CD-EXCALIBUR-FMS0007-Bham-workshop-summary_SummaryDiscussionSessionsAtExcaliburNeptuneWorkshop05022020
======================================================================================================

.. meta::
   :description: technical note

   :keywords: ExCALIBUR,Summary,of,Discussion,Sessions,Workshop,,05-02-2020,Abstract,This,document,contains,a,short,summary,of,the,discussion,sessions,of,the,05-02-2020,ExCALIBUR,NEPTUNE,workshop,(Binrmingham),UKAEA,REFERENCE,AND,APPROVAL,SHEET,Client,Reference:,UKAEA,Reference:,CD/EXCALIBUR-FMS/0007,Issue:,Date:,1.00,14,February,2020,Project,Name:,ExCALIBUR,Fusion,Modelling,System.,Version,1.10,–,modifications,in,response,to,reviewer,recommendations.,Name,and,Department,Signature,Date,Prepared,By:,Wayne,Arter,Lucian,Anton,Debasmita,Samaddar,Martin,O’Brien,Rob,Akers,N/A,N/A,N/A,N/A,N/A,MSSC,Reviewed,By:,14/02/2020,Modifiedd,By:,Rob,Akers,14/02/2020,MSSC,Approved,By:,Martin,O’Brien*,14/02/2020,MSSC,*,Chairman,of,UKAEA,internal,ExCALIBUR,Project,Board.,1,Summary,of,discussion,sessions,1,Physics,models,In,this,session,the,discussion,was,focused,on,the,selection,of,the,referent,model,for,numerical,implementation.,At,the,beginning,XGC,(a,well-known,gyrokinetic,code,simulating,the,plasma,edge),was,analysed,,the,session,agreed,that,is,not,an,actionable,code.,The,magnetic,fusion,community,uses,a,number,of,gyrokinetic,(GK),codes,–,but,except,for,a,very,few,such,as,XGC,and,Gkeyll,,most,of,their,simulations,are,restricted,to,the,core,plasma,,rather,than,the,edge,plasma,that,is,the,focus,of,NEPTUNE.,Fluid,models:,The,discussion,produced,the,following,recommendations,or,points,worthy,of,further,investigation:,-,-,-,-,potential,for,fluid/GK,region,matching,procedure,o,identify,a,fluid,approach,with,good,performance,for,the,suitable,regions,,which,includes,turbulence,consistently,can,this,fluid,model,also,support,ETASC,aims?,(ETASC,is,related,European,fusion,project,that,UKAEA,participates,in),identifying,suitable,intermediate,proxy,apps,identify,UQ,and,consider,validation,process,Gyrokinetics:,The,discussion,has,produced,the,following,observations,and,suggestion,for,a,GK,proxyapp:,-,-,-,-,could,start,with,full-f,,simple,geometry,,simple,mesh,,open,field,line,region,,2D,GK,proxyapp,to,demonstrate,modelling,of,edge,region,where,the,open,magnetic,field,lines,touch,the,metal,surface,–,the,divertor,,basic,data,flow,open,field,lines,easier,as,electrostatic,potential,set,by,sheath,,closed,line,region,need,vorticity,equation,the,session,agreed,there,was,potential,to,employ,Gkeyll,for,comparison,to,problems,solved,using,the,hp,spectral,method,coupling,to,fluid,model,longer,term,aim,Impurities,The,discussion,pointed,to,the,need,to,explore,suitable,numerical,methods,to,handle,low,plasma,density,,a,large,number,of,species,,etc.,2,Neutrals,Typically,,neutral,particles,are,not,included,in,gyrokinetics,,whereas,fluid,approaches,treat,them,differently,from,ions.,An,initial,exploration,could,be,done,along,the,following,lines,-,-,include,basic,charge,exchange,operator,in,a,simple,GK,code,with,simple,geometry,to,consider,how,this,affects,the,core,,can,it,create,a,pedestal,as,the,neutrals,in,an,open,field,line,region,,can,carry,momentum.,-,wouldn’t,be,the,fastest,way,to,develop,a,general,physics,model,base,,but,can,provide,a,basic,understanding,theory,deliverable,Atomic,physics/detachment,Both,gyrokinetic,and,fluid,theories,fail,in,detachment,studies,due,to,insufficient,handling,of,atomic/molecular,reactions.,The,discussion,concluded,that,further,exploration,is,needed,for,the,following:,-,-,suitable,numerical,methods,and,study,of,what,reactions,are,handled,in,current,codes,–,mainly,Eirene.,accuracy,of,atomic,data,3,2,Algorithms,The,main,outcome,was,that,the,mini-apps,or,other,input,could,be,requested,in,contracts,from,universities.,However,,it,was,recognised,that,not,all,would,be,covered,,and,that,some,topics,were,not,specific,to,fusion/NEPTUNE,and,may,well,be,provided,from,the,UKRI,call,if,not,on,the,critical,path,for,NEPTUNE.,Conversations,revealed,that,some,university,have,consultancy,companies,that,could,interface,to,academics,to,provide,quick,amount,of,small,consultancy,(weeks,,even,months,depending,on,staff/teaching,ratio).,The,following,topics,were,considered,to,be,important:,1.,Higher,order,mesh,generation,2.,Connected,particle,and,fluid,calculation,3.,Multi-precision,approaches,–,it,was,felt,that,could,be,left,until,later,if,"separation,of,concerns",adequately,implemented,4.,Diffusion,coefficient,with,very,high,(~10^6,?),parallel,to,perpendicular,asymmetry,5.,Time,integration,in,problems,with,a,wide,range,of,timescales,,implicit,PIC,as,a,challenge,with/without,enslavement,6.,Solution,of,1D,hyperbolic,equation,with,strong,sources,and,sinks,,with,spectral,accuracy,,compare,with,chebfun,solution,7.,Elliptic,solver,issues,–,compare,pre-conditioners?,How,good,is,algebraic,multigrid?,8.,Data,compression,4,3,Software,Engineering,Topics,discussed,in,this,session:,Short,term,contracts,The,general,opinion,was,that,short-term,contracts,are,not,ideal,because,of,the,large,overheads,and,the,constraints,of,hiring,practices,of,academia,e.g.,agree,that,some,percentage,of,FTE,will,be,funded,rather,than,assert,that,the,contract,finishes,inside,a,specified,number,of,months.,Requirements,gathering,/,documentation,The,attendees,who,are,involved,in,developing,and,maintaining,public,CSE,applications,are,following,an,informal,process,,with,the,accent,on,modularisation,and,API,specification.,No,Software,Requirements,Specification,document,is,used.,It,was,suggested,to,check,publicly,available,requirements,documents,for,CSE,software,projects.,Automated,testing,procedure,Attendees,involved,in,large,scale,software,developments,acknowledged,that,the,unit,testing,procedure,is,embedded,in,their,development,team,culture,,in,order,to,ensure,software,sustainability,and,the,efficiency,of,the,development,process.,The,developer,has,to,produce,the,test,associate,with,the,module,being,developed.,The,testing,needs,to,be,done,across,platforms,,compiler,versions,and,vendors,and,sometimes,operating,systems.,Automation,tools,are,used,to,support,these,processes.,None,of,the,attendees,is,using,the,formal,roles,such,as,validation,,performance,,maintenance,tester,and,manager.,The,process,oversight,is,done,informally,by,the,senior,developers.,A,large,scale,project,(,biological,tissue,simulation),has,certain,tasks,,such,as,verification,,assigned,to,distinct,groups.,Uncertainty,Quantification,The,attendees,pointed,to,several,UQ,techniques,that,can,be,used,,intrusive,should,be,designed,into,the,project,from,the,start.,Exascale,computation,capability,comes,in,handy,for,the,extra,numerical,work,that,is,needed.,However,,the,interpretation,of,the,results,needs,deep,domain,knowledge.,Model,errors,could,be,larger,than,any,other,error.,Separation,of,concerns,,Domain,specific,languages,,programming,models,DSL,were,commended,as,a,good,solution,for,separation,of,concerns,and,complexity,management,,however,they,come,with,their,own,cost.,One,has,to,support,the,associated,code,generators.,One,has,to,mitigate,the,risk,of,DSL,project,termination,,if,this,is,done,by,a,third,party.,Met,Office,is,collaborating,with,STFC,on,code,generator,and,they,are,also,developing,internal,expertise,for,GungHo.,It,was,mentioned,that,Kokkos,is,transferring,some,of,its,idioms,in,the,C++,standard.,No,code,generator,for,nodes,with,different,architectures,is,universal.,There,is,the,risk,of,vendor,lock,in.,5,Fault,tolerance,Large,scale,applications,might,need,to,consider,recovering,from,single,node,failure,and,continue,the,computation.,The,implementation,used,by,Nektar++,based,on,MPI,functionality,was,presented,in,detail.,Hardware,availability,The,HPC,systems,currently,available,to,the,UK,academic,community,and,their,near-term,upgrades,were,reviewed,together,with,their,access,policies.,ExCALIBUR,has,a,small,fund,for,hardware.,6

:pdfembed:`src:_static/CD-EXCALIBUR-FMS0007-Bham-workshop-summary_SummaryDiscussionSessionsAtExcaliburNeptuneWorkshop05022020.pdf, height:1600, width:1100, align:middle`