CD-EXCALIBUR-FMS0001-1.10-Fusion_Modelling_System_Science_Plan_ExcaliburFusionModellingSystemSciencePlan
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ExCALIBUR,Fusion,Modelling,System,Science,Plan,Abstract,This,document,outlines,the,Science,Plan,for,research,to,be,commissioned,by,the,Met,Office,for,the,“Fusion,Modelling,System”,use,case,of,the,SPF,“Exascale,Computing,Algorithms,and,Infrastructures,Benefiting,UK,Research”,programme,(ExCALIBUR).,Amendments,to,this,document,will,be,tracked,in,the,change,log,on,p.1,and,each,change,will,require,review,and,approval,by,the,UKAEA,internal,ExCALIBUR,+,E-TASC,Project,Board,Director,as,well,as,other,associated,interfaces,as,deemed,appropriate,by,the,Board.,Commercial,in,Confidence,Commercial,in,Confidence,UKAEA,REFERENCE,AND,APPROVAL,SHEET,Client,Reference:,UKAEA,Reference:,CD/EXCALIBUR-FMS/0001,Issue:,Date:,1.10,29,November,2019,Project,Name:,ExCALIBUR,Fusion,Modelling,System.,Version,1.10,–,modifications,in,response,to,reviewer,recommendations.,Prepared,By:,Name,and,Department,Signature,Wayne,Arter,Lucian,Anton,Debasmita,Samaddar,Rob,Akers,N/A,N/A,N/A,N/A,MSSC,Reviewed,By:,Ash,Vadgama,(AWE),N/A,Modifiedd,By:,Rob,Akers,MSSC,Approved,By:,Martin,O’Brien*,MSSC,*,Chairman,of,UKAEA,internal,ExCALIBUR,Project,Board.,Date,21/10/19,21/10/19,21/10/19,22/10/19,14/11/19,27/11/19,1/12/19,1,Commercial,in,Confidence,ExCALIBUR,Fusion,Modelling,System,Science,Plan,Purpose,This,document,outlines,the,Science,Plan,for,research,to,be,commissioned,by,the,Met,Office,for,the,“Fusion,Modelling,System”,use,case,of,the,SPF,“Exascale,Computing,Algorithms,and,Infrastructures,Benefiting,UK,Research”,programme,(ExCALIBUR).,It,complements,ExCALIBUR,Met,Office,Science,Plan,and,Activities,document,[1],,setting,out,a,vision,for,the,project’s,contribution,to,the,overarching,ExCALIBUR,plan.,This,document,is,aimed,at,stakeholders,including,the,SPF,ExCALIBUR,Programme,Board,and,Steering,Committee,,has,been,informed,by,consultation,with,the,Met,Office,,with,domain,experts,from,across,the,UKRI,community,and,from,within,UKAEA.,This,Science,Plan,is,intended,to,complement,other,ExCALIBUR,work,funded,through,the,UKRI,Research,Councils,and,the,Met,Office,“Weather,&,Climate,Prediction”,use,case.,The,ExCALIBUR,programmatic,aims,described,in,[1],are,common,with,those,of,the,Fusion,Modelling,System,use,case,and,so,are,not,repeated,here.,Fusion,Modelling,Use,Case,activities,The,aim,of,the,“Fusion,Modelling”,use,case,of,ExCALIBUR,is,,via,the,exploitation,of,the,ExCALIBUR,principles,outlined,in,[1],,to,develop,new,algorithms,,software,and,related,e-,Infrastructure,that,will,result,in,the,efficient,use,of,current,Petascale,and,future,Exascale,supercomputing,hardware,in,order,to,a),draw,insights,from,ITER,[2],“Big,Data”,and,b),to,guide,and,optimise,the,design,of,the,UK,demonstration,nuclear,fusion,power,plant,STEP,[3],and,related,fusion,technology,as,we,approach,the,Exascale.,The,aims,of,the,work,are,to,deliver,expertise,in,,and,tools,for,,“in-silico”,reactor,interpretation,and,design,,initially,with,a,focus,upon,the,“edge”,region,of,the,tokamak,[4],plasma,where,hot,plasma,comes,into,contact,with,the,material,walls,of,the,machine,(see,project,NEPTUNE,below).,This,challenging,,multi-physics,,multi-scale,intersection,between,plasma,physics,and,engineering,has,long,been,heralded,as,an,“exascale”,modelling,and,simulation,problem,and,its,solution,is,well,established,as,critical,to,the,success,of,commercial,fusion,energy.,Existing,legacy,(and,often,“black,box”),codes,do,not,scale,and,do,not,contain,all,the,latest,physics,that,is,believed,to,be,important,in,the,“burning,plasma,regime”,(notably,kinetic,effects);,without,a,significant,investment,in,this,area,,it,will,not,be,possible,to,design,the,“divertor”,region,of,future,fusion,power,plants,(the,region,of,the,machine,where,hot,plasma,comes,into,contact,with,the,surrounding,first,wall,–,see,Figure,1,below).,2,Commercial,in,Confidence,Figure,1:,Schematic,diagram,of,a,generic,tokamak,“poloidal,cross,section”,showing,the,areas,of,plasma,and,first,wall,that,will,be,targeted,by,project,NEPTUNE,(shaded,circles).,Attribution:,G.,Federici,et,al.,[CC,BY,3.0,(https://creativecommons.org/licenses/by/3.0)]†.,This,is,an,activity,that,must,be,performed,“in-silico”,using,“actionable”,modelling,and,simulation,as,the,highly,coupled,physics,in,the,divertor,cannot,be,created,in,the,laboratory,with,conditions,approaching,the,reactor,regime.,It,is,also,well,established,that,there,is,a,need,for,further,development,of,the,science,(which,will,take,place,in,close,cooperation,with,ExCALIBUR,numericists),–,the,codes,of,the,ITER,and,Exascale,era,must,therefore,be,easy,to,adapt,as,new,knowledge,becomes,established,(e.g.,through,ITER,operations).,The,programme,itself,is,designed,to,exploit,commonality,of,solutions,across,the,disciplines,and,domains,represented,by,ExCALIBUR,and,to,foster,the,development,of,a,UK,interdisciplinary,community,(within,our,National,laboratories,and,institutes,across,UKRI,and,throughout,Academia).,Activities,will,initially,be,around,an,ambitious,programme,to,develop,a,computational,model,that,includes,plasma,kinetic,effects,believed,to,be,essential,for,a,first-principles,description,of,the,complex,dynamics,of,high,temperature,fusion,plasma,in,the,divertor,region.,Codenamed,NEPTUNE,(NEutrals,&,Plasma,TUrbulence,Numerics,for,the,Exascale),,work,will,initially,focus,upon,coupling,the,turbulent,plasma,periphery,to,the,surrounding,neutral,gas,and,partially,ionized,impurities,that,exist,between,the,plasma,and,plasma,facing,components,,in,the,presence,of,an,arbitrary,tokamak,magnetic,field,and,full,3D,first,wall,geometry.,Figure,1,shows,a,schematic,of,a,generic,tokamak,“poloidal,cross,section”,,highlighting,the,targeted,regions,of,plasma,and,machine,,namely,the,main,chamber,between,core,plasma,,scrape,off,layer,and,wall,(upper,shaded,circle),and,the,so,called,“plasma,†,Minor,modifications,to,figure.,3,Commercial,in,Confidence,exhaust”,or,“divertor”,region,(lower,shaded,circle),where,heat,and,particles,come,into,direct,contact,with,material,surfaces.,Infrastructure,and,workflows,will,be,developed,so,that,the,resulting,close,coupled,models,can,be,constructed,routinely,based,around,a,high-fidelity,representation,of,the,geometry,described,by,Computer,Aided,Design,(CAD),systems,(this,likely,requiring,the,development,of,high,order,meshing,technology,,e.g.,using,Nektar++).,Quality,control,,verification,,validation,and,uncertainty,quantification,(VVUQ,,e.g.,via,intrusive,or,ensemble-based,methods),will,be,embedded,across,all,areas,of,the,project,to,ensure,numerical,predictions,are,“actionable”.,The,initial,aim,is,to,develop,knowledge,and,UK,capability,around,how,to,design,world,leading,Exascale,targeted,software,for,the,benefit,of,the,UK,academic,community,,UKRI,and,the,UK,nuclear,supply,chain.,Emphasis,will,be,placed,upon,building,a,connected,community,,delivering,training,and,skills,development,activities,as,necessary,,aligned,with,Pillar,4,of,the,ExCALIBUR,aims,(Investing,in,People).,Together,,the,UK,plasma,and,HPC,communities,have,the,required,expertise,to,deliver,this,project.,UKAEA,will,bring,together,world-class,experts,in,tokamak,edge,physics,,gyrokinetic,theory,,and,highly,scalable,algorithms,,to,address,arguably,one,of,the,most,important,unsolved,challenges,of,fusion,research,–,how,to,design,a,plasma,“exhaust,system”,that,can,reliably,restrict,power,flux,reaching,the,material,surfaces,to,tolerable,levels,,i.e.,no,more,than,~10MW/m2,in,the,steady-state.,Later,in,the,project,,further,packages,of,work,will,be,designed,to,address,other,aspects,around,the,“in-silico”,design,of,fusion,technology.,It,is,recognised,that,the,project,poses,a,significant,human,resource,and,project,management,challenge,,notably,to,develop,and,manage,a,team,across,many,different,sites,and,from,many,different,backgrounds,in,order,to,build,state-of-the-art,software,that,can,reliably,and,accurately,account,for,a,plethora,of,different,complex,physical,phenomena.,Further,,the,project,must,maintain,an,international,context,and,connect,to,the,European,EUROfusion,programme,(in,which,the,UK,is,a,key,player),and,the,US,Exascale,programme,(ECP).,Crucially,,the,emerging,software,environment,must,be,trusted,and,“actionable”,to,guide,procurements,potentially,involving,hundreds,of,millions,of,pounds,(e.g.,in,the,case,of,the,DEMO,[5],first,wall),,and,ultimately,to,ensure,the,safe,operation,of,a,multi-billion,pound,nuclear,plant.,The,UK,is,world-leading,in,the,study,of,the,edge,region,of,tokamak,plasmas.,The,flagship,EPSRC/EUROfusion,MAST-Upgrade,experiment,[6],recently,commissioned,by,UKAEA,at,Culham,has,been,built,with,the,primary,goal,of,testing,a,novel,“Super-X,divertor”,design,for,handling,the,plasma,exhaust.,Combined,with,software,developed,under,ExCALIBUR,,the,result,will,be,a,significant,step,forward,in,our,understanding,of,how,heat,and,particle,flows,can,be,controlled,and,kept,to,within,material,limits,inside,a,reactor.,Project,NEPTUNE,(NEutrals,&,Plasma,TUrbulence,Numerics,for,the,Exascale),-,background,The,UK,plasma,community,–,in,UKAEA,and,several,universities,-,currently,makes,extensive,use,of,“fluid”,codes,in,its,research,into,the,edge-plasma,region,of,fusion,devices.,“Fluid”,implies,that,the,plasma,can,be,treated,in,one,sense,like,“the,atmosphere”,in,the,Met,Office’s,Dynamical,Core,,but,with,the,added,complication,of,significant,effects,due,to,the,electrically,4,Commercial,in,Confidence,charged,nature,of,the,plasma.,For,example,,plasma,electrons,and,ions,can,to,an,extent,be,treated,as,separate,fluids,with,different,temperatures,,interacting,via,the,electromagnetic,field.,Plasma,fluid,codes,(such,as,BOUT++,[7]),are,relatively,efficient,up,to,only,~1000,cores,,but,there,are,a,large,range,of,effects,in,the,tokamak,plasma,edge,that,prevent,the,plasma,from,isotropising,to,a,Maxwellian,distribution,with,same,temperature,ion,and,electron,populations,(which,would,correspond,most,closely,to,the,atmospheric,fluid,concept).,Firstly,,the,strong,imposed,and,directed,magnetic,field,leads,to,anisotropy,since,charged,particles,move,rapidly,in,tight,,spiral,orbits,(gyro-orbits),along,the,closed,field,lines,and,only,slowly,normal,to,the,field.,Secondly,there,may,be,an,inadequate,number,of,collisions,(especially,in,the,burning,plasma,or,“reactor”,regime),for,the,species,to,equilibrate,,leaving,significant,tails,in,the,particle,velocity,distributions.,Such,tails,may,be,driven,by,external,heating,and/or,by,collisions,with,relatively,rarefied,neutral,particle,species,that,are,themselves,non-,Maxwellian.,Inclusion,of,these,effects,in,the,fluid,models,introduces,significant,modelling,uncertainty,(which,would,have,to,be,quantified,if,the,models,are,to,be,“actionable”,–,this,would,require,a,significant,investment).,Moreover,,existing,simulations,show,that,attempting,to,include,the,required,extra,physics,can,significantly,add,to,execution,cost,overhead,or,a,breakdown,of,scaling,,e.g.,when,stability/accuracy,issues,are,addressed,,a,large,reduction,in,allowable,timestep,can,ensue.,Unfortunately,,there,are,significant,challenges,with,moving,to,a,straightforward,particle-based,model,(e.g.,PIC,[8],,which,could,in,principle,address,these,problems),-,the,strength,of,the,electric,field,in,the,plasma,edge,exaggerates,the,effects,of,noise,when,sampling,charged,particles.,Together,,all,these,issues,conspire,to,make,it,impossible,to,achieve,converged,solutions,using,existing,codes,within,an,acceptable,timeframe.,The,next,most,widely,studied,level,of,treatment,of,velocity,space,,namely,“gyrokinetics”,[9],,averages,over,gyro-orbits,so,that,velocity,space,is,treated,as,a,2D,problem,(perpendicular,and,parallel,to,the,local,magnetic,field).,This,leads,to,5D,gyrokinetic,models,,which,in,principle,are,detailed,enough,and,accurate,enough,to,model,reality.,Ideas,around,the,discretisation,of,the,velocity,(phase),space,dependence,include,techniques,suitable,for,dealing,with,infinite,coordinates,,such,as,moment-based,methods,using,truncated,series,and/or,mapped,finite,elements,perhaps,combined,with,spherical,harmonics.,The,alternative,,particle-based,simulations,that,run,on,existing,petascale,hardware,such,as,SUMMIT,,e.g.,using,the,XGC,PIC,code,,can,take,many,weeks,for,just,a,single,simulation.,Unfortunately,,the,competing,and,potentially,more,attractive,5D,gyrokinetic,models,are,currently,at,or,beyond,the,limit,of,current,HPC,capability,in,terms,of,scalabiliy,,requiring,further,work,around,both,the,models,themselves,and,the,algorithms,used,to,instantiate,them,on,modern,HPC,systems.,Kinetic,levels,of,complexity,are,nonetheless,going,to,be,necessary,(at,least,locally),for,modelling,the,burning,plasma,regime,,due,to,the,inherent,uncertainty,in,the,fluid,codes.,The,plasma,in,a,fusion,reactor,may,well,behave,significantly,differently,to,plasma,in,existing,devices,because,it,will,in,general,contain,two,main,ionic,species,(Deuterium,and,Tritium),,neutral,fuel,particles,and,ionised,Helium,ash,(or,alpha,particles),,as,well,as,impurity,ions,originating,from,the,wall.,Further,,the,plasma,will,be,hotter,,reducing,collisions,so,that,yet,more,complicated,terms,need,to,be,added,to,the,fluid,approximations.,These,additional,contributions,to,the,fluid,models,will,require,tuning,in,much,the,same,way,as,meteorological,micro-physical,effects,,but,in,advance,preferably,of,suitable,experimental,data,from,ITER,or,5,Commercial,in,Confidence,other,reactors.,Kinetic,code,results,will,inevitably,be,needed,for,this,“tuning”,exercise,(i.e.,providing,kinetic,closures,to,the,fluid,codes).,Each,plasma,species,will,contribute,different,levels,of,uncertainty,,and,a,different,scaling,and,performance,overhead,to,the,workflow,made,up,of,close,coupled,codes,that,will,be,developed,under,FM-WP2,and,FM-WP3,(see,below,and,Table,1).,Identifying,,quantifying,and,mitigating,uncertainty,and,the,computational,overhead,of,adequately,modelling,each,will,be,a,core,theme,within,the,project.,Evidently,the,interpretation,of,data,from,ITER,and,consequently,the,design,of,a,DEMO,fusion,power,plant,will,require,a,hierarchy,of,models,,from,those,that,can,be,deployed,upon,Exascale,hardware,down,to,the,surrogate,models,that,will,be,deployed,at,scale,upon,the,high,throughput,computing,platforms,of,the,ITER,era,(e.g.,for,uncertainty,quantification,and,parametric,optimisation).,High,fidelity,,exascale,“hero,run”,codes,capable,of,modelling,all,the,required,physics,to,accurately,describe,the,edge,region,of,the,tokamak,plasma,will,be,used,to,develop,order,reduced,“surrogate”,models,that,can,be,scaled,out,for,testing,against,large,volumes,of,experimental,data,and,for,routine,uncertainty,quantification,as,part,of,the,process,shown,in,Figure,2,(left,hand,branch).,Currently,,this,iterative,“discovery,loop”,is,not,possible,for,the,edge,plasma,problem,due,to,the,unacceptable,run-time,overhead,of,existing,codes,and,lack,of,flexibility,for,introducing,new,physics.,Similarly,,the,high,fidelity,and,surrogate,models,of,the,future,will,be,crucial,for,designing,future,fusion,plant,“in-silico”,(this,is,shown,as,the,right-hand,branch,of,Figure,2,–,an,iterative,“optimization”,loop).,Figure,2:,Typical,“Modelling,&,Simulation”,workflow,for,fusion,applications.,The,left-hand,iterative,loop,is,largely,around,model,validation,against,experimental,data,whereas,the,right-hand,loop,focuses,upon,“engineering,design”.,The,existing,code,base,is,currently,limited,in,its,ability,(for,the,same,reasons,as,the,left-,hand,branch),to,make,accurate,predictions,that,will,lead,to,robust,engineering,solutions,(leading,to,the,introduction,of,unnecessary,and,expensive,engineering,overhead).,The,6,Commercial,in,Confidence,current,paradigm,is,to,make,predictions,,then,build,expensive,prototypes,at,scale,to,confirm,that,the,code,predictions,are,valid,–,this,will,be,impossible,for,STEP,and,DEMO,for,cost,reasons,and,due,to,the,fact,that,we,simply,cannot,recreate,the,operating,conditions,under,which,components,will,have,to,survive,–,instead,,quantified,uncertainty,and,“trust”,must,be,associated,with,modelling,and,simulation,through,rigorous,,modern,VVUQ,–,i.e.,our,codes,must,be,“actionable”.,Lastly,,there,are,also,likely,to,be,additional,demands,upon,code,execution,speed,from,DEMO,operation,,for,example,there,will,inevitably,be,a,safety-related,need,for,surrogate,models,that,can,be,deployed,as,part,of,future,real-time,systems,to,help,control,the,temperature,of,the,first,wall.,These,future,needs,will,all,be,embedded,within,the,heart,of,the,project,requirements,throughout,the,development,lifecycle,of,the,NEPTUNE,software,stack.,The,project,itself,has,been,designed,in,stages,,so,that,early,work,will,make,significant,contributions,to,existing,software,capability,and,to,the,development,of,standalone,proxy-,apps,[10],that,capture,the,scaling,characteristics,of,the,full,models,being,targeted,in,the,long,term.,The,overall,aim,,which,will,guide,the,direction,of,the,project,and,choice,of,Activites,and,sub-tasks,(most,of,which,will,be,defrayed,across,UKRI,and,the,Universities),,is,to,build,a,hierarchy,of,models,that,are,capable,of,representing,edge,plasma,behavior,to,within,a,specific,level,of,uncertainty,,with,the,option,of,at,least,partial,incorporation,into,the,development,of,software,across,the,EUROfusion,work,programme,,notably,the,TSVV,(Theory,,Simulation,,Verification,and,Validation),activities.,There,will,be,no,attempt,to,refactor,or,improve,the,performance,of,existing,legacy,codes,(unless,the,overhead,of,doing,so,is,low).,Instead,,emphasis,will,be,upon,building,new,insight/knowledge,and,new,software,and,infrastructure,from,the,ground,up,using,modern,software,engineering,design,principles,and,futureproofing,those,tools,to,create,an,agile,platform,that,can,respond,to,the,rapidly,changing,vision,of,what,the,exascale,will,look,like,,and,to,the,emergence,of,new,physics,understanding.,All,codes,that,are,capable,of,making,predictions,will,have,embedded,within,them,the,concepts,of,VVUQ,,to,ensure,that,they,are,“actionable”,to,within,specified,levels,of,uncertainty,(e.g.,using,“intrusive”,UQ,methods).,Existing,legacy,codes,will,of,course,be,an,invaluable,resource,for,guiding,development,towards,the,flexible,,scalable,and,performant,codes,of,the,future.,High,level,aims,of,the,ExCALIBUR,Fusion,use,case,,aligned,with,the,Met,Office,Weather,&,Climate,prediction,system,use,case,include:,•,To,apply,the,principles,of,ExCALIBUR,to,deliver,the,benefits,outlined,above.,•,To,develop,and,deliver,cross-cutting,research,that,aligns,with,the,UKRI,Research,Council,contribution,(i.e.,to,help,deliver,a,UK,interdisciplinary,team,that,can,address,aspects,of,Exascale,software,design,that,lie,in,common,across,the,represented,use,cases).,•,To,help,train,the,software,engineers,,architecture,specialists,,computer,scientists/algorithms,specialists,and,data,scientists,of,the,ITER,and,Exascale,era.,UKAEA,will,work,with,the,SPF,ExCALIBUR,Programme,Board,and,Steering,Committee,to,ensure,alignment,and,a,close,working,relationship,with,the,UKRI,funded,research,activities,,which,for,example,could,include,participation,in,workshops,and,knowledge,exchange,activities,,participation,in,stakeholder,engagement,exercises,etc.,7,Commercial,in,Confidence,As,part,of,this,Science,Plan,,four,work,packages,will,initially,be,commissioned,by,the,Met,Office,,i.e.,FM-WP1/2/3/4.,As,outlined,in,the,Met,Office,Science,Plan,[1],,the,Met,Office,will,manage,the,cross-cutting,theme,work,packages,XC-WP1/2,(see,below).,The,four,initial,Fusion,Modelling,System,work,packages,are:,1.,Numerical,representation;,2.,Plasma,multiphysics,model;,3.,Neutral,gas,&,impurity,model;,4.,Code,structure,and,coordination,,as,shown,in,table,1,(and,in,[1]).,Code,Coupling,R&D,activity,will,thread,FM-WP1,(performance),and,FM-WP4,(flexibility),as,well,as,through,the,two,referent,model,work,packages,FM-WP2,and,FM-WP3.,All,work,packages,will,be,built,around,modern,best,practice,in,co-design,and,there,will,be,significant,interaction,between,the,work,packages.,Each,work,package,will,be,supported,by,Research,Software,Engineers,(RSEs),(including,engagement,with,the,Society,of,RSE,[11],where,necessary).,PSRE,Use,Cases,Weather,&,Climate,prediction,system:,WC-WP1:,Component,model,co-design,WC-WP2:,System,co-,design,WC-WP3:,System,integration,Fusion,Modelling,system:,FM-WP1:,Numerical,representation,FM-WP2:,Plasma,multiphysics,model,FM-WP3:,Neutral,gas,&,Impurity,model,FM-WP4:,Code,structure,&,coordination,Cross-Cutting,Themes,XC-WP1:,Common,approaches,&,solutions,XC-WP2:,Emerging,technologies,Table,1:,SPF,ExCALIBUR,Met,Office,commissioned,Work,Packages.,FM-WP1,will,focus,upon,the,suitability,of,available,numerical,algorithms,(or,the,development,of,new,algorithms),for,Exascale,targeted,plasma,modelling.,As,stated,above,,elements,of,this,work,package,together,with,FM-WP4,will,also,surround,the,“coupling,technology”,that,will,be,required,to,connect,the,edge/pedestal,region,of,the,plasma,(addressed,by,FM-WP2),and,the,neutral,gas/impurity,model,(FM-WP3).,An,agile,approach,will,be,adopted,around,the,legacy,codes,that,might,be,necessary,for,helping,to,develop,a,roadmap,for,the,FM-WP1,referent,models,,e.g.,through,community,workshops,(the,first,being,in,Feb,2020).,FM-WP2,and,FM-WP3,will,concentrate,upon,development,of,the,two,close,coupled,models,of,the,NEPTUNE,programme,,specifically,FM-WP2,around,the,inclusion,of,kinetic,effects,into,existing,and,new,edge,plasma,models,,and,FM-WP3,of,particle,based,models,for,describing,the,region,outside,and,just,inside,the,plasma,(neutral,atoms/molecules,and,partially,ionized,impurities).,Initial,exploratory,work,will,be,carried,out,using,existing,codes,8,Commercial,in,Confidence,(as,per,above),and,via,the,development,of,proxy-apps,,for,example,to,expose,options,for,exascale,targeted,hardware,(GPUs,,ARM,technology,etc.).,FM-WP4,will,focus,upon,the,design,of,data,structures,to,interface,between,the,different,models,and,generally,ensure,best,practice,in,scientific,software,engineering,(being,responsible,for,Quality,Assurance,,co-design,,integration,etc.).,Aligned,with,Met,Office,work,package,WC-WP1,,this,programme,of,work,will,also,explore,the,use,of,a,“separation,of,concerns”,methodology,for,the,Fusion,use,case,critical,components,(e.g.,by,exploring,the,use,of,Kokkos,[12],and,Domain,Specific,Language,(DSL),[13],technologies).,Scoping,work,for,the,Met,Office,led,cross-cutting,themes,(XC-WP1,and,2),will,be,defined,in,collaboration,with,the,other,ExCALIBUR,partners,early,in,year,2,with,a,view,towards,starting,work,later,that,year.,The,specifics,of,the,cross-cutting,themes,are,here,assumed,to,be,covered,by,the,two,overarching,themes,of,“Common,Approaches,and,Solutions”,and,“Emerging,Technologies”,(discussed,further,below).,Note,,many,of,the,Activities,and,sub-tasks,that,will,be,defrayed,to,UKAEA,,the,Universities,and,UKRI,(STFC),will,inevitably,contribute,to,more,than,one,of,the,overarching,Work,Packages,due,to,the,highly,coupled,nature,of,the,target,infrastructure.,UKAEA,Research,Plans,Numerical,representation,(Fusion,modelling,,work,package,FM-WP1),The,ideal,numerical,algorithms,for,forming,the,Exascale,edge,plasma,codes,of,the,future,will,have,(but,will,not,be,restricted,to),the,following,properties:,P1.,Accurate,solution,of,hyperbolic,problems.,P2.,Ability,to,deliver,efficient,and,accurate,solutions,of,corresponding,elliptic,problems.,P3.,Accurate,modelling,of,highly,anisotropic,dynamics.,P4.,Accurate,representation,of,first,wall,geometry,(face,normals,to,within,0.1°),,and,correspondingly,of,complex,magnetic,field,geometries.,P5.,Accurate,representation,of,velocity,(phase),space.,P6.,Preservation,of,conservation,properties,of,the,underlying,equations.,P7.,Scalability,to,likely,Exascale,architectures:,interaction,between,models,of,different,dimensionality,,interaction,between,particle,and,fluid,models,,a.,b.,c.,dynamic,construction,of,surrogates.,P8.,Performance,portability,to,allow,rapid,deployment,upon,emerging,hardware.,It,is,difficult,at,this,point,in,time,to,rank,the,importance,of,these,properties,,or,to,identify,the,cost,associated,with,achieving,each,in,a,timely,fashion,–,a,clearer,understanding,of,immediate,needs,and,achievable,SMART,deliverables,will,emerge,as,the,project,matures,via,extensive,community,engagement,and,team,building,across,the,UK,partners,–,this,exercise,will,start,in,Feb,2020,via,an,open,workshop.,9,Commercial,in,Confidence,It,is,clear,however,that,the,choice,of,geometrical,representation,and,numerical,scheme,will,have,a,profound,impact,upon,almost,all,areas,of,the,project.,Options,will,be,identified,by,means,of,literature,and,code,surveys,and,via,consultation,with,UKRI,and,industry,experts.,Research,will,be,commissioned,where,necessary,to,eliminate,unsuitable,choices,as,early,as,possible.,Relatively,small,development,tasks,will,initially,be,undertaken,to,test,remaining,candidate,methods,for,accuracy,,stability,and,HPC,scalability,potential.,This,task,,along,with,FM-WP4,will,have,a,prioritised,start,to,provide,initial,inputs,into,FM-WP2,and,FM-WP3,developments,and,work,to,be,defrayed,in,year,2.,Tasks,FM-WP1-3,will,incorporate,numerical,,finite,element,and,other,plasma,physics,libraries,of,suitable,quality,and,exascale,applicability.,Options,,which,do,not,preclude,consideration,of,others,,have,been,tentatively,identified,for,initial,investigation,as,follows:,1.,Spectral/hp,element,[14],,combined,with,Discontinuous,Galerkin,[15],,to,meet,P1,P3,and,possibly,P5,above.,2.,Multigrid,methods,for,P2.,3.,Nekmesh,for,P4.,4.,For,Exascale,(P7):,a.,matrix-based,approaches,,hierarchical,geometric,structures,,b.,kinetic,enslavement,,multi-index,Monte-Carlo,methods,,c.,physics,based,Neural,Network,approaches.,5.,MUSCLE,2,etc.,as,referenced,in,[16],,MUI,[17],,ADIOS,[18],etc.,for,code,coupling,P6,,P7.,As,per,the,algorithm,requirements,,these,will,be,ranked,via,the,community,workshop,planned,for,Feb,2020.,Activities,for,defrayment,will,then,be,defined,around,SMART,deliverables,together,with,an,integrated,delivery,plan,for,the,entire,project.,Plasma,multiphysics,model,(Fusion,modelling,,work,package,FM-WP2),This,work,package,will,begin,by,identifying,a,referent,in,conjunction,with,potential,users,,whereby,“referent”,is,meant,a,model,that,establishes,the,maximum,detail,and,complexity,of,plasma,that,the,software,could,ever,be,reasonably,expected,to,model,(beyond,exascale).,Critical,features,of,the,referent,will,be,identified,and,prioritised,for,implementation,as,part,of,the,project.,This,may,involve,replacing,a,kinetic,model,by,moment-based,or,fluid,models.,Input,from,the,European,Boundary,Code,(EBC),development,(funded,by,EUROfusion,wherein,UKAEA,is,a,core,partner),will,be,important,to,this,process.,In,addition,,the,speed,of,model,execution,will,be,a,consideration,as,indicated,earlier.,A,provisional,sequence,of,developments,is,as,follows,(and,will,be,tuned,as,part,of,the,initial,NEPTUNE,requirements,capture,exercise,funded,in,year,1):,1.,2D,model,of,anisotropic,heat,transport.,2.,2D,elliptic,solver,in,complex,geometry.,3.,1D,fluid,solver,with,simplified,physics,but,with,UQ,and,realistic,boundary,conditions.,4.,Spatially,1D,plasma,model,incorporating,velocity,space,effects.,5.,Spatially,1D,multispecies,plasma,model.,6.,Spatially,2D,plasma,model,incorporating,velocity,space,effects.,10,Commercial,in,Confidence,7.,Interaction,between,models,of,different,dimensionality.,8.,Spatially,3D,plasma,kinetic,models.,Users,from,the,wider,fusion,community,will,be,engaged,via,a,workshop,in,Feb,2020,to,firm,up,on,the,plan,,to,help,define,work,for,defrayment,that,they,themselves,can,carry,out,and,will,be,engaged,throughout,the,project,to,help,define,and,add,new,surrogate,models,through,a,wide,engagement,programme,and,co-design,(e.g.,to,treat,boundary,sheaths),and/or,other,important,physical,effects,(e.g.,radiation,,charge,exchange,recombination,,etc.),and,compare,with,existing,codes,and,experiments.,Neutral,gas,&,Impurity,model,(Fusion,modelling,,work,package,FM-WP3),This,work,package,will,begin,by,identifying,a,referent,(as,above),in,conjunction,with,potential,users,and,experts,in,atomic,physics.,Critical,features,of,the,referent,will,be,identified,and,prioritised,for,implementation,as,part,of,the,project.,This,may,involve,deploying,a,particle-,based,method,,a,moment-based,model,or,a,fluid,model,(or,even,a,combination,thereof).,Input,from,the,European,EBC,programme,will,be,important,to,this,process,,as,will,the,speed,of,model,execution,as,indicated,earlier.,A,careful,assessment,of,existing,codes,currently,in,use,will,be,necessary,,as,will,cross,validation,with,the,established,models,(notably,B2-,EIRENE,[19]).,A,provisional,sequence,of,developments,is,as,follows:,1.,2D,particle-based,model,of,neutral,gas,&,impurities,with,critical,physics.,2.,2D,moment-based,model,of,neutral,gas,&,impurities.,3.,Interaction,with,2D,plasma,model,when,available.,4.,3D,model,of,neutral,gas,&,impurities.,5.,Interaction,with,3D,plasma,model.,6.,Staged,introduction,of,additional,neutral,gas/impurity,physics.,As,per,FM-WP2,,users,from,the,wider,fusion,modelling,community,will,first,be,engaged,through,a,workshop,in,Feb,2020,,and,will,help,build,a,UK,team,that,will,add,new,physics,and,compare,with,existing,codes,and,experiments,,providing,detailed,and,rigorous,verification,and,validation,(V&V).,This,is,likely,to,require,the,provision,of,databases,for,different,ionisation,and,excitation,reactions,,both,in,the,plasma,volume,and,at,surfaces.,Code,structure,and,coordination,(Fusion,modelling,,work,package,FM-WP4),The,most,important,aim,of,this,work,package,will,be,to,drive,user,engagement,and,ensure,that,the,software,is,fit,for,its,defined,purpose,,first,by,requirements,capture,,then,by,defining,suitably,flexible,code,structures,and,related,e-Infrastructure,for,users,,ultimately,supporting,uptake,of,the,new,code(s).,In,order,to,achieve,this,aim,,this,work,package,will,coordinate,across,the,other,tasks,FM-WP1-3,,to,ensure,that,outcomes,are,compatible,and,of,sufficiently,high,quality.,There,will,be,management,and,coordination,tasks,that,will,grow,as,the,project,matures,,connecting,with,the,EUROfusion,E-TASC,(TSVV),programme,,the,EPSRC,T.P.,Turbulence,Programme,[20],and,the,US,ECP,programme,etc.,Coordination,tasks,will,include,(but,are,not,restricted,to):,11,Commercial,in,Confidence,1.,Allocation,of,resource,between,tasks,and,setting,project,priorities.,2.,Ensuring,a,consistent,choice,of,definitions,(ontology),of,objects,or,equivalently,classes.,3.,Definition,of,common,interfaces,to,components,for,data,input,and,output.,4.,Design,of,suitably,flexible,data,structures,for,common,use,by,all,developers.,5.,Establishment,,promotion,and,support,of,good,scientific,software,engineering,practice.,6.,Evaluation,and,deployment,of,performance,portability,tools,and,DSLs,targeting,Exascale-,relevant,architectures.,7.,Integration,of,the,developed,software,into,a,VVUQ,framework,(exploiting,common,approaches,developed,under,XC-WP1,and,XC-WP2).,8.,Coordination,of,a,benchmarking,framework,for,correctness,testing,and,performance,evaluation,of,the,developed,software,stack.,Along,with,FM-WP1,,this,work,package,will,be,prioritised,for,an,early,start,,as,good,scientific,software,engineering,practice,needs,to,be,agreed,quickly,,and,well,documented,interfaces,to,components,need,to,be,available,early,to,ensure,that,best,practice,design,is,embedded,from,the,start.,Common,approaches,and,solutions,(Cross-cutting,themes,,XC-WP1),The,examples,listed,in,[1],are,very,well,aligned,with,the,needs,of,the,Fusion,use,case,comprising,initially,NEPTUNE,,especially,the,methodologies,surrounding,a,“separation,of,concerns”,,coupling,technologies,,the,use,of,mixed,precision,arithmetic,and,fault,tolerance.,In,addition,,project,NEPTUNE,will,benefit,from,an,exploration,of,the,convergence,of,HPC,and,AI,(e.g.,the,use,of,Neural,Network,PDE,solvers,[21],or,for,advanced,preconditioners),and,parallel,in,time,methods,[22].,These,areas,of,common,ground,and,opportunities,for,interdisciplinary,working,therein,shall,be,explored,and,agreed,by,partners,as,outlined,in,the,Met,Office,Science,Case.,Emerging,Technologies,(Cross-cutting,themes,,XC-WP2),The,examples,listed,for,XC-WP2,in,the,Met,Office,Science,Case,[1],are,again,highly,aligned,with,the,Fusion,use,case.,Other,technologies,that,are,deserving,of,consideration,include,High,Bandwidth,Memory,(HBM,[23]),,novel,exascale,targeted,IO/storage,technology,(e.g.,H2020,project,SAGE,II,[24],led,by,Seagate,wherein,UKAEA,is,a,partner),,next,generation,accelerator,technology,(Nvidia,Volta,Next,,A64fx),and,ARM,systems,for,efficient,scaling,of,Flops/Watt.,It,is,not,clear,at,this,stage,which,technologies,offer,the,best,route,forward,for,the,FM-WP2,and,FM-WP3,close,coupled,system,but,it,is,clear,that,the,UK,is,well,placed,to,explore,all,of,them,(e.g.,through,Isambard,II).,As,stated,earlier,,a,core,theme,within,the,project,is,to,build,solutions,around,a,“separation,of,concerns”,philosophy,(using,tools,such,as,Kokkos,and,One-API),in,order,to,develop,an,agile,environment,that,can,adapt,rapidly,to,disruptive,emergent,HPC,technology.,12,Commercial,in,Confidence,References,[1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24],Strategic,Priorities,Fund:,ExCALIBUR,Met,Office,Science,Plan,and,Activities,https://www.iter.org,https://www.gov.uk/government/news/uk-to-take-a-big-step-to-fusion-electricity,https://en.wikipedia.org/wiki/Tokamak,https://www.euro-fusion.org/programme/demo/,https://reuters.screenocean.com/record/1366443,https://bout-dev.readthedocs.io/en/latest/user_docs/introduction.html,https://en.wikipedia.org/wiki/Particle-in-cell,https://en.wikipedia.org/wiki/Gyrokinetics,https://proxyapps.exascaleproject.org/app/,https://society-rse.org,https://cfwebprod.sandia.gov/cfdocs/CompResearch/docs/Kokkos-Multi-CoE.pdf,https://en.wikipedia.org/wiki/Domain-specific_language,https://en.wikipedia.org/wiki/Spectral_element_method,https://www.sciencedirect.com/topics/engineering/discontinuous-galerkin,https://royalsocietypublishing.org/doi/10.1098/rsta.2018.0144,https://www.sciencedirect.com/science/article/pii/S0021999115003228,https://www.olcf.ornl.gov/center-projects/adios/,https://www.tandfonline.com/doi/abs/10.13182/FST47-172,https://www.york.ac.uk/physics/news/departmentalnews/plasma-fusion/major-grant-,award-supports-fusion-energy-research/,https://arxiv.org/abs/1906.01200,https://parallel-in-time.org,https://en.wikipedia.org/wiki/High_Bandwidth_Memory,http://sagestorage.eu/about/overview,13

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