WEO2LR —  Working Group C   (12-Nov-14   10:50—12:30)
Chair: S.M. Lund, FRIB, East Lansing, Michigan, USA

Paper	Title	Page
WEO2LR01	Code Requirements for Long Term Tracking with Space Charge	249
	F. Schmidt CERN, Geneva, Switzerland
	In view of the LHC In­jec­tors Up­grade (LIU) for the LHC pre-ac­cel­er­a­tors Leir, PSB, PS, SPS we have started a new work­ing group at CERN to deal with space charge is­sues of these ma­chines. The goal is to op­er­ate these ma­chines with ba­si­cally twice the num­ber of par­ti­cles per bunch which will fur­ther in­crease the space charge tune shifts which are large al­ready now in pre­sent op­er­a­tion. Be­sides the ob­vi­ous reme­dies of in­creas­ing the in­jec­tion en­ergy we are obliged to bet­ter un­der­stand the space charge force to op­ti­mize our ma­chines. To this end it has be­come clear that we need com­puter mod­els that faith­fully rep­re­sent the lin­ear but also the non-lin­ear fea­tures of our ma­chines. We have started close col­lab­o­ra­tions with sev­eral lab­o­ra­to­ries around the world to up­grade ex­ist­ing self-con­sis­tent Space Charge Par­ti­cle-In-Cell (PIC) codes for our CERN needs. In par­al­lel, we have cre­ated a frozen space charge fa­cil­ity in CERN's MAD-X code. Both types of codes are being used to study long-term sta­bil­ity of our ma­chines and to com­pare it with ma­chine ex­per­i­ments.
	Slides WEO2LR01 [3.171 MB]
WEO2LR02	Status of PY-ORBIT: Benchmarking and Noise Control in PIC Codes	254
	J.A. Holmes, S.M. Cousineau, A.P. Shishlo ORNL, Oak Ridge, Tennessee, USA
	Funding: ORNL is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. PY-OR­BIT is a broad col­lec­tion of ac­cel­er­a­tor beam dy­nam­ics sim­u­la­tion mod­els, writ­ten pri­mar­ily in C++, but ac­cessed by the user through Python scripts. PY-OR­BIT was con­ceived as a mod­ern­iza­tion, stan­dard­iza­tion, and ar­chi­tec­tural im­prove­ment of ORBIT, a beam dy­nam­ics code de­signed pri­mar­ily for rings. Al­though this goal has been sub­stan­tially achieved, PY-OR­BIT has now in­cor­po­rated ad­di­tional ca­pa­bil­i­ties. A major con­sid­er­a­tion in high in­ten­sity beam dy­nam­ics codes, such as PY-OR­BIT and ORBIT, is the sim­u­la­tion of space charge ef­fects. Com­pu­ta­tional space charge sim­u­la­tion is, of ne­ces­sity, ac­com­pa­nied by noise due to dis­cretiza­tion er­rors, which can com­pro­mise re­sults over long time scales. Dis­cretiza­tion er­rors occur due to fi­nite step sizes be­tween space charge kicks, due to grain­i­ness of the nu­mer­i­cal space charge dis­tri­b­u­tion, and due to the ef­fects of spa­tial grids em­bed­ded in cer­tain solvers. In order to sim­u­late space charge, most track­ing codes use solvers con­tain­ing some or all of these ef­fects. We com­pare the man­i­fes­ta­tion of dis­cretiza­tion ef­fects in dif­fer­ent types of space charge solvers with the ob­ject of long time scale space charge sim­u­la­tion.
	Slides WEO2LR02 [23.093 MB]
WEO2LR03	Artificial Noise in PIC Codes and Consequences on Long Term Tracking	259
	K. Ohmi KEK, Ibaraki, Japan
	Par­ti­cle in Cell codes are widely used in stud­ies on beam-beam, space charge and elec­tron cloud ef­fects. Nu­mer­i­cal noise due to macro-par­ti­cle sta­tis­tics ap­pears in orbit off­set and beam size (beta func­tion). The noise in­duces art­fi­cial emit­tance growth. It is in­dis­pens­able to un­der­stand un­der­ly­ing mech­a­nism of the emit­tance growth for the va­lid­ity of sim­u­la­tion re­sults.
	Slides WEO2LR03 [4.279 MB]