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TUPAF20 Mean-Field Density Evolution of Bunched Particles With Non-Zero Initial Velocity electron, simulation, emittance, space-charge 233
 
  • B.S. Zerbe, P.M. Duxbury
    MSU, East Lansing, Michigan, USA
 
  Funding: NSF Grant 1625181 NSF Grant RC108666 MSU Col. Nat. Sci., Provost Off., Col. Comm. Art and Sci.
Reed (2006) pre­sented a 1D mean-field model of ini­tially cold pan­cake-beam ex­pan­sion demon­strat­ing that the evo­lu­tion of the en­tire spa­tial dis­tri­b­u­tion can be solved for all time where the 1D as­sump­tion holds. This model is rel­e­vant to ul­tra-fast elec­tron mi­croscopy as it de­scribes the evo­lu­tion of the dis­tri­b­u­tion within the pho­to­elec­tron gun, and this model is sim­i­lar to An­der­son’s sheet beam den­sity time de­pen­dence (An­der­son 1987) ex­cept that Reed’s the­ory ap­plies to freely ex­pand­ing beams in­stead of beams within a fo­cussing chan­nel. Our re­cent work (Zerbe 2018) gen­er­al­ized Reed’s analy­sis to cylin­dri­cal and spher­i­cal geome­tries demon­strat­ing the pres­ence of a shock that is seen in the Coulomb ex­plo­sion lit­er­a­ture under these geome­tries and fur­ther dis­cussed the ab­sence of a shock in the 1D model. This work is rel­e­vant as it of­fers a mech­a­nis­tic ex­pla­na­tion of the ring-like den­sity shock that arises in non-equi­lib­rium pan­cake-beams within the pho­to­elec­tron gun; more­over, this shock is co­in­ci­dent with a re­gion of high-tem­per­a­ture elec­trons pro­vid­ing an ex­pla­na­tion for why ex­per­i­men­tally aper­tur­ing the elec­tron bunch re­sults in a greater than 10-fold im­prove­ment in beam emit­tance(Williams 2017), pos­si­bly even re­sult­ing in bunch emit­tance below the in­trin­sic emit­tance of the cath­ode. How­ever, this the­ory has been de­vel­oped for cold-bunches, i.e. bunches of elec­trons with 0 ini­tial mo­men­tum. Here, we briefly re­view this new the­ory and ex­tend the cylin­dri­cal- and spher­i­cal- sym­met­ric dis­tri­b­u­tion to en­sem­bles that have non-zero ini­tial mo­men­tum dis­tri­b­u­tions that are sym­met­ric but oth­er­wise un­re­stricted demon­strat­ing how ini­tial ve­loc­ity dis­tri­b­u­tions cou­ple to the shocks seen in the less gen­eral for­mu­la­tion. Fur­ther, we de­rive and demon­strate how the lam­i­nar con­di­tion may be prop­a­gated through beam foci.
 
slides icon Slides TUPAF20 [1.396 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF20  
About • paper received ※ 19 October 2018       paper accepted ※ 15 December 2018       issue date ※ 26 January 2019  
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WEPLG05 Review of Spectral Maxwell Solvers for Electromagnetic Particle-in-Cell: Algorithms and Advantages plasma, simulation, laser, electron 345
 
  • R. Lehé, J.-L. Vay
    LBNL, Berkeley, California, USA
 
  Elec­tro­mag­netic Par­ti­cle-In-Cell codes have been used to sim­u­late both ra­dio-fre­quency ac­cel­er­a­tors and plasma-based ac­cel­er­a­tors. In this con­text, the Par­ti­cle-In-Cell al­go­rithm often uses the fi­nite-dif­fer­ence method in order to solve the Maxwell equa­tions. How­ever, while this method is sim­ple to im­ple­ment and scales well to mul­ti­ple proces­sors, it is li­able to a num­ber of nu­mer­i­cal ar­ti­facts that can be par­tic­u­larly se­ri­ous for sim­u­la­tions of ac­cel­er­a­tors. An al­ter­na­tive to the fi­nite-dif­fer­ence method is the use of spec­tral solvers, which are typ­i­cally less prone to nu­mer­i­cal ar­ti­facts. In this talk, I will re­view re­cent progress in the use of spec­tral solvers for sim­u­la­tions of plasma-based ac­cel­er­a­tors. This in­cludes tech­niques to scale those solvers to large num­ber of proces­sors, ex­ten­sions to cylin­dri­cal geom­e­try, and adap­ta­tions to spe­cific prob­lems such as boosted-frame sim­u­la­tions.  
slides icon Slides WEPLG05 [2.861 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-WEPLG05  
About • paper received ※ 06 November 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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