ÕªÒª: ¸ßÄÜÖÊ×ÓÊøÔÚµÈÀë×ÓÌåÖÐͨ¹ý×Ôµ÷ÖƲ»Îȶ¨¼¤·¢Î²²¨µÄÑо¿ÔÚ¹ýÈ¥µÄÊ®ÄêÀïÓÐÁ˳¤×ãµÄ·¢Õ¹, ÔÚÅ·ÖÞºË×ÓÑо¿ÖÐÐÄ(CERN)ÈËÃÇÒѾÔÚÏà¹ØAWAKEʵÑéÖÐÀûÓÃÕâÖÖⲨ¼ÓËÙµç×Ó, ²¢»ñµÃÁË×î¸ßÄÜÁ¿Ô¼2 GeVµÄµç×ÓÊø. Õë¶Ô¸ßÄÜÁ£×Ó¼ÓËÙÓ¦ÓÃÐèÇó, ½ü¼¸ÄêÈËÃÇÓÖ½øÒ»²½Ìá³öÁËÀûÓõç×ÓÊøÖÖ×ÓⲨ¿ØÖÆÖÊ×ÓÊø×Ôµ÷Öƹý³ÌµÄ·½°¸, ÓÃÓÚÌáÉýⲨµÄÇ¿¶ÈÓëÎȶ¨ÐÔ. ±¾ÎÄÑо¿Á˵ç×ÓÊøÖÖ×ÓⲨ¶ÔÖÊ×ÓÊø×Ôµ÷ÖÆⲨÏàËٶȵÄÓ°Ïì, ×ÅÖØÌÖÂÛÁ˵¼ÖÂⲨÏàËٶȸıäµÄ¶àÖÖÎïÀí»úÀí¼°µç×ÓÊøËùÆðµ½µÄ×÷ÓÃ. ͨ¹ýÀíÂÛ·ÖÎöºÍ¶þάÁ£×ÓÄ£ÄâÑо¿·¢ÏÖ, µç×ÓÊøµÄÒýÈë¿ÉÒÔÌáÉýÖÊ×ÓÊø×Ôµ÷ÖÆⲨµÄÔö³¤ÂʺÍⲨµÄÏàËÙ¶È, ÇÒµç×ÓÊøµÄµçºÉÃܶÈÔ½¸ßÆäЧ¹ûÓúÃ÷ÏÔ. ±¾ÎÄ»¹Ì½ÌÖÁ˵ç×ÓÊøÄÜÁ¿ºÍÖÊ×ÓÊøµÄ×ÝÏòÃܶȷֲ¼¶ÔÏàËٶȱ仯µÄÓ°Ïì.
¹Ø¼ü´Ê: µÈÀë×ÓÌåⲨ¼ÓËÙ /
ÖÊ×ÓÊø×Ôµ÷ÖÆ /
ⲨÏàËÙ¶È /
µç×ÓÊøÖÖ×ÓⲨ English Abstract Theoretical and numerical studies of the phase velocity of wakefields in plasma driven by self-modulated proton beams with electron beam seeding Hua Jin-Yu 1 ,Sheng Zheng-Ming 1,2 1.Key Laboratory for Laser Plasmas of Ministry of Education, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China 2.Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai 200240, China Fund Project: Project supported by the National Natural Science Foundation of China (Grant No. 11991074) Received Date: 08 December 2020Accepted Date: 22 January 2021Available Online: 26 June 2021Published Online: 05 July 2021 Abstract: Significant progress has been made in the studies of wakefield excitation in plasma by a self-modulated high energy proton beam in the past decade. The electron beams accelerated up to 2 GeV by using such a wakefield were demonstrated in the AWAKE experiment at CERN in 2018. Aiming at the application of high energy particle accelerators, new ideas have been investigated in recent years, such as seeding the proton beam self-modulation with an electron beam in order to enhance the strength and stability of the wakefield or adding a density transition in the plasma distribution to enhance the phase velocity and the strength of the wakefield. Here in this work, we investigate the effects of electron beam seeding on the phase velocity of the wakefield generated by the modulated proton beam in plasma. The physical mechanisms responsible for the phase velocity change and the roles played by the electron beam seeding are discussed. The theoretical analysis and two-dimensional particle-in-cell simulations show that both the growth rate and the phase velocity of the wakefield generated by the modulated proton beam can be enhanced by the electron beam seeding. The higher the charge density of the electron beam, the more significant the enhancement effects. The effects of electron beam energy and proton beam longitudinal profiles on the increase of phase velocity are also studied. It is shown that the evolution of the electron beam distribution has a significant effect on the seeding self-modulation process, and thus affecting the phase velocity. A self-focusing electron seeding beam can increase the phase velocity of the wakefield even to superluminal while an expanding seeding beam can reduce the phase velocity and destroy the stability of the whole process. This work may benefit the proton beam seeding self-modulation acceleration and its applications. Keywords: plasma wakefield acceleration /self-modulation of proton beams /wakefield phase velocity /electron beam seeding È«ÎÄHTML --> --> --> 1.Òý¡¡ÑÔ µÈÀë×ÓÌåⲨ¼ÓËÙ¸ÅÄî[1 ,2 ] ×Ô´ÓÉÏÊÀ¼Í70Äê´úÄ©±»Ìá³öÒÔÀ´ÒѾȡµÃÁ˳¤×ãµÄ·¢Õ¹, Ëüͨ¹ý¸ßÇ¿¶ÈµÄ¼¤¹âÂö³å»òÕ߸ßÄÜ´øµçÁ£×ÓÊøÔÚµÈÀë×ÓÌåÖм¤·¢³öÒ»¸ö´óÕñ·ùÇÒ¾ßÓÐÏà¶ÔÂÛÏàËٶȵĵç×ÓµÈÀë×ÓÌ岨À´¼ÓËÙµç×Ó[3 -5 ] . µÈÀë×ÓÌåⲨµÄ³¡Ç¿½Ó½üÓÚËùνµÄµÈÀë×ÓÌ岨ÆÆÁÑ·ù¶È$ {E}_{0}={m}_{\mathrm{e}}{\omega }_{\mathrm{p}}c/e $ , ÆäÖÐ$ {\omega }_{\mathrm{p}}=\sqrt{4\mathrm{\pi }{n}_{0}{e}^{2}/{m}_{\mathrm{e}}} $ ΪµÈÀë×ÓÌåÕñµ´ÆµÂÊ, $ {n}_{0} $ ΪµÈÀë×ÓÌåµç×ÓÃܶÈ, $ e $ Ϊµç×ÓµçºÉ, $ {m}_{\mathrm{e}} $ Ϊµç×ÓÖÊÁ¿, $ c $ Ϊ¹âËÙ. ¸Ã³¡Ç¿±È´«Í³¼ÓËÙÆ÷²úÉúµÄ¼ÓËٵ糡¸ß³öºÃ¼¸¸öÊýÁ¿¼¶[6 ] , ʹµÃµÈÀë×ÓÌåⲨ¼ÓËÙÒѾ³ÉΪδÀ´×îÓÐÇ°¾°µÄÐÂÐͼÓËÙ·½Ê½Ö®Ò», ÎüÒýÁËÖÚ¶à¹úÄÚÍâÑо¿ÕßµÄÄ¿¹â[7 -9 ] . ÔÚÖÚ¶àµÈÀë×ÓÌåⲨ¼ÓËٵķ½°¸ÖÐ, ÖÊ×ÓÊøⲨ¼ÓËÙ×îÔçÓÉCaldwellµÈ[10 ] ÔÚ2009ÄêÌá³ö, ËüµÄ»úÖÆÓëµç×ÓÊøÇý¶¯Î²²¨¼ÓËÙ¼«ÎªÏàËÆ, ¶¼ÊÇͨ¹ýÒ»ÊøºÜ¶ÌµÄ´øµçÁ£×ÓÊøÔÚµÈÀë×ÓÌåÖм¤·¢Î²²¨. ÓÉÓÚÖÊ×ÓµÄÖÊÁ¿Ô¶Ô¶´óÓÚµç×Ó, ×÷ΪⲨÇý¶¯Ô´µÄÖÊ×ÓÊøËùЯ´øµÄÄÜÁ¿Ò²Ô¶Ô¶µØ³¬¹ýÁ˼¤¹âºÍµç×ÓÊøµÄÄÜÁ¿, ÕâʹµÃÖÊ×ÓÊøÇý¶¯µÄⲨ¼ÓËÙ³ÉΪĿǰ×îÓпÉÄÜͨ¹ýµ¥¼¶¼ÓËÙ°ÑÇá×ÓÄÜÁ¿¼ÓËÙµ½TeVÁ¿¼¶µÄ¼ÓËÙ·½Ê½[11 ] . È»¶øÖ»Óг¤¶È½Ó½üÓÚµÈÀë×ÓÌåµÄ²¨³¤$ {\lambda }_{\mathrm{p}}=c/{\omega }_{\mathrm{p}} $ µÄÖÊ×ÓÊø²ÅÄÜÔÚµÈÀë×ÓÌåÖвúÉú½Ó½üÓÚ²¨ÆƵĵ糡ǿ¶È, ²¢ÇÒÏÖÓеļ¼ÊõÊÖ¶ÎȴûÓа취»ñµÃÈç´ËÖ®¶ÌµÄ¸ßÄÜÖÊ×ÓÊø. ÔÚ2010ÄêKumarµÈ[12 ] Ìá³öÁËͨ¹ý³¤ÖÊ×ÓÊøÔÚµÈÀë×ÓÌåÖÐͨ¹ý×Ôµ÷ÖƲ»Îȶ¨ (self-modulation instability) À´¼¤·¢µÈÀë×ÓÌåⲨµÄ¸ÅÄî. µ±Ò»Êø³¤ÖÊ×ÓÊøÔÚµÈÀë×ÓÌåÖд«²¥Ê±, ÖÊ×ÓÊø±¾Éí²úÉúµÄÖÜÆÚÐÔºáÏòµ÷ÖÆ»áʹµÃ³¤ÖÊ×ÓÊø×ÝÏò½á¹¹·¢ÉúÑÝ»¯, ´Ó¶ø²úÉúµÈÀë×ÓÌ岨µÄ½Ø¶ÏЧӦ, ʹµÃÖÊ×ÓÊøÑݱä³ÉÒ»³¤´®ÓëµÈÀë×ÓÌ岨³¤ÏàÆ¥ÅäµÄ¶ÌÖÊ×ÓÊø´®. ÓÉ´Ë¿ÉÒÔ¼¤·¢³öÒ»¸ö·Ç³£Ç¿µÄµç³¡, ÓÃÀ´¼ÓËÙÍⲿעÈëµÄµç×ÓÊø. Õâ¸öÀíÂÛÒÑÓÚ2018ÄêÔÚÅ·ÖÞºË×ÓÖÐÐÄ(CERN)±»AWAKEʵÑéºÏ×÷×é֤ʵ[13 ,14 ] . ËûÃÇÔÚʵÑéÖÐʹÓÃÁËÒ»Êø³¤6 cm¡¢ÖÐÐÄÄÜÁ¿400 GeVµÄÖÊ×ÓÊø. ÔÚÖÊ×ÓÊøͨ¹ý³¤¶È10 mµÄµÈÀë×ÓÌå¹ÜµÀÖ®ºó, ¸ßËÙÉãÏñ»úÅÄÉãÏÂÁËÖÊ×ÓÊø×Ôµ÷ÖÆÖ®ºó·ÖÁѳÉÒ»³¤´®¶ÌÖÊ×ÓÊøµÄͼÏñ. ÔÚ¸ÃʵÑéÖÐ, ÖÊ×ÓÊø´®¼¤·¢µÄµÈÀë×ÓÌåⲨ½«Íâ×¢ÈëµÄÄÜÁ¿Ô¼18 MeVµÄµç×ÓÊø¼ÓËÙÖÁ½ü2 GeVµÄ×î¸ßÄÜÁ¿[15 ] . µ«ÊÇ, ÃÀÖв»×ãµÄÊÇ, ÖÊ×ÓÊø×Ôµ÷ÖƵĹý³Ì»á³ÖÐø²»¶ÏµØ·¢Õ¹, ÌرðÊÇÓÉÓÚÖÊ×ÓÊøÍ·²¿µÄ³ÖÐøÀ©É¢ºÍºóÍË, ×îÖÕµ¼ÖÂÁËÕû¸öⲨÏàλµÄµ¹ÍË, ´Ó¶øÆÆ»µÁËÖÊ×ÓÊø´®µÄÐͬÐÔ, Ôì³ÉÁ˺óÆÚⲨµç³¡Ç¿¶ÈµÄϽµ, ͬʱҲʹµÃⲨµÄÏàËÙ¶ÈϽµ, ²»ÀûÓÚ¼ÓËÙ´øµçÁ£×Ó. ÕâÒ»ÏÖÏóÒѾ±»ÀíÂÛºÍʵÑéËùÖ¤Ã÷[13 -16 ] . Ïà¹ØÖÊ×ÓÊø×Ôµ÷ÖƵÄÀíÂÛÒѾ±»ºÜ¶àÎÄÕÂËù²ûÊö[17 -21 ] , ÕâЩÎÄÕ½ÒʾÁË×Ôµ÷ÖÆÕâÒ»²»Îȶ¨ÐÔ¹ý³ÌµÄÔö³¤ÂÊ¡¢ÏàËٶȵı仯µÈ, ¿ÉÒÔ˵ÔÚÏßÐÔ»¯½×¶Î, ¸ÃÀíÂÛÒѾ·¢Õ¹µÃÏ൱³ÉÊì. ½üÄêÀ´, Ëæ×ÅÈËÃǶÔ×Ôµ÷ÖÆÕâÒ»¹ý³ÌÑо¿µÄÉîÈë, ÀûÓÃÖÖ×ÓµÈÀë×ÓÌåⲨ¿ØÖÆ×Ôµ÷ÖÆ(seeding-self-modulation)µÄÏë·¨Öð½¥³öÏÖÔÚÁËÈËÃǵÄÊÓÏßÖ®ÖÐ. Ëüͨ¹ýÔÚÖÊ×ÓÊøµÄÇ°·½Ìí¼ÓÒ»¸ö¼¤¹âÊø»òÕ߶̵ç×ÓÊø, ÒÀ¿¿¼¤¹âÊø[18 ] »òÕ߶̵ç×ÓÊø[22 ] ²úÉúµÄⲨ×÷ΪÖÖ×ÓÀ´µ÷ÖÆÖÊ×ÓÊø, ´Ó¶øʹµÃÕû¸ö×Ôµ÷ÖƵĹý³Ì±äµÃ¿É¿Ø. 2020ÄêLotovºÍMinakov[23 ] ͨ¹ýÀíÂÛÑо¿ÓëÊýֵģÄâ, ·¢ÏÖͨ¹ý°Ñ¶Ìµç×ÓÊøÖÖ×ÓⲨ×Ôµ÷ÖÆÓëµÈÀë×ÓÌåÃܶÈÌݶÈÏà½áºÏ, ¿ÉÒÔ»ñµÃÒ»¸öÏà¶ÔÎȶ¨¡¢µç³¡Ç¿¶ÈÓÖ±£³ÖÔڽϸßË®×¼µÄⲨ. ×ÛÉÏËùÊö, ÀûÓÃÖÖ×ÓµÈÀë×ÓÌ岨À´¿ØÖÆÖÊ×ÓÊøµ÷Öƹý³Ì¾ßÓо޴óµÄDZÁ¦, Ò²ÊÇÄ¿Ç°AWAKEÏîÄ¿µÄÖ÷ÒªÑо¿·½ÏòÖ®Ò». Õâ·½ÃæµÄÑо¿²Å½øÈëÈËÃǵÄÊÓÏß, ¶ÔÓÚÆä»úÖÆÒÔ¼°µç×ÓÊø¶ÔÖÊ×ÓÊøÇý¶¯µÄⲨÏàËٶȵÄÓ°ÏìÄ¿Ç°ÉÐûÓб»ÍêÈ«ÈÏÖª. ÓÉÓÚµç×ÓÔÚⲨÖмÓËÙÄÜÁ¿×îÖÕÈ¡¾öÓÚⲨµÄÏàËÙ¶È, Òò´ËÈçºÎ¿ØÖÆⲨÏàËٶȡ¢²¢¾¡¿ÉÄÜÌá¸ßÕâ¸öÏàËÙ¶ÈÖÁ·Ç³£½Ó½üÕæ¿ÕÖйâËÙÊǸöÖØÒªÑо¿¿ÎÌâ. ±¾ÎÄÖ÷ÒªÑо¿ÒÔµç×ÓÊøÇý¶¯µÈÀë×ÓÌåⲨ×÷ΪÖÖ×ÓµÄÖÊ×ÓÊø×Ôµ÷Öƹý³Ì, ¼°Æä²úÉúµÈÀë×ÓÌåⲨµÄÏàËٶȱ仯, ²¢¸ù¾ÝÄ£Äâ½á¹û̽ÌÖÖÊ×ÓÊøⲨÏàËÙ¶ÈÓëµç×ÓÊøµÄ¹ØÁª. ͨ¹ý¶þάÖù×ø±êÄ£ÄâÈí¼þLCODE[24 ] , Ñо¿²»Í¬µçºÉÃܶȡ¢ÄÜÁ¿µÄ¶Ìµç×ÓÊø¶ÔÖÊ×ÓÊø×Ôµ÷Öƹý³ÌµÄÓ°Ïì, ÌرðÊÇÖÊ×ÓÊøⲨÏàËٶȵı仯, ͬʱ»¹²ûÊöÁ˶̵ç×ÓÊøÔÚµÈÀë×ÓÌåÖÐ×ÔÉíµÄÑÝ»¯¶Ô¸ÃÏàËٶȵÄÓ°Ïì, ΪÖÊ×ÓÊøÇý¶¯Î²²¨¼ÓËÙµÄÏà¹ØÑо¿Ìṩ²Î¿¼.2.ÀíÂÛÄ£ÐÍÓëÊýֵģÄâ Ê×ÏȽéÉܹØÓÚÖÖ×Ó×Ôµ÷ÖƵÄÀíÂÛÄ£ÐÍ. Ïà¹ØµÄÄ£ÐÍÇ°ÈËÒѾÓÐËùÑо¿[19 -21 ] , µ«ÊǺÍÏàÓ¦µÄÄ£Äâ½á¹û²¢²»Ò»ÖÂ, ¿É¼ûÏà¹ØµÄÀíÂÛ²¢²»ÍêÉÆ. ¶ø¹ØÓÚÎÞÖÖ×ÓÇé¿öϵÄÖÊ×ÓÊø×Ôµ÷ÖƵÄÀíÂÛÄ£ÐÍÔòÒѾ·¢Õ¹µÃÏ൱Í걸. ÔÚÎÞÖÖ×Ó×Ôµ÷ÖƵĶþάÀíÂÛÄ£ÐÍÖÐ, Ò»Êø·Ç³£³¤µÄ¾ùÔÈÖÊ×ÓÊøÑØ×Å$ z $ ·½ÏòÒÔ$ {v}_{\mathrm{b}} $ µÄËÙ¶ÈÔÚ¾ùÔȵÈÀë×ÓÌåÖд«Êä. ÓÉÓÚÖÊ×ÓÊøµÄÄÜÁ¿·Ç³£´ó, ¿ÉÒÔÖ±½ÓºöÂÔÖÊ×ÓÔÚ×ÝÏòµÄλÒÆ. ÄÇô, ¿ÉÒÔд³öËüµÄ°üÂç·½³Ì[21 ] : ·½³ÌÖÐ$ {\epsilon}_{\mathrm{n}} $ ΪÖÊ×ÓÊøµÄ¹éÒ»»¯·¢Éä¶È, $ {r}_{\mathrm{b}} $ ΪÖÊ×ÓÊø°ë¾¶, $ f\left(\xi \right) $ ΪÖÊ×ÓÊøµÄ×ÝÏò·Ö²¼, $ t $ Ϊʱ¼ä, $ \gamma $ ΪÖÊ×ÓµÄÂåÂ××ÈÒò×Ó, $ {k}_{\mathrm{p}}={\omega }_{\mathrm{p}}/c=\sqrt{4\mathrm{\pi }{n}_{0}{e}^{2}/{m}_{\mathrm{e}}{c}^{2}} $ ΪµÈÀë×ÓÌ岨Êý, $ {n}_{0} $ ΪµÈÀë×ÓÌåµç×ÓÃܶÈ, ÆäÖÐ${k}_{\mathrm{b}}= $ $ {\omega }_{\mathrm{b}}/c=\sqrt{4\mathrm{\pi }{n}_{\mathrm{b}}{e}^{2}/{m}_{\mathrm{p}}{c}^{2}}$ , $ {n}_{\mathrm{b}} $ ΪÖÊ×ÓÊøÃܶÈ, $ {m}_{\mathrm{p}} $ ΪÖÊ×ÓÖÊÁ¿, ´«²¥×ø±ê±äÁ¿$ \xi ={v}_{\mathrm{b}}t-z\approx ct-z $ , K 1 ºÍI 2 ÔòÊDZ´Èû¶ûº¯Êý. ·½³ÌµÄ×ó±ßµÚ¶þÏîÀ´×ÔÓÚÖÊ×ÓÊø·¢Éä¶Èµ¼ÖµĺáÏòÅòÕÍ, ¶øÓұߵÚÒ»ÏîÔòÀ´×ÔÓÚµÈÀë×ÓÌåºáÏòⲨ´øÀ´µÄÔ˶¯Ç÷ÊÆ. ͨ¹ý¼ÙÉè$ {{k}_{\mathrm{p}}r}_{\mathrm{b}}\ll 1 $ , ͬʱ¼Ù¶¨¾ßÓÐÒ»¶¨³¤¶ÈµÄ¾ùÔÈÖÊ×ÓÊø$ f\left(\xi \right)=1 $ , ·½³Ì(1 )¿ÉÒÔת±äΪ[21 ] ÆäÖз½³ÌµÄÓÒ±ßÊÇ$ {{k}_{\mathrm{p}}r}_{\mathrm{b}}\ll 1 $ Çé¿öϵĶþάÁ£×ÓÊø²úÉúµÄºáÏòⲨ·Ö²¼. ¿ÉÒÔͨ¹ýËüÀ´ÒýÈëµç×ÓÊøµÄºáÏòⲨ. ÕâÀï¼ÙÉèµç×ÓÊøµÄ³¤¶ÈΪ$ {\xi }_{1} $ , °ë¾¶µÈÓÚÖÊ×ÓÊøµÄ°ë¾¶(ͬÑù·ûºÏ$ {{k}_{\mathrm{p}}r}_{\mathrm{b}}\ll 1 $ ), ÃܶÈΪ$ N{n}_{\mathrm{b}} $ , ¾ùÔÈ·Ö²¼ÔÚ0¡ª$ {\xi }_{1} $ Ö®¼ä, ÕâÒâζ×ÅÔÚÄ£ÐÍÖÐ, ÖÊ×ÓÊø½ô¸úÔÚµç×ÓÊøµÄºó·½, Á½ÕßÖ®¼äµÄ¾àÀëΪ0. ÁíÍâÔڸ÷½³ÌÖÐ, ¼Ù¶¨µç×ÓÊøµÄ·Ö²¼²»Ëæʱ¼äÑÝ»¯. °Ñµç×ÓÊøµÄ·Ö²¼´úÈë·½³ÌÖ®ºó, ¾ÍµÃµ½ÁËÒ»¸öеİüÂç·½³Ì: ¸Ã·½³Ì°üº¬ÁËÖÊ×ÓÊøÇ°·½µç×ÓÊøµÄ×ÝÏòⲨ·Ö²¼. ´Ó¸Ã·½³Ì¾Í¿ÉÒÔ¿´³ö, µç×ÓÊø²úÉúµÄºáÏòⲨ¾ÍÊǵç×ÓÊøÖÖ×Ó×Ôµ÷ÖÆÓëÖÊ×ÓÊø×Ôµ÷Öƹý³ÌÖ®¼ä×î´óµÄ²»Í¬Ö®´¦. ½Ó×ŶԷ½³Ì(3 )×öÏßÐÔ»¯´¦Àí[19 ] , ¼ÙÉè$ {\mathrm{r}}_{\mathrm{b}}\approx {r}_{0}+{r}_{1} $ , $ {r}_{0} $ ΪÖÊ×ÓÊø×îÖÕƽºâ̬, $ {r}_{1} $ ΪÖÊ×ÓÊø×Ôµ÷ÖÆÆÚ¼ä²úÉúµÄ°ë¾¶ÈŶ¯, ²¢ÇÒ$ {r}_{1}\ll {r}_{0} $ , ÁíÍâ¼ÙÉè°üÂçÅòÕ͵ÄËٶȱȽϻºÂý${r}_{1}=\hat{r}\exp\left(\mathrm{i}\xi \right)+\mathrm{C}.\mathrm{C}$ , ¼°$\left|{\partial }_{\xi }\hat{r}\right|\ll \hat{r}$ . ÕâÑù¾ÍµÃµ½Á˼ò»¯ºó¹ØÓÚ$\hat{r}$ µÄ·½³Ì: ÆäÖÐ$ {k}_{\mathrm{\beta }}^{2}={k}_{\mathrm{b}}^{2}/2\gamma $ , ÁíÍâ¼ÙÉè·½³ÌµÄ³õʼÌõ¼þΪ$\hat{r}\left(z, \xi =0\right)=\mathrm{\delta }r\varTheta \left(z\right)$ , $\hat{r}\left(z=0, \xi \right)=\mathrm{\delta }r$ , ${\partial }_{z}\hat{r}(z=0, \xi ) $ $ =0$ [19 ] , $ \varTheta \left(z\right) $ Ϊ½×Ìݺ¯Êý, $ \mathrm{\delta }r $ Ϊ¼ÙÉèÖÐÖÊ×ÓÊø°ë¾¶ÔÚ³õʼʱ¿ÌµÄ΢СÈŶ¯, ÓÚÊÇ¿ÉÒԵõ½·½³ÌµÄ½â: ÓÉ´Ë¿ÉÖª, µ±µç×ÓÊøÃܶȷdz£Ð¡Ê±, ÖÖ×Ó×Ôµ÷ÖƵÄÕû¸ö¹ý³Ì½«½Ó½üÓÚÖÊ×ÓÊø×Ôµ÷Öƹý³Ì. ͨ¹ý°ÑÖÊ×ÓÊø°ë¾¶·Ö²¼´úÈëµÈÀë×ÓÌåⲨ¼ÆË㹫ʽ, ¾Í¿ÉÒÔ¼ÆËã³öµÈÀë×ÓÌåⲨµÄÇ¿¶È. ÔÙÒýÈëÎÄÏ×[19 ]ÖеÄÏàËٶȹ«Ê½ ÆäÖÐ$\tilde {S}{\hat{E}}_{z}$ Ϊµç³¡${\hat{E}}_{z}$ µÄÐ鲿, $\hat{R}{\hat{E}}_{z}$ Ϊµç³¡${\hat{E}}_{z}$ µÄʵ²¿. ͨ¹ý(6 )ʽ, Çó½âⲨµÄÏàËÙ¶È, ¾Í¿ÉÒԵõ½´æÔÚÖÖ×Óβ²¨Ê±ÖÊ×ÓÊøµ÷ÖÆⲨµÄÏàËÙ¶ÈËæʱ¼ä¼°¿Õ¼äµÄ·Ö²¼.ͼ1 Ϊͨ¹ýÉÏÊö¹«Ê½½øÐÐÊýÖµÇó½âµÃµ½µÄÏàËٶȷֲ¼. ͼ1 ÖÐËùʹÓõĵÈÀë×ÓÌåÃܶÈΪ$ {n}_{0}= $ $ 7\times {10}^{14}/\mathrm{c}{\mathrm{m}}^{3} $ , ÖÊ×ÓÊøÃܶÈΪ$ {n}_{\mathrm{b}}=0.0056{n}_{0} $ , ¾ùÔÈ·Ö²¼, ¶øµç×ÓÊø³¤¶È$ {\xi }_{1}=1.57 c/{\omega }_{\mathrm{p}} $ , ÃܶÈΪ¾ùÔÈ·Ö²¼. ͼÖзֱð¼ÆËãÁ˵ç×ÓÊøÃܶÈ$ {n}_{\mathrm{b}\mathrm{e}}=0{n}_{\mathrm{b}} $ , $ 0.25{n}_{\mathrm{b}} $ , $ 0.5{n}_{\mathrm{b}} $ , $ 1{n}_{\mathrm{b}} $ , $ 10{n}_{\mathrm{b}} $ , $ 20{n}_{\mathrm{b}} $ ʱµÄÖÊ×ÓÊø×Ôµ÷Öƹý³ÌÔڦΠ= 100ʱµÄⲨÏàËٶȷֲ¼. Èçͼ1(a) Ëùʾ, ÔÚµç×ÓÊøÃܶȷdz£Ð¡µÄÇé¿öÏÂ, ÖÖ×Ó×Ôµ÷ÖÆⲨÏàËÙ¶ÈÓëÎÞµç×ÓÊøÇé¿öϵÄÖÊ×ÓÊø×Ôµ÷ÖƼ¸ºõÒ»ÖÂ, ÏàËٶȽö½öÓÐ׿«Æäϸ΢µÄ²î¾à. ¶ø´Óͼ1(b) Ôò¿ÉÒÔ¿´µ½, ÔÚµç×ÓÊøÃܶȽϴóʱ, Õû¸ö×Ôµ÷Öƹý³ÌÖеÄⲨÏàËÙ¶ÈËæ×ŵç×ÓÊøµÄÃܶÈÔö´óÓÐ×ÅÃ÷ÏÔµÄÌá¸ß. ²¢ÇÒÏàËٶȵÄ×îСֵҲËæ֮΢ÈõµØÏò×óÒƶ¯, ÕâÒ²±íʾÕû¸ö×Ôµ÷Öƹý³ÌËæ×ŵç×ÓÊøÃܶȵÄÔö¼Ó¶ø¼Ó¿ì, µç×ÓÊø¾ßÓÐÌá¸ß×Ôµ÷ÖÆÔö³¤ÂʵÄÌØÐÔ. ͼ 1 ÔÚ$ \xi =100 c/{\omega }_{\mathrm{p}} $ ´¦Î²²¨ÏàËÙ¶ÈËæʱ¼ä±ä»¯¡¡(a) µç×ÓÊøÃܶȽϵÍʱ; (b) µç×ÓÊøÃܶȽϴóʱ Figure1. Change of the phase velocity with time at $ \xi =100 c/{\omega }_{\mathrm{p}} $ : (a) Low electron beam density; (b) high electron density. ÉÏÊöµÄ¼ÆËãʹÓÃÁËÒ»¸ö¼ÙÉè, ÓÉÓÚ$ {r}_{0} $ ±ØÈ»ÊǸö²»Îª¸ºµÄʵÊý, µ±$1-2 N\sin\left(\xi - {{\xi }_{1}}/{2}\right)\sin\left(-{\xi }_{1}\right)$ Ϊһ¸ö¸ºÊýʱ, Ö±½Ó¼Ù¶¨$ 1/{r}_{0}=0 $ , ÁíÍâ, ÔÚN µÄÈ¡Öµ·Ç³£´óµÄÇé¿öÏÂ, ±ÈÈçN = 40, ´Ëʱµç×ÓÊø²úÉúµÄµç³¡ÒѾ´¦ÓÚ·ÇÏßÐÔÇ¿¶È, ¶ø±¾ÀíÂÛÖ»ÊÊÓÃÓÚÏßÐԽ׶Î, ËùÒÔÉÏÊöµÄÀíÂÛÆäʵ¶ÔÓÚN ÓÐÒ»¸öÊÊÓ÷¶Î§. ½Ó×Åͨ¹ýLCODE³ÌÐòÄ£ÄâÀíÏë״̬ÏÂ, Ïàͬ·Ö²¼¡¢²»Í¬µçºÉÁ¿µÄµç×ÓÊøËùÒý·¢µÄÖÖ×Ó×Ôµ÷ÖÆÖв»Í¬Î»Öᢲ»Í¬Ê±¿Ì×ÝÏòⲨ¼«ÖµµÄλÖñ仯. LCODEÊÇÓÉLotov¿ª·¢µÄ¶þάÖù×ø±êÄ£ÄâÈí¼þ[25 ] , רÃÅÓÃÓÚÄ£ÄâÖù¶Ô³ÆÁ£×ÓÊøÔÚµÈÀë×ÓÌåÖд«²¥ËùÒýÆðµÄⲨ¼¤·¢ºÍµç×Ó¼ÓËÙ¹ý³Ì. ÔÚÄ£ÄâÖÐ, Ñ¡È¡µÄÄ£Äâ´°¿Ú³¤¶ÈΪ${600\; c/\omega }_{\mathrm{p}} $ , µÈÀë×ÓÌåµÄÃܶÈΪ$ {n}_{0}=7\times {10}^{14}/\mathrm{c}{\mathrm{m}}^{3} $ ÇÒ¾ùÔÈ·Ö²¼, ÖÊ×ÓÊø³¤¶È$L= $ $ 1500\; c/\omega _{\mathrm{p}}$ (~3 cm), °ë¾¶$ {{r}_{\mathrm{b}}=1 c/\omega }_{\mathrm{p}} $ (~200 ¦Ìm), ÖÐ ÐÄÄÜÁ¿$ {E}_{\mathrm{b}}=400\;\mathrm{G}\mathrm{e}\mathrm{V} $ , ÖÐÐÄÃܶÈΪ$ {n}_{\mathrm{b}}=0.0056\;{n}_{0} $ , ×ÝÏòÃܶÈΪ¾ùÔÈ·Ö²¼, ºáÏòΪ¸ß˹·Ö²¼. ËùʹÓõĵç×ÓÊøÖÐÐÄÃܶÈΪ$ {n}_{\mathrm{b}\mathrm{e}} $ , ×ÝÏò¾ùÔÈ·Ö²¼, ºáÏòΪ¸ß˹·Ö²¼, µç×ÓÊø³¤¶È${{\xi }_{1}=\dfrac{\mathrm{\pi }}{2} c/}\omega _{\mathrm{p}}$ , °ë¾¶$ {{r}_{\mathrm{b}\mathrm{e}}=1\; c/\omega }_{\mathrm{p}} $ , ½ô¸úÔÚÖÊ×ÓÊøºó·½, Ë«·½Ö®¼äûÓмä¸ô. ÕâÀïÏÈ¿¼ÂÇÒ»¸öÀíÏëÇé¿ö, °Ñµç×ÓµÄÄÜÁ¿ÉèÖÃΪ${E}_{\mathrm{b}\mathrm{e}}= $ $ {10}^{15}\;\mathrm{G}\mathrm{e}\mathrm{V}$ , ÔÚÄÜÁ¿Èç´Ë¸ßµÄÇé¿öÏÂ, µç×ӵķֲ¼²»»áËæʱ¼äÑÝ»¯, Èç´Ë¾Í¿ÉÒÔÓëÉÏÊöµÄÀíÂÛ½øÐбȽÏ.ͼ2(b) ¡¢Í¼2(d) ºÍͼ2(f) ·Ö±ð¸ø³öÁËÔÚÉÏÊöÌõ¼þϸıäµç×ÓÊøµÄÖÐÐÄÃܶÈËùÄ£Äâ³öµÄÖÊ×ÓÊø×Ôµ÷ÖÆⲨÏàËÙ¶ÈÔÚʱ¼äÓë¿Õ¼äÉϵķֲ¼. ¶øͼ2(a) ¡¢Í¼2(c) ºÍͼ2(e) ¸ø³öÁËÉÏÊöÌõ¼þÏÂÖÊ×ÓÊø×Ôµ÷ÖÆⲨµç³¡×î´óÖµÔÚʱ¼äÓë¿Õ¼äÉϵķֲ¼. ͨ¹ý¶Ô±ÈÕâЩͼÏñ¿ÉÒÔ·¢ÏÖ, Ëæ×ŵç×ÓÊøÖÐÐÄÃܶȵÄÔö¼Ó, µç³¡×î´óÖµ·åÖµ³öÏÖµÄʱ¼äÔÚÕû¸ö×Ôµ÷ÖƵĹý³ÌÖÐÔ½À´Ô½Ôç(´ÓÎÞµç×ÓÊøµÄ´óÔ¼$20000c/{\omega }_{\mathrm{p}}$ µ½$ {n}_{\mathrm{b}\mathrm{e}}=10{n}_{\mathrm{b}} $ ʱµÄ´óÔ¼$10000c/{\omega }_{\mathrm{p}}$ ), Ïà¶ÔÓ¦µÄⲨÏàËٶȱ仯½á¹¹Ò²ÓÐ×ÅͬÑùµÄ±ä»¯, Óɴ˿ɼû, µç×ÓÊøµÄÒýÈë¿ÉÒÔÌá¸ß×Ôµ÷ÖƵÄÔö³¤ÂÊ, ѹËõÕû¸ö×Ôµ÷Öƹý³Ì´Ó³õʼµ½±¥ºÍËùÐèµÄʱ¼ä, ²¢ÇÒËæ×ŵç×ÓÊøµÄµçºÉÁ¿µÄÔö¼Ó, Õû¸ö¼ÓËٵij̶ÈÓú·¢Ã÷ÏÔ. ͼ 2 µç×ÓÊøÖÖ×Ó×Ôµ÷ÖÆÄ£Äâ½á¹û¡¡(a) ÎÞµç×ÓÊøʱµÄ×î´óµç³¡·Ö²¼; (b) ÎÞµç×ÓÊøʱµÄÏàËٶȷֲ¼; (c) µç×ÓÊøÖÐÐÄÃܶÈΪ$ 1{n}_{\mathrm{b}} $ ʱµÄ×î´óµç³¡·Ö²¼; (b) µç×ÓÊøÖÐÐÄÃܶÈΪ$ 1{n}_{\mathrm{b}} $ ʱµÄÏàËٶȷֲ¼; (e) µç×ÓÊøÖÐÐÄÃܶÈΪ$ 10{n}_{\mathrm{b}} $ ʱµÄ×î´óµç³¡·Ö²¼; (f) µç×ÓÊøÖÐÐÄÃܶÈΪ$ 10{n}_{\mathrm{b}} $ ʱµÄÏàËٶȷֲ¼ Figure2. Results of the simulation: (a) Distribution of Emax when no seeding; (b) distribution of phase velocity when no seeding; (c) distribution of Emax when $ {n}_{\mathrm{b}\mathrm{e}}=1{n}_{\mathrm{b}} $ ; (d) distribution of phase velocity when $ {n}_{\mathrm{b}\mathrm{e}}=1{n}_{\mathrm{b}} $ ; (e) distribution of Emax when $ {n}_{\mathrm{b}\mathrm{e}}=10{n}_{\mathrm{b}} $ ; (f) distribution of phase velocity when $ {n}_{\mathrm{b}\mathrm{e}}=10{n}_{\mathrm{b}} $ . ͼ3(a) ¸ø³öÁËÔÚ²»Í¬µç×ÓÊøÌõ¼þÏÂⲨµÄ·åÖµÏàλ±ä»¯Çé¿ö. ͨ¹ý¶Ô±Èͼ3(a) Öеĸ÷¸öÇúÏßµÄתÕÛµãλÖÃ, ¿ÉÒÔ·¢ÏÖËùÓеÄÇúÏ߶¼ÓµÓÐÏàͬµÄ±ä»¯¹æÂÉ, ËüÃǵı仯Ç÷ÊÆÒ²ÊÇÏàͬµÄ, Ωһ²»Í¬µÄÊÇÏàËٶȹյãµÄλÖúÍÏàËٶȵĴóС. ͼ3(b) ºÍͼ3(c) Ôò¸ø³öÁË($\xi =100\; c/{\omega }_{\mathrm{p}} $ Óë$\xi =300\; c/{\omega }_{\mathrm{p}} $ ´¦)²»Í¬$ {n}_{\mathrm{b}\mathrm{e}} $ ϸ÷´¦Î²²¨ÏàËÙ¶ÈËæʱ¼äµÄ±ä»¯Çé¿ö. ͨ¹ý¶Ô±Èͼ3(b) ºÍͼ3(c) ²»Í¬$ {n}_{\mathrm{b}\mathrm{e}} $ Çé¿öϵÄⲨÏàËٶȿÉÒÔ·¢ÏÖ, Ïà±ÈÓÚÎÞµç×ÓÊøµ÷ÖÆ, ÔÚÓеç×ÓÊøµ÷ÖƵÄÇé¿öÏÂ, ⲨÏàËÙ¶ÈÓÐËùÌáÉý, ¶øÇÒⲨµÄÔö³¤ÂÊÒ²Ã÷ÏÔÔö¼ÓÁË. ÖÊ×ÓÊø×Ôµ÷ÖƵÄÔö³¤ÂÊËæ×ŵç×ÓÊøÖÐÐÄÃܶÈ$ {n}_{\mathrm{b}\mathrm{e}} $ µÄÌá¸ß¶øÔö´ó, ´Ó¶øËõ¶ÌÁËÕû¸ö¹ý³ÌµÄʱ¼ä, ʹµÃⲨÏàËٶȵÄÑÝ»¯½øÕ¹¼Ó¿ì, ¸üÔçµØ´ïµ½Á˺óÆÚÏàËٶȽӽüÓÚ¹âËÙµÄÎȶ¨×´Ì¬. ÕâÓë֮ǰÀíÂÛÍƵ¼Ëù¸ø³öµÄ½áÂÛÍêÈ«Ò»ÖÂ, µ«ÊÇ¿ÉÒÔ·¢ÏÖÄ£Äâ½á¹ûÓëÀíÂÛÏà±ÈÔÚϸ½ÚÉϲ¢²»Ò»ÖÂ, ¿É¼ûÏëÒª»ñµÃÒ»¸ö¾«È·µÄ¹ØÓÚÏàËٶȵķֲ¼, ÊýֵģÄâÈÔÈ»ÊDz»¿É»òȱµÄ. ͼ 3 (a) ²»Í¬µç×ÓÊøÃܶÈ$ {n}_{\mathrm{b}\mathrm{e}} $ Çé¿öÏÂⲨ·åÖµÏàλµÄ±ä»¯; (b) $ \xi =100\; c/{\omega }_{\mathrm{p}} $ ´¦²»Í¬$ {n}_{\mathrm{b}\mathrm{e}} $ Ìõ¼þÏÂÄ£ÄâµÃµ½µÄⲨÏàËÙ¶ÈËæʱ¼ä±ä»¯; (c) $ \xi =300\; c/{\omega }_{\mathrm{p}} $ ´¦²»Í¬$ {n}_{\mathrm{b}\mathrm{e}} $ Ìõ¼þÏÂÄ£ÄâµÃµ½µÄⲨÏàËÙ¶ÈËæʱ¼ä±ä»¯ Figure3. (a) Phase change of the wakefield peak with different electron beam density $ {n}_{\mathrm{b}\mathrm{e}} $ ; (b) evolution of the phase velocity at $ \xi =100 c/{\omega }_{\mathrm{p}} $ with different $ {n}_{\mathrm{b}\mathrm{e}} $ ; (c) evolution of the phase velocity at $ \xi =300 c/{\omega }_{\mathrm{p}} $ with different $ {n}_{\mathrm{b}\mathrm{e}} $ . ͼ4 ¸ø³öÁË×ÝÏò×ø±ê$0 c/{\omega }_{\mathrm{p}}¡ª600 c/{\omega }_{\mathrm{p}} $ ·¶Î§µÄÄ£Äâ´°¿ÚÄÚ×ÝÏòµç³¡×î´óÖµËæʱ¼äµÄ±ä»¯ÇúÏß, ´ÓͼÖеÄÇúÏ߱仯¿ÉÒÔÇåÎúµØ¿´³öËæ×ŵç×ÓÊøµÄµçºÉÁ¿ÌáÉý, Õû¸ö×Ôµ÷Öƹý³ÌµÄÔö³¤ÂÊ(µç³¡Ôö³¤ÂÊ)ÓÐÁËÃ÷ÏÔµÄÌáÉý, Ëù´ïµ½µÄ×î´óµç³¡Ò²ËæÖ®Ìá¸ß. ͼ 4 ²»Í¬µç×ÓÊøÃܶÈ$ {n}_{\mathrm{b}\mathrm{e}} $ Çé¿öÏÂ×î´óµç³¡Ëæʱ¼äµÄ·Ö²¼ Figure4. Evolution of the maximum electric field with different electron beam density $ {n}_{\mathrm{b}\mathrm{e}} $ . ×ÛÉÏËùÊö, µç×ÓÊø¿ÉÒÔÌáÉý×Ôµ÷ÖƵÄÕû¸ö¹ý³ÌµÄ·¢Õ¹ËÙ¶È, ʹµÃÕû¸ö¹ý³ÌËùÐèµÄʱ¼äËõ¶Ì, ÕâҲʹµÃⲨÏàËٶȵı仯·ù¶È¼Ó¿ì, ¸üÔçµØ´ïµ½Á˺óÆÚÏàËٶȽӽüÓÚ¹âËÙµÄÎȶ¨×´Ì¬, ÓÐÀûÓÚºóÐøµÄµç×Ó¼ÓËÙ.3.µç×ÓÊø²ÎÊý¶ÔⲨÏàËٶȵÄÓ°Ïì ÉÏÒ»½ÚÌÖÂÛÁËÀíÏë״̬ϵç×ÓÊøÖÖ×ÓⲨ¶ÔÖÊ×ÓÊø×Ôµ÷Öƹý³ÌÖÐⲨÏàËٶȵÄÓ°Ïì, Ëù²ÉÓõĵç×ÓÊøÄÜÁ¿¼«¸ß, ʹÆäÔÚ´«Êä¹ý³ÌÖв»·¢Éú±ä»¯, ÊÇÒ»ÖÖ¼ò»¯ºóµÄÄ£ÐÍ. È»¶øÔÚʵ¼ÊµÄÇé¿öÖÐ, µç×ÓÊøµÄÄÜÁ¿²»¿ÉÄÜÈç´ËÖ®¸ß, ÏàÓ¦µØ, µç×ÓÊøÔÚµÈÀë×ÓÌå´«²¥µÄ¹ý³ÌÖÐ, ËüµÄÃܶȷֲ¼¡¢ÐÎ×´¡¢ÄÜÁ¿¶¼»á·¢Éú±ä»¯. ÕâЩ¸Ä±äÒ²»áÓ°ÏìⲨÏàËÙ¶È. ±¾½Ú¿¼ÂÇÁËÓÐÏÞÄÜÁ¿µç×ÓÊø´«Êä¹ý³ÌµÄÑÝ»¯¶ÔⲨÏàËٶȵÄÓ°Ïì. Ê×ÏȽéÉÜÀíÂÛ¼ÆËã. µ±µç×ÓÊøÔÚµÈÀë×ÓÌåÖд«²¥Ê±, Ëü»áÊܵ½Ò»¸öÀ´×ÔµÈÀë×ÓÌåµÄ¾¶ÏòµÄ×÷ÓÃÁ¦ÒÔ¼°±¾ÉíµÄ¿âÂØÅųâÁ¦, ÆäºáÏò³ß¶ÈÂú×ã[17 ] ÆäÖÐ$ \tau =t $ Ϊ´«²¥Ê±¼ä, I 1 ºÍK 1 ΪÐÞÕý±´Èû¶ûº¯Êý. ¼ÙÈçµç×ÓÊøµÄ·¢Éä¶È·Ç³£Ð¡, ÄÇôµç×ÓÊø½«Êܵ½Ò»¸ö¾¶ÏòѹËõµÄ×÷ÓÃÁ¦, ½øÈëÒ»¸ö×Ô¾Û½¹µÄ¹ý³Ì. ÔÚÕâ¸ö¹ý³ÌÖÐ, µç×ÓÊøµÄ°ë¾¶ÔÚ²»¶ÏµØ±äС, ÃܶÈÔÚ²»¶ÏµØ±ä¸ß, ´Ó¶øËüËù¼¤·¢µÄµç³¡Ò²ÔÚ²»Í£µØ±äÇ¿. ¼ÙÉèÁ£×ÓÊøµÄƽºâ̬Âú×ãÈçÏÂÌõ¼þ: ²¢ÇÒÁ£×ÓÊøµÄÍ·²¿Âú×ãÕæ¿ÕÖз¢Éä¶È×ÔÓÉÅòÕÍ·½³Ì[17 ] ¿ÉÒÔÀûÓ÷½³Ì(8 )ºÍ·½³Ì(9 )À´Çó½â³ö²»Í¬Ê±¿ÌÁ£×ÓÊøµÄƽºâ̬.ͼ5(a) ºÍͼ5(b) ¸ø³öÁËͨ¹ý(8 )ʽºÍ(9 )ʽ¼ÆËãµÄÒ»Êø³¤¶È${\xi }_{1}=\dfrac{\mathrm{\pi }}{2}c/{\omega }_{\mathrm{p}}$ , °ë¾¶$ r=1 c/{\omega }_{\mathrm{p}} $ , ·¢Éä¶È$ {\varepsilon }_{\mathrm{e}}=3\times {10}^{-4}~\mathrm{r}\mathrm{a}\mathrm{d}/\mathrm{m}\mathrm{m} $ , ÄÜÁ¿Îª$ {E}_{\mathrm{b}\mathrm{e}} $ µÄµç×ÓÊø¸Õ½øÈëµÈÀë×ÓÌåÖÐʱµÄƽºâ̬·Ö²¼. ¿ÉÒÔ¿´µ½µç×ÓÊøµÄ°ë¾¶, ÌرðÊǺó°ë²¿·Ö, ÓÐÒ»¸ö·Ç³£Ã÷ÏÔµÄѹËõ. Óɴ˿ɼû, ÔÚµÈÀë×ÓÌåÖд«²¥µÄ³õÆÚ, µç×ÓÊø½«¾ÀúÒ»¸ö¼«ÆäÏÔÖøµÄѹËõ¹ý³Ì, ¶øѹËõºó²úÉúµÄ¸ßÃܶÈÒ²×ÔȻʹµÃÆä²úÉúµÄµç³¡ÓÐÁ˾޴óµÄÌáÉý, ´Ó¶ø¸Ä±äÁËÕû¸öⲨµÄ·Ö²¼. ͼ 5 (a) µç×ÓÊøÄÜÁ¿$ {E}_{\mathrm{b}\mathrm{e}}=100\mathrm{M}\mathrm{e}\mathrm{V} $ ʱ²»Í¬µç×ÓÊøÃܶÈ$ {n}_{\mathrm{b}\mathrm{e}} $ µÄƽºâ̬·Ö²¼; (b) $ {n}_{\mathrm{b}\mathrm{e}}=10{n}_{\mathrm{b}} $ ʱ²»Í¬µç×ÓÊøÄÜÁ¿$ {E}_{\mathrm{b}\mathrm{e}} $ µÄƽºâ̬·Ö²¼ Figure5. (a) Equilibrium configuration with different electron beam density $ {n}_{\mathrm{b}\mathrm{e}} $ when E be =100 MeV; (b) equilibrium configuration with different E when $ {n}_{\mathrm{b}\mathrm{e}}=10{n}_{\mathrm{b}} $ . ͼ6 ¸ø³öÁ˸ù¾Ý(7 )ʽ¡ª(9 )ʽ¼ÆËãËùµÃµÄ´æÔÚµç×ÓÊøÖÖ×Óʱ, ÖÊ×ÓÊø×Ôµ÷Öƹý³ÌÖеÄƽºâ̬Ãܶȷֲ¼. ¼ÆËã¹ý³ÌÖÐËùʹÓõIJÎÊýÈçÏÂ: µÈÀë×ÓÌåÃܶÈ$ {n}_{0} $ , µç×ÓÊø³õʼÃܶÈ$ {n}_{\mathrm{b}\mathrm{e}}=5{n}_{\mathrm{b}} $ , ¾ùÔÈ·Ö²¼, µç×ÓÊøÄÜÁ¿$ {E}_{\mathrm{b}\mathrm{e}} $ = 100 MeV, ·¢Éä¶È${\varepsilon }_{\mathrm{e}}=3\times $ $ {10}^{-4}~\mathrm{r}\mathrm{a}\mathrm{d}/\mathrm{m}\mathrm{m}$ , ³¤¶È$ {\xi }_{1}=1.57 c/{\omega }_{\mathrm{p}} $ , ³õʼ°ë¾¶${r}_{\mathrm{b}\mathrm{e}}= $ $ c/{\omega }_{\mathrm{p}}$ ; ÖÊ×ÓÊøÃܶÈ$ {n}_{\mathrm{b}}=0.0056{n}_{0} $ , ×ÝÏòÎÞÏÞ³¤ÇÒ¾ùÔÈ·Ö²¼, ÖÐÐÄÄÜÁ¿Îª$ {E}_{\mathrm{b}} $ = 400 GeV, ·¢Éä¶È${\varepsilon }_{\mathrm{p}}= $ $ 3\times {10}^{-4}~\mathrm{r}\mathrm{a}\mathrm{d}/\mathrm{m}\mathrm{m}$ , ³õʼ°ë¾¶$ {r}_{\mathrm{b}}=c/{\omega }_{\mathrm{p}} $ . ¸Ã¼ÆËãÖвÉÓÃÁËÁ½¸ö¼ÙÉè: 1)ºöÂÔµç×ÓÊø°ë¾¶·Ö²¼µÄ±ä»¯, ¼´$ {r}_{\mathrm{b}\mathrm{e}}\left(\xi, t\right)={r}_{\mathrm{b}\mathrm{e}}\left(t\right) $ ; 2)ºöÂÔµç×ÓÊøµÄÄÜÁ¿Ë¥¼õ. Ê×ÏÈ, ͨ¹ýÉÏÊö¼ÙÉèºÍ·½³Ì(7 )ÇóµÃµç×ÓÊøÔÚijһʱ¿Ìϵİ뾶; Æä´Î, ½«µç×ÓÊø·Ö²¼ºÍÖÊ×ÓÊø²ÎÊý´úÈë·½³Ì(7 ), ´Ó¶øÇóµÃÔÚ¸Ãʱ¿Ìµç×ÓÊøºó·½µÄÖÊ×ÓÊøƽºâ̬Ãܶȷֲ¼, ×îºóÔÙͨ¹ý$n\left(\xi, t\right)= $ $ {n}_{{\text{³õʼ}}}\left(\xi \right){q}_{\mathrm{b}}\dfrac{{\left({r}_{0}\right)}^{2}}{r{\left(\xi, t\right)}^{2}}$ ¼ÆËã³ö¸Ãʱ¿Ì¸÷¸ö×ÝÏòλÖõÄƽºâ̬Ãܶȷֲ¼. ͼ6 ÖÐÑ¡È¡ÁËÈý¸öʱ¿Ì($ t=0 $ , $ 410/{\omega }_{\mathrm{p}} $ , $ 589/{\omega }_{\mathrm{p}} $ ), ·Ö±ð¶ÔÓ¦×ŵç×ÓÊø°ë¾¶${r}_{\mathrm{b}\mathrm{e}}= $ $ c/{\omega }_{\mathrm{P}}$ , $ 0.75 c/{\omega }_{\mathrm{P}} $ , $ 0.5 c/{\omega }_{\mathrm{P}} $ ÈýÖÖÇé¿ö, չʾÁ˵ç×ÓÊø(0ÖÁÐéÏß·¶Î§ÄÚ)ºó·½ÖÊ×ÓÊøµÄƽºâ̬Ãܶȷֲ¼µÄ±ä»¯Í¼Ïñ. ͨ¹ý¶Ô±È²»Í¬Ê±¿ÌµÄÖÊ×ÓÊøƽºâ̬Ãܶȷֲ¼, ¿ÉÒÔµÃÖªµ±µç×ÓÊø´¦ÓÚ±»Ñ¹Ëõ״̬ʱ(¿ÉÒÔ¿´µ½µç×ÓÊøµÄÃܶÈÔ½À´Ô½¸ß), ÖÊ×ÓÊøµÄ°üÂç»áÓÐÏòÇ°Ô˶¯µÄÇ÷ÊÆ, ÄÇôÏàÓ¦ÖÊ×ÓÊø²úÉúµÄⲨÏàλҲ»á´æÔÚÏòÇ°Ô˶¯µÄÇ÷ÊÆ, ÕâÒ²ÊÇÐγɳ¬¹âËÙⲨÏàËٶȵÄÖ÷ÒªÔÒò. ×ÜÖ®, µ±µç×ÓÊø´¦ÓÚ×Ô¾Û½¹×´Ì¬Ê±, ¿ÉÒԵõ½Ò»¸ö³¬¹âËÙµÄⲨÏàËÙ¶È. ͼ 6 µç×ÓÊøѹËõÒýÆðµÄÖÊ×ÓÊøƽºâ̬±ä»¯, ¼´ÔÚÈý¸öʱ¿ÌµÄÖÊ×ÓÊøƽºâ̬·Ö²¼ Figure6. Equilibrium configuration of proton beam with a compressing electron beam. ½ÓÏÂÀ´µÄÄ£ÄâÊÇ»ùÓÚ֮ǰµÄµÈÀë×ÓÌåºÍÖÊ×ÓÊø²ÎÊý, ¿¼ÂÇÁËÏàͬµç×ÓÊø·Ö²¼ºÍµçºÉÁ¿, µ«²»Í¬ÄÜÁ¿µÄÄ£Äâ²ÎÊý¶ÔⲨÏàËٶȵÄÓ°Ïì. ÔÚÄ£ÄâÖÐ, µÈÀë×ÓÌåµÄÃܶÈΪ$ {n}_{0}=7\times {10}^{14}/\mathrm{c}{\mathrm{m}}^{3} $ ÇÒ¾ùÔÈ·Ö²¼, ÖÊ×ÓÊøÖÐÐÄÄÜÁ¿$ {E}_{\mathrm{b}}=400~\mathrm{G}\mathrm{e}\mathrm{V} $ , ³¤¶È$ {L=1500 c/\omega }_{\mathrm{p}} $ (´óÔ¼3 cm), °ë¾¶$ {r=1 c/\omega }_{\mathrm{p}} $ (´óÔ¼200 ¦Ìm), ÖÐÐÄÃܶÈΪ$ {n}_{\mathrm{b}\mathrm{m}}=0.0056{n}_{0} $ , ×ÝÏò·Ö²¼Îª¾ùÔÈ·Ö²¼, ºáÏòΪ¸ß˹·Ö²¼. ËùʹÓõĵç×ÓÊø³¤¶È${{\xi }_{1}=\dfrac{\mathrm{\pi }}{2} c/\omega }_{\mathrm{p}}$ , °ë¾¶$ {r=1 c/\omega }_{\mathrm{p}} $ , µç×ÓÊøÖÐÐÄÃܶÈ$ {n}_{\mathrm{b}\mathrm{e}\mathrm{m}}=10{n}_{\mathrm{b}} $ , ×ÝÏò·Ö²¼Îª¾ùÔÈ·Ö²¼, ºáÏòΪ¸ß˹·Ö²¼, µç×ÓÊøÖÐÐÄÄÜÁ¿×ܹ²Ñ¡È¡ÁËÈýÖÖ, ·Ö±ðÊÇ$ {E}_{\mathrm{b}\mathrm{e}}$ = 100 MeV, 500 MeV, 1 GeV.ͼ7(a) ¡ªÍ¼7(c) ¸ø³öÁËÔÚÉÏÊöÌõ¼þϸıäµç×ÓÊøµÄÄÜÁ¿(100 MeV, 500 MeV, 1 GeV)ËùµÃµ½µÄÖÊ×ÓÊø×Ôµ÷ÖÆⲨµç³¡×î´óÖµÔÚʱ¼äÓë¿Õ¼äÉϵķֲ¼. ͼ7(d) €¡ªÍ¼7(f) Ôò¸ø³öÁËÉÏÊöÌõ¼þÏÂÖÊ×ÓÊø×Ôµ÷ÖÆⲨÏàËÙ¶ÈÔÚʱ¼äÓë¿Õ¼äÉϵķֲ¼. ͼ8(a) ºÍͼ8(b) ÔòÊÇÌôÑ¡ÁË$\xi =100 c/{\omega }_{\mathrm{p}}$ Óë$\xi = $ $ 300 c/{\omega }_{\mathrm{p}}$ µÄλÖÃ, ²»Í¬ÄÜÁ¿µÄµç×ÓÊøËùµÃµ½µÄⲨÏàËٶȽøÐбȽÏ. ¿ÉÒÔ·¢ÏÖ, ÔÚ×Ôµ÷ÖƳõʼµÄʱÆÚ, ³öÏÖÁËÏàËٶȴóÓÚ¹âËÙµÄÏÖÏó, ÕâÓë֮ǰÌáµ½µÄµç×ÓÊø×Ô¾Û½¹ÀíÂÛÏà·ûºÏ. ÄÜÁ¿Ô½¸ß, ¸ÃÏÖÏó¾ÍÔ½²»Ã÷ÏÔ. ÁíÍâͨ¹ý¶Ô±Èͼ7 ºÍͼ8 ÖеÄÊý¾Ý, ¿ÉÒÔ·¢ÏÖ¶Ô×Ô¾Û½¹Æ𵽹ؼü×÷ÓõÄÓÐÁ½¸ö²ÎÊý, ¼´µç×ÓÊøµÄÄÜÁ¿ºÍÃܶÈ. Èç¹ûµç×ÓÊøµÄÄÜÁ¿¦Ã ¹ý¸ß, ÄÇôËüÊܵ½µÄ¾¶Ïò¼ÓËÙ¶ÈÒ²ËæÖ®¼õÈõ, Èçͼ8(a) ºÍͼ8(b) Ëùʾ, ×Ô¾Û½¹¶ÔÏàËٶȵÄÓ°Ïì³Ì¶ÈËæ×ÅÄÜÁ¿µÄÔö¸ß¶ø½¥½¥¼õÈõ. ¶øÈç¹ûÔöÇ¿µç×ÓÊøµÄÃܶÈ, Ôò×Ô¾Û½¹µÄËٶȾͻáÃ÷ÏÔ¼Ó¿ì, Õû¸ö×Ô¾Û½¹µÄ¹ý³ÌËùÒý·¢µÄ³¬¹âËÙÏàËÙ¶ÈÒ²»áÓú·¢Ã÷ÏÔ. ͼ 7 ÀûÓõç×ÓÊøÖÖ×ÓⲨµ÷ÖÆÖÊ×ÓÊøµÄÄ£Äâ½á¹û¡¡(a), (b), (c)·Ö±ð¶ÔÓ¦µç×ÓÊøÄÜÁ¿$ {E}_{\mathrm{b}\mathrm{e}} $ = 100 MeV, 500 MeV, 1 GeVʱµÄ×î´óµç³¡Ëæʱ¼ä±ä»¯; (d), (e), (f) ·Ö±ð¶ÔÓ¦µç×ÓÊøÄÜÁ¿$ {E}_{\mathrm{b}\mathrm{e}} $ = 100 MeV, 500 MeV, 1 GeVʱµÄÏàËÙ¶ÈËæʱ¼ä±ä»¯ Figure7. Simulation of proton beam modulation with electron beam seeding:(a), (b), (c) The maximum electric fields as a function of time for the electron beam energy at ${E}_{\mathrm{b}\mathrm{e}}=100~\mathrm{M}\mathrm{e}\mathrm{V}$ , 500 MeV, and 1 GeV, respectively; (d), (e), (f) the phase velocity as a function of time for the electron beam energy at ${E}_{\mathrm{b}\mathrm{e}}=100~\mathrm{M}\mathrm{e}\mathrm{V}$ , 500 MeV, and 1 GeV, respectively. ͼ 8 (a) ÔÚ$ \xi =100 c/{\omega }_{\mathrm{p}} $ ´¦²»Í¬µç×ÓÊøÄÜÁ¿Ä£ÄâµÃµ½µÄⲨÏàËÙ¶ÈËæʱ¼ä±ä»¯; (b) ÔÚ$ \xi =300 c/{\omega }_{\mathrm{p}} $ ´¦²»Í¬µç×ÓÊøÄÜÁ¿Ä£ÄâµÃµ½µÄⲨÏàËÙ¶ÈËæʱ¼ä±ä»¯ Figure8. (a) Phase velocity as a function of time at $ \xi =100 c/{\omega }_{\mathrm{p}} $ for different electron energy; (b) phase velocity as a function of time at $ \xi =300 c/{\omega }_{\mathrm{p}} $ for different electron energy. ÁíÍâ, µç×ÓÊøÔÚⲨÖд«²¥Ê±»¹Êܵ½ÁËÒ»¸ö×ÝÏòµÄµç´ÅÁ¦[25 ] : ¶øÓëÖ®Ïà¶ÔµÄ, µç×ÓÊø×÷ΪⲨµÄÄÜÁ¿À´Ô´, Ëüÿʱÿ¿Ì¼õÉÙµÄÄÜÁ¿ÕýºÃÓëÖ®²úÉúµÄβ²¨Ç¿¶ÈÏà¶ÔÓ¦, ¿ÉÒԵóöµç´ÅÁ¦F Õý±ÈÓÚµç×ÓÊøÃܶÈn be , ÕâÒ²Òâζ×Å, µç×ÓÊøµÄÄÜÁ¿ºÄÉ¢ËÙ¶ÈÕý±ÈÓÚµç×ÓÊøËùЯ´øµÄµçºÉÁ¿. µ±µç×ÓÊøµÄÄÜÁ¿Ë¥ÍË, Æä·¢Éä¶ÈËùÒýÆðµÄÅòÕÍЧӦ»á³¬¹ýⲨÒýÆðµÄѹËõЧӦ, Õâ¸öʱºò, µç×ÓÊø¾Í»áÅòÕÍ, ËüµÄÃܶȽµµÍ, ´Ó¶ø²úÉúÁËÓëÉÏÊö×Ô¾Û½¹¹ý³ÌÏà·´µÄÏÖÏó, ʹµÃÏàËÙ¶ÈÓÐËù½µµÍ. ²»¹ý, ¼ÙÈçµç×ÓÊøÓÐ×Å×ã¹»µÄÄÜÁ¿, ÄÇôÕâ¸ö¹ý³Ì¾Í»á·¢ÉúµÄ±È½Ï»ºÂý. ÁíÍâ, µ±µç×ÓÊøµÄÄÜÁ¿ºÄ¾¡Ê±, Ëü»áÔÚ×ÝÏòÉϱäÐηÖÁÑ, ´Ó¶ø²úÉú²»Îȶ¨µÄÏàËÙ¶È, Èçͼ8(a) ºÍ8(b) Ëùʾ. ͬÀí, Èç¹û½µµÍµç×ÓÊøµÄµçºÉÁ¿, ÄÇôҲ×ÔÈ»¿ÉÒÔ¼õ»º¸Ã¹ý³Ì. µ±µÈÀë×ÓÌåⲨÖеĵ糡Ôö¼Óµ½½Ó½üÓÚE 0 ʱ, ÓÉÓÚÏà¶ÔÂÛ·ÇÏßÐÔЧӦ, µÈÀë×ÓÌåÖÐⲨµÄ²¨³¤¾Í»á±»À³¤[26 ] , ¿ÉÒÔ½üËÆÃèÊöΪ${\lambda }_{\mathrm{P}}= $ $ {\lambda }_{\mathrm{p}0}[1+\alpha {\left({E}_{\mathrm{m}}/{E}_{0}\right)}^{2}]$ , ÆäÖÐ$ {\lambda }_{\mathrm{p}0} $ ΪÏßÐÔÀíÂÛÖеĵÈÀë×ÓÌ岨³¤, $ \alpha $ ÊÇÒ»¸ö²ÎÊý. ¼Ù¶¨Õû¸ö³¤ÖÊ×ÓÊøËùÐγɵÄⲨ½á¹¹ÔÚ×ÝÏòÉÏ°üº¬ÁËN ¸ö²¨³¤, ÄÇôµ±Ã¿Ò»¸ö²¨³¤¶¼±»À³¤Ò»µãµãʱ, ¶ÔÓÚⲨµÄÏàλ, ÌرðÊǾàÀëÖÊ×ÓÊøÍ·²¿½ÏÔ¶µÄλÖÃ, ¾ßÓм«´óµÄÓ°Ïì. Ò»°ã¶øÑÔ, ÎÞÂÛÊÇÖÊ×ÓÊø×Ôµ÷ÖÆ»¹Êǵç×ÓÊøÖÖ×ÓⲨÓÕµ¼µ÷ÖÆ, ËüÃǵÄⲨ´óÖ±仯¶¼ÊÇÏÈÉÏÉýºóϽµµÄ, ¶øËüÃDzúÉúµÄⲨËùÄÜ´ïµ½µÄ×î´óµç³¡´óÖÂÔÚ0.4E 0 ¡ª0.7E 0 . µ±Ò»¸öλÖõĵ糡´ÓE 1 ±ä»¯µ½E 2 ʱ, ¸ù¾ÝÉÏÊö$ {\lambda }_{\mathrm{P}} $ ¹«Ê½, ËüµÄ²¨³¤±ä»¯¼°Ïàλ±ä»¯´óԼΪ ËùÒÔ, µ±Î²²¨ÔÚ¿ìËÙÔö´óʱ, ¸Ã·ÇÏßÐÔЧӦ»áʹµÃⲨµÄÏàËٶȷ¢Éú¾Þ´óµÄϽµ, ²¢ÇÒËæ×ŦΠ(N )µÄÔö´ó¶øÓú·¢Ã÷ÏÔ; µ±Î²²¨ÔÚ¿ìËÙϽµÊ±, ⲨµÄÏàËٶȻá¿ìËÙµØÉÏÉý, ÉõÖÁÓÚÍ»ÆƹâËÙ, ²úÉú³¬¹âËÙµÄÏàËÙ¶È. È»¶ø¸Ã¹ý³ÌÊÇ·ÇÏßÐÔЧӦ, ºÜÄѱ»¾«È·ÃèÊö, Ö»Äܸù¾Ý¹«Ê½¶¨ÐÔÃèÊö³ö´óÖµÄÎïÀíͼÏñ. ¸Ã»úÖÆÔÚûÓÐÖÖ×Óµç×ÓÊøⲨ´æÔÚµÄÖÊ×ÓÊø×Ôµ÷Öƹý³ÌÖÐÒ²»á¶ÔⲨÏàËٶȵÄÑÝ»¯Æðµ½Ï൱ÖØÒªµÄ×÷ÓÃ.4.ÖÊ×ÓÊø×ÝÏòÃܶȷֲ¼¶ÔⲨÏàËٶȵÄÓ°Ïì ÏÖ½ñAWAKEʵÑé[15 ] ÖÐËùʹÓõÄÄ£ÐͲ¢²»ÊÇÈçÒÔÉÏËùÊöµÄÔÚ×ÝÏòÉÏÍêÈ«¾ùÔÈ·Ö²¼, ¶øÊÇÓàÏÒº¯ÊýµÄ°ë²¨ÐÍ, º¯Êý±íÊöΪ${n}_{\mathrm{b}}\left(r, \xi \right)= \dfrac{{n}_{\mathrm{b}\mathrm{m}}}{2}\times $ $ \mathrm{e}\mathrm{x}\mathrm{p}\left(-\dfrac{{r}^{2}}{{\sigma }_{r}^{2}}\right)\left[1-\cos \left(2\mathrm{\pi }\xi /L\right)\right]$ , ÆäÖÐ$ {n}_{\mathrm{b}\mathrm{m}}=0.0056{n}_{0} $ ΪÖÐÐÄÃܶÈ, $ {\sigma }_{r}=1 c/{\omega }_{\mathrm{P}} $ , ËüÊÇÒ»¸ö×ÝÏòÃܶȴÓ0¿ªÊ¼ÉÏÉý²¢×îÖջص½0µÄÕâÑùÒ»ÖÖ·Ö²¼. ¸ÃʵÑéÀûÓü¤¹âÊø²úÉúµÄÒƶ¯µÈÀë×ÓÌå±ß½çÀ´¶ÔÖÊ×ÓÊø²úÉúµ÷ÖÆ. ÔÚûÓеç×ÓÊøµÄÇé¿öÏÂ, ÕâÑùµÄ¹ý³Ì·Ç³£²»ÀûÓÚÖÊ×ÓÊøµÄ×Ôµ÷ÖÆ, ÒòΪ²»½öÔö³¤ÂÊ»ºÂý, ¶øÇÒ¼«Ò×¼¤·¢Èí¹Ü²»Îȶ¨ÐÔ[14 ] , ²»ÀûÓÚºóÐøÁ£×ÓÊøµÄ¼ÓËÙ. ¶øÔÚÏÖÓеĵç×ÓÊøÖÖ×Óµ÷ÖÆ·½°¸[22 ] ÖÐ, µç×ÓÊøµÄÒýÈ뽫ʹµÃÔ±¾´¦ÓÚ¼¤¹âÊøÇ°°ë¶ÎµÄÖÊ×ÓÊøÒ²¿ÉÒÔÔËÓÃÓÚⲨ¼ÓËÙµÄÕû¸ö¹ý³Ì, ´Ó¶ø±ÜÃâ²»±ØÒªµÄÀË·Ñ. Ôڸ÷½°¸Öеç×ÓÊøÒýÈëËù´øÀ´µÄ±ä»¯ºÍÉÏÊöÒƶ¯µÈÀë×ÓÌå±ß½çÒýÆð×Ôµ÷ÖƵĹý³ÌÓкܴóÇø±ð. ÔÚÒýÈëÉÏÊöµÄÖÊ×ÓÊø·Ö²¼µÄÇé¿öÏÂ, ±È½ÏÁËûÓеç×ÓÊøÓëÒýÈëµç×ÓÊøµÄÇé¿ö. ÔÚÓеç×ÓÊøµÄÄ£ÄâÖÐ, µç×ÓÊøµÄ²ÎÊýÈçÏÂ: ÄÜÁ¿E = 100 MeV, ³¤¶È$ {\xi }_{1}=1.57\mathrm{ }\mathrm{ }\mathrm{c}/{\omega }_{\mathrm{p}} $ , $ {\sigma }_{r\mathrm{e}}=1\mathrm{ }\mathrm{c}/{\omega }_{\mathrm{p}} $ , ÖÐÐÄÃܶÈ${n}_{\mathrm{b}\mathrm{e}\mathrm{m}}= $ $ 0.0056{n}_{0}$ , µç×ÓÊøµÄ¿Õ¼ä·Ö²¼±íÊöΪ${n}_{\mathrm{b}\mathrm{e}}\left(r, \xi \right)= $ $ \dfrac{{n}_{\mathrm{b}\mathrm{e}\mathrm{m}}}{2}\mathrm{e}\mathrm{x}\mathrm{p}\left(-\dfrac{{r}^{2}}{{\sigma }_{r\mathrm{e}}^{2}}\right)\left[1-\cos \left(2\mathrm{\pi }\xi /{\xi }_{1}\right)\right]$ , ¼´×ÝÏò·Ö²¼ÎªÓàÏÒº¯Êý°ë²¨ÐÍ, ºáÏò·Ö²¼Îª¸ß˹·Ö²¼.ͼ9(a) ºÍͼ9(b) ·Ö±ð¶Ô±ÈÁË$\xi =500 c/{\omega }_{\mathrm{p}} $ , $\xi = $ $ 750c/{\omega }_{\mathrm{p}}$ Á½¸ö×ø±êÏÂÎÞÖÖ×ÓⲨµÄ×Ôµ÷ÖÆÓëÓÐÖÖ×ÓⲨµ÷ÖÆÇé¿öÏÂÖÊ×ÓÊøⲨÏàËÙ¶ÈËæʱ¼äµÄ±ä»¯Çé¿ö. ¿ÉÒÔÃ÷ÏԵؿ´³öÓеç×ÓÊøµÄÇé¿öÏÂ, ⲨÏàËÙ¶ÈÓÈÆäÊÇÔÚÄ£ÄâºóÆÚÓÐÁËÃ÷ÏÔµÄÔö¼Ó. ÁíÍâ, ÓÉÓÚµç×ÓÊøµÄµçºÉÁ¿±È½ÏµÍ, ÔÚµÈÀë×ÓÌåÖеÄÄÜÁ¿Ë¥¼õËٶȱȲ»ÉÏͼ8 ÖÐ100 MeVËù¶ÔÓ¦µÄÄ£Äâ, ¹Ê¶øͼ9 Öв¢Ã»ÓÐͼ8 ºóÆÚ³öÏֵIJ»Îȶ¨ÏàËÙ¶È, ÕâÓëÉÏÒ»½ÚËù²ûÊöµÄ½áÂÛÊÇÒ»ÖµÄ. ×ÛÉÏËùÊö, ¼´±ã¸Ä±äÁËÖÊ×ÓÊøµÄ·Ö²¼, µç×ÓÊøÒÀÈ»¿ÉÒÔÌá¸ßƽ¾ùÏàËÙ¶È, ֮ǰËùµÃµ½µÄ½áÂÛÔڸıäÖÊ×ÓÊø·Ö²¼µÄÇé¿öÏÂÒ²ÒÀÈ»ÊÊÓÃ. ͼ 9 (a) ÔÚ$ \xi =500 c/{\omega }_{\mathrm{p}} $ ´¦Ä£ÄâµÃµ½µÄⲨÏàËÙ¶ÈËæʱ¼ä±ä»¯; (b) ÔÚ$ \xi =750 c/{\omega }_{\mathrm{p}} $ ´¦Ä£ÄâµÃµ½µÄⲨÏàËÙ¶ÈËæʱ¼ä±ä»¯ Figure9. (a) Phase velocity as a function of time at $ \xi =500 c/{\omega }_{\mathrm{p}} $ ; (b) phase velocity at $ \xi =750 c/{\omega }_{\mathrm{p}} $ . 5.½á¡¡ÂÛ ±¾ÎÄͨ¹ýÀíÂÛ·ÖÎö²¢ÀûÓöþάÖù×ø±êÄ£ÄâÈí¼þLCODEÑо¿Á˵ç×ÓÊøµÄÖÖ×ÓⲨ¶ÔÖÊ×ÓÊø×Ôµ÷ÖÆⲨÏàËٶȵÄÓ°Ïì. ·¢ÏÖµç×ÓÊø¿ÉÒÔÌáÉýÕû¸öÖÊ×ÓÊø×Ôµ÷ÖƵÄÔö³¤ÂÊ, ÌáÉýⲨÏàËÙ¶È, ²¢ÇÒµç×ÓÊøµÄµçºÉÁ¿Ô½¸ß, ÌáÉýµÄЧ¹ûԽͻ³ö. ÁíÍâÑо¿»¹·¢ÏÖ, µç×ÓÊøÔÚÖÊ×ÓÊø×Ôµ÷Öƹý³ÌµÄÇ°ÆÚ»áͨ¹ý×Ô¾Û½¹µÄЧӦÌáÉýÏàËÙ¶È. µç×ÓÊøµÄµçºÉÁ¿Ô½¸ß¡¢ÄÜÁ¿Ô½µÍÔòÏàËÙ¶ÈÌáÉýÓú·¢Ã÷ÏÔ; ͨ¹ýÑ¡È¡ºÏÊʵIJÎÊý, ÉõÖÁ¿ÉÒÔ»ñµÃÒ»¸ö³¬¹âËÙµÄÏàËÙ¶È. ´ËÍâ, ±¾ÎÄ»¹Ì½ÌÖÁËÖîÈçµç×ÓÊøÄÜÁ¿ºÄÉ¢¡¢Ïà¶ÔÂÛЧӦÒýÆðµÄµÈÀë×ÓÌ岨³¤À³¤µÈЧӦ¶ÔÏàËٶȵÄÓ°Ïì, ²¢ÔÚ×îºó±È½ÏÁ˲»Í¬ÖÊ×ÓÊø·Ö²¼Çé¿öÏÂÏàËٶȵÄÑÝ»¯, ÑéÖ¤ÁËÉÏÊöµç×ÓÊøÖÖ×ÓⲨ¶ÔÖÊ×ÓÊø×Ôµ÷ÖÆⲨµÄÏàËÙ¶ÈÓ°ÏìµÄÏà¹Ø½áÂÛÊÊÓÃÓÚ²»Í¬ÖÊ×ÓÊøÃܶȷֲ¼. ±¾Ñо¿¶ÔÓÚδÀ´µÄµç×ÓÊøÖÖ×Ó×Ôµ÷ÖÆⲨ¼ÓËÙ·½°¸¾ßÓÐÒ»¶¨µÄ²Î¿¼¼ÛÖµ. ×÷Õ߸Ðл¶íÂÞ˹BudkerºËÎïÀíÑо¿ËùKonstantin Lotov½ÌÊÚÔÊÐíʹÓÃËû¿ª·¢µÄLCODE³ÌÐò, ²¢ÌṩÏà¹Ø°ïÖú.