are utilized to ignite the compressed fuel core in the ICF fast ignition scheme. A large number of hot electrons can stimulate pressure oscillations in the high density plasma. As the component parallel to the electron velocity dominates the pressure tensor, the electron density distribution perturbation propagates rapidly in this direction. In order to keep those hot electrons in the high density fuel plasma core for a period long enough for them to deposit energy and momentum, a magnetic field perpendicular to the electron velocity is used. The PIC simulation results indicate that the hot electrons can be trapped by the magnetic field, and the components of the anisotropic pressure tensor related to the parallel direction are significantly affected, thereby producing a high peak near the incidence surface. Since it is a relatively long process for the energy transfer from electrons to fuel ions and the nuclear interaction to be completed, the fluid effects take their roles in the fuel target evolution. The anisotropic electron pressure will deteriorate the fuel core symmetry, reduce the density, and achieve a lower efficiency of nuclear fuel burning and a lower gain of nuclear reaction than expected. The effects of the hot electron anisotropic pressure tensor in the fast ignition scheme should be considered as a factor in experiments where the nuclear reaction gain is measured to be much lower than the theoretical prediction.
引文
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[25]Divin A,Markidis S,Lapenta G,Semenov V S,Erkaev N V,Biernat H K 2010 Phys.Plasmas 17 122102
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[31]Mottez F 2004 Ann.Geophys.22 3033
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[34]Le A,Daughton W,Karimabadi H,Egedal J 2016 Phys.Plasmas 23 032114
[35]Yin L,Winske D 2003 Phys.Plasmas 10 1595
[2]Lindl J 1995 Phys.Plasmas 2 3933
[3]Drake R P 2006 High-Energy-Density Physics:Fundamentals,Inertial Fusion,and Experimental Astrophysics(1st Ed.)(Berlin:Springer Science&Business Media)pp392–419
[4]Mc Crory R L,Meyerhofer D D,Betti R,Craxton R S,Delettrez J A,Edgell D H,Glebov V Yu,Goncharov V N,Harding D R,Jacobs-Perkins D W,Knauer J P,Marshall F J,Mc Kenty P W,Radha P B,Regan S P,Sangster T C,Seka W,Short R W,Skupsky S,Smalyuk V A,Soures J M,Stoeckl C,Yaakobi B,Shvarts D,Frenje J A,Li C K,Petrasso R D,Séguin F H 2008Phys.Plasmas 15 055503
[5]Rosen M D 1999 Phys.Plasmas 6 1690
[6]Bodner S E,Colombant D G,Gardner J H,Lehmberg R H,Obenschain S P,Phillips L,Schmitt A J,Sethian J D 1998 Phys.Plasmas 5 1901
[7]Sharp D H 1984 Physica D 12 3IN111
[8]Brouillette M 2002 Annu.Rev.Fluid Mech.34 445
[9]Wesson J,Campbell D J 2011 Tokamaks(4th Ed.)(Oxford:Oxford University Press)pp356–358
[10]Li C K,Séguin F H,Frenje J A,Petrasso R D,Delettrez JA,Mc Kenty P W,Sangster T C,Keck R L,Soures J M,Marshall F J,Meyerhofer D D,Goncharov V N,Knauer J P,Radha P B,Regan S P,Seka W 2004 Phys.Rev.Lett.92 205001
[11]Shigemori K,Azechi H,Nakai M,Honda M,Meguro K,Miyanaga N,Takabe H,Mima K 1997 Phys.Rev.Lett.78 250
[12]Honda M,Mima K,Shigemori K,Nakai M,Azechi H,Nishiguchi A 1999 Fusion Eng.Des.44 205
[13]Lindl J D,Mc Crory R L,Campbell E M 1992 Phys.Today 45 32
[14]Wouchuk J G 2001 Phys.Rev.E 63 056303
[15]Gu J F,Dai Z S,Fan Z F,Zou S Y,Ye W H,Pei W B,Zhu S P 2014 Phys.Plasmas 21 012704
[16]Tabak M,Hammer J,Glinsky M E,Kruer W L,Wilks S C,Woodworth J,Campbell E M,Perry M D 1994 Phys.Plasmas 1 1626
[17]Wu F J,Zhou W M,Shan L Q,Li F,Liu D X,Zhang Z M,Li B Y,Bi B,Wu B,Wang W W,Zhang F,Gu Y Q,Zhang B H 2014 Acta Phys.Sin.63 94101(in Chinese)[吴凤娟,周维民,单连强,李芳,刘东晓,张智猛,李博原,毕碧,伍波,王为武,张锋,谷渝秋,张保汉2014物理学报6394101]
[18]Kodama R,Norreys P A,Mima K,Dangor A E,Evans R G,Fujita H,Kitagawa Y,Krushelnick K,Miyakoshi T,Miyanaga N,Norimatsu T,Rose S J,Shozaki T,Shigemori K,Sunahara A,Tampo M,Tanaka K A,Toyama Y,Yamanaka T,Zepf M 2001 Nature 412 798
[19]Gu Y Q,Cai D F,Zheng Z J,Yang X D,Zhou W M,Jiao C Y,Chen H,Wen T S,Chunyu S T 2005 Acta Phys.Sin.54 186(in Chinese)[谷渝秋,蔡达锋,郑志坚,杨向东,周维民,焦春晔,陈豪,温天舒,淳于书泰2005物理学报54 186]
[20]Wu S Z,Zhang H,Zhou C T,Wu J F,Cai H B,Cao L H,He M Q,Zhu S P,He X T 2015 High Power Laser and Particle Beams 27 77(in Chinese)[吴思忠,张华,周沧涛,吴俊峰,蔡洪波,曹莉华,何民卿,朱少平,贺贤土2015强激光与粒子束27 77]
[21]Cai H B,Zhou C T,Jia Q,Wu S Z,He M Q,Cao L H,Chen M,Zhang H,Liu J,Zhu S P,He X T 2015 High Power Laser and Particle Beams 27 27032001(in Chinese)[蔡洪波,周沧涛,贾青,吴思忠,何民卿,曹莉华,陈默,张华,刘杰,朱少平,贺贤土2015强激光与粒子束2727032001]
[22]Zhang J 1999 Physics 28 0(in Chinese)[张杰1999物理28 0]
[23]Cassak P A,Baylor R N,Fermo R L,Beidler M T,Shay M A,Swisdak M,Drake J F,Karimabadi H 2015 Phys.Plasmas 22 020705
[24]Wang W M,Gibbon P,Sheng Z M,Li Y T 2015 Phys.Rev.Lett.114 015001
[25]Divin A,Markidis S,Lapenta G,Semenov V S,Erkaev N V,Biernat H K 2010 Phys.Plasmas 17 122102
[26]Hoshino M 2005 J.Geophys.Res.110 A10215
[27]Liu C,Fox W,Bhattacharjee A 2015 Phys.Plasmas 22053302
[28]Wan W G,Lapenta G 2008 Phys.Rev.Lett.101 015001
[29]Yin L,Winske D,Gary S P,Birn J 2001 J.Geophys.Res.106 10761
[30]Wang L,Hakim A H,Bhattacharjee A,Germaschewski K 2015 Phys.Plasmas 22 012108
[31]Mottez F 2004 Ann.Geophys.22 3033
[32]Heinz H,Paul W,Binder K 2005 Phys.Rev.E 72 066704
[33]Cai H S,Li D 2009 Phys.Plasmas 16 052107
[34]Le A,Daughton W,Karimabadi H,Egedal J 2016 Phys.Plasmas 23 032114
[35]Yin L,Winske D 2003 Phys.Plasmas 10 1595